Note: Descriptions are shown in the official language in which they were submitted.
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IMAGING, ELECTRICAL POTENTIAL SENSING AND ABLATION CATHETERS
Backcround of the Invention
The action of the human heart is controlled by
propagation of electrical activity in various regions of
the heart. The presence of abnormal accessory pathways
in the heart can lead to conditions such as ventricular
tachycardia and atrial flutter. These conditions are
very common. Approximately 20% of the population will
have some type of electrical disturbance activity in the
heart during their lifetimes.
Physicians have found that they can detect
malfunctions of the heart by probing the heart with a
catheter fitted with one or more electrodes and having
steering capability, measuring voltages within the heart,
and observing the waveforms. Once a physician
understands how the electrical activity of the heart is
operating he can, if he wishes to do so, choose to
"disconnect" certain portions of the heart electrically
by the process of ablation. If multiple electrode are
used, the catheter can make multiple readings
simultaneously when it is curved inside the heart. Thus,
the use of multiple electrodes shortens the time required
to map the heart.
The electrical activity of the heart is detected
and read in accordance with a mapping procedure to
determine the presence of abnormal accessory pathways in
the heart. A typical mapping procedure involves using
electrophysiology sensing electrodes mounted on a
catheter as remote-controlled voltage-testing probes to
test various locations in the heart.
The process of ablation is a destructive process
in which the catheter is used to burn a certain section
of the heart which stops the propagation of an electrical
signal from one portion of the heart to another.
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Alternate means to perform ablation have been to inject a
chemical such as ethanol in specific regions of the
heart, to apply very cold temperatures in a process
called cryo-ablation, and to use sonic energy, which is
sometimes referred to as ultrasonic ablation. The
ablation process may alternatively consist of applying
low-frequency RF energy to the heart tissue in order to
create a burn. This burn will cause the tissue to heat
up and desiccate and finally necrose.
l0 Electrophysiology catheters are typically
positioned at various positions in the heart under x-ray
guidance. The x-rays show the catheter, and can also
show the heart itself and thus the position of the
catheter relative to the heart if dye injections are
made. The clinician tries to visualize the position of
the catheter in the heart in the various chambers.
Electrical means are used to determine whether or not the
electrode is in contact with the heart, and this
information is shown on an EKG display. During the
course of a typical procedure the operator will
frequently return to one or more positions, and will look
for particular waveforms that he sees from the sensing
electrodes to determine whether the catheter has returned
to the desired position. Typically, more than one
catheter is used in a given procedure, and the catheters
are constructed with steering or torquing devices that
assist in positioning of the catheters within the heart.
The sensing or ablation electrodes of intracardiac
catheters are typically made of tantalum, gold, or
platinum. There can be as few as one or as many as five
or more electrodes in a sensing and ablation catheter.
Typical sensing and ablation catheters will have at least
one tip electrode and two, three, or four ring electrodes
proximal to the tip electrode. The proximal ring
electrodes are typically spaced from the distal tip in
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two, three, or four-millimeter increments. The ring
electrodes are generally bonded or crimped onto the
catheter body or blended into the catheter body. The
rings are sufficiently thick to have enough mechanical
strength when crimped to adhere to the catheter shaft.
It is known that the injections of chemicals such
as ethanol into the heart can produce a response which is
similar to that produced when a burn is made in the
heart. Basically, the injection of chemicals disrupts or
cuts off electrical pathways in the heart by causing
localized cell death.
The disorders that can be treated by ablating
cardiac tissue include general arrhythmias, ventricular
tachycardia, atrial fibrillation, atrial flutter, and
Wolff-Parkinson-White Syndrome (WPW). Typically,
ventricular tachycardia and WPW are treated by RF
coagulation or DC discharge applied to cardiac tissue by
electrode-tipped, deformable, and preset curved
catheters. These catheters are of similar construction
to those used in the art for electrically mapping the
heart.
In order to navigate through the patient s
vascular system, cardiac catheters are limited to small
diameters. A typical mapping or ablation catheter has
small electrodes mounted on the distal end of the
catheter shaft. The electrodes can be arranged in
bipolar pairs at the distal end of a catheter to ablate
tissue by passing RF or DC electrical current between
them through the surrounding myocardium. Alternatively,
a single electrode could be disposed at the distal tip of
a catheter, the single electrode being used to cause RF
or DC electrical energy to pass directly through the
heart tissue to a grounding plate on the surface of the
patient s body.
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Typically, the area of cardiac tissue that must be
ablated is several times the size of the ablation region
of the small electrode ablation catheters. Thus, a
carpet bombing approach (i.e., ablating at many discrete
sites) can be used to successfully treat cardiac
disorders. This technique can lead to nonuniform
ablation, as well as incomplete ablation if the ablation
electrodes are not always directly in contact with
myocardial tissue at each discrete site.
It is known to use a suction hole at a distal end
of a catheter to engage tissue and thereby to hold the
catheter in a fixed location in a patient's body while a
distal ring electrode is placed in contact with tissue.
An alternative method for treating disorders in
the heart is described in PCT application US93/09422,
filed October 4, 1993 by Daniel Bruce Pram et al. As
described in that application, a catheter having a
balloon mounted on its distal end is inserted into the
coronary sinus or great cardiac vein. The balloon is
inflated with fluid within the coronary sinus and is
heated by a heating device located within the balloon.
Tissue surrounding the coronary sinus is ablated by
thermal conduction from the fluid to the tissue through
the wall of the balloon.
Electrophysiological catheters can apply radio
frequency energy to produce burn lesions at selected
points in the heart to correct arrhythmias. By
destroying the cells that constitute defective conductive
pathways, the arrhythmias are stopped. Typically, rigid
electrodes, of ring form either partially or totally
surrounding the catheter shaft, are used, though it is
desirable at times to produce larger lesions than can be
produced with such electrodes. By using a larger
electrode, one could apply higher power, and by spreading
the current at conventional current intensity over a
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larger area, the larger lesion can be produced. The
diameter of such conventional electrodes, however, has
been limited by the size of access hole that can be
tolerated in the artery. Also, the length of these
electrodes has been limited by the need to maintain
maneuverability for the catheter to pass through tight
curves in proceeding through the arterial system and into
the heart.
S~,mm~ of the Invention
In one aspect, the invention features an acoustic
imaging system for use within a body of a living being,
having an elongated, flexible catheter constructed to be
inserted into the body, an ultrasound device incorporated
into the elongated, flexible catheter, and an electrode
mounted on a distal portion of the elongated, flexible
catheter. There are a plurality of electrical conductors
extending from a proximal portion of the elongated,
flexible catheter to the distal portion. At least two of
the plurality of electrical conductors are connected to
the ultrasound device and at least one of the plurality
of electrical conductors is connected to the electrode.
The ultrasound device is arranged to direct ultrasonic
signals toward an internal structure within the body for
the purpose of creating an ultrasonic image of the
internal structure, and the electrode is arranged for
electrical contact with the internal structure imaged by
the ultrasound device.
The invention enables precise control and
directability of catheters used in electrophysiology
procedures, with the aid of high resolution images that
reveal the cardiac anatomy and the location of the
catheter and electrodes relative to the various chambers
of the heart, the valves, the annuluses of the valves,
and the other areas of the heart. Electrophysiology
catheters according to the invention can be used without
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x-ray guidance, thereby eliminating dye injections and
prolonged exposure of the patient and clinician to x-rays
during the procedure. The clinician need not rely on his
own imagination when trying to visualize the position of
the catheter in the various chambers of the heart, and
need not struggle to read an EKG display to determine
whether an electrode is in contact with heart tissue.
Thus, the invention reduces the time that it takes to
obtain a reliable reading from a particular region of the
heart that can be identified with ultrasound. Moreover,
the physician need not look for particular waveforms from
a sensing electrode to determine whether the electrode
has returned to a desired position in the heart, and can
reposition the electrode quickly and precisely. Also, by
reducing the time required for electrophysiology sensing
procedures and enhancing the precision with which an
electrode can be positioned within the heart, the
invention reduces the need for the catheter to include a
large number of electrodes in order to reduce the time
required to map the heart.
If the electrode is used for ablation, the on-
catheter imaging also ensures that the electrode makes
adeguate contact with the endocardium, which is important
because even if the catheter is in a position that is
good enough to record the cardiac electrical activity it
may not be good enough to deliver sufficient current to
the portion of the heart requiring the ablation. There
is no need to look at the impedance between the electrode
and the heart itself to determine whether the electrode
is in actual contact with the heart and there is no
uncertainty as to whether the electrode is only in
contact with blood, which of course is an electrical
conductor and which would boil without creation of a
lesion at all.
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The invention also enables monitoring of the
ablation process once it begins. The desiccation of
tissue can be monitored by ultrasound, and it is useful
to be able to see with ultrasound the depth and the
extent of the lesion that is formed in the ablation
procedure.
In another aspect, the invention features an
acoustic imaging system for use within a body of a living
being, having an elongated, flexible catheter, an
ultrasound device incorporated into the elongated,
flexible catheter, and a chemical ablation device mounted
on a distal portion of the elongated, flexible catheter.
The ultrasound device is arranged to direct ultrasonic
signals toward an internal structure within the body of
the living being for the purpose of creating an
ultrasonic image of the internal structure, and the
chemical ablation device is arranged to ablate at least a
portion of the internal structure imaged by the
ultrasound device by delivery of fluid to the internal
structure.
By providing a mode of ablation that does not
require electrophysiology sensing electrodes to be used
also as ablation electrodes, the invention lowers the
current delivery requirement for electrophysiology
electrodes in electrophysiology catheters. I.e., an
electrophysiology electrode used solely for sensing need
not be as good an electrical conductor as an
electrophysiology electrode that is also used for
ablation.
Another aspect of the invention features an
acoustic imaging system for use within a body of a living
being, having an elongated, flexible catheter, an
ultrasound device incorporated into the elongated,
flexible catheter, and an ablation device comprising a
transducer mounted on the distal portion of the
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elongated, flexible catheter. The ultrasound device is
arranged to direct ultrasonic signals toward an internal
structure within the body for the purpose of creating an
ultrasonic image of the internal structure. The
transducer is constructed arranged to convert electrical
signals into radiation and to direct the radiation toward
the internal structure within the body for the purpose of
ablating tissue. The ablation device is arranged to
ablate at least a portion of the internal structure
imaged by the ultrasound device.
Another aspect of the invention features a
catheter system that includes an elongated, flexible
catheter, an imaging system, a data collection system, a
central processing unit, and a graphic display system.
The imaging system is constructed and arranged to provide
information from which a graphical representation of an
internal structure within the body may be created. The
data collection system is at least partially located on a
distal portion of the elongated, flexible catheter., and
is constructed and arranged to produce a plurality of
items of data corresponding to a respective plurality of
locations within the internal structure. The central
processing unit is electrically connected to the imaging
system and the data collection system, and is configured
and arranged to create the graphical representation of
the internal structure from the information provided by
the imaging system, and to super-impose onto the
graphical representation the plurality of items of data
provided by the data collection system. The plurality of
items of data are super-imposed at locations on the
graphical representation that represent the respective
plurality of locations within the internal structure
corresponding to the plurality of items of data. The
graphic display system is electrically connected to the
central processing unit, and is constructed to display
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the graphical representation onto which the plurality of
items of data are super-imposed.
By super-imposing items of data on a graphical
representation of an internal structure such as the
heart, the invention provides an improved way to display
in a meaningful and readily understandable manner the
substantial information that is stored and saved in
connection with a mapping procedure.
Another aspect of the invention features an
acoustic imaging system for use within a body of a living
being, having an elongated, flexible catheter, an
ultrasound device incorporated into the elongated,
flexible catheter, and at least one sonolucent,
electrically conductive structure incorporated into the
elongated, flexible catheter. In one embodiment the
sonolucent structure is an electrode imprinted onto the
catheter shaft as a thin film. The ultrasound device is
arranged to direct ultrasonic signals through the
sonolucent, electrically conductive structure toward an
internal structure within the body for the purpose of
creating an ultrasonic image of the internal structure.
By eliminating the thickness of ordinary metal
ring electrodes bonded or crimped onto the body of a
catheter, the invention enables an acoustic imaging
electrophysiology catheter (capable of sensing, ablation,
steering, and imaging) to have a profile that is small
enough to permit easy access of several such catheters
into the heart and to permit great maneuverability and
flexibility of the catheters with minimal trauma to the
patient. In particular, the ultrasound imaging device
occupies considerable space in the assembly, and in order
to make space for the ultrasound imaging device the
electrical wires can be placed on the periphery of the
catheter in accordance with the invention without adding
substantially to the size of the catheter or interfering
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with imaging. The invention also allows an acoustic
imaging electrophysiology catheter to be sufficiently
flexible, because very thin traces do not add to the
stiffness of the catheter in the way that individual
wires sometimes do.
Another aspect of the invention features an
ablation system for use within a body of a living being,
having an elongated, flexible catheter, and an ablation
device mounted on a distal portion of the elongated,
flexible catheter, and a plurality of electrical
conductors extending from a proximal portion of the
elongated, flexible catheter to the distal portion. The
ablation device includes a material that vibrates in
response to electrical excitation, and the ablation
device is constructed and arranged to cause ablation of
at least a portion of an internal structure within the
body. The ablation is at least assisted by vibration of
the material.
Another aspect of the invention features a
catheter system, having an elongated, flexible catheter,
an acoustic imaging system constructed and arranged to
direct ultrasonic signals toward an internal structure
within the body for the purpose of creating an ultrasonic
image of the internal structure, and constructed and
arranged to provide the ultrasonic image, and an acoustic
marker mounted on at least a distal portion of the
elongated, flexible catheter. The acoustic marker is
constructed to emit a sonic wave when the acoustic marker
is electrically excited. The acoustic imaging system is
constructed in a manner such that interference of the
sonic wave emitted by the acoustic marker with the
ultrasonic signals directed toward the internal structure
by the acoustic imaging system causes an identifiable
artifact to appear on the ultrasonic image of the
internal body structure.
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Another aspect of the invention features a method
of ablating heart tissue. An elongated, flexible
catheter is provided that has an ultrasound device and an
ablation device incorporated into a distal portion
thereof. The elongated, flexible catheter is inserted
into a body of a living being, and the distal portion of
the elongated, flexible catheter is introduced into the
heart. The ultrasound device is positioned in the
vicinity of an internal structure within the heart, and
ultrasonic signals are directed from the ultrasound
device toward the internal structure to create an
ultrasonic image of the internal structure. The internal
structure is ablated through use of the ablation device
mounted on the distal portion of the elongated, flexible
catheter.
In another aspect, the invention features a method
of ablating heart tissue within a body of a living being.
A balloon catheter is provided that includes a catheter
shaft constructed for insertion into a blood vessel, an
inflatable balloon mounted on a distal portion of the
catheter shaft, and a heating device mounted on the
distal portion of the catheter and arranged for heating
tissue in contact with the balloon while the balloon is
inflated. The catheter shaft and the balloon are sized
and constructed to permit the distal portion of the
catheter shaft to be inserted into an atrium or ventricle
of a heart while the balloon is deflated. The distal
portion of the catheter is positioned within the atrium
or ventricle and adjacent to a wall of the atrium or
ventricle. The balloon is inflated with fluid while the
balloon is within the atrium or ventricle, and while the
balloon is inflated it is engaged in direct contact with
a wall of the atrium or ventricle. Tissue surrounding
the balloon is heated through use of the heating device
while the balloon is inflated.
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The invention provides a large area of ablation in
an atrium or ventricle of the heart, through direct
contact of a relatively large ablation device with a wall
of an atrium or ventricle. The balloon is preferably
sufficiently deformable under stress to conform to the
irregular shape of the various chambers of the heart.
The deformability of the balloon also allows for a
uniform ablation of cardiac tissue. In addition, the
area of ablation can be controlled relatively easily by
adjusting the pressure inside the balloon thereby,
thereby adjusting the length of the balloon.
Another aspect of the invention features a cardiac
ablation catheter constructed for insertion into a body
of a living being. The cardiac ablation catheter
includes a catheter shaft, an inflatable balloon mounted
on a distal portion of the catheter shaft, a heating
device mounted on the distal portion of the catheter
shaft for heating tissue in contact with the balloon
while the balloon is inflated, an electrode located on
the distal portion of the catheter shaft, and a control
circuit connected to the electrode and arranged to apply
radio-frequency electrical current to the electrode for
ablating tissue in contact with the electrode.
By combining together, in a single catheter, an
ablation electrode at the distal tip of the catheter and
a heated balloon, the invention provides for both
discrete localized ablation of small areas of myocardium
with the ablation electrode, as well as large area
ablation with the heated balloon.
Another aspect of the invention features a cardiac
ablation catheter that includes a catheter shaft
constructed for insertion into a body of a living being,
an inflatable balloon disposed annularly around a distal
tip of the catheter shaft, a heating device mounted on a
distal portion of the catheter shaft for heating tissue
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in contact with the balloon while the balloon is
inflated, and an electrode located on the distal tip of
the catheter for directly contacting tissue while the
balloon is pressed against the tissue in an axial
direction. The catheter shaft and balloon are sized and
constructed to permit the distal portion of the catheter
shaft to be inserted into the body while the balloon is
deflated and to permit the balloon to be filled with a
fluid inside the body.
The invention achieves the advantage of monitoring
the ablation procedure with a single catheter by coupling
the distal electrode to mapping circuitry. The distal
electrode provides for sensing during ablation with the
heated balloon, allowing for a highly controlled ablation
procedure.
Another aspect of the invention features an
ablation catheter that includes a catheter shaft
constructed for insertion into a body of a living being
and having a lumen extending longitudinally through it
for coupling a proximal source of suction to a distal
port located at the distal tip of the catheter, an
electrode mounted on the distal portion of the catheter
shaft, and a tissue-engagement device surrounding the
distal port and constructed to engage tissue with suction
when the port is placed adjacent to the tissue. The
tissue-engagement device is constructed to cause the
distal portion of the catheter shaft to be held in a
fixed position relative to the tissue while the electrode
is placed in contact with an internal body structure. In
certain preferred embodiments, the electrode is mounted
directly on the tissue-engagement device or is adjacent
thereto.
By combining, on a single catheter, a tissue-
engagement device with an ablation electrode, the
invention reduces the likelihood of the electrode being
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moved from an identified ablation site, which could
result in damage to normal tissue. In addition, the
invention provides a means for assuring that the
electrode remains in direct contact with the tissue to be
ablated or mapped, especially if the electrode is mounted
directly on the tissue-engagement device itself or
adjacent thereto, thereby reducing the likelihood of
insufficient ablation or poor mapping due to the
electrode not being in contact with the tissue.
Another aspect of the present invention provides a
catheter with an expandable ablation electrode
constructed to access the heart. When it is introduced
to the heart, the electrode is small and suitably
flexible to maneuver through the torturous path.
However, when the catheter is in place in the heart, the
electrode is expansible in diameter to a substantially
larger dimension, and is relatively rigid, enabling a
large conductive surface to press against the heart
tissue with the desired contact pressure. When RF energy
is then applied to the electrode it produces a burn
lesion of desired large size and depth. This overcomes
the limitations to size that have been encountered using
conventional rigid electrodes.
According to one preferred embodiment, there is
provided on the electrophysiology catheter, a balloon the
exterior of which is coated uniformly with a conductive
material, preferably gold, or other material that is both
electrically and thermally conductive. Such conductive
coating materials can be deposited on the surface of the
material forming the balloon, by conventional vacuum
deposition techniques, or a thicker coating of gold for
larger current capacity can be produced with
electroplating techniques.
Substantial thermal conductivity of the electrode
material is important to prevent heat build-up in the
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electrode which might cause sticking of the electrode to
tissue, or if the temperature gets high enough, even
cause the thin electrode layer to deteriorate.
In preferred embodiments, a balloon of the type
commonly used for balloon angioplasty dilatation, is
employed. Such a balloon is made of a very strong, low
elongation resinous material such as PET (polyethylene
terepthalate). As is known, PET can be formed into a
balloon of thin wall thickness using modified bottle
blowing techniques. Such a balloon, in uninflated state,
is folded about the catheter using folding techniques
commonly applied to dilatation balloons to achieve the
size corresponding substantially to that of the catheter
on which it is mounted.
The dimension of the balloon is enlarged during
use by infusing into the balloon fluid containing a
significant concentration of radiopaque contrast agent
such as the conventional viscous inflation fluid used for
balloon dilatation. Inflation causes the balloon to
unfold and to expand to its set, relatively large
diameter. By inflating to high pressure, e.g. 5 or more
atmospheres, the enlarged balloon becomes significantly
rigid.
Typically, the balloon is of a set length, which
may be substantially longer than conventional rigid
electrodes. When in deflated condition, at its smaller
dimension, it and the portion of the catheter on which it
is carried is sufficiently flexible to enable maneuvering
through the tight bends of the arterial system and into
the heart. Upon inflation, the rigidity of the expanded,
pressurized balloon is realized to be appropriate for
effective RF ablation.
A degree of rigidity is an important requirement
because the electrode must push against the heart tissue
with pressure to cause the heart tissue to conform to the
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electrode shape and establish good, uniform electrical
contact. The degree of conformity and the uniformity of
pressure along the length of the balloon is facilitated
in the present invention by operation of Pascal's law,
which enables pressure against the tissue to be
equilibrated.
In the case of balloons comprised of PET, a power
supply conductor is attached to the conductive coating at
the proximal or rearward end of the balloon, on the -
exterior surface. The conductor such as a wire, is lead
through the wall of the catheter and through the shaft to
appropriate terminal at the proximal end.
In another embodiment, the balloon is made of more
compliant material than PET. In one case, advantageous
for certain purposes, the balloon is comprised of an
elastomer. Due to its elasticity, one cannot only change
the diameter from small to large, but one can chose the
particular inflated dimension over a range by careful
metering of the inflation fluid into the balloon. Thus
there is achievable an electrode having an inflated
dimension that may be selected from between e.g. 5 mm and
10 mm, depending on the size of the lesion the physician
desires to create. This provides to the user the option,
after introduction of the catheter of, establishing a
first electrode shape, and size of the lesion to be
produced, by introducing a preselected volume of fluid.
Typically the operating physician may choose to produce
the smallest region possible that in his judgment may
cure the arrhythmia. Therefore he may initially start
with the balloon inflated to 5 mm, and only increase its
size if deeper and larger lesions are found to be
necessary. The balloon size can be increased by metered
addition of additional inflation fluid.
For the purpose of controlling the size of the
inflation of the expansible balloon, a high accuracy
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I
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screw syringe is employed to precisely control the amount
of fluid introduced to the balloon. The type of screw
syringe used for balloon angioplasty is suitable for this
purpose.
The balloon can be seen on the fluoroscope due to
the contrast agent in the inflation fluid, and its size
can be fluoroscopically judged. Thus one can control the
diameter with the amount of fluid introduced and one can
monitor its size fluoroscopically.
In the case of the elastomeric, variable sized
balloon, in order to allow the balloon to expand and
contract, the electrode coating on the outside of the
balloon, is of a pattern chosen to enable the balloon to
stretch. In one case it may be a serpentine pattern of
narrow conductive elastomeric stripes on the balloon
surface that effectively hinge while maintaining
continuity as the balloon expands, to accommodate the
change in geometry. In another embodiment a series of
metal conductive dots is applied to the exterior of the
balloon, while flexible, narrow conductive paths may be
defined to introduce power to the dot-shaped electrodes.
Another technique for introducing energy to the
dots may be by capacitive coupling. In this case,
electrically conductive fluid is employed as the
inflation medium for the balloon. Monopolar RF energy is
applied to the fluid via an electrode fixed to the
exterior of the portion of the catheter shaft that
extends through the balloon, and capacitive coupling
occurs across the thickness of the balloon to the
conductive coated dots on the outside of the balloon.
Instruments described so far are intended for
monopolar operation. There is typically only one
electrode on the catheter and the current is conducted
through the tissue to another electrode in the form of a
ground plate that has a surface area many times that of
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18
the catheter electrode. This ground plate is maintained
in contact with the skin of the patient. Because of the
large sire of the ground plate, when the current reaches
it, the density is so low that no burning or heating
occurs, as is well known.
In certain instances, however, the balloon is
advantageously constructed for bipolar introduction of RF
current to the tissue. This can be advantageous for
cases where one wishes to create a large area lesion but
not cause deep penetration. This may be useful in the
case of diseased arrhythmia producing tissue that lies
only near the surface.
In one preferred embodiment, a balloon has two
annular bands of conductive material on its exterior for
bipolar operation, with the RF current flowing through
the tissue between the two bands.
Other ways to construct the balloon will occur to
those skilled in the art. For instance, a balloon may be
of electrically conductive material such as conductive
elastomer filled with silver particles.
Other examples of operable, expansible electrodes
include mechanical structures.
The first preferred mechanical device is comprised
of a series of expansible members that are constrained
either by spring force or mechanical force so that when
they are uncovered, in the manner of a conventional stone
retrieval basket sold by Boston Scientific Corporation,
the wire ribbons expand outward and provide a larger
electrode surface for engagement of the tissue with
suitable pressure.
In one instance a straight cage formed of spring
wires that are generally axially disposed is employed.
It is so constructed that when the wires are released by
removal of the sheath, they are allowed to expand to a
rest dimension of generally spherical shape. Self-
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expanding wires may be constructed of conductive spring
metal or a relatively poor conductor with good spring
properties can be employed such as nitinol on which is
deposited a highly conductive material such as gold. For
such a self-expanding embodiment, as mentioned, a
constraining sheath is employed. It confines the springy
wires in distorted condition at a much smaller diameter.
Upon removal of the sheath, such as sliding it proximally
of the catheter, the spring wires are released to form
the rounded shape.
In another embodiment, a tension wire can be
employed which acts to pull the wires of the basket
structure radially inwardly to keep the wires close to
the shaft during introduction. Release of tension on the
tensioning wire enables the structure to expand radially
to its enlarged rest condition.
In another embodiment, a central member
independent of the outer catheter wall is employed to
move the distal tip of the spring basket distally
independently of the proximal end, to reduce the diameter
of the basket by pulling it axially. Release allows the
distal tip to draw back and the electrode basket to
expand.
other variations of this aspect are a spiral cage
and a braided weave each made of heat conductive,
electrically conductive wires. These again are
embodiments in which the wire members lie close to the
shaft in the reduced sized state and expand to the larger
diameter in the released or expanded state. Such more
complex structures are preferable in cases where it is
desired to maximize the wire contact coverage when the
basket is expanded.
In many instances use of the balloon is preferred
to obtain the most uniform distribution of energy, but
there are instances in which the mechanical structures
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have advantage, such as for conforming to special
profiles of particular locations of the heart cavity.
In certain embodiments, a further electrode is
disposed on the portion of the shaft that protrudes
beyond the balloon. Such an electrode can be used for
producing small area ablation, when desired, to increase
the capability of the single catheter. The distal
electrode may also be employed, along with additional
electrodes, for instance, ring electrodes on the catheter
shaft both proximal and distal of the balloon, for
electrophysiological mapping. In some cases, it is
preferred to activate the mapping electrodes
simultaneously while performing ablation. In this way,
the change in the electrical activity of the adjacent
tissue can be monitored as ablation proceeds, thus to
produce an indication monitoring of the result being
produced. Control of the duration of the application of
the RF current may be determined by the detected values.
It is also advantageous in certain instances to
employ ultrasound imaging in connection with the ablation
technique to observe the lesion forming and to measure
its dimension.
In certain instances, it is advantageous to
provide a fluid dispensing lumen as part of the catheter
for the purpose of augmenting the ablation effect at the
tissue. The fluid may be selected to be highly
electrically conductive relative to the conductivity of
blood and thus can render the zone where the fluid is
introduced preferentially conductive, to establish a zone
that tends to concentrate the heat, as a result of I2R
losses being greatest where the largest current flows.
In another instance, fluid introduced through the
lumen is selected to be destructive of tissue, such as
alcohol which tends to be ablative due to its osmotic
CA 02471106 2004-07-05
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behavior. In this way fluid ablation and RF ablation effects can
be advantageously combined,
In preferred embodiments, the catheter is of 7 French size.
The balloon in deflated condition in this case is also about 7
French and is expansible to e.g. 5 or 10 mm in diameter.
A principal advantage of the invention is that it enables
larger lesions to be created with a single catheter to achieve a
definitive result for the patient in less time, hence with less
risk to the patient and better utilization of the physician's
time, than with prior electrodes.
Thus advantages of the present invention are that quite
large electrodes can be achieved which act faster and can produce
lesions deeper than prior devices, all in a device that is
practical to maneuver through the arterial system and into the
heart. The instrument is useful in any chamber of the heart where
it is desired to produce a large lesion.
According to one embodiment, there is disclosed an acoustic
imaging system for use within a body of a living being,
comprising: an elongated, flexible catheter constructed to be
inserted into the body of the living being, an ultrasound device
incorporated into the elongated, flexible catheter, the ultrasound
device being arranged to direct ultrasonic signals toward an
internal structure within the body of the living being for the
purpose of creating an ultrasonic image of the internal structure,
an electrode mounted on a distal portion of the elongated,
flexible catheter, the electrode being arranged for electrical
contact with the internal structure imaged by the ultrasound
device, a balloon mounted on the distal portion of the elongated,
flexible catheter, the balloon being constructed and electrically
coupled to the electrode to cause ablation of at least a portion
of the internal s-tructure, the balloon comprising a ma.t.erial that
vibrates in response to electrical excitation, the ablation being
at least assisted by vibration of the material.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the internal structure comprises
heart tissue.
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According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the electrode comprises an
electrophysiology electrode constructed to sense electrical
potentials within the internal structure when the electrode is
placed in electrical contact with the internal structure.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the electrode comprises an
ablation electrode constructed to ablate tissue when the electrode
is placed in electrical contact with the internal structure.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein at least a portion of the
ablation electrode is constructed to be inserted into the internal
structure.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the ablation electrode is a wire.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the wire is shaped as a cork
screw.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the elongated, flexible catheter
comprises a steering device constructed to cause bending of the
distal portion of the catheter, the steering device comprising a
control mechanism at a proximal portion of the catheter arranged
to control the bending of the distal portion of the catheter.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein: the elongated, flexible catheter
comprises an elongated tubular member and an elongated drive shaft
extending through the tubular member, at least a portion of the
ultrasound device being mounted on a distal portion of the drive
shaft, and the acoustic imaging system further comprises a
mechanism constructed to cause r-e-lative longitudinal movement
between the drive shaft and the tubular member.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the ultrasound device comprises
an ultrasound transducer.
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According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the ultrasound device further
comprises a mirror arranged to reflect ultrasound signals produced
by the ultrasound transducer in a manner such that the ultrasound
signals are directed toward the internal structure.
According to a further embodiment, there is disclosed an
acoustic imaging, wherein the balloon is constructed to assist in
positioning the catheter in the vicinity of the internal
structure.
According to a further embodiment, there is disclosed an
acoustic imaging, wherein the balloon is fillable with a gas to
cause the balloon mounted on the distal end of the catheter to
float from one location within the body of the living being to
another location within the body of the living being.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the balloon is fillable with a
liquid to cause the balloon mounted on the distal end of the
catheter to travel with flow of fluid within the body of the
living being.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the balloon is constructed to
press the catheter against a wall of the internal structure of the
body of the living being.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the electrode is mounted on the
balloon.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the catheter comprises a tubular
shaft member and the electrode is mounted on the tubular shaft
member.
According to a.further..embadiment,__there is disclo.sedan
acoustic imaging system, wherein the balloon is sonolucent.
According to a further embodiment, there is disclosed an
acoustic imaging system, further comprising a chemical ablation
device mounted on a distal portion of the elongated, flexible
catheter.
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According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the ablation device comprises a
wall of the balloon having ports for delivery of fluid to the
internal structure of the body of the living being.
According to a further embodiment, there is disclosed the
use of an acoustic imaging system, wherein the system is adapted
so that the electrode is positionable relative to a the internal
structure by reference to an ultrasonic image of the internal
structure.
According to a further embodiment, there is disclosed the
use, wherein the system is adapted so that: the ultrasound device
is slidable between at least two longitudinally spaced positions,
the ultrasonic signals from the ultrasound device at least one of
the positions are useable to create an ultrasonic image of the
internal structure at the position, and the position of the
electrode relative to the internal structure, is determinable
based on the plurality of ultrasonic images.
According to a further embodiment, there is disclosed an
acoustic imaging system for use within a body of a living being,
comprising: an elongated, flexible catheter having a distal
portion and constructed to be inserted into the body of the living
being, an ultrasound device incorporated into the elongated,
flexible catheter, the ultrasound device being arranged to direct
ultrasonic signals toward an internal structure within the body of
the living being for the purpose of creating an ultrasonic image
of the internal structure, an ablation device comprising a
transducer mounted on the distal portion of the elongated,
flexible catheter, the transducer being constructed arranged to
convert electrical signals into radiation and to direct the
radiation toward the internal structure within the body of the
living--being for the.__purpos~__-of__~blating tis.sue.,._and -a .p-1urality
of electrical conductors extending from a proximal portion of the
elongated, flexible catheter to the distal portion, at least two
of the plurality of electrical conductors being connected to the
ultrasound device and at least two of the plurality of electrical
conductors being connected to the ablation device, the ablation
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device being arranged to ablate at least a portion of the internal
structure imaged by the ultrasound device.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the ultrasound device comprises
an ultrasound transducer arranged to direct the ultrasound signals
in a first direction and the ablation device also comprises the
ultrasound transducer.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the ultrasound device comprises
an ultrasound transducer arranged to direct the ultrasonic signals
in a first direction and the ablation device comprises a
transducer constructed to direct the radiation in a second
direction differing from the first direction.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the radiation comprises sonic
radiation.
According to a further embodiment, there is disclosed an
acoustic imaging system, wherein the radiation comprises microwave
radiation.
According to a further embodiment, there is disclosed the
acoustic imaging system, further comprising: an acoustic marker
mounted on at least a distal portion of the elongated, flexible
catheter, the acoustic marker being constructed to emit a sonic
wave when the acoustic marker is electrically excited, the
acoustic imaging system being constructed in a manner such that
interference of the sonic wave emitted by the acoustic marker with
the ultrasonic signals directed toward the internal structure by
the acoustic imaging system causes an identifiable artifact to
appear on the ultrasonic image of the internal body structure.
According to a further embodiment, there is disclosed the
ac.ousxic imag.ing_system-, wherein the- .acousti.c marker. ia____
sonolucent.
According to a further embodiment, there is disclosed the
acoustic imaging system, wherein the acoustic marker comprises
polyvinylidene fluoride.
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According to a further embodiment, there is disclosed the
acoustic imaging system, wherein the elongated, flexible catheter
comprises an elongated tubular member that comprises
polyvinylidene fluoride along its entire length.
According to a further embodiment, there is disclosed the
acoustic imaging system, wherein one portion of the acoustic
marker is constructed to emit a sonic wave having a first
frequency and another portion of the acoustic marker is
constructed to emit a sonic wave having a second frequency
differing from the first frequency.
According to a further embodiment, there is disclosed the
acoustic imaging system, wherein the system comprises: a plurality
of elongated, flexible catheters constructed to be inserted in to
a body of a living being, a plurality of acoustic markers mounted
on at least a distal portion of respective ones of the elongated,
flexible catheters, each of the acoustic markers being constructed
to emit a sonic wave when the second acoustic marker is
electrically excited, at least one of the acoustic markers being
constructed to emit a sonic wave having a first frequency and at
least another of the acoustic markers being constructed to emit a
sonic wave having a second frequency differing from the first
frequency.
According to a further embodiment, there is disclosed the
acoustic imaging system, wherein the acoustic imaging system
comprises a trans-esophageal ultrasound imaging device.
According to a further embodiment, there is disclosed the
acoustic imaging system, wherein the identifiable artifact
comprises a color representation of the acoustic marker, the color
being a function of the frequency of the sonic wave emitted by the
acoustic marker.
According--to afurther-Embodiment,-them --is disclosed. the
acoustic imaging system, further comprising: a plurality of
electrical conductors extending from a proximal portion of the
elongated, flexible catheter to the distal portion, at least two
of the plurality of electrical conductors being connected to the
ultrasound device, at least one of the plurality of electrical
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conductors being connected to the electrode, and at least two of
the plurality of electrical conductors being connected to the
material of the balloon to cause vibration thereof.
According to a further embodiment, there is disclosed the
use of an ultrasound device to create an ultrasound image of an
intermal body structure and the use of an ablation device to
ablate heart tissue, wherein, the ultrasound device and the
ablation device are positioned in a distal portion of an
elongated, flexible catheter the elongated, flexible catheter
being adapted to be insertable into a body of a living being, the
distal portion of the elongated, flexible catheter being adapted
to be insertable into the heart, the ultrasound device being
adapted to be positionable in the vicinity of an internal
structure within the heart, the elongate, flexible catheter being
adapted so that ultrasonic signals from the ultrasound device are
directable toward the internal structure to create an ultrasonic
image of the internal structure.
According to a further embodiment, there is disclosed the
use of an inflatable balloon to engage heart tissue and the use of
a heating device to ablate at least a portion of the heart tissue:
the heating device and the inflatable balloon being mounted on a
catheter having a catheter shaft comprising a distal portion
wherein the heating device and the inflatable balloon are mounted
on the distal portion, the catheter shaft being adapted to be
insertable into a blood vessel; the catheter shaft and the balloon
being adapted so that: (a) the distal portion of the catheter
shaft is insertable into an atrium or ventricle of a heart while
the balloon is deflated; and (b) the balloon is fillable with a
fluid whilst inside the atrium or ventricle; the heating device
and the balloon being adapted so that the at least a portion of
the t-issue-can--be-.-heated by the.hea ingdevicewhile_ theportion
of the tissue is in contact with the balloon while the balloon is
inflated; the catheter being adapted to be insertable into the
body and being adapted so that the distal portion of the catheter
is positionable within an atrium or ventricle and adjacent to a
wall of the atrium or ventricle; the balloon being
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adapted to be inflatable within the atrium or the ventricle, and
to be engageable while the balloon is inflated and in direct
contact with the wall of the atrium or ventricle.
According to a further embodiment, there is disclosed the
use, the adaptation for heating of the at least a portion of the
tissue comprising adaptation for heating of fluid within the
balloon.
According to a further embodiment, there is disclosed the
use, wherein the catheter further comprises a temperature feedback
device mounted on the distal portion of the catheter shaft, and
wherein the use further comprises the step of monitoring a
temperature using the temperature feedback device.
According to a further embodiment, there is disclosed the
use, wherein the catheter further comprises an electrode located
on a distal portion of the catheter shaft, and wherein the
temperature feedback device is adapted to use the electrode to
monitor electrical potentials within the heart.
According to a further embodiment, there is disclosed the
use, wherein the electrode is mounted directly on the catheter
shaft.
According to a further embodiment, there is disclosed the
use, wherein the electrode is coated onto the balloon, which is
mounted on the catheter shaft.
According to a further embodiment, there is disclosed the
use, wherein the catheter further comprises an electrode located
on the distal portion of the catheter shaft, and wherein the
catheter is further adapted to use the electrode to ablate the at
least a portion of the heart tissue.
According to a further embodiment, there is disclosed the
use, wherein the catheter further comprises an ultrasound device
on the list-al portion of the catheter shaft, and wherein. the
ultrasound device is further adapted for use to image the heart.
According to a further embodiment, there is disclosed the
use, wherein the adaptation for engagement of the balloon in
direct contact with the tissue comprises an adaptation for
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engaging a side wall of the balloon with the tissue in a radial
direction.
According to a further embodiment, there is disclosed the
use, wherein the adaptation for engaging the balloon in direct
contact with the tissue comprises an adaptation fox engaging a
distal end wall of the balloon with the tissue in an axial
direction.
According to a further embodiment, there is disclosed the
use, wherein the catheter further comprises an anchoring device
mounted on the distal portion of the catheter shaft, and wherein
the adaptation to permit positioning the distal portion of the
catheter shaft in the atrium or ventricle comprises an adaptation
to permit anchoring the distal portion of the catheter shaft in a
fixed location using the anchoring device.
Numerous other features, objects and advantages of the
invention will become apparent from the following detailed
description when read in combination with the accompanying
drawings.
Brief Description of the Drawings
Fig. 1 is a schematic diagram of a system showing use of an
acoustic catheter.
Fig. 2 is a side view of a disposable catheter sheath for
the acoustic catheter,
Fig. 3 is a longitudinal, partially cut away view of the
distal end of the rotating assembly of the acoustic catheter.
Fig. 4 is a longitudinal, cross-sectional view of the distal
end of the assembled acoustic catheter.
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Fig. 5 is a longitudinal sectional view of the
transducer element of the catheter on a greatly magnified
scale.
Fig. 6 is a diagrammatic representation of sound
waves emanating from the acoustic lens of the catheter.
Figs. 7-7d are longitudinal views of a catheter
assembly illustrating steps in filling the sheath and
assembling the acoustic catheter, the syringes shown in
the figures being on a reduced scale.
Fig. 8 is a cross-sectional view of the
motor-connector assembly to which the catheter is
connected, and Fig. 8a is a cross-sectional view on an
enlarged scale of a portion of Fig. 8.
Figs. 9, 10 and 11 are graphical representations
of torque in relation to angular deflection.
Fig. 12 is a block diagram of the electronic
components useful with the acoustical catheter.
Fig. 13 is a longitudinal view of an acoustic
imaging catheter sheath having electrodes for
2o electrophysiology or cardiac ablation mounted on the
catheter sheath.
Fig. 14 is a block diagram of the principle
components of an acoustic imaging and electrophysiology
system that includes the catheter shown in Fig. 13.
Fig. 15 is a partially cut-away view of a heart
showing an acoustic imaging and electrophysiology
catheter being used to image a chamber of the heart.
Fig. 15a is a partially cut-away view of a heart
showing an acoustic imaging and electrophysiology
catheter being used to image a portion of a chamber of
the heart that has been ablated by means of the
electrodes on the catheter sheath.
Fig. 16 is a longitudinal view of an acoustic
imaging catheter sheath which is deflectable by actuation
from the proximal end, and which includes electrodes for
CA 02471106 2004-07-05
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electrophysiology or ablation mounted on the catheter
sheath.
Fig. 1~ is a longitudinal cross-sectional view of
an acoustic imaging catheter sheath having a sonolucent
metallic electrode and having a sonolucent metallic trace
leading to the electrod~.
Fig. 18 is a longitudinal cross-sectional view of
an acoustic imaging catheter sheath having a sonolucent
metallic electrode and having a protective covering over
the electrode with micro-apertures drilled through the
covering.
Fig. 18a is a longitudinal cross-sectional view of
the acoustic imaging catheter sheath of Fig. 18 showing
the micro-apertures filled with conductive material.
Fig. 19 is a longitudinal view of a catheter
sheath having a balloon in combination with an electrode
for electrophysiology or cardiac ablation, and Figs. 19a,
19b and 19c are longitudinal views of the distal portion
of the catheter sheath shown in Fig. 19, illustrating
stages of inflation of the balloon.
Fig. 20 is a partially cut-away longitudinal view
of a catheter sheath having a balloon on which a set of
electrodes is coated, the balloon being constructed of
electrically excitable material and having a set of
perfusion ports in its wall.
Fig. 21 is a partially cut-away longitudinal view
of a catheter sheath having a balloon through which a
fluid-injection needle passes, the balloon being
constructed of electrically excitable material and having
a set of perfusion ports in its wall.
Fig. 21a is an enlarged view, partially in cross-
section of the fluid-injection needle shown in Fig. 21
exiting through a wall of the balloon.
Fig. 22 is a longitudinal view of one embodiment
of an acoustic imaging balloon catheter.
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Fig. 23 is an expanded longitudinal cross-
sectional view of the proximal end of the catheter
coupling of the acoustic imaging balloon catheter of Fig.
22, in partial cross-section.
Figs. 24, 25, and 26 are longitudinal views of
alternative embodiments of acoustic imaging balloon
catheters enabling relative axial positioning of the
transducer and the balloon.
Fig. 27 is a longitudinal view of an acoustic
imaging catheter sheath having a hollow needle, extending
from the distal tip of the catheter sheath, for injection
of fluid into cardiac tissue, and Fig. 27a is a detailed
cross-sectional view of the distal tip of the catheter
sheath shown in Fig. 27.
Fig. 28 is a longitudinal view of an acoustic
imaging catheter sheath having a needle, extending from
the distal tip of the catheter sheath, constructed of an
electrically excitable material that generates acoustic
energy when excited, and Fig. 28a is a detailed,
partially cross-sectional view of the distal tip of the
catheter sheath shown in Fig. 28.
Fig. 29 is a perspective view of an acoustic
imaging catheter sheath having a hollow needle, extending
from a side wall of the catheter sheath, for injection of
fluid into cardiac tissue, and having electrodes for
electrophysiology or cardiac ablation mounted on the
catheter sheath, and Fig. 29a is a detailed, partially
cross-sectional view of the distal tip of the catheter
sheath shown in Fig. 29.
Fig. 30 is a longitudinal view of an acoustic
imaging catheter sheath having a wire in the shape of a
cork screw attached to its distal end, and Fig. 30a is a
detailed, partially cross-sectional view of the distal
tip of the catheter sheath shown in Fig. 30.
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Fig. 31 is a longitudinal view of an acoustic
imaging catheter sheath having a wire in the shape of a
cork screw passing through its distal end, the wire being
attached to the drive shaft within the sheath, and Fig.
31a is a detailed, partially cross-sectional view of the
distal tip of the catheter sheath shown in Fig. 31.
Fig. 32 is a longitudinal view of an acoustic
imaging catheter sheath enclosing a drive shaft on which
an imaging transducer and an ablation transducer are
mounted, and Fig. 32a is a detailed, partially croes-
sectional view of the distal tip of the catheter sheath
shown in Fig. 32.
Fig. 33 is a partially cut-away view of a heart
and a portion of an esophagus, showing the use of a
trans-esophageal probe in combination with two catheters
whose distal portions are located within a heart chamber.
Fig. 34 is a block diagram of the principle
components of an acoustic imaging and electrophysiology
system that includes an electrophysiology catheter and a
display that super-imposes electrophysiology data on an
image of the heart.
Fig. 35 is a cross-sectional view of a catheter
having a rotatable drive shaft on which a mirror is
mounted, the mirror being configured to reflect
ultrasound signals produced by a transducer.
Fig. 36 is a side view of a catheter having a
balloon mounted thereon.
Fig. 37 is an enlarged side view of a portion of
the catheter shaft of Fig. 36.
Fig. 38 is a side view of the distal end of the
catheter of Fig. 36 with the balloon deflated.
Fig. 39 is a side view of the distal end of the
catheter of Fig. 36 with the balloon inflated.
Fig. 40 is a pictorial representation of a human
body illustrating a portion of the vascular system.
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Fig. 41 is a pictorial representation of the
catheter of Fig. 36 in the left ventricle with the
balloon deflated and with the tip of the catheter in
contact with heart tissue.
Fig. 42 is a pictorial representation of the
catheter of Fig. 36 in the left ventricle with the
balloon inflated and with the tip of the balloon in
contact with heart tissue.
Fig. 43 is a pictorial representation of the
catheter of Fig. 36 in the left ventricle with the
balloon deflated and with the side of the balloon in
contact with heart tissue.
Fig. 44 is a pictorial representation of the
catheter of Fig. 36 in the left ventricle with the
balloon inflated and with the side of the balloon in
contact with heart tissue.
Fig. 45 is a side view of a catheter having an
inflated balloon mounted at the distal end of the
catheter shaft.
Fig. 46 is a side view of another catheter having
an inflated balloon spaced from the distal end of tha
catheter shaft.
Fig. 47 is a side view of another catheter having
an inflated balloon spaced from the distal end of the
catheter shaft and having a distal extension for
anchoring the distal end of the catheter in a fixed
location.
Fig. 48 is a side view of a catheter having a
suction cup at its distal end.
Fig. 49 is a sectional view of the catheter of
Fig. 48 taken along line I-I in Fig. 48.
Fig. 50 is a side view of a catheter having an
inflated balloon at its distal end that performs a
suction anchoring function.
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Fig. 51 is a sectional view of the catheter of
Fig. 50 taken along line II-II in Fig. 50.
Fig. 52 is a side view of a catheter having a
suction cup at its distal end.
Fig. 53 is a sectional view of a catheter having
an inflated balloon and electrodes mounted thereon and
having an ultrasonic sensor for producing an ultrasonic
image within a patient s body.
Fig. 54 is a schematic view of an
electrophysiological heart catheter.
Fig. 55 is a side view of a distal portion of the
electrophysiological heart catheter of Fig. 54, having a
deflated balloon.
Fig. 56 is a side view of a distal portion of the
electrophysiological heart catheter of Fig. 54, having an
inflated balloon.
Fig. 5? is a side view of a distal portion of an
electrophysiological heart catheter having a deflated
balloon with two conductive stripes applied to the
2o surface of the balloon.
Fig. 58 is a side view of the electrophysiological
heart catheter of Fig. 57, with the balloon in its
inflated state.
Fig. 59 is a schematic view of an
electrophysiological heart catheter coupled to an
inflation metering device.
Fig. 60 is a side view of a distal portion of the
electrophysiological heart catheter of Fig. 59, showing a
deflated balloon having a plurality of conductive dots
mounted on its surface.
Fig. 61 is a side view of the distal portion of
the electrophysiological heart catheter of Fig. 59,
showing the balloon partially inflated.
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Fig. 62 is a side view of the distal portion of
the electrophysiological heart catheter of Fig. 59,
showing the balloon more fully inflated.
Fig. 63 is a side view of a distal portion of an
electrophysiological heart catheter having a sheath that
compresses a set of flexible members.
Fig. 64 is a side view of the electrophysiological
heart catheter of Fig. 63, with the sheath retracted and
the flexible members in an expanded condition. -
Fig. 65 is a side view of a distal portion of an
electrophysiological heart catheter shaft having a set of
flexible members drawn tightly around the catheter shaft.
Fig. 66 is a side view of the electrophysiological
heart catheter of Fig. 65, showing the flexible members
expanded away from the catheter shaft.
Fig. 67 is a side view of a distal portion of an
electrophysiological heart catheter shaft having a set of
flexible members wrapped tightly around the catheter
shaf t .
Fig. 68 is a side view of the electrophysiological
heart catheter shaft of Fig. 67, showing the flexible
members expanded away from the catheter shaft.
Fig. 69 is a partially sectional view of the
distal portion of a catheter of the type shown in Fig. 56
that additionally includes an ultrasound transducer.
Fig. 70 is a partially cross-sectional view of a
catheter in the left side of a heart, showing a balloon
electrode in a deflated condition and in contact with
heart tissue.
Fig. 71 is an enlarged view of a portion of Fig.
70.
Fig. 72 is a partially cross-sectional view of a
catheter in the left side of a heart, showing a balloon
electrode in an inflated condition.
n CA 02471106 2004-07-05
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Fig. 73 is an enlarged view of a portion of Fig.
72.
Fig. 74 is a partially cross-sectional view of a
catheter in the left side of a heart, showing a balloon
electrode in a deflated condition and removed from
contact with heart tissue.
Fig. 75 is a partially cross-sectional view of a
catheter in the left side of a heart, showing a
mechanical electrode in a non-expanded condition and in
contact with heart tissue.
Fig. 76 is an enlarged view of a portion of Fig.
75.
Fig. 77 is a partially cross-sectional view of a
catheter in the left side of a heart, showing a
mechanical electrode in an expanded condition.
Fig. 78 is an enlarged view of a portion of Fig.
77.
Fig. 79 is a partially cross-sectional view of a
catheter in the left side of the heart, showing a
mechanical electrode in a non-expanded condition and
removed from contact with heart tissue.
Fig. 80 is a partially sectional view of the
distal portion of a catheter of the type shown in Fig. 56
that additionally includes a port for introduction of
fluid to an ablation site.
General Structure
Referring to Fig. 1, a micro-acoustic imaging
catheter 6 according to the invention is driven and
monitored by a control system 8. The catheter is
comprised of a disposable catheter sheath 12 (Figs. 2 and
4) having a sound-transparent distal window 24 provided
by dome element 25 (Fig. 4), in which is disposed a
miniature, rotatable ultrasonic transducer 10 (Figs. 3
and 4) driven by a special, high fidelity flexible drive
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shaft 18. A relatively rigid connector 11 is joined to
the proximal end of the main body of the catheter sheath,
adapted to be joined to a mating connector of drive and
control system 8.
The catheter is adapted to be positioned within
the heart by standard catheter procedures by guiding the
flexible catheter through various blood vessels along a
circuitous path, starting, for example, by percutaneous
introduction through an introducer sheath 13 disposed in
a perforation of the femoral artery 15.
Referring to Fig. 2, disposable catheter sheath 12
is a long tube, extruded from standard catheter
materials, here nylon, e.g. with outer diameter, D, of 2
mm, wall thickness of 0.25 mm and length of 1 meter.
Dome element 25, connected to the distal end of the tube,
is a semi-spherically-ended cylindrical transducer cover
constructed of material which is transparent to sound
waves, here high impact polystyrene. This dome element
has a thickness of approximately 0.125 mm and a length E
of about 8 mm. For purposes described later herein,
catheter sheath 12 in its distal region preferably tapers
down over region R as shown in Fig. 4 to a narrowed
diameter D' at its distal end, achieved by controlled
heating and drawing of this portion of the original tube
from which the sheath is formed. Catheter sheath 12 and
acoustically transparent dome element 25 are adhesively
bonded together.
Referring to Figs. 3 and 4, the drive shaft
assembly 18 is formed of a pair of closely wound multi-
filer coils 26, 28 wound in opposite helical directions.
These coils are each formed of four circular
cross-sectional wires, one of which, 30, is shown by
shading. Coils 26, 28 are soldered together at both the
distal and proximal ends of the assembly in interference
contact, here under rotational pre-stress. By also
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providing a pitch angle of greater than about 20°, a
substantial part of the stress applied to the wire
filaments of the coil is compression or tension in the
direction of the axis of the filaments, with attendant
reduction of bending tendencies that can affect fidelity
of movement. There is also provision to apply a
torsional load to the distal end of the assembly to cause
the drive shaft to operate in the torsionally stiff
region of its torsional spring constant curve, achieved
by viscous drag applied to the rotating assembly by
liquid filling the narrowed distal end 'of the catheter
sheath (Fig. 4). Such loading, together with initial
tight association of the closely wound filaments in the
concentric coils, provides the assembly with a
particularly high torsional spring constant when twisted
in a predetermined direction. Thus, despite its lateral
flexibility, needed for negotiating tortuous passages,
the assembly provides such a torsionally stiff and
accurate drive shaft that rotary position information for
the distal end can, with considerable accuracy, be
derived from measurement at the proximal end of the drive
shaft, enabling high quality real-time images to be
produced. Further description of the coils of the drive
shaft and their condition of operation is provided below.
Coaxial cable 32 within coils 26, 28 has low power
loss and comprises an outer insulator layer 34, a braided
shield 36, a second insulator layer 38, and a center
conductor 40. Shield 36 and center conductor 40 are
electrically connected by wires 42, 44 (Fig. 5) to
piezoelectric crystal 46 and electrically conductive,
acoustical backing 48 respectively, of the transducer.
Helical coils 26, 28, especially when covered with a
highly conductive metal layer, act as an additional
electric shield around cable 32.
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32
Transducer crystal 46 is formed in known manner of
one of a family of ceramic materials, such as barium
titanates, lead zirconate titanates, lead mataniobates,
and PVDFs, that is capable of transforming pressure
distortions on its surface to electrical voltages and
vice versa. Transducer assembly 10 is further provided
with an acoustic lens 52. The radius of curvature B of
lens surface 52 is greater than about 2.5 mm, chosen to
provide focus over the range f (Fig. 6) between about-2
l0 to 7 mm. The lens is positioned at an acute angle to the
longitudinal axis of the catheter so that, during
rotation, it scans a conical surface from the transducing
tip, the angle preferably being between 10° and 80°,
e.g., 30°. Transducer backing 48 is acoustically matched
to the transducer element to improve axial resolution.
The transducer assembly 10 is supported at the
distal end of the drive shaft by a tubular sleeve 29
which is telescopically received over a distal extension
of the inner coil 28, as shown in Fig. 3.
Referring again to Fig. 4, the length, E, of dome
element 25 is sufficient to provide headroom F for
longitudinal movement of transducer 10 within the dome
element as catheter sheath 12 and coils 26, 28 are
twisted along the blood vessels of the body. In the
untwisted state, transducer 10 is a distance F, about 2
to 3 mm, from the internal end surface of the dome
element 25. The dome element, along with catheter sheath
12 is adapted to be filled with lubricating and
sound-transmitting fluid.
Figs. 7-7b show the filling procedure used to
prepare ultrasound catheter sheath 12 (or any of the
other interchangeable sheaths described below) for
attachment to the ultrasound imaging drive shaft and
transducer assembly. A sterile, flexible filling tube 17
attached to a syringe 19 is filled with sterile water.
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This filling catheter is inserted into the ultrasound
catheter sheath 12, all the way to the distal tip. The
Water is then injected until it completely fills and the
excess spills out of the ultrasound catheter while held
in a vertical position, see Fig. 7a. This expels air
from the catheter which could impair good acoustic
imaging. Continued pressure on the plunger of the
syringe causes the flexible tube 17 to be pushed upward,
out of catheter 12, Fig. 7b, leaving no air gaps behind.
This eliminates the necessity to carefully withdraw the
flexible filling tube at a controlled rate which could be
subject to error. A holding bracket 21 is used to hold
the catheter vertical during this procedure.
After the catheter sheath 12 is filled, the
acoustic transducer l0 and shaft 18 are inserted,
displacing Water from the sheath 12, until the installed
position, Fig. 7d, is achieved.
Figs. 8 and 8a (and Fig. 1, diagrammatically) show
the interconnection arrangement for a connector 7 at
proximal end of the acoustic catheter with connector 16
of the driving motor 20, and the path of the electric
wires through the center shaft 43 of the driving motor.
The center shaft and connector 16 rotate together, as do
the wires that pass through the hollow motor shaft. The
latter connect to a rotating electrical joint 27, which
is held stationary at the back end and is connected to
stationary coaxial cable 45 through a suitable connector
such as a common BNC type. The enlarged view shows how
the motor connector 16 and the driveshaft connector 7
mate when the two assemblies are pushed together, thereby
making both electricah and mechanical contact. The
driveshaft connector 7is held in position by an ordinary
ball-bearing which provides._.a .thrusting surface for the
rotating connector 16 and driveshaft 18 while allowing
free rotation. The disposable catheter sheath 12
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includes an inexpensive, relatively rigid hollow bushing
11 of cylindrical construction that allows it to be slid
into and held by means of a set screw in the housing that
captures the non-disposable bearing, connector and
driveshaft 18. The longitudinal and rotational position
of hollow bushing 11 relative to the housing is
adjustable. Drive shaft coil assembly 18, thus attached
at its proximal end to connector 16 of drive motor 20,
rotates transducer 10 at speeds of about 1800 rpm. The
transducer 10 is electrically connected by coaxial cable
32 extending through coil assembly 18 and via the cable
through the motor to the proximal electronic components
22 which send, receive and interpret signals from the
transducer. Components 22 include a cathode ray tube 23,
electronic controls for the rotary repetition rate, and
standard ultrasonic imaging equipment; see Fig. 12. A
rotation detector, in the form of a shaft encoder shown
diagrammatically at 19, detects the instantaneous
rotational position of this proximal rotating assembly
and applies that positional information to components 22,
e.g., for use in producing the scan image.
Because the rotation detector depends upon the
position of proximal components to represent the
instantaneous rotational position of the distal
components, the rotational fidelity of the drive shaft is
of great importance to this embodiment.
M~"~,factnre and Assembly of the Drive Shaft
Referring to Figs. 3 and 4, coils 26, 28 are each
manufactured by winding four round cross-section
stainless steel wires of size about 0.2 mm, so that Do is
about 1.3 mm, Df is about 0.9 mm, do is about 0.9 mm and
di is about 0.5 mm. The coils are closely wound with a
pitch angle ao and ai where ao is smaller than ai, e.g.,
22 1/2° and 31°, respectively. Flat wires having a
cross-sectional depth of about 0.1 mm may also be used.
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The pitch angles are chosen to eliminate clearances 60
between the wires and to apply a substantial part of the
stress in either tension or compression along the axis of
the wire filaments. The coils, connected at their ends,
are adapted to be turned in the direction tending to make
outer coil 26 smaller in diameter, and inner coil 28
larger. Thus the two assemblies interfere with each
other and the torsional stiffness constant in this
rotational direction is significantly increased (by a
factor of about 6) due to the interference. Operation of
the driveshaft in the torsionally stiff region with
enhanced fidelity is found to be obtainable by adding a
torsional load to the distal end of the rotating assembly
of the catheter. The importance of rotational fidelity
and details of how it is achieved warrant further
discussion.
For ultrasound imaging systems, the relative
position of the ultrasound transducer must be accurately
known at all times so that the return signal can be
2o plotted properly on the display. Any inaccuracy in
position information will contribute to image distortion
and reduced image quality. Because position information
is not measured at the distal tip of the catheter, but
rather from the drive shaft at the proximal end, only
with a torsionally stiff and true drive shaft can
accurate position information and display be obtained.
Furthermore, it is recognized that any drive shaft
within a catheter sheath will have a particular angular
position which is naturally preferred as a result of
small asymmetries. Due to this favored position, the
shaft tends, during a revolution, to store and then
release rotational energy, causing non uniform rotational
velocity. This phenomenon is referred to as "mechanical
noise" and its effect is referred to as "resultant
angular infidelity" for the balance of this explanation.
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According to the present invention, use is made of
the fact that suitably designed concentric coils
interfere with each other, as has been mentioned
previously. When twisted in one direction, the outer
layer will tend to expand and the inner layer contract
thus resulting in a torsional spring constant which is
equal only to the sum of the spring constants of each of
the two shafts. When, however, twisted in the opposite
direction, the outer layer will tend to contract while
the inner layer will expand. When interference occurs
between the inner and outer layers the assembly will no
longer allow the outer coil to contract or the inner to
expand. At this point, the torsional spring constant is
enhanced by the interference between the shafts and the
torsional spring constant is found to become five or ten
times greater than the spring constant in the
"non-interference" mode.
Referring to Fig. 9, the relationship between
torque and angular deflection for such a coil assembly is
shown, assuming one end fixed and torque applied at the
opposite end. 'Y' represents mechanical noise; 'Z'
resultant angular infidelity; 'T' the interference point;
the slope of the line 'U', the torsional spring constant
(TSC) without interference (i.e., the sum of the
torsional spring constant of each of the two coils); and
the slope of the line 'V', the TSC with interference.
Thus, TSC is shown to increase dramatically at the
interference point.
Referring to Fig. 10, by pre-twisting the shafts
relative to one another and locking their ends together
in a pre-loaded assembly, the interference point is moved
to be close to the rest angle and resultant angular
infidelity, Z, is reduced in the given direction of
rotation.
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To improve upon this effect even further, dynamic
frictional drag is intentionally introduced at the distal
end of the shaft to raise the level of torque being
continually applied to the system. This ensures
operation of the shaft in the region of the high
torsional spring constant or "interference" mode
throughout its length, producing a rotationally stiffer
shaft. This is shown in Fig. 11, where 'W' is dynamic
load and 'X' is the region of operation. The use of such
dynamic drag is of particular importance in certain
catheters of small diameter, e.g. with outer diameter
less than about 2 mm.
To form inner coil 28, four individual wires are
simultaneously wound around a mandrel of about 0.5 mm
outer diameter. The free ends of this coil are fixed, and
then four wires are wound in opposite hand directly over
this coil to form the outer coil 26. The wires are wound
under moderate tension, of about 22.5 gm/wire. After
winding, the coils are released. The inner mandrel,
which may be tapered or stepped, or have a constant
cross-sectional diameter, is then removed. The wire ends
are finished by grinding. One end is then soldered or
epoxied to fix the coils together for a distance of less
than 3 mm. This end is held in a rigid support and the
coils are then twisted sufficiently, e.g. 1/4 turn, to
cause the outer coil to compress and the inner coil to
expand, causing the coils to interfere. The free ends
are then also fixed.
The coil assembly 18 is generally formed from
wires which provide a low spring index, that is, the
radius of the outer coil 26 must be not more than about
2.5 to 10 times the diameter of the wires used in its
construction. With a higher index, the inner coil may
collapse. The multi-filar nature of the coils enables a
smaller diameter coil to be employed, which is of
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particular importance for vascular catheters and other
catheters where small size is important.
After the coil assembly is completed, coaxial
cable 32 is inserted within the inner coil. The cable may
be silver-coated on braid 36 to enhance electrical
transmission properties. It is also possible to use the
inner and outer coils 26, 28 as one of the electrical
conductors of this cable, e.g. by silver coating the
coils.
Referring back to Figs. 3 and 5, to form
transducer 10, wire 42 is soldered to either side of
electrically conducting sleeve 29 formed of stainless
steel. Wire 44 is inserted into a sound absorbent
backing 48 which is insulated from sleeve 29 by insulator
72. Piezoelectric element 46 of thickness about 0.1 mm
is fixed to backing 48 by adhesive and electrical
connection 74 is provided between its surface and the end
of sleeve 29. Thus, wire 42 is electrically connected to
the outer face of piezoelectric element 46, and wire 44
2o electrically connected to its inner face. Spherical lens
52, formed of acoustic lens materials is fixed to the
outer surface of element 46.
Referring to Figs. 4 and 7-7d, the completed drive
shaft 18 and transducer 10 are inserted into disposable
catheter sheath 12, positioning transducer 10 within
acoustically transparent dome element 25, with liquid
filling the internal open spaces. The catheter thus
prepared is ready to be driven by the drive assembly; see
Fig. 8.
During use, rotation of drive shaft 18, due to
exposure of the helical surface of the outer coil to the
liquid, tends to create helical movement of the liquid
toward the distal- end of the sheath. This tends to
create positive pressure in dome element 25 which reduces
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the tendency to form bubbles caused by out-gassing from
the various surfaces in this region.
As has been mentioned, it is beneficial to provide
added drag friction at the distal end of the rotating
drive shaft 18 to ensure operation in the torsionally
stiff region of the torsional spring constant curve. It
is found that this may be done by simply necking down the
distal portion of the catheter sheath 12, as shown in
Fig. 4 to provide a relatively tight clearance between
the distal portion of the shaft 18 and the inner surface
of the sheath, to impose the desired degree of viscous
drag. As an alternative, the dynamic drag may be
provided by an internal protrusion in catheter sheath 12
to create a slight internal friction against drive shaft
18.
The acoustic catheter may be constructed so that
it may be preformed prior to use by standard methods.
Thus, if the investigator wishes to pass the catheter
through a known tortuous path, e.g., around the aortic
arch, the catheter can be appropriately shaped prior to
insertion. Such preformation can include bends of about
1 cm radius and still permit satisfactory operation of
the drive shaft.
Electronics
Figure 12 is a block diagram of the electronics of
a basic analog ultrasound imaging system used with the
acoustical catheter. The motor controller (D) positions
the transducer B for the next scan line. The transmit
pulsed (A) drives the ultrasound transducer. The
transducer (B) converts the electrical energy into
acoustic energy and emits a sound wave. The sound wave
reflects off various interfaces in the region of interest
and a portion returns to the transducer. The transducer
converts the acoustic energy back into electrical energy.
The receiver (C) takes this wave-form and gates out the
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transmit pulse. The remaining infonaation is processed
so that signal amplitude is converted to intensity and
time from the transmit pulse is translated to distance.
This brightness and distance information is fad into a
vector generator/scan converter (E) which along with the
position information from the motor controller converts
the polar coordinates to rectangular coordinates for a
standard raster monitor (F). This process is repeated
many thousands of times per second. -
By rotating the transducer at 1800 rpm, repeated
sonic sweeps of the area around the transducer are made
at repetition rate suitable for TV display, with plotting
based upon the rotary positional information derived from
the proximal end of the device. In this way a real time
ultrasound image of a vessel or other structure can be
observed.
Due to its rotational fidelity, the device
provides a relatively high quality, real time image of
heart tissue. It is also possible to form 3-dimensional
images using appropriate computer software and by moving
the catheter within the heart.
Selectable Catheter Sheaths
A wide variety of novel disposable catheter
sheaths can be substituted for catheter sheath 12 and
used in the system.
Fig. 13 shows a flexible, disposable catheter
sheath 12c on which are mounted a plurality of
electrophysiology or ablation electrodes 300. Catheter
sheath 12c may be combined with any of the technologies
described below in connection with Figs. 24, 25, and 26
to permit relative longitudinal movement between the
transducer and electrodes 300.
With reference to Fig. 14, an ultrasound/
electrophysiology catheter 392 such as the one shown in
Fig. 13 is connected to an ultrasound imaging system 338
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that receives signals from the ultrasound transducer and
transmits image data to display system 390 for display as
an ultrasound image. RF generator 340 generates RF
electrical signals for excitation of the ultrasound
transducer or the electrodes. By observing in real time,
on display system 390, the region of the heart near
ultrasound/ electrophysiology catheter 392, a physician
can determine the position of the catheter sheath and
electrodes relative to cardiac tissue and can also
reposition catheter 392 at the same location at a later
time. In order to reposition the catheter at the same
location the physician either remembers the image or
"captures" and stores the image using videotape or
computer storage capabilities, so that the physician can
compare the real time image with the captured or
remembered image to determine whether the catheter has
returned to the desired location.
One of the questions that arises during the course
of positioning the catheter is whether or not a
particular electrode is really in good electrical contact
with the cardiac tissue. By visualizing the position of
the electrode relative to the endocardium, the physician
can make a judgment whether that electrode is in the
proper position for a reliable reading. If not, the
catheter can be readily repositioned by twisting the
catheter and manipulating a steering wire, such as the
one described in connection with Fig. 16 below, until the
electrode or electrodes are in position. Without the use
of visual information, the physician could continue to
reposition the catheter in many locations of the heart
and could compare these readings until he gets a picture
in his mind of what the overall electrical activity of
the heart is like. Using visual information, however,
the physician can develop a better strategy that will
tell him what areas of the heart he may ablate (using any
CA 02471106 2004-07-05
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of a.variety of ablation techniques) in order to correct
any perceived deficiencies in the electrical activity of
the heart. Figs. 15 and 15a show an acoustic imaging and
electrophysiology catheter 348 being used to image a
chamber of heart 350 before and after ablation of heart
tissue, respectively.
Because the ultrasound transducer is being used to
image points of actual contact of the surface of the
electrode with cardiac tissue, it is necessary for the
transducer to have close-up imaging capability, i.s., the
ability to image from essentially the surface of the
catheter outward. This close-up imaging capability is
accomplished by using a very high frequency, such as 20
megahertz or higher. In certain circumstances, in which
a compromise between close-up imaging and depth of
penetration is desired, lower frequencies such as 10
megahertz could bs used (there tends to be a trade-off
between close-up and depth of penetration).
It is also possible to have more than one
transducer on the same rotary shaft, one transducer being
used for close-up imaging and the other being used for
depth of penetration. Alternatively, there may bs a
single, multifrequency transducer, which is a step
transducer having a piezo-electric element that has a
series of concentric plates or zones of varying
thicknesses. In one embodiment there would be two zones:
a central zone that occupies half of the surface area of
the transducer and that has thickness appropriate for
generating acoustic waves in the order of 30 megahertz,
and an annular zone around the central zone that has a
greater thickness appropriate for generating acoustic
waves around 10 megahertz. It is advantageous to have a
single, multifrequency transducer rather than two
different transducers because if a single, multifrequency
transducer is used the user can select at will the depth
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of penetration desired and the frequency of operation
desired without having to shift the position of the
catheter, whereas if two transducers are used it may be
necessary to shift the position of the catheter unless
the two transducers oppose each other on opposite sides
of the drive shaft.
The electrophysiological information obtained from
electrodes 300 can be used to determine the location of
catheter sheath 12c within the heart, as an alternative
to using the ultrasound transducer. In particular, there
are certain voltage patterns that are obtained during the
electrophysiology procedure that identify certain
landmarks in the heart.
If electrodes 300 are used for ablation, the
imaging capability of the catheter can be used to
determine immediately whether a specific change to the
tissue has resulted from the ablation. Desiccation of
tissue manifests itself as a brightening of the region of
the ultrasound image corresponding to the location of the
lesion. This brightening corresponds to increased
reflection of ultrasonic signals.
Fig. 16 shows sheath 12f on which are mounted
electrodes 300 for electrophysiology or ablation. Sheath
12f has a two lumen construction. The large lumen
contains the transducer and drive shaft while the small
lumen contains a wire 94. As shown, wire 94 is a
deflecting or steering wire attached near the distal end,
and is free to slide through its lumen under tension
applied to ring 96 to cause the catheter to bend when
pulled taut, thus providing a measure of control of the
orientation of the distal end of the acoustic catheter
while negotiating the passages of the body or the like.
In another embodiment wire 94 may be a preformed stylet,
which, when inserted through the second lumen, causes
deflection of the tip.
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Fig. 17 shows an acoustic imaging catheter sheath
302 having a sonolucent metallic electrode 304 for
sensing electrical potentials or for ablation, and having
a pair of sonolucent metallic traces 306 leading to
electrode 304. Catheter sheath 302 has a diameter of
nine french or less, and most preferably six french or
less. Imaging transducer 308, because it is slidable (in
accordance with any of the techniques described below in
connection with Figs. 24, 25, and 26), can be placed
under or near electrode 304.
Because metal electrodes are very efficient
reflectors of ultrasound energy, one would expect that
there would be a high likelihood that reverberation
artifacts would result when trying to image directly
near, or as close as possible to, electrode 304 itself.
Nevertheless, as described below, it is possible to make
the electrode acoustically transparent, so that such
reverberation artifacts do not tend to result, while the
electrode is sufficiently conductive to perform the task
of sensing and has a sufficiently low resistance to
perform the function of ablation. The resistance from
the proximal connector of the catheter to electrode 304
should be no more than 50 to 100 ohms for sensing and no
more than 25 to 50 ohms for ablation. Otherwise, undue
heating of the catheter could occur.
In one method of fabricating catheter sheath 302,
a sonolucent tube of polyethylene is imprinted with
conductive material to form electrode 304 and traces 306
leading to electrode 304. Electrode 304 and conductive
traces 306 are made of aluminum that is deposited by
vacuum deposition, which has been found to produce a low
resistance, high reliability, conductive path that is
sufficiently thin to allow ultrasound energy to pass
through the aluminum almost unhindered. Then a covering
310, which is also sonolucent, is applied over the
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conductively treated catheter body to protect and seal
electrode 304 and traces 306. Covering 310 includes
micro-apertures filled with conductive material, as shown
in Fig. 18a below. Because catheter sheath 302 and
covering 310 are formed of a sonolucent material and
because electrode 304 and traces 306 do not tend to
reflect ultrasound energy, the presence of electrode 304
and traces 306 does not tend to create artifacts in the
ultrasound image.
We now describe the vacuum deposition technique by
which electrode 304 and traces 306 are deposited onto the
sonolucent tubs. First, the sonolucent tube, which is a
single-lumen extrusion, is placed on a mandrel in a
manner such that it can be held straight. Then a flat
copper plate, such as is used for lithography, is
photoetched over an area as long as the sonolucent tube
and as wide as the circumference of the sonolucent tube
in a manner such that a negative of the pattern of the
traces and the electrode is imprinted upon the plate.
The pattern is in the form of a waxy ink material rolled
onto the copper plate. The sonolucent tube is than
placed onto the copper plate at one side and rolled to
the other side, which causes the sonolucant tube to be
printed around its entire periphery in the manner of a
printing roll.
The sonolucent tube is then placed into a chamber
that is evacuated, with the mandrels being placed on a
rotisserie so that they rotate. The sonolucent tube is
coated with metal by a vacuum deposition process in which
the metal is caused to melt in a graphite boat by
induction heating and then the metal evaporates and
deposits over the entire surface of the sonolucent tube.
The metal covers both the areas where the ink is located
and the areas where there is no ink. Then the sonolucent
tube is removed from the chamber and is washed with a
CA 02471106 2004-07-05
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solvent such as trichlorethylene. This process washes
away the ink with the aluminization that covers the ink,
leaving the areas that are not printed with the ink
intact with a thin aluminum coating.
The metal may alternatively be deposited onto the
sonolucent tube by laser xerography, according to which a
charge is put on the surface of the sonolucent tube,
which tends to selectively accept aluminum ions or
charged molecules as they are deposited. The metal is
deposited by a vacuum deposition process in which the
metal is caused to melt in a boat on which a charge has
been placed, and the metal evaporates and charged metal
particles deposit in the appropriate places on the
sonolucent tube in accordance with xerographic
techniques.
Alternative methods of depositing the metal onto
the sonolucent tube include spraying a conductive paint
onto a pattern on the sonolucent tube or spraying with a
plasma gun (a small electron gun) that is capable of
selectively depositing evaporated metal in specific areas
on the sonolucent tube. The gun doesn't actually touch
the surface of the sonolucent tube, but sprays the
surface in a manner analogous to a very tiny airbrush.
If multiple electrode rings are formed on the
sonolucent tube, some of the electrode rings may not
completely encircle the sonolucent tube because certain
traces would have to pass through these electrode rings.
Alternatively, the traces and protective sonolucent
coverings could be deposited as a multi-layer structure.
For example, an electrode near the tip of the sonolucent
tube could be deposited as a complete ring connected to a
trace extending along the length of the sonolucent tube,
and then a protective sonolucent covering could be placed
over the deposited metal, and then a second deposition
process could be performed to lay down a second ring, and
CA 02471106 2004-07-05
47 -
so on as various layers of material are built up one on
top of the other.
Another method of fabricating the catheter is to
first print electrode 304 and traces 306 on a flat sheet
of acoustically transparent material such as polyimide,
and to roll that sheet up in a spiral like a jelly-roll
and either place the sheet on the sonolucent tube or have
the sheet be the sonolucent tube itself.
To prevent damage to the fragile electrodes and
to traces, a thin, acoustically transparent covering is
placed over the aluminized or metallized catheter body.
The covering may be nylon that is expanded and then
shrunk onto the catheter body, or polyethylene that is
shrunk onto the catheter body. Alternatively, the
covering may be formed by spraying or dipping methods.
Nylon and polyethylene are dialectic materials, and thus
function as electrical insulators that would prevent the
electrodes functioning when placed in proximity to the
heart tissue were it not for the fact that microapertures
2o are drilled through the protective coating.
As shown in Figs. 18 and 18a, the microapertures
330 in a protective coating 332 over a sonolucent
electrode 334 and a sonolucent substrate 366 are very
small holes, e.g., one micron in diameter or up to ten
microns in diameter, drilled by W eximer laser machining
techniques, and are as thick as protective coating 332.
The number of pulses of the eximer laser is selected in a
manner such that the laser penetrates the thickness of
the coating but does not to go below metal electrode 334;
in any event, when the laser hits the metal it is just
reflected anyway. The eximer laser technology could be
provided by Resonetics, Nashua, New Hampshire 03063.
The density of microapertures 330 is as high as
possible consistent with the strength of the materials.
Generally, one needs to have 62,500 apertures in an area
CA 02471106 2004-07-05
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that is 3 square millimeters. The apertures can be
formed very rapidly by indexing and also by optical
steering while the catheter body is rotating. After
these apertures are formed, the apertures are filled with
a conductive jell material 336 such as that used for EKG
electrodes at the place of manufacture of the catheter
sheath. The conductive jell is then wiped clear of the
catheter sheath. Alternatively, the apertures can be
filled with an epoxy that includes tantalum, gold powd~r,
or silver powder, or PVDF filled with a metal powder.
If the electrode is to be used for high-current
ablation, the electrode-to-terminal resistance should be
no more than 20 to 50 ohms, rather than the limit of 50
to 100 ohms that is acceptable for sensing purposes. The
better conduction required for ablation can be achieved
by applying additional gold plating over the areas that
have been drilled with the micro-apertures, using masking
and plating techniques or vacuum deposition, or using a
gold plating solution.
An alternative to using the micro-apertures is to
have the aluminized surfaces of the electrode simply
exposed and to put protective covering over the traces
but not the electrode. In order to minimize problems due
to wear and handling of the electrodes, the exposed
electrodes should be subjected to proper surface
treatment and texturing.
Figs. 19-19c show a catheter sheath 12d on which
is mounted a balloon 55 very near the tip of catheter
sheath 12d. The balloon is adapted to be pressurized
with liquid, such as saline or water, or a gas, such as
air, through the same lumen that holds the ultrasound
imaging device, via an inflation opening in the wall of
the catheter sheath. The balloon may be used to center
or position the ultrasound device securely within a heart
chamber and maintain its position away from an area of
CA 02471106 2004-07-05
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interest on a wall of the heart. The balloon in its
collapsed or unpressurized state is easily inserted prior
to positioning and may be accurately positioned by use of
ultrasound imaging during initial placement. In other
embodiments a separate lumen is provided for inflation of
the balloon and/or the balloon is spaced from the distal
end of the catheter.
If balloon 55 is filled with air at an appropriate
point in time the balloon floats in a manner that assists
the positioning of the catheter. For example, the
balloon might float upwards from a lower ventricle to a
higher atrium, for instance. The balloon physically
moves the tip of the catheter from one location in the
heart to another in a manner which is not possible with
steering and pushing, although the balloon can be used in
conjunction with such steering and pushing techniques.
For example, the embodiment shown in Fig. 19 may be
modified to include the steering wire shown in Fig. 16.
If balloon 55 is filled with air it can move
either with the flow of blood or against the flow. If
the balloon is inflated with liquid, such as saline, it
becomes a flow-directed balloon that can travel only with
the flow of blood. Such a flow-directed balloon is also
useful to direct the catheter in the heart.
Cardiologists know the path of flow in the heart very
well, and if a cardiologist knows that the direction of
flow in the heart is favorable for use of a flow-directed
balloon, he can fill the balloon with fluid to cause it
to move with the flow.
Thus, the air-filled or fluid-filled balloon
simplifies the task of positioning the catheter, even if
the catheter includes steering or torquing devices that
assist in positioning of the catheter within the heart.
Balloon 55 can also be used to perform other functions in
the heart, such as valvularplasty.
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In one embodiment balloon 55 is acoustically
transparent, so that it doesn~t obstruct the field of
view of the acoustic imaging transducer. Materials such
as cross-link polyethylene have high inflation strength,
good biocompatability, processability, freedom of
pinholes, and very low acoustic attenuation. These are
commonly used balloon materials. It is also possible to
use a latex or silicone balloon.
Frequently, when performing an electrophysiology
sensing procedure or an electrode ablation procedure the
clinician would like to apply pressure to the electrode
and its adjacent heart tissue in order to assure a firm
contact. Accordingly, in one embodiment, balloon 55 is
an "opposing positioning balloon," i.e., a balloon that
engages a wall of the heart or a structure such as the
coronary sinus when the balloon is inflated in such a way
as to cause one or more electrodes to press firmly
against the cardiac tissue. Fig. 19 shows a single
sensing or ablation electrode 394 mounted on the distal
end of catheter sheath 12d, but in alternative
embodiments there is more than one electrode. The
electrode or electrodes may be mounted on catheter sheath
12d (as in Fig. 19), or on balloon 55 (as in Fig. 20), or
on both catheter shaft 12d and balloon 55. With
reference to Fig. 20, electrodes 394 can be printed on or
placed on balloon 55 as rings or stripes by vacuum
deposition, in a manner analogous to the method,
described above, of creating acoustically transparent
electrodes vn a catheter sheath. Electrodes on catheter
sheath 12d can also be created by this method, or can be
simple metal rings of gold, silver, tantalum etc. Fig.
19 shows opposing positioning balloon 55 concentric to
catheter sheath 12d, but in other embodiments the
opposing positioning balloon is eccentric to the catheter
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sheath and the balloon is used to press the side of the
catheter sheath itself the heart wall.
Fig. 21 shows balloon 55 combined with a chemical
ablating needle 396, such as the one described below in
connection with Figs. 27 and 27a, that is constructed to
inject a chemical into heart tissue to ablate the tissue.
Needle 396 exits through a side wall of balloon 55, as
shown in detail in Fig. 21a. Alternatively, needle 396
may exit catheter sheath 12d near balloon 55. Balloon 55
to is made of an electrically excitable, acoustic generating
material such as polyvinylidene fluoride (PVDF). During
use, needle 396 is inserted into tissue under ultrasound
guidance, the balloon is inflated, and the balloon
material is electrically excited to side the transfer of
fluid from the needle into the adjacent tissue.
With reference to the embodiments shown in Figs.
and 21, balloon 55, which is made of polyvinylidene
fluoride (PVDF), has a number of small apertures 398 in
the wall of the balloon. The inside of balloon 55 is
2o connected to a source of a drug by means of a lumen
extending through catheter sheath 12d. Apertures 398 are
force fed with the drug while the balloon material is
caused to vibrate. The vibrations feed the transfer of
the fluid from balloon 55 into tissue with which the
balloon is in contact. Radiopaque markers 410 and 412
are provided on catheter sheath 12d.
Referring still to Figs. 20 and 21, PVDF is a
material that is similar to mylar and can be fabricated
in sheets and then formed into balloons that have wall
thicknesses in the range from 1-2 thousands of an inch.
In order to permit excitation of the balloon wall, the
PvDF material has to be aluminized inside and out with
aluminum.-.layers 400. A very.. thin layer of aluminization
is all that is needed because the electrically excitable
balloon 55 is a high impedance device. 'During use, an
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alternating electric currant is applied to balloon 55 at
frequencies in the kilohertz to megahertz range (the
frequency depending on the thickness of the balloon and
the mode of excitationj. The electric current causes the
balloon to exhibit either transverse or planar vibration,
which fs therapeutically helpful in speeding the delivery
of drugs and fluid into adjacent tissue. The vibration
creates localized variations in pressure in the tissue,
and given that fluid tends to migrate in the direction of
areas of low pressure, the vibration helps migration of
fluid through the tissue. The vibration also can create
heat, which is known to improve the diffusion of some
chemicals through tissue. Very high levels of vibration
can be used as a massaging action to actually disrupt
tissue and to directly create an ablative response.
Referring to Fig. 22, a plan view of an acoustic
imaging balloon catheter system is shown. This acoustic
imaging balloon catheter system may include all of the
features of the catheter system shown in Figs. 19-19c,
including one or more electrodes for electrophysiology or
ablation mounted on the catheter sheath. The system 120
includes a boot member 122 including a ferrule member 124
at its proximal and, constructed to enable electrical and
mechanical connection, as discussed for example with
respect to Figs. 8-8a, to the acoustic imaging control
system as discussed for example with respect to Fig. 1,
for transmitting rotary power and control signals to the
acoustic imaging transducer held within the balloon
catheter sheath 139 near balloon 140 and for receiving
acoustical image signals from the transducer. The
proximal end of the apparatus further includes a seal 126
(Fig. 23j which enables intimate but relatively
frictionless contact with the portion of the rotating
drive shaft.
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Sheath 128 extends from the end of the seal 126 to
a "Y" double flare compression fitting 130. Fitting 130
includes a side arm 132 for introduction of inflation
fluid such as water or saline by means of a screw syringe
134 for inflation of balloon 140 near the distal end of
the catheter 139.
Extending distally from the compression fitting
130 is catheter body sheath 139. The catheter may be
adapted to track a guide wire which passes through a
sonolucent saddle member beneath the balloon.
A rotating ultrasound transducer having a coil
form drive shaft, as discussed herein above, is
positioned on the central axis of the catheter sheath 139
at a position corresponding to the inflatable balloon
140. The catheter sheath 139 forms a sonolucent guide
for the transducer and drive shaft. The catheter sheath
is formed of a thin sonolucent material such as
polyethylene to provide sufficient guidance for the drive
shaft and transducer without causing excessive
attenuation of the ultrasound signal emitted by the
transducer. The catheter body material and the balloon
material are in general selected to be sonolucent and
have an acoustic impedance substantially matched to the
body fluid, e.g., blood, to which the catheter is
exposed, to minimize attenuation of the acoustic signals
emitted and received from the transducer. Polyethylene
is advantageous in that it has an acoustic impedance that
substantially matches blood and saline, it is capable of
withstanding high inflation pressures and is only
slightly elastic, enabling a reliable balloon inflation
diameter. It will be understood that the catheter may be
formed having sonolucent regions corresponding to the
location of the transducer while the rest of the catheter
is not sonolucent, e.g., made of thicker material. Fluid
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communication between the balloon and the catheter may be
provided through a port.
The balloon 140 which is preferably polyethylene,
as discussed, may be mounted at its ends by, for example,
melt-sealing. The balloon may also be secured by clips
or the like as conventionally known.
Referring to Fig. 23, proximally, the catheter of
Fig. 22 is provided with a stationary pressure tight
shaft seal 126 that fits in intimate, but relatively
l0 frictionless contact with a portion of the rotating drive
shaft 162. The seal includes a ball seal 170 (available
from Hal-seal Engineering Company, Inc., Santa Anna,
California), securely held in place by a seal holder 172
(stainless steel or elastomer), which abuts the distal
end of the internal open area of the boot 122 and is held
by compression of the ferrule assembly 164 (although
other means of attachment such as injection molding are
possible). The seal holder 172 includes a retainer sleeve
174 that extends coaxially with respect to the catheter
139. At the proximal end, within the ferrule, the drive
shaft is held within a gland 178, preferably formed from
hypotubing, which makes relatively frictionless contact
with the ball seal 170, enabling rotation while
preventing back flow of inflation fluid into the ferrule.
The ball seal, as shown, is an annular U-shaped member,
including within the U a canted coil spring 179 (such
that the axis of each coil is tangent to the annulus)
that presses the legs 175, 177 of the seal radially. The
outer leg 175 of the seal engages an extension 176 of the
seal holder, while the inner leg 177 of the seal engages
the gland 178. The boot also includes a thin (few
thousands of an inch) metal sleeve 171 for additional
sealing around the catheter.
The drive shaft 162 is modified in the sealing
area 168 by impregnating it with a thermoplastic material
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that fills the gaps in the individual wires to prevent
flow of inflation fluid through the drive shaft inner
lumen. Alternatively, the drive shaft may be sealed by
impregnating it with a liquid that is hardenable, such as
epoxy, and then covering that area with a section of
cylindrical metal, such as hypotube, in order to form a
smooth, fluid tight seal. It will also be understood
that other sealing members may be used, e.g. an O-ring.
Preparation of the device is accomplished by the
following steps: A Leveen inflator is connected to the
side arm. The side arm valve is opened and air is
evacuated by suction. Generally, the balloon contracts
in a folded manner which leaves air passages through the
interior of the balloon. A hypodermic syringe fitted
with a small gauge needle and filled with a fluid such as
water or saline is then inserted through a septum seal at
the distal tip of the catheter sheath. Fluid is
introduced until surplus exits the side arm, at which
point the valve is closed, reducing the chances that air
will re-enter the catheter. Alternately, the fluid may
be introduced via the side arm when an air venting needle
is inserted into the distal septum.
The catheter is then attached to the driving
motor, (not shown), by mating the ferrule 124 with a
mateable receptacle that connects it to the ultrasound
imaging electronics. Because the balloon material and
sonolucent guide effectively transmit ultrasound energy,
continuous imaging and monitoring can be achieved.
The pressure and fluid tight connector that is
mounted distally to the location of the side arm
connector enables various catheters, such as those with
balloons of different sizes, to be effectively attached
at the location of the side arm connector.
In other embodiments, the transducer may be
positioned proximal to the balloon.
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Referring now to Figs. 24, 25, and 26, other
embodiments of the acoustic imaging catheter device allow
relative movement of the transducer and balloon so that
the ultrasound transducer may be positioned in any
longitudinal position in the balloon, or distal or
proximal to th~ balloon. The embodiments shown in Figs.
24, 25, and 26 may include all of the features of the
catheter system shown in Figs. 19-19c, including one or
more electrodes for electrophysiology or ablation mounted
on the catheter sheath, and may include all of the
features of the catheter system shown in Figs. 22 and 23.
Moreover, the features shown in Figs. 24, 25, and 26 may
be used in conjunction with any of the catheter sheaths
disclosed in this application, including catheter sheaths
that do not include balloons and including all of the
catheter sheaths on which electrophysiology or ablation
electrodes are mounted. In Fig. 24, the drive shaft and
transducer 146 may be slid axially as indicated by arrows
195 to move the transducer, for example, continuously to
positions between position I, proximal to the balloon and
position II, distal to the balloon. A slide assembly 240
is provided including a housing 244 having a distal end
which receives the catheter sheath 139 and drive shaft
145. The drive shaft contacts a pair of oppositely
arranged, relatively frictionless ball seals 245, 246
press fit within the housing against an inner body
extension 249 and the distal end member 248 of the body
Which is threaded into the body 244. The ball seals
engage a gland 250 as discussed with respect to Fig. 23.
The gland is attached to a thumb control 252, provided
within the body to enable axial motion of the drive shaft
to position the transducer within the catheter
corresponding to regions within the balloon and in the
distal extension, both of which are sonolucent.
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The axially translatable transducer device further
includes a carbon resistor 254 within the slide assembly
housing, and contact means 258 attached to the thumb
control and in contact with the resistor. Probe wires
256, 257 are connected to the resistor 254 and contact
means 258 to provide variable resistance between the
probe wires as the thumb control is slid axially, which
is detected at detector 260, to provide monitoring of the
axial position of the transducer. The thumb control may
be hand actuated or controlled by automatic translator
means 264 which receives control signals from a
controller 266. The output from the detector 260 may be
provided to an analysis means 268 which also receives the
acoustic images from the transducer corresponding to
various axial positions of the transducer within the
catheter body to provide registry of the images with the
axial transducer position on a screen 270. In certain
embodiments, the transducer is slid axially, along a
continuous length or at selected positions of the
catheter body, for example, from the balloon to the
distal tip, and the analysis means includes storage means
for storing images along the length to reconstruct a
three-dimensional image of the lumen along the axial
length of transducer travel.
Fig. 25 shows an embodiment iri which the catheter
includes a bellows member 280 to enable axial motion of
the catheter body with respect to the transducer.
Fig. 26 shows an embodiment in which a proximal
portion of the drive shaft is enclosed within tubing 360,
which is engaged by a user-graspable housing 362 that is
attached to the proximal end of catheter sheath 364. The
user can push tubing 360 into housing 362 and can pull it
out of housing 364 to adjust the relative longitudinal
position of the transducer on the end of the drive shaft
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with respect to catheter sheath. User-graspable housing
362 engages tubing 360 by means of a fluid-tight seal.
In another embodiment of the acoustic imaging
catheter device, the balloon is asymmetrical, either in
shape or expansion capability, or both, and is mounted on
a catheter shaft that is torquable, and can be positioned
using acoustic imaging. The positioning of the balloon
relative to surrounding tissue and the inflation and
deflation of the balloon can be monitored with cross-
sectional ultrasonic images.
Figs. 27 and 27a show sheath 12b having needle 86
securely anchored to the tip, useful for impaling a
surface, such as that found in the interior of the heart,
and injecting chemicals such as ethanol into the heart.
Needle 86 can also be used to anchor temporarily and
steady the ultrasound device in a fixed position. In
another embodiment, it can have a safety wire extending
to a proximal securing point. This acoustic catheter may
be introduced through an introducing catheter. In
another embodiment, the needle can be retracted during
introduction.
Figs. 28 and 28a show a solid needle 324 made of
an electrically excitable material that emits acoustic
energy when excited through conductor 326 by RF
electrical signals applied to electrical terminal 328.
Vibration of needle 324 creates a massaging action that
disrupts tissue and creates an ablative response.
In an alternative embodiment, needle 324 is
hollow, and the vibration of the needle assists the
process of injecting the drug into the tissue. The
hollow metal is covered with a shrink of polyvinylidene
fluoride, and the polyvinylidene fluoride is aluminized
over its outside. This construction produces an assembly
that vibrates when electrically excited. The purpose of
the aluminum is to conduct electric power. The aluminum
can be seen in the image formed by means of the
ultrasound transducer, and it can also serve as an
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acoustic marker that can be seen by an external
ultrasound device or an ultrasound probe placed a
distance away from the ablation catheter.
Figs. 29 and 29a show steerable catheter sheath
312, capable of electrophysiology sensing and acoustic
imaging, in which the tip of retractable injecting needle
314 exits catheter sheath 312 near the tip of the
catheter sheath and also near ring electrode 316 and the
position of the scan plane of transducer 318.
Visualization of the location of the electrode can be
performed under ultrasound guidance, and then the needle
can be extended into the endocardium to inject fluid into
the endocardium. Electrode 316 is the most distal of
several electrodes 316, 320, and 322. Ring electrode 316
may be of a conventional type that can be located with
ultrasound. In another embodiment electrode 316 is a tip
electrode rather than a ring electrode.
In one embodiment, the longitudinal position of
the transducer is adjustable, in accordance with any of
the techniques described above in connection with Figs.
24, 25, and 26. In another, simpler embodiment,
transducer 318 is located permanently in a fixed
longitudinal location at which the plane of acoustic
imaging intersects the needle when the needle at the
beginning of its extended position.
In use, the catheter is put into position in the
heart with needle 314 retracted, a site that is suspected
of electrical malfunction is probed with the steerable
catheter under ultrasound visualization, and electrical
potentials are read and recorded. Once a specific
location is found that appears to be problematic,
ablation can then be performed by deploying the needle
and the needle can inject the tissue with an ablative
drug such as ethanol. The needle can penetrate 2-3
millimeters if necessary. The catheter can be left in
position during this time and a change in the electrical
properties of the tissue can be monitored.
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In another embodiment, a highly conductive wire,
such as gold-plated metal or gold-plated stainless steel,
can be used in place of the needle. The wire ablates
tissue in a manner analogous to the ablation electrodes
described above, but the wire can be used to anchor the
catheter and could be curved to pull the electrode into
position to enhance the electrical ablation. The wire
can include an acoustic marker that can be seen by an
external ultrasound device or an ultrasound probe placed
a distance away from the ablation catheter.
In certain embodiments, shown in Figs. 30, 30a,
31, and 31a, the wire is formed as a little cork screw
402 that can be twisted into the heart, in a manner
similar to twisting a pacing lead into the heart, to
anchor the tip of catheter sheath 404 very securely under
ultrasound guidance. Figs. 30 and 30a show cork screw
402 directly attached to catheter sheath 404. In this
embodiment cork screw 402 is twisted into heart tissue by
rotating the entire catheter. Figs. 31 and 31a show cork
screw 402 directly attached to drive shaft 406, distally
beyond transducer 408. In this embodiment cork screw 402
is twisted into heart tissue by rotating drive shaft 406.
In other embodiments, the corkscrew is attached to an
elongated, torsionally rigid but laterally flexible
assembly, similar to the ultrasound imaging driveshaft
but much smaller in diameter, so that the corkscrew can
be automatically caused to turn and corkscrew into
tissue. The corkscrew exits a small hole in the catheter
sheath in the same manner as needle 314 described above,
but the corkscrew follows a curved path.
Referring to Figs. 32 and 32a, in catheter sheath
418, an ultrasound transducer 414 is used to ablate
tissue sonically. Ultrasound transducer 414 is similar
to, and located adjacent to, ultrasound imaging
transducer 416 of the type described in detail above.
Transducer 416 images by rotating a full 360 degrees
while catheter sheath 418 is in a fixed position or a
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relatively stationary position, the image is stored, and
then the rotation of the transducer is stopped and the
position of transducer 414 is aligned, based on the
stored image, so that transducer 414 is pointed toward
the region of interest. During ablation, transducer 414
radiates at least 2-5 watts of acoustic power at a
frequency of around 25 to 50 kilohertz. This frequency
that is so low that the radiation is not focused, but
instead tends to radiate from the source in a more or
to less cardioid pattern without a fixed focus. The energy
has its greatest density normal to the surface of
transducer 414.
In another embodiment the ablation transducer is
positioned in a manner such that it directs radiation in
a direction 180 degrees away from the direction in which
the imaging transducer directs ultrasound energy, and the
ablation transducer and imaging transducer are at the
same longitudinal location. The ablation transducer can
be aligned in the desired direction for ablating tissue
by positioning the imaging transducer in a manner such
that the imaging transducer is facing 180° away from the
region of interest to be ablated. In yet another
embodiment a single transducer is capable of both imaging
and very high-power, low-frequency radiation.
Fig. 33 illustrates an alternative imaging mode
that is useful in conjunction with the needle-equipped
and balloon-equipped catheters for chemical ablation
described above, and also even the electrode-equipped
catheters described above, if the electrodes are fitted
with polyvinylidene fluoride coverings. According to
this imaging mode, the heart 352 is imaged through the
esophagus 354, by means of one of many commonly available
traps-esophageal probes 356 such as those made by Hewlett
Packard, Vingmead and others. This traps-esophageal
imaging provides a cross-sectional image of the heart,
i.e., a scan plane that is a slice of the heart. Various
improved traps-esophageal probes can vary the plane
CA 02471106 2004-07-05
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scanned through the heart through various angles and
various rotational and azimuthal positions, and can
therefore be used to image a very wide area of the heart
through manipulation of controls on the proximal end of
the transesophageal probe. During use, transesophageal
probe 356 is first placed in a patient s esophagus prior
to the beginning of an electrophysiology procedure, and
electrophysiology or ablation catheters 358 and 359 are
then placed in the heart through the venous or the
arterial system. These catheters can be visualized by
means of esophageal probe 356 if the catheters are fitted
with acoustic markers.
The marker may be, for example, a PVDF covering
placed over a sensing or ablation electrode, or a PVDF
:5 balloon. The acoustic markers are used to create
distinct color artifacts on the image created by color
flow imaging machines equipped with color capability.
The color flow display is a black and white display that
has a graphic overlay of flow information, which is
denoted by a color shown on the CRT display. When the
PVDF is electrically excited it emits a low-frequency
sonic wave that is mis-interpreted by the trans-
esophageal imaging system as the difference between the
outgoing ultrasound pulse and the Doppler-shifted return
pulse that the traps-esophageal system uses to deduce the
direction and quantity of blood flow (the imaging system
determines blood flow by measuring the difference between
the outgoing and the incoming ultrasound signal and
assigning a false color to the frequency shift that
occurs due to the Doppler effect). Thus, by radiating at
a frequency near the expected Doppler shift frequency,
the PVDF basically fools the traps-esophageal imaging
system into thinking the low-frequency sonic wave is the
difference signal and can induce the imaging system to
show false colors that identify particular catheters. A
catheter shows up on the display as either a bright mark
or dot that represents the cross-section of the catheter.
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To energize the PVDF a sinusoidal, continuous-wave,
voltage signal is applied to the PVDF through a simple,
alternating-current, radio-frequency generator. This
signal can be pulsed as well, if desired.
One or more of the intra-cardiac catheters may
include an ultrasound transducer, which may be adjacent
to or at the precise location of sensing and ablation
electrodes, as described above. Vacuum-deposited traces
may extend along the length of the catheter sheath to the
electrodes, as described above. The traces provide good
electrical coupling and can serve as an attachment point
for PVDF or a crimped-on transducer. The incorporation
of the traces into the wall of the catheter sheath leaves
the bore of the catheter free to be used for a pacing
lead, an anchoring screw, a drug injection channel, a
biopsy channel, etc.
In one embodiment, an entire catheter sheath is
made of PVDF. The catheter sheath will show up on the
display no matter which portion of the catheter sheath
intersects with the imaging plane of the transesophageal
probe, because the whole catheter sheath emanates
radiation. In another embodiment, a first catheter used
during the procedure emits a frequency that shows up as a
first color on the color flow imaging, a second catheter
emits a frequency that shows up as a second color, and so
on. In another embodiment the tip or the actual
electrode portion of a catheter sheath has a frequency
that is distinct from the rest of the catheter sheath, so
that when the tip or the electrode is located by the
imaging system it is distinguishable from the remainder
of the catheter sheath. In another embodiment, there is
a graduation in frequency along the length of a catheter,
so that a distal tip shows up as a first color, a
midsection shows up as a second color, and a proximal
section shows up as a third color. The change in
frequency along the length of the catheter may be gradual
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or may be in the form of distinct stripes of different
frequencies.
Fig. 34 illustrates a system of electrophysiology
equipment that includes an acoustic imaging
electrophysiology catheter 368 of the type shown in Fig.
13, a trans-esophageal probe 370, a central processing
unit 372 that receives data from catheter 368 or trans-
esophageal probe 370 and transmits video ultrasonic image
data to ultrasound display 374, and another display
to system 376 that displays, either graphically,
schematically, or with a wire frame, specific regions of
the heart, and that records and displays on a specific
location of the graphical, schematic, or wire frame
display either an instantaneous voltage or a voltage
throughout an entire cardiac cycle.
In one embodiment, display system 376 displays a
two-dimensional cross-sectional image of the heart, which
shows important features of the heart such as the area of
the HIS bundle. The cross-sectional image is based on
ultrasound image received from catheter 368 or trans-
esophageal probe 370 or is based on a fluoroscopic image
from fluoroscope 382. Other possible sources of the
cross-sectional image include I~tI, CT, and scintigraphy.
When catheter 368 is placed in specific regions of the
heart, which can be done with great certainty because of
the ultrasound imaging capability, the voltage potentials
sensed by catheter 368 are recorded instantaneously by
central processing unit 372 and then displayed in the
specific locations in the graphic. Many voltage
potentials are sensed at various locations in the heart
until an electrophysiological map of the heart is built
up, which can be done very quickly.
Because the user or the clinician will want to
concentrate on maneuvering the catheters, and not on data
acquisition, writing information down, or shouting out
numbers, a foot pedal 378 is provided so that when
catheter 368 is in a specific location the clinician can
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depress foot pedal 378 to instruct central processing
unit 372 to record voltage potential information.
Because central processing unit 372 receives ultrasound
imaging data, central process unit 372 knows the specific
location of each electrophysiology electrode and thus
knows the location at which to super-impose voltage data
on the image shown by display system 376. Alternatively,
the clinician can observe the image displayed by display
system 374 and can indicate to central processing unit
372 the specific location of an electrode.
Thus, central processing unit 372 records both an
ultrasonic image at a particular instant and a voltage
values at that instant and at a particular location.
Thus, the clinician can return the sensing electrode to
the particular location at a later point in time to
compare the voltage sensed at the later point in time
with the earlier-recorded voltage.
Moreover, the information recorded by central
processing unit 372 permits analysis of various voltage
potentials throughout a cardiac cycle as the heart moves
during the cycle, because central processing unit 372 is
able to keep track of the various locations in the heart
even though the heart is moving.
A set of electrocardiogram or EKG leads 380 are
connected to central processing unit 372. In one
embodiment, when the clinician wants to record a voltage
potential, central processing unit 372 records the
voltage information throughout one complete cardiac
cycle. The clinician can view a representation of the
voltage at any instance in time during the cardiac cycle
by replaying the image displayed by display system 376
with the super-imposed voltage information. Central
processing unit 372 processes ultrasound imaging
information and voltage information in the manner of a
cine loop or repeating image, which is gated by EKG leads
380 attached to the patient while the patient is left in
a still position. The central processing unit causes
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display system 376 to display a series of successive
frames in a loop that repeats over and over again. In
one embodiment there are 32 ultrasound imaging frames
that go through one complete cardiac cycle from systole
to diastole and back to systole, and there are 32
different voltages that are super-imposed on the
ultrasound imaging frames at any given location. The
super-imposed voltage information at a given location is
a number that rises and falls throughout the cardiac
cycle, or is alternatively a color coded mark. Thus,
there is no need to image the heart continuously, which
could take up a lot of software and hardware time, and
yet display system 376 displays an image of the heart
timed in exact synchronization with the actual heart
beating (through use of EKG leads 380) and replayed over
and over again. While this image is being replayed, the
clinician can concentrate on simply locating the position
of catheter 368 itself in the heart and can follow the
catheter with traps-esophageal echo probe 370, or through
x-rays because catheter 368 is marked with radiopaque
markers.
Any additional information that the clinician
obtains while the image is being replayed can be super-
imposed over the repeating image without the need to re-
image the heart. For example, a live fluoroscopic or
ultrasound image can be super-imposed over the image
being replayed on display system 376. If the super-
imposed live image is a fluoroscopic image, it is not
necessary to use dye injection while obtaining this live
image because the location of the heart tissue relative
to the catheter 368 can be seen on display system 376
without any need for the live image itself to show the
heart. If the clinician wishes, however, he may update
the image by obtaining a new image of the heart, if the
patient has moved or if the clinician believes that the
heart has changed position or has changed its cycle.
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In another embodiment, the display system 376
displays a false three-dimensional image of the heart or
a true three-dimensional image of the heart. A false
three-dimensional image of the heart is a three-
s dimensional projection onto a two-dimensional surface
that can be generated using commonly available computer
imaging hardware and software that takes a number of
successive two- dimensional images and assembles them
into a false three- dimensional image that can be rotated
l0 and manipulated by the user by the user interfacing with
central processing unit 372. False three-dimensional
ultrasound images can be obtained through the use of
accessory software and hardware such as that provided by
ImageComm in Sunnyvale, California. A true three-
15 dimensional is an image that is not displayed on a flat
screen but rather on an oscillating mirror that has a
scanning system associated with it that can display a
three-dimensional image by stereoscopic means. It is not
necessary to wear stereoscopic glasses to view
20 oscillating mirror systems that are currently being
marketed.
Alternatively, display system 376 may display a
wire-frame image, which is a graphical depiction of the
boundaries of the heart and is a simple version of a
25 false 3-dimensional image. The beauty of a wire frame
image is that it requires relatively less software and
hardware to display and is inherently transparent or
translucent so that potentials can be seen through it
intuitively by the user. Also, a wire-frame images does
30 not require a large amount of hardware or software to
rotate and manipulate the image. The nodal points, i.e.
the places where the wires cross, can be used as the data
collection points.
One of the very important aspects of the
35 electrophysiology procedure is that once the operation of
the heart is diagnosed, the clinician will want, as
precisely as possible, to position an ablation device at
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the source of trouble and ablate the tissue at this
location precisely. This requires relocalization of the
tip of catheter 368 to a previously located position.
All positions at which the catheter tip has been
positioned are accurately located on the display of
display system 376, and the clinician can determine when
the tip of catheter 368 has been relocated by examining
the ultrasound image. Thus, the clinician can,return to
the spot to be ablated with a great degree of confidence.
In one embodiment, traps-esophageal probe 370
creates ultrasound images that are processed by central
processing unit 372 and displayed by display system 376,
and the ultrasound transducer on catheter 368 is used to
create an image displayed on display system 374 to assure
good contact of electrodes with tissue. Alternatively, a
general sense of the catheter position is obtained
through the use of an imaging modality such as
fluoroscope 382, and a more precise image is obtained by
traps-esophageal probe 370 or the ultrasound transducer
on catheter 368 and is processed by central processing
unit 372 to create the display for display system 376.
The electrophysiology catheters described in
detail above are especially useful for creating an
accurate two-dimensional, three-dimensional, or wire-
frame image because these catheters are highly
maneuverable by their ability to deflect or to be
positioned with the assistance of a positioning balloon,
because the transducer within these catheters is highly
accurate in identifying the position of the catheter
relative to tissue, and because these catheters are
easily recognizable in traps-esophageal images.
A data recorder 384 is provided in the system of
electrophysiology equipment shown in Fig. 34 to record
data from ERG leads 380 and the electrophysiology
electrodes on catheter 368 in tabular form for analysis.
An oscilloscope 388 displays signals from each of the
electrophysiology electrodes on catheter 368. A
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programmable external stimulator 386 is used to provide
slight electrical pulses to electrodes on catheter 368 to
cause fibrillation so that the action of the heart can be
observed while the heart is in this condition.
Other embodiments are within the claims. For
example, it is contemplated that each of the various
selectable catheter sheaths may incorporate any of the
features shown or described in connection with one or
more of the other selectable catheter sheaths.
Furthermore, the ultrasound transducer described above
may be used in conjunction with catheter sheaths
incorporating the features of any of the other catheters
described in this patent application.
It is contemplated that each of the various
selectable catheter sheaths may be used in conjunction
with any of the technologies shown in Figs. 24, 25, and
26 for enabling relative longitudinal movement between
the transducer and the catheter sheath during use of the
catheter. Also, each of the various selectable catheter
sheaths may be used in conjunction with a drive shaft of
the type shown in Fig. 35, in which drive shaft 342 has a
rotating mirror 344 on its distal end that reflects an
ultrasound signal emitted by an ultrasound transducer
346, which may also be attached to drive shaft 342 as
shown or alternatively may be fixed in a stationary
position while the drive shaft rotates.
Various Ablation Catheters
Fig. 36 shows a heated balloon ablation catheter
for constructed for insertion into a heart and useful for
ablating heart tissue containing abnormal electrical
pathways, such as arrhythmogenic foci. The heated
balloon ablation catheter comprises catheter shaft 510
having a proximal segment 512 and a distal segment 514.
Proximal segment 512 includes an extruded wire 532
braided into catheter shaft 510 (see Fig. 37) for
providing strength to the catheter while still
maintaining the flexibility required to maneuver the
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catheter through a vascular system. Wire 532 is
preferably made from stainless steel. Distal segment 514
comprises a flexible shaft material, preferably
polyurethane, although other flexible biocompatible
materials could be used. Catheter shaft 510 is
constructed to have one-to-one torqueability.
In one embodiment, distal end 516 of catheter
shaft 510 is capable of controlled deflection. A pull-
wire (not shown) extends from a handle at the proximal
end of the catheter through a lumen in catheter shaft 510
and is fastened to distal end 516 of catheter shaft 510.
Distal segment 514 is constructed to be more flexible
then proximal segment 512, so that when the handle is
pulled back the pull wire causes distal end 516 to bend
preferentially from an undeflected position to a
deflected position.
Electrode pairs 518 and 520 are mounted on distal
end 516 at either side of balloon 522, and are attached
to conductors 549 (Fig. 38) that extend through the
catheter shaft and that are connected to control circuit
525 by electrical connector 524. Control circuit 525
provides RF energy to the electrodes for ablating cardiac
tissue, and also receives voltage potentials from the
electrodes when the electrodes are used as
electrophysiology mapping electrodes.
Balloon 522 is mounted circumferentially on distal
end 516. Balloon 522 is elastic and preferably made from
polyethylene cross-linked latex, although other
biocompatible elastomer materials can be used. Balloon
522 is coupled to inflation port 526 through an inflation
lumen extending along the length of catheter shaft 510.
Balloon 522 is inflatable with fluid, preferably saline,
which is injected by a syringe at balloon inflation port
526.
Fig. 38 shows a side view of distal end 516 with
the balloon deflated, and Fig. 39 shows the balloon in
its inflated condition. Electrodes 542 and 544 and
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thermistor 550 within the balloon are coupled to control
circuit 525 by wires 549 through electrical connector
528. An RF current can be established between electrodes
542 and 544 for heating the fluid. Control circuit 525
receives signals from thermistor 550 representative of
the temperature of the fluid and uses those signals to
control the temperature of the fluid by controlling the
amount of RF current passed between electrodes 542 and
544, in a manner described in detail in PCT application
US93/09422, filed October 4, 1993 by Daniel Bruce Pram et
al.
Fig. 53 shows a catheter having inflatable balloon
522 and electrodes 518 and 520, and further including an
ultrasound transducer 650 mounted at the distal tip of a
drive shaft 652 disposed inside catheter shaft 510.
Ultrasound transducer 650 is used to produce ultrasound
images from which the location of balloon 522 and
electrodes 518 and 520 relative to heart tissue may be
ascertained. The construction and operation of such an
ultrasound transducer is described in detail above. It
is contemplated that each of the catheters described in
the present application may be combined with such an
ultrasound transducer and drive shaft.
Referring to Figs. 40-44, there are shown
pictorial representations of human body 558 illustrating
a part of the vascular system. Distal section 516 of
catheter shaft 510 is introduced into the vascular system
of human body 558 through an opening in femoral vein 560.
The catheter is shown entering the left side of the
heart, but if the tissue to be ablated is located in the
right atrium or ventricle, the catheter is inserted into
the right side of the heart. Conventional fluoroscopic
techniques can be used to navigate the catheter through
the vascular system, if the catheter is provided with
radiopaque markers or if a radiopaque contrast medium is
used to inflate the balloon.
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As shown in Fig. 41, distal tip 564 of the
catheter shaft can be brought into contact with a wall of
heart 562 by controllably deflecting the distal end of
the catheter. The electrode senses electrical potentials
within the heart for the purpose of locating cardiac
tissue, containing abnormal electrical pathways. Control
circuit 525 (Fig. 36) can supply RF current to the
electrode at distal tip 564 for ablation of localized
cardiac tissue. '
To ablate a larger area of cardiac tissue near
distal tip 564, balloon 522 is inflated with fluid as
shown in Fig. 42. The catheter maintains its position by
virtue of its torsional rigidity. Alternatively, an
ablation suction cup (described below in connection with
Fig. 48) is included at the tip of the catheter shaft,
the ablation suction cup being used to attach the
catheter to the cardiac tissue. Balloon 522 conforms to
the heart wall and thus allows a large area of cardiac
tissue to be ablated.
When balloon 522 is used to ablate tissue, it is
possible to monitor the progress of the ablation by
sensing cardiac signals through the electrode located at
distal tip 564. The sensed cardiac signals are used by
control circuit 525 (Fig. 36) to regulate the RF energy
supplied to the fluid inside balloon 522. For example,
control circuit 525 can turn off the RF generation the
instant the arrhythmogenic myocardium has been ablated to
minimize damage to normal cardiac tissue.
As shown in Fig. 43, the distal end of the
catheter can be positioned laterally against a heart
wall. Cardiac tissue containing abnormal electrical
pathways is located by mapping cardiac signals sensed
through any of the electrodes. With balloon 522
deflated, localized myocardium can be ablated by passing
RF current from control circuit 525 between bipolar
electrode pairs 518 or 520.
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7~arge areas of myocardium can be ablated by
. filling balloon 522 with fluid, as shown in Fig. 44.
Balloon 522 conforms uniformly to the cardiac tissue o~rer
a large area of myocardium. The fluid is heated by
passing an RF current between electrodes 542 and 544, and
heat is transferred between the fluid and the myocardium,
through balloon 522, thereby ablating the myocardium.
Following the ablation, balloon 522 is deflated,
as shown in Fig. 43. Electrode pairs 518 and 520 are
then used to sense local cardiac electrical activity to
determine whether the tissue has been sufficiently
ablated. If necessary, the ablation procedure can be
repeated.
Fig. 45, Fig. 46 and Fig. 47 illustrate different
configurations of inflatable balloons and electrodes.
Fig. 45 shows distal end 570 of a catheter having
electrodes 571, 572, 573 and 574 positioned on the
proximal side of balloon 575. These electrodes are used
primarily for mapping of cardiac tissue. However, it is
also contemplated that bi-polar pairs of these electrodes
may be used to ablate surrounding cardiac tissue.
Electrode 576 is used for mapping tissue, as well as for
electrophysiological sensing while balloon 575 is being
used for ablation. Electrode 576 can also be used for
monopolar ablation of tissue at select sites on the
cardiac wall.
Fig. 46 shows distal end 577 of a catheter having
two sets of bipolar electrodes pairs 578 and 579 mounted
on either side of balloon 580. Electrode 581 is mounted
on the tip of the catheter for providing additional
mapping and/or ablation capability.
Fig. 47 shows a distal end 582 of another
catheter, which is identical_.._to_ the distal end of the
catheter shown in Fig. 46 except for the elimination of
electrode 581 and the addition of anchoring tip 586~
Anchoring tip 586 is made of flexible material,
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preferably polyurethane, and is capable of controlled
deflection in a manner similar to that described above.
Anchoring tip 586 can be positioned in various
locations of the heart to stabilize balloon 522 at a
desired position against a cardiac wall. For example,
anchoring tip 586 can be extended into the coronary sinus
while positioning balloon 522 against an atrial wall.
Anchoring tip 572 can also be extended through a valve
between chambers in the heart for providing additional
to stability.
Fig. 48 shows a suction catheter for ablating
cardiac tissue. Rubber tube 591 couples vacuum pump 590
to vacuum port 592. Vacuum pump 59o can be any non-
cycling pump (e. g., an electric pump). A peristaltic
pump or other cycled pump should not be used because the
vacuum provided would not be uniform.
Vacuum port 592 couples rubber tube 591 to vacuum
lumen 612 (see Fig. 49j, which extends the entire length
of catheter shaft 595. The outside diameter of catheter
shaft 595 is approximately eight to ten french, and its
length is between one hundred to one hundred-twenty
centimeters. Electrical connector 593 couples wires
extending through mapping lumen 610 to an external
monitoring apparatus and also couples wires extending
through lumen 614 tv an RF generator.
Retractable handle 594 includes base 596 coupled
to catheter shaft 595 and grip 598 slidably mounted on
catheter shaft 595 and coupled to retractable shaft 600.
Retractable handle 594 has an open position, as shown in
Fig. 48, and a closed position, which is obtained by
moving grip 598 proximally and engaging it against base .
596. Lock 597 restrains retractable handle 594 in either
its open or closed position.
Suction cup 602 is coupled to the distal end of
retractable shaft 600 and is drawn into cavity 608 at the
distal end of catheter shaft 595 by moving retractable
handle 594 into its closed position. Suction cup 602
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comprises a flexible polymer cup and an ablation
electrode 604 lining the inner portion of the polymer
cup. Ablation electrode 604 is made of conductive foil
as shown in Fig. 48. Alternatively, ablation electrode
604 is made of a series of longitudinally disposed wires
extending from the base of suction cup 602 to the outer
rim as shown in Fig. 52. Wires extending through lumen
614 couple electrical connector 593 and ablation
electrode 604.
It is contemplated that the suction cup feature of
the catheter shown in Fig. 48 may be combined with any of
the heated balloon electrophysiology catheters described
above (substituting the suction cup of Fig. 48 for the
distal electrode or distal anchoring extension shown in
certain of the drawings).
Referring to Fig. 49, there is shown a sectional
view of the suction catheter of Fig. 48, taken along the
line I-I in Fig. 49. Conductors extending through
mapping lumen 610 couple ring electrodes 606 and
electrical port 593. Lumen 614 extends through
retractable shaft 600, which is slidably mounted in lumen
601. Conductors disposed in vacuum lumen 612 extend
through retractable shaft 600 and couple the electrode on
suction cup 602 with an electrical connector at vacuum
port 592.
The suction catheter is typically used to ablate
tissue in the heart. The distal end of catheter shaft
595 enters the desired chamber of the heart and, local
cardiac signals are sensed using ring electrodes 606
which are coupled to electrical connector 593 by
conductors extending through mapping lumen 610.
Electrodes other than ring electrodes may be used, such
as orthogonal electrodes.
Once ring electrodes 606 have located cardiac
tissue containing an abnormal electrical pathway,
retractable handle 594 is moved into the open position,
thereby releasing suction cup 602 from cavity 608.
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Ablation electrode 604 is then positioned against the
tissue, and vacuum pump 590 is turned on. The
established vacuum between suction cup 602 and the
abnormal tissue causes ablation electrode 604 to be
brought into intimate contact with the heart wall. The
area of contact between the electrode-lined inner portion
of suction cup 602 and the heart wall can be several -
times larger than the area of contact between a typical
tip electrode (e. g., see Fig.45, distal end 570) and a heart wall, thereby
allowing a larger area of tissue to be ablated. Once the
suction cup is attached to the abnormal tissue, an RF
generator coupled to electrical connector 593 causes an
RF ablation current to pass between ablation electrode
604 and the cardiac tissue in a monopolar configuration.
Referring to Fig. 50, there is shown a balloon
suction ablation catheter. Rubber tube 591 couples
vacuum pump 590 and vacuum port 592. Vacuum lumen 630
(Fig. 51) extends the length of the balloon suction
ablation catheter and couples vacuum port 592 and distal
lumen 625.
Electrical port 624 couples an RF generator to
electrodes 635 and 636 inside balloon 628 via conductors
that extend the entire length of the catheter through
wire lumen 634. Additional conductors disposed in wire
lumen 634 couple ring electrodes 621 to electrical
connector 622,. which is further coupled to a monitor.
Inflation port 620, which is constructed to engage a
syringe, is coupled to vacuum port 626 inside balloon 628
by inflation lumen 632.
In use of the device, ring electrodes 621 identify
abnormal cardiac tissue to be ablated. Fluid, preferably
saline, is injected by means of a syringe into inflation
lumen_632 to inflate balloon 628 to a desired pressure,
which is measured by a pressure gauge.
As shown in Fig. 50, balloon 628 is constructed
such that when inflated the distal portion of balloon 628
forms horn cavity 638. Balloon 628, being compliant,
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allows horn cavity 638 to function as a suction cup. The
distal portion of balloon 628 is placed against the
cardiac tissue to be ablated and vacuum pump 590 is
turned on. The vacuum established between balloon 628
and the tissue causes the balloon suction ablation
catheter to become attached to the tissue. An RF current
is then established between electrodes 635 and 636, which
heats the fluid in balloon 628.
Alternatively, an annular electrode 639, which is
coupled to RF port 624 via conductors extending through
wire lumen 634, can be used to ablate cardiac tissue.
Annular electrode 639 comprises conductive material
(e. g., silver or gold) deposited on the surface of horn
cavity 638. Alternatively, an annular electrode may be
mounted on the distal tip of the catheter. shaft
immediately surrounding the suction port and immediately
adjacent to the balloon.
The temperature inside balloon 628 is monitored by
thermistor 627 coupled to electrical port 622 by
conductors extending through wire lumen 634. The signal
from thermistor 627 can then be used in a feedback
circuit for controlling the current delivered by the RF
generator for optimizing the ablation of the tissue and
to minimize damage to normal tissue.
Fig. 51 is a sectional view of the catheter in
Fig. 50 along line II-II showing three lumens disposed
therein: vacuum lumen :620, inflation lumen 632 and wire
lumen 634.
Other embodiments are within the following claims.
For example, any of the inflatable balloons described
above may be coated with a conductive material so that
the balloon functions as a large, expandable electrode.
Exa-mp3es of such large; expandable electrodes are
described below.
Various H~~t Ablation Catyeters
With Expandable Electrodes
Fig. 54 shows, in schematic view, an
electrophysiological heart catheter comprising catheter
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shaft 710 including deflectable tip 712 and deflection
actuator 714. On the deflectable portion 712 an
expansible balloon 716 is included. At the proximal end'
an introductory lumen 718 communicates with a source of
inflation fluid under pressure. An inflation lumen
extending through the catheter shaft connects the
interior of the balloon with the introductory lumen 718
for inflation of the catheter.
Referring to Fig. 55, the catheter has ring
electrodes 720 and 722 at the respectively proximal and
distal ends of the balloon 716. A tip electrode 724 and
further ring electrodes proximal of the balloon 726 and
728 are also included. An electrical power source wire
730 makes electrical contact with a conductive coating
732 that is generally applied over the balloon surface.
As suggested, the wire proximal of the balloon passes
inwardly through the wall thickness of the catheter and
then proceeds to the proximal end where it connects to a
cable 733 that couples to a suitable RF control unit.
The handle 734 is grasped while moving the actuator 714
axially to cause deflection as suggested in the dotted
lines in Fig. 54.
As seen in Fig. 55, the balloon in uninflated
condition has a diameter substantially corresponding to
that of the catheter. Fold lines 736 are shown
suggesting that the balloon is folded in the way employed
with dilatation catheters.
In Fig. 56 the balloon is shown to be inflated,
e.g, at 8 to 10 atmospheres. So inflated the balloon
becomes quite rigid and capable of pressing against heart
tissue sufficiently to make good electrical contact. The
area of tissue contacted is in proportion to the diameter
of the balloon which as can be seen in Fig. 56, when
inflated can be as much as three times as large as the
diameter of the shaft per se.
The embodiment of Figs. 57 and 58 employs a
similar catheter shaft and a similar balloon material.
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In this case, two axially spaced-apart conductive stripes
740 and 742 are applied to the balloon surface,
preferably made from gold. In this embodiment, RF
current is introduced in a bipolar manner for ablating
surface tissue.
Fig. 57 indicates that the balloon 741 can fold in
a similar manner as the balloon of Fig. 55 to conform
substantially to the size of the catheter.
Fig. 58 shows the balloon inf fated, e.g., at 8 to
IO 10 atmospheres. Electrical leads 743 and 744 deliver the
RF current to the conductive stripes.
Fig.. 59 shows, in schematic view, an
electrophysiological heart catheter that includes
. catheter shaft .745, distal portion 761 and inflation port
747. Metering device 746 couples to inflation port 747
J
for injecting a controlled amount of fluid into balloon
748 through an inflation lumen extending the length of
catheter shaft 745. Metering device 746 is preferably a
screw syringe as used in balloon angioplasty.
As seen in Fig. 60, the balloon in uninflated
condition has a diameter substantially corresponding to
that of the catheter. Balloon 748 is made from
elastomeric material which has a plurality of tightly
spaced conductive dots 750 disposed on its surface. Tip
electrode 749 is provided for sensing cardiac signals.
Any number of ring electrodes may als o be disposed along
distal portion 761 to provide additional sensing
capability.
Fig. 61 shows the balloon 748 inflated to a mid-
size while Fig. 62 illustrates the balloon inflated more
fully. The spacing between the dots allows the balloon
to expand to a desired size. The size of the balloon can
be_precisely controlled by employing metering device 746.
Electrode 752 is coupled to a suitable RF control unit
via wire 753. Monopolar RF energy delivered to electrode
752 capacitively couples to conductive dots 750 which are
used to ablate cardiac tissue. In this case,
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' 80 '
electrically conductive fluid is employed as the
inflation medium for the balloon. Capacitive coupling
occurs across the thickness of the balloon to the
conductive dots on the surface of the balloon.
The embodiments of Figs. 63 and 64 employ a
retractable sheath 760 to compress flexible members 764
to conform substantially to the diameter of catheter
shaft 762 for navigation through the venous system and
into the heart. Flexible members 764 are either made
from conductive material or are coated with a conductive
material for suitably receiving RF energy to ablate
cardiac tissue. The conductive material is preferably
gold.
Fig. 63 shows the sheath extended to the distal
end of catheter shaft 762 thereby restraining flexible
members 764. Fig. 64 shows sheath 760 retracted
proximally of the catheter, allowing the flexible members
to expand away from catheter shaft 762.
Sensing electrodes 766 are longitudinally disposed
along the length of the catheter shaft. Figs. 63 and 64
show sensing electrodes 766 axially rotated relative to
each other. Each electrode shown has a corresponding
electrode mounted on the opposite side of the catheter
shaft in the plane perpendicular to the longitudinal axis
of the catheter shaft. These electrodes form orthogonal
electrode pairs for sensing local cardiac electrical
signals. Alternatively, sensing ring electrodes could be
disposed along catheter shaft 762. A sensing and/or
ablation tip electrode may also be disposed at the distal
tip of the catheter shaft.
In an alternative embodiment the catheter shaft
could comprise two slidably moveable segments having an
extended position and a retracted position. The extended
position is characterized by having a tensioning wire
maintaining the distal ends of the moveable segments
farthest apart, while the retracted position is
characterized by releasing the tension in the tensioning
CA 02471106 2004-07-05
81
wire and having the distal ends of the moveable segments
move closer together. Flexible members 764 are mounted
such that the two ends of each member are connected to
different segments of the catheter shaft. With the
catheter segments in the extended position the flexible
members are drawn against the catheter shaft, while in
the retracted position the flexible members bow away from
the catheter shaft.
The embodiments of Figs. 65 through 69 employ
catheter shafts having two slidably moveable segments,
the inner segment having an extended position and a
retracted position as described above.
Fig. 65 shows inner catheter segment 776 in the
extended position, with flexible members 772 drawn
against outer catheter segment 770. Fig. 66 shows inner
catheter segment 776 in the retracted position, segment
776 resting deeper within segment 770 than in Fig. 65.
As shown in Fig. 66, in the retracted position flexible
members 772 bow away from the catheter shaft providing a
larger ablation region. If a more spatially uniform
ablation is desired, a greater number of flexible members
may be employed.
Sensing electrodes 774 can be disposed along the
catheter shaft for sensing. A sensing and/or ablation
electrode can also be included at the distal tip of
catheter segment 776.
Another embodiment is shown in Figs. 67 and 68.
Fig. 67 illustrates the distal segment 784 in an extended
position (distal segment 784 being pulled out from
segment 780). In the extended position alternating
flexible members 782 are drawn against the catheter
shaft. Fig. 68 shows distal segment 784 in the retracted
position (segment 784 being retracted inside segment
780), allowing flexible members 782 to extend away from
the catheter shaft.
In certain circumstances it is advantageous to
employ ultrasound imaging in connection with the ablation
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technique. Fig. 69 shows a sectional view of the
catheter shown in Fig. 56, taken along the line I-I, the
catheter additionally including an ultrasound transducer
790 coupled to drive shaft 792, which extends the entire
length of the catheter through a lumen disposed therein.
Ultrasound imaging can be used to monitor the lesion
forming during ablation. It is contemplated that
ultrasound imaging could be employed with any of the
embodiments described. Details of ultrasound imaging
catheters are described above.
In other instances, it is advantageous to provide
a fluid dispensing lumen as part of the catheter for the
purpose of augmenting the ablation effect at the tissue.
Fig. 80 shows a sectional view of the catheter shown in
Fig. 56 taken along the line I-I, the catheter additional
including a dispensing lumen 797, which is coupled with a
fluid dispenser at the proximal end of the catheter and
feeds into dispensing port 795. The fluid introduced
into the dispensing port may be selected to be highly
electrically conductive relative to that of blood and
thus can render the zone where the fluid is introduced to
tissue at dispensing port 795 preferentially conductive
and thus create a zone where most of the ablative current
will flow. Other fluids, such as alcohol, may be added
to augment the ablation effect. The dispensing port may
be located at any desirable location on the distal
portion of the catheter.
Figs. 70 through 74, which show a catheter
extending through the left atrium of a heart and into the
left ventricle, illustrate a typical method of use for
the balloon electrode embodiments of Figs. 54 through 62.
The left side of the heart is typically accessed by
inserting the distal end of a catheter in an opening in
the femoral vein of a patient and navigating the catheter
through the venous system. Other chambers of the heart
are also accessible to the invention and are treatable by
means of catheters according to the invention.
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Fig. 70 shows the deflected distal end of a
.catheter shaft extending through the left atrium of a
heart and positioned against a wall of the ventricle.
Fig. 71 shows an enlarged view of the portion of Fig. 70
contained in region 800. Positioned against the heart
wall, the ring electrodes and the distal tip electrode
can be employed to locate regions of cardiac tissue to be
ablated.
Once an ablation site has been located, the
balloon electrode is controllably inflated to the desired
size, corresponding to the area of the ablation region,
and is pressed against the tissue at the ablation site as
shown in Figs. 72 and 73. The tissue is ablated in
accordance with the electrode embodiment employed. The
ablation effect may be augmented by introducing
conductive fluid or alcohol to the ablation site. During
the ablation, ultrasound imaging can be employed to
observe the resulting lesion being formed.
Alternatively, the ring or distal tip electrodes may be
used to sense electrical potentials during the ablation
procedure.
Fig. 74 shows the catheter with a deflated balloon
electrode approaching a different wall of the ventricle,
where the above procedure can be repeated if necessary.
Figs. 75 through 79 illustrate a typical method of
use for the mechanical electrode embodiments of Figs. 63
through 68. Specifically, the embodiment of Figs. 63 and
64 is illustrated, although the other embodiments would
function similarly.
Fig. 75 shows the deflected distal end of a
catheter shaft extending through the left atrium of a
heart and positioned against a wall of the ventricle.
Fig. 76 shows an enlarged view of the portion of Fig. 75
contained in region 830. Positioned against the heart
wall, the mapping electrodes can be employed to locate
regions of cardiac tissue to be ablated.
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Once an ablation site has been located, the
mechanical electrode is controllably expanded to the
desired size, corresponding to the area of the ablation
region, and is pressed against the tissue at the ablation
site as shown in Figs. 77 and 78. The tissue is ablated
by passing RF current between the mechanical electrode
and an electrode external to the patient's body in a
monopolar configuration. The ablation effect may be
augmented by introducing conductive fluid or alcohol to
the ablation site. During the ablation, ultrasound
imaging can be employed to observe the resulting lesion
being formed. Alternatively, the mapping electrodes may
be used to sense electrical potentials during the
ablation procedure.
Fig. 79 shows the catheter with a retracted
mechanical electrode approaching a different wall of the
ventricle, where the above procedure can be repeated if
necessary.
Other embodiments are within the following claims.
For example, the expandable balloons in accordance with
the present invention may be heated balloons of the type
described above.
What is claimed is:
