Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LEAD SYSTEM
S
This patent application is related to pending patent applications entitled:
SINGLE PASS DEFIBRILLATION/PACING LEAD WITH PASSIVELY
ATTACHED ELECTRODE FOR PACING AND SENSING, Serial No.
09/121,020, and Attorney Docket No.: 279.116US1; HIGH IMPEDANCE
ELECTRODE TIP, Serial No. 091121,288, and Attorney Docket No.:
279.093US1; SINGLE PASS LEAD AND SYSTEM WITH ACTIVE AND
PASSIVE FIXATION ELEMENTS, Serial No. 09/121,005, and Attorney
Docket No.: 279.081US1; SINGLE PASS ENDOCARDIAL LEAD FOR
MULTI-SITE ATRIAL PACING, Serial No. 09/121,019, and Attorney Docket
No.: 279.079US1; SINGLE PASS LEAD HAVING RETRACTABLE,
ACTIVELY ATTACHED ELECTRODE FOR PACING AND SENSING,
Serial No. 09/121,006, and Attorney Docket No.: 279.058US1; and SINGLE
PASS DEFIBRILLATIONIPACING LEAD WITH PASSIVELY ATTACHED
ELECTRODE FOR PACING AND SENSING, Serial No. 09/121,018, and
Attorney Docket No.: 279.054US1; all filed July 22, 1998, and
DISCRIMINATION OF ATRIAL AND VENTRICULAR SIGNALS FROM A
SINGLE CARDIAC LEAD, Serial No. 08/996,355, filed December 22, 1997,
Attorney Docket No.: 279.O10US2; RETRACTABLE LEAD WITH MESH
SCREEN, Serial No. 08/992,039, filed December 17, 1997, Attorney Docket No.
279.064US1; RETRACTABLE LEAD WITH MESH SCREEN, Serial No.
08/998,174, filed December 24, 1997, Attorney Docket No. 279.085US1, each
of which is assigned to a common assignee and all of which are incorporated
herein by reference.
The present invention relates to the field of leads for correcting
arrhythmias of the heart. More particularly, this invention relates to a
single lead
which can simultaneously pace, sense, and/or defibrillate one or more chambers
of the heart.
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Electrodes implanted in the body for electrical cardioversion or pacing of
the heart are well known. More specifically, electrodes implanted in or about
the
heart have been used to reverse (i.e., defibrillate or cardiovert) certain
life
threatening arrhythmias, or to stimulate contraction (pacing) of the heart,
where
electrical energy is applied to the heart via the electrodes to return the
heart to
normal rhythm. Electrodes have also been used to sense near the sinus node in
the atrium of the heart and to deliver pacing pulses to the atrium. An
electrode
positioned in any chamber of the heart senses the electrical signals that
trigger
the heartbeat. Electrodes detect abnormally slow (bradycardia) or abnormally
fast (tachycardia) heartbeats. In response to the sensed bradycardia or
tachycardia condition, a pulse generator produces pacing or defibrillation
pulses
to correct the condition. The same electrode used to sense the condition is
also
used in the process of delivering a corrective pulse or signal from the pulse
1 ~ generator of the pacemaker.
There are four main types of pulses or signals which are delivered by a
pulse generator. Two of the signals or pulses are for pacing the heart. First
of
all, there is a pulse for pacing the heart when it is beating too slowly. The
pulses
trigger the heart beat. These pulses are delivered at a rate to increase the
abnormally low heart rate to a normal or desired level. The second type of
pacing is used on a heart that is beating too fast. This type of pacing is
called
antitachycardia pacing. In this type of pacing, the pacing pulses are
delivered
initially at a rate much faster or slower than the abnormally beating heart
until
the heart rate can be returned to a normal or desired level. The third and
fourth
types of pulses are delivered through large surface area electrodes used when
the
heart is beating too fast or is fibrillating, respectively. The third type is
called
cardioversion. This is delivery of a relatively lo~~ energy shock, typically
in the
range of 0.5 to ~ joules, to the heart. The fourth type of pulse or signal is
a
defibrillation signal which is the delivery of a high energy shock, typically
greater than 25 joules, to the heart.
Sick sinus syndrome and symptomatic AV block constitute the major
reasons for insertion of cardiac pacemakers today. Cardiac pacing may be
performed by the transvenous method or by electrodes implanted directly onto
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the epicardium. Most commonly, permanent transvenous pacing is performed
using one or more leads with electrodes positioned within one or more chambers
of the heart. The distal end of a lead, sometimes referred to as a catheter,
may be
positioned in the right ventricle or in the right atrium through a subclavian
vein.
The lead terminal pins are attached to a pulse generator which is implanted
subcutaneously.
Some patients require a pacing system to detect and correct an abnormal
heartbeat in both the atrium and ventricle which may have independent rhythms,
as well as a defibrillation system to detect and correct an abnormally fast
heart
rate (tachycardia condition). In the past, a common practice for a patient
having
to pace both of these chambers would be to provide two different leads
attached
to the heart. One would be implanted for delivering
pacing/sensing/defibrillating
to the ventricle and one to the atrium to both pace and sense.
Having two separate leads implanted within the heart is undesirable for
many reasons. Among the many reasons are that the implantation procedure for
implanting two leads is more complex and also takes a longer time when
compared to the complexity and time needed to implant a single lead. In
addition, two leads may mechanically interact with one another after
implantation which can result in dislodgment of one or both of the leads. In
vivo
mechanical interaction of the leads may also cause abrasion of the insulative
layer along the lead which can result in an electrical failure of one or both
of the
leads. Another problem is that as more leads are implanted in the heart, the
ability to add other leads is reduced. If the patient's condition changes over
time
the ability to add leads is restricted. Two separate leads also increase the
risk of
infection and may result in additional health care costs associated with re-
implantation and follow-up.
Because of these problems, catheters having electrodes for both pacing
and sensing in both chambers of the heart on a single lead body have been
used.
These leads, known as single pass lead designs, have drawbacks since the
single
pass lead designs utilize "floating" electrodes or electrodes which are not
attached to the endocardial wall of the heart. The catheter having the
electrodes
which forms the lead body is essentially straight. The electrode or electrodes
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may float or move slightly at a distance from the endocardial wall within the
heart.
The portion of the lead positioned within the atrium of current single-
pass endocardial leads has one or more electrodes which are incorporated into
the lead body as an electrically conductive cylindrical or semicylindrical
ring
structure. In other words, the lead body is basically cylindrical and the one
or
more electrodes positioned within the atrium of the heart are cylindrical
metal
structures incorporated into the cylindrical lead body. The ring electrode
structures do not allow for tissue ingrowth into the electrode to enhance
electrode stabilization within the atrium. Since the location of the
electrodes is
not fixed against the atrial wall, the performance of these leads is more
variable.
In other words, variations with respect to electrical contact with the wall of
the
atrium results in suboptimal electrical sensing capability and pacing delivery
capability. Typically, the pacing characteristics of a floating electrode are
less
desirable than the pacing characteristics associated with an electrode fixed
to the
endocardial wall of the heart. The performance of a lead using a floating
electrode is poorer than a lead having electrodes which contact or are nearer
the
walls of the heart.
Another problem associated with the current straight single pass leads, is
that these electrodes may be unable or less able to sense an arrhythmic
condition.
In addition, the applied voltage or current needed for pacing may be
ineffective.
Additional energy may have to be used to pace the heart thereby depleting
energy from the battery of the pulse generator of the pacing system.
There is a real need for a single-pass transvenous pacing or defibrillation
lead. A single-pass lead equipped with such an electrode arrangement would
allow for better sensing capability and better pacing therapy to the heart. In
addition, there is a need for a single-pass lead having an electrode for
positioning
within the atrium that allows for tissue ingrowth. Such an electrode would
further enhance lead stabilization within the heart. There is also a need for
a
single-pass endocardial lead which has an electrode for placing within the
right
atrium of the heart that accommodates eluting anti-inflammatory drugs. There
is
still a further need for a single pass endocardial lead that is easier for a
surgeon
to implant.
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Summa~~ of the Invention
A single-pass endocardial lead electrode adapted for implantation and for
connection to a system for monitoring or stimulating cardiac activity includes
a
lead body. The lead, in one embodiment, includes a first distal end electrode
or
electrode pair which has a first electrical conducting surface. The lead body
also
has a second electrode or electrode pairs which has a second electrical
conducting surface. The second electrode or electrode pair is adapted for
positioning and fixation to the wall of the atrium of the heart. A passive
fixation
element is used as part of the second electrode or electrode pair. The lead
body
also includes a curved portion which facilitates the positioning and fixing of
the
second electrode or electrode pair. The curved portion has a radius near the
natural radius of the atrium. The first and second electrode may be a single
electrode or a bipolar pair. The curve in the lead body, which is positioned
in the
right atrium of the heart after implantation, positions the electrode closer
to the
wall of the atrium to enhance the sensing and pacing performance of the lead.
The electrical conducting surface of the second electrode has a relatively
small diameter when compared to previous electrodes. The small diameter
electrode results in superior electrical performance when compared to previous
single-pass endocardial leads. The benefits include increased pacing
impedance,
increased P-wave signal amplitudes and decreased atrial pacing capture
thresholds. The increased impedance lets the battery energy source last
longer.
The single-pass lead equipped with an atrial electrode capable of being fixed
to
the endocardial wall allows for better sensing capability and better current
delivery to the heart. The second electrode may be placed on the outside of
the
2~ curved portion of the lead body. The fixed atrial electrode enhances lead
stabilization within the heart and the result is no need for two leads in the
heart.
The costs and complexity associated with implanting and follow-up care for the
single pass lead is less than two separate leads.
In another embodiment, the lead includes a first distal end electrode or
pair of electrodes for positioning in the ventricle and a second proximal
electrode
or pair of electrodes for positioning in the atrium. The second electrode or
pair
of electrodes are adapted for positioning and fixation to the wall of the
atrium of
the heart. An active fixation element is used as part of the second electrode
or
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electrode pair. The lead body also may include a curved portion which
facilitates the positioning and fixing of the second electrode or second pair
of
electrodes. The lead body also includes at least one recess for positioning an
active fixation element within the recess.
In yet another embodiment, the recess is able to house the active fixation
electrode as well as a portion of a lead body associated with the atrium
(atrial
lead body). By moving the terminal pin with respect to a yoke, the lead body
is
moved out of the recess. The atrial lead body can be a straight lead or a J-
shaped
lead. The type of atrial lead body used will depend on the placement of the
lead
within the atrium of the heart and the preference of the surgeon doing the
placement. The advantage is that the active fixation electrode is placed into
the
recess during placement of the lead to prevent it from attaching inadvertently
to
the subclavian vein or other tissue while it is being inserted.
In another embodiment, an active fixation electrode is included with the
lead that can be controllably moved from a recessed position to an attachment
position by rotating the terminal pin attached to the conductor coil which is
attached to the body of the active fixation electrode.
In yet another embodiment, the lead includes a distal end having a first
pacing electrode or electrode pair. The distal end of the lead body also has a
second electrode or electrode pair. The second electrode or electrode pair is
positioned away from the first electrode or electrode pair. The first and
second
electrodes fit within a single chamber of the heart for multi-site pacing or
pulse
delivery to the single chamber. In a first embodiment, the distal end of the
lead
body includes a curved portion which facilitates the positioning of the first
and
second electrode or electrode pair within the single chamber. The first
electrode
may be a single electrode associated with a unipolar arrangement or may be one
of a pair of electrodes associated with a bipolar electrode. The second
electrode
may be either unipolar or bipolar as well.
In another embodiment, the lead includes a first leg for the first electrode
and a second leg for the second electrode. One of the first or second legs is
movable between a withdrawn position and an extended position. When
inserting the lead, the withdrawn leg is within the lead body which eases the
task
of insertion. In yet another embodiment, the two legs may be withdrawn to a
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position within the lead for easy insertion. In each of the embodiments, the
first
electrode and second electrode can be passively or actively fixed.
In another embodiment, the lead extends from two terminal legs at a
proximal end of the lead to two electrode legs at a distal end of the lead.
Each
electrode leg includes a first electrode and a second electrode. The second
electrode is adapted for positioning and fixation to the wall of the atrium of
the
heart.
In one embodiment, a bifurcated lead includes a main lead body which is
adapted to carry signals to and from the heart. The main body extends to a
first
electrode assembly which has a first electrode and a second electrode, and is
adapted to be implanted within a first chamber of the heart. The body also
extends to a second electrode assembly which has a third electrode and a
fourth
electrode, and is adapted to be implanted within a second chamber of the
heart.
In another embodiment, the lead body has an intermediate portion which
comprises a quad lumen body. In yet another embodiment, the first electrode
leg
and the second electrode leg each have a semi-circular profile. A yoke, in
another configuration, couples the first electrode leg and the second
electrode leg
with the intermediate portion. The first electrode assembly and the second
electrode assembly can be either actively or passively fixated within the
heart. A
mesh screen can also be provided to allow for better tissue in-growth.
In another embodiment, a bifurcated lead includes a main lead body
which is adapted to carry signals to and from the heart. The main body extends
to a first electrode assembly which has a first electrode and a second
electrode,
and is adapted to be implanted within a first chamber of the heart. The body
also
extends to a second electrode assembly which has a third electrode and a
fourth
electrode, and is adapted to be implanted within a second chamber of the
heart.
The first electrode assembly and the second electrode assembly include an
active
fixation portion, to which a movement assembly is coupled. In one embodiment,
the movement assembly includes an externally threaded portion which is
engaged with an internally threaded housing. In another embodiment, the
internally threaded portion comprises an insert disposed within the lead.
In another embodiment, a bifurcated lead includes a main lead body
which is adapted to carry signals to and from the heart. The main body extends
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to a first electrode assembly which has a first electrode and a second
electrode,
and is adapted to be implanted within a first chamber of the heart. The body
also
extends to a second electrode assembly which has a third electrode and a
fourth
electrode, and is adapted to be implanted within a second chamber of the
heart.
The lead is coupled with a signal generator which is adapted for producing
pulses to apply to the heart.
According to one embodiment of the present invention, there is provided
a body-implantable lead assembly comprising a lead, one end of the lead being
adapted to be connected to electrical supply for providing or receiving
electrical
pulses. The other end of the lead comprises a distal tip which is adapted to
be
connected to tissue of a living body. The lead is characterized by having
either
a) a porous electrode at the base of the' helix and/or b) an insulating
coating over
a portion of the helix so that the impedance is increased for the helix as
compared to a helix of the same size and materials without an insulating
coating.
The lead also has an increased impedance or a high impedance which can act to
extend the life of the battery. The high or at least the increased impedance
may
be effected in any of an number of ways, including, but not limited to one or
more of the following structures: I) a fully insulated tissue-engaging tip
with an
electrode at the base of the insulated tip, 2) a partially insulated (only a
portion
of the surface area of the engaging tip being insulated), 3) a mesh or screen
of
material at the distal end of the lead, at the base of an extended engaging
tip
(whether a fxed or retractable tip), 4) the selection of materials in the
composition of the mesh and/or tip which provide higher impedance, 5) the
partial insulative coating of a mesh or screen to increase its impedance, and
6)
combinations of any of these features. There may be various constructions to
effect the high impedance, including the use of helical tips with smaller
surface
areas (e.g., somewhat shorter or thinner tips). There may also be a sheath of
material inert to body materials and fluids and at least one conductor
extending
through the lead body. The use of these various constructions in the tip also
allows for providing the discharge from the tip in a more highly resolved
location or area in the tip.
According to another embodiment of the present invention, there is
provided a body-implantable lead assembly comprising a lead, one end being
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adapted to be connected to electrical supply for providing or receiving
electrical
pulses. The lead further comprises a distal tip which is adapted to be
connected
to tissue of a living body. The lead also has a high impedance to extend the
life
of the battery. There may be various constructions to effect the high
impedance.
S There may also be a sheath of material at the distal end of the lead
assembly,
with the sheath being inert to body materials and fluids and at least one
conductor extending through the lead body.
The distal tip electrode is adapted, for example, for implantation
proximate to the heart while connected with a system for monitoring or
stimulating cardiac activity. The distal tip electrode includes an electrode
tip
(preferably with only a percentage of its entire surface area being
electrically
conductively exposed [only a portion of the surface is insulated] to increase
its
impedance), preferably a mesh screen disposed at a distal end of the electrode
tip, a fixation helix disposed within the electrode tip, and a helix guiding
1 S mechanism. The mesh screen preferably is electrically active (conductive
as
well as active), and the area of the mesh screen and the percentage of
electrically
exposed surface area of the electrode tip can be changed to control electrical
properties. Further, the mesh screen can entirely cover an end surface of the
electrode tip, or a portion of the end surface in the form of an annular ring.
1n
one embodiment, the helix guiding mechanism includes a hole punctured within
the mesh screen. Alternatively, the helix guiding mechanism can include a
guiding bar disposed transverse to a radial axis of the electrode. The helix
is
retractable, and is in contact with a movement mechanism. The movement
mechanism provides for retracting the helix, such as during travel of the
2S electrode tip through veins. The helix is aligned with the radial axis of
the
electrode and travels through the guiding mechanism. The mesh may be tightly
woven or constructed so that there are effectively no openings, or the mesh
can
be controlled to provide controlled porosity, or controlled flow through the
mesh.
In another embodiment, the electrode tip includes a mesh screen forming
a protuberance on the end surface of the electrode tip. The protuberance is
axially aligned with the radial axis of the electrode. The helix travels
around the
protuberance as it passes through the mesh while traveling to attach to tissue
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within the heart. The helix also travels around the protuberance as it is
retracted
away from the tissue within the heart. If the mesh screen is insulated around
the
protuberance, then a high impedance tip is created. Advantageously, the
protuberance allows for better attachment to the cardiac tissue without having
the
S electrode tip penetrating therethrough.
Additionally, a distal tip electrode is provided including an electrode tip,
a mesh screen disposed at a distal end of the electrode tip, a fixation helix
disposed within the electrode tip, and a helix guiding mechanism. The
electrode
tip further may include a piston for moving the helix. The piston further may
10 include a slot for receiving a bladed or fixation stylet. When engaged and
rotated, the piston provides movement to the helix. The base provides a
mechanical stop for the helix and piston when retracted back in to the
electrode
tip.
In another embodiment, the distal tip assembly is adapted for
implantation proximate to the heart while connected with a system for
monitoring or stimulating cardiac activity. A fixation helix/piston assembly
is
housed by an electrode collar, housing, and base assembly. Attached to the
proximal end of the helix is a piston which includes a proximal slot for
receiving
a bladed or fixation stylet. When a stylet is engaged in the slot and rotated,
the
piston provides movement to the helix. Depending on the embodiment, the
fixation helix/piston assembly may be electrically active or inactive. The
electrode collar, housing, and base all house the fixation helix/piston
assembly.
The proximal end of the electrode collar is attached to the distal end of the
housing. Furthermore, the proximal end of the housing is attached to the
distal
end of the base, and the proximal end of the base is directly attached to the
conductor coils of the lead.
A mesh screen may be attached to the distal tip of the electrode collar.
The mesh screen, in another embodiment, is electrically active and serves as
the
electrode on the distal tip assembly. The tip may then be fully insulated to
34 increase the impedance of the tip or may be partially insulated (with
preselected
areas of the helix tip being insulated and other areas being non-insulated) to
adjust the impedance of the tip to the specific or optimal levels desired. The
area of the mesh screen can be modified to cover differing portions of the end
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surface of the distal tip assembly to control electrical properties of the
lead. The
fixation helix travels through a guiding mechanism, where the guiding
mechanism allows the fixation helix to be extended and retracted. In one
embodiment, the helix guiding mechanism includes a hole formed within the
mesh screen. Alternatively, the helix guiding mechanism can include a guiding
bar disposed transverse to a radial axis of the electrode collar. The mesh
screen
andlor guiding bar also serve as a full extension stop when the helix is fully
extended. The base serves as a stop when the fixation helix/piston assembly is
fully retracted.
In yet another embodiment, the electrode uses a partially insulated
fixation helix to provide a relatively high pacing impedance electrode. The
fixation helix is insulated using insulating coatings over a portion of the
fixation
helix.
The above lead embodiments are also incorporated into a system,
1 ~ wherein the lead is operatively coupled with a pulse generator. Signals or
pacing
pulses produced by the pulse generator which are sent and/or received from the
electrodes. The pulse generator can be programmed and the electronics system
includes a delay portion so that the timing between a pulse at a first
electrode
and a pulse at a second electrode.
The provided electrode tip supplies a retractable helix and a mesh screen
which advantageously allows for sufficient tissue in-growth. The guide
mechanism provides a convenient way to direct the rotation of the helix. A
further advantage of the electrode tip is the provided mechanical stop. The
mechanical stop aids in preventing over-retraction of the helix during the
installation or removal of the electrode tip.
The electrodes are attached to the endocardium so that the electrical
signals received from the heart are better than with floating, unattached
electrodes. In addition, the active fixation electrodes can be placed into a
recess
so that mechanisms, such as a helical hook, used to attach the electrode to
the
wall of the heart will not catch undesired tissue. A further advantage is that
only
one lead needs to be placed into the patient to do both sensing and pacing of
all
types. The lead can also be shaped to facilitate placement of the lead.
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A further advantage is that the bi-polar single pass lead allows for two
chambers of the heart to be paced andlor sensed, while only one lead is
implanted within the patient. This assists in preventing added stress and
expense
for the patient. In addition, the active fixation element will not hook nor
snag
tissue when it is retracted within the lead. The active fixation element does
not
require the use of a stylet, since the terminal pins are used to extend and
retract
the active fixation element. An additional benefit is that only one lead is
placed
into the patient for both sensing and pacing, thereby eliminating the need for
placement of the second lead.
Yet another advantage is that the extendable portion of the lead is
mechanically isolated from the main lead body so that the helical screw or
hook
can turn independently of the lead body. In other words, the body of the lead
does not need to be turned to affix the helical screw to the heart.
These and other embodiments, aspects, advantages, and features of the
present invention will be set forth in part in the description which follows,
and in
part will become apparent to those skilled in the art by reference to the
following
description of the invention and referenced drawings or by practice of the
invention. The aspects, advantages, and features of the invention are realized
and attained by means of the instrumentalities, procedures, and combinations
particularly pointed out in the appended claims and their equivalents.
Figure 1 is a schematic view of a single-pass lead with electrodes
for pacing at multiple sites within a single chamber of the
heart.
Figure 2 is a schematic view of a single-pass lead with electrodes
for pacing at multiple sites within a single chamber of the
heart, positioned within the right ventricle of the heart.
Figure 3 is a block diagram illustrating a system for delivering
signals to the heart constructed in accordance with one
embodiment of the present invention.
Figure 4 is a first perspective view illustrating a single-pass lead
constructed in accordance with one embodiment of the
present invention.
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Figure S is a second perspective view illustrating a single-pass lead
constructed in accordance with one embodiment of the
presentmvention.
Figure 6 is a cross-section view taken along 6-6
of Figure 4
illustrating a single-pass lead constructed
in accordance
with another embodiment of the present
invention.
Figure 7 is a cross-section view illustrating a
portion of a
single-pass lead constructed in accordance
with yet
another embodiment of the present invention.
Figure 8 is a cross-section view illustrating a
portion of a
single-pass lead constructed in accordance
with one
embodiment of the present invention.
Figure 9 is a cross-section view illustrating a
portion of a
single-pass lead constructed in accordance
with one
1 S embodiment of the present invention.
Figure 10 is a cross-section view illustrating a
portion of a
single-pass lead constructed in accordance
with one
embodiment of the present invention.
Figure I I is a perspective view illustrating a single-pass
lead
constructed in accordance with one embodiment
of the
present invention.
Figure 12 is a perspective view illustrating a single-pass
lead
constructed in accordance with one embodiment
of the
present invention.
Figure 13 is a perspective view illustrating a single-pass
lead
constructed in accordance with another
embodiment of the
presentinvention.
Figure 14 is a side view of the single-pass endocardial
lead for
sensing and electrically stimulating the
heart, positioned
within the right ventricle and right atrium
of the heart,
constructed in accordance with one embodiment
of the
present invention.
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Figure 1 SA is a side view of a single-pass lead
for sensing and
electrically stimulating the heart constructed
in accordance
with one embodiment of the present invention.
Figure 15B is a side view of a single-pass lead
for sensing and
electrically stimulating the heart constructed
in accordance
with one embodiment of the present invention.
Figure 16 is a side view of a single-pass endocardial
lead for sensing
and electrically stimulating the heart
constructed in
accordance with one embodiment of the
present invention.
Figure 17A is a side view of a single-pass endocardial
lead for sensing
and electrically stimulating the heart
constructed in
accordance with one embodiment of the
present invention.
Figure 17B is a side view of stylet for use with
the endocardial lead.
Figure 18 is a perspective view of the atrial electrode
portion of the
lead showing a passive attachment element
for attachment
to the atrial wall of the heart.
Figure 19 is a perspective view of another embodiment
of the
electrode for passive attachment to the
atrial wall of the
heart.
Figure 20 is a perspective view of another embodiment of the
electrode for passive attachment to the atrial wall of the
heart.
Figure 21 is a perspective view of another embodiment of the
electrode for passive attachment to the atrial wall of the
heart.
Figure 22 is a perspective view of another embodiment of the
electrode for passive attachment to the atrial wall of the
heart.
Figure 23 is a perspective view of another embodiment of the
electrode for passive attachment to the atrial wall of the
heart.
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Figure 24 is a perspective view of another embodiment of the
electrode for passive attachment to the atrial wall of the
heart.
Figure 25 is a side view of a portion of a lead body showing an
5 electrode for passive attachment to the atrial wall of the
heart.
Figure 26 is a side view of a single-pass endocardiai lead for
electrically stimulating the heart constructed in accordance
with another embodiment of the present invention.
10 Figure 27 is a side view of a single-pass endocardial lead implanted
within the heart constructed in accordance with another
embodiment of the present invention.
Figure 28 is a side view of a single-pass endocardial lead for
multi-site pacing during insertion with a first atrial leg
15 straight and one atrial leg withdrawn into the lead body
constructed in accordance with one embodiment of the
present invention.
Figure 29 is a side view of a single-pass endocardial lead for
mufti-site pacing during insertion with a first atrial leg
formed into atrial 'J' after withdrawal of stylet and one
atrial leg withdrawn into the lead body constructed in
accordance with one embodiment of the present invention.
Figure 30 is a side view of a single-pass endocardial lead for
mufti-site pacing during insertion with both atrial legs
formed into a 'J' constructed in accordance with one
embodiment of the present invention.
Figure 31 is a side view of a single-pass endocardial lead for
mufti-site pacing during insertion with one atrial leg
formed into a 'J' and one leg straight constructed in
accordance with one embodiment of the present invention.
Figure 32 is a side view of a single-pass endocardial lead for
mufti-site pacing during insertion with two atrial legs
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16
formed into a 'J' and one leg straight constructed in
accordance with one embodiment of the present invention.
Figure 33 is a side view of a single-pass endocardial, lead for
mufti-site pacing constructed in accordance with one
embodiment of the present invention.
Figure 34 is a side view of a single-pass endocardial lead for
mufti-site pacing constructed in accordance with one
embodiment of the present invention.
Figure 35 is a side view of a single-pass endocardial lead for
mufti-site pacing constructed in accordance with one
embodiment of the present invention.
Figure 36 is a side elevational view illustrating a single-pass lead
constructed in accordance with another embodiment of the
present invention.
I S Figure 37 is a cross-section view illustrating a single-pass lead
constructed in accordance with one embodiment of the
present invention.
Figure 38 is a cross-section view illustrating a single-pass lead
constructed in accordance with one embodiment of the
present invention.
Figure 39 is a cross-section view illustrating a single-pass lead
constructed in accordance with one embodiment of the
present invention.
Figure 40 is a perspective view illustrating a movement assembly of
2~ the lead constructed in accordance with one embodiment
of the present invention.
Figure 41 is a first side elevational view illustrating a lead
constructed in accordance with one embodiment of the
present invention.
Figure 42A is a cross-sectional view of an electrode tip of a lead for
monitoring and stimulating the heart constructed in
accordance with one embodiment of the present invention.
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Figure 42B is an end view of the electrode tip of the lead shown in
Figure 42A.
Figure 43A is a cross-sectional view of an electrode tip of a lead for
monitoring and stimulating the heart constructed in
accordance with one embodiment of the present invention.
Figure 43B is an end view of the electrode tip of the lead shown in
Figure 43A.
Figure 44A is a cross-sectional view of an electrode tip of a lead for
monitoring and stimulating the heart constructed in
accordance with one embodiment of the present invention
Figure 44B is an end view of the electrode tip of the lead shown in
Figure 44A.
Figure 45A is a cross-sectional view of an electrode tip of a lead for
monitoring and stimulating the heart constructed in
accordance with one embodiment of the present invention
Figure 45B is an end view of the electrode tip of the lead shown in
Figure 45A.
Figure 46 shows a partially insulated helical tip constructed in
accordance with one embodiment of the present invention.
Description of the Embodiments
In the following detailed description, reference is made to the
accompanying drawings which form a part hereof, and in which is shown by way
of illustration specific embodiments in which the invention may be practiced.
These embodiments are described in sufficient detail to enable those skilled
in
the art to practice the invention, and it is to be understood that other
embodiments may be utilized and that structural changes may be made without
departing from the scope of the present invention. Therefore, the following
detailed description is not to be taken in a limiting sense, and the scope of
the
present invention is defined by the appended claims and their equivalents.
Figure 1 illustrates a schematic view of a system 100 for delivering
electrical pulses or signals to stimulate and/or pace the heart. The system
for
delivering pulses 100 includes a pulse generator 102 and a lead 110, where the
lead 110 includes a connector end or connector terminal 120 and extends to a
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18
distal end 130. The distal end 130 of the lead 110 includes at least two
electrodes 132 and 134, which comprise either unipolar or bipolar type
electrodes. For bipolar type electrodes, the electrode 132 would be part of a
bipolar set including two electrodes. Similarly, the electrode 134, if
bipolar,
would be part of a set.
The lead 110 includes a lead body 112 which, in one embodiment, is
comprised of a tubing material formed of a biocompatibIe polymer suitable for
implementation within the human body. Preferably, the tubing is made from a
silicon rubber type polymer. The lead body 110 includes at least one lumen
(not
shown) which carries each electrical conductor from the connector terminal 120
to the electrodes 132 and 134. The electrical conductors carry current and
pulses
between the pulse generator 102 and the electrodes 132 and 134 located in the
distal end 130 of the lead 1 I 0.
The pulse generator 102 includes a source of power as well as an
electronic circuitry portion 104. The pulse generator is a battery-powered
device
which generates a series of timed electrical discharges or pulses used to
initiate
depolarization of excitable cardiac tissue. The pulses are delivered to the
cardiac
tissue and operate as an artificial pulse formation source when used to pace
the
heart. The pulse generator is generally implanted into a subcutaneous pocket
made in the wall of the chest. Alternatively, the pulse generator 102 can be
placed in a subcutaneous pocket made in the abdomen, or other locations.
The lead I I O is connected to the pulse generator 102 by the connector
terminal 120. The lead 110 travels from the pulse generator 102 into a major
vein, and the distal end 130 of the lead is placed inside the heart. The lead
110 is
placed underneath the skin and travels to the shoulder and neck where it
enters a
major vein such as the subclavian vein. The distal end 130 of the lead 110 is
placed directly within the endocardium. In one embodiment, the lead 110 will
be actively or passively affixed to the endocardial wall of a chamber of the
heart,
as will be further described below.
As can be seen in Figure 1, the distal end 130 of the lead 110 is curved,
where the electrodes 132, 134 are disposed along the curve 136. The curve 136
is sized and positioned to allow the electrodes 132 and 134 to be positioned
within one chamber of the heart. In Figure 1, the chamber selected for
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19
implantation is the right atrium 150. The lead 110 will include a lumen into
which a stylet may be placed. The stylet is basically a wire that straightens
out
the lead while it is being placed within the heart. By removing the stylet,
the
lead will take on its natural or manufactured shape, which in this case, is a
curved distal end 130. The curve within the distal end 130 of the lead 110 has
a
small enough radius such that it fits within the right atrium 150 of the
heart.
The electronics 104 associated with the pulse generator 102 include a
delay circuit which allows the pulse delivered to one of the electrodes 132 or
134
to be delayed with respect to the pulse delivered to the other of the
electrodes.
This delay can be either a delay of zero or it can be a delay that can be
programmed to be any desired length of time. The delay portion of the
electronics 104 typically will include a clock source. The clock source will
produce a clocking pulse that can be used to produce the delay. In other
words,
if a delay of so many clocking signals equals the appropriate or selected
delay,
the pulse generator 102 and the electronics 104 will initially deliver a pulse
to a
first electrode, then the electronics will count the selected number of pulses
from
a clock signal and then deliver a pulse to the other of the electrodes 132 and
134.
Also shown in Figure 1 is a programmer 106. The programmer is
typically an external-type programmer that can be used to program many of the
parameters of the electronics 104 and other parameters of the pulse generator
102. One of the parameters that can be programmed includes the length of delay
between the pulse to the electrode 132 and the pulse to the electrode 134. It
should be noted that the length of delay can also be set so that it's
nonexistent.
In other words, if a delay of zero is used, the pulse generator 102 and the
electronics associated with the pulse generator 104 will send pacing pulses to
the
electrode 132 and the electrode 134 at substantially the same time. The
programmer can also be an external handheld-type programmer which a patient
might be able to use. The other type of programmer might be one that a
physician would have in his or her office which can be used to program various
parameters associated with the pulses produced by the pulse generator. The
programmer 106 will typically have a feature which will allow readout of the
status of the pulse generator.
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Figure 2 is a schematic of a single-pass endocardial lead for electrically
stimulating multiple sites within a single chamber of the heart which is
positioned within the right ventricle of the heart, where the lead 110 is
shown as
having a distal end 130. The distal end 130 features includes a first
electrode
5 I32 and a second electrode 134. In Figure 2, the distal end 130 of the lead
body
110 passes through the right atrium and is positioned within the right
ventricle
160 of the heart. Again, as before, the electrodes 132 and 134 may be unipolar
or may be bipolar. In the instance when each of the electrodes 132 and I34 are
bipolar, there is an additional electrode associated with each of the
electrodes
10 I 32 and 134. Alternatively, in another embodiment, one of the electrodes
132 is
unipolar and one of the electrodes 134 is bipolar.
The electrodes I34 and 132 are positioned along the curve 136 in the
distal end 130 so that electrical stimulation or pulse generation can be
delivered
to two sites within a single chamber of the heart, namely, the right ventricle
160.
1 S The curve I36 is sized and positioned to be received within the ventricle,
where
the electrodes 132 and 134 are in contact with the wall of the heart, as
shown.
The electrodes 132 and 134 are attached to the endocardial wall of the heart
with
either passive f xation or active fixation, as will be further described
below. The
shape of the curve 136 associated with the distal end may be varied to achieve
a
20 selected placement of the electrodes 134 and 132 within the right ventricle
of the
heart. In addition, the distance between the first electrode 132 and second
electrode 134 can also be changed for various applications for mufti-site
pacing
within the right ventricle. The pulse generator and electronics as well as the
connector end or terminal end 120 of the lead I 10 and the programmer I 06,
are
all the same in Figure 1 as in Figure 2 and, therefore, were not shown here.
Figure 3 illustrates another embodiment of the present invention,
showing a lead 170 adapted for delivering electrical pulses to stimulate the
heart.
The lead 170 has a lead body 172 extending from a proximal end 174, which is
adapted to connect with equipment which supplies electrical pulses, to a
distal
end 176 which is adapted to be inserted into the heart. The lead body 172
includes an intermediate portion I 78 which includes quad-lumen tubing as will
be further discussed below. Proximate to the distal end 176 is a first
electrode
tip 180 including a first electrode assembly 182. A second electrode tip 184
is
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21
also provided, as discussed below, which includes a second electrode assembly
186.
Proximate to the proximal end 174 of the lead 170 are connector
terminals 188. The connector terminals 188 electrically connect the various
electrodes and conductors within the lead 170 to a pulse generator and signal
sensor 190. The pulse sensor and generator 190 contains electronics to sense
various electrical signals of the heart and also produce current pulses for
delivery
to the heart, depending on the type of lead 170 used. The pulse sensor and
generator 190 also contains electronics and software necessary to detect
certain
types of arrhythmias and to correct for them. The lead terminal connector I 88
provides for the electrical connection between the lead 170 and the pulse
generator 190.
To implant the lead 170 within a patient, a single sheath can be used for
the single electrode 170 to implant the lead 170 within the heart, which
prevents
unnecessary trauma to the patient. The first electrode assembly 182 is
advanced
into the ventricular portion 192 of the heart 194. The first electrode
assembly
182 is secured to the wall of the heart 194 using either passive or active
fixation.
In one embodiment, the active fixation elements are advanced using the
terminal
pins (Figure 4). In another embodiment, the active fixation elements are
advanced using a stylet, as discussed further below.
The second electrode assembly 186 is advanced, in one embodiment, into
the atrium portion 196 of the heart 194 using a straight stylet (not shown).
To
secure the second electrode assembly 186 into the atrium, the straight stylet
is
removed and a J-shaped stylet (not shown) is insert into the second electrode
assembly 186 and the second electrode assembly 186 takes on the J-shape..
Alternatively, the second electrode assembly 186 is placed within the atrium
portion 196 using a J-shaped lead, as shown and discussed below in Figures 1 I
and 12. Similar to the first electrode assembly, the second electrode assembly
I 86 is secured to the heart 194 using either passive or active fixation.
Figure 4 illustrates the lead of Figure 3 in greater detail. The lead 200
extends from a proximal end 202 to a distal end 204 and includes a first and
second connector terminal 280, 282 near the proximal end 202. The lead 200
also includes a lead body 220, a first electrode assembly 210, and a second
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electrode assembly 212, as will be further described below. The connector
terminals 280, 282 electrically connect the various electrodes and conductors
with the lead body to a pulse sensor and generator 190 (Figure 3). The pulse
sensor and generator 190 (Figure 3) contain electronics to sense various
pulses of
the heart and also produce pulsing signals for delivery to the heart. The
pulse
sensor and generator 190 also contain electronics and software necessary to
detect certain types of arrhythmias and to correct for them. Physicians are
able
to program the pulse sensor and generator to correct a particular arrhythmia
that
the patient may have. Numerous types of connector terminals which connect to
a pulse sensing and generating unit can be used. In one embodiment, the
connector terminals 280, 282 are designed to conform with International
Standards.
The lead body 220, in one embodiment, is formed from a polymer
biocompatible material, and can include tubing made from a silicone rubber
polymer. The lead body 220 extends from the proximal end 202 of the lead 200
to the distal end 204 of the lead 200, and has an intermediate portion 206
therebetwEen. Near the proximal end 202 of the lead body 220, the lead body
220 has at least two IS 1 terminal legs, including a first terminal leg 230
and a
second terminal leg 232.
At the proximal end 202 of the first terminal leg 230 and the second
terminal leg 232 are terminal pins 234, 236 which can be operatively coupled
with a pulse sensor and signal generator 190, as discussed above. In one
embodiment, the terminal pins 234, 236 are used to rotate the active fixation
device, discussed further below. In another embodiment, a stylet driven
mechanism is used to rotate the active fixation device. The first terminal leg
230
and the second terminal leg 232 extend from the terminal pins 234, 236 of the
proximal end 202 of the lead 200 to the intermediate portion 206 of the lead
200,
where the first terminal leg 230 and the second terminal leg 232 are coupled
with
the intermediate portion 206 at a proximal bifurcation point 208. In one
embodiment, the first terminal leg 230 and the second terminal leg 232 are
coupled with the intermediate portion 206 with a yoke 240 which operates as a
strain relief. The yoke 240, in one embodiment, comprises a sheath for
covering
at least portions of the first and second terminal legs 230, 232 and the
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23
intermediate portion 206, where the sheath can be attached using medical
adhesive or other attachment methods. In another embodiment, the yoke 240 is
over-molded encompassing the intermediate portion 206 and the first and second
terminal legs 230, 232.
The intermediate portion 206 of the lead body 220, as shown in Figure 6,
is comprised of quad-lumen tubing 242, which in one embodiment comprises
PTFE insulation. Disposed within each lumen of the quad-lumen tubing 242 is a
conductor 246, consisting of either a cable or a coil. Referring again to
Figures 4
and 5, the intermediate portion 206 extends from the proximal bifurcation
point
1 U 208 to a distal bifurcation point 209. At the distal bifurcation point
209, in one
embodiment, the intermediate portion 206 transitions into two bi-lumen tubes
250, including a first electrode leg 252 and a second electrode leg 254. The
first
electrode leg 252, in one embodiment, is shorter in length than the second
electrode leg 254, where the first electrode leg 252 is for implantation into
an
atrium (not shown) and the second electrode leg 254 is for implantation within
the ventricle (not shown). In another embodiment, the first electrode leg 252
and
the second electrode leg 254 are coupled with the intermediate portion 206
with
a yoke 241, similar to the yoke 240 discussed above. The first electrode leg
252
and the second electrode leg 254 each extend to the first electrode assembly
210
and the second electrode assembly 212, respectively.
In one embodiment, as shown in Figure 4, the first electrode assembly
210 and the second electrode assembly 212 are both bipolar. In another
embodiment, as shown in Figure 5, the first electrode assembly 210 is bipolar
and the second electrode assembly 212 is unipolar. In yet another embodiment,
similar to Figure 5, the first electrode assembly 210 is unipolar and the
second
electrode assembly 212 is bipolar. To form a unipolar electrode assembly, only
a single conductor, discussed further below, is provided within the electrode
assembly, and a single electrode is provided. The electrode, for either the
bipolar or unipolar embodiments of the first and second electrode assemblies
210, 212, comprises a singular electrode or a combination of electrodes of the
following: a tip electrode, a ring electrode, a defibrillator coil, or their
equivalents. The various electrodes can be used for pacing, sensing,
defibrillating, or a combination of the same.
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In another embodiment, a first conductor set is disposed within the first
electrode leg 252 and comprises a coil and a cable which terminate in a first
pacing tip 256 and a first pacing ring 258, respectively. Similarly, as shown
in
Figure 4, a second conductor set is disposed within the second electrode leg
254
and comprises a coil and a cable which terminate in a second pacing tip 260
and
a second pacing ring 262, respectively. For the embodiment shown in Figure 5,
the second conductor set comprises only a second pacing tip 260, thereby
forming a unipolar leg.
The first electrode leg 252, in one embodiment, has a semi-circular
cross-section, as shown in Figure 7. Similarly, the second electrode leg 254,
in
another configuration, also has a semi-circular cross-section. When placed
adjacent to one another, the first electrode leg 252 and the second electrode
leg
254 form a circular cross-section, as shown in Figure 9. In one configuration,
medical adhesive or other equivalents 266, including dissolvable substances
such
as mannitol, are disposed between the first electrode leg 252 and the second
electrode leg 254 to aid in the installation of the lead 200 within a patient.
Alternatively, the first electrode leg 252 has an elliptical cross-section, as
shown in Figure 8. Similarly, the second electrode leg 254 has an elliptical
cross-section. When placed adjacent to one another, the first electrode leg
252
and the second electrode leg 254 easily fit together, as shown in Figure 10.
In
another embodiment, medical adhesive or other equivalents 266, including
dissolvable substances such as mannitol, are disposed between the first
electrode
leg 252 and the second electrode leg 254, as shown in Figure 10, to assist in
the
installation of the lead 200 within a patient. The cross-section of the first
and
second electrode legs 252, 254 are not limited to the above and can have other
cross-sections.
Figure 11 illustrates another embodiment showing a lead 300. The lead
300 extends from a proximal end 302 to a distal end 304 and comprises a first
and second connector terminal 380, 382 near the proximal end 302. The lead
300 also includes a lead body 320, a first electrode assembly 310, and a
second
electrode assembly 312. Near the proximal end 302 of the lead body 320, the
lead body 320 has at least two IS 1 terminal legs, including a first terminal
leg
330 and a second terminal leg 332.
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At a distal bifurcation point 309, an intermediate portion 306 of the lead
body 320 transitions into two bi-lumen tubes 350, including a first electrode
leg
352 and a second electrode leg 354. The first electrode leg 352 and the second
electrode leg 354 each extend to the first electrode assembly 310 and the
second
5 electrode assembly 312, respectively. A first conductor set is disposed
within
the first electrode leg 352 and comprises, in one embodiment, a coil and a
cable
which terminate in a first pacing tip 356 and a first pacing ring 358,
respectively.
Similarly, a second conductor set is disposed within the second electrode leg
354
and comprises, in another embodiment, a coil and a cable which terminate in a
10 second pacing tip 360 and a second pacing ring 362, respectively. In
another
embodiment, as shown in Figure 12, the first conductor set and the second
conductor set disposed within the first electrode leg 352 and the second
electrode
leg 354, respectively, terminate in a first pacing tip 356 and a first
defibrillator
electrode 359 second pacing tip 360 and a second defibrillator electrode 363.
15 The first electrode leg 352 and the second electrode leg 354, in one
embodiment, comprise bipolar lead legs. In another embodiment, the first
electrode leg 352 is unipolar and the second electrode leg 354 is bipolar (See
Figure 5). In yet another embodiment, the first electrode leg 352 is bipolar
and
the second electrode leg 354 is unipolar. The electrode, for either the
bipolar or
20 unipolar embodiments of the first and second electrode assemblies 310, 312,
comprises a tip electrode, a ring electrode, a defibrillator coil, or their
equivalents. The various electrodes can be interchanged and used for pacing,
sensing, defibrillating, or a combination of the same.
The second electrode leg 354, in one embodiment, has a J-shape, which
25 can have either passive or active fixation, as will be further discussed
below.
Using a straight stylet (not shown) to straighten the electrode leg 354 prior
to
implant, the second electrode leg 354 is positioned within the right atrium of
the
heart. As the stylet {not shown) is removed, the second electrode leg 354
re-assumes the J-shape and becomes positioned within the atrium of the heart.
If
a passive configuration is used, as further discussed below (for example,
Figure
36), the distal end 355 of the second electrode leg 354 becomes embedded
within
the wall of the heart as tissue in-growth begins. If an active fixation
configuration is used, the distal end 355 of the second electrode leg 354 is
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26
positioned adjacent the wall of the heart. The fixation helix is advanced so
that it
screws into the wall of the heart and the second electrode leg 312 is engaged.
The discussions of leads for multi-site pacing and/or passive and active
fixation
devices in related co-pending applications entitled SINGLE PASS LEAD AND
SYSTEM WITH ACTIVE AND PASSIVE FIXATION ELEMENTS, Serial No.
091121,005, and Attorney Docket No. 279.081US1 and SINGLE PASS
ENDOCARDIAL LEAD FOR MULTI-SITE ATRIAL PACING, Serial No.
09/121,019 and Attorney Docket No. 279.079US1.
Figure 13 shows another embodiment of the invention. In this
configuration, the atrial lead 390 andlor the ventricle lead 396 each have an
active fixation element 394, as further described below, for fixating the
leads
390, 396 to the endocardial wall of a heart. The active fixation element 394
is
rotatable by terminal pins 398, and the active fixation element 394 is not
retractable. Alternatively, the active fixation element 394 can be rotated
using
other manners, for example, a stylet. To protect the patient during
implantation
or to prevent snagging of the fixation element 394, the active fixation
element
394 of the atrial lead 390 and/or the ventricle lead 396 is covered with a
dissolvable coating 397, such as mannitol. The dissolvable coating 397 remains
intact during insertion of the leads 390, 396 through the subclavian vein and
into
the heart. The dissolvable coating 397 prevents the active fixation element
394
from catching tissue in the vein during insertion. Once implanted, the coating
397 dissolves to expose active fixation element 394 and allow it to be turned
into
the atrial wall of the heart. The dissolvable coating 397 is depicted by a
dotted
line enclosure around the active fixation element 394.
Figures 14 - 27 illustrate another embodiment of a lead coupled with a
system and the heart, wherein a portion of the lead body is curved and at
least
one electrode is coupled with the curved portion 450 of the lead 400. The lead
400 and, more specifically, the distal end 430 of the lead 400 positioned
within a
heart 402. The heart 402 includes four chambers which are the right atrium
404,
the right ventricle 405, the left ventricle 406 and the left atrium 407. Also
shown
in Figure I4 is the superior vena cava 408.
The distal end 430 of the lead 400, in one embodiment, is positioned
within the superior vena cava 408, the right atrium 404 and the right
ventricle
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405. The curved portion 450 of the lead 400 positions the atrial electrode 461
on
the curved portion 450 or biased section closer to the wall of the heart 402
in the
right atrium 404. This enhances electrical performance as electrode 461 will
be
closer to the portion of the heart 402, namely the right atrium 404, where the
S signal will pass. In addition, the electrode 46I is positioned closer to the
wall of
the right atrium 404 such that passive fixation can occur. If passive fixation
is
achieved, the distal end 430 of the lead 400 will be more stably fixed within
the
heart 402. Even if the passive fixation is not achieved, the electrode 161
will be
biased closer to the wall of the right atrium 202 so as to enhance the
electrical
sensing capability of that electrode. In another embodiment, a plurality of
tines
480 are coupled near the electrode 454. The plurality of tines 480 aid in
positioning the distal end 430 in the right ventricle 405 at the time of lead
insertion. At the time of lead implantation, the distal electrode 454 is
generally
positioned in the right ventricle. The tines 480 are used to engage tissue
structures which line the endocardial surface of the ventricle 405 and then
hold
the lead 400 in place after it is implanted. Fibrous tissue grows over these
tines
480 over time to produce an attachment to the wall of the heart in the right
ventricle 405 and further secure the lead 400 within the heart 402.
Figure 14 also shows the lead terminal connector 410 and its connection
into the pulse generator 440. The lead terminal connector 410 makes electrical
connection with a signal processing/therapy circuit 442 which in turn is
electrically connected to a microcontroller 444. Within the microcontroller
444
is a synchronizer 446. The signal processing/therapy circuit 442 determines
the
type of therapy that should be delivered to the heart 402. The microcontrolier
444 controls the delivery of the therapy to the heart 402 through the
synchronizer
446. The synchronizer 446 times the delivery of the appropriate signal to the
heart 402.
Figure 15A shows the lead 400 in greater detail. The lead 400 includes a
connector terminal 410, a distal end 430, and an intermediate portion 420
which
interconnects the distal end 430 and the connector terminal 410, and include
conductive wires (not shown} covered by a silicone rubber tubing which is
biocompatible, to form the lead body 422. The connector terminal 410
electrically connects the various electrodes and conductors within the lead
body
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422 to the pulse generator 440 (discussed above). The distal end 430 is the
portion of the lead 400 that includes electrodes and is positioned within the
heart
during implantation. The lead body 422 is a tubing material formed from a
biocompatible polymer for implantation, and preferably tubing made from a
silicone rubber polymer. The silicone rubber polymer tubing contains several
electrical conductors (not shown). The electrical conductors are made of a
highly conductive, highly corrosion resistant material.
After the lead 400 has been implanted, the distal end 430 of the lead body
422 is situated predominantly within the heart 402 (Figure 14). The distal end
130 of the lead body 422 includes a curved or bias portion 450 and, in one
embodiment, a straight portion 460. After implantation, the curved portion 450
of the electrode end 130, in one embodiment, will generally be located in the
right atrium of the heart 402 (Figure 14), and the straight portion 460 will
be
located in the right ventricle 405. It should be noted that the lead 400 could
also
be implanted within the left atrium 407 and the left ventricle 406 of the
heart
402.
In one embodiment, the electrode end 130 of the lead 400 has four
electrodes 453, 454, 461, and 462. Referring again to Figure 14, two of the
electrodes 461, 461 are located in the atrium 404, and two of the electrodes
453,
454 are located in the ventricle 405. The first electrode 454 is provided at
the
farthest distal end 455 of the lead 400 for the purpose of delivering
ventricular
pacing therapy. The first electrode 454 is referred to as the RV pace/sense
tip.
A second electrode 453 is located proximate and proximal to electrode 454 and
can be used as a counter electrode or as an electrode for defibrillation
therapy.
The electrode 453 is also known as the distal coil or the RV shock coil. The
second electrode 453, in one embodiment, is a shocking coil and is much longer
than the first electrode 454. The first electrode 454 and the second electrode
453
can each be coupled with the heart wall using either passive or active
fixation.
A third electrode 461 is located at a more proximal position, for example,
along the curved portion 450, for the purpose of delivering atrial pacing
therapy.
The third electrode 461 is also used for atrial sensing, and is referred to as
the
atrial sense/pace electrode. In one embodiment, the third electrode 461 is
passively attached to the atrial wall of the heart. The atrial electrode 461
has a
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29
relatively small electrically active surface area. The advantages of this
small
surface area are high impedance for lower current drainage and a small lead
cross
section for ease of venous access and transport through the subclavian vein. A
fourth electrode 462 is located proximate and proximal to electrode 461 and
can
S be used with electrode 461 for atrial sensinglpacing and as counter to 4S3
as part
of a defibrillation therapy system. Electrodes 4S3 and 462, in one
configuration,
are coils of a biocompatible metal or metal alloy such as, but not restricted
to,
platinum, or platinum/iridium. The coils are generally known as shocking coils
and deliver large amounts of energy used in cardioversion and defibrillation.
Electrode 462 is also referred to as the proximal coil or the SVC shock coil.
The
SVC shock coil 462 is positioned in the upper atrium or the superior vena
cava.
- Figure 1SB shows an alternative embodiment, which includes a fifth
electrode 463 on the lead 400. The electrode 463 is positioned on the lead 400
adjacent the electrode 461 so that there are two sensing electrodes, 461 and
463
1 S in the atrium of the heart to enhance the sensing capability of this lead.
In one
embodiment, the electrode 461 comprises a porous tip electrode, as will be
further described below.
Figure 16 shows a lead 500 used to treat a bradycardia condition. The
reference numerals associated with the lead 400 shown in Figures 14 and 1 S
which describe similar parts have been used here for the purposes of
simplicity.
The lead S00 includes a distal or RV pace sense tip 454, an atrial sense
electrode
461, and a ring electrode 510. The distal end 430 of the lead S00 includes a
straight portion 460 and a curved portion 450. The atrial sense electrode 461
is
positioned on the curved portion 450. The atrial sense electrode 461 can also
be
provided with a means for passive fixation to the wall of the heart. In this
unipolar application, the distal tip electrode 4S4 serves as the negative pole
and
the pulse sensor and generator 440 serves as the positive pole when a pacing
pulse is delivered to the right ventricle of the heart. It should be noted
that this is
not the only possible unipolar arrangement, but that other unipolar
arrangements
are possible. Furthermore, it should be noted that a bipolar arrangement may
also be used.
The electrode 461 on the curved portion is disposed such that points out
in the direction of the bias of the curved portion 450. In one embodiment, the
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electrode 461 is a ring electrode which is disposed transverse to the lead
body
422. In another embodiment, the electrode 461 is on the larger radius of the
curved portion 450 of the lead. This assures that the distance between the
electrode 161 and the wall of the atrium 404 is minimized. This also maximizes
5 the possibility that the electrode 461 will become passively fixed to the
wall of
the heart. In another embodiment, the outside surface of the curved portion
450
of the lead 500 can be textured to further enhance the passive fixation of the
lead
461 to the heart.
In another embodiment, the ring electrode 510 is also placed a selected
10 distance from the electrode 461. The ring electrode 510 has the opposite
polarity
of the electrode 461. The ring electrode 510 is placed so that it is near the
superior vena cava of the heart when the lead 500 is placed in the heart. The
electrodes 510 and 461 are used as a bipolar pair for sensing and pacing. The
lead 500 is a single pass lead that can be used for both sensing a bradycardia
15 condition and treating it by pacing.
Figure 17A illustrates an alternative form of a lead 520. A conventional
endocardial lead, having standard electrodes for the RV tip 522, RV coil 524,
and SVC coil 526 on a generally flexible multi-lumen tubular body 530 is
shown. Also included is an additional SVC sense ring 528, and a curved shape
20 532 to hold the sense ring into contact with the interior wall of the
atrium or
superior vena cava. The lead 520 includes a curved portion 532 which in one
embodiment, comprises a semi-flexible, semi-rigid arch which is set in the
lead
to form a lateral protrusion. The curved portion 532 mechanically biases the
atrial sense ring into contact with the inside wall of the atrium, or can be
used to
25 bias the lead 520 into contact with other parts of the heart wall. In one
embodiment, the curved portion 532 is spaced from the distal tip 534 of the
lead
520 so as to be placed in the atrium when the lead 520 is in its use position
with
the RV tip 522 is in the ventricle. In one embodiment, the atrial sense ring
528
is a small ring electrode paced around the lead at the curved portion 532, in
a
30 position where it will be in contact with the atrium when the lead is
placed in the
heart. In another embodiment, the axis of the sense ring 528 is aligned with
the
axis of the lead body 530. In yet another embodiment, the axis of the sense
ring
X28 is co-axial with the axis of the lead body 530. The advantage of the above
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31
embodiments is that the atrial sense ring 528 is held in direct contact with
the
atrial wall, which provides better signals for P wave discrimination, as
compared
with lead designs which do not ensure such direct contact.
The lead may be constructed generally according to known techniques
for mufti-lumen intravascular electrode leads, an example of which is shown
and
described in U.S. Patent 4,603,705 to Speicher et al. The addition of atriaf
sense
ring 528 will require an additional conductor inside the body of the lead. For
this reason, the lead of Figure 17A has four lumens 536, which are seen in the
section 550 drawn at the top of the Figure 17A. The four lumens 536 are the
atrial ring lumen, the distal RV coil lumen, the proximal SVC coil lumen, and
the lumen for the stylet coil 540 (Figure 17B) which may also serve as the
conductor for the tip electrode. A stylet coil 540, as illustrated in Figure
I7B, is
normally found in mufti-lumen intravascular electrode leads, consisting of a
flexible metallic coil in one of the lumens serving to receive a stylet as is
generally known for facilitating directional control of the lead during its
placement in the heart. The double-bend portion or curved portion 542 of the
stylet coil 540 which forms the curved portion 532 may preferably be formed by
forming the bends in the stylet coil to take a 'set' in which the curved
portion
532 is shaped as shown in Figure 17A. The stylet coil 540 has sufficient
flexibility to straighten, then return towards the set shape after removal of
the
stylet.
In one embodiment, the distance 548 of the offset of the curved portion
532 as indicated in Figure 17A ranges from 1 to 3 centimeters. The length or
axial extent 546 of atrial sense ring 528, in one embodiment, as indicated in
Figure 17A is .5 to 3.0 millimeters. The axial distance 547, in another
embodiment, of atrial sense ring 528 from the SVC coil 526 as indicated in
Figure 17A is 0.5 to 3.0 centimeters.
Figures 18 - 25 further detail certain elements of the passive fixation
single pass electrode used for an electrode to be disposed along the curved
portion. Figure I 1 shows a conductive ring made of a highly conductive, and
highly corrosion resistant, material such as an alloy of platinum-iridium. The
ring 552 includes a small porous tip electrode 554. The ring 552 is
electrically
insulated from body fluids. The porous tip electrode is electrically active
and in
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32
contact with body fluids and tissue. The active porous tip electrode 552
includes
a screen of porous conductive material such as the alloy of platinum and
iridium.
Over time, the tissue encapsulation grows into the screen made of a
platinum-iridium alloy to attach the electrode or electrodes to the
endocardial
wall of the heart. The ring 552, in one embodiment, has a nominal radius of
0.04
inches ( 1 mm). The advantage of this small radius is ease of venous access
and
high impedance for conserving pacing energy.
Figure 19 shows another passive fixation electrode. Figure 19 shows a
conductive ring 560 made of a highly corrosion-resistant material such as an
alloy of platinum and iridium, and in one embodiment is electrically insulated
from body fluids. The ring includes two small porous tip electrodes 556 and
558, which are electrically active and in contact with body fluids. The active
porous tip electrodes 556 and 558 each include a screen of porous conductive
material made of the highly corrosion-resistant alloy of platinum and iridium.
Tissue encapsulation grows into the screen on the tips 556 and 558 to attach
the
electrode to the endocardial wall of the heart.
Figure 20 shows another passive fixation element associated with the
curved portion of the lead. A conductive ring 562 made of a highly
corrosion-resistant material such as an alloy of platinum and iridium, and in
one
embodiment is electrically insulated from body fluids. The ring 562 includes a
porous tip electrode 564, which is electrically active and in contact with
body
fluids. The porous tip 564 in Figure 20 is larger than the porous tip 554
shown
in Figure 18, where the porous tip 564 extends across a substantial amount of
the
tip 564. In one embodiment, the porous tip 564 is made of corrosion-resistant
material and comprises a screen. When the porous tip 564 rests against the
endocardial wall of the heart, the tissue of the heart encapsulates and grows
into
the screen to passively attach the electrode to the heart.
Figure 21 illustrates a variation of the electrode shown in Figure 20,
where the conductive ring 570 includes a first porous tip 572 and a second
porous tip 574. The ring 570 is electrically insulated from body fluids, and
the
first and second porous tips 572 and 574 are electrically active and in
contact
with body fluids. The porous tips 572, 574 are also made of highly
corrosion-resistant material. Like the previous conductive rings shown, the
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33
tissue of the heart encapsulates and grows into the porous screen in order to
provide passive attachment of the electrode to the endocardial wall of the
heart.
Figure 22 shows that a smooth ring 578 can also be used~.as the main
element of the electrode in the curved portion of the lead. The smooth ring
578
is made of a corrosion-resistant material that is highly conductive. All of
the
ring 578 can be exposed or a portion of it can be masked or insulated, so that
a
portion is nonconductive.
Figure 23 shows another variation and includes a ring 580. A surface
582 of the ring 580 is comprised of layers of conductive mesh or other porous
materials attached to the ring 580. The layers of conductive mesh or porous
materials create an active surface for pacing and sensing and a layer for
enhanced
tissue ingrowth. Alternatively, texturization or other surface treatment could
be
applied directly to the ring 580 to enhance tissue ingrowth.
Figure 24 illustrates another embodiment of an electrode for use with the
1 S curved portion of the lead. A ring 584, made of highly conductive material
insulated from body fluids includes a modified raised ridge 586. In one
embodiment, layers of conductive porous material are deposited on an
electrically conductive thin band 587 rather than across the entire width of
the
ring. In another embodiment, all of the ring 584 can be exposed or a portion
of it
can be masked or insulated so that a portion is nonconductive.
Figure 25 shows an portion of a lead 590 including a porous tip type of
electrode 594 (similar to the porous tip shown in Figures 18 and 19) which is
not
mounted on a ring. The porous tip electrode 594 is placed in either a straight
or
curved portion of the lead. In one embodiment, the porous tip electrode 594 is
placed directly into the surface of the lead 590, and an electrical conductor
596 is
attached to the electrode. In another embodiment, the surface of the lead 590
near the electrode 594 may be textured to enhance the ability of the lead 590
to
become passively fixed to the wall of the heart. It should be noted that the
above
described electrodes illustrated in Figures 18 - 25 can be used along any
curved
or straight portion of a lead, and can be disposed in the various positions
described above. The pacing and sensing tip points out in the direction of the
bias or, alternatively, is on the portion of the lead body that is closest to
the wall
of the heart.
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34
Figure 26 is a side view of one type of lead 600 for delivering electrical
pulses to stimulate the heart. The lead 600 is comprised of a connector
terminal
610 and a lead body 620. The lead 600 attaches to a pulse sensor and generator
640. The lead body has a number of electrodes in the distal end 630 which is
implanted within, on, or about the heart (Figure 27). The distal end 130 of
the
lead body 120 includes a curved or bias portion 150 and a straight portion
160.
The connector terminal 610 electrically connects the various electrodes and
conductors within the lead body to the pulse sensor and generator 640. The
pulse sensor and generator 640 contains electronics to sense various pulses of
the
heart and also produce pulsing signals for delivery to the heart. The pulse
sensor
and generator 640 also contains electronics and software necessary to detect
certain types of arrhythmias and to correct for them. Physicians are able to
program the pulse sensor and generator to correct a particular arrhythmia that
the
patient may have. It should be noted that there are numerous types of
connector
terminals which connect to a pulse sensing and generating unit 640. The lead
terminal connector 610 provides for the electrical connection between the
electrodes on the lead 100 and pulse generator 640. The connector terminal end
610 shown is designed to international IS-1 Standard ISO 5841-3(E).
The lead body 620, in one embodiment, is cylindrical in shape and
includes tubing material formed from a polymer biocompatible for implantation,
and preferably the tubing is made from a silicone rubber polymer. The silicone
rubber polymer tubing contains several electrical conductors (not shown). The
electrical conductors are made of a highly conductive, highly corrosion-
resistant
material which is formed into a helix, and are housed within the lead body
620.
When there is more than one such electrical conductor within the lead body
620,
the lead is called a multifilar lead. The electrical conductors carry current
and
signals between the pulse sensor and generator 640 and the electrodes located
at
the distal end 630 of the lead 600.
After implantation within or on or about the heart 612, as illustrated in
Figure 27, the curved or biased portion 650 will generally be located in the
right
ventricle 613 of the heart. The straight portion 660 of this lead body will
generally be located in the right atrium 614.
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In one embodiment, the distal end 630 of the lead 600 has four
electrodes. The first electrode 654, also referred to as the distal electrode,
is
provided at the farthest distal end of the lead for the purpose of delivering
ventricular pacing therapy. A second electrode 653 is located near the first
or
5 distal electrode 654 and can be used as a counter electrode for electrode
654 or
as a current source for defibrillation therapy. This electrode 653 is
sometimes
referred to as a ventricular shocking coil. A third electrode 661 is located
at a
more proximal position for the purpose of delivering atrial pacing therapy.
The
electrode 661, in another embodiment, is actively attached to the atrial wall
of
10 the heart 612. The third electrode 661 is also referred to as the proximal
electrode. A fourth electrode 662 is located near the electrode 661 and can be
used as a counter electrode for electrode 661 or as part of a defibrillation
therapy
system. The fourth electrode 662 is sometimes called the SVC shocking coil.
The lead 600 may be generally described as a tachycardia or tachy lead. The
15 shocking coils 653 and 662 are electrically conductive rings made of an
alloy of
platinum and iridium which is highly conductive and highly resistant to
corrosion. The electrode 661 uses, in one embodiment, the active fixation
element described further below. The electrode 654 may include an active
fixation or passive fixation portion. It should be noted that the lead shown
and
20 described above is a bipolar lead in that the positive and negative
portions of a
circuit are located in the lead body 600. It should be noted that this lead
may
also be made a unipolar lead. In other words, one electrode of the lead body
600
can be the shocking coil and the other electrode can be the signal generator.
In one embodiment, the relaxed shape of the lead body 620 conforms to
25 the shape the lead is expected to take after implantation. The distal
portion of
the straight portion 660 and the proximal portion of the curved portion 650
are
biased to conform to the mid-portion of the atrial wall. This shape
facilitates the
placement of electrode 661 against the atrial wall during implantation.
Furthermore, because the natural unstressed shape of the lead before
30 implantation is approximately the same after implantation, this reduces the
nominal residual stresses in the lead body. Also, this will reduce the nominal
forces between the atrial wall and the point of attachment of the electrode
661 in
the atrium. In another embodiment, the shape of the middle and end portions of
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36
portion 650 conforms to the shape of the upper ventricular chamber below the
tricuspid valve and ventricular septal wall. This shape will tend to cause the
lead
600 to lie across the top of the ventricle in a gradual arc with the.
electrode 653
lying against the ventricular septum and electrode 654 resting in the
ventricular
apex. This lead position is advantageous because the arc shape will tend to
reduce the transmitted forces between the lead fixation points at electrode
661 in
the atrium and electrode 654 in the ventricle as they move relative to each
other
during heart rhythm. This preformed shape will ease the surgeon's task of
positioning of lead 600 and, particularly, of the electrode end 630 such that
less
time is required and the placement procedure is less prone to error.
The discussions of Ieads having a curved portion in related co-pending
applications entitled SINGLE PASS DEFIBRILLATIONIPACING LEAD
WITH PASSIVELY ATTACHED ELECTRODE FOR PACING AND
SENSING, Serial No. 09/121,010, and Attorney Docket No.: 279.116US1;
SINGLE PASS LEAD HAVING RETRACTABLE, ACTIVELY ATTACHED
ELECTRODE FOR PACING AND SENSING, Serial No. 091121,006, and
Attorney Docket No.: 279.058US1; SINGLE PASS
DEFIBRILLATION/PACING LEAD WITH PASSIVELY ATTACHED
ELECTRODE FOR PACING AND SENSING, Serial No. 09/121,018, and
Attorney Docket No.: 279.054US1, all filed even date herewith and
DISCRIMINATION OF ATRIAL AND VENTRICULAR SIGNALS FROM A
SINGLE CARDIAC LEAD, Serial No. 08/996,355, filed Dec. 22, 1997. The
above described leads, including but not limited to multi-site pacing leads
for
one or more chambers of the heart, as well as bifurcated leads can also be
combined with the embodiments relating to the leads having a curved portion.
Figure 28 illustrates a side view of a single-pass endocardial lead 700 for
multi-site pacing within a single chamber of the heart. During insertion, a
stylet
or wire is placed down a lumen within the lead 700. This makes for a stiffened
lead body 700 which can be pushed through the body into the appropriate
chamber of the heart. The lead 700 includes a connector end 720 which, in one
embodiment, has a yoke 710 and extends to a distal end 730. The lead 700 also
includes a first leg 740 and a second leg 750, which each include at least one
electrode.
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37
The lead 700 includes a recess 712 which houses the second leg 750.
The second leg 750 is maintained within the recess 712 while the lead 700 is
being routed through the body, into the major vein or subclavian vein and
ultimately into one of the chambers of the heart. The electrode 732 associated
with the first leg 740, in one embodiment, includes a passive fix element 733.
The passive fix element 733, in one embodiment, includes a wire mesh screen
which allows for the fibers of the heart to grow within the fiber mesh screen
over
time. In yet another embodiment, the passive fix element 733 includes a set of
tines 734 near the electrode 732. The tines 734 also provide for attachment of
the electrode 732 to the endocardial wall of the specific chamber in the heart
to
which the first leg 740 of the lead 700 is to be attached.
Figure 29 illustrates another side view of the lead 700 after the stylet (not
shown) which extends down the body of the lead 700 and into the first leg 740
has been removed. When the stylet is removed, the first leg 740 is allowed to
1 S return to its natural state. In this particular case, the first leg 740 of
the lead 700
includes a curve therein, for example, a J-shaped curve. The radius of the
curve
and the length of the leg 740 are or may be varied in order to accomplish
placement of the lead 732 at various positions within a particular single
chamber
of the heart. It should be noted that Figure 29 illustrates the second leg 750
still
housed within the recess 712 in the body of the lead 700.
Now turning to Figure 30, the single-pass endocardial lead 700 for
mufti-site pacing is shown after the second leg 750 has been removed or pushed
out of the recess 712 within the body of the lead 700. The second leg 750 is
also
J-shaped or curved and has an electrode 752 positioned near the free end 755
of
the leg 750. The free end 755 of the second leg 750 also includes an active
fix
element 754 which is used to actively fix the electrode 754 to an endocardial
wall of a chamber of the heart. It should be noted that the first leg 740 and
the
second leg 750 need not be J-shaped or curved and that either the first leg or
the
second leg each can either include a passive fix element or an active fix
element.
The advantage of this particular configuration is that the passive fix element
will
not catch on any of the veins or tissue as it is passing through the
subclavian vein
and into the heart. As this is being done, the active fix portion 754 of the
second
leg is kept within the recess 712 of the lead 700 so that the active fix
element
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38
754 will not catch on any tissue during insertion. It should also be noted
that the
radius of the curve and the position and length of the first leg 740 and the
second
leg 750 can be varied for various applications of mufti-site pacing within a
single
chamber of the heart. It should be noted that for different chambers,
different
lengths of the legs 750 and 740 might be appropriate, as well as different
radii.
The configuration shown in Figure 30 could be placed or positioned within the
atrium (not shown) of the heart. This configuration could be used for
simultaneous atrial appendage and Bachman's Bundle pacing.
Figure 31 shows a variation of a single-pass endocardial lead 760 for
mufti-site pacing from the ones shown in Figures 28 - 30. The lead 760 shown
in Figure 31 includes many of the same elements of the lead shown in Figures
28, 29, and 30. Rather than repeat all the same elements or similar elements
between the lead 760 and the lead 700 shown in Figures 28, 29, and 30, only
the
differences will be touched upon or described in the following paragraph.
1 S The lead 760 differs from the lead 700 in that the lead 760 includes a
second leg 762 which is straight after it has been removed or forced out of
the
recess in the lead body 764. The second leg 762 includes an electrode 752 as
well as an active fix portion 754 for attaching to the endocardial wall of the
heart. If this configuration was placed in the atrium, it could be used for
simultaneous atrial appendage pacing, and pacing at the entrance of the
coronary
sinus.
Figure 32 shows yet another embodiment of a single-pass endocardial
lead 770 for mufti-site pacing within a single chamber of the heart. The lead
770
includes a connector end 774 and a distal end 776 having a first leg 778, a
second leg 780 and a third leg 782. The lead 700 has a recess which is capable
of holding a second leg 780, and a third leg 760. The first leg 778 is, in one
embodiment, J-shaped or, alternatively, curved and includes an electrode 784.
The electrode 784, in another embodiment, is used as part of an active fix
element 786. The first leg 778 also includes a set of tines 788 which enables
or
allows active fixation of the electrode 778 to an endocardial wall of the
heart.
The second leg 780 is a straight leg having an electrode 792 and an active fix
portion 794. The third leg 782 includes an electrode 796 and an active fix
portion 798.
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39
During insertion of the lead 770 into a patient, a stylet (not shown) is
piaced into a lumen of the lead 770. The stylet will pass all the way down to
and
into the first leg 778 of the lead 770. During insertion, the second leg 780
and
the third leg 782 will be housed or in a withdrawn position within either a
single
recess 790, or alternatively a pair of recesses within the lead 770. With the
stylet
in place, the lead can be maneuvered and positioned through the major arteries
and into the heart. Once the lead 770 is positioned within the heart, the
stylet is
removed and a J-shaped natural shape is assumed by the first leg 778. After
the
lead 770 has been placed within the selected chamber of the heart, the second
leg
780 and the third leg 782 can be removed or extended out of the recess in the
body of the lead 770. It should be noted that the first, second and third legs
778,
780, 782 may either be curved or alternatively J-shaped and can also either be
attached to the endocardial wall of the heart by active fixation or passive
fixation. The position and length of the legs can be varied to produce
different
mufti-site placements of the electrodes within the heart. Each of the
electrodes
784, 792 and 796 can be either a bipolar or unipolar configuration. The
particular configuration shown in Figure 32, if placed within the atrium of
the
heart, can be used for a simultaneous atrial appendage, pacing at the
Bachman's
Bundle and pacing at the entrance to the coronary sinus.
Figures 33, 34, and 35 show several other embodiments of the invention.
Figure 33 is a side view of a lead 800 which includes an active fixation
element
832 for attachment to the atrial wall of the heart. The lead 800 includes a
main
lead body 802, an atrial lead body 805 (Figures 34 and 35) and a ventricle
lead
body 804. The main lead body 802 is attached to a yoke 806. The yoke 806 acts
as a strain reliever and also has a series of terminal pins 808, 810 and 812
attached to the yoke/strain reliever 806. The terminal pins 808, 810, and 812
are
attached to the pulse generator (not shown). The main lead body 802 is longer
than as shown; a break has been put into the main lead body 802 to illustrate
that
the main lead body 802 is longer than that shown in Figure 33.
The main lead body 802 includes a recess 814 where the atrial lead body
805 (Figures 34 and 35) fits within the recess 814 in the main lead body 802.
When the atrial lead body 805 is housed within the recess 814, an active
fixation
element 832 on the end of the atrial lead body 805 and associated with the
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WO 99130772 PCTIUS98I26767
proximate electrode is also housed within the recess 814. Advantageously, the
active fixation element 832 will not hook or snag tissue when it is housed
within
the recess 814. Typically, the atrial lead body 805 is pulled back or housed
within the recess 814 when the lead 800 is being surgically implanted into the
5 patient. Typically, the lead 800 is placed in the subclavian vein of the
patient
and then passed through the subclavian vein to the inner chambers of the
heart.
Once the lead and, more specifically, the distal electrode and the proximal
electrode are within the ventricle and atrium of the heart, the various leads
are
removed from their respective recesses so that a surgeon can attach them to
the
10 inner wall of the heart.
Figure 34 is a side view of the embodiment of a lead 800 shown in Figure
33. Figure 34 has a J-shaped atrial lead body 807 which emerges from the
recess
814 in the main body 802 of the lead 820. On the end of the atrial lead 807 is
an'
active-fixation element 832. The active fixation element 832, in one
15 embodiment, includes a helically shaped hook for screwing into the atrium
of the
heart. The J-shape of the lead facilitates positioning of the end of the
electrode
having the active fixation element 832 to a desired position within the
atrium.
The J-shape eases positioning within the atrium of the heart when certain
portions of the atrium are the target for connection of the active fixation
element
20 832. Once properly positioned, a surgeon can turn andlor advance the active
fixation element 832 causing it to hook the tissue in the inner wall of the
heart.
The atrial lead 807, in one embodiment, is moved with respect to the recess
814
by pushing the respective terminal pin 810 toward the yoke 806. By moving the
terminal pin 810 toward the yoke 806, a conductor, which connects the terminal
25 pin 810 and the active fixation element 832, moves with respect to the main
body 802 of the lead 820. Alternatively, the terminal pin 810 can be moved
longitudinally with respect to the main body 802. This movement causes the
atrial lead body 807 to emerge or pass through or pass out of the recess 814
in
the main body 802. The terminal pin 810 and the active fixation element 832
30 attached to it, in one embodiment, move independently of the lead body 820.
Twisting the terminal pin causes the active fixation element 832 on the atrial
lead body 807 to turn and affix itself to the atrial wall of the heart. This
additional degree of freedom allows for movement of the lead body relative to
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41
the fixed atrial electrode without unscrewing (or over-screwing) the electrode
from the endocaridal tissue. A locking mechanism may be provided to prevent
the active fixation element 832 from "backing out" after it has been affixed
to
the wall. The atrial lead 807, in another embodiment, is prestressed so that
it
will take the J-shape upon leaving or coming out of the recess 814.
Figure 35 is a side view of another embodiment of the lead shown in
Figure 33. In this particular embodiment, the lead 830 has a straight atrial
lead
body 840 which comes out of the recess 814 in the main lead body 802. The
position of the atrial lead body 840 is controlled by movement of the terminal
pin 810 with respect to the yoke 806. Moving the terminal pin 810 with respect
to the yoke 806 causes the atrial lead 840 to come out of the recess 814. An
active fixation element 832 is positioned on the end of the atrial lead 840.
Once
the surgeon positions the atrial lead 840 and the active fixation element 832
at
the end of the atrial lead 840 in a proper position or desired position, the
active
fixation element 832 is used to attach the proximal electrode to the
endocardial
wall of the atrium.
The above and below-discussed lead embodiments can each be provided
with, for example, active or passive fixation devices. Figure 36 illustrates
one
embodiment of a passive fixation device 856. A plurality of tines 852 are
disposed about the distal end 854 of the electrode 850. Other examples of a
passive fixation device 856 include a mesh screen (further discussed below)
which can be used independently or in combination with other passive fixation
devices such as the plurality of tines 852. Other passive fixation devices are
also
shown in Figures 14, 15A, 15B, 16, 17A, and 28-35.
In another embodiment, the above and below discussed lead
embodiments can alternatively and/or additionally be provided an active
fixation
device. One example of an active fixation device for the lead is a retractable
screw, as shown in Figures 10-13, 26, 30 - 32, 34, and 35, and also further
described below. Figures 37 and 38 illustrate another embodiment of an active
fixation device. As mentioned previously, the electrode 861 is designed to be
attached to the wall of the heart. Figure 37 shows electrode 861 in a recessed
position and Figure 38 shows electrode 861 actively extended. In this
embodiment, the electrode 861 includes an active fixation screw 863 which, in
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42
one embodiment, comprises a helical screw. The electrode 861, in one
embodiment, is configured to initially rest inside the lead body 860, and then
extend and rotate independent of the lead body 860 for attachment to the wall
of
the heart. Figure 37 shows the electrode 86i and the fixation screw 863
resting
within the lead body 860. A seal 870 is provided, in another embodiment, which
assists in preventing body fluids from traveling into the recess in the lead
body.
The seal 870 is made of a biocompatible material such as silicone rubber and
may take any appropriate shape. In this instance, the seal 870 is shaped as a
permanent O-ring affixed to the recess in the lead body 860. This covered
position of the electrode 861 and active fixation screw 763 makes the lead
placement process easier since the electrode 861 does not snag the vein during
- initial venous access and subsequent movement of the lead to the heart. The
seal
870 can also be used to hold a lubricant {not shown) within the recess of the
body 860 of the lead. The lubricant will allow the electrode 861 to move from
l 5 inside the recess to outside the recess with greater ease. The lubricant
can be a
substance such as fluorosilicone which is biocompatible.
Figure 38 shows the electrode 861 extended from the lead body 860. The
electrode 161 and active fixation screw 863 move independent of the lead body
860. This relative movement allows the electrode to come in contact with the
wall without manipulation of the lead body 860. The electrode 861 can then be
fixed by rotating the electrode 861 and attached fixation screw 863. The
fixation
screw 863 of the electrode 861 can be advanced and retracted independent of
rotation of the lead body 860. The active fixation screw and attached
electrode,
in one embodiment, are controlled from the terminal end, as discussed above.
As mentioned previously, the electrically conductive portion 864 which
either senses electrical energy produced by the heart or delivers pacing
signals to
the heart is a small radius electrode. The electrode 861 has a diameter, in
one
embodiment, in the range of 0.024 inches to 0.050 inches. The advantage of
this
small radius is ease of venous access and small surface area resulting in high
impedance for saving energy. Saving energy makes the battery used to power
the pulse generator (discussed above) last longer.
Also shown in Figures 37 and 38 is a multifilar coil 86~ and an
electrically conductive sleeve 866. The conductive sleeve 866 has the smaller
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43
radius electrode tip 864 attached at one end of the sleeve. At the other end
of the
sleeve 866, the multifilar coil 865 is attached. The multifilar coil 865
includes at
least one conductor which is used to carry electrical signals to and from the
electrode tip 864.
In yet another embodiment, the active fixation device comprises the
movement assembly as shown in Figures 39 and 40. A lead 900 is provided
extending to a distal end 904 which includes an active fixation element 970.
The
active fixation element 970, in one embodiment, comprises a helical screw 972.
In one configuration, the active fixation element 970 is retractable, which
assists
in avoiding injury to the patient during implantation. Alternatively, the
active
fixation element 970 rotates without translating along the lead 900. For the
configuration where the active fixation element 970 rotates without
translating
along the lead 900, a material, such as mannitol, is disposed about the active
fixation element 970 to prevent snagging the interior of the vein as the lead
900
is positioned within the patient. The lead 900, in one embodiment, includes a
movement assembly 902 which is adapted to transport the active fixation
element 970. Alternatively, in another configuration, the distal end 904 of
the
lead 900 can include a passive fixation element, as discussed above.
The movement assembly 902 includes external threads 920 associated
therewith. In one configuration, the external threads 920 are disposed about a
collar 922 of the lead 900. The external threads 920 are adapted to engage
with
internal threads 926 disposed within a housing 924 of the lead 900. The
external
threads 920 provide a helical path for the internal threads 926. The movement
assembly 902 is not, however, limited to the components described herein. For
instance, the external threads 920 and the internal threads 926 can be
provided
on alternative components, and still be considered within the scope of the
invention.
In one configuration, an insert 930 is provided for the internal threads
926, as shown in Figure 40. The insert 930 contains internal threads 926 which
are adapted to engage with the external threads 920 of the collar 922.
Although
internal and external threads are described, other equivalent movement
assemblies can also be incorporated such as those incorporating a track.
During
use, the terminal pins (discussed above) are rotated which causes the collar
922
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44
to rotate. As the collar 922 is rotated and the external threads 920 and the
internals threads 926 engage, the active fixation element 970 moves along the
axis of the lead 900. The movement assembly 902 can be used with a wide
variety of leads implementing active fixation, including, but not limited to,
single pass dual chamber pacing leads, single pass dual chamber
pacing/defibrillator leads, single chamber pacing leads, and single chamber
pacing/defibrillator leads.
Refernng again to Figure 39, a mesh screen 940 is provided in another
embodiment. The mesh screen 940 allows for better tissue in-growth, as well as
enhanced sensing capabilities. The mesh screen 940 is disposed proximate to
the
active fixation element 970. In one embodiment, as the active fixation element
970 is translated and extended from the lead 900, mesh screen 940 moves with
the active fixation element 970. The fixation element 970 engages the heart
tissue and draws the mesh screen 940 into contact with the surface of the
heart.
In another configuration, the lead 900 is provided with a medication
distribution member which is adapted to release medicine after the lead 900
has
been implanted into a patient. In one embodiment, the medication distribution
member comprises a steroid plug 942 which is provided proximate to the mesh
screen 940. The steroid plug 942 is located behind the mesh screen 940
relative
to the heart. In another embodiment, the medication distribution member
comprises a medication collar 943 to release drugs, such as a steroid
medication.
Drugs can be provided which prevent tissue inflammation after the electrode
has
been attached to the heart or which assist in blood clotting, or assist in
providing
other treatments.
In yet another embodiment, the lead, as described above and below, has
an increased impedance or a high impedance which can act to extend the life of
the battery. The discussion of leads having a curved portion in related co-
pending application entitled HIGH IMPEDANCE ELECTRODE TIP, Serial No.
09,'121,288, filed July 22, 1998 Attorney Docket No. 279.093US1. It should be
noted that, in an alternative embodiment, the below discussed high impedance
embodiments can also be combined with the above described lead embodiments
including, but not limited to multi-site pacing for one or more chambers of
the
heart, bifurcated leads, and leads having curved portions. There are a number
of
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ways in which increased impedance may be effected for mechanically fastened
electrode connections in atrial/ventricular implantable catheters (AVIC)
systems.
These include at least the following: 1 ) a fully insulated tissue engaging
tip (at
least with respect to all surfaces that are in electrical contact or
electrically active
physical relationship to heart muscles so that a pace would be effective if
discharged at that portion of the tip), 2) a partially insulated (only a
portion of
the surface area of the engaging tip being insulated, preferably there is
sufficient
coating so that at there is at least 5%, or at least 10%, or at least 20 or
30%, or at
least 40, SO or 60%, or at least 70, 75, 80 or 90% of the surface area of the
tip
10 which can discharge to heart muscle [or as percentages of the entire tip or
as
percentages of the entire tip that extends physically beyond the end plane of
the
catheter and which may therefore penetrate tissue or muscle]), 3) a porous,
electrically conductive element, such as a mesh or screen of material at the
proximal end of the helix or the distal end of the lead (excluding the helix),
at the
15 base of an extended engaging tip, 4) the selection of materials in the
composition
of the mesh and/or tip which provide higher impedance, 5) the partial
insulative
coating of a porous conductive element, such as the mesh or screen to increase
its impedance, and 6) combinations of any of these features. There may be
various constructions to effect the increased or high impedance, including the
20 use of helical tips with smaller surface areas (e.g., somewhat shorter or
thinner
tips). There may also be other elements associated with the catheter and~or
leads, such as a sheath of material inert to body materials and fluids,
circuitry,
microcatheters, and at least one conductor extending through the lead body.
One aspect of the present invention comprises an implantable electrode
2~ with a helical tip comprising:
an electrode having a distal end and a proximal end; and
a helix disposed within the electrode, which helix is aligned along a
radial axis of the electrode towards the distal end, and which helix is either
retractable or fixed; and
30 the implantable electrode having at least one feature selected from the
group consisting of:
a) the helix having a coating of an insulating material on its
surface which covers at least 5% of its surface area but less than
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46
95% of its surface area (which is exposed beyond the distal end of
the electrode),
b) the helix extending beyond the distal end of the -.
electrode and the distal end of the electrode having a
porous conductive surface at a base of the helix,
c) a porous conductive element such as a screen or mesh at a base
of the helix, which is retractable/extendable, with the helix being
either active or inactive (electrically), and
d) a partially insulated (partially insulation coated) porous
conductive element (e.g., screen or mesh) at the base of an active
or inactive, retractable/extendable or fixed helix.
The implantable electrode preferably has the helix with a coating of
insulating
material on it surface which covers from 5-100% (to 100% where there is an
additional electrode element within the system) or 5-95% of surface area of
the
helix beyond the distal end of the electrode, or surface of the helix which
can be
considered to be in electrically discharge-functional physical relationship
with
tissue or muscle into which it is embedded. For purposes of measuring or
determining the distal end of the electrode, the tip extends beyond a tubular
or
cylindrical housing or structural portion which is considered the electrode,
and
the tip is an engaging portion that extends beyond the housing portion of the
electrode. The distal end of the electrode is usually characterized as the end
of
the cylindrical housing or tubing carrying the tip, circuits, conductive
elements,
guides, etc. It is more preferred that the helix of the implantable electrode
has a
coating of insulating material on it surface which covers from 5-95% or 10-90%
of the surface area of said helix beyond the distal end of the electrode.
A lead 1010 is illustrated in Figure 1. The lead 1010 comprises a lead
body 1011, an elongate conductor 1013 contained within the lead body, and a
lead tip 1020 with an optional retractable tip assembly 1024 contained in the
lead
tip 1020. In addition, a stylet 1014 is shown inserted into the lead body I
011. A
helix 1100 {Figures 42A - 4~A), which consists of an electrical conductor
coil, is
contained in the retractable lead tip 1024. In an alternative practice of the
invention, the helix 1100 extends and retracts by rotation of the stylet 1014,
as
will be discussed further below. A Brady lead body is shown, although the
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47
invention could be incorporated with other leads, such as Tachy leads. The
lead
body 1011 consists of electrical conductors 1013 which are covered by a
biocompatible insulating material 1022. Polymers, such as silicone rubber,
fluorinated resins, polyacrylates, polyamides ceramic or composite materials
or
other insulating material can be used for covering the lead body 1011.
In one embodiment shown in Figure 43A and 43B, the helix 1100 is
formed of electrically conductive material offering low electrical resistance
and
also resistant to corrosion by body fluids. A biocompatible metal, such as
titanium or platinum-iridium alloy is an example of a suitable material.
Alternatively, the helix 1100 is electrically inactive or insulated. In one
embodiment, the helix 1100 may be coated with an insulative material (not
shown) or may be constructed of a rigid, corrosion resistant,
non-electrically-conductive material (e.g., a ceramic). A housing 1182,
described in further detail below, is made from an electrically conductive
material and covered with an insulating material such as a synthetic or
natural
polymer such as a silicone rubber. The housing 1182 is directly connected to
an
electrical conductor within the lead 1120. These materials are additionally
suitable because they tend to be biologically inert and well tolerated by body
tissue.
The helix 1100 defines a lumen and thereby is adapted to receive a
stiffening stylet 1014 that extends through the length of the lead. The stylet
1014 stiffens the lead 1120, and can be manipulated to introduce an
appropriate
curvature to the lead, facilitating the insertion of the lead into and through
a vein
and through an intracardiac valve to advance the distal end of the lead 1120
into
2~ the right ventricle of the heart (not shown). A stylet knob 1154 is coupled
with
the stylet 1014 for rotating the stylet 1014 and advancing the helix 1100 into
tissue of the heart.
In one embodiment, as shown in Figures 42A and 42B, a lead 1310 has
an electrode tip 1320 which is provided with a mesh screen 1330. The mesh
screen 1330, in one embodiment, completely encapsulates the diameter of the
lead, and may serve, at least in part, as a pacinglsensing interface with
cardiac
tissue. If the helix I 100 is electrically active, it too can help serve as a
portion of
a pacing or sensing interface. The mesh screen 1330 is of a porous
construction,
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48
preferably made of electrically conductive, corrosion resistant material.
Using a
mesh screen 1330 having a porous construction allows for fibrotic ingrowth.
This provides for a further anchoring of the lead tip 1320 and also increases
the
sensing capability of the lead 1310 by increasing the surface area in contact
with
the cardial tissue. The mesh screen 1330 may be attached to an electrode
collar
1040, which is electrically active. In a retractable catheter system, a
housing
1380, which is electrically conductive, encapsulates the piston 1350 and the
fixation helix 1100. Insulation 1382 is disposed about the housing 1380 and
collar 1040.
Disposed within the lead 1310 is a lead fastener 1100 for securing the
lead 1310 to cardiac tissue. The lead fastener 1100 can be disposed along the
radial axis 1015 of the electrode lead 131'0. In this embodiment, the lead
fastener 1100 comprises a fixation helix 1100. The fixation helix 1100 can be
made electrically active or inactive as discussed above. Attached to the
fixation
helix 1100 in a retractable tip system is a piston 1350. The piston 1350 is
configured to mate with a bladed locking stylet 1014 at a stylet slot 1354,
and
acts as an interface between the stylet 1014 and the helix 1100. The stylet
1014,
coupled with the piston 1350 at the stylet slot 354, extends and retracts the
fixation helix 1 100 when the stylet 1014 is rotated. The piston 1350 can
either
be electrically active or inactive. The piston 1350 also has a slot 1352,
which
allows the piston 1350 to mate with a base 1360.
Fitted with a knob 1362, as shown in Figure 42A, the base 1360 mates
with the slot 1352 of the piston 1350. The base 1360 serves as a stop once the
fixation helix 1100 is fully retracted. The electrically conductive base 1360
also
allows passage of a bladed locking stylet 1014 and attachment of electrode
coils
(not shown).
In addition, the lead 1310 has a guide groove 1370. The groove 1370 is
formed, in one embodiment, by puncturing a hole (not shown) within the mesh
screen 1330, although the guide groove 1370 can be formed by other methods
known by those skilled in the art. Having a circular cross-section, the guide
groove 1370 may have a diameter greater than that of the conductor forming the
helix 1100. The groove 1370 is disposed within the mesh screen 1330, and
directs the fixation helix 1100 from its retracted position, as illustrated in
Figure
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49
42A, to an extended position (not shown). The groove 1370 also reversibly
directs the fixation helix 1100 from an extended position to the retraction
position.
In a second embodiment, as shown in Figures 43A and 43B, a lead 1110
has an electrode tip 1120 which is provided with a mesh screen 1130. The mesh
screen 1130 completely encapsulates the diameter of the lead or electrode tip
1120, and serves as the pacing/sensing interface with cardiac tissue. The
screen
1130 is of a porous construction, made of electrically conductive, corrosion
resistant material. Using a mesh screen 1130 having a porous construction
I 0 allows for fibrotic ingrowth. This provides for a further anchoring of the
lead tip
1120 to tissue and also increases the sensing capability of the lead 1110. The
sensing capability is enhanced because the mesh screen 1130 has more surface
area than corresponding solid material. The ingrowth of fibrotic tissue into
the
mesh screen 1130 increase the sensing capability of the lead 1110 by
increasing
the surface area in contact with the cardial tissue. Furthermore, the geometry
of
the mesh screen 1130, particularly any protuberance, as will be discussed
below,
creates a high pacing impedance tip.
The mesh screen 1130 may form a protuberance 1135 from a flat edge
portion 1137 of the mesh screen 1130 in a generally central portion of the
electrode tip 1120. The protuberance 1135 may be generally circular in
cross-section, but may be any shape (e.g., truncated cylindrical, truncated
pyramidal, oval, ellipsoidal, etc.) as a result of design or circumstance
which
provides a flat or conformable surface (preferably not a rigid, sharp face
which
will not conform to tissue) abutting tissue, and preferably has a diameter
smaller
than a diameter of the lead 1110 (although a larger. In addition, the
protuberance
1135 is aligned with the radial axis 1015 of the lead 1110. Sintered to an
electrode collar 1040, a process known by those skilled in the art, the mesh
screen 1130 is attached to the electrode tip 1120. The electrode collar 1040
is
electrically active.
Disposed within the electrode lead 1110 is a lead fastener for securing
the electrode lead 1110 to cardiac tissue. The lead fastener can be disposed
along the radial axis 1015 of the electrode lead 1110. In this embodiment, the
lead fastener comprises a fixation helix 1100. The fixation helix 1100 can be
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made electrically active or inactive to change sensing and pacing
characteristics,
as discussed above. Attached to the fixation helix I 100 is a piston 1150. The
piston 1150 is configured to mate with a bladed locking stylet 1014, thereby
providing a movement assembly. The stylet 1014 extends and retracts the
5 fixation helix 1100 when the stylet 1014 is rotated. The piston 1150 can
either
be electrically active or inactive. The piston 1150 also has a slot 1152. The
slot
1152 of the piston 1150 allows the piston 1150 to mate with a base 1160 upon
full retraction.
The base 1160 is modified with a knob 1162 to mate with the slot 1152
I 0 of the piston 1150. The knob 1162 mates with the piston 1150 to prevent
over-retraction once the helix 1100 has been fully retracted. The stylet 1014
operates to advance the fixation helix 1100. As the implanter rotates the
stylet
1014, the stylet 1014 engages the piston 1150 at the stylet slot 1154 and
rotates
the piston 1150, which moves the fixation helix 1100 through a guide groove
15 1170. The guide groove 1170 is for ensuring that the fixation helix 1100 is
properly guided out of and into the end of the electrode. Once the fixation
helix
1 I00 is fully retracted, the base 1160 serves as a mechanical stop. The base
1160 also allows passage of a bladed locking stylet 1014 and attachment of
electrode coils. Additionally, the base 1060 is electrically active.
20 The electrode lead 1110 also has a guide groove 1170. The groove 1170
is formed by puncturing a hole within the mesh screen. Having a circular
cross-section, the groove 1170 has a diameter greater than that of the
conductor
forming the helix 1 T00. The groove 1 I 70 is disposed within the mesh screen
1130, and directs the fixation helix 1100 from its retracted position, as
illustrated
25 in Figure 42A, to an extended position (not shown). During implantation,
after
the electrode is in contact with tissue at the desired location in the heart,
the
stylet 1014 is rotated which causes the piston to advance the fixation helix
out of
the groove 1170. As the fixation helix 1100 is placed in an extended position,
the helix 1100 travels through groove 1170 and circles around the protuberance
30 1135. The groove 1170 also directs the fixation helix 1100 from an extended
position to the retracted position. Advantageously, the mesh screen 1130
prevents the implanter from overextension and advancing the helix 1100 too far
into the tissue. An electrically conductive housing 1180 encapsulates both the
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51
piston 1050 and the fixation helix 1100. Insulation 1182 covers the housing
1 180, the collar 1040, and a portion of the mesh screen 1130. The insulation
1182 over the mesh screen 1130 controls the impedance of the electrode tip
1120.
In a third embodiment as shown in Figures 44A and 44B, a lead 1010 has
an electrode tip 1020 which is provided with a mesh screen 1030. The mesh
screen 1030 completely encapsulates the diameter of the lead tip. Sintered to
an
electrode collar 1040, the mesh screen 1030 is attached to the electrode tip
1020.
The electrode collar 1040 is electrically active. A housing 1080 is disposed
about the helix 1100, and is electrically active. Insulation 1082, encompasses
the housing 1080 and collar 1040.
In one embodiment, as shown in Figures 42A and 42B, a lead 1310 has
an electrode tip 1320 which is provided with a mesh screen 1330. The mesh
screen 1330 completely encapsulates the diameter of the lead, and serves as
the
pacing/sensing interface with cardiac tissue. If the helix 1100 is
electrically
active, it too can help serve as a pacing or sensing interface. The mesh
screen
1330 is of a porous construction, made of electrically conductive, corrosion
resistant material. Using a mesh screen 1330 having a porous construction
allows for fibrotic ingrowth. This provides for a further anchoring of the
lead tip
1320 and also increases the sensing capability of the lead 1310 by increasing
the
surface area in contact with the cardial tissue. The mesh screen 1330 is
attached
to an electrode collar 1040, which is electrically active. A housing 1380,
which
is electrically conductive, encapsulates the piston 1350 and the fixation
helix
1100. Insulation 1382 is disposed about the housing 1380 and collar 1040.
Disposed within the lead 1310 is a lead fastener for securing the lead
1310 to cardiac tissue. The lead fastener can be disposed along the radial
axis
101 S of the electrode lead 1310. In this embodiment, the lead fastener
comprises
a fixation helix 1100. The fixation helix 1100 can be made electrically active
or
inactive as discussed above. Attached to the fixation helix 1100 is a piston
1350.
The piston 1350 is configured to mate with a bladed locking stylet 1014 at a
stylet slot 1354, and acts as an interface between the stylet 1014 and the
helix
1100. The stylet 1014, coupled with the piston 1350 at the stylet slot 1354,
extends and retracts the fixation helix 1100 when the stylet 1014 is rotated.
The
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piston 1350 can either be electrically active or inactive. The piston 1350
also
has a slot 1352, which allows the piston 1350 to mate with a base 1360.
Fitted with a knob 1362, as shown in Figure 42A, the base I 360 mates
with the slot 1352 of the piston 1350. The base 1360 serves as a stop once the
fixation helix 1100 is fully retracted. The electrically conductive base 1360
also
allows passage of a bladed locking stylet 1014 and attachment of electrode
coils.
In addition, the lead 1310 has a guide groove 1370. The groove 1370 is
formed by puncturing a hole within the mesh screen, although the guide groove
can be formed by other methods known by those skilled in the art. Having a
circular cross-section, the groove 1370 has a diameter greater than that of
the
conductor forming the helix 1100. The groove 1370 is disposed within the mesh
screen 1330, and directs the fixation helix 1100 from its retracted position,
as
illustrated in Figure 42A, to an extended position (not shown). The groove
1370
also directs the fixation helix 1100 from an extended position to the
retraction
position.
In a second embodiment, as shown in Figures 43A and 43B, a lead 1 I 10
has an electrode tip 1120 which is provided with a mesh screen 1130. The mesh
screen 1130 completely encapsulates the diameter of the lead tip, and serves
as
the pacing/sensing interface with cardiac tissue. The screen I 130 is of a
porous
construction, made of electrically conductive, corrosion resistant material.
Using
a mesh screen 1130 having a porous construction allows for fibrotic ingrowth.
This provides for a further anchoring of the lead tip 1120 and also increases
the
sensing capability of the lead 1110. The sensing capability is enhanced
because
the mesh screen 1130 has more surface area than corresponding solid material.
The ingrowth of fibrotic tissue into the mesh screen 1130 increase the sensing
capability of the lead 1110 by increasing the surface area in contact with the
cardial tissue. Furthermore, the geometry of the mesh screen, particularly the
protuberance, as will be discussed below, creates a high pacing impedance tip.
The mesh screen 1130 forms a protuberance 1 I 35 from a flat edge
portion 1137 of the mesh screen 1130 in a generally central portion of the
electrode tip 1120. The protuberance 1135 is generally circular in cross-
section,
and has a diameter smaller than a diameter of the lead 1110. In addition, the
protuberance 1 I 35 is aligned with the radial axis 1015 of the lead 1110.
Sintered
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53
to an electrode collar 1040, a process known by those skilled in the art, the
mesh
screen 1130 is attached to the electrode tip 1120. The electrode collar 1040
is
electrically active.
Disposed within the electrode lead 1110 is a lead fastener for securing
the electrode lead 1110 to cardiac tissue. The lead fastener can be disposed
along the radial axis 1015 of the electrode lead 1110. In this embodiment, the
lead fastener comprises a fixation helix 1100. The fixation helix 1100 can be
made electrically active or inactive to change sensing and pacing
characteristics,
as discussed above. Attached to the fixation helix 1100 is a piston 1150. The
piston 1150 is configured to mate with a bladed locking stylet 1014, thereby
providing a movement assembly. The stylet 1014 extends and retracts the
fixation helix 1100 when the stylet 1014 is rotated. The piston 1150 can
either
be electrically active or inactive. _ The piston 1150 also has a slot 1152.
The slot
I 152 of the piston 1150 allows the piston 1150 to mate with a base 1160 upon
full retraction.
The base 1160 is modified with a knob 1162 to mate with the slot 1152
of the piston 1150. The knob 1162 mates with the piston 1150 to prevent
over-retraction once the helix 1100 has been fully retracted. The stylet 1014
operates to advance the fixation helix 1100. As the implanter rotates the
stylet
1014, the stylet 1014 engages the piston I 150 at the stylet slot 1154 and
rotates
the piston I 150, which moves the fixation helix 1100 through a guide groove
1170. The guide groove 1170 is for ensuring that the fixation helix 1100 is
properly guided out of and into the end of the electrode. Once the fixation
helix
1100 is fully retracted, the base 1160 serves as a mechanical stop. The base
1160 also allows passage of a bladed locking stylet 1014 and attachment of
electrode coils. Additionally, the base 1060 is electrically active.
The electrode lead 1 I 10 also has a guide groove 1170. The groove I 170
is formed by puncturing a hole within the mesh screen. Having a circular
cross-section, the groove 1170 has a diameter greater than that of the
conductor
forming the helix 1100. The groove 1170 is disposed within the mesh screen
1130, and directs the fixation helix I 100 from its retracted position, as
illustrated
in Figure 42A, to an extended position (not shown). During implantation, after
the electrode is in contact with tissue at the desired location in the heart,
the
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54
stylet 1014 is rotated which causes the piston to advance the fixation helix
out of
the groove 1170. As the fixation helix 1100 is placed in an extended position,
the helix 1100 travels through groove 1170 and circles around the protuberance
1135. The groove 1170 also directs the fixation helix 1100 from an extended
position to the retracted position. Advantageously, the mesh screen 1130
prevents the implanter from overextension and advancing the helix 1100 too far
into the tissue. An electrically conductive housing 1180 encapsulates both the
piston 50 and the fixation helix 1100. Insulation 1182 covers the housing
1180,
the collar 40, and a portion of the mesh screen 1130. The insulation 1182 over
the mesh screen 1130 controls the impedance of the electrode tip 1120.
In a third embodiment as shown in Figures 44A and 44B, a lead 1010 has
an electrode tip 1020 which is provided with a mesh screen 1030. The mesh
screen 1030 completely encapsulates the diameter of the lead tip. Sintered to
an
electrode collar 1040, the mesh screen 1030 is attached to the electrode tip
1020.
The electrode collar 1040 is electrically active. A housing 1080 is disposed
about the helix I 100, and is electrically active. Insulation 1082,
encompasses
the housing 1080 and collar 1040.
Disposed within the lead 1010 is a lead fastener for securing the lead
1010 to cardiac tissue. The lead fastener can be disposed along the radial
axis
1015 of the lead 1 Ol 0. In this embodiment, the lead fastener comprises a
fixation helix 1100. The fixation helix 1100 can be made electrically active
or
inactive to change sensing and pacing characteristics.
The helix 1100 is of a well known construction. Using a conductor coil
such as helix 1100 has been shown to be capable of withstanding constant,
rapidly repeated flexing over a period of time which can be measured in years.
The helix 1100 is wound relatively tightly, with a slight space between
adjacent
turns. This closely coiled construction provides a maximum number of
conductor turns per unit length, thereby providing optimum strain
distribution.
The spirally coiled spring construction of helix 1100 also permits a
substantial
degree of elongation, within the elastic limits of the material, as well as
distribution along the conductor of flexing stresses which otherwise might be
concentrated at a particular point.
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Attached to the fixation helix 1100 is a piston 1050. The piston 1050 is
configured to mate with a bladed locking stylet 1014. The piston 1050 advances
the fixation helix 1100 once the lead is placed in position within the heart.
The
piston 1050 can either be electrically active or inactive. The piston 1050
also
5 has a slot 1052 and a stylet slot 1054. The stylet 1014 couples with the
stylet
slot 1054 and extends or retracts the fixation helix 1100 when the stylet 1014
is
rotated. The slot 1052 of the piston 1050 allows the piston 1050 to mate with
a
base 1060 when the helix 1100 is retracted to prevent over retraction. The
base
1060 is configured with a knob 1062 to mate with the slot 1052 of the piston
10 1050. Once the fixation helix 1100 is fully retracted, the base 1060 serves
as a
stop at full retraction. The base 1060 also allows passage of a bladed locking
stylet 1014 and attachment of electrode coils. In addition, the base 1060 is
electrically active.
The lead 1010 also includes a guiding bar 1070. Extending across the
15 diameter of the tip, the guiding bar 1070 is generally cylindrical in
shape. The
guiding bar 1070 directs the fixation helix 1100 from its retracted position,
as
illustrated in Figure 42A, to an extended position (not shown) as the piston
1052
advances the helix 1100. The guiding bar 1070 also directs the fixation helix
1100 as it is retracted from an extended position to the retraction position
20 through the mesh screen. Although a guiding bar 1070 is described, other
types
of guiding mechanisms can be used such as helical passageways, threaded
housings, springs, and are considered within the scope of the invention.
Additionally, the lead 1010 is provided with a seal (not shown) for preventing
entry of body fluids and tissue from entering the lead through the opening
25 therein. The seal could be a puncture seal between the piston 1050 and the
base
1060. Alternatively, O-rings could be used to seal the electrode.
In a fourth embodiment as shown in Figures 45A and 45B, a lead 1210
has an electrode tip 1220 which is provided with a mesh screen 1230. The mesh
screen 1230 forms an annular ring having an open center, where the annular
ring
30 is centered at a radial axis 1015 of the electrode lead 1210. The mesh
screen
1230 provides more surface area than a smooth tipped electrode which aids in
sensing. The removal of the center portion of the mesh screen creates a high
impedance pacing tip due to the nature of the surface geometry. Sintered,
fused,
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56
bonded, adhesively secured or mechanically attached to an electrode collar
1040,
the mesh screen 1230 is attached to the electrode tip 1220. The electrode
collar
1040 is electrically active.
Disposed within the lead 1210 is a lead fastener for securing the lead
1210 to cardiac tissue. The lead fastener can be disposed along the radial
axis
1015 of the electrode lead 1210. In this embodiment, the lead fastener
comprises
a fixation helix 1100. The fixation helix 1100 can be made electrically active
or
inactive as discussed above. Attached to the fixation helix 1100 is a piston
1250.
The piston 1250 has a stylet slot 1254 and is configured to mate with a bladed
locking stylet 1014. The stylet 1014, coupled with the piston 1250 at the
stylet
slot 1254, extends and retracts the fixation helix 1100 when the stylet 1014
is
rotated. The piston 1250 can either be electrically active or inactive. The
base
1260 serves as a stop once the fixation helix 1 Z 00 is fully retracted. The
base
1260 also allows passage of a bladed locking stylet 1014 and attachment of
1 S electrode coils. The base 1060 is electrically active.
Additionally, the lead also has a guiding bar 1270. The guiding bar 1270
directs the fixation helix 1100 from its retracted position, as illustrated in
Figures
45A and 45B, to an extended position (not shown). The guiding bar 1270 also
directs the fixation helix 1100 from an extended position to the retracted
position. Although a guiding bar 1270 has been described, other types of
mechanisms could be used to extend the helix, and are considered within the
scope of the invention. A housing 1280 encapsulates the piston 1250 and the
fixation helix 1100, and insulation 1282 is disposed over the housing 1280 and
collar 1040.
Insulation generally covers the housing, the collar, and a portion of the
electrical discharge surface (e.g., the cathode, the helix and/or the porous
material or mesh). The insulation over the mesh screen further controls the
impedance of the electrode tip. The insulated coating, whether present on the
helix or the mesh or other elements which are potentially electrically active
or on
which electrical activity is to be suppressed, should be biocompatible,
non-thrombogenic, and otherwise safe for implantation. The insulation coating
should be of dimensions which effect the insulation, increase the impedance
(where desired), but which dimensions do not interfere with the performance of
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57
the tip, the lead or the helix or the health of the patient. The insulation is
present
as a coating ( a material which tends to conform to the surface rather than
completely reconfigure it, as would a lump of material). The coating usually
should be at least 0.5 microns in thickness, usually between 0.5 and 100
microns,
preferably between 1.0 and 30 or 50 microns, more preferably between 1 and 20
microns, still more preferably between 1.5 and 15 microns, and most preferably
between 1.5 or 2.0 microns and 10 or 15 microns. The coating may be provided
by any convenient process, such as electrophoretic deposition, dip coating,
spin
coating, in situ polymerization, vapor deposition, sputtering and the like.
Any
insulating material is useful, such as polymers, ceramics, glasses, and the
like,
but because of their convenience in application, flexibility and availability,
polymers are preferred. Polymers from such classes as polyesters, polyamides,
polyurethanes, polyethers, polysiloxanes, polyfluorinated resins, polyolefins,
polyvinyl polymers, polyacrylates (including polymethacrylates), and the like
may be used with various leads and tips according to the practice of the
present
invention. Parylene is a preferred material, as described herein, with a
thickness
of between 1.5 and 10 microns.
In yet another embodiment, a partially insulated fixation helix is used to
provide a relatively high impedance electrode design. Leads comprising a
distal
or electrode end and a proximal or connector end may be used. A "miniature"
wire-in-basket porous electrode may be sintered upon the distal end of a
metallic
pin, provided with a blind hole. Circumferential to this subassembly, a
sharpened wire fixation helix may be positioned and attached at a general
location proximal to the electrode by any convenient means which allows
electrical continuity. This attachment includes, but is not limited to,
crimping,
spot welding, laser welding, the use of grooves upon the surface of the pin,
the
use of thin metallic overband (also not shown) or any combination thereof. A
portion of this fixation helix is provided with an extremely thin layer of a
biostable, biocompatible polymer, which, inter alia, provides electrical
insulation
between the fixation helix and the cardiac tissue. In one embodiment, the
insulated portion is the majority of the fixation helix, leaving a relatively
small
uninsulated region of fixation helix. This approach offers increased impedance
to reduce energy dissipation in pulsing functions, such as pacing functions.
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Other varying embodiments include, but are not limited to, a portion which is
approximately or substantially equal to half of the fixation helix, and a
portion
which is approximately or substantially equal to a minority of the fixation
helix.
Such embodiments provide different amounts of uninsulated region and different
amounts of impedance. The thin coating of electrically insulating coating must
usually be at least 1 micron in thickness to provide a significant insulating
effect,
depending upon its insulating ability and properties. The thickness of the
coating is limited primarily by physical limitations on the system. The
coating
can not be so thick as to interfere with the fastening ability of the helix or
to in
crease the size of the helix beyond that which is tolerable for the use of the
helix
and the patient. Typically, the coating is at least one micron up to about 100
microns, more typically the coating is between 1 and 30 microns, preferably
between 1.5 and 20 microns, more preferably between 1.5 and 15 microns, and
most preferably between 2 and 10 microns. The material used for the coating
should, of course, be biocompatible and even more preferably
non-thrombogenic. Materials such as Parylene TM, polyurethanes, polyacrylates
(including polymethacrylates), polyesters, polyamides, polyethers,
polysiloxanes, polyepoxide resins and the like can be used. Crosslinked
polymers within these classes may be preferred for their resistance to
breakdown
and their physical durability. As the coating is to be maintained within the
body
of a recipient, the coating composition should not be water-soluble or aqueous
soluble within the parameters and environment encountered within animal
bodies (e.g., it should not be soluble within blood, serum or other body
fluids
with which it might come into contact).
To the proximal end of this pin, a metallic conductor coil may be
conveniently attached to provide electrical connection to the implantable
pacemaker (not shown) by means of a connector . In one embodiment, local
(e.g., steroid or other medicinal) therapy is provided by a (e.g.,
circumferential)
steroid/polymer matrix positioned immediately proximal to the porous
electrode.
In one embodiment, the circumferential steroid/polymer matrix is provided with
a distal taper. Other embodiments include other distal configurations,
including,
but not limited to, non-tapered or "inflated" configurations. In one
embodiment,
an internalized, medicinal or biologically active (e.g., steroid) releasing
matrix is
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used. Proximal to this biologically active (e.g., steroid) eluting matrix, a
generally cylindrical polymeric tubing (this is the preferred shape, but the
shape
is a matter of choice) 1820 is used to provide electrical insulation of this
entire
assembly. In one embodiment the lead is "unipolar." In one embodiment an
ablative protective covering positioned over the entirety of distal end 520 is
used
(not shown). One example of such a covering is the mannitol "Sweet Tip"TM
electrode of Cardiac Pacemaker, lnc. CPI/Guidant.. In one embodiment, a
"bipolar" lead is provided with the distal electrode features described.
During an in vitro evaluation of this electrode design, polymeric coatings
intended to partially insulate the fixation helix were prepared and evaluated.
In
one embodiment, the Parylene coating is extremely thin (~3 u), providing a
coating with uniform coverage which is adherent to the metallic substrate, and
which is controllable to provide an abrupt margin. The silicone rubber coating
is
known to be somewhat thicker (~10 p), uniform in coverage, somewhat less
1 S adherent to the metallic substrate, and controllable to an abrupt margin.
Other
coatings may be used without departing from the spirit and scope of the
present
invention.
The Parylene or other insulative coating effectively increases in vitro
"pacing impedance." Application of a non-continuous or partially extensive
coating of an electrically insulating polymer such as Parylene to the metallic
fixation helix produces the desired increase in impedance compared to an
uninsulated helix as well as other existing designs. For example, it has been
demonstrated that one embodiment using a coated fixation helix provides a
pacing impedance of over approximately 800 ohms which is larger than the
impedance of some electrodes using an uncoated fixation helix. The
post-implant pacing impedance of an embodiment using a coated fixation helix
remains higher than that of typical electrodes using an uncoated fixation
helix.
In one experiment, a coated fixation helix using Parylene as an insulating
layer
provided over 1200 ohms average pacing impedance on the day of implantation
and over 900 ohms ten days after the implant.
Additionally, post-implant average voltage threshold of the Parylene
insulated miniaturized electrode is less than the other high impedance
electrodes.
Such performance is considered to be desirable. In one experiment, an
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embodiment with a coated fixation helix 1804 having a voltage threshold of
approximately 0.2 volts on the day of implant was measured at about 0.7 volts
at
ten days after the implant (using a 0.5 ms pulse width). An electrode with an
uncoated fixation helix demonstrated over 0.8 volts average voltage threshold
at
5 ten days after the implant, illustrating the benefits of the coated fixation
helix.
An additional benefit is that the coated fixation helix embodiments may
provide an improvement in both the implant as well as post-implant average
S-wave amplitude detection.
The miniaturized high impedance, positive fixation porous electrode
10 technology described here provides the following advantages over the prior
art.
For one example, the coated fixation helix embodiments provide an electrode
where the benefits of high impedance pacing are realized through downsizing
the
porous electrode and insulating the fixation helix. Downsizing of the porous
electrode may be accomplished, for example, by having a smaller porous (e.g.,
15 mesh) electrode supported on a non-conductive surrounding support element
(e.g., a polymeric or composite film with a mesh central area, particularly a
mesh
truncated conical or pyramidal area of flexible, conductive mesh). An area of
the
completely conductive mesh may also be discontinuously coated leaving a
conductive central or conductive raised area, particularly surrounding a
contact,
20 engaging element, or helix. Further, an external steroid collar provides a
fabrication advantage since such a component can be readily mass produced
compared to smaller components with elaborate profiles. Still further,
fabrication of a lead with this external collar is streamlined. The higher
impedance design conserves battery power to provide longer battery life with
25 fewer battery replacements. Other benefits exist which are not described in
detail herein, however, which those skilled in the art will appreciate.
Figure 46 shows a high impedance catheter tip 1800 with a partially
insulated tip 1802 and a partially insulated mesh 1808. The partially
insulated
tip (or helix) 1802 comprises one fully insulated section 1804 and one
30 uninsulated section 1806. The partially insulated mesh 1808 comprises a
first
area 1810 of the mesh 1808 which is insulated and second are 1812 of the mesh
I 808 which is not insulated. The impedance of the catheter tip can be readily
controlled by the amount of surface area of the helical tip itself and the
area of
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the mesh (if present) which is insulated. With a fixed conductivity in the tip
and
the mesh (if present), the impedance can be increased by increasing the
percentage of the surface area of the tip or mesh which is insulated.
A hole 1820 is shown in the mesh 1808. The mesh 1808 may be flat and
flush with the end 1822 of the catheter 1816 or may be partially wrapped (not
shown) over the end 1820 or inside the end 1820 to affix the mesh to the
catheter
1816. The mesh 1808 may also be hemispherical, truncated conical, truncated
pyramidal or any other shape which may assist in allowing the mesh 1808 to
more compliantly contact tissue (not shown) surface to transmit the pacing
signal
or discharge. Within the catheter 1816 may be a soluble, elutable or
dispersible
material which carries medication or biologically active material along with
the
catheter. For example, anti-inflammatants, antibiotics, analgesics, pain-
reducing
medication, vitamins, anti-viral medication, or the like may be transmitted to
the
attachment site along with the catheter by inclusion within a material 1814
carried within or on the catheter 1816.
The coating of insulation on the helical tip or mesh may be applied by
any convenient method, including, but not limited to coating (e.g., dip
coating),
printing, spraying, brush application, resist application and removal and the
like.
The insulation may also contain active ingredients (such as those recited
within
material 1814) to benefit the patient. The insulation carrying the active
material
must not be soluble, so a polymer or other material that is porous or has
elutable
materials must be used. The material delivery does not have to be coextensive
with the life of the implant or the tip, and delivery of the material may be
desirable only over a short time period after insertion of the helical tip and
catheter.
A soluble or dispersible protective cap may also be placed over the
helical tip to reduce the possibility of any incidental damage while
catheterizing
or moving the tip within a patient. As previously noted, the cap material
should
preferably be biocompatible or even digestible and may include such materials
as
natural and synthetic materials such as sugars, starches, gelation
(unhardened),
gums, resins, polymers, and the like. All components of the catheter and tip
which are exposed to the tissue or fluids within a patient should be
non-thrombogenic, and bio-acceptable. There are extensive classes of
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commercially available materials which meet these needs for metal, polymeric,
composite and other materials described within the practice of the present
invention.
It is contemplated that slight variations in the design of the lead could be
used for a particular application as required. One such variation would be the
provision of steroid elution from any of the electrodes provided on the lead.
Steroid elution can be provided by using one or more of the steroid-releasing
technologies such as sleeves or collars positioned in close proximity to the
electrodes or by the use of internalized steroid-containing plugs. Steroids
are
generally used in order to reduce the inflammation associated with attaching
an
electrode to the endocardial wall of the heart. By reducing the inflammation
at
the time of implantation, the threshold values associated with the electrodes
are
usually lower when compared to threshold values associated with electrodes
that
did not elute a steroid over the attachment site. An example of the
composition
of at least one collar is dexamethasone acetate in a simple silicone medical
adhesive rubber binder or a steroid-releasing plug similarly fabricated.
Advantageously, the single pass lead allows for one, two, or more
chambers of the heart to be paced and/or sensed, while only one lead is
implanted within the patient. This assists in preventing added stress and
expense
for the patient. In addition, the active fixation element will not hook nor
snag
tissue when it is retracted within the lead. The active fixation element also
does
not require the use of a stylet, since the terminal pins are used to extend
and
retract the active fixation element. The active fixation allows for the lead
to be
positioned almost anywhere in the atrium. The movement assembly assists in
protecting the shape of the helix even when the helix is under tension.
It is to be understood that the above description is intended to be
illustrative, and not restrictive. Many other embodiments will be apparent to
those of skill in the art upon reading and understanding the above
description.
For example, the present invention can be used with a variety of medical
devices.
Although the use of the lead has been described for use in a cardiac pacing
system, the lead could also be applied to other types of body stimulating
systems. It should also be noted that the above described embodiments of the
systems and Leads include combinations of the various embodiments described
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herein. The scope of the invention should, therefore, be determined with
reference to the appended claims, along with the full scope of equivalents to
which such claims are entitled.
