During the implantation of an endocardial lead body, the lead is introduced into the heart using a venous approach, usually from the subclavian or cephalic vein in the shoulder area under the pectoral muscle. To stabilize the lead body at the venous entry site, the lead body is secured to both the vein and to the surrounding fascia tissue. A suture placed around the vein near the lead entry point ties the lead body to the vein, and a suture sleeve around the lead body is used to anchor the lead body to adjacent tissue.
Suture sleeves in present use are generally tubular structures molded out of a soft, implantable elastomer such as silicone. After the lead body is tied to the vein, the sleeve is slid along the lead body to the location at which the lead is to be anchored to the underlying tissue. One or more sutures are then tied around the sleeve to compress it and thereby secure it to the lead body. Circumferential grooves in the outer surface of the sleeve are typically provided for this purpose. The last step is to anchor the sleeve to adjacent body tissue; sutures passed through eyelets formed in a pair of tabs projecting from the sleeve provide the required anchoring.
These existing suture sleeves have several drawbacks. For example, it is difficult for the physician to control the degree to which these sleeves are compressed when they are secured to the lead body. The ligature around the sleeve must be tight enough to prevent the lead body from sliding in the suture sleeve but not so tight as to damage the insulation of the lead body. This is especially important with bipolar coaxial leads because an excessively tight ligature could rupture the lead insulation and cause the outer and inner electrical leads to come into contact with each other, resulting in a short circuit. Overtightened ligatures can also result in electrical lead fractures. These problems are common enough to warrant the inclusion of cautionary information in pacemaker product literature or in notices included in the product packaging regarding the use of anchoring sleeves. It would therefore be desirable to eliminate the need for sutures for compressing the sleeve.
U.S. Pat. No. 4,672,979 discloses another type of suture sleeve comprising an outer, elastomeric tubular sleeve and a relatively stiff collet member. The collet includes a plurality of axially extending legs having inner surfaces that are serrated so as to firmly grip the lead body. In use, the collet and the tubular sleeve are separately threaded onto the lead body. With the collet positioned at the lead body anchoring site, the tubular sleeve is forced over the collet thereby urging the serrated surfaces of the collet inwardly into engagement with the lead body. The assembly is then sutured to surrounding tissue to anchor the lead body.
The suture sleeve of the '979 patent has several disadvantages. The serrations have a tendency to pinch and puncture the outer insulative layer of the lead body. Moreover, because the tubular sleeve and collet are separate elements, during positioning of the collet the tubular sleeve may slide down the lead body due to its lubricity when covered with body fluids. In this event, the suture sleeve installation is substantially complicated.
Accordingly, it is an object of the present invention to provide a suture sleeve for securely gripping and anchoring the lead body of an implantable medical device, such as a cardiac pacemaker, that does not require the use of sutures to compress the sleeve.
It is another object of the present invention to provide a lead body gripping and anchoring suture sleeve that does not damage the lead body.
It is yet another object of the present invention to provide a compressible lead body gripping and anchoring suture sleeve in which the compression of the sleeve is self-limiting so as to prevent lead body damage.