Tip assembly for a carbon fiber implantable lead

A termination for a carbon fiber implantable lead. A tip assembly includes an electrode to which carbon fiber tips are cemented with a conductive adhesive. An outer housing cooperatively interacts with the electrode to mechanically secure the carbon fiber bundle sheathing to the electrode, and also to establish good electrical contact between the carbon fiber bundles and the electrode.

REFERENCE TO RELATED APPLICATION 
The subject matter of this application is related to that of U.S. Pat. No. 
4,198,991 entitled "Cardiac Pacer Lead" and also to that of my U.S. patent 
application entitled "Terminal Assembly for a Carbon Fiber Implantable 
Lead", filed on even data herewith. The patent and application are 
incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
The present invention is in the field of implantable leads, more 
particularly, terminations for carbon fiber implantable leads. 
There have been increasing applications in recent years for implantable 
electrical leads for coupling electrical signals to and from or between 
various points in human or animal bodies. The incorporated reference 
patent describes one such application, that is, cardiac pacing by means of 
an implantable stimulator. As particularly pointed out in that reference, 
such implantable leads are typically subject to continuous flexing which 
may result from heartbeat, breathing or other body movements. 
Consequently, the leads are designed to be both pliant and 
fatigue-resistant. 
The incorporated reference patent discloses a carbon fiber lead which is 
particularly well-suited for cardiac pacing and which is highly pliant and 
fatigue-resistant. 
One of the difficulties with implantable carbon fiber leads in the prior 
art is the coupling of a termination assembly to the carbon fiber leads at 
both the tip end (which is implantable within a patient), and the terminal 
end (which is the end to be coupled to either sensor instrumentation or 
signal generating instrumentation). In typical prior art carbon fiber 
leads, particularly those having bundles of carbon fibers, or yarn, 
sheathed in tetrafluoroethylene, there has proven to be a substantial 
problem due to the inability to maintain a long life mechanical coupling 
between the terminations and the sheathing material. 
It is an object of the present invention to provide an improved tip 
assembly for carbon fiber implantable leads. 
It is yet another object to provide an improved tip assembly for a carbon 
fiber implantable lead which provides good electrical contact between an 
electrode tip and the internal carbon fiber bundles, while maintaining 
good mechanical coupling between the tip assembly and the lead. 
SUMMARY OF THE INVENTION 
Briefly, the present invention includes a tip assembly for an implantable 
carbon fiber lead having an outer cover positioned about a stylet tube and 
one or more carbon fiber bundles. Each carbon fiber bundle has an 
insulating outer sheath (for example, made of a fluorocarbon material such 
as polytetrafluoroethylene, PTFE) and has an exposed carbon fiber tip at 
one end. The tip assembly includes an electrode having a tip portion at 
one end and a contact portion, a neck portion interconnecting the tip and 
contact portions along a central axis, and a post portion extending along 
the central axis at its other end. The neck portion has a relatively small 
cross-sectional area compared to the adjacent portions of the tip and 
contact portions. The contact portion includes a plurality of 
substantially planar lateral contact surfaces. 
The exposed tips of the carbon fiber bundles and the stylet tube extend to 
respective axes of the contact surfaces, and extend beyond to the neck 
portion of the electrode. 
An electrically conductive adhesive cements a portion of each of the 
exposed tips of the carbon fiber bundles to an associated one of the 
contact surfaces. 
A hollow, cylindrical electrically conductive electrode housing member, 
having a lip at one end, is positioned about the post portion, contact 
portion and region of the neck of the electrode. The portion of the 
housing member which overlies the neck portion is crimped in a manner 
mechanically securing (and electrically coupling) the exposed tips between 
the housing and electrode in the region of the crimp. In addition, the 
housing crimp mechanically secures the fiber bundle sheathing between the 
housing lip and the post portion of the electrode. In some forms of the 
invention, the housing interior surface frictionally engaging two or more 
of the regions of the contact portion between, or at the intersections of, 
the contact surfaces. 
With this configuration, the carbon fiber lead is provided with an 
electrode termination which is securely coupled to the carbon fiber lead 
in a manner minimizing slipping and dislodging of the termination from the 
lead, thereby providing a relatively long life assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1-10 show an implantable carbon fiber lead 10 embodying the present 
invention. Lead 10 generally includes an outer cover 12 (e.g. made of a 
suitable material such as polyurethane or silastic) which encloses a 
stylet tube 14 and two carbon fiber bundles 16a and 16b. Each of bundles 
16a and 16b has an insulating sheath (18a and 18b, respectively) and has 
an exposed carbon fiber tip at each end. In the present embodiment, the 
sheathed carbon fiber bundles 16a and 16b are helically wound around the 
exterior of the stylet guide 14. In this embodiment, the sheaths 18a and 
18b, and stylet tube 14, are made of a fluorocarbon material, such as 
polytetrafluoroethylene (PTFE). 
The lead 10 also includes a tip assembly 20 at its distal end which 
provides an exterior electrically conductive surface which is coupled to 
the carbon fiber bundles passing within the cover 12. At the proximal end 
of lead 10, a terminal assembly 22 provides a conductive electrical 
termination to the carbon fiber bundles. This termination is suitable for 
coupling to conventional electronic sensor or signalling devices, such as 
an implantable cardiac pacer. In addition, the terminal assembly 22 
includes a central opening 23 which is coupled to the interior of stylet 
tube 14. This opening 23 is particularly adapted for permitting the 
insertion of a stylet into the stylet tube 14. 
FIGS. 2-5 show the distal end tip assembly 20 and its component parts in 
detail. More particularly, FIG. 2 show a cutaway view of the tip assembly 
20. Assembly 20 includes an electrode 30 (shown in detail in FIGS. 3 and 
4) which has a tip portion 32 at one end, a contact portion 34, a neck 
portion 36 interconnecting the contact portion 34 and the tip portion 32 
along a central axis 38, and a post portion 44 at its other end. The post 
portion 44 extends along the central axis 38 away from the contact portion 
34. In the present embodiment, the neck portion 36 has a relatively small 
cross-sectional area relative to the adjacent sections of the tip 32 and 
contact portion 34. The contact portion 34 includes three substantially 
planar lateral contact surfaces 41, 42 and 43. In alternate embodiments, 
differing numbers of contact surfaces may be used. As shown in FIG. 4, the 
contact portion 34 includes regions 46, 47 and 48 which respectively lie 
between the planar surfaces 41, 42 and 43. 
An electrically conductive hollow electrode housing member 50 is positioned 
about the contact portion 34 and the post portion 44 of the electrode 30. 
Electrode housing member 50 includes a lip 51 at one end. 
In the assembled form, the exposed tips of carbon fiber bundles 16a and 16b 
as well as the end stylet tube 14 extend to respective ones of the contact 
surfaces 41-43, and beyond to the neck portion 36. The exposed tips are 
cemented to a respective one of the surfaces 41-43, as well as to the 
inside surface of housing member 50. The adhesive used for cementing the 
carbon fiber tips to their respective contact surfaces is electrically 
conductive, such as a silver or platinum-loaded epoxy material. In 
addition, the end of housing member 50 is crimped (at 53) to mechanically 
secure, as well as electrically couple, the carbon fiber tips and end of 
tube 14 to the electrode 30. The crimp 53 of housing 50 at neck portion 36 
forces the lip 51 of housing 50 to cooperatively interact with the post 
portion 44 to mechanically secure the sheathing from the fiber bundles and 
the tube 14 against electrode 30. 
In the present embodiment, a conductive potting 52 is also positioned 
within the housing 50 in contact with electrode 30. In addition, the 
assembly 20 includes an insulating member 60 which may be of silastic or 
polyurethane or other suitable moldable material, which is positioned 
about the housing member 50 and overlaps the cover 12 and the neck portion 
of electrode 30, bonding and moisture sealing the entire tip and lead body 
assembly. 
With this configuration, the exposed tips of the two carbon fiber bundles 
16a and 16b are cemented to the contact surfaces of the electrode 32. The 
electrically conductive adhesive on tips of bundles 16a and 16b, and the 
crimp coupling at neck 36 provide electrical contact, as well as 
mechanical coupling, between the fiber bundles and the electrode 30. 
Moreover, the conductive potting 52 within the electrode housing 50 
further insures good electrical contact between the carbon fiber bundles 
and the electrode 30. The frictional engagement of the housing 50 to the 
portions 46, 47 and 48 of contact portion 34, together with the potting 
52, as well as frictional engagement of tip 51 and post 44 with the 
bundles 16a and 16b insure good mechanical contact between the carbon 
fiber bundles within the cover 12 and the electrode tip 30. 
FIGS. 6-10 show the proximal end terminal assembly 22 and its component 
parts in detail. More particularly, FIG. 6 shows a cutaway view of the 
terminal assembly 22. The assembly 22 includes a terminal member 60 (shown 
in detail in FIGS. 7 and 8) which includes two connected hollow, 
cylindrical ends 62 and 64 which are coaxial about an axis. In the 
preferred embodiment, the first end 64 has a relatively small outer 
diameter compared with the second end 62. In other forms of the invention, 
both ends 62 and 64 may have the same diameter. 
In the terminal assembly 22, the ends of sheaths 18a and 18b near the 
terminal end of 10 are split and the fibers at that end pass through the 
split to form an exposed tip. The first end 64 is positioned about one end 
of the stylet tube 14, and the second end 62 is in part positioned about a 
portion of the stylet tube 14 as well as portions of the carbon fiber 
bundles 16a and 16b within their sheaths 18a and 18b, respectively. The 
terminal member end 62 includes two ports denoted by reference designation 
70 and 72. Each of ports 70 and 72 is adapted to guide one of the carbon 
fiber bundles 16a and 16b from its respective split portion of sheating 
18a and 18b from the region interior to terminal member end 62 and to the 
region exterior to that end 62. The exposed tips and sheathing are folded 
back against the outer surface of end 62, with the fiber bundles 
outermost. 
The terminal assembly 22 further includes an electrically conductive 
housing member 80, shown in detail in FIG. 9. The housing member 80 is 
positioned about the cylindrical portion 62 so that the inner surface of 
housing 80 sandwiches the exposed tips and associated sheathing between 
that inner surface and the outer surface of terminal member end 62. The 
housing member 80 may be mechanically coupled, or secured, to terminal 
member 60, for example, by a threaded coupling, crimp (particularly in the 
region of ports 70 and 72), or spot weld. In some forms of the invention, 
an electrically conductive adhesive cements those exposed tips and 
shething between the housing member 80 and end 62. In alternate 
embodiments, a conductive potting may be used within housing 80 and end 62 
to further insure good electrical contact between the carbon fiber bundles 
and terminal member 60. 
The terminal assembly 22 further includes a stylet entry guide member 84 
having a hollow end portion 88 coupled to a coaxial, hollow body portion 
90. Guide member 84 is positioned within the terminal member end 64 of 
terminal member 60 so that the outer surface of guide member 84 
frictionally engages the inner surface of end 64. The outer surface of 
part of the body portion 90 is threaded and is frictionally engaged with 
the inner surface of the stylet tube 14. In the present embodiment, a 
molded insulating member 92 is positioned about a portion of the 
cylindrical portion 64 as well as the housing member 80 and the end of 
outer sheathing 12 forming a moisture seal. As shown, member 92 is a seal 
particularly adapted for use with an implanted cardiac pacemaker. 
With this configuration, the exposed tips of the two carbon fiber bundles 
16a and 16b are mechanically and electrically coupled to the terminal 
assembly 22. The electrically conductive adhesive on the tips of bundles 
16a and 16b provides additional mechanical and electrical contact between 
the fiber bundles and terminal member 60. The frictional engagement of the 
housing 80 to the fiber tips and to the sheathing insures good mechanical 
contact between the carbon fiber bundles within the cover 12 and the 
terminal member 60. 
The invention may be embodied in other specific forms without departing 
from the spirit or essential characteristics thereof. The present 
embodiments are therefore to be considered in all respects as illustrative 
and not restrictive, the scope of the invention being indicated by the 
appended claims rather than by the foregoing description, and all changes 
which come within the meaning and range of equivalency of the claims are 
therefore intended to be embraced therein.