WO1980002231A1

WO1980002231A1 - Long-life flexible electrode lead

Info

Publication number: WO1980002231A1
Application number: PCT/US1980/000473
Authority: WO
Inventors: J Donachy; G Tyers; R Brownlee; H Hughes
Original assignee: J Donachy; G Tyers; R Brownlee; H Hughes
Priority date: 1979-04-24
Filing date: 1980-04-24
Publication date: 1980-10-30
Also published as: EP0027465A4; EP0027465A1

Abstract

Flexible electrode lead (1) for use with pacemakers and other organ stimulators and method for making the lead wherein improved flex-stress resistance is achieved by the use of a larger coil diameter lead wire (3), having a diameter in the range from 0.040 to about 0.100 inch, preferably about 0.065 inch, to which wire the tip (2) and terminal (4) electrodes are securely connected before the application of the insulation (5) and wherein the insulation is of segmented polyurethane that is bonded to the wire and electrodes enhancing durability and permitting reduction of the overall diameter of the lead. The reduction in lead diameter also permits the construction of multipolar concentric leads (1'), no larger than currently available standard unipolar leads with the additional advantage that a pacemaker connector block (50) with a single port may be used for connecting multiple electrically active members. Further, the larger diameter lead wire results in a markedly larger lumen or channel (8) within the conductive coil (0.045 inch or larger) allowing the insertion of an improved guide mechanism (20) which achieves unprecedented torque and flex control of the electrode tip. Finally, the coating technique can be used with coils of standard external diameters of about 0.039 inch to attain leads with very tiny total external diameters (e.g. 0.050 inch) suitable for pediatric and other applications requiring access through a very small vein, or through an intravascular needle or guide sheath.

Description

LONG-LIFE FLEXIBLE ELECTRODE LEAD

^"Background of the- Invention

The present invention relates to the electrical stimulation art and more particularly to a long-life flexible electrode lead for connecting a cardiac pacer to the heart of a patient. Improved pacemaker power sources have increased the demand for a pacemaker electrode lead that will last for the life of the patient and the implanted pacer, and yet will not increase the energy drained from the im¬ planted power source. A pacemaker electrode lead in normal use is flexed approximately 37,000,000 times a year if the pacer and/or the heart are firing at a rate of 70 beats per minute. In a 10-year period this comes to over 360,000,000 flexes. Presently-available leads cannot reliably withstand this stress, so that there exists a critical need for an electrode lead with a re¬ liable lifetime to compare with that of the newer long life power sources.

Conventional pacemaker electrode leads are formed of coiled, insulated wires having tip and terminal elec- trodes connected at their opposite ends. The wire itself has a diameter of 0.010 inch and the external coil diam¬ eter ranges from 0.037 to 0.039 inch. During cardiac implantation thin guide wires are passed axially through these coils, but due to their small diameter provide the implanting physician with minimal torque control of the electrode tip and no remote flex control. The insu¬ lation is in the form of silicone rubber tubing into which the wire coil is inserted during manufacture, and which encapsulates, but usually is not anchored or bonded to, the wire. To complete the manufacture, the neces¬ sary metal connectors and electrode tips are crimped onto the exposed ends of the insulated wire, and silicone rubber ends are molded in place. The diameter of the layer of insulation is considerably larger than that of the wire, so that the variability of the coil diameter is considerably limited.

In accordance with the present invention it has been found that the flex-stress resistance of pacer elec- trode leads can be considerably improved with the use of larger wire coil diameters, and an improved insulation and method of construction has been found to permit in¬ creasing of the wire coil diameter, while in most cases, decreasing the overall diameter of the lead. The inven- tion facilitates improved torque and flex control of the electrode tip and the construction of multipolar con¬ centric leads. Su mary of the Invention

The present invention involves a pacemaker elec¬ trode lead having a larger internal wire coil diameter and improved insulation and other construction qualities which permit a smaller outside lead diameter as compared to conventional leads of the same type and which provides significant long-life reliability.

The electrode lead of the present invention, while conveniently employing a conventional 0.010 inch diameter lead wire, uses an enlarged coil diameter for the helix in the range of from 0.040 to about 0.100 inch, and pref¬ erably about 0.065 inch, which markedly reduces the stress on the wire as compared with that imposed on the smaller coil diameter standard lead. In the manufacturing pro¬ cess the tips and connectors are joined to the lead wire with a special solder,-welding, or plating, technique be¬ fore the insulation is .applied. The wire is then primed to accept the bonding of a polymer coating for the insu- lation. The coating is in the form of segmented poly- urethane which is a much higher strength material than the previously-used silicone rubber and yet has consid¬ erable elasticity which adds to the improved mechanical function of the electrode lead. This insulation material has a 700% elongation factor and a high modulus charac¬ teristic which allows a very thin layer to be used in coating the wire, while still achieving improved strength

^•^UREA£T

OMPI

Λ fy W1PO

$£?NAT10 _* and insulation as compared to silicone rubber. The thin¬ ner layer of insulation results in a final electrode lead no larger, and usually smaller,, than those currently available, but differing substantially in that it may be made up of a large conductor with a^•small layer of insu¬ lation, in contrast with previous leads having a relatively tenuous conductor encased in a very large layer of insu¬ lation. Also, the coating process offers better control of electrode lead flexibility by permitting variations in thickness along the length.

A method of manufacturing the lead has been de¬ veloped involving dipping which is easily applicable to mass production of the lead and therefore should make the cost comparable with or even less than currently- available mechanically and functionally inferior elec¬ trode leads. In this regard the electrodes can be con-^" _. veniently manufactured in volume using one or more con¬ trolled dipping machines. These machines in their pres¬ ently commercially-obtainable form can be readily modi- fied to dip four to six leads at a time, and two of these machines may be disposed at a time under a conventional laminar flow hood. A single operator can suitably con¬ trol at least four dipping machines at a time which will permit the simultaneous production of at least 16 elec- trodes per worker.

The resulting electrode lead of the present inven¬ tion permits easy implantation of the electrode into the

OM

, Λ_* WIP right ventricular apex of the heart of a patient when used as a transvenous lead, because a larger channel or lumen, of 0.045 inch or larger, within the new wire coil allows the insertion of either a steerable mechanism or a much larger guide wire and an improved steering device is disclosed which facilitates the application of both torque and angle changes to the tip of the electrode. Conversely, using a standard wire coil diameter of ap¬ proximately 0.039 inches, the segmented polyurethane- coated electrode lead may also be made much smaller (e.g. 0.050 inch O.D.) than current silicone-coated electrodes to accommodate it to special applications such as in elderly patients with very tiny friable veins or in - youger children. Such an external diameter is signifi- cantly smaller than any heretofore achieved with a re¬ liable permanent electrode, and facilitates percutaneous insertion.

This invention also permits the development of multipolar concentric leads, no larger than current stan- dard unipolar leads, with the further advantage that a single slot in the pacemaker connector block may be used for connecting multiple electrically active members, thus avoiding the bulky configuration of existing bipolar con¬ nectors.

OMPI Brief Description of the Drawings

Fig. 1 is a diagrammatic view in section of a long- life electrode lead constructed in accordance with the present invention.

Fig. 2a is a plan view of an electrode lead of the type shown in Fig. 1 in combination with an electrode steering device in accordance with the present invention. Fig. 2b is a side view of the lead and steering device of Fig. 2a.

Fig. 3 is a diagrammatic view in section of a concentric bipolar type electrode lead connected to a pacer connector block in accordance with the present in¬ vention. Fig. 4a is a perspective view of a pacemaker hav¬ ing a connector block with a single port and two elec¬ trode-connecting set screws arranged linearly therealong for use with the bipolar electrode lead shown in Fig. 3. Fig. 4b is a perspective view of a prior art pacer having a connector block with a double port arrangement and two electrode-connecting set screws arranged thereon in the manner of the prior art.

OMPI Detailed Description of- the Invention

A long-life pacer electrode lead in accordance with the present invention is shown in section in Fig .1. The electrode lead member 1 is constructed with an elec¬ trode tip 2 at one end for contacting the heart of a patient and with a terminal electrode 4 at the other end which is connected to the pacer. A coiled or helical lead wire 3 is connected between the electrodes 2 and 4 with its opposite coiled ends accommodated in appropriate cavities formed within cylindrical portions or extensions 2a and 4a on the electrodes. The coiled ends of the lead wire 3 are conductively connected to the portions 2a and 4a by a low-temperature silver solder or other suitable means 7. The lead wire 3 and the portions 2a and 4a are covered with an insulating material 5, and the terminal end may also be provided with a flex stress resisting, tapered shield member 6 for connecting the lead member 1 to the connector on the pacemaker. An axial channel or lumen 8 is formed within the electrode lead and permits the insertion of a steering mechanism or other guiding tool as will be more fully explained in connection with Figures 2a-b.

The lead wire itself may be of the conventional type used with cardiac pacers such as manufactured by the Elgiloy Co. of Elgin, Illinois, having a diameter of 0.010 inch. Smaller wire diameters have been tested

vJfcff lO and further increase the flexibility and flex stress resistance. Multifilar helical coils may be used rather than monofilar, and MP35N or pl^'atinum-iridium may be used instead of Elgiloy. However, unlike the conventional leads which have a coil diameter of from about 0.037 to 0.039 inch, the outside diameter of the coil or helix is made larger such as at least 0.040 inch and preferably much larger, for example, 0.065 or 0.100 inch. The larger diameter reduces the stress on the wire during flexure as compared with that imposed on a lead with a smaller diameter.

The insulation 5 is of a polymer which will bond to the wire, preferably segmented polyurethane. Seg¬ mented polyurethane has been tested intravascularly in left heart bypass pumps in both patients and animals and found suitable in this environment, as reported in the medical literature and has proven successful in unpub¬ lished animal electrode tests. This preferred material is much tougher than the conventionally used silicone rubber while having an elasticity which adds to the mechanical function of the electrode member already im¬ proved by the larger outside diameter wire coil. Seg¬ mented polyurethane also has a memory so that by heat setting, specific memory effects can be induced into the electrode lead structure for regulating its shape and stiffness. This feature is of value, for example, in right atrial applications where a hook- or J-shaped

_OMPI configuration would be preferable. For atrial applica¬ tions an increased degree of rigidity may be required in the distal^"portion of the electrode member so that it may be pulled back into the atrial appendage with a less- end chance of displacement from the atrium. -These re¬ quirements cannot be met with conventional silicone rubber insulated leads without a significant increase in their diameter, and even with large diameters, the stiffness control is less with silicone tube leads. A commercially-obtainable segmented polyurethane that may be used is BIOMER, produced by Ethicon Corporation, but other polyurethane-based materials such as AVCOTHANE or biocompatible polymers may also be found suitable.

A suitable process for manufacturing an electrode lead member in accordance with the present invention involves the following steps. The lead wire 3 which has been coiled to the desired enlarged diameter is thoroughly cleaned and its coiled ends conductively con¬ nected to the tip portion 2a and terminal portion 4a using low temperature silver solder. Suitable welding techniques, heliarcing,electroplating, or the like may also be used in making this connection or even a mechan¬ ical crimp as in current art can be used, although this last technique is- not preferred. The tip and terminal electrode connections to the coil 3 may be made inside the coil, rather than outside as shown, or optimally, the tip portion 2a may be disposed inside to permit reduction of the tip diameter, while the terminal or hub portion may be attached outside the coil, to maximize the size of the steerable guide wire that can be inserted in the channel 8. In any event, a secure permanent attach- ment of the lead wire and the electrodes is performed be¬ fore application of the insulation.

After the connecting operation, the lead wire and the portions 2a and 4a are again cleaned with propyl al¬ cohol and treated with a primer such as 607 Chemlock primer after which a 15 to 20 minute drying time is al¬ lowed. The lead wire 3 and the end portions 2a and 4a are then mounted on a mandrel, which extends axially therethrough, and dipped in the polymer, that is seg¬ mented polyurethane,-whose viscosity will be controlled in accordance with the diameter of the wire being dipped. After dipping, the polymer is cured for from 45 minutes to 1 hour at 150° F. The same dipping procedure is then repeated until the proper wall thickness is obtained. Typically a single wall thickness of 0.005 to 0.007 inch, or 0.014 inch total additional diameter, will be suffi- ^• cient, but the^' electrode member can be coated to any thickness desired, depending upon the application planned for the finished electrode member. Normally the viscosity of the polymer will be such that 0.002 inch is applied with each dipping.

When the desired insulation thickness is achieved, the electrode member may be cured for about 25 hours and

OM _* then removed from the dipping mandrel, leaving the in¬ terior cavity or channel 8 therein. The tapered, flex stress resisting sleeve or shield member 6, which may be of silicone or segmented polyurethane is then molded over the terminal or hub end for .connecting the electrode mem¬ ber to the pacemaker. If desired, a special anchor or tip, such as a flange or tine, can be molded on the op¬ posite end of the lead for fixing it to the heart of a patient. The finished electrode lead can then be cleaned and inspected and will be ready for use.

To specially adapt the electrode member to differ¬ ent applications, particular operations can be performed during the manufacturing process. For example, the stiffness of the lead can be controlled by the spacing of the wire coils and the thickness of the polymer coat ing, a tightly wound helical coil being stiffer than one that has each coil spaced at a specific dimension. Thus, the stiffness can be varied along the full length of the member or in any specified area, for example, towards the * tip end to provide increased flexibility and reduce the risk of perforation.

The manufacturing operation lends itself to mass production as the dipping may be conveniently carried out in a controlled dipping machine. As previously noted, currently-available machines of this type can be readily modified by the skilled artisan to dip four to six leads at a time under a normal laminar flow hood, which in turn can hold two machines. As one operator can productively control at least four machines at a time, one person should be able to polymer coat at least 16 electrode leads at one time. Alternative forms and materials which have been found suitable for the various additional elements of the electrode member are as follows: the stimulating electrode tip 2 may be in the form of a ball tip, spher¬ ical, bullet shaped, cylindrical or other similar con- figuration and of Elgiloy, platinum, platinum-iridium or other biocompatible material; the end terminal 4 may be of Elgiloy, 316L stainless steel, vitalium, or other corrosion-resistant material; and the flex-stress resist¬ ing tapered connector and shield 6 may be of silicone rubber, segmented polyurethane, AVCOTHANE or other bio¬ compatible material.

The thickness of the segmented polyurethane coat¬ ing can be tapered toward the tip of a transvenous or transthoracic version of the electrode member to provide maximum tip flexibility and decrease cardiac tissue trauma and the risk of perforation. Similarly, the coat¬ ing can be gradually thickened toward the terminal con¬ nector end to maximize fracture resistance.

The smaller the helical coil diameter, the more brittle and stress-susceptible the electrode member.

Conversely, the larger the helical coil diameteter, Re¬ gardless of the maleable material used, the more flexible,

υ ^]P limp or "slinky"-like the electrode lead becomes. If a transvenous lead is too flexible, it will not stay in position, but will provide maximal fracture resistance. If the coil diameter is made much larger than 0.065 inch, it has limitations with respect to peripheral vein size, even though much larger bipolar transvenous leads are presently available. Transthoracic leads on the other hand, may have diameters up to a centimeter (0.394 inch), although a somewhat smaller diameter would be optimal. Consequently, coil diameters in the range from 0.040 inch to about 0.100 inch are regarded as optimal with 0.065 inch particularly preferred.

In contrast to the diameter of the helical coil, the larger the diameter of the wire used to wind the helix, the stiffer the electrode. Ordinarily, wire diam-- eters of greater than 0.010 inch would be applicable with a helix of greater than 0.065 inch and suitable in appli¬ cations where greater stiffness was considered advanta¬ geous as in atrial J-shaped electrodes. Also, for transthoracic applications where the electrode is sutured or attached directly to the heart even heavier wire sizes and larger helical coils can be adapted to the present electrode lead design to reduce its resistance and to further increase its mechanical reliability and stability.

As a result of the improved electrode lead con¬ struction a larger channel 8 is available within the wire coil 3 than previously obtainable. The larger channel allows the insertion of a much larger guide wire or a steerable flex-torque control mechanism through the lead to the tip or distal end, thus permitting the application of better torque and angle changes to the electrode tip when manipulating and implanting the electrode apparatus. 'This particularly facilitates the implantation of the electrode apparatus into the right ventrical apex when used as a transvenous lead. Following satisfactory elec- trode positioning the flex-torque control mechanism or the guide wire is easily removed. Am improved steering mechanism 20 for this purpose is shown in Figs. 2a-b. As seen in the igures, the mechanism 20 has a handle composed of three rings 21a, 21b and 21c for re- spectively receiving the index, thumb and middle fingers of an operator who, in the present case, would be the physician implanting the electrode lead in the heart of a patient. The^" rings 21a and 21c are mounted on the op¬ posite ends of a crosspiece 22 which is slidable along a rod-like member 23 having ring 21b on one end. The other end of the rod-like member 23 is connected to or integral with a body portion 24 having a longitudinal bore 24a therein. A guide wire member 25 of the flex type is connected to crosspiece 22, by block 22' and set screw 22", and extends through bore 24a into the channel 8 in the electrode lead 1. This three-ring handle and controlled flex guide wire arrangement is essentially knσwn,in the art, particularly for use in selective vascu¬ lar radiology and bronchial brushing techniques and may be of the type^" manufactured by €ook Inc., Bloomington, Ind., as Deflecting Handle, Cat. No. TDH100. In accord- 5 ance with the present invention, body portion 24 is modi¬ fied for use with the improved electrode lead. More par¬ ticularly, the body portion 24 is adapted at the forward end of the bore 24a to receive the hub or terminal end of an electrode lead, and a bore 27 is provided, which

10 communicates with the bore 24 and receives a set screw 26. The set screw 26 may be used to engage and fix the end of the lead in the bore 24a so that the lead 1 will fol¬ low rotational motion of the handle.

In operation, when the electrode lead 1 is to be

15 implanted in a patient, the flex guide wire 25 is in¬ serted into the channel or lumen 8 in the lead and may . be extended as far as the electrode tip end. The oppo¬ site or hub end of the electrode lead is inserted in the handle bore 24a, and the set screw 26 is tightened there-

20 on to fix the electrode lead htib with respect to the han¬ dle. The operating physician then places his thumb, in¬ dex and middle fingers in the appropriate rings whereupon the drawing of the middle and index rings towards the thumb ring results in angulation of the tip of the guide

25. wire 25 and thus the end of the electrode lead 1. A de¬ gree of flexion from 5° to over 90° may be achieved with this guide wire, depending upon the tension applied to the three ring handle. Rotation of the handle in either the clockwise or counterclockwise direction produces identical rotation of the lead^' ip due to the fixing of the electrode hub in the handle by the set screw 26. Thus, complete flexion and rotational control of the lead tip is possible. The combined capabilities resulting from this complete torque and flexion^'control and the resistance of the lead to fracture renders the lead par¬ ticularly suitable for combination with a myocardial grasping mechanism at the electrode tip to firmly anchor the stimulating surface in any position desired within a ventricle or atrium.

When optimal lead positioning is achieved, the set screw 26 is released, and the guide wire 25 is removed from the interior of the lead by withdrawing the hub or terminal end of the lead from the three ring handle body. The terminal end of the lead may then be inserted into the receptacle or port in the connector block of a pace¬ maker. An additional advantage of the improved manufac¬ turing technique and construction is the enhancement of the ability to construct redundant electrodes as required for EMI protection sheaths, bipolar pacing, and/or when separate electrodes are used for pacing and sensing, and/or unipolar pacing and bipolar sensing as disclosed in U.S. Pat. No. 3,977,411. The embodiment of the inven¬ tion shown in Fig. 3 represents one multipolar electrode

IsυREΛ

OMPI WIPO arrangement which may be used for such redundant or bi¬ polar applications where two or more conductive elements are essential or considered advantageous. As seen in the figure, a small insulation-coated helical coil 3' having a diameter, for example of 0.037 inch, may be fitted in¬ side a larger insulation-coated helical coil 3" of a diam¬ eter of 0.065 inch to provide a two-conductor element or bipolar coil in the form of a single electrode lead mem¬ ber 1*. The inner and outer coils 3' and 3" may be coated separately with the segmented polyurethane, or other suit¬ able polymer material. A larger contact area, ring elec¬ trode 2ⁿ , at the tip or distal end of the lead is connected to outer coil 3" and may be used to sense cardiac activity, while the smaller contact area, tip electrode 2', con- nected to inner coil 3* applies stimulating pulses to the heart. The two coils 3' and 3", at the opposite hub or proximal end of the lead 1' , are respectively connected to a terminal electrode 40 and a ring electrode 41 which are embedded in the insulating material 5' with their outer surfaces exposed. With this ring and terminal ar¬ rangement the connector block 50 on the pacemaker for re¬ ceiving the hub end of ^"the electrode lead is provided with respective block and screw connectors 41a and 40a which conductively contact the exposed surfaces of the ring and terminal electrodes 41 and 40. The lead elec¬ trodes are held in place in the connector block 50 by the respective set screws 41b and 40b. In this arrangement th'e electrodes are connected with opposite polarity, the ring electrode 41a usually being of positive polarity, while the terminal electrode 40a is of negative polarity. The remaining structural features of the tip and hub of 5 the lead 1* may be essentially the same as those shown in connection with the unipolar lead 1 in Fig. 1, such as the inclusion of a flexion shield at the hub end.

It will be seen that with the improved structural combination in Fig. 3 that only a single port or channel

10 is required in the pacer connector block 50, such as il¬ lustrated in Fig. 4a, as the two set screws 40b and 41b may be linearly disposed in the block along the channel. This concentric coil arrangement is of advantage over the bipolar arrangements of the prior art, such as shown in

15. Fig. 4b, wherein two channels are necessary to accommo¬ date the separate parallel leads, and the set screws are disposed one above the other on'the side of the connector block, resulting in a bulkier configuration. The concen¬ tric arrangement also permits the use of the external

20 coil as an EMI sheath.

It will accordingly be seen that a long-life flex¬ ible electrode lead has been described which is capable of indefinitely withstanding flexural stress and is con¬ structed in an improved manner to comprise a wire coil

25 diameter in the range from 0.040 to -about 0.100 inch, and preferably about 0.065 inch, with an insulating sheath of segmented polyurethane bonded thereto. This improved

OMPI construction while permitting greater variability of coil size also lends itself to adaptation to simplified, small¬ er bipolar electrode leads, the- use of smaller diameter electrodes and the unprecedented application of 360° torque control and over 90° flex control to the electrode tip by means of an improved steering device. The larger coil diameter also facilitates the incorporation of a re¬ motely (hub) operated lead tip myocardial grasping mech¬ anism to fully take advantage of permanent electrode po¬ sitioning in any of the unprecedented variety of locations enabled by the flex torque control mechanism. The leads can be used in a wide variety of applications as well as with pacemakers and other organ stimulators.

Claims

We claim:

1. A flexible electrode apparatus comprising: coiled lead wire means having a coil diameter in the range from 0.040 to about 0.100 inch for conduct- ing electrical signals therethrough; terminal electrode means having a portion conduc- tively connected to one end of said wire means for contacting a source of said electrical signals; tip electrode means having a portion conductively connected to the opposite end of said wire means for contacting a member to receive said electrical sig- nals; and polymer insulation means surrounding and bonded to said wire means and said portions of said tip and terminal electrode means for insulating the signals in said wire means.

2. Apparatus as in claim 1 wherein said polymer insulation means comprises segmented polyurethane.

3. Apparatus as in claim 1 wherein the coil diam- eter is about 0.065 inch.

4. Apparatus as in claim.1 wherein said portion of said tip electrode means is substantially cylindrical and said one end of said wire means is connected to the outer surface of said portion.

5. Apparatus as in claim 1 wherein said portion of said terminal electrode means is substantially cylin- drical and said opposite end of said wire means is con- nected to_tϊιe inner surface of said portion.

6. Apparatus as in claim 1 further comprising: ring electrode means disposed about said polymer insulation means adjacent said tip electrode means for sensing electrical signals from said member; and second coiled lead wire means, bonded within said polymer insulation means and concentrically disposed about said coiled lead wire means, for conducting sensed electrical signals from said ring electrode means.

7. Apparatus as in claim 1 further comprising a ring electrode disposed about said polymer insulation means adjacent said tip electrode means, said ring elec- trode being of opposite electrical polarity from said tip electrode means.

8. Apparatus as in claim 1 further comprising: a first ring electrode disposed about said polymer insulation means adjacent said tip electrode means; a coiled lead wire connected at one end to said first ring electrode and bonded within said polymer insulation means concentrically about said coiled lead wire means; and a second ring electrode disposed about said poly- mer insulation means adjacent said terminal electrode means and connected to the opposite end of said coiled lead wire.

9. Apparatus as in claim 8 wherein said second ring electrode and said terminal electrode means are of opposite electrical polarity.

10. Apparatus as in claim 8 wherein said second ring electrode and said terminal electrode means are im- bedded in said polymer insulation means juxtaposed to each other.

11. A process for manufacturing a flexible elec- trode apparatus comprising the steps of: coiling a lead wire into a helix; cohductively connecting one end of said coiled lead wire to a portion of a tip electrode; conductively connecting the other end of said ' coiled lead wire to a portion of a terminal elec- trode; supporting the lead wire and connected electrode arrangement axially along the length of the coiled lead wire; dipping said lead and electrode arrangement while axially supported into liquid polymer insulation; and bonding said insulation to said leaid wire and said portions of said tip and terminal electrodes by curing the polymer to form an insulating covering on said wire and said portions and then removing the axial support therefrom.

12. A process as in claim 11 wherein said polymer is segmented polyurethane.

13. A process as in claim 12 wherein said curing is^" carried out for from 45 minutes to an hour at 150° F.

14. A process as in claim 11 wherein said dipping step comprises forming a layer of insulation with a single wall thickness of about 0.002 inch.

15. A process as in claim 14 wherein said dipping and bonding steps are repeated until said covering adds a total additional diameter to said wire coil of about 0.014 inch before said axial support is removed.

16. A process as in claim 11 wherein the viscosity of the polymer is chosen in accordance with the diameter of the wire being dipped.

17. A process as in claim 11 wherein the stiff- ness of the electrode apparatus is varied along its length by varying the spacing of the wire coils.

18. A process as in claim 11 wherein the stiff- ness of the electrode apparatus is varied along its length by varying the thickness of the insulating cover- ing.

19. A process as in claim 11 wherein the diam- eter of said helix is in the range from 0.040 inch to about 0.100 inch.

20. A process as in claim 11 wherein the diam- eter of said helix is about 0.065 inch.

21. Apparatus for implanting a cardiac electrode comprising: coiled lead wire means connected at one end to said cardiac electrode for conducting electrical sig- nals therethrough to said cardiac electrode; polymer insulation means surrounding and bonded to said lead wire means for electrically insulating said lead wire means and having a channel therein with a diameter of at least about 0.045 inch running axially within said lead wire means; flex guide wire means insertable in said channel for steering said cardiac electrode; handle means connected to said flex guide wire means for controlling the flex movement thereof; and means for fixing the end of said polymer ins la- tion means opposite from said cardiac electrode, with respect to said handle means for rotation therewith.

22. Apparatus as in claim 21 further comprising anchoring means disposed at said cardiac electrode for grasping the myocardium to anchor said electrode to the myocardium .