Threaded suture sleeve
FIELD OF THE INVENTION 
     This invention relates generally to suture sleeves for anchoring the lead bodies of implantable medical devices and more particularly to a suture sleeve for securely gripping a lead body while preventing damage thereto. 
     BACKGROUND OF THE INVENTION 
     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 keep the lead body from shifting in the vein, the lead body is secured to both the vein and to the underlying muscle tissue. A suture placed around the vein near the lead entry point ties the lead 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 is tied to the vein, the sleeve is slid along the vein 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. 
     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 a 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. It would therefore be desirable to eliminate the need for sutures for compressing the sleeve. 
     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 in which the compression of the sleeve is self-limiting so as to prevent lead body damage. 
     SUMMARY OF THE INVENTION 
     In accordance with the broad aspects of the present invention, there is provided a suture sleeve eliminating the need for compression sutures. 
     In accordance with a preferred embodiment of the invention, the suture sleeve includes a tubular member having a lumen for receiving a lead body. The tubular member has external threads for receiving a mating, internally threaded collar. The tubular member and collar are so configured that the collar, when tightened on the sleeve, radially compresses a portion of the sleeve into gripping engagement with the lead body. The sleeve includes an abutment surface engaged by an end surface of the collar, thereby limiting the travel of the collar and the gripping action imposed thereby. In this fashion, the compression of the lead body is positively controlled so that while providing an adequate degree of gripping, the compression of the lead body is limited, thereby preventing damage thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects, advantages and features of the invention will become apparent from the detailed description of the preferred embodiments below, when read in conjunction with the accompanying drawing, in which: 
     FIG. 1 is an axial cross section of a suture sleeve for anchoring the lead body of an implantable medical device in accordance with a preferred embodiment of the present invention, the suture sleeve being shown in its open configuration; and 
     FIG. 2 is an axial cross section of the sleeve of FIG. 1 shown in its closed, lead body-gripping configuration. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The drawing shows a suture sleeve 10 for gripping and anchoring the lead body 12 of an implantable medical device such as a cardiac pacemaker. Because the structure of lead bodies is well known in the art, the details thereof have been omitted from the drawings for the sake of simplicity. 
     The suture sleeve 10 includes an elongated tubular member 14 defining a longitudinal lumen 16 through which the lead body 12 extends. The tubular member 14 has three sections: a first section 18 defining a gently tapered portion 20 of the lumen 16 to facilitate lead body insertion; a second or mid section 22 having threads 24 on the outer surface thereof; and a third section 26 having an outer tapered surface 28 and an enlarged annular end 30. At the junction of the first and second sections is an annular shoulder or abutment surface 32. 
     The third section 26 of the tubular member 14 is made of a soft implantable elaster, such as silicone or polyurethane, while the remainder of the tubular member is preferably fabricated of relatively hard but flexible implantable plastic, such as polysulfone or acetal resin. A common acetal resin is sold under the name Delrin, which is a registered trademark of E.I. du Pont de Nemours &amp; Co. (Inc.). The soft and hard plastic portions of the tubular member 14 are bonded at an interface 34 using techniques well known in the art. 
     Disposed about the tubular member 14 and bridging the second and third sections thereof is a collar 36 a portion of which has internal threads 38 received by the threads 24 on the tubular member 14. For a .065-inch diameter outer insulation on the lead body, the preferred thread is 8-36 UNF. 
     The remaining portion of the collar 36 has a tapered inner wall 40 in engagement with the tapered surface 28 on the tubular member. The tapered inner wall 40 and surface 28 preferably have substantially corresponding slopes. The collar further has a radially extending end surface 42 facing the abutment surface 32 on the tubular member, and an opposite end 44. 
     A pair of projecting tabs 46 formed integrally with the collar have eyelets 48 adapted to receive sutures (not shown) for tying the suture sleeve to the surrounding tissue. 
     The collar 36 is preferably made of hard implantable plastic, such as polysulfone or delrin, by way of example. Alternatively, the collar 36 may be fabricated of an implantable metal or metallic alloy such as titanium, platinum, platinum-iridium or stainless steel. 
     In use, the suture sleeve 10 is initially in the open configuration shown in FIG. 1 in which, by way of example, the collar 36 is open by about three turns. 
     In this initial, open configuration the end 44 of the collar 36 is in engagement with the enlarged end 30 which thereby functions as a stop to prevent further unscrewing of the collar. In its open configuration, the suture sleeve 10 can move freely on the lead body for proper placement. When the sleeve location has been determined, tightening of the threaded collar 36 on the threads of the tubular member 14 causes the tapered wall 40 of the collar, acting in cooperation with the tapered surface 28 on the tubular member, to compress a portion 29 of the soft section 26 of the tubular member. This action forces the portion 29 inwardly to securely grip the lead body 12, as shown in FIG. 2. Engagement of the end surface 42 of the collar with the abutment surface 32 on the tubular member limits the tightening of the collar, thereby limiting compression of the lead body. Because compression of the lead body insulation is thereby limited, the suture sleeve 10 is designed to provide reliable, secure gripping of the lead body while preventing damage thereto. 
     More specifically, when the soft plastic section 26 of the tubular member 14 is deformed by tightening the threaded collar 36 until it engages the abutment surface 32, the diameter of the lumen at the compressed portion 29 decreases to a predetermined minimum size &#34;d&#34; (FIG. 2). This dimension is selected so that compression of the lead body does not crush the coil just inside the outer insulation of the lead body. 
     By making the diameter of the lumen 16 substantially the same as the diameter of the outer insulation of the lead body 12, sliding of the suture sleeve 10 in the open configuration when the lead body is held in a vertical position is prevented. 
     While various modification and alternative constructions of the invention will be obvious to those skilled in the art, only a specific, preferred embodiment thereof has been shown in the drawings and described in detail. It should be understood, however, that there is no intention to limit the invention to the specific form or example illustrated and described. On the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention as defined by the appended claims.