Note: Descriptions are shown in the official language in which they were submitted.
CA 02441396 2003-09-11
APPARATUS FOR DEPLOYMENT OF MICRO-COIL USING A CATHETER
Related Applications:
This is a continuation in part of Serial No. 09/143,904 filed August 31,
1998 and Serial No. 09/501,466 filed February 9, 2000, which is a continuation
in part
of 09/218,117 filed December 21, 1998.
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates generally to devices for interventional therapeutic
treatment or vascular surgery for treatment of defects in the vasculature, and
more
particularly concerns a system and method for delivering intravascular
interventional
devices, such as for treatment of aneurysms.
Description of Related Art:
Vascular interventional devices such as vasoocclusive devices are typically
placed within the vasculature of the human body by use of a catheter. Vascular
interventional devices such as stems can be placed within an occluded vessel
to
facilitate blood flow through the vessel, and vasoocclusive devices are
typically either
placed within a blood vessel to block the flow of blood through a vessel
making up
that portion of the vasculature through the formation of an embolus, or are
placed
within an aneurysm stemming from the vessel to form such an embolus within the
aneurysm. Stems can have a wide variety of configurations, but generally need
to be
placed and then released at a desired location within a blood vessel.
Vasoocclusive
CA 02441396 2003-09-11
2
devices used for these procedures can also have a wide variety of
configurations, and
aneurysms have been treated with external surgically placed clips, detachable
vasoocclusive balloons and embolus generating vasoocclusive devices such as
one or
more vasoocclusive coils.
The delivery of such vasoocclusive devices have typically been
accomplished by a variety of means, including via a catheter in which the
device is
pushed through an opening at the distal end of the catheter by a'pusher to
deploy the
device. The vasoocclusive devices can be produced in such a way that they will
pass
through the lumen of a catheter in a linear shape and take on a complex shape
as
originally formed after being deployed into the area of interest, such as an
aneurysm.
Some conventional vasoocclusive devices are operated by pulling or
jerking the catheter tip from the balloon, thus potentially compromising the
position
of the implant. One such device provides for an endovascular wire and tip that
can be
separated from the holding wire mechanically or electrolytically for the
formation of
thrombus in blood vessels. However, such devices that release the
interventional
device by mechanically breaking an intermediate section between the catheter
tip and
balloon can potentially leave broken or jagged ends that can potentially
injure the
vasculature.
One conventional releasable balloon catheter used to embolize vascular
lesions has a tube portion made of a material such as a hydrophilic polymer,
located
between the catheter and the balloon, that can be broken by torsion of the
tube. The
tube can be melted by heating the tube, or can be dissolved in the blood when
heated,
and electrodes are provided for heating the tube. Another conventional
technique for
separating a balloon from a balloon catheter involves the melting and breaking
of a
connecting member made from polyvinyl alcohol or trans-polyisoprene between
the
balloon and the catheter body, when power is supplied to electrodes provided
for
heating the connecting member. When the connecting member is heated to
temperatures of about 70°C and slight tension is applied, the balloon
can be separated
CA 02441396 2003-09-11
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3
from the main catheter body. However, such devices that release the
interventional
device by melting or dissolving the intermediate section between the catheter
tip and
balloon can also potentially release undesirable particles of materials into
the
bloodstream.
S There is therefore a need for a precise method of deploying therapeutic
interventional devices without compromising the position of the implant,
without
presenting broken or jagged ends that can potentially injure the vasculature,
and
without releasing undesirable particles of materials into the bloodstream.
The transmittal of energy of various types through a catheter to a remote
location in the body has been used in the past, both for therapeutic purposes
and to
perform actuation or chemical reactions for delivery systems. In one such
system, a
temporary stmt formed from a coil of tubular thermoplastic material is
delivered
activated for use by a heating element. The thermoplastic stmt body is
introduced into
the vessel to be supported and is then heated by the heating element above its
softening temperature and expanded to a second dimension in order to support
the
vessel. Cooling of the stmt body allows the stmt to temporarily support the
vessel,
and the stmt body can be heated at a later time to soften and remove the stmt
from the
vessel. However, the thermoplastic stent body contains an electrical
resistance heating
element, and heat is generated in the stent by a current is passed through
electrically
conductive wires.
An endovascular stmt and delivery system is also known in which a
partially cured material is delivered to a selected site in a blood vessel and
is then
crosslinked in the blood vessel by Laser light energy delivered to the
partially cured
material. The delivery system can also use thermal energy as from a resistive
heating
element, radio frequency energy, or beta rays in order to cause the
crosslinking.
A flexible guide is also known that is formed from a two-way shape
memory alloy fox use in non-invasive procedures. The device comprises an
elongated,
flexible guide having a core of a shape memory alloy which allows for tip-
deflection
CA 02441396 2003-09-11
4
and rotational movement to the guide wire in response to heating provided by
transmission of an electrical current through the shape memory alloy.
Another catheter is known that is composed of a main body fitted with a
shape memory alloy, with a liquid injector for supplying a warming liquid such
as a
S physiological saline or transfusion solution when the shape memory alloy is
to recover
an original shape.
In another delivery system for an occlusive device, energy is transmitted
through a catheter to a coil and a polymeric material to occlude an aneurysm.
The
polymeric material is solidified by light, heat or RF energy emitted from the
end of a
light or energy emitting device placed outside the distal end of the guiding
catheter.
A common problem with such known delivery and activation systems,
conveying heat by such methods as warm liquids, light, electrical energy,
radio
frequency energy or beta rays, is that they are typically highly inefficient
or not
particularly powerful, so that once a device to be delivered is placed in the
desired
location, there can be a delay while sufficient thermal energy is conducted to
the
activation site, or in the process heat energy can be radiated or otherwise
lost during
transmission. It would therefore be desirable to provide a thermal energy
activated
delivery system for vascular interventional devices that is highly efficient
and
immediate, and can allow the delivery of a necessary amount of thermal energy
to a
specific location for deployment of an interventional device.
Heat pipes are known as extremely efficient heat transfer devices, and are
much more efficient than solid metal heat sinks, for example. Such heat pipes
typically have a hollow interior chamber that has been evacuated, then filled
with a
small amount of working fluid, and sealed. When heat is applied to one end,
serving
as an evaporator end, the fluid vaporizes, and carries the heat in the
vaporized working
fluid extremely rapidly to the other end, serving as a condenser end, where
the latent
heat of vaporization is released as the vapor condenses back into liquid form.
The
CA 02441396 2003-09-11
. ~a .rc~,
working fluid is then carried back in liquid form to the evaporator end by
capillary
action. There is thus a need for application of a flexible heat pipe for
conducting heat
to a specific desired site for the purpose of deploying interventional devices
such as
stents and occlusive devices. The present invention meets these and other
needs.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention provides a precise
system and method for efficiently and cleanly releasing a therapeutic device
such as
a vasoocclusive coil, a stmt, or other therapeutic device for use in
interventional
therapy and vascular surgery, and which is particularly adapted to be inserted
into a
portion of a vasculature for treatment of a body vessel such as an aneurysm
without
compromising the position of the implant.
In a presently preferred aspect of the invention, the intravascular delivery
1 S system for release and deployment of a therapeutic device within the
vasculature of a
patient comprises an elongated, flexible heat pipe pusher member; a
therapeutic device
to be placed within the vasculature of a patient; and a shape memory device
detachably
mounting the therapeutic device for placement of the therapeutic device within
the
vasculature, the shape memory device having a closed configuration connecting
the
therapeutic device to the flexible heat pipe pusher member, and an open
configuration
for detaching and deploying the therapeutic device from the flexible heat pipe
pusher
member when a desired placement of the therapeutic device within the
vasculature is
achieved. The shape memory device is typically a shape memory collar disposed
on
one of the therapeutic device and the flexible heat pipe pusher member and
connects
the therapeutic device and the heat pipe pusher member, and in a presently
preferred
embodiment, the shape memory device is a shape memory collar disposed on the
distal
tip of the flexible heat pipe pusher member and connecting the therapeutic
device to
the flexible heat pipe pusher member. In a presently preferred embodiment, the
shape
CA 02441396 2003-09-11
6
memory collar is made of nickel titanium alloy.
In a presently preferred aspect of the invention, the elongated, flexible heat
pipe pusher member comprises a flexible heat pipe having a hollow interior
chamber
containing a working fluid, the flexible heat pipe having a metal evaporator
end
portion for conducting heat to the working fluid in the interior chamber of
the heat
pipe, a flexible insulated mid-portion, and a metal condenser end portion for
conducting heat from the working fluid to the shape memory device. In another
presently preferred aspect, the insulated mid-portion comprises an outer
covering of
resinous material so that the mid-portion does not radiate heat. The flexible
heat pipe
typically comprises a metal hollow tube, and in a presently preferred
embodiment, the
metal hollow tube is formed from a beryllium copper alloy. In another
presently
preferred aspect, the evaporator end portion comprises a stainless steel
portion for
conducting heat to the metal hollow tube and the working fluid in the interior
chamber
of the heat pipe, and the condenser end portion is partially covered with
1 S polytetrafluoroethylene, leaving a distal end portion of the condenser end
portion
exposed to transfer heat to the shape memory collar.
The shape memory collar can be heated to thereby assume a configuration
disconnecting the therapeutic device and the flexible heat pipe pusher member,
and
the heat pipe pusher member advantageously can be connected to a heat source
for
transferring heat to the collar to induce the collar to detach the therapeutic
device from
the flexible heat pipe pusher member. In one presently preferred embodiment,
the
therapeutic device comprises a stem, and the collar clamps onto the stem. The
therapeutic device can comprise a vasoocclusive coil, a stmt, or another
similar
therapeutic device adapted to be placed in the vasculature.
The invention thus also provides for a method for release and deployment
of a therapeutic device within the vasculature of a patient. In a presently
preferred
embodiment, the steps of the method comprise providing a therapeutic device to
be
placed within the vasculature of a patient; providing an elongated, flexible
heat pipe
CA 02441396 2003-09-11
7
pusher member; providing a shape memory device; detachably mounting the shape
memory device to one of the therapeutic device and the elongated, flexible
heat pipe
pusher member, the shape memory device having a closed configuration
connecting
the therapeutic device to the flexible heat pipe pusher member, and an open
S configuration for detaching and deploying the therapeutic device from the
flexible heat
pipe pusher member when a desired placement of the therapeutic device within a
patient's vasculature is achieved; positioning the therapeutic device at a
desired
placement within a patient's vasculature; and disconnecting the therapeutic
device
from the elongated, flexible heat pipe pusher member, thereby deploying the
therapeutic device. In a presently preferred aspect of the method of the
invention, the
step of disconnecting the therapeutic device from the elongated, flexible heat
pipe
pusher member comprises causing heat to be transmitted through the flexible
heat pipe
member to the shape memory collar to heat the shape memory collar to cause the
shape
memory collar to expand to release the therapeutic device.
The present invention also provides for an apparatus for release and
deployment of a therapeutic device within the vasculature of a patient,
comprising an
elongated, flexible pusher member having an interior lumen and a distal
portion, and
a connector fiber detachably mounting the therapeutic device to the pusher
member
for placement of the therapeutic device within the vasculature, the connector
fiber
being capable of being broken by heat. An elongated, flexible heat pipe member
is
disposed within the interior lumen of the elongated, flexible pusher member,
and has
a distal heating end disposed adjacent to the connector fiber for heating the
connector
fiber to cause the connector fiber to break and release the therapeutic device
for
detaching and deploying the therapeutic device from the flexible pusher member
when
a desired placement of the therapeutic device within the vasculature is
achieved. In
a presently preferred aspect, the connector fiber is formed from a
thermoplastic
material, such as polyethylene. In another presently preferred aspect, the
pusher
member includes at least one entry port communicating with the interior lumen
of the
CA 02441396 2003-09-11
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g
pusher member, and the distal heating end of the heat pipe member is disposed
in the
interior lumen of the pusher member adjacent to the at least one entry port.
In a
preferred embodiment, the connector fiber extends from a proximal portion of
the
pusher member to form a loop through the connector ring, and back through the
at
S least one port through the pusher member to the proximal portion of the
pusher
member. In another preferred aspect, the therapeutic device to be placed
within the
vasculature of a patient is connected to an annular connector ring; and the
connector
fiber mounting the therapeutic device to the pusher member passes through the
connector ring to secure the therapeutic device to the pusher member.
These and other aspects and advantages of the invention will become
apparent from the following detailed description and the accompanying
drawings,
which illustrate by way of example the features of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an exploded side sectional view of a first preferred embodiment
of the heat pipe activated interventional device delivery system of the
present
invention in which a portion of a therapeutic device is detachably gripped by
a shape
memory collar mounted to the heat transfer member of the delivery system,
showing
the shape memory collar in a closed configuration gripping the therapeutic
device;
Fig. 2 is an enlarged side sectional view of the heat pipe activated
interventional device delivery system of Fig. 1, showing the shape memory
collar in
an open configuration;
Figure 3 is an exploded side sectional view of a second preferred
embodiment of the heat pipe activated interventional device delivery system of
the
present invention in which ~ shape memory collar is mounted to a therapeutic
device
detachably mounted to the heat transfer member of the delivery system, showing
the
shape memory collar in a closed configuration gripping the heat transfer
member;
CA 02441396 2003-09-11
9
Fig. 4 is an enlarged side sectional view of the heat pipe activated
interventional device delivery system of Fig. 3, showing the shape memory
collar in
an open configuration;
Fig. S is a top sectional view of a second embodiment of the apparatus for
release and deployment of a therapeutic device;
Fig. 6 is a side sectional view of the apparatus of Fig. S;
Fig. 7 is a bottom sectional view of the apparatus of Fig. S; and
Fig. 8 is a side sectional view of the apparatus of Fig. S, illustrating
release
of the therapeutic device upon heating of the elongated connector fiber.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Vasoocclusive devices that are operated by pulling or jerking the catheter
tip from the balloon can compromise the position of the implant, while other
devices
1 S that release such devices by breaking an intermediate section between the
catheter tip
and balloon can potentially injure the vasculature, and those that melt or
dissolve an
intermediate section can release undesirable particles of materials into the
bloodstream.
While the transmittal of energy of various types through a catheter to a
remote location
in the body has been used in the past, both for therapeutic purposes and to
perform
actuation or chemical reactions for delivery systems, a common problem with
such
known delivery and activation systems is that they are typically particularly
inefficient.
As is illustrated in the drawings, which are provided for the purposes of
illustration and not by way of limitation, the invention is accordingly
embodied in an
intravascular delivery system for release and deployment of a therapeutic
device within
the vasculature of a patient. According to the invention, a shape memory
collar may
be disposed on either the therapeutic device or a flexible heat pipe pusher
member, and
releasably connects the therapeutic device and the heat pipe pusher member
together.
Referring to Figs. 1 and 2, in a first preferred embodiment, the
CA 02441396 2003-09-11
intravascular delivery system 10 comprises an elongated, flexible heat pipe
pusher
member 12, having a distal tip 14, and a therapeutic device, such as a coil
16, having
at least one configuration which may serve as a vasooclusive coil or a stmt,
for
example, to be placed within the vasculature of a patient. The therapeutic
device is
5 detachably mounted to the distal tip of the pusher member by a shape memory
collar
18, for placement of the therapeutic device within the vasculature. The shape
memory
collar is preferably tubular, having a closed configuration or narrowed
configuration
with a relatively smaller inner diameter as shown in Fig. 1, connecting the
therapeutic
device to the flexible heat pipe pusher member, and an open configuration,
with a
10 relatively larger inner diameter as shown in Fig. 2, for detaching and
deploying the
therapeutic device from the flexible heat pipe pusher member when a desired
placement of the therapeutic device within the vasculature is achieved. The
shape
memory collar can, for example, be made of nickel titanium alloy, and the
therapeutic
device can, for example, be a stmt, vasoocclusive coil or wire, having a stem
20 to
which a wire coil is mechanically attached, although the wire coil could also
be
suitably soldered or welded to the stem. The shape memory collar is preferably
heat
treated in an unextended position, and can be heated to a temperature that
allows it to
be worked and crimped into an extended position gripping over the end of the
stem
of the wire coil to connect the therapeutic device to a flexible heat pipe
pusher member
of the placement catheter shaft.
The elongated, flexible heat pipe pusher member preferably comprises a
flexible heat pipe 22 or rod, having a hollow interior chamber 24 that has
been
evacuated, filled with a small amount of a working fluid, and then sealed. The
flexible
heat pipe has a metal evaporator end portion 26 for conducting heat to the
working
fluid in the interior chamber of the heat pipe, a flexible insulated mid-
portion 28, and
a metal condenser end portion 30 for conducting heat from the working fluid to
the
shape memory device. The insulated mid-portion preferably has an outer
covering 32
of flexible, resinous material so that the mid-portion does. not radiate heat.
The
CA 02441396 2003-09-11
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11
flexible heat pipe typically is formed from a hollow metal tube 34, and in a
presently
preferred embodiment, the hollow metal tube is made of an alloy of beryllium
and
copper. The evaporator end portion preferably comprises a stainless steel
portion 35
for conducting heat to the metal hollow tube and the working fluid in the
interior
chamber of the heat pipe, and the stainless steel evaporator end portion can
be formed
from a ground stainless steel hypo tube. The condenser end portion is
preferably
partially covered with polytetrafluoroethylene (PTFE) 36, leaving a distal end
portion
38 of the condenser end portion exposed to transfer heat to the shape memory
collar.
When the therapeutic device is delivered to an appropriate location in the
vasculature, and an operator is satisfied that the device is properly placed,
the shape
memory collar can be heated, and thereby induced to shrink and pull back to
assume
a configuration disconnecting the therapeutic device from the placement
catheter shaft.
The proximal evaporator end of the flexible heat pipe pusher member can thus
be
connected to a heat source 40, such as an RF heat source or ultrasound heat
source, for
1 S example, for conducting heat from the proximal evaporator end to the
distal condenser
end of the flexible heat pipe pusher member and to the shape memory collar at
the
distal end of the pusher member, to thus heat the collar to return to its
previous shape
and induce the collar to detach the therapeutic device from the shape memory
collar.
Heating of the collar can at the same time heat the therapeutic device to
cause the
therapeutic device to change to a desired configuration.
Referring to Figs. 3 and 4, in a second preferred embodiment, the
intravascular delivery system 10' comprises an elongated, flexible heat pipe
pusher
member 12', having a distal tip 14', and a therapeutic device, such as a coil
16',
having at least one configuration which may serve as a vasooclusive coil or a
stmt, for
example, to be placed within the vasculature of a patient.
In the second preferred embodiment, the shape memory collar 18' can be
disposed on the stem 20' of the therapeutic device, and is adapted to be
crimped and
thus detachably mounted to the distal end 14' of the flexible heat pipe pusher
member,
CA 02441396 2003-09-11
12
for placement of the therapeutic device within the vasculature. The shape
memory
collar is preferably tubular, having a closed configuration or narrowed
configuration
with a relatively smaller inner diameter as shown in Fig. 3, connecting the
therapeutic
device to the flexible heat pipe pusher member, and an open configuration,
with a
relatively larger inner diameter as shown in Fig. 4, for detaching and
deploying the
therapeutic device from the flexible heat pipe pusher member when a desired
placement of the therapeutic device within the vasculature is achieved. The
shape
memory collar is preferably heat treated in an unextended position, and can be
heated
to a temperature that allows it to be worked and crimped into an extended
position
gripping over the end of the stem of the wire coil to connect the therapeutic
device to
a flexible heat pipe pusher member of the placement catheter shaft.
The elongated, flexible heat pipe pusher member preferably comprises a
flexible heat pipe 22' or rod, having a hollow interior chamber 24' that has
been
evacuated, filled with a small amount of a working fluid, and then sealed. The
flexible
1 S heat pipe has a metal evaporator end portion 26' for conducting heat to
the working
fluid in the interior chamber of the heat pipe, a flexible insulated mid-
portion 28', and
a metal condenser end portion 30' for conducting heat from the working fluid
to the
shape memory device. The insulated mid-portion preferably has an outer
covering 32'
of flexible, resinous material so that the mid-portion does not radiate heat.
The
flexible heat pipe typically is formed from a hollow metal tube 34', and in a
presently
preferred embodiment, the hollow metal tube is made of an alloy of beryllium
and
copper. The evaporator end portion preferably comprises a stainless steel
portion 35'
for conducting heat to the metal hollow tube and the working fluid in the
interior
chamber of the heat pipe, and the stainless steel evaporator end portion can
be formed
from a ground stainless steel hypo tube. The condenser end portion is
preferably
partially covered with a coating 36' of PTFE, leaving a distal end portion 38'
of the
condenser end portion exposed to transfer heat to the shape memory collar.
The proximal evaporator end of the flexible heat pipe pusher member can
CA 02441396 2003-09-11
13
be connected to a heat source 40', such as an RF heat source or ultrasound
heat source,
for example, for conducting heat from the proximal evaporator end to the
distal
condenser end of the flexible heat pipe pusher member and to the shape memory
collar
at the distal end of the pusher member, to thus heat the collar to return to
its previous
S shape and induce the collar to detach the therapeutic device from the shape
memory
collar.
In a presently preferred embodiment, the shape memory collar is formed
from a shape memory material such as nickel titanium alloy, that can be heat
treated
to have shape memory behavior, such that the alloy has a desired closed
configuration
at a temperature appropriate for introduction into the body, and after
placement, the
collar wilt take on a more open shape for detaching the therapeutic device
from the
flexible, heat pipe pusher member. Those skilled in the art will recognize
that the
invention can also be used with a variety of other placement catheter systems,
and it
is not intended that the invention be limited to the placement concepts
illustrated by
way of example.
In another presently preferred embodiment, the invention is embodied in
an apparatus for deployment of a therapeutic device such as a micro-coil using
a
catheter by connecting the therapeutic device to a distal portion of a pusher
member
by a connector fiber that can be broken by heating a portion of the connector
fiber to
break the connector fiber and thereby release the therapeutic device for
placement in
the vasculature.
With reference to Figs. 5-8, the invention accordingly provides for an
apparatus 140 including an elongated, flexible pusher member 142 for release
and
deployment of a therapeutic device 144 such as a vasoocclusive device, which
may for
example be a microcoil, only a portion of which is shown, within the
vasculature of
a patient, through a delivery catheter 146. The pusher member has a shaft 147
that
provides a measure of thermal insulation to an interior lumen 148, as will be
further
explained below. The shaft of the pusher member typically has an outer
diameter of
CA 02441396 2003-09-11
14
approximately 0.01 S", and an inside diameter of approximately .007, and can
be
formed from polyethylene terephthalate (PET) tubing. The pusher member has a
distal
portion 150 with entry ports 152 in communication with the interior lumen, and
a plug
154 at the distal end of the pusher member, typically secured within the
distal end of
S the pusher member by adhesive, such as a cyanoacrylate adhesive, for
example.
The therapeutic device is typically connected to a stem 156 such as by
solder 158, and the stem is in turn connected to an annular connector ring
160,
typically by an adhesive such as a cyanoacrylate adhesive, for example. The
therapeutic device is mounted and secured to the distal portion of the pusher
member
by an elongated connector thread or fiber 162 extending from a proximal
portion of
the pusher member to form a loop 164 through the connector ring, and extending
back
through the entry ports of the pusher member to the proximal portion of the
pusher
member. In a presently preferred embodiment, the connector fiber is formed of
polyethylene, and is typically about 0.015 to 0.030 inches in diameter,
although the
1 S connector fiber can be as thin as about 0.0005 inches in diameter, and can
be formed
from a variety of thermoplastic materials with high tensile strength and
suitable melt
temperatures. The connector fiber may also optionally be formed of a suitable
high
tensile strength material, such as a biodegradable material, for example, that
would
merely degrade or decompose to break upon being heated.
A portion of the connector fiber to be broken to deploy the therapeutic
device passes adjacent to the distal heating end 166 of an elongated, flexible
heat pipe
member I68, such as described above. The elongated, flexible heat pipe member
preferably comprises a flexible heat pipe 170 or rod, having a hollow interior
chamber
172 that has been evacuated, filled with a small amount of a working fluid,
and then
sealed. The flexible heat pipe has a metal evaporator end portion 174 for
conducting
heat to the working fluid in the interior chamber of the heat pipe, a flexible
insulated
mid-portion 176, and a metal condenser end portion at the distal heating end
166 for
conducting heat from the working fluid to the shape memory device. The
insulated
CA 02441396 2003-09-11
mid-portion preferably has an outer covering 180 of flexible, resinous
material so that
the mid-portion does not radiate heat. The flexible heat pipe typically is
formed from
a hollow metal tube 182, and in a presently preferred embodiment, the hollow
metal
tube is made of an alloy of beryllium and copper. The evaporator end portion
S preferably comprises a stainless steel portion 184 for conducting heat to
the metal
hollow tube and the working fluid in the interior chamber of the heat pipe,
and the
stainless steel evaporator end portion can be formed from a ground stainless
steel hypo
tube. The proximal evaporator end of the flexible heat pipe member can be
connected
to a heat source 185, as noted above. The condenser end portion is preferably
partially
10 covered with polytetrafluoroethylene (PTFE) 186, leaving the distal heating
end
portion of the condenser end portion exposed to transfer heat to cause the
connector
fiber to break and release the therapeutic device. The lumen of the pusher
member
advantageously provides an insulative space and wall thickness to contain the
heating
of the connector fiber to avoid thermal damage to surrounding tissues, and to
help
15 contain pieces of the connector fiber that may be formed during heating of
the
connector fiber to deploy the therapeutic device.
It will be apparent from the foregoing that while particular forms of the
invention have been illustrated and described, various modifications can be
made
without departing from the spirit and scope of the invention. Accordingly, it
is not
intended that the invention be limited, except as by the appended claims.
