Abstract:
In one embodiment, the present invention provides a cardiac lead device including a fixation mechanism slidably attached to the lead such that when the fixation mechanism is expanded into contact with a body lumen, the lead may be moved relative to the fixation mechanism if desired. Such lead movement may be limited by complimentary structure on the lead body and the fixation mechanism that prevents the lead from moving unless sufficient force is applied to the lead.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to implantable medical devices and, in particular, to fixation of cardiac leads in a patient&#39;s vascular system.  
       BACKGROUND  
       [0002]     Cardiac function management systems are used to treat arrhythmias and other abnormal heart conditions. Such systems generally include cardiac leads, which are implanted in or about the heart, for delivering an electrical pulse to the cardiac muscle, for sensing electrical signals produced in the cardiac muscle, or for both delivering and sensing. The lead typically consists of a flexible conductor, defining a central channel or lumen, surrounded by an insulating tube or sheath extending from an electrode at the distal end to a connector pin at the proximal end.  
         [0003]     Cardiac lead placement may be accomplished by introducing the lead through a major blood vessel and advancing a distal end of the lead to a final destination in or near the heart. To facilitate cannulation of the vasculature, it is often helpful to first advance a guiding catheter through the desired vascular path. One difficulty with implanting leads in this fashion is that the cardiac lead has a tendency to become dislodged from its desired location during or after lead implantation. For example, when a clinician withdraws the guiding catheter, the lead may dislodge or otherwise reposition. Until tissue in-growth ultimately fixes the lead at the desired site, cardiac leads may also become dislodged by subsequent physiological activity.  
         [0004]     A variety of screws, anchors, and other devices have been secured to cardiac leads to affix the leads at a desired location in a patient&#39;s vasculature. Nonetheless, there is a need in the art for a cardiac lead having a fixation mechanism which effectively affixes the cardiac lead at a desired position, but which also allows the lead to be repositioned within or removed from the patient&#39;s vasculature, even after an extended implantation period.  
       SUMMARY  
       [0005]     In one embodiment, the present invention provides a cardiac lead system adapted for anchoring in a vessel. The system includes a conductive lead body and an expandable fixation mechanism. The lead body has a proximal end and a distal end and defines a lead lumen extending between the proximal and distal ends. The expandable fixation mechanism has an expanded position adapted to engage an inner surface of the vessel, and is slidably secured to an outer surface of the lead body. The lead body and the fixation mechanism include respective first and second structures that are adapted to contact each other to resist relative longitudinal movement.  
         [0006]     The first structure on the lead body may include one or more stops, curves, bends, coils, ridges or other protrusions on the lead body the second structure may include one or more rings connected to the fixation mechanism and encircling the lead body. In one embodiment, the system further includes a stylet, which may be inserted into the lead body to straighten any curves, bends, or ridges in the lead body, thus reducing the overall diameter of portions of the lead body.  
         [0007]     The fixation mechanism may be self-expanding or balloon-expanding. For self-expanding embodiments, the fixation mechanism may be compressed by an outer guide or by a dissolvable material which dissolves upon contacting bodily fluid. In one embodiment, the fixation mechanism is formed similarly to a conventional stent.  
         [0008]     In another embodiment, the present invention provides a cardiac lead device including a conductive lead body and an expandable fixation mechanism as reported above, means for compressing the fixation mechanism, and means for resisting the relative movement when the fixation mechanism is secured to the outer surface of the tubular wall of the lead body. The means for compressing the fixation mechanism may include one or more guides through which the lead body and/or fixation mechanism are slidably movable. The means for compressing may also include a dissolvable material as reported above. The means for resisting relative movement may include the first and/or second structure reported above.  
         [0009]     The present invention also provides a method for implanting a cardiac lead device in a body lumen. A cardiac lead device as reported herein is guided into the body lumen. A fixation mechanism, which is slidably securable to the lead body, is then deployed from a compressed position to an expanded position to engage the internal wall of the body lumen. The lead can be moved relative to the expanded fixation mechanism in order to reposition the lead. Prior to guiding the lead device, one or more guides may be inserted into the body lumen to facilitate the lead implantation process.  
         [0010]     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 obvious 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. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows a schematic view of a cardiac lead implanted in a patient&#39;s vasculature according to an embodiment of the present invention.  
         [0012]      FIG. 2  shows a schematic view of a distal portion of a cardiac lead according to an embodiment of the present invention implanted in a patient&#39;s vasculature.  
         [0013]      FIG. 3  illustrates the embodiment of  FIG. 2  after insertion of a stylet into a lumen of the cardiac lead.  
         [0014]      FIG. 4  shows a distal portion of a cardiac lead implanted in a patient&#39;s vasculature according to another embodiment of the present invention.  
         [0015]      FIG. 5  illustrates the embodiment of  FIG. 4  after insertion of a stylet into a lumen of the cardiac lead.  
         [0016]      FIGS. 6A-6D  show end plan views of multiple embodiments of the present invention.  
         [0017]      FIG. 7  is a flowchart illustrating a method for implanting a cardiac lead according to one embodiment of the present invention.  
         [0018]      FIG. 8  shows a cardiac lead being implanted according to the method described in  FIG. 7 .  
         [0019]      FIG. 9  is a flowchart describing an alternate method for implanting a cardiac lead according to one embodiment of the present invention.  
         [0020]      FIG. 10  illustrates a cardiac lead implanted according to the method illustrated in  FIG. 9 . 
     
    
       [0021]     While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION  
       [0022]      FIG. 1  is a schematic drawing of a cardiac rhythm management device  12  coupled to an intravascular endocardial lead  14  having a proximal end  16  and a distal end  18 . Distal portions of the lead  14  are disposed in the patient&#39;s heart  20 , which includes a right atrium  22 , a right ventricle  24 , a left atrium  26 , and a left ventricle  28 . In the embodiment illustrated in  FIG. 1 , the distal end  18  of lead  14  is transvenously guided into the right atrium  22 , through a coronary sinus  30 , and into a cardiac vein  31 . The illustrated disposition of the lead  14  may be used for delivering pacing and/or defibrillation energy through any cardiac vessel, including the cardiac sinus  30 , coronary veins or pulmonary artery, to the left ventricle  28  for the treatment of cardiac arrhythmias.  
         [0023]      FIGS. 2-5  show cross-sectional views of a vessel  31  into which the cardiac lead  14  has been implanted. The cardiac lead  14  generally includes a lead body  33  and an expandable fixation mechanism  34 , which is secured to the lead body  33 . The lead body  33  has a proximal end  16  (see  FIG. 1 ) and a distal end  18  and at least one lead lumen  38  extending between the proximal and distal ends  16 ,  18 . The lead body  33  further includes at least one electrode  37  at distal end  18  for delivering electrical pulses to a patient&#39;s heart. Although not illustrated, the electrode  37  may be affixed to the wall of vessel  31 .  
         [0024]     The fixation mechanism  34  is configured to contact the vessel  31  when in an expanded position as shown in  FIGS. 2-5 . The fixation mechanism  34  shown in  FIGS. 2-5  is configured in a stent-like form. Other shapes and configurations may also be suitable for embodiments of the present invention. The fixation mechanism  34  may be formed from conventional stent materials, for example, stainless steel, nitinol, or shape memory alloys or polymers. In a particular embodiment, the fixation mechanism  34  is (or is a modified version of) a Palmaz-Shatz type stent commonly used in vascular intervention procedures. In another embodiment, the fixation mechanism  34  is partially or completely formed from a biodegradable and or dissolvable material that degrades when contacted with body fluid.  
         [0025]     The fixation mechanism  34 , is slidably secured to the lead body  33  such that the lead body  33  is selectively moveable relative to the fixation mechanism  34  along the longitudinal path of the vessel  31  when the fixation mechanism  34  is in the expanded position shown. Such selective relative movement is accomplished by providing both the lead body  33  and the fixation mechanism  34  with cooperating or corresponding structures as described in detail below.  
         [0026]     The structure on the lead body  33  may be configured to increase a major dimension (e.g. diameter) of the lead body  33  at select locations. Numerous configurations may be employed for the structure on the lead body  33 . In the embodiment illustrated in  FIG. 2 , for example, the lead body  33  includes one or more coiled or looped portions  44 , which cooperate with structure on the fixation mechanism  34  to limit undesired or unintentional longitudinal movement of the lead body  33 . In an alternate embodiment, the structure includes a two-dimensional shape such as a sinusoidal shape or a J-bend.  
         [0027]     The embodiment illustrated in  FIG. 4  includes protrusions  46  secured along a plurality of ridges  48  formed in the lead body  33 . The protrusions  46  may be formed as bumps, spheres, ears, rings, or other shapes formed on and extending from the surface of the lead body  33 . The protrusions  46  may be formed from silicone or other biocompatible materials and may remain substantially permanently secured to the lead body  33  or may be biodegradable.  
         [0028]     The looped portions  44 , protrusions  46 , or ridges  48  may be positioned anywhere along the length of the lead body  33 . In the illustrated embodiments, structure is located both proximal and distal to the fixation mechanism  34  to allow for a range of proximal and distal movement of lead body  33 . Other configurations may also be appropriate depending on the specific application of the cardiac lead  14 . Furthermore, although  FIGS. 3-4  show specific structures for limiting movement of the lead body  33 , it should be appreciated that a wide range of structures, either individually or in combination, may be used in embodiments of the present invention. The loops  44 , protrusions  46 , or ridges  48  may be spaced at various adjustment intervals depending on the magnitude of adjustments desired. In one embodiment, for example, these structures are located between about  1  and about  10  millimeters apart, or more preferably between about 2 and about 5 millimeters apart, along the lead body  33 .  
         [0029]      FIGS. 6A-6C  show plan views of the cardiac lead  14  from the perspective of the line  6 - 6  shown in  FIG. 2 . As shown in  FIGS. 6A-6D , the fixation mechanism  34  includes one or more fixation rings  40  which contact or otherwise interact with structure on the lead body  33  to provide selective movement of the lead body  33 . The fixation rings  40  generally encircle the lead body  33 , and are generally connected to the outside (i.e. vessel engaging) surface of the fixation mechanism  34  via struts  42 . As further shown in  FIGS. 6A-6D , the struts  42  may be have a variety of configurations. The fixation rings  40  may be formed anywhere along the length of the fixation mechanism  34 , but in one embodiment, the fixation rings  40  are disposed on opposing ends of the fixation mechanism  34 .  
         [0030]     The fixation rings  40  and struts  42  may be formed from a variety of materials, including materials commonly used to form stents. In certain embodiments either or both of the rings  40  and the struts  42  may be formed from an elastic, string, fibrous, or thread-like material. Additionally the fixation rings  40  and the struts  42  may be formed to be biodegradable and/or dissolvable upon contact with bodily fluid, or to remain substantially permanently in the vessel  31 . In one embodiment, the fixation rings  40  and the struts  42  may be formed to biodegrade after a period of time sufficient to allow the lead body to become secured within the vessel  31  by tissue in-growth. For example, the fixation mechanism  34  could be temporarily fixed to the lead body with a resorbable material that would dissolve over a period of weeks or months to allow extraction of the lead at a later date.  
         [0031]     As shown in  FIGS. 2 and 4 , the structures disposed on both the lead body  33  and the fixation mechanism  34  resist longitudinal movement of the lead body  33  relative to the fixation mechanism  34  because the structure on the lead body  33  (i.e. coiled portions  44 , protrusions  46  and/or ridges  48 ) has a major dimension that is greater than the diameter of the fixation rings  40  such that longitudinal movement of the lead body  33  is limited or selectively prevented.  
         [0032]     To reposition the lead body  33  according to one embodiment, the major dimension of the lead body  33  in the vicinity of the fixation mechanism  34  may be reduced to a size that is smaller than the diameter of the fixation rings  40 , by inserting a stylet or guidewire into the lead lumen  38 . For example,  FIG. 3  shows the embodiment of  FIG. 2  after inserting a stylet or guidewire  50  such that the coiled portions  44  are straightened.  FIG. 5  shows the embodiment of  FIG. 4  after inserting a stylet or guidewire  50  such that the ridges  48  are straightened. In both cases, the lead body  33  becomes movable relative to the fixation mechanism  34  along the longitudinal path of the vessel  31 . After repositioning the lead body  32 , the stylet or guidewire  50  may be removed such that the structure returns to the shape shown in  FIGS. 2 and 4 , which again limits longitudinal movement of the lead  33  with respect to the fixation mechanism  34 . According to another embodiment, instead of changing the major diameter of the lead, the interacting structures on the lead body  33  and the fixation rings  40  have sufficient flexibility to allow the structures to pass through the rings upon application of a sufficient force at the proximal end  16  of the lead body  33 .  
         [0033]      FIGS. 7-8  depict a method of implanting the cardiac lead  14  according to an embodiment of the present invention.  FIG. 7  is a flow-chart showing a method of implanting the cardiac lead  14  according to one embodiment of the present invention. The cardiac lead  14  is pre-loaded into an inner guide catheter  58  such that the fixation mechanism  34  is in a compressed position (block  52 ). The inner guide catheter  58  is then directed through the patient&#39;s vasculature, optionally through an outside guide catheter or sheath  60 , to a desired location in the patient&#39;s vasculature (block  54 ) as shown in  FIG. 8 . The inner guide catheter  58  is then withdrawn such that the fixation mechanism  34  deploys to an expanded position (block  56 ) shown in  FIGS. 2-5 . The fixation mechanism  34 , in this embodiment, may expand by, for example, self-expansion or balloon expansion. After the fixation mechanism  34  is expanded and secured to the wall of the vessel  31 , the longitudinal position of the lead  33  may be adjusted. The stylet or guidewire  50  is then removed, which allows the lead  33  to resume its default shape (see, for example,  FIGS. 2 and 4 ) having an increased major diameter, which, in turn, limits or resists further longitudinal movement of the lead  33 .  
         [0034]     In a variation of the method described in  FIGS. 7-8 , the fixation mechanism  34  may be fixed to the lead body in a compressed state with a dissolvable material such as manitol. The lead  14  is inserted through inner guide catheter  58  until positioned as desired. The lead  14  could then be advanced out of the inner guide catheter  58  to the desired position, which would also expose the dissolvable material to blood. After a short period of time the dissolvable material would dissolve, allowing the fixation mechanism  34  to expand and contact the vessel wall.  
         [0035]      FIGS. 9-10  depict a method of implanting the cardiac lead  14  according to another embodiment of the present invention.  FIG. 9  is a flow-chart summarizing a method of implanting the cardiac lead  14  according to an embodiment of the present invention, in which the fixation mechanism  34  is initially positioned on an outer surface of the inner guide catheter  58  (block  62 ) with an optional inflation balloon  59  disposed between the fixation mechanism  34  and the inner guide catheter  58 . The inner guide catheter  58  is then directed through an outside guide catheter  60  and into a desired location in a patient&#39;s vasculature (block  64 ). The lead body  33  is then directed through the inner guide catheter  58  (block  66 ) until the distal end  18  of the lead body  33  extends past the distal end of the inner guide catheter  58  and into a desired location (block  66 ) as shown in  FIG. 10 . The fixation mechanism  34  is then expanded via self-expansion or by inflating the optional balloon  59  in a conventional manner (block  70 ). The inner guide catheter  58  is then withdrawn such that the fixation rings  40  encircle the lead body  32  as shown in  FIGS. 2-5  (block  72 ). After the fixation mechanism  34  is expanded and secured to the wall of the vessel  31 , the longitudinal position of the lead  33  may be adjusted. The stylet or guidewire  50  is then removed, which allows the lead  33  to resume its default shape (see, for example,  FIGS. 2 and 4 ) having an increased major diameter, which, in turn, limits or resists further longitudinal movement of the lead  33 .  
         [0036]     In a variation to the method shown in  FIGS. 9-10  and described above, the fixation mechanism  34  is disposed on the inner guide catheter  58  and is pre-loaded into the outside guide catheter  60 . After positioning the inner and outer guide catheters  58 ,  60  and the lead body  33  as described above, a tube or other structure (not shown) may be directed between the inner and outer guide catheters  58 ,  60  to deploy the fixation mechanism  34  into an expanded position shown in  FIGS. 2-5 .  
         [0037]     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.