Abstract:
A medical electrical lead and a method of its use. The lead has an elongated lead body having an outer circumference and provided with an electrode. A push tube is mounted circumferentially around the lead body and the lead body is longitudinally movable with respect thereto. A fixation helix is mounted to the push tube, extending along a generally helical axis around the outer circumference of the lead body. The lead may be employed by advancing the lead to a desired location for the fixation helix and then rotating the push tube to secure the helix to tissue. The lead body may then be moved longitudinally with respect to the push tube to place the electrode in a desirable location.

Description:
TECHNICAL FIELD 
       [0001]    The present invention pertains to medical electrical leads and more particularly to implantable medical electrical leads including active fixation elements. 
       BACKGROUND 
       [0002]    Implantable medical devices, for example cardiac pacemakers and defibrillators, often include elongate medical electrical leads having one or more electrodes to sense electrical activity and deliver therapeutic stimulation. In recent years, with the advent of left ventricular pacing to alleviate heart failure, leads have been advanced into the coronary veins in order to position the electrodes of the leads at left ventricular pacing sites, typically located in proximity to the base of the left ventricle. Although a variety of left ventricular pacing leads, along with methods for implanting such leads, have been developed, there is still a need for a lead including features that facilitate delivery to, and fixation at, sites in the coronary vasculature. 
         [0003]    One type of left lead adapted for placement in the coronary vasculature is that disclosed in U.S. Pat. No. 7,860,580, issued to Sommer, et al. and incorporated herein by reference in its entirety. Another type of left lead adapted for placement in the coronary vasculature is that disclosed in U.S. Pat. No. 7,532,939, issued to Sommer, et al. and also incorporated herein by reference in its entirety. An improvement to leads of this type is disclosed in U.S. patent application Ser. No. 13/793,622, filed Mar. 11, 2013 by Sommer, et al. also incorporated herein by reference in its entirety. 
         [0004]    Additional designs for a side-helix leads are disclosed in U.S. Pat. No. 5,443,492, issued to Stokes, et al. U.S. Pat. No. 7,529,584, issued to Laske, et al, U.S. Pat. No. 7,313,445, issued to McVenes, et al., U.S. Pat. No. 6,493,591, issued to Stokes, U.S. Pat. No. 6,556,874, issued to Audoglio, all of which are incorporated herein in their entireties. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention may comprise an improvement to the prior art leads as disclosed in U.S. Pat. No. 7,860,580, cited above. Similarly, the present invention may comprise an improvement to the any of the other prior art leads disclosed in the patents cited above of the same general type, including fixation mechanisms taking the form of a hook or coil extending from the lead body. 
         [0006]    In a preferred embodiment, the invention comprises left ventricular (LV) pacing lead having one or more electrodes and having a push tubing overlying the lead body and provided with a fixation mechanism. The fixation mechanism is preferably a fixation helix extending from the push tubing and extending circumferentially around the lead body. The helix may extend distally from a distal end of the push tubing and may be spaced outward from the lead body to define a gap between the two. 
         [0007]    In a preferred embodiment, the helix is one which, like that of the above-cited Stokes, et al. &#39;492 patent, extends from the lead body for less than one full turn around the lead body. Preferably, the helix extends from around one half to three quarters of the circumference of the lead body. 
         [0008]    The push tubing is preferably rotatable with respect to the lead body and slidable along the length thereof. In use, the lead may be advanced through the vasculature to a desired location, for example by advancing the lead body and push tubing together by means of a guide catheter. When distal end of the guide catheter has reached a desirable location for the fixation mechanism, the lead may be advanced distally out of the guide catheter and the push tubing may be rotated to engage the fixation helix with vascular tissue. The lead body may then be advanced distally through the push tubing to place the electrode or electrodes in a desired location. 
         [0009]    After the electrodes are satisfactorily located, the push tubing may then be coupled to the lead body in such a manner as to prevent further relative longitudinal movement, which in turn stabilizes the location of the electrodes relative to the location of the fixation device. In particular, the push tubing and lead body may be stabilized with regard to one another by means of a retention sleeve and/or sutures as described in U.S. Pat. No. 8,551,113 issued to Hanse, et al. and incorporated herein by reference in its entirety. Other retention mechanisms could be substituted, such as those described in U.S. Pat. No. 7,747,333 issued to Zarembo, et al. and U.S. Pat. No. 7,890,174 issued to Soltis, et al., both also incorporated herein by reference in their entireties. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements. 
           [0011]      FIG. 1  is a plan view generally illustrating, a lead, according to the invention. 
           [0012]      FIG. 2  is an illustration if a human heart and of the lead of  FIG. 1  as implanted. 
           [0013]      FIG. 3  is a flow chart illustrating the steps of implantation of a lead according to the invention. 
           [0014]      FIG. 4  is a plan view of a portion of a lead as shown generally in  FIG. 1 , according to a first embodiment. 
           [0015]      FIG. 5  is a plan view of a portion of a lead as shown in  FIG. 1 , according to a second embodiment. 
           [0016]      FIG. 6  is a plan view of a portion of a lead as shown in  FIG. 1 , according to a third embodiment. 
           [0017]      FIG. 7  is a cross sectional view through a lead as generally illustrated in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical illustrations for implementing exemplary embodiments of the present invention. Constructions, materials, dimensions, and manufacturing processes suitable for making embodiments of the present are known to those of skill in the field of the invention. 
         [0019]      FIG. 1  is a plan view of a lead  100  including a fixation mechanism  120 , similar to mechanism  220 . Fixation mechanism  120  takes the form of a metal fixation helix mounted to push tube  160 , which may be fabricated of an appropriate biocompatible polymer. In the illustrated preferred embodiment, helix  120  has a sharpened free end  122  which extends distally from its attachment point adjacent the distal the end of push tube  160  and extends circumferentially around and spaced from lead body  150 . In alternative embodiments, the helix  120  might be located proximal to the distal end of  160 , extending circumferentially around both the push the  160  and the lead body  150  therein. In still other embodiments, helix  120  may have a free end extending proximally from its attachment point on the push tube  160 . 
         [0020]    Lead body  150  is sized such that it may be freely moved longitudinally and rotationally within push tube  160 , unless otherwise retained in position by means of retention sleeve  161 . Sleeve  161  corresponds to that described in the above-cited U.S. Pat. No. 8,551,113 issued to Hanse, et al. According this embodiment of the present invention, retention sleeve  161  includes features adapted to create a frictional interface between fixation mechanism  160  and lead body  150 . Retention sleeve  961  may be formed as an independent component, separate from push tube  960  and subsequently fixedly coupled to push tube  160 , or may be formed as an integral segment of push tube  160 . Sleeve  161  including retention grooves  164  formed on an outer surface thereof. Grooves  164  are adapted to receive a retaining element, which engage grooves to press sleeve  161  against lead body  950 , thereby fixedly retaining rube  160  in a prescribed position upon lead body  150  after helix  120  is secured to a desired implant site. According to this embodiment of the present invention, a suture may be tied about each groove or a spring clip fitted about each groove  164  to compress sleeve  161  against lead body  15  so that longitudinal and preferably rotational movement of lead body  150  relative to sleeve  160  is prevented. According to yet another embodiment, one of grooves  164  may accommodates a holding tool to temporarily fix the location if the sleeve  161  relative to lead body  150 , as described in the cited Hanse &#39;113 patent. As noted above, other retention mechanisms may be substituted. 
         [0021]    Lead body  150  has a proximal portion, to which a connector  105  is coupled, a distal portion along which electrodes  125  and  126  are located. Lead body  150  is formed by an insulative sheath of a biocompatible polymer surrounding internal metallic conductors. The conductors extend from electrodes  125  and  126  to connector  105 , coupling the electrodes to contacts  130  and  132  of connector  105  in a conventional fashion. Anchoring sleeve  180  is used in a conventional fashion to stabilize the lead and seal the venous insertion site. 
         [0022]    Connector  105  as illustrated takes the firm of an IS-1 bipolar connecter, but any appropriate connector mechanism may be substituted. Electrodes  125  and  126  take the form of ring and barrel shaped electrodes, respectively, provided with ring-shaped steroid eluting MCRD&#39;s as described in US Patent Publication No. 2006/0229693 by Bauer, et al., incorporated herein by reference in its entirety. Other known electrode designs may of course be substituted. 
         [0023]      FIG. 2  illustrates the location of lead  100  of  FIG. 1  as used to provide left ventricular cardiac pacing and or sensing.  FIG. 3  is a flow-chart illustrating the steps of lead placement corresponding to the positioning of the lead  100  as illustrated in  FIG. 2 . 
         [0024]    As illustrated, the lead  100  is located in the heart by advancing the lead transvenously into the right atrium and thereafter into the coronary sinus and into a cardiac vein extending therefrom. This may be accomplished by first introducing the lead into the vascular system (step  200 ,  FIG. 3 ) by any conventional techniques. The lead is then advanced into the coronary venous system (Step  210 ,  FIG. 3 ). This may be accomplished by passing the lead through a guide catheter or by advancing the lead over a guidewire or by means of a stylet inserted into the lead. Any conventional mechanism for placing the lead into and within the coronary venous system may be employed. If necessary, during advancement of the lead, the push tubing  160  and fixation helix may be rotated opposite the direction of rotation used to attach the fixation helix in order to avoid snagging or entanglement of the helix with vascular or heart tissue. 
         [0025]    When helix  120  is located at an appropriate location for fixation, as determined by the physician, the push tubing is rotated to screw the fixation helix into heart tissue (Step  220 ,  FIG. 3 ). Thereafter, the lead body  150  may be advanced and/or retracted through the push tube  160  until the electrodes  125  and  126  are located in a desirable position (Step  230 ,  FIG. 3 ). Determination of the position for electrode location may be accomplished by any conventional method, such as pacing threshold texting and/or measurement of R-wave amplitudes. Alternatively or additionally, appropriate electrode locations may also be determined based upon determinations of hemodynamic characteristics of the heart as associated with stimulation of heart tissue at various electrode locations. In some cases, the time order of steps  220  and  230  might be reversed. 
         [0026]    Once the electrodes are placed at the desired location, the push tube  160  and fixation helix  120  are coupled to the lead body to prevent subsequent relative longitudinal movement as described above in conjunction with  FIG. 1  (Step  240 ,  FIG. 3 ). Any equipment not intended for long term implant, e.g. guide catheter, stylet, guidewire, etc. can be removed. Repositioning of the electrodes after implant may also be possible. 
         [0027]    While  FIG. 2  illustrates the electrodes  126  and  125  as located in the great cardiac vein, it should be understood that other locations in the heart&#39;s venous system may also be accessed using this lead, including the coronary sinus itself and other cardiac veins. Electrode placement may alternatively be optimized for atrial stimulation and/or sensing. Alternatively, the lead may be useful in other vascular or non-vascular location within the body wherein the distance between a suitable fixation location and a desired electrode location may be variable. 
         [0028]      FIG. 4  shows the fixation helix  120  of  FIG. 1  in more detail. In this view, it can be seen that helix  120  takes the form of a multiple turn coil, having one or more close-wound turns encircling the distal portion of push tube  160 , with at least a portion of an open-turn extending distally over and spaced from lead body  150 . As illustrated, helix  12  has a constant pitch open wound section if approximately ¾ of a turn. Additional open wound turns could be added in alternative embodiments. 
         [0029]      FIG. 4  shows an alternative embodiment of the fixation helix. Here, the fixation helix  120 A, also takes the form of a multiple turn coil, having one or more close-wound turns encircling the distal portion of push tube  160 , with at least a portion of an open-wound turn extending distally over and spaced from lead body  150 . However, in this embodiment, an additional plastic component  121  is provided, providing a stop surface generally perpendicular to the helical axis of helix  120 A. As described in the above-cited U.S. patent application Ser. No. 13/793,622, filed Mar. 11, 2013 by Sommer, et al., this stop surface prevents pinching and wedging of tissue between the helix and lead body  150 . 
         [0030]      FIG. 5  shows an alternative design of a fixation helix  121 B wherein the pitch of the open-wound portion of the helix decreases as the distal tip of the helix is reached to a generally zero pitch segment  122 , Segment  122  extends essentially perpendicular to the axis of the lead body. Unlike fixation helixes in which the pitch remains constant along their open-wound portions, this embodiment provides a helix that allows for easier tissue entry during rotation of the push tube  160 . Additionally, a reduced pitch along the distal tip portion and/or along last winding increases the holding force to the vein wall. 
         [0031]      FIG. 7  illustrates a cross section through the lead as illustrated in  FIG. 4 , with numbered components corresponding to identically numbered components in  FIGS. 1 and 4 . The inside surface  123  of the helix  121  tip is ground to produce a sharpened tip. The inside tip grind allows for a safer passage of the exposed helix at implant and reduces any vein damage that may occur at implant. 
         [0032]    Conductors  190  are also illustrated in cross section. In this embodiment, conductors  190  take the form of four filar coil with each filar provided with an insulation coating. In the embodiment of  FIG. 1  with two electrodes, typically two filars would be coupled to each electrode. If four electrodes were used, one filar would be coupled to each electrode. If only one electrode is used, all four filars could be coupled to that electrode. Other numbers of filars and other conductor types could be substituted. Use of conductors taking the form of a coil as illustrated provides the benefit of an internal lumen  18  through which a guidewire or stylet may be passed. 
         [0033]    In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.