GB1560411A

GB1560411A - Implantable electromedical lead assembly

Info

Publication number: GB1560411A
Application number: GB3172876A
Authority: GB
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 1975-07-29
Filing date: 1976-07-29
Publication date: 1980-02-06
Also published as: FR2319384B1; NL7608363A; IT1066586B; JPS5231592A; CA1081794A; SE427524B; NL175883C; DE2533766C2; DE2533766A1; JPS5644756B2; NL175883B; FR2319384A1; SE7608505L

Description

(54) IMPLANTABLE ELECTROMEDICAL LEAD ASSEMBLY (71) We, MEDTRONIC INC., a corporation organised and existing under the laws of the State of Minnesota, United States of America, 3055 Old Highway Eight, Minneapolis Minnesota 55418 United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to transvenously implantable electromedical lead assemblies.

Pacemaker lead assemblies represent the electrical link between a cardiac pacemaker and the heart tissue which is to be stimulated.

Two methods are known for the long-lasting implantation of such assemblies: (W. Hager, A. Seling, Praxis der Schrittmachertherapie; F. K. Schattauer Verlag 1974 - Practice of pacemaker therapy; F. K. Schattauer publishers, 1974).

1. Following thoracotomy and pericardiotomy, the electrode is sewn onto the myocardium tissue, or eIse screwed from outside into this tissue with the help of a special device. This technique requires relatively major surgery, with the corresponding risks, and is therefore not always suitable, particularly in the case of elderly patients.

2. A transvenous implantation method, which can be carried out under local anaesthetic, in which the assembly is pushed into the heart through a vein and an electrode at the end of the assembly makes contact with heart tissue. Difficulties arise with this method owing to a tendency, as a result of heart motions and blood flow, for the electrode to be dislodged. More Farticularly, when the electrode is to be fixed in an atrium, this being often desirable from the medical point of view, the risk of dislodging is high, because of the smoothness of the atrial muscles.

On account of this, it has been proposed to use other types of electrodes with transvenous lead assemblies which are designed so as to be firmly anchored in the heart by means of mechanical fixation devices in the form of metal or plastics hooks. In one known lead assembly the electrode is in the form of a wire hook. This requires the lead assembly to be inserted through a vein with a voluminous guide tube. The selection of the place of stimulation in the heart is rendered much more difficult by the stiffness of the guide tube; similarly, it is only possible to remove the assembly with the help of the guide tube, owing to the wire hook.

In other known lead assemblies use is made of the pressure of a guide wire (mandrel) positioned inside the lead, to drive and to push into the heart tissue an electrode formed as a penetrating device whcih electrode must be retracted during the introduction through the vein. The penetrating device may be in the form of either nylon bristles or small steel hooks, but these have no real "counter-hook" effect. A secure firm hooking is achievable with all these systems only when the electrode lies perpendicular to the tissue. If electrodes of this type come to rest at an acute angle, it can happen that only one of the hooks will engage and that the electrode will be disloged by correspondingly directed forces, such as may result from blood flow or heart motions.

When assemblies with such electrodes have to be withdrawn from the heart, the hook device must be pulled back with a nylon thread, according to one system, or else, with another type of electrode, the electrodes are pulled back together with the released hooks.

It is therefore an objective for the lead assembly according to the present invention to be easily implanted through a vein and preferably without necessarily requiring an auxiliary stiffening device. It should above all, to meet the requirements of an optimal electrotherapy of the heart, provide for a reliable fixation in the smooth wall of the atrium. If the need should arise, during the implantation, to place the electrode in a location other than the one found at first,, the assembly according to the invention should desirably then be capable of being released easily after its fixation, so as to be shifted to another location.

According to the invention, there is provided an implantable electromedical lead assembly sufficiently flexible for insertion through a blood vessel of a living body, comprising an electrically insulating sheath, a helically wound conductor disposed within the sheath and extending along the length thereof and having at its distal end a helical electrode adapted to penetrate living body tissue, and including means operable from the proximal end of the lead for causing the conductor and electrode to advance axially relative to the sheath from a first position in which the electrode is within the sheath for transvenous insertion of the lead to a second position in which the electrode extends beyond the sheath for penetrating body tissue.

According to a preferred embodiment of the invention, a device located in the head of the lead assembly causes the electrode to be propelled out of a protective sheathe or to retract it inside it, according to the direction of rotation of the conductor relative to the sheath. Through a mechanical limitation of the rotation angle and/or through markings identifiable by X-rays, which show clearly the positions of the protection sheath and of the electrode, relative to each other, it is ensured that the electrode is screwed into the tissue only to the desired extent (about 2-4 mm).

The structure according to the invention has a number of important advantages: the helical shape of the electrode provides for a reliable fixation in the heart tissue; its removal is only possible by unscrewing it. A repeated fixation attempt can be made immediately after unscrewing, without having to pull the electrode out of the heart. After fixation, forces from practically any direction can act on the head of the lead assembly, without the electrode becoming dislodged.

The insertion of the preferred embodiment, the diameter of which need not be different from that of non-fixable electrodes, requires no stiff guide tube. The fixation operation does not require a guide wire (mandrel) which would impair the flexibility of the device; the angle at which the electrode should come to rest against the tissue is to a large extent irrelevant and there is no need to ensure that small hooks are anchored on all sides.

The invention will be further described while referring to the appended drawing, which shows exemplary preferred embodiments of electrode end portions of transvenously implantable electromedical lead assemblies according to the present invention.

In all three figures, a helical electrode 3 is shown in retracted position.

Figure 1 represents an axial cross-section of an electrode head.

The lead assembly comprises an electrically insulating sheath 2 within which is disposed a helically wound conductor 1, having at its distal end a helical electrode 3. The electrode 3 is shown in a first position in which it is retracted within the sheath 2. Preferably, an electrode of this type is designed in such manner that the inner conductor 1 is formed of helically closely wound wire, and that at its end 3 to be inserted in the heart, it is coiled loosely, that is with a longer winding pitch, over about 10mum. The electrode may comprise more than one helical wire, the winding sense being the same for each wire. The external sheath 2 of the electrode consists of a flexible tube made of electrically insulating material, inside which the inner conductor can be easily rotated. The insulating tube 2 serves simultaneously as an electrode head and as a protective sheath for the loosely wound portion 3 of the electrode, which must not cause any injuries during the introduction phase through the veins and heart valves. Preferably, the forward end of the electrode 3 is ground to a sharp point. The insulating tube comprises also, at the electrode head, a device 5 which causes axial advance of the electrode when the internal conductor 1 is rotated. This effect can be achieved for instance, as shown in Figure 1, by forming this device 5 as a cylindrical block of silicone rubber provided with grooves matching exactly the windings of the electrode 3 and in which the electrode 3 can easily rotate. The block may limit the axial movement of the electrode relative to the sheath such that when the more closely wound conductor 1 reaches the block, further movement is only possible by applying a stronger torque.

Figure 2 shows another embodiment of the electrode head, seen in longitudinal crosssection. The conversion of the rotary motion into an axial motion is obtained here by means of one or more plastics filaments 6 which are helically wound with the same pitch as the electrode portion 3 of the coiled inner conductor. These plastics filaments 6 are inserted inside the insulating tube 2 to which their ends are welded, forming small retaining butts 8 which hold them in place and prevent their sliding out. The wire(s) 6 have the same effect as the block 5 in limiting the outward axial movement of the electrode.

A ring 4, preferably metallic, is attached to the end of tube 2 and coated with an electrically insulating silicone covering 7. This ring serves, in both embodiments of Figure 1 and Figure 2, to ascertain by X-ray examination, how far the electrode portion 3 of the inner conductor 1 has been screwed beyond the protection sheath. The outer cover 7 serves further, in the embodiment of Figure 2, to cover the butts 8 so as to prevent the formation of a thrombosis.

Figure 3 shows a further preferred embodiment of the electrode head, also in longitudinal cross-section. Here is again shown the inner conductor 1 which provides - the electrical connection from the pulse generator to the electrode head. The forward end of this conductor is again wound with. a long pitch so as to allow it to be screwed into the tissue.

The lead assembly also includes a further helical conductor 9 external to the conductor 1. As an additional feature, the diameter of the electrode 3 and of the external conductor 9 at the distal end of the electrode can be increased. The axial motion is achieved by bringing the inner conductor 1 into engagement over a certain length with the external conductor 9 which is similarly closely wound into a helix having a larger diameter than the helix of conductor 1, so that a screwing effect is possible. Alternatively, the conductor 1 may be located in a rigid metal cylinder, externally insulated, the inner wall of which is threaded with helical grooves so that the con- ductor 1 may slide therein for being driven axially. At the front end of the electrode head, the external conductor 9 terminates in a ring 10 which is not insulated by the silicone cover 2, so that the tissue may already be stimulated through this ring before the electrode 3 is screwed into the tissue. When an internally threaded metal cylinder is used, the front end of the cylinder may have the effect of the ring 10. The ability to stimulate the heart before the electrode 3 is screwed into the tissue may also be acheived in the embodiments of Figs. 1 and 2 by disposing a further helical conductor, similar to conductor 9, around the sheath 2, the further conductor being surrounded by a further insulating sheath along its length and uninsulated at its distal end. The further conductor can be connected to a pulse generator.

In order to keep as small as possible, in each embodiment of the invention, the area of conductive material contacting tissues, an electrically insulating layer, preferably of silicone rubber, may cover those surfaces of the helically wound electrode portion 3 of the electrode head which are not needed for the electrical stimulation. Alternatively, the whole or part of the electrode 3 may be given an electrically conductive coating. In use the electrode 3 remains retracted within tthe sheath 2 while the lead assembly is inserted through a blood vessel and when the correct position in the heart is attained the electrode is advanced relative to the sheath to its second position by rotating the proximal end of the conductor 1 relative to the sheath 2.

WHAT WE CLAIM IS:- 1. An implantable electromedical lead assembly sufficiently flexible for insertion through a blood vessel of a living body, comprising an electrically insulating sheath, a helically wound conductor disposed within the sheath and extending along the length thereof and having at its distal end a helical electrode adapted to penetrate living body tissue, and including means operable from the proximal end of the lead for causing the conductor and electrode to advance axially relative to the sheath from a first position in which the electrode is within the sheath for transvenous insertion of the lead to a second position in which the electrode extends beyond the sheath for penetrating body tissue.

2. A lead assembly as claimed in claim 1 wherein the winding pitch of the electrode is larger than that of the conductor.

3. A lead assembly as claimed in claim 1 or 2 including means positioned at the distal end of the lead for causing said axial advance when the proximal end of the conductor is rotated relative to the sheath.

4. A lead assembly as claimed in claim 3 wherein said advancing means are arranged to engage said conductor or electrode to provide a screwing advance of the electrode when the conductor is rotated.

5. A lead assembly as claimed in claim 4 wherein said advancing means comprises a plastics block provided with grooves of a configuration matching the helical electrode and through which the electrode may slide.

6. A lead assembly as claimed in claim 4 wherein said advancing means comprises one or more plastics filaments extending within the sheath and helically wound with a winding pitch matching that of the electrode, the ends of the or each filament passing through the sheath and being fused outside the sheath to form retaining butts.

7. A lead assembly as claimed in claim 4 wherein the sheath comprises a helically wound conductor coaxially surrounding the first mentioned conductor and externally insulated along its length and wherein the windings of the two conductors mesh to provide the screwing axial advance.

8. A lead assembly as claimed in claim 7 wherein the distal end of said coaxial conductor provides an electrode for contacting living body tissue, the coaxial conductor being electrically connected to the firstmentioned conductor through close contact therewith, so that stimulation of the tissue is possible even when the helical electrode is in said first position.

9. A lead assembly as claimed in claim 4 wherein the sheath comprises a hollow metal cylinder coaxially surrounding the conductor, and externally insulated along its length and wherein the inner wall of the cylinder is provided with a helical groove matching the conductor to provide the screwing axial advance.

10. A lead assembly as claimed in claim 9 wherein the distal end of said cylinder provides an electrode for contacting living body tissue, the cylinder being electrically connected to the conductor through close contact therewith, so that stimulation of the tissue is possible even when the helical electrode is in said first position.

11. A lead assembly as claimed in any of claims 4 to 6 including means for limiting the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The lead assembly also includes a further helical conductor 9 external to the conductor 1. As an additional feature, the diameter of the electrode 3 and of the external conductor 9 at the distal end of the electrode can be increased. The axial motion is achieved by bringing the inner conductor 1 into engagement over a certain length with the external conductor 9 which is similarly closely wound into a helix having a larger diameter than the helix of conductor 1, so that a screwing effect is possible. Alternatively, the conductor 1 may be located in a rigid metal cylinder, externally insulated, the inner wall of which is threaded with helical grooves so that the con- ductor 1 may slide therein for being driven axially. At the front end of the electrode head, the external conductor 9 terminates in a ring 10 which is not insulated by the silicone cover 2, so that the tissue may already be stimulated through this ring before the electrode 3 is screwed into the tissue. When an internally threaded metal cylinder is used, the front end of the cylinder may have the effect of the ring 10. The ability to stimulate the heart before the electrode 3 is screwed into the tissue may also be acheived in the embodiments of Figs. 1 and 2 by disposing a further helical conductor, similar to conductor 9, around the sheath 2, the further conductor being surrounded by a further insulating sheath along its length and uninsulated at its distal end. The further conductor can be connected to a pulse generator. In order to keep as small as possible, in each embodiment of the invention, the area of conductive material contacting tissues, an electrically insulating layer, preferably of silicone rubber, may cover those surfaces of the helically wound electrode portion 3 of the electrode head which are not needed for the electrical stimulation. Alternatively, the whole or part of the electrode 3 may be given an electrically conductive coating. In use the electrode 3 remains retracted within tthe sheath 2 while the lead assembly is inserted through a blood vessel and when the correct position in the heart is attained the electrode is advanced relative to the sheath to its second position by rotating the proximal end of the conductor 1 relative to the sheath 2. WHAT WE CLAIM IS:-

1. An implantable electromedical lead assembly sufficiently flexible for insertion through a blood vessel of a living body, comprising an electrically insulating sheath, a helically wound conductor disposed within the sheath and extending along the length thereof and having at its distal end a helical electrode adapted to penetrate living body tissue, and including means operable from the proximal end of the lead for causing the conductor and electrode to advance axially relative to the sheath from a first position in which the electrode is within the sheath for transvenous insertion of the lead to a second position in which the electrode extends beyond the sheath for penetrating body tissue.

axial advance of the conductor and electrode relative to the sheath.

12. A lead assembly as claimed in claims 2 and l l wherein the axial advance is limited by the shorter pitch conductor engaging the advancing means whereby further advance is only possible by applying a greater torque to the conductor.

13. A lead assembly as claimed in any of claims 1 to 6 wherein a ring made of a material opaque to X-rays is placed at the distal end of the sheath and is coated with an electrically insulating material so that it may be ascertained by X-ray inspection where are the respective locations of the electrode and the sheath.

14. A lead assembly as claimed in any of claims 1 to 4 or 7 to 10 wherein the sheath defines a portion of increased diameter at the distal end and surrounding the electrode in the first position.

15. A lead assembly as claimed in any preceding claim wherein the electrode is provided with an electrically conductive coating.

16. A lead assembly as claimed in any preceding claim wherein the elcetrode comprises more than one helically wound wire, the winding sense being the same for each wire.

17. A lead assembly as claimed in any of claims 1 to 6 wherein the sheath comprises an insulation layer surrounded by a further helical conductor surrounded by another insulating layer, the distal end of the further conductor being uninsulated, so that stimulation of tissue can take place via the further conductor.

18. Transvenously implantable electromedical lead assemblies substantially as hereinbefore described with reference to the accompanying drawing.