Abstract:
Certain aspects of the disclosure pertain to methods and apparatus for providing positive fixation of medical components to a portion of incised pericardial tissue. Accordingly, a resilient member protrudes through an incision in the pericardium and produces a positive biasing force to adjacent pericardial tissue against a side surface of an attached body structure. The resilient member can optionally be compressed during implantation and then relaxed to thereafter provide the positive biasing force. Diverse medical components can thus be safely and reliably chronically deployed into the pericardial space, including without limitation, cardiac sensing/pacing, defibrillation and/or cardioversion electrodes, mechanical and/or metabolic sensors and the like. More than one body structure can be linked to a single medical electrical lead and the medical components can couple within and/or upon a portion of the body structure, the resilient member, and the lead in myriad configurations.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS AND PATENT  
       [0001]     The present disclosure relates to the following co-pending applications; namely, U.S. application Ser. No. 11/000,539 by Morris et al. entitled, “METHODS AND SYSTEMS FOR ACCESSING THE PERICARDIAL SPACE” and U.S. application Ser. No. 11/000,538 by Sigg et al. captioned, “Methods and Systems for Providing Therapies into the Pericardial Space,” and U.S. application Ser. No. ______ (Atty Dkt. P-25642.00) entitled, “APPARATUS AND METHODS FOR VACUUM- AND MECHANICALLY-ASSISTED FIXATION OF MEDICAL ELECTRICAL LEADS,” filed on common day herewith, the contents of which are incorporated herein by reference. In addition, this disclosure incorporates the contents of U.S. Pat. No. 6,613,062 to Leckrone et al. captioned, “METHOD AND APPARATUS FOR PROVIDING INTRA-PERICARDIAL ACCESS,” which issued 2 Sep. 2003. 
     
    
     BACKGROUND  
       [0002]     Certain embodiments in the present disclosure pertain to medical component delivery and more particularly to tools for delivering active medical components for chronic attachment within the pericardial space.  
         [0003]     In certain instances, a patient suffering from bradycardia, tachyarrhythmia and/or heart failure will benefit from electrical stimulation pacing and/or defibrillation electrodes implanted on an epicardial surface of the patient&#39;s heart. Minimally invasive methods for accessing the epicardial surface, which is enclosed within a pericardial sac, have recently been developed; these methods provide for piercing through the pericardial sac in order to access the epicardial surface; an example of one such method is described in commonly assigned U.S. Pat. No. 6,837,848. These methods may be used by way of a mini-thoracotomy or in conjunction with a trocar, canula or catheter that has been passed, via a percutaneous incision, through an interstitial space between the patient&#39;s ribs, via a supramanubrial or a sub-xiphoid approach or with a jugular-type access; those skilled in the art are familiar with these techniques.  
         [0004]     Once access to the epicardial surface is established, the implanting physician may desire to implant into the pericardial space a medical electrical lead, including an appropriate electrode configuration and/or one or more physiologic sensors suited to the patient&#39;s need. The physician will almost always need to maneuver the electrode-bearing portion of the lead within the space in order to implant the components at an appropriate location and in a way to provide effective and stable chronic cardiac therapy and/or monitoring of various physiologic parameters.  
       SUMMARY  
       [0005]     Certain embodiments of the present invention pertain to methods and apparatus for providing positive fixation of medical components to a portion of incised pericardial tissue. According to the diverse embodiments of the present invention, a resilient member protrudes through an incision in the pericardium and produces a positive biasing force to adjacent pericardial tissue against a side surface of a body structure. In some embodiments the resilient member can be temporarily compressed during implantation and then relaxed to thereafter provide the positive biasing force.  
         [0006]     Diverse medical components can thus be safely and reliably chronically deployed into the pericardial space, including without limitation, cardiac sensing/pacing, defibrillation and/or cardioversion electrodes, mechanical and/or metabolic sensors and the like. In addition, one or more surface portions or apertures formed in the body or the resilient member can be coated or filled with biologic, genetic and/or pharmacologic substances. A related aspect also involves a coating of slow-release molecules or substances (e.g., steroid eluting material coated over a portion of an electrode surface). More than one body structure can be linked to a single medical electrical lead and the medical components can couple within and/or upon a portion of the body structure, the resilient member, and the lead in myriad configurations.  
         [0007]     It should be noted that, although most embodiments of the present invention are described herein in the context of epicardial sensing/pacing, cardioversion and/or defibrillation and diverse physiologic sensing applications, the invention is not so limited. Those skilled in the art will appreciate that numerous minor alterations and modifications can be implemented to provide a wide variety of cardiac therapies, diagnostics and/or monitoring capabilities. For example, while not specifically depicted herein the present invention can be used to deliver so-called paired- and coupled-pacing therapy whereby a pacing stimulus delivered immediately following the end of the refractory period causes an extra-systole for subsequent cardiac cycles. Also, so-called non-excitatory stimulation can be delivered in which electrical stimulation is delivered during the refractory period (absolute and/or relative) to provide contractility benefits and the like. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     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.  
         [0009]      FIGS. 1A and 1B  are a perspective view and a side elevational view, respectively, depicting certain aspects of one form an active pericardial fixation apparatus according to the invention.  
         [0010]      FIGS. 2A and 2B  are a perspective view and a side elevational view, respectively, depicting certain aspects of one form an active pericardial fixation apparatus according to the invention.  
         [0011]      FIGS. 3A and 3B  are a perspective view and a side elevational view, respectively, depicting certain aspects of one form an active pericardial fixation apparatus according to the invention.  
         [0012]      FIG. 4  is a photographic depiction of an embodiment of the invention as depicted in FIGS.  2 A-B and  3 A-B fixedly engaging an edge of an incision through the pericardium of a heart.  
         [0013]      FIGS. 5A and 5B  are a perspective view and a side elevational view, respectively, depicting certain aspects of one form an active pericardial fixation apparatus according to the invention.  
         [0014]      FIG. 6  is a perspective view depicting certain aspects of one form an active pericardial fixation apparatus according to the invention.  
         [0015]      FIGS. 7A and 7B  are perspective photographic views depicting certain aspects of one form an active pericardial fixation apparatus according to the invention.  
         [0016]      FIG. 8 a  perspective photographic views depicting certain aspects of one form an active pericardial fixation apparatus according to the invention fixedly engaging an edge of an incision through the pericardium of a heart.  
         [0017]      FIGS. 9A-9D  are perspective photographic views depicting a method of progressively deploying an active pericardial fixation apparatus according to an embodiment of the invention.  
         [0018]      FIG. 10  is a perspective photographic view of the embodiment depicted in  FIGS. 9A-9D .  
         [0019]      FIGS. 11A and 11B  are perspective views depicting certain aspects of one form an active pericardial fixation apparatus according to the invention wherein said apparatus is shown in a compressed state and a relaxed state.  
         [0020]      FIG. 12  is a perspective view depicting yet another embodiment of the present invention.  
         [0021]      FIGS. 13A and 13B  are perspective photographic views depicting a method of progressively deploying the active pericardial fixation apparatus according to an embodiment of the invention depicted in  FIG. 12 .  
         [0022]      FIGS. 14A-14D  are perspective photographic views depicting a method of progressively deploying an active pericardial fixation apparatus according to the embodiment of the invention depicted in  FIGS. 12, 13A , and  13 B.  
         [0023]      FIG. 15  is a side-elevational perspective view depicting yet another embodiment of the present invention.  
         [0024]      FIGS. 16A and 16B  are perspective views depicting certain aspects of one form an active pericardial fixation apparatus according to the invention wherein said apparatus is shown in a compressed state and a relaxed state.  
         [0025]      FIG. 17  is a perspective photographic view of the embodiment depicted in  FIGS. 16A-16B  (in a relaxed state).  
         [0026]      FIGS. 18A-18B  are perspective photographic views depicting a related form of the active pericardial fixation apparatus according to the embodiment of the invention depicted in  FIGS. 16A, 16B , and  17 .  
         [0027]      FIGS. 19A-19D  are perspective photographic views depicting a method of progressively deploying an active pericardial fixation apparatus according to the embodiment of the invention depicted in  FIGS. 16A, 16B ,  17 ,  18 A, and  18 B.  
         [0028]      FIGS. 20A, 20B , and  20 C are perspective, side elevational, and perspective views, respectively, of another embodiment of the invention with said embodiment shown in a relaxed state ( FIGS. 20A and 20B ) and compressed state ( FIG. 20C ).  
         [0029]      FIGS. 21A-21B  are perspective photographic views depicting a related form of the active pericardial fixation apparatus according to the embodiment of the invention depicted in  FIGS. 20A, 20B , and  20 C.  
         [0030]      FIGS. 22A and 22B  are perspective views depicting certain aspects of one form an active pericardial fixation apparatus according to the invention wherein said apparatus is shown in a relaxed state and a compressed state, respectively.  
         [0031]      FIG. 23  is a perspective view of yet another embodiment of the present invention.  
         [0032]      FIG. 24  is a perspective view of an embodiment of the present invention that is related to that depicted in  FIG. 23 .  
         [0033]      FIG. 25  is a perspective view of another related embodiment of the present invention including active mechanical fixation according to another aspect of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0034]     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.  
         [0035]     As is known to those in the art of cardiac surgery, electrophysiology, and/or interventional cardiology, an exemplary delivery tool is used to position a medical electrode assembly and/or a physiologic sensor which couples to a portion of a medical electrical lead for deployment of the assembly and/or sensor to an epicardial surface of a heart. According to some embodiments of the present invention, the assembly and/or sensor include one or more pacing or defibrillation electrodes and a physiologic sensor (e.g., a metabolic sensor, a mechanical sensor such as an accelerometer or the like, a pressure sensor, etc.). In addition, more than one electrode and/or sensor assembly can be deployed on a single medical electrical lead or dedicated electrode units and dedicated sensor units can be deployed individually or coupled to a common lead or several dedicated medical electrical leads. Known electrical multiplexing techniques can be used to provide and receive signals from the units.  
         [0036]     A proximal end of a medical electrical lead operatively couples the unit or units to pacing, sensing, and/or cardioversion/defibrillation circuitry, in the case of electrodes, and to appropriate signal processing circuitry, in the event that sensors are deployed.  
         [0037]     A variety of deployment techniques and delivery tools can be used in conjunction with the apparatus of the present invention that would typically include an elongated shaft having a distal portion coupled to a shaft portion. During deployment the distal portion is inserted between an epicardial surface of the heart and a pericardial sac surrounding the heart through a pericardial incision. According to certain embodiments of the present invention, the shape of the distal portion can be adjusted to facilitate insertion of the assembly and/or sensor between the pericardium and epicardium.  
         [0038]      FIGS. 1A and 1B  are a perspective view and a side elevational view, respectively, depicting certain aspects of one form an active pericardial fixation apparatus  100  according to the invention. As shown in  FIG. 1A  a body structure  101  couples to a portion of an elongated medical electrical lead  104 , which as depicted is shown coupled (at side portion  108 ) to a distal end portion of the lead  104  although the body structure could couple to an intermediate portion of the lead  104  and/or the lead  104  can couple to other side portions ( 106 ,  112 ,  116 ) or the upper portion ( 114 ) of the body structure  101 . The embodiment of the apparatus  100  depicted in  FIG. 1A  includes optional lateral support members  113  coupled to side portion  112 . Although not depicted in  FIG. 1A , one or more electrode and/or sensor units operatively couple to a remote medical device via lead  104  from a location on a surface of body structure  101 . For example, the apparatus  100  can include one or more electrodes coupled to the major lower surface of the body structure  101  in electrical communication with a portion of epicardial tissue while one or more physiologic sensor units reside within or on another part of the body structure  101 , a part of an active fixation member  102 , and/or a portion of the lead  104 . The active mechanical fixation member  102  is adapted to engage at least an edge portion of an incision in the pericardial sac couples to a portion of the body structure  101 . As depicted, the fixation member  102  couples at  105  to side wall  106  and extends through a curved portion  109  toward an end  103 .  
         [0039]     As shown in  FIG. 1B , the fixation member  102  is configured with a major radius portion between curved portion  109  and end  103  so that a region of reduced spacing is provided between the member  102  and the side portion  114 . When deployed a portion of pericardial tissue is retained in this region. As noted above, although depicted as coupled to side portion  106 , the fixation member  102  could couple to side portion  112  (or  114 ,  116 ). The fixation member  102  can comprise a hollow member, a solid member or a porous or perforated member of varying dimension (e.g., length, width, shape, etc.) composed of a resilient biocompatible material. For example, according to some embodiments of the invention body structure  101  and/or fixation member  102  can be comprised of a biocompatible polymer. The structure  101  and member  102  can be injection molded from a polymer having a relatively high modulus of elasticity, yet being sufficiently elastic and not prone to brittle fracture, for example 75 D durometer polyurethane or high density polyethylene or polyamide. Alternately, one or both can be insert molded or formed by molding or an extrusion process. According to some embodiments, fixation member  102  can be wholly or partially formed from a metal having suitable elastic and elastomeric properties, examples of which include, but are not limited to, titanium alloys, Ni—Ti super-elastic alloys and stainless steel and the like. Other suitable materials can also be used as known in the art.  
         [0040]      FIGS. 2A and 2B  are a perspective view and a side elevational view, respectively, depicting certain aspects of one form an active pericardial fixation apparatus  100  according to the invention. While other differences can be implemented or appreciated with respect to the apparatus  100  herein depicted versus the apparatus  100  of  FIG. 1A , primarily the fixation member  102  has been modified so that in lieu of a tubular member a member having a major surface  107  and the end  103  has a relatively straight portion. Of course, the end  103  can be contoured or curved without sacrificing the utility of the member  102 . Furthermore, as depicted the end  103  includes an enlarged and rounded portion which can optionally be utilized to increase the possibility of smooth insertion and retention of a portion of the pericardial sac.  
         [0041]      FIGS. 3A and 3B  are a perspective view and a side elevational view, respectively, depicting certain aspects of the form of an active pericardial fixation apparatus according to the invention substantially as depicted in  FIG. 2A . As shown the major surface  107  terminates at end  103  with a gradually curving edge devoid of the enlarged and rounded portion depicted in  FIG. 2A  although such a feature can of course be incorporated into the apparatus depicted in  FIG. 3A .  
         [0042]      FIG. 4  is a photographic depiction of an embodiment of the invention substantially as depicted in FIGS.  2 A-B and  3 A-B with the member  102  having a rounded end portion  103  fixedly engaging an edge of an incision  125  through the pericardial sac  124  of a heart and includes an exposed portion of epicardial tissue  126 . Lead  104  includes elongated conductors to transfer power and/or signals to and from electrodes and/or sensor units disposed in, on, or about the apparatus  100  and/or lead  104  to operative electronic circuitry (not depicted).  
         [0043]      FIGS. 5A and 5B  are a perspective view and a side elevational view, respectively, depicting certain aspects of another form of an active pericardial fixation apparatus  100  according to the invention. Inspection of  FIGS. 5A and 5B  reveals that the fixation member  102  couples at  105  to side portion  108 . Thus, the curved portion  109  is disposed near the lead  104 . During deployment this embodiment can be advanced into retaining engagement with a portion of pericardial tissue whereas the previously-discussed embodiments were initially advanced and then reversed to engage the pericardial tissue. The lateral members  113  can be configured to improve ease of deployment and electrode communication or contact with the epicardial tissue (e.g., sloped or enlarged or the like). To further promote such communication or contact an electrode can be disposed between lateral members  113  and directly aligned with the most narrow spacing between surface  114  and the fixation member  102 . As depicted the end  103  extends slightly beyond the side portion  106  although this is not a requirement of this embodiment of the invention (e.g., the end could terminate before or at the plane defined by side portion  106 ).  
         [0044]      FIG. 6  is a perspective view depicting certain aspects of another form an active pericardial fixation apparatus  100  according to the invention. In this embodiment, as before, an active fixation member  102  couples to a side wall portion (in this case  114 ) at  105  and includes an initial curved portion  109  and extends toward an end  103 . A second curved portion  111  is intermediate portion  109  and end  103  and a major surface  107  lies therebetween. Although this embodiment is depicted as including a substantially planar member a thin hollow or solid member could also be configured too. In the depicted embodiment, the major surface  107  includes an optional aperture  121 . The aperture  121  can be disposed elsewhere on the surface  107  or additional apertures can be added, as desired for a given application or clinician preference. The aperture  121  is adapted to receive a tool during manual manipulation at initial implant. Subsequently the aperture  121  can be used to receive sutures to further secure the apparatus  100  in a desired location.  
         [0045]      FIGS. 7A and 7B  are perspective photographic views depicting certain aspects of the form an active pericardial fixation apparatus  100  according to the invention as depicted in  FIG. 6  in both a relaxed and a compressed orientation, respectively.  
         [0046]      FIG. 8 a  perspective photographic views depicting certain aspects of one form an active pericardial fixation apparatus  100  according to the invention fixedly engaging an edge of an incision through a portion of the pericardium  124  of a heart. As shown, the aperture  121  receives an elongated member, for instance surgical thread  128 . In  FIG. 8  the member  102  engages the pericardium  124  the pericardium is lodged at curved portion  109  in lieu of portion  111 . Of course, the pericardium could be lodged at portion  111  for chronic implantation.  
         [0047]      FIG. 9  is a perspective photographic view of the embodiment of the active pericardial fixation apparatus  100  depicted in  FIGS. 10A-10D . In this embodiment the fixation member  102  is configured into a ring coupled at  105  to the body member  101 . The ring essentially defines an optional aperture  121  that can be used to receive a tool for manually advancing the apparatus  100  through an incision in through the pericardium. Thus, as with other embodiments the body structure  101  remains fixated within the pericardial space and the fixation member  102  remains fixated to at least a portion of the pericardium surrounding the incision.  FIGS. 10A-10D  are perspective photographic views depicting a method of progressively deploying an active pericardial fixation apparatus  100  according to an embodiment of the invention as depicted in  FIG. 9 . In one form of this aspect of the invention a incision is made through first and second portions of pericardial tissue and the apparatus  100  is advanced through the first portion of pericardial tissue  123  into the pericardial space and fixated to a second portion of pericardial tissue  125  so that the curvilinear active fixation member  102  provides a mechanically-biasing force retaining the apparatus  100  in place intermediate the epicardium  126  and the pericardium  124 . As shown in FIGS.  10 B-D once a portion of the member  102  emerges from the second portion  125  a length of cord or other appropriate material can be optionally inserted through the member  102  which, as noted with reference to  FIG. 9 , comprises the ring formed by the curvilinear member  102  (although it could comprise an aperture, such as aperture  121  formed in the surface  107  as depicted in  FIG. 6  and  FIG. 8 , as previously described).  
         [0048]      FIGS. 11A and 11B  are perspective views depicting certain aspects of one form an active pericardial fixation apparatus  100  according to the invention wherein said apparatus is shown in a compressed state ( FIG. 11A ) and a relaxed state ( FIG. 11B ). Turning first to  FIG. 11B  wherein the fixation member  102  comprises a ring configuration coupled to body structure  101  at  105 , an elongated post  130  having a distal end  134  aligns with aperture  121 . The post has at least one mechanical interlock ( 132 , 136 ) disposed on an intermediate portion of post  130  and sized to engage aperture  121  when the fixation member  102  is compressed. With reference to  FIG. 11A , one can appreciate that the mechanical interlock  132  retains fixation member  102  in a compressed state so that pericardial tissue intermediate member  102  and body structure  100  is fixated therebetween. Deployment of this embodiment of the apparatus  100  can be implemented similar to that described with reference to FIGS.  10 A-D with the additional step of compressing the member  102  until aperture  121  engages mechanical interlock  132  (or optionally interlock  136 ). The interlock feature can comprise a wide variety of shapes and sized (e.g., an enlarged portion, a rib member, a frustoconical portion, a boss, a protuberance, a ring feature, an interlocking flange, a shelf, protruding edge, a collar, etc.).  
         [0049]      FIG. 12  is a perspective view depicting yet another embodiment of the pericardial fixation apparatus  100  of the present invention. In this embodiment the body structure  101  couples to an extended coupling location  105  for the fixation member  102 . Member  102  is depicted in a relaxed state, but the member  102  includes two spaced apart apertures  121 , 121 ′ which can receive a tool (not shown) thus binding the apertures together and rending the member  102  into a compressed state while also providing convenient access to manually pull the apparatus  100  through a pericardial incision. Thus, while in the compressed state the member  102  more readily advances through an incision in the pericardium or can be advanced through a relatively smaller incision as will be described with reference to FIGS.  14 A-D herein.  
         [0050]      FIGS. 13A and 13B  are perspective photographic views depicting a method of progressively deploying the active pericardial fixation apparatus  100  according to an embodiment of the invention depicted in  FIG. 12 . In  FIG. 13A  the major surface  107  of member  102  is shown which includes two apertures  121 , 121 ′. In  FIG. 13B , the epicardial-contacting side of the body  101  is shown and the location  122  for receiving an electrode and/or other sensor unit or component. Note that in the case one or more physiologic sensing units are included with the apparatus  100  said units can couple within and/or on the body structure  100 , the fixation member  102  and/or the lead  104 . The electrode(s) can comprise one or more pacing/sensing (mono- or multi-polar), defibrillation, and/or cardioversion electrodes such electrodes can be used to register temporal traces of cardiac activity and/or to register impedance measurements on diverse vectors between extant electrodes (including housing- or can-based electrodes, endocardial electrodes, other epicardial electrodes, etc.). The sensing unit(s) can comprise one or more metabolic sensors, such as optical-type oxygen sensor, a lactate sensor, a glucose sensor, a potassium sensor, a calcium sensor, a thrombin sensor, a carbon dioxide sensor, etc. and/or mechanical sensors, for example single- or multi-axis accelerometers, pressure sensors, and the like.  
         [0051]      FIGS. 14A-14D  are perspective photographic views depicting a method of progressively deploying an active pericardial fixation apparatus  100  according to the embodiment of the invention depicted in  FIGS. 12, 13A , and  13 B. In  FIG. 14A , the apparatus  100  can be seen emerging from an incision  125  in the pericardium in the compressed state. The compressed state is achieved with an elongated segment of cord  128  binding apertures  121 , 121 ′ together so that member  102  more readily can be drawn through the incision  125 . Alternatively, as depicted in  FIG. 14B  an elongated tool  126 , such as a forceps, can be used to engage one or both of the apertures  121 , 121 ′ to manually assist the emergence of the member  102  from the incision  125  in the pericardium  124 . In  FIG. 14C  the member  102  is shown in the compressed state due to the cord  128  binding the apertures  121 , 121 ′ and the sharp edge  131  of a sharp instrument  129 , such as a scalpel, can be used to sever the cord  128  thus rendering the member  102  into the relaxed state (shown in  FIG. 14D ). Thus, once deployed through a first incision  123  in the pericardium  124  and allowed to return to the relaxed state the fixation member  102  provides a biasing force upon a portion of pericardium disposed between the body structure  101  and the member  102 . Optionally, the first incision  123  and/or second incision  125  can be sutured (closed) thereby further fixating the apparatus  100  and allowing chronic cardiac rhythm management monitoring, therapy delivery and/or diagnostics to be implemented.  
         [0052]      FIG. 15  is a side-elevational perspective view depicting yet another embodiment of a pericardial fixation apparatus  100  according to the present invention. In this embodiment the major surface  107  of fixation member  102  is not substantially parallel to the opposing major surface  107 ′ which, in this depiction, comprises a substantially planar surface. However, according to the invention one or both major surface  107 , 107 ′ can include diverse surface features. Such features can comprise for example, an irregular surface, a curved surface, a curvilinear surface, a convex surface, a convex surface, a complex surface, a faceted surface, a conical surface, a perforated surface, a ribbed surface, and the like.  
         [0053]      FIGS. 16A and 16B  are perspective views depicting certain aspects of one form an active pericardial fixation apparatus  100  according to the invention wherein said apparatus  100  is shown in a compressed state ( FIG. 16B ) and a relaxed state ( FIG. 16A ). This embodiment is somewhat similar to embodiments depicted in  FIGS. 12, 13A ,  13 B, and  14 A-D with a couple of exceptions. For example, additional apertures  123 , 123 ′ appear on laterally extending portions of body structure  101  (denoted as  102 ′) and the fixation member  102  is configured in a rectangular configuration in lieu of a circular configuration (in plan view). Also, optional features similar to the previously depicted and described mechanical interlock members  132 , 136  are provided on the side surface  114  of the body structure  101 . The members  132 , 136  are configured to provide an additional amount of fixation by impinging upon pericardial tissue intermediate the structure  101  and the fixation member  102  following implantation. In  FIG. 16B  the member  102  is depicted in the compressed state which can be optionally utilized during implantation substantially as previously described.  
         [0054]      FIG. 17  is a perspective photographic view of the embodiment of the apparatus  100  depicted in  FIGS. 16A-16D  (in a relaxed state). In this view the major surface  107  includes two apertures  121 , 121 ′ and optionally includes beveled, or clipped, corner portions of the substantially rectangular member  102 .  
         [0055]      FIGS. 18A-18B  are perspective photographic views depicting a related form of the active pericardial fixation apparatus  100  according to the embodiment of the invention depicted in  FIGS. 16A, 16B , and  17 . Although these views reveal that the member  102  includes rounded edges that define the substantially rectangular major surface  107 . In  FIG. 18B , a location  122  for receiving an electrode and/or sensor is depicted as residing upon opposing major surface  107 ′ of the body  101 . Of course, the electrode and/or sensor mechanically couples to the body structure  101  and electrically couples via the lead  104  to operative circuitry.  
         [0056]      FIGS. 19A-19D  are perspective photographic views depicting a method of progressively deploying an active pericardial fixation apparatus  100  according to the embodiment of the invention depicted in  FIGS. 16A, 16B ,  17 ,  18 A, and  18 B. In  FIG. 19D , the apparatus  100  is shown in a relaxed state disposed near an incision  125  in the pericardium  124  of a heart and coupled to lead  104 . This embodiment includes two apertures  121 , 121 ′ which are coupled together to render the fixation member in a compressed state during implantation. Now referring to  FIG. 19A , the fixation member  102  is depicted partially protruding through the incision  125  in the pericardium  124  while configured in the compressed state due to the cord  128  connected through apertures  121 , 121 ′. In  FIG. 19B , the sharp edge  131  of a tool  129 , such as a scalpel, is used to sever the cord  128 . As seen in  FIG. 19C  once the cord  128  is severed and removed, the member  102  returns to a relaxed state thereby providing positive mechanical fixation to the portion of pericardium  124  adjacent incision  125  disposed between the body  101  and the member  102 .  
         [0057]      FIGS. 20A, 20B , and  20 C are perspective, side elevational, and perspective views, respectively, of another embodiment of an active pericardial fixation apparatus  100  according to the invention. The apparatus  100  is depicted in both a relaxed state ( FIGS. 20A and 20B ) and compressed state ( FIG. 20C ). In  FIG. 20A , which resembles the embodiment depicted in  FIG. 16A-16B  except that member  102  is configured as a substantially round member (in plan view) and roughly corresponds in size and shape to the enlarged portion of body  101  (denoted as  102 ′). The enlarged portion  102 ′ includes optional raised interlocking members  132  and  136  which tend to retain pericardial tissue disposed intermediate member  102  and portion  102 ′ when implantation is complete according to the invention.  
         [0058]      FIGS. 21A-21B  are perspective photographic views depicting a related form of the active pericardial fixation apparatus  100  substantially according to the embodiment of the invention depicted in  FIGS. 20A, 20B , and  20 C. As shown in  FIG. 21A  the apparatus is in a relaxed state (i.e., member  102  and enlarged portion  102 ′ are substantially parallel). The electrode- and/or sensor-receiving location  122  is depicted as residing upon the epicardium-contacting side of body  101  and couples to an elongated conductor  127  (shown in ghost) extending through the body  101  and through the lead  104 . In  FIG. 21B , the location  122  is depicted in ghost as a location within body  101  with conductor  127  extending therefrom. As mentioned elsewhere herein, diverse electrode- and/or sensor-receiving locations can be implemented according to the invention, including locations within and/or upon a surface portion of any part of apparatus  100  including the lead  104 , the body  101 , the member  102 , the enlarged portion  102 ′, etc.  
         [0059]      FIGS. 22A and 22B  are perspective views depicting certain aspects of one form an active pericardial fixation apparatus  100  according to the invention wherein said apparatus  100  is shown in a relaxed state and a compressed state, respectively. In this embodiment the member  102  includes two different major surfaces  107 , 107 ′ each having an end  103 , 103 ′ and apertures  121 , 121 ′, respectively. A connecting portion  105 ′ couples the member  102  to the body  101 . Referring now to  FIG. 22B , the apparatus  100  is shown in the compressed state wherein the apertures  121 , 121 ′ are brought together (e.g., with a wire, tool, cordage, etc.—not shown) to promote easier passage through an incision in the pericardium substantially as previously described.  
         [0060]      FIG. 23  is a perspective view of yet another embodiment of an active fixation apparatus  100  according to the present invention. In this embodiment the fixation member  102  has a slot  142  extending to a central region of the member  102  and sized to receive a distal portion of the connector  105 ′ that connects to body  101 . Thus, the member  102  can be twisted or manipulated to open the slot  142  and engaged upon the connector  105 ′ intermediate an enlarged end portion  105 ″. The end portion  105 ″ can be integral with connector  105 ′ or can comprise a cap member suitably attached to the connector  105 ′. Thus following deployment of the apparatus  100  of  FIG. 23  the fixation member  102  can be attached to the connector  105 ′ following the emergence of end portion  105 ″ from a pericardial incision thereby not requiring transition between a compressed and relaxed state.  
         [0061]      FIG. 24  is a perspective view of an embodiment of the fixation apparatus  100  according to the present invention that relates to the embodiment depicted in  FIG. 23 . In this embodiment, the fixation member  102  couples to the body  101  with a cam member  105 ′″ that includes an axial slot  144  that positively mechanically interlocks with corresponding structure surrounding an aperture of the member  102 . The cam member  105 ′″ can be integral with the connector ( 105 ′—not shown) or can be coupled to connector  105 ′ following emergence of the connector following emergence from an incision in the pericardium. In any event, once exposed through the incision the fixation member  102  is coupled to the cam member  105 ′″ and rotated into positive engagement thereto thus providing positive biasing forces to pericardial tissue disposed between body  101  and member  102 .  
         [0062]      FIG. 25  is a perspective view of another related embodiment of the present invention including active mechanical fixation apparatus  100  according to another aspect of the present invention. In this embodiment, the member  102  comprises two discrete major curvilinear surfaces  107 , 107 ′ separated by a narrow slot  140  disposed at a distal end of connector  105 ′. Each major surface  107 , 107 ′ terminates at an end  103  and defines a resilient loop of material each having a portion closely spaced from surface  114  of the body  101 . It is in this location that the pericardium impinges upon by the positive biasing forces produced by the surfaces  107 , 107 ′ that comprise the flexible member  102  thereby providing the positive fixation as previously described with respect to other embodiments of the present invention.  
         [0063]     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.