U.S. patent application number 09/851850 was filed with the patent office on 2001-08-30 for co-extruded, multi-lumen medical lead.
This patent application is currently assigned to Medtronic, Inc.. Invention is credited to Borgersen, Svenn E., Kramer, Hans W..
Application Number | 20010018607 09/851850 |
Document ID | / |
Family ID | 23035852 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010018607 |
Kind Code |
A1 |
Borgersen, Svenn E. ; et
al. |
August 30, 2001 |
Co-extruded, multi-lumen medical lead
Abstract
Medical electrical leads for sensing or electrical stimulation
of body organs or tissues, particularly implantable cardiac leads
for delivering pacing pulses and cardioversion/defibrillation
shocks, and/or sensing the cardiac electrogram (EGM) or other
physiologic data and their methods of fabrication are disclosed. A
lead body sheath is co-extruded in a co-extrusion process using
biocompatible, electrically insulating, materials of differing
durometers in differing axial sections thereof, resulting in a
unitary lead body sheath having differing stiffness sections
including axial segments or webs or lumen encircling rings or other
structures in its cross-section. The lead body sheath is
co-extruded to have an outer surface adapted to be exposed to the
environment or to be enclosed within an outer sheath and to have a
plurality of lead conductor lumens for receiving and enclosing a
like plurality of lead conductors of the same or differing types.
The lead body sheath can be co-extruded of a plurality of sheath
segments containing a lead conductor lumen and formed of a first
durometer material or of differing durometer materials. A web of a
further durometer material can be co-extruded extending between the
adjoining boundaries of the axial sheath segments and bonding the
adjacent segments together. The lead body sheath can be tailored to
exhibit differing bending stiffnesses away from the lead body
sheath axis in selected polar directions around the 360.degree.
circumference of the sheath body.
Inventors: |
Borgersen, Svenn E.; (Eagan,
MN) ; Kramer, Hans W.; (Temucula, CA) |
Correspondence
Address: |
GIRMA WOLDE-MICHAEL
Medtronic, Inc., MS 301
7000 Central Avenue NE
Minneapolis
MN
55432
US
|
Assignee: |
Medtronic, Inc.
|
Family ID: |
23035852 |
Appl. No.: |
09/851850 |
Filed: |
May 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09851850 |
May 9, 2001 |
|
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09271498 |
Mar 18, 1999 |
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Current U.S.
Class: |
607/121 |
Current CPC
Class: |
A61N 1/056 20130101;
A61N 1/05 20130101 |
Class at
Publication: |
607/121 |
International
Class: |
A61N 001/05 |
Claims
1. In a medical electrical lead for implantation within the living
body of the type comprising an elongated lead body enclosing a
plurality of lead conductors each extending between a distal a
distal electrode or sensor element and a proximal connector
element, the improvement in the lead body comprising: an elongated
lead body sheath having an outer sheath surface that is formed of a
plurality of axial sheath segments each co-extruded of a
bio-compatible, electrically insulating, material, the plurality of
axial sheath segments extending in side by side relation through
the length of the lead body and bonded together at adjoining
segment boundaries; a like plurality of elongated lead conductor
lumens formed in and extending the length of each lead body sheath
segment to be enclosed thereby; and a like plurality of electrical
lead conductors, each lead conductor extending through a lead
conductor lumen.
2. The medical electrical lead of claim 1, wherein at least two of
the axial sheath segments are formed of materials of differing
durometers.
3. The medical electrical lead of claim 2, wherein at least two of
the lead conductors have differing bending stiffnesses.
4. The medical electrical lead of claim 1, wherein said plurality
of lead conductors comprises a first lead conductor having a first
bending stiffness that differs from the stiffnesses of the
remaining lead conductors of the plurality of lead conductors; and
said plurality of axial sheath segments comprises a first axial
sheath segment having a first leaden receiving the first lead
conductor, the first axial segment formed of a material having a
hardness that is correlated to the first bending stiffness.
5. The medical electrical lead of claim 1, wherein each one of said
plurality of lead conductors have a bending stiffness that differs
from the bending stiffnesses of the remaining lead conductors of
the plurality of lead conductors; and each one of said plurality of
axial sheath segments are formed of a material having a hardness
that is correlated to the bending stiffness of the lead conductor
received in the lead conductor lumen of the axial sheath
segment.
6. The medical electrical lead of claim 1, further comprising a
further lumen formed centrally in said lead body sheath.
7. The medical electrical lead of claim 6, wherein at least two of
the axial sheath segments are formed of materials of differing
durometers.
8. The medical electrical lead of claim 7, wherein at least two of
the lead conductors have differing bending stiffnesses.
9. The medical electrical lead of claim 6, wherein said plurality
of lead conductors comprises a first lead conductor having a first
bending stiffness that differs from the stiffnesses of the
remaining lead conductors of the plurality of lead conductors; and
said plurality of axial sheath segments comprises a first axial
sheath segment having a first lead lumen receiving the first lead
conductor, the first axial segment formed of a material having a
hardness that is correlated to the first bending stiffness.
10. The medical electrical lead of claim 6, wherein each one of
said plurality of lead conductors have a bending stiffness that
differs from the bending stiffnesses of the remaining lead
conductors of the plurality of lead conductors; and each one of
said plurality of axial sheath segments are formed of a material
having a hardness that is correlated to the bending stiffness of
the lead conductor received in the lead conductor lumen of the
axial sheath segment.
11. The medical electrical lead of claim 1, further comprising a
tubular member enclosing a further lumen formed centrally in said
lead body sheath.
12. The medical electrical lead of claim 11, wherein at least two
of the axial sheath segments are formed of materials of differing
durometers.
13. The medical electrical lead of claim 12, wherein at least two
of the lead conductors have differing bending stiffnesses.
14. The medical electrical lead of claim 11, wherein said plurality
of lead conductors comprises a first lead conductor having a first
bending stiffness that differs from the stiffnesses of the
remaining lead conductors of the plurality of lead conductors; and
said plurality of axial sheath segments comprises a first axial
sheath segment having a first lead lumen receiving the first lead
conductor, the first axial segment formed of a material having a
hardness that is correlated to the first bending stiffness.
15. The medical electrical lead of claim 11, wherein each one of
said plurality of lead conductors have a bending stiffness that
differs from the bending stiffnesses of the remaining lead
conductors of-the plurality of lead conductors; and each one of
said plurality of axial sheath segments are formed of a material
having a hardness that is correlated to the bending stiffness of
the lead conductor received in the lead conductor lumen of the
axial sheath segment.
16. In a medical electrical lead for implantation within the living
body of the type comprising an elongated lead body enclosing a
plurality of lead conductors each extending between a distal a
distal electrode or sensor element and a proximal connector
element, the improvement in the lead body comprising: an elongated
lead body sheath having an outer sheath surface that is formed of a
plurality of axial sheath segments each co-extruded of a
biocompatible, electrically insulating, material, the plurality of
axial sheath segments extending in side by side relation through
the length of the lead body; and a web co-extruded of a further
biocompatible, electrically insulating, material extending between
and bonded with adjoining boundaries of each axial sheath segment;
a like plurality of elongated lead conductor lumens formed in and
extending the length of each lead body sheath segment to be
enclosed thereby; and a like plurality of electrical lead
conductors, each lead conductor extending through a lead conductor
lumen.
17. The medical electrical lead of claim 16, wherein at least two
of the axial sheath segments are formed of materials of differing
durometers.
18. The medical electrical lead of claim 17, wherein at least two
of the lead conductors have differing bending stiffnesses.
19. The medical electrical lead of claim 16, wherein said plurality
of lead conductors comprises a first lead conductor having a first
bending stiffness that differs from the stiffnesses of the
remaining lead conductors of the plurality of lead conductors; and
said plurality of axial sheath segments comprises a first axial
sheath segment having a first lead lumen receiving the first lead
conductor, the first axial segment formed of a material having a
hardness that is correlated to the first bending stiffness.
20. The medical electrical lead of claim 16, wherein each one of
said plurality of lead conductors have a bending stiffness that
differs from the bending stiffnesses of the remaining lead
conductors of the plurality of lead conductors; and each one of
said plurality of axial sheath segments are formed of a material
having a hardness that is correlated to the bending stiffness of
the lead conductor received in the lead conductor lumen of the
axial sheath segment.
21. The medical electrical lead of claim 16, further comprising a
further lumen formed centrally in said lead body sheath.
22. The medical electrical lead of claim 21, wherein at least two
of the axial sheath segments are formed of materials of differing
durometers.
23. The medical electrical lead of claim 22, wherein at least two
of the lead conductors have differing bending stiffnesses.
24. The medical electrical lead of claim 21, wherein said plurality
of lead conductors comprises a first lead conductor having a first
bending stiffness that differs from the stiffnesses of the
remaining lead conductors of the plurality of lead conductors; and
said plurality of axial sheath segments comprises a first axial
sheath segment having a first lead lumen receiving the first lead
conductor, the first axial segment formed of a material having a
hardness that is correlated to the first bending stiffness.
25. The medical electrical lead of claim 21, wherein each one of
said plurality of lead conductors have a bending stiffness that
differs from the bending stiffnesses of the remaining lead
conductors of the plurality of lead conductors; and each one of
said plurality of axial sheath segments are formed of a material
having a hardness that is correlated to the bending stiffness of
the lead conductor received in the lead conductor lumen of the
axial sheath segment.
26. The medical electrical lead of claim 16, further comprising a
tubular member coupled to said web and enclosing a further lumen
formed centrally in said lead body sheath.
27. The medical electrical lead of claim 26, wherein at least two
of the axial sheath segments are formed of materials of differing
durometers.
28. The medical electrical lead of claim 27, wherein at least two
of the lead conductors have differing bending stiffnesses.
29. The medical electrical lead of claim 26, wherein said plurality
of lead conductors comprises a first lead conductor having a first
bending stiffness that differs from the stiffnesses of the
remaining lead conductors of the plurality of lead conductors; and
said plurality of axial sheath segments comprises a first axial
sheath segment having a first lead lumen receiving the first lead
conductor, the first axial segment formed of a material having a
hardness that is correlated to the first bending stiffness.
30. The medical electrical lead of claim 26, wherein each one of
said plurality of lead conductors have a bending stiffness that
differs from the bending stiffnesses of the remaining lead
conductors of the plurality of lead conductors; and each one of
said plurality of axial sheath segments are formed of a material
having a hardness that is correlated to the bending stiffness of
the lead conductor received in the lead conductor lumen of the
axial sheath segment.
31. A method of manufacturing the lead body of a medical electrical
lead for implantation within the living body of the type comprising
an elongated lead body enclosing a plurality of lead conductors
each extending between a distal a distal electrode or sensor
element and a proximal connector element, the method comprising the
steps of: co-extruding a plurality of axial sheath segments of a
bio-compatible, electrically insulating, material each with a lead
conductor lumen into an elongated lead body sheath that is formed
of the plurality of axial sheath segments extending in side by side
relation through the length of the lead body and bonded together at
adjoining boundaries and enclosing a like plurality of elongated
lead conductor lumens; and fitting each one of a like plurality of
electrical lead conductors through a lead conductor lumen.
32. The method of claim 31, wherein the co-extruding step further
comprises the step of co-extruding at least two of the axial sheath
segments of materials of differing hardness.
33. The method of claim 32, wherein at least two of the lead
conductors have differing bending stiffnesses.
34. The method of claim 31, wherein said plurality of lead
conductors comprises a first lead conductor having a first bending
stiffness that differs from the stiffnesses of the remaining lead
conductors of the plurality of lead conductors; and wherein the
co-extruding step further comprises the step of co-extruding said
plurality of axial sheath segments with a first axial sheath
segment having a first lead lumen receiving the first lead
conductor, the first axial segment formed of a material having a
hardness that is correlated to the first bending stiffness.
35. The method of claim 31, wherein each one of said plurality of
lead conductors have a bending stiffness that differs from the
bending stiffnesses of the remaining lead conductors of the
plurality of lead conductors; and wherein the co-extruding step
further comprises the step of co-extruding each one of said
plurality of axial sheath segments of a material having a hardness
that is correlated to the bending stiffness of the lead conductor
received in the lead conductor lumen of the axial sheath
segment.
36. The method of claim 31, wherein the co-extruding step further
comprises the step of co-extruding a further lumen centrally in
said lead body sheath.
37. A method of manufacturing the lead body of a medical electrical
lead for implantation within the living body of the type comprising
an elongated lead body enclosing a plurality of lead conductors
each extending between a distal a distal electrode or sensor
element and a proximal connector element, the method comprising the
steps of: co-extruding a plurality of axial sheath segments of a
bio-compatible, electrically insulating, material each with a lead
conductor lumen together with a web of a further bio-compatible,
electrically insulating, material extending between adjoining
boundaries of each axial sheath segment into an elongated lead body
sheath that is formed of the plurality of axial sheath segments
extending in side by side relation through the length of the lead
body and bonded together at adjoining boundaries by the web and
enclosing a like plurality of elongated lead conductor lumens; and
fitting each one of a like plurality of electrical lead conductors
through a lead conductor lumen.
38. The method of claim 37, wherein the co-extruding step further
comprises the step of co-extruding at least two of the axial sheath
segments of materials of differing hardness.
39. The method of claim 38, wherein at least two of the lead
conductors have differing bending stiffnesses.
40. The method of claim 37, wherein said plurality of lead
conductors comprises a first lead conductor having a first bending
stiffness that differs from the stiffnesses of the remaining lead
conductors of the plurality of lead conductors; and wherein the
co-extruding step further comprises the step of co-extruding said
plurality of axial sheath segments with a first axial sheath
segment having a first lead lumen receiving the first lead
conductor, the first axial segment formed of a material having a
hardness that is correlated to the first bending stiffness.
41. The method of claim 37, wherein each one of said plurality of
lead conductors have a bending stiffness that differs from the
bending stiffnesses of the remaining lead conductors of the
plurality of lead conductors; and wherein the co-extruding step
further comprises the step of co-extruding each one of said
plurality of axial sheath segments of a material having a hardness
that is correlated to the bending stiffness of the lead conductor
received in the lead conductor lumen of the axial sheath
segment.
42. The method of claim 37, wherein the co-extruding step further
comprises the step of co-extruding a further lumen centrally in
said lead body sheath.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Reference is hereby made to commonly assigned, U.S. patent
application Ser. No. 08/990,647 filed Dec. 15, 1997, for MEDICAL
ELECTRICAL LEAD in the name of Alan Rausch et al.
FIELD OF THE INVENTION
[0002] The present invention relates to medical electrical leads
for sensing or electrical stimulation of body organs or tissues and
their method of fabrication, such leads having multiple electrical
conductors encased in a lead body, and particularly to implantable
cardiac leads for delivering electrical stimulation to the heart,
e.g., pacing pulses and cardioversion/defibrillation shocks, and/or
sensing the cardiac electrogram (EGM) or other physiologic
data.
BACKGROUND OF THE INVENTION
[0003] Implantable medical electrical stimulation and/or sensing
leads are well known in the fields of cardiac stimulation and
monitoring, including cardiac pacing and
cardioversion/defibrillation, and in other fields of electrical
stimulation or monitoring of electrical signals or other
physiologic parameters of the body. A pacemaker or
cardioverter/defibrillator implantable pulse generator (IPG) or a
cardiac monitor is typically coupled to the heart through one or
more of such endocardial leads. The proximal end of such leads
typically is formed with a connector which connects to a terminal
of the IPG or monitor. The lead body typically comprises one or
more insulated, conductive wire surrounded by an insulating outer
sleeve. Each conductive wire couples a proximal lead connector
element with a distal stimulation and/or sensing electrode. An
endocardial cardiac lead having a single stimulation and/or sensing
electrode at the distal lead end and a single conductive wire is
referred to as a unipolar lead. An endocardial cardiac lead having
two or more stimulation and/or sensing electrodes at the distal
lead end and two or more conductive wires is referred to as a
bipolar lead or a multi-polar lead, respectively.
[0004] In order to implant an endocardial lead within a heart
chamber, a transvenous approach is utilized wherein the lead is
inserted into and passed through a pathway comprising the
subclavian, jugular, or cephalic vein and through the superior vena
cava into the right atrium or ventricle. It is necessary to
accurately position the sense and/or stimulation electrode surface
against the endocardium or within the myocardium at the desired
site in order to achieve reliable sensing of the cardiac
electrogram and/or to apply stimulation that effectively paces or
cardioverts the heart chamber. The desired heart sites include the
right atrium, typically the right atrial appendage, the right
ventricle, typically the ventricular apex, and the coronary sinus
and great vein.
[0005] The transvenous pathway can include a number of twists and
turns, and the lead body can be forced against bony structures of
the body that apply stress to it. Moreover, the heart beats
approximately 100,000 times per day or over 30 million times a
year, and each beat stresses at least the distal portion of the
lead body. The lead conductors and insulation are subjected to
cumulative mechanical stresses, as well as material reactions as
described below, that can result in degradation of the insulation
or fractures of the lead conductors with untoward effects on device
performance and patient well being.
[0006] Early implantable, endocardial and epicardial, bipolar
cardiac pacing leads employed separate coiled wire conductors in a
side by side configuration within a silicone rubber sheath and
incorporated a lumen for receiving a stiffening stylet inside the
lumen of at least one of the conductor coils to facilitate
advancement through the transvenous pathway. The stiffening stylet
was advanced through a proximal connector pin opening to stiffen
the lead body during the transvenous introduction and location of
the distal electrodes deeply inserted into the right ventricular
apex and was then withdrawn. The relatively large diameter and
stiff lead body provided column strength that was relied upon to
maintain the distal electrodes embedded into the trabeculae of the
right ventricular apex. Fibrous tissue growth about the distal lead
body was also relied upon to hold the distal pace/sense electrodes
in position.
[0007] Similar atrial, J-shaped lead bodies were developed that
relied upon the lead body stiffness and shape to lodge and maintain
distal pace/sense electrodes lodged into the right atrial appendage
after the stiffening stylet was removed from the lead conductor
lumen. In the case of early J-shaped atrial leads formed of
silicone rubber, the lead body was reinforced with an outward
extending silicone rubber rib to maintain the J-shape bend when the
stylet was removed. In later J-shaped atrial leads, internally
encased metal coils or wires have been employed to maintain the
J-shape bend.
[0008] Such relatively large and stiff lead bodies were
disadvantageous in a number of respects. The available
bio-compatible conductor material alloy presented an impedance that
limited current carrying capacity. The large diameter body made it
difficult to implant more than one lead through the venous system.
The relatively high column strength was often still insufficient to
maintain the pace/sense electrodes in the atrial appendage or
ventricular apex, and physicians often resorted to leaving the
stylets in place, resulting in fracture of the lead conductor and
lead body sheath when the stylet wire broke. Once the lead bodies
fibrosed in, they were difficult to retract from the heart if they
needed to be replaced. Finally, the lead conductors tended to
fracture at stress sites, in bipolar leads sometimes due to
stresses applied unevenly to the side-by-side arrangement of the
conductor coils.
[0009] In the efforts to solve these problems, more flexible lead
bodies were developed using smaller diameter coiled wire conductors
and other insulating materials, most notably polyurethane
compositions. Passive and active fixation mechanisms incorporated
were into the distal end of the endocardial lead to fix the
electrode at a desired site in a heart chamber during the acute
postoperative phase before fibrous tissue growth envelops the lead
body. Passive fixation mechanisms, e.g., a plurality of soft,
pliant tines that bear against the trabeculae in the right
ventricle or the atrial appendage to urge the distal tip electrode
against the endocardium, do not invade the myocardium. Active
fixation mechanisms are designed to penetrate the endocardial
surface and lodge in the myocardium without perforating through the
epicardium or into an adjoining chamber. The most widely used
active fixation mechanism employs a sharpened helix, which
typically also constitutes the distal tip electrode, that is
adapted to be rotated by some means from the proximal end of the
lead outside the body in order to screw the helix into the
myocardium and permanently fix the electrode at the desired atrial
or ventricular site.
[0010] The side by side, bipolar, coiled wire lead body design was
also replaced by a coaxial configuration which is more resistant to
fracture and smaller in diameter and which was typically formed of
polyurethane or silicone rubber inner and outer sheathes. More
recently, each such coiled wire conductor of both unipolar and
bipolar leads was formed of a plurality of multi-filar,
parallel-wound, coiled wire conductors electrically connected in
common in an electrically redundant fashion as shown in commonly
assigned U.S. Pat. No. 5,007,435, for example, incorporated herein
by reference. Such redundant coiled wire conductors of bipolar and
multi-polar lead bodies are coaxially arranged about the stiffening
stylet receiving lumen and insulated from one another by coaxially
arranged insulating sheaths separating each coiled wire conductor
from the adjacent coiled wire conductor(s).
[0011] In the implantation of a cardiac device of the types listed
above, and in the replacement of previously implanted cardiac
leads, two or more transvenous cardiac leads are typically
introduced through the venous system into the right chambers or
coronary sinus of the heart. It has long been desired to minimize
the diameter of the transvenous cardiac lead body to facilitate the
introduction of several cardiac leads by the same transvenous
approach. Moreover, a number of multi-polar, endocardial cardiac
leads have been designed to accommodate more than two electrodes or
to make electrical connection with other components, e.g., blood
pressure sensors, temperature sensors, pH sensors, or the like, in
the distal portion of the lead. In addition, endocardial
cardioversion/defibrillation leads were developed for unipolar or
bipolar pacing and sensing functions and for delivering
cardioversion/defibrillat- ion shocks to a heart chamber intended
to be implanted in a heart chamber or a cardiac blood vessel, e.g.,
the coronary sinus. The increased number of separate polarity and
insulated coiled wire conductors is difficult to accommodate in the
conventional coaxial coiled wire conductor winding arrangement
having a desired, small, lead body outer diameter. One approach
involved the use of separately insulated, coiled wire conductors
that are parallel-wound with a common diameter and are separately
coupled between a proximal connector element and to a distal
electrode or terminal as disclosed in commonly assigned U.S. Pat.
No. 5,796,044, incorporated herein by reference.
[0012] Moreover, the use of thin polyurethane inner and outer
sheathes along with certain lead conductor alloys became
problematic as the bio-stability of such lead materials in chronic
implantation came into question as described in commonly assigned
U.S. Pat. No. 5,419,921. In general, it is acknowledged that there
are a number of mechanisms for degradation of elastomeric
polyurethane pacing leads in vivo. One is environmental stress
cracking (ESC), the generation of crazes or cracks in the
polyurethane elastomer produced by the combined interaction of a
medium capable of acting on the elastomer and a stress level above
a specific threshold. Another is metal ion induced oxidation (MIO)
in which polyether urethane elastomers exhibit accelerated
degradation from metal ions such as cobalt ions, chromium ions,
molybdenium ions and the like which are used alone or in alloys in
pacing lead conductors. As explained therein, certain polyurethane
elastomers that have desirable characteristics for lead bodies are
more susceptible to ESC and MIO degradation than others that are
less desirable. In the '921 patent, the polyurethane elastomers
that are susceptible to ESC and MIO degradation are coated or
co-extruded with the less susceptible polyurethane elastomers to
form tubular sheaths having their inner and outer surfaces
protected by a less susceptible material layer.
[0013] All of the above considerations as to the increased
complexity of the leads, the number of leads implanted in a common
path, and desire to advance leads deep in the relatively small
diameter coronary veins have led to efforts to at least not
increase and optimally to decrease the overall diameter of the
cardiac lead body without sacrificing bio-stability, resistance to
crushing forces, and usability. It has been proposed to diminish
the lead body further by eliminating the lumen for receiving the
stiffening stylet and by replacing the large diameter coiled wire
conductors with highly conductive miniaturized coiled wire
conductors, stranded filament wires, or cables formed of a
plurality of such stranded filament wires. In bipolar or
multi-polar leads, each such wire or cable extends through a
separate lumen extending in parallel within a lead body sheath that
maintains electrical isolation between them.
[0014] Examples of such lead body insulating sheaths formed to
enclose a plurality of straight, typically stranded, wire lead
conductors, miniaturized coiled wire conductors or combinations of
such straight and coiled wire conductors are disclosed in U.S. Pat.
Nos. 4,608,986, 5,324,321, 5,545,203, and 5,584,873, all
incorporated herein by reference. These patents and U.S. Pat. Nos.
4,640,983, 4,964,414, 5,246,014, 5,483,022, and 5,760,341, all
incorporated herein by reference, present a number of alternative
designs of such stranded filament wires or cables.
[0015] In the '873 patent, a unitary lead body insulating sheath is
extruded having a plurality of spaced apart, outer lead conductor
lumens that extend longitudinally and in parallel to one another
for receiving coiled and/or straight wire conductors extending
therethrough. The sheath is extruded in a single piece of a single
material, and a like plurality of compression lumens that are
preferably tear drop shaped are formed and extend longitudinally
between the conductor lumens that absorb compression force that
otherwise would crush a solid extruded lead body sheath. In certain
embodiments an inner, centrally disposed lumen is formed in the
lead body sheath that can be employed as a lead conductor lumen or
as a compression lumen that can be made large enough in diameter to
receive a stiffening stylet during introduction of the lead.
[0016] The above-referenced U.S. patent application Ser. No.
08/990,647 discloses a lead body sheath formed of separate parts
including an extruded strut member or core and a separately
extruded tubular outer tube. The core is extruded to form a
plurality of longitudinally extending grooves in which lead
conductors may be located and the assembly of the core and lead
conductors is fitted within the lumen of the outer tube which
thereby encloses the core and holds the conductors in the grooves.
This construction simplifies the manufacture of the lead bodies, as
it allows the conductors simply to be laid in the elongated grooves
of the core rather than requiring that they be pushed or pulled
along the lengths of pre-formed lumens. In some embodiments, the
core is provided with a central, reinforcing strand, extending
along the length of the lead body, providing for structural
integrity and high tensile strength. The core may be manufactured
as a single extrusion, extending the entire length of the lead
body, or may take the form of sequentially aligned multiple
extrusions of differing materials to provide for differential
stiffness along the length of the lead.
[0017] In all of these lead body designs, the adjacent conductor
lumens are separated from one another by very thin webs of the
extruded insulating material. Despite these improvements, the
cumulative affects of applied bending stresses can cause the
extruded insulation webs of the lead body to split, thereby
allowing the adjacent lead conductors to contact one another and to
short-circuit the electrodes they are connected with. Each
conductor lumen except for a centrally disposed conductor lumen is
also separated from the outer surface of the insulating body sheath
by a thin web. This outer thin web can also split, exposing the
conductor to body fluids and tissues. The loss of support of the
lead conductors upon splitting of the lead body sheath webs can
also result in excessive bending and eventual fracture of the
conductor. This problem is exacerbated when lead conductors of
differing types each having a differing bending stiffness are
enclosed in the outer lead conductor lumens leading to a lead body
that is more flexible when bent in one direction than when bent in
another direction.
SUMMARY OF THE INVENTION
[0018] The present invention addresses these problems by forming a
lead body comprising an electrically insulating lead body sheath
enclosing one or more lead conductors and separating the lead
conductors from contacting one another. The lead body sheath is
co-extruded in a co-extrusion process using bio-compatible,
electrically insulating, materials of differing durometers in
differing axial sections thereof, resulting in a unitary lead body
sheath having differing stiffness axial sections including axial
segments or webs or lumen encircling rings or other structures in
its cross-section. The selection of the durometer of the materials
and the configuration of the co-extruded lead body sheath sections
may be used to control the geometric properties--e.g. bending
stiffness, torsional stiffness, axial tension-compression
stiffness, shear stiffness, and transverse compression stiffness of
the lead body sheath. The lead body sheath is co-extruded to have
an outer surface adapted to be exposed to the environment or to be
enclosed within a further outer sheath and to have a plurality of
lead conductor lumens for receiving and enclosing a like plurality
or a fewer number of lead conductors.
[0019] In one embodiment, the lead body is co-extruded of a
plurality of sheath segments, each segment containing a lead
conductor lumen and formed of a first durometer material, and of a
web of a second durometer material extending between the adjoining
boundaries of the sheath segments. The web bonds with the adjacent
segment boundaries to form the unitary lead body insulating sheath.
The web may be formed by co-extrusion of a higher durometer
material than the first durometer material.
[0020] In a further embodiment, the lead body sheath is co-extruded
of a plurality of sheath segments, wherein each sheath segment
contains a lead conductor lumen and is formed of a selected
durometer material, whereby the lead body sheath can be tailored to
exhibit differing bending stiffness away from the lead body sheath
axis in selected polar directions around the 360.degree.
circumference of the sheath body.
[0021] This embodiment is particularly suitable for use with lead
conductors of differing types that have differing bending
stiffnesses. In one application of this embodiment, the durometer
of the sheath segments are selected in relation to the lead
conductor to compensate for the lead conductor bending stiffness.
For example, relatively stiff lead conductors can be enclosed in
segment lumens formed within segments of relatively low stiffness
due to relatively low durometer materials, whereas relatively
flexible lead conductors can be enclosed in segment lumens formed
within segments of relatively high stiffness due to relatively high
durometer materials. In this way, the bending stiffness of the lead
body in all polar directions through 360.degree. can be brought
into equilibrium.
[0022] In a further application of this embodiment, it may be
desired to form a lead body that does exhibit a bias to bend more
readily in one polar direction than in the other directions. In
this case, one of the sheath segments can be co-extruded of a more
flexible material than the other sheath segments, and can enclose a
relatively flexible lead conductor within that sheath segment
lumen.
[0023] In a third embodiment, the web of the first embodiment and
the differing stiffness sheath segment materials of the second
embodiment can be advantageously combined. In this way, additional
control of cross section geometric properties may be achieved by
the use of different durometer materials not only for the
sheath/webs, but also for each sheath segment around the cross
section of extruded lead body material containing the lumens.
[0024] The sheath segments are preferably shaped as arcuate
sections of the generally circular cross-section insulating sheath,
and each preferably encloses a single lead conductor lumen. In a
fourth embodiment, a centrally located lead conductor and/or
stiffening stylet receiving lumen can also be formed of the same or
differing durometer material as the sheath segments of the first or
second embodiment or surrounded by the web material of the first or
third embodiment.
[0025] In these embodiments of the invention, the adjoining
boundaries of the longitudinally extending sheath segments with one
another or with an intervening web are in intimate physical contact
and bonded with one another in the co-extrusion process.
[0026] Thus, the co-extruded lead body sheath may be constructed in
a variety of ways and may or may not be enclosed in a co-extruded
outer sheath. The lead body sheath may contain a plurality of
lumens either empty or containing electrical conductors, with or
without a co-extruded sheaths surrounding each lumen. The lead body
sheath may be co-extruded in sheath segments, sheath each segment
connected by a radially oriented co-extruded sheath of various
geometries which may or may not contact sheaths lining the
lumens.
[0027] The co-extrusion of lead body sheath allows for selectivel
control of lead body stiffness for bending, torsion, axial tension
or compression, shear and transverse compression over the full
length of the lead body or for a localized portion of the lead body
length. Moreover, it allows the sheath segments and/or webs to act
as barriers to prevent crack propagation in the lead body sheath
which might lead to electrical contact between the lead conductors
producing a short or incorrect signals, or cracking to the outer
surface allowing the electrical lead conductors to be damaged by
exposure to body fluids.
[0028] This summary of the invention and the advantages and
features thereof have been presented here simply to point out some
of the ways that the invention overcomes difficulties presented in
the prior art and to distinguish the invention from the prior art
and is not intended to operate in any manner as a limitation on the
interpretation of claims that are presented initially in the patent
application and that are ultimately granted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] These and other advantages and features of the present
invention will be more readily understood from the following
detailed description of the preferred embodiments thereof, when
considered in conjunction with the drawings, in which like
reference numerals indicate identical structures throughout the
several views, and wherein:
[0030] FIG. 1 is a schematic illustration of a typical implantation
of an IPG and endocardial lead system in which the lead conductor
construction and method of fracture detection of present invention
is implemented;
[0031] FIG. 2 is a plan view of a typical endocardial pacing and
cardioversion/defibrillation lead that incorporates the lead
conductors of the present invention; and
[0032] FIGS. 3-8 are cross-section views of the lead body of the
exemplary lead of FIG. 2 illustrating various embodiments and
variations of embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0033] The present invention finds particular utility in the
fabrication and implantation of cardiac leads, e.g., atrial and/or
ventricular pacing leads and/or cardioversion/defibrillation leads
having elongated lead bodies and lead conductors that are subject
to fracture. Preferred embodiments of such lead conductor
fabrications of such endocardial cardiac leads that are implanted
transvenously will be described in detail. But, it is to be
understood that the present invention is not limited to the same.
The present invention can be implemented in the fabrication and use
of other epicardial cardiac leads that are implanted subcutaneously
and in electrical leads intended to be disposed within the patients
body, including nerve, brain, organ, and muscle stimulation
leads.
[0034] FIG. 1 depicts a typical arrangement of a pacing or
implantable cardioverter/defibrillator (ICD) system implanted in a
patient 10, the system comprising a subcutaneously disposed
implantable pulse generator (IPG) 12 and one or more endocardial
atrial lead 14 and ventricular lead 16. The IPG 12 is implanted in
a subcutaneous location in the upper chest as shown in FIG. 1 or in
the abdomen, and the proximal ends of the endocardial leads 14 and
16 are coupled with it. The distal end of atrial lead 14 bearing
one or more atrial pace/sense electrode is shown disposed generally
in the atrial region of the patient's heart 18. The distal end of
ventricular lead 16 bearing one or more pace/sense electrode is
disposed generally in the ventricular region of heart 18. The
distal end of lead 14 can also be disposed in the coronary sinus
and even extend into a branching vein of the coronary sinus to
dispose one or more distal pace/sense electrode in relation to the
atrium or the ventricle to function as an atrial or ventricular
pace/sense lead in a manner well known in the art. Alternatively,
one or more of the leads 14 and 16 can disposed epicardially about
the heart 18. Moreover, one or more of the endocardial leads 14 and
16 can include a cardioversion/defibrillation electrode disposed at
any of the above described locations.
[0035] An exemplary cardioversion/defibrillation lead 20 in which
the present invention may be advantageously implemented and that
can be used in the locations of endocardial leads 14 and 16 is
depicted in FIG. 2. Lead 20 is provided with an elongated
insulating lead body 40, preferably fabricated of a plurality of
co-extruded bio-compatible elastomers, as described further below,
and enclosing at least three lead conductors. Although not visible
in FIG. 2, it should be noted that the elongated conductors passing
through lead body 40 may be any of the various known available
conductors for use in conjunction with implantable electrical
leads, including mono-filar or multi-filar coiled wire conductors,
stranded wires formed of filaments, and the like as further
described below with reference to FIG. 3.
[0036] An elongated cardioversion/defibrillation electrode 42, a
pace/sense ring electrode 44, and a pace/sense tip electrode 46 are
supported along a distal segment of the lead body 40 and are each
coupled to a lead conductor located within the lead body 40.
Electrodes 42, 44 and 46 may correspond to any conventionally
available pace/sense and cardioversion/defibrillation electrodes.
When the lead 20 is intended for implantation in the right
ventricular chamber, a fixation mechanism, e.g. the depicted soft,
pliant tines 48 are provided to be lodged within right ventricular
trabeculae to maintain electrode 46 in contact with the endocardium
of the right ventricle. Alternatively, an active fixation
mechanism, e.g., a retractable and rotatable helix, can be
substituted for the tines 48, and the distal tip electrode can be
fixed in the right atrial or ventricular heart chamber. The distal
electrodes of the lead 40 can also be advanced into a cardiac
vessel, e.g., the coronary sinus, if no fixation mechanism is
provided.
[0037] A connector assembly is formed at the proximal end of the
lead body 40 for making electrical and mechanical connection with
the IPG 12 of FIG. 1 in a manner well known in the art. The
connector assembly comprises a molded lead bifurcation which splits
off two of the conductors within lead body 40 coupled to the distal
pace/sense electrodes 44 and 46 to a bipolar, in-line connector
assembly 24 which generally corresponds to the IS1 connector
standard for pacing leads. Connector assembly 24 is provided with a
first set of sealing rings 28, a connector ring 32, a second set of
sealing rings 34, and connector pin 36. Connector pin 36 is coupled
to the lead conductor that extends through the lead body 40 to the
distal tip electrode 46. The connector ring 32 is coupled to the
lead conductor that extends through the lead body 40 to pace/sense
ring electrode 44. The lead conductor coupled to
cardioversion/defibrillation electrode 42 extends to connector
assembly 22 which comprises a set of sealing rings 26 and a
connector pin 36. The illustrated connector assemblies 22 and 24
are conventional elements and may correspond to any of the numerous
known electrical connector assemblies provided on implantable
medical leads.
[0038] In the specific context of the lead 20 illustrated in FIG.
2, the lead conductor coupling connector pin 32 to distal electrode
16 preferably takes the form of a multi-filar, wire coil to allow
passage of a stylet through a lumen of the wire coil. The lead
conductors coupling ring electrode 14 to connector ring 32 and
coupling the cardioversion/defibrillation electrode 12 to connector
pin 30 preferably take the same form or the form of stranded cables
formed of wire filaments. But, the present invention is believed
workable in the context of any of the numerous conductors known for
use in implantable electrical leads, in any combination with one
another, with or without the capability of receiving a stiffening
stylet.
[0039] In conjunction with embodiments of the present invention
which employ bundled, stranded conductors, interconnection of the
conductors to the electrodes and connector rings may be
accomplished by crimping, swaging and/or welding, as known to the
art. In particular, interconnection of bundled, stranded conductors
to connectors and electrodes may be accomplished according to U.S.
patent application Ser. No. 08/439,332, filed May 11, 1995, by
Swoyer et al., and in the above-incorporated '014 patent and in
U.S. Pat. No. 5,676,694, all incorporated herein by reference.
[0040] The lead body 40 of the present invention is realized in a
number of embodiments depicted in the cross-section views of FIGS.
3-8. In each case, the lead body 40 is formed as a lead body sheath
that is co-extruded in a co-extrusion process using bio-compatible,
electrically insulating, materials of differing durometers in
differing axial sections thereof, resulting in a unitary lead body
sheath having differing stiffness sections or areas or structures
in its cross-section. The lead body sheath is co-extruded to
provide a lead body outer surface 50 that is either exposed to the
environment or enclosed within an outer sheath and to have a
plurality of lead conductor lumens for receiving and enclosing a
like plurality of lead conductors.
[0041] In FIG. 3, the lead body sheath 118 is co-extruded of three,
for example, sheath segments 106, 108 and 110, each segment
containing a lead conductor lumen and formed of a first durometer
material. Sheath 118 is co-extruded with a web 120 of a second
durometer material extending between the adjoining boundaries of
the sheath segments 106, 108 and 110 and bonding the adjacent
segments together into the unitary lead body insulating sheath 118.
The web 120 may be formed by co-extrusion of the second durometer
material, typically a higher durometer material than the first
durometer material used to extrude the sheath segments 106, 108 and
110. The web 120 comprises three web arms 122, 124 and 126 that
adhere to the adjoining sheath segment boundaries, while separating
the adjoining sheath segment boundaries from one another.
[0042] The lead conductors 112, 114 and 116 illustrated in lead
conductor lumens 100, 102 and 104 in the cross-section view of FIG.
3 are exemplary of lead conductor types that can be employed in the
practice of the invention. All of the lead conductors 112, 114 and
116 are formed in an electrically redundant manner of a plurality
of wire coiled wires or stranded wire filaments that are coated on
their exterior surfaces with PTFE to facilitate inserting the lead
conductors through the lead conductor lumens 100, 102 and 104,
respectively.
[0043] Two different versions of straight lead conductors 112 and
114 are depicted in the lead conductor lumens 100 and 102,
respectively. Each of the straight conductors 112 and 114 may take
the form of a bundled, stranded filament conductors disclosed in
the above-incorporated '986 and '321 patents or the '829
application, for example. The invention may also be practiced using
any of the numerous other stranded filament conductors known to the
art. The stranded filament conductors of the present invention can
also be wound into a plurality of intertwined, parallel wound,
coils that are electrically connected together as described above
with respect to the above-incorporated '983 and '022 patents, for
example. The lead conductor 114 is formed of a straight, inner core
filament 142 surrounded by six outer filaments 144, 146, 148, 150,
152 and 154 helically wound into a single 1.times.7 wire strand or
cable. The lead conductor 112 is formed in the manner described in
the above-incorporated '414 patent of seven strands, and each
strand is formed of seven filaments of smaller gauge than those
forming lead conductor 114, resulting in a "7.times.7" wire cable
of 49 total filaments. The straight, centrally disposed, core wire
strand 128 is formed of six outer filaments helically wound around
a straight inner core filament. The six outer or perimeter wire
strands 130, 132, 134, 136, 138, and 140 are formed in the same
manner as the core wire strand 128, that is, by an inner core
filament surrounded by six outer filaments that are helically wound
about it. The six outer or perimeter wire strands 130, 132, 134,
136, 138, and 140 are themselves wound helically around the
straight core wire strand 128.
[0044] Lead conductor 116 is formed in a parallel wound,
multi-filar, coiled wire of the type disclosed in the
above-incorporated '435 patent. The four parallel wound wires 156,
158, 160 and 162 are electrically connected together at the
proximal connection with one of the proximal connector elements and
distal connection with one of the distal electrodes.
[0045] Each of the conductive wires or filaments can be formed of a
single alloy material or formed as depicted with an inner core of a
highly conductive alloy or metal, e.g. silver, surrounded by an
outer sheath of another conductor, e.g., stainless steel or MP35N
alloy, that is more resistant to degradation using the DBS or the
drawn-filled-tube (DFT) extrusion techniques described in the
above-incorporated '044 patent as is well known in the art. The
current carrying capacity of cardioversion/defibrillation lead
conductors, e.g. the stranded filament and cable conductors 114 and
112 formed in these ways is maximized for the cross-section
dimensions of the individual filaments and cables.
[0046] These differing lead conductors 112, 114 and 116 are merely
exemplary of different lead conductor types that may be employed in
any combination in the lead conductor lumens 100,102 and 104 and
any further lead conductor lumens that can be formed in the
insulating lead body sheath 118. Such lead conductor types have
differing outer diameters and bending stiffness
characteristics.
[0047] The extrusion of the insulating lead body sheath 118 of the
lead body 40 can be effected in many ways in accordance with the
present invention. In the first embodiment depicted in FIG. 3, the
insulating sheath 118 the lead body sheath is co-extruded of the
plurality of arcuate or pie piece shaped, sheath segments 106, 108
and 110 in which the lead conductor lumens 100, 102 and 104 are
formed. Each segment 106, 108 and 110 is formed of the same
elastomeric material, e.g. a polyurethane a first durometer. The
arms 122, 124 and 126 of web 120 are co-extruded of a second
durometer material between the adjoining boundaries of the sheath
segments 106, 108 and 110 to bond them together into the unitary
lead body insulating sheath 118. The Y-shaped web 120 is depicted
schematically and can be of any suitable width that strengthens the
lead body 40.
[0048] The web 120 is preferably formed by co-extrusion of a single
second durometer material, typically a higher durometer material
than the first durometer material of the sheath segments 106, 108
and 110. However, it will be understood that the arms 122, 124 and
126 can be co-extruded separately of differing materials that are
tailored, in this instance in durometer to complement and offset
bending characteristics of the lead conductors 112,114 and 116 or
to otherwise affect the bending characteristics of the lead body
40.
[0049] Also, in the depicted view of this embodiment, the ends of
the arms 122, 124 and 126 of web 120 extend to and becomes part of
the exposed lead body surface 50. However, it will be understood
that the outer ends of the arms 122, 124 and 126 can terminate
within the sheath body 118 such that the adjoining sheath segments
106, 108 and 110 merge together in a peripheral band adjacent to
the exposed lead body surface 50 and totally enclose the web
120.
[0050] In a first variation of the further embodiment depicted in
FIG. 4, the lead body sheath 218 is co-extruded of a plurality of
sheath segments 206, 208 and 210 enclosing lead conductor lumens
200, 202 and 204, respectively. Each sheath segment 206 is formed
of a selected durometer material, whereby the lead body sheath 218
as a whole can be tailored to exhibit differing bending
flexibilities away from the lead body sheath axis (perpendicular to
the plane of the cross-section view) in selected polar directions
around the 360.degree. circumference of the sheath body 218. As a
result of the co-extrusion process, the sheath segments 206, 208
and 210 are bounded by and form the exposed surface 50 and the
boundaries 220, 222 and 224.
[0051] The lead conductors 212, 214 and 216 are shown schematically
in this view and may take any of the known forms described herein
or otherwise known in the art at the time of filing this
application for patent and that become known thereafter. This
embodiment and the following described variations are particularly
suitable for use with above described lead conductors of differing
types that have differing bending stiffnesses. In one application
of this embodiment, the durometers of the sheath segments 206, 208
and 210 are selected in relation to the lead conductor to
compensate for the lead conductor bending stiffness. For example,
relatively stiff lead conductors can be enclosed in segment lumens
formed within segments of relatively low stiffness due to
relatively low durometer materials, whereas relatively flexible
lead conductors can be enclosed in segment lumens formed within
segments of relatively high stiffness due to relatively high
durometer materials. In this way, the bending stiffness of the lead
body 40 in all polar directions through 360.degree. can be brought
into equilibrium.
[0052] In a further application of this embodiment, it may be
desired to form a lead body that does exhibit a bias to bend more
readily in one polar direction than in the other directions. In
this case, one of the sheath segments 206, 208 and 210 can be
co-extruded of a more flexible material than the other sheath
segments, and can enclose a relatively flexible lead conductor
within that sheath segment lumen.
[0053] In the third embodiment of an insulating sheath 318 is
depicted in FIG. 5, wherein a web 320 like web 120 of the first
embodiment is employed to strengthen the boundary between the
adjacent lead conductor lumens 200, 202 and 204 while providing the
differing stiffness sheath segment materials of the second
embodiment. The web 320 can be formed of any suitable durometer
material that is compatible with and can be co-extruded with the
materials of the sheath segments 206, 208 and 210.
[0054] In the three variations of a fourth embodiment depicted in
FIGS. 6-8, a centrally located lead conductor and/or stiffening
stylet receiving lumen 400 can also be formed of the same or
differing durometer material as the sheath segments of the first or
second embodiment or surrounded by the web material of the first or
third embodiment. In FIG. 6, the insulating sheath 418 is formed in
the manner of the embodiment of FIG. 4 except that the centrally
disposed lumen 400 is formed therein. In FIG. 7, the insulating
sheath 518 is formed in the same manner as the embodiment of FIG.
6, except that the central lumen 400 is surrounded by a tube 404 of
differing durometer than those of the three sheath segments 206,
208 and 210.
[0055] In the further variation of the insulating sheath 618
depicted in FIG. 8, a Y-shaped web 420 is formed of three arms 422,
424 and 426 extending from the tube 404 surrounding the central
lumen 400. The arms 422, 424 and 426 are preferably extruded of the
material of the tube 404. However, they could be formed separately
of materials tailored to complement the materials forming the
sheath segments 206, 208 and 210.
[0056] In a further variation of FIG. 8, the sheath segments 206,
208 and 210 could be formed of the same material as taught in the
first embodiment of FIG. 3. Moreover, the outer ends of the three
arms 422, 424 and 426 extending from the tube 404 surrounding the
central lumen 400 could be shortened so that the material used to
extrude the segments 206, 208 and 210 merge together in a band
adjacent to the outer surface 50.
[0057] In these embodiments of FIGS. 6-8, central lumen 400 would
extend through lead body 40 to the lumen of proximal connector pin
36 and would be adapted to receive a stiffening stylet or lead
conductor or both as represented by element 402. For example, the
coiled wire lead conductor 116 of FIG. 3 would advantageously be
disposed in central lumen 400 to use that lumen as a conductor
lumen while still providing a lumen for receiving a stiffening
stylet in a manner well known in the art.
[0058] In the embodiments and variations depicted in FIGS. 4-8, the
sheath segments 206, 208 and 210 are depicted as being formed of
different durometer elastomeric materials that are co-extruded
together with or without a web 220 and/or tube 404 surrounding the
central lumen 400. It will be understood that two of the
illustrated three segments 206, 208 and 210 could be formed of the
same durometer hardness material
[0059] It will also be understood that only two or more than three
such sheath segments can be formed in the lead body sheath in
accordance with the teachings of the present invention.
[0060] The elastomeric insulating sheathes 118, 218, 318, 418, 518,
618 and the above-described variations thereof can be fabricated
using co-extrusion techniques that are well known in the art. For
example, U.S. Pat. Nos. 4,790,831, 5,546,674 and 5,622,665 disclose
exemplary extrusion and co-extrusion techniques that are employed
in the co-extrusion of side walls of catheter bodies for
selectively altering the side wall characteristics around its
circumference.
[0061] Acceptable polyurethane elastomers comprise polyether
urethane elastomers having a durometer on the Shore A durometer
scale of at least about 80A or a substantially ether-free
polyurethane elastomer. The elastomer must also be hydrolically
stable, not oxidize, and have a toughness in the range of
polyurethanes generally. A suitable urethane is Pellethane 2363-55D
or Pellethane 2363-55DE of Dow Chemical Co. of Midland, Mich.
Polyurethanes essentially equivalent to Pellethane 2363-55D are
available from other sources such as B. F. Goodrich, Inc. The
Pellethane 2363 family of polymers, including 2363-80A and
2363-55D, are composed of methylene bis-isocyanato benzene (MDI),
butane diol (BD) hard segments and polytetramethylene ether oxide
(PTMO) soft segments. The proportion of hard to soft segments is
higher for the harder (Shore 55D) polymer than for the softer
(Shore 80A) material thereby providing fewer ether linkages which
may be subject to in vivo degradation.
[0062] Preferably, the urethane is a substantially ether-free
polyurethane since stress cracking appears to have a relation to
the ether content of the polymer, with fewer ether linkages being
desirable. A polymer without ether linkages may be made by
substituting aliphatic, polycarbonate or polydimethylsiloxane
groups for the polyether groups of the soft segments. Ether-free
polyurethanes said to be suitable for in vivo use are disclosed
in-U.S. Pat. Nos. 4,873,308, 5,109,077, and 5,133,742, and in
published International Patent Application WO 92/04390, all
incorporated herein by reference in their entirety. Biostable
ether-free polymers include PolyMedica's Chronoflex AL-80A and
Chronoflex AL-55D, the family of bistable polyurethanes disclosed
in the above-incorporated '308 patent and AKZO/ENKA'S PUR series of
polyurethanes. These materials can be coated over the preferred
lead insulator material, Pellethane 2363-80A, by methods such as
solution coating or co-extrusion.
[0063] In accordance with the method of the present invention, the
lead body sheath 118, 218, 318, 418, 518, 618 is fabricated to form
each of the sheath cross-sections depicted in FIGS. 3-8 and
above-described variations thereof using such co-extrusion
techniques. The selected lead conductors are inserted through the
sheath lumens for the length of the lead body sheath to form the
lead body 40. Surface electrodes, e.g. the distal ring electrode 44
and the elongated cardioversion/defibrillation electrode 42 are
formed over the distal exterior surface 50 and electrically
attached to the distal ends of the appropriate lead conductors. The
distal tip electrode 46 is electrically attached to the distal end
of the appropriate lead conductor, and the distal electrode 46 and
fixation mechanism, e.g. the tines 48, are mechanically attached to
the distal end of the lead body 40. The proximal end of the lead
body 40 is attached to the proximal connector assemblies 22 and 24
in a manner well known in the art.
[0064] The principles of the present invention can also be applied
to the fabrication of an insulating sheath comprising an inner core
surrounded by an external sheath as disclosed in the
above-incorporated U.S. patent application Ser. No. 08/990,647. The
inner core can be fabricated in the co-extrusion process to have a
plurality of sheath segments as described above in reference to
FIGS. 3-8 but having a lead conductor receiving groove, rather than
a fully enclosed lead conductor lumen formed therein. The inner
core and lead conductors fitted into the grooves are encased within
an outer tubing member of an elastomeric material.
[0065] Although particular embodiments of the invention have been
described herein in some detail, this has been done for the purpose
of providing a written description of the invention in an enabling
manner and to form a basis for establishing equivalents to
structure and method steps not specifically described or listed. It
is contemplated by the inventors that the scope of the limitations
of the following claims encompasses the described embodiments and
equivalents thereto now known and coming into existence during the
term of the patent. Thus, it is expected that various changes,
alterations, or modifications may be made to the invention as
described herein without departing from the spirit and scope of the
invention as defined by the appended claims.
* * * * *