US3244174A - Body implantable conductor - Google Patents

Description

April 5, 1966 w. H. WESBEY ETAL 3,244,174

BODY IMPLANTABLE CONDUCTOR Filed Jan. 51, 1964 INVENTORS WILLIAM H. WESBEY WILLIAM D. SHADDUCK BY MM- W ATTORNEY United States Patent 3,244,174 BODY IMPLANTABLE CONDUCTOR William H. Wesbey, West Allis, and William D. Shadduck, Hales Corners, Wis, assignors to General Electric Company, a corporation of New York Filedlan. 31, 1964, Ser. No. 341,525 l Claim. (Cl. 128-418) This invention pertains to a conductor that is intended tor implantation in a living body for the purpose of delivering electric energy from an implanted source to an organ :that is to be stimulated thereby. An illustrative use of the invention is with a cardiac pacemaker constituting an implanted electric pulse source that delivers energy to the human heart so that it may be stimulated to beat at essentially a normal rate.

Experience has shown that one of the most frequently encountered problems with cardiac stimulators has been breakage of the leads between the source and heart. This is to be expected in view of the fact that the conductors of the leads must be very fine and flexible and yet durable enough to withstand thousands of flexures per day due to expansion and contraction of the heart. It has been diflicult to find lead insulating materials that have the properties of being body compatible and yet flexible and small enough to avoid interference with normal body iunctiqns. Synthetic plastic. coverings that were used formerly often cracked and caused a sharp flexure of the wireconductor, causing it to fatigue and break shortly thereafter. The present invention is concerned with a conductor lead and conductor lead assembly that avoids this disadvantage.

:It is the general object of the present invention to provide a body implantable conductor that is small in crosssection, that has good insulating properties, that is easily used by the surgeon, and that is durable.

A more specific object of the present invention is to provide a conductive lead that comprises a flexible stranded wire cable on which there are insulating layers of silicone rubber, a Dacron fabric impregnated with silicone rubber and another layer of silicone rubber.

Another object of this invention is to provide an implantable conductor assembly that is made up as a twin lead.

Another object is to provide new means for anchoring the ends of the conductor assembly to the organ that is to be stimulated .or energized from the electrical source.

The achievement of these and other more specific objects will appear from time to time throughout the course of the ensuing specification.

A more detailed explanation of the invention will now be set forth in reference to the drawings in which:

FIGURE 1 shows the outline of a human heart to which an implanted cardiac pacemaker is connected by means of the new lead assembly;

FIGURE 2 is a side View of the new body implantable lead;

FIGURE 3 is across-section of the lead shown in FIG- URE 2 taken on the line 2-2 of the latter;

"FIGURE 4 is a plan view of the lead and means for terminating and connecting the same to a body organ;

FIGURE 5 is a modified side view of the assembly shown in FIGURE 4;

FIGURE 6 is a plan view of a suture pad; and

FIGURE 7 is an alternative form of lead termination and is comparable with that employed in the example of FIGURE 1.

In FIGURE 1 use of the new lead assembly 10 is illustrated as connecting an implantable electronic pacemaker 11 with a human heart 12. The pacemaker 11 may be placed by suitable surgical technics in the patients abdominal muscular wall a little below the umbilicus or 3,244,174 Patented Apr. 5, 19.66

belt line, for instance. The pacemaker is a known type of solid state pulse power source that is encapsulated in body compatible material and is usually about two inches square and under one inch thick. It produces electric pulses that are generally under four volts at a repetition rate of 70 pulses per minute, this being the normally desired rate of heart beat.

The lead 10 is usually run from pacemaker 11 t0 he heart through an intercostalspace where it is admitted to the thoracic cavity. Terminal connection of lead 10 to the heart is made to the myocardium layer after a suitable incision has been made in the sheathing pericardium to permit exposure of the former. It may be assumed that one is viewing the myocardium in FIGURE 1 and that the pericardium has been omitted.

The insulated ends 24 of the lead lie .on the myocardium layer and one insulated portion 24A lies below the layer as indicated by dashed lines. This concealed excursion 24A may be around 1.5 centimeters in length. A bared insulated stranded conductor 20 is brought out in an exposed loop and then permitted to re-enter and be con sealed for another 1.5 centimeter distance, approximately, whereupon it terminates in a stainless steel ferrule 16. A suture loop 17 is then brough through the .myocardium and around the insulated portion 24 and the bare wire next to ferrule 16 to efiect an anchorage. Electric current is transferred to the heart by the concealed bare conductor wire 20 contacting heart tissue of the myocardium.

The above remarks are not intended as a proposal for a surgical technic but they are made for roughly illustrating an application of the new leads and to serve as a basis for further discussion.

The two most crucial regions of lead 10, insofar as breakage is concerned, lie immediately next to the pacemaker power supply 11 and next to the region where the individual insulated end portions 24 of the leads are admitted to the heart tissue. In the first case, normal body muscular movements flex and stress the leads. The expansive and contractile movements of the heart, of course, stress and flex the terminal ends of the leads more than 100,000 times per day. When this is multiplied by the number of days in a year, one may readily realize that a rigorous performance of the leads is required if replacement at unduly short intervals is to be avoided. I

The new lead may be made up as either a pair of individual insulated leads that run from the power source to the organ being stimulated, or they may be bound together as a twin lead assembly. In either case, the leads are made in a new way that is illustrated in FIG- URE 2. Here the actual current carrying portion comprises a stainless steel stranded cable 20 which is usually composed of No. 316 stainless steel which has a total diameter of 0.015 inch and is made up of 49 individual wires in seven bundles. Each wire is less than two-thousandths of an inch in diameter. Cables such as 20 have been used with insulating coatings other than the new one which will now be described.

In accordance with the invention, stranded stainless steel conductor 20 is coated with a layer of medical grade silicone rubber 21. This layer may penetrate between the strands of cable 20 but the material is not intimately bonded with the strands as that term is ordinarily understood. A suitable silicone material for layer 21 that is known by Dow-Corning Corporations trademark Silastic. Immediately on top of silicone rubber layer 21 is deposited a mesh material 22. The mesh material may be a braid of ten picks per inch and constitute a single wrap. The mesh is preferably a polyester fiber such as that sold under the Du Pont Company trademark Dacron. There is then concentrically extrudedover mesh layer 22 another external layer of Silastic 24 which goes through ordinarily have mesh in it. at the same time and integral with the extruded layer 24 'that penetrates the mesh 22 which is ordinarily only the mesh and joins with layer 21. The layers 24, 22 and 21 and the stranded cable 20 constitute a round crosssection insulated conductor that is useable by itself as a means for interconnecting a power source and an organ in a living body. In a practical case, the outside circular part of the lead that is bounded by Silastic layer 24 may have a diameter of about V of an inch.

In FIGURE 3 an extension of this basic construction is evident. In this figure a twin conductor lead assembly is formed by joining two of the conductors above described by a web 25 of silicone rubber which does not The web 25 may be formed wrapped around the individual conductors 20. The straight part of the web 25 between the circumferences of the adjacent insulated conductors may have a length and thickness of 0.04 inch. The overall width of the twin lead as viewed in FIGURE 3 is 0.16 inch in a practical case. The twin conductor of FIGURE 3 is also useful for connecting other types of electric stimulators to body organs besides the cardiac pacemaker application discussed above.

A new means for utilizing and terminating and connecting the above described lead assembly to an organ is shown in FIGURES 4 and 5. Here the lead assembly 10 is provided with a suture pad 26 that facilitates connection with the heart, for example. Suture pad 26 is shown in detail in FIGURE 6 and is seen to comprise a fiat silicone rubber rectangular pad that has a Dacron mesh 40 similar to that described above imbedded in it to improve toughness. The pad has a pair of spaced slits 27 and 27' that are separated by an imperforate region 28. Suture V pad 26 may be slid over lead assembly 10 by passing the end of the lead under the left end of suture pad 26 as viewed in FIGURE 6 whereupon the lead may be passed in a serpentine path upwardly through slit 27 and over intervening portion 28 and then down through slit 27 so that the outside insulating layer terminates under the suture pad 26 in a manner that may be seen best in FIGURE 5. Pad 26 may also have any desired number of holes 34 to facilitate suturing it to tissue. It is desirable to apply an adhesive such as Silastic medical adhesive in the vicinity of the slits 27 so that the lead cannot slip with respect to the pad. For instance, a few droplets 41 of adhesive may be applied as shown in FIGURE 4.

One may see particularly well in FIGURE that the bare stranded conductor section 20 is formed into an eye 29 which is seized by a ferrule 30 which may be stainless steel. Before installation, eye 29 is engaged by a suture 31 or other suitable material that is in turn swedged to a surgical needle 32. Needle 32 is cut off of suture 31 after installation which Will now be described.

Making an electrical connection between the lead and tissue may be readily understood by referring to FIGURE '5 where it is seen that the lead rests on the myocardium layer 12 of the heart, which is shown in outline, with suture pad 26 on top. Before the assembly is pulled down, the needles 32 are passed through the heart tissue and back through suture pad 26 until the eye- 29 is brought up tightly against the bottom of the pad. A knot 33 is then made so as to' prevent eye 29 from drawing away from the suture pad. In due course, it is expected that tissue fibrosis will occur in the vicinity of eye 29 and ferrule 30 to serve as a more secure anchor for the conductor. However, there remains a constant impedance current interchange surface between the tissue and the bared portion 20 of the conductor. Both eyes 29 are secured in the manner just described and suture pad 26 is further secured by appropriately suturing through small holes 34 in the latter, for instance.

An advantage of using suture pad 26 as a supporting and fastening means for lead is that it serves as an insulator between the my c rdi m an pe icardium l y rs of the heart. Hence, current that is conducted from bare conductor 20 to the "myocardium does not find a dire'ct path into the pericardium. The benefit of this is that the phrenic nerve is not stimulated inadvertently by the elec trical energy that is being supplied to the heart. The phenic nerve passes from the brain along the pericardium layer, not shown, and to the diaphragm. If it is stimulated, the patient may hiccup at the pulse rate and further surgical procedures may be necessary.

Another form of lead assembly which is constructed according to the concepts described primarily in conned tion with FIGURES 2 and 3, is seen in FIGURE 7. It this construction that is shown applied to the heart in FIGURE 1 except that surgical needles 32 and the continuous stainless steel conductive suture 20 are still intact. In FIGURE 7, the twin conductor assembly terminates in the region of broken line 37 after which conductors 24 that are insulated according to the invention continue separately. Along line 37, where web 25 is discontinued, there is provided a loop of mesh 38 that is impregnated with silicone rubber. The purpose of the mesh is to act as a re-enforcement for preventing the spreading and tearing away of the twin conductors 13. It will be observed that conductors 24 have their insulating layers terminated in a conical or pointed configuration which is obtained by installing a tapered plug 39 of silicone rubber on the conductor cables before the ferrule 16 and needles 32 are fastened. This permits the individual conductors to be drawn through tissue with less resistance and without undue trauma.

It should be understood that the new lead may be used as individual or separated conductors or in its twin con-r figuration. In some cases it is preferred to run for a distance with separated conductors and then continue unin terruptedly with the twin configuration. For example, in FIGURE 1, the leads are separate where they emerge from pacemaker 11. This facilitates introducing slack in the line and it has been discovered that in the abdominal muscle site where the pacemaker is implanted that muscular action constrains the twin configuration to bend in a manner that may increase the likelihood of breakage as compared with the use of separated leads. This slack is necessary for allowing the source and organ to change distance due to normal body movements and body growth. On the other hand, the twin configuration has been found to offer greatest surgical convenience and ruggedness for the remainder of the lead to the organ. In some instances, a suture pad such as 26 may be placed on the lead and sutured to the tissue intermediate the twin and separated parts to isolate one stress condition from another.

In summary, a body implantable lead has been described that insulates a stranded cable with alternate layers of silicone rubber. Dacron mesh that is impregnated with silicone rubber, and an extended layer of silicone rubber over it. The invention includes single conductors that are insulated in this manner and in the alternative and V as a further extension, contemplates joining such con: ductors in a twin configuration by a web of flexible insulating material. Further, a new suture pad fastenin means has been described.

Although specific embodiments of the invention have been described, these are to be considered illustrative. rather than limiting, for the invention may be variously embodied and is to be limited only by the scope of the claim which follows,

It is claimed: A body implantable lead assembly comprising: (a) at least two spaced apart substantially parallel flexible wire conductors, (b) a first coating of pliable silicone rubber surrounding each of said conductors, (c) a polyester fiber mesh that surrounds each of, Saidi first coatings individ ally,

(d) a second coating of pliable silicone rubber that penetrates the mesh layers individually and which coating is continuous to form a Web that joins the conductors together along at least part of their length,

(e) a suture pad of polyester fiber mesh that is impregnated vvith silicone rubber,

(f) said pad having spaced apart slits therein for passing said lead consecutively through them,

(g) and silicone medical adhesive applied in the vicinity of the slits to join the suture pad with the second coating,

(11) said adhesive joining said lead and pad in the region between the slits where the lead extends through the pad.

References Cited by the Examiner UNITED STATES PATENTS 1,729,160 9/1929 Engle 1741l3 3,057,356 10/1962 Greatbatch.

FOREIGN PATENTS 93 8,976 2/ 1956 Germany. 743,396 1/1956 Great Britain. 830,644 3/ 1960 Great Britain.

RiCHARD A. GAUDET, Primary Examiner.

W. E. KAMM, Assitant Examiner.

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