WO2009025597A1

WO2009025597A1 - Medical lead with a cover

Info

Publication number: WO2009025597A1
Application number: PCT/SE2007/050567
Authority: WO
Original assignee: St. Jude Medical Ab; ÖRNBERG, Andreas; Barlov, Armin
Priority date: 2007-08-22
Filing date: 2007-08-22
Publication date: 2009-02-26

Abstract

Present invention discloses a medical lead comprising a helix electrode intended to be screwed into the body tissue, where the distal end of the lead is covered with a convex cover, provided with an opening for directing the helix electrode from its retracted position.

Description

Medical lead with a cover

Field of the invention

The present invention relates to methods for manufacturing active fixation electrodes for electrical medical leads, in particular helix electrodes intended to be screwed into body tissue.

Background of the invention

Implantable medical electrical stimulation and/or sensing leads (also called "leads" or "electrode leads") are well known in the fields of tissue and organ stimulation and monitoring. Such fields include cardiac pacing. Leads may be attached to an organ by an active fixation means which is designed to penetrate the surface of the organ that is to be stimulated or sensed. A common active fixation means employs a helix which has a sharpened tip and is mounted at the end of the electrode lead. Such an active fixation means can be called a fixation helix, a helical screw, a screw-in anchoring means or a corkscrew- type anchoring means. Typically the helix is electrically connected to one or more conductors in the electrode lead in order to permit stimulation and/or sensing of the tissue which it is attached to. These conductors can be electrically connected to one or more exposed surfaces of the helix which then can be used as stimulating and/or sensing electrodes. A fixation helix therefore may contain one or a plurality of conductors. Typically the outer surface of the helix, including the exposed surfaces used as electrodes, is partly covered with a biocompatible coating to minimise interference with the tissue to which it is to be attached. The biocompatible coating on a helix may be electrically conducting in which case it is arranged in a predetermined pattern with continuous gaps on the insulating material around the exposed electrode surfaces in order to prevent the different electrodes from being in electrical contact with each other. The sizes of the surface areas of the exposed electrodes are set at levels which are compatible with the organ they are attached to. The fixation helix typically has an outside helix diameter which is slightly less than that of the lead body and extends in axial alignment with the lead body. During positioning of the lead in the patient the helix is retracted into the lead body in order to prevent its sharp tip damaging the patient. Once the lead is correctly positioned the surgeon maintains the distal end of the lead in contact with the tissue that the lead is to be attached to and rotates the proximal end of the helix which causes the sharpened tip of the helix to advance out of the lead body and to screw itself into the tissue. US4311153 shows an example of a screw-in lead tip having a membrane which covers the distal end of the lead during positioning and which the helix can penetrate when the surgeon rotates the helix.

A problem which may occur when attaching helices is that the pressure applied by the surgeon to hold the lead in place which the helix is being rotated may cause the annular end of the lead to punch a hole in the tissue - the so-called "cookie cutter effect". This problem becomes more acute as the diameter of leads decrease and the area of the end of the lead decreases thereby increasing the contact force per unit contact area.

Summary of the invention

The present invention relates to electrical medical leads comprising helix electrodes intended to be screwed into body tissue in which the risk of damage to tissue caused by the end of the lead punching holes in the tissue is reduced. This is achieved by providing the end of the lead with a cover which has a shape which reduces the contact force per unit contact area at the end of the lead during attachment of the helix

A first embodiment of a method in accordance with the present invention comprises a convex lead end cover with a curved opening which is concentric with the lead body and helix , said opening being arranged at a radial distance which corresponds to the radius of the helix and subtending through an arc which is less than 180°.

While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

Description of the figures

Fig. Ia) shows schematically a section through a first embodiment of an electrical medical lead provided with an active fixation means and a cover in accordance with the present invention with the active fixation means retracted; Fig Ib) shows and end-on view of the lead of figure 1;

Figs. 2a) and 2b) shows schematically views corresponding to those of figures Ia)-Ib) with the active fixation means in the insertion position: and

Figs. 3a) and 3b) shows schematically views corresponding to those of figures Ia)-Ib) with the active fixation means extended.

Detailed description of the invention

Figs. Ia) and Ib) show schematically an example of an electrical medical lead 1 in accordance with the present invention. Lead 1 comprises an elongated hollow lead body 3 which encloses active fixation means, for example helix 5. Helix 5 may be made of conducting material or non-conducting material. The distal end of lead 1 is covered by a hemispherical convex cover 7 which has an asymmetrically positioned opening 9. The edge of opening 9 which is nearest the centre of the cover is positioned at a distance Ro from the centre of the cover 7 which distance Ro is substantially the same as the radius Rh of the part of the coils at the distal end of helix 5 which is nearest the centre of the cover so that opening 9 extends radially over a portion of the cover 7 which is aligned with the coils of material forming helix 5. Preferably opening 9 has a diameter Do which is substantially the same as, or slightly smaller (for example up to 20% smaller) than, the diameter Dh of the material of which the coils of helix 5 is made, in order than when a portion of helix 5 of diameter Dh passes through opening 9 the surface of helix 5 is in sealing engagement with, and substantially forms a fluid tight seal with, the wall 11 of opening 9. Opening 9 is inclined so it forms curved, sloping grooves 13', 13" in the inner and outer surfaces 15, 17 of cover 7. The radius of curvature of the grooves 13', 13" substantially match that of helix 5 and the slope of grooves 13', 13" substantially matches the pitch of the helix 5.

In these figures helix 5 is retracted away from the distal end of cover 7 as might occur during assembly, storage or pre-insertion testing of lead 1.

Figures 2a) and 2b) show the lead of figures Ia) and Ib) where helix 5 has been advanced by being rotated so the tip 19 of helix 5 has entered opening 9 and then moved along groove 13', 13" so that the tip 19 is flush with the end 17 of groove 13" which is furthest away from opening 9. Preferably the surface 21 of tip 19 which faces in the longitudinal direction of helix 5 is shaped so that it in this position forms a smooth surface together with the outer surface 17 of cover 7. Preferably it simultaneously also it substantially fills grooves 13', 13". Preferably the helix is moved to this position before the lead is inserted into a patient. In this position body fluids cannot enter the distal end of the lead and as the opening is filled there are no sharp edges exposed which otherwise could damage tissue as the lead is being positioned. As the outer surface 17 and tip surface 21 form a continuous convex surface, there are no sharp edges which can punch into tissue when the lead is push up against the tissue it is intended to be used with, and the risk of tissue damage is reduced.

Figures 3a) and 3b) show the lead of the previous figure where helix 5 has been further advanced so that one revolution of it is outside cover 7.

A second embodiment of a lead in accordance with the present invention has a convex cover which has a radius of curvature in the longitudinal direction of the lead which is greater than the radius of the lead. This forms a cover which is flatter than the cover of the first embodiment.

While the invention has been illustrated by examples of leads in which the cover is provided with an opening, it is also conceivable to provide a solid convex cover which during implantation of the lead is intended to be pierced by the active fixation means as the active fixation means is advanced into contact with the tissue to which the lead is being attached.

All embodiments of a convex cover in accordance with the present invention may be covered with an electrically conducting coating and attached to a conductor extending the length of the lead in order to enable it to be used for stimulation and/or sensing. Preferably any coatings used, electrically conducting or not, are biocompatible.

The above description relates only to examples of embodiments of the invention and it should be understood that further modifications may be made to the invention without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. A lead comprising a lead body (3) which encloses active fixation means (5), characterised in that the distal end of lead body (3) is covered by a convex cover (7).

2. A lead in accordance with claim 1 wherein said convex cover, wherein said cover is provided with an opening (9) positioned asymmetrically on said cover.

3. A lead according to claim 2, wherein said active fixation means (5) at its distal end comprises a plurality of coils and that said opening (9) is arranged at the same radial position as said coils.

4. A lead according to any of claims 2 or 3 wherein said opening (9) has a diameter Do which is the same as or up to 20% smaller than the diameter Dh of the material of which the coils of active fixation means (5) is made.

5. A lead according to any of claim 2-4 wherein the said opening is inclined and forms internal and external sloping curved grooves (13', 13") and the tip (19) of active fixation means (5) is shaped in order to be able to form a smooth surface together with the outer surface (17) of cover (7) when positioned flush with said outer surface (17).

6. A lead according to any of claims 1-5 wherein said active fixation means (5) is comprised of non-conducting material.

7. A lead according to any of claims 1-5 wherein said active fixation means (5) is comprised of conducting material.

8. A lead according to any of claims 1-7 wherein said convex cover (7) is electrically conducting.