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 . 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 . 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 . 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 . fig1 a 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 fig1 a 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 fig1 a includes optional lateral support members 113 coupled to side portion 112 . although not depicted in fig1 a , 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 . as shown in fig1 b , 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 . fig2 a 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 fig1 a , 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 . fig3 a 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 fig2 a . as shown the major surface 107 terminates at end 103 with a gradually curving edge devoid of the enlarged and rounded portion depicted in fig2 a although such a feature can of course be incorporated into the apparatus depicted in fig3 a . fig4 is a photographic depiction of an embodiment of the invention substantially as depicted in fig2 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 ). fig5 a 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 fig5 a 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 ). fig6 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 . fig7 a 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 fig6 in both a relaxed and a compressed orientation , respectively . fig8 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 fig8 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 . fig9 is a perspective photographic view of the embodiment of the active pericardial fixation apparatus 100 depicted in fig1 a - 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 . fig1 a - 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 fig9 . 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 fig1 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 fig9 , 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 fig6 and fig8 , as previously described ). fig1 a 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 ( fig1 a ) and a relaxed state ( fig1 b ). turning first to fig1 b 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 fig1 a , 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 fig1 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 .). fig1 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 fig1 a - d herein . fig1 a 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 fig1 . in fig1 a the major surface 107 of member 102 is shown which includes two apertures 121 , 121 ′. in fig1 b , 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 . fig1 a - 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 fig1 , 13a , and 13 b . in fig1 a , 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 fig1 b 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 fig1 c 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 fig1 d ). 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 . fig1 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 . fig1 a 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 ( fig1 b ) and a relaxed state ( fig1 a ). this embodiment is somewhat similar to embodiments depicted in fig1 , 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 fig1 b the member 102 is depicted in the compressed state which can be optionally utilized during implantation substantially as previously described . fig1 is a perspective photographic view of the embodiment of the apparatus 100 depicted in fig1 a - 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 . fig1 a - 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 fig1 a , 16b , and 17 . although these views reveal that the member 102 includes rounded edges that define the substantially rectangular major surface 107 . in fig1 b , 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 . fig1 a - 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 fig1 a , 16b , 17 , 18 a , and 18 b . in fig1 d , 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 fig1 a , 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 fig1 b , the sharp edge 131 of a tool 129 , such as a scalpel , is used to sever the cord 128 . as seen in fig1 c 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 . fig2 a , 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 ( fig2 a and 20b ) and compressed state ( fig2 c ). in fig2 a , which resembles the embodiment depicted in fig1 a - 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 . fig2 a - 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 fig2 a , 20b , and 20 c . as shown in fig2 a 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 fig2 b , 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 . fig2 a 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 fig2 b , 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 . fig2 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 fig2 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 . fig2 is a perspective view of an embodiment of the fixation apparatus 100 according to the present invention that relates to the embodiment depicted in fig2 . 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 . fig2 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 . 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 .
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 .