Abstract:
The present application discloses a tissue marker that may be permanently applied to cardiac (or other) tissue by means such as, but not limited to, a minimally-invasive procedure to allow for pre- and post-op lesion site testing, with the marker also preferably being radiopaque to facilitate post-op imaging. More specifically, the marker may preferably comprise or include an electrode as part of an integrated assembly. The marker may be mounted on the tissue with a suitable tissue retention member for securing the marker in place. The disclosed examples include one or more tissue retention members, and in an exemplary embodiment comprises a pair of clips for securing the assembly to a target tissue. Each retention member or clip has a conductive lead with an electrically conductive surface in the form of a patch associated therewith. Each clip is preferably associated with a discrete electrically conductive area on the surface of the patch so that the assembly may function as a bi-polar electrode, with a voltage applied between the discrete conductive areas.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 61/109,552, filed Oct. 30, 2008, the entire contents of which are incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    Methods and apparatus have been developed for treating atrial fibrillation by creating lines of scar tissue that pose an interruption in the path of errant electrical impulses in the heart tissue. Scar tissue may be created by, e.g., surgical cutting of the tissue, freezing of the tissue by cryogenic probe, heating the tissue via RF energy, and other technologies. Methods and apparatus for creating transmural lines of ablation using RF energy are shown and described in, e.g., U.S. Pat. No. 6,517,536, U.S. Pat. No. 6,974,454, and U.S. Pat. No. 7,393,353, which are incorporated herein by reference. 
         [0003]    Various methods for determining the efficacy of the lines of ablation have been developed using pacing and sensing electrodes. See U.S. Pat. No. 6,905,498, also incorporated herein by reference. For example, if a pacing pulse or signal is applied to cardiac tissue on one side of a line of ablation, but not sufficiently detected by an EKG sensor located on the tissue on the other side of the line of ablation, the line of ablation may be deemed effective for blocking electrical impulses. There may also be instances in which it is desirable to post-surgically locate the line of ablation for further testing its efficacy at blocking electrical impulses. 
       SUMMARY 
       [0004]    The present application discloses a tissue marker that may be permanently applied to cardiac (or other) tissue by means such as, but not limited to, a minimally-invasive procedure to allow for pre- and post-op lesion site testing, with the marker also preferably being radiopaque to facilitate post-op imaging. More specifically, the marker may preferably comprise or include an electrode as part of an integrated assembly. The marker may be mounted on the tissue with a suitable tissue retention member for securing the marker in place. The disclosed examples include one or more tissue retention members, and in an exemplary embodiment comprises a pair of clips for securing the assembly to a target tissue. Each retention member or clip has a conductive lead with an electrically conductive surface in the form of a patch associated therewith. Each clip is preferably associated with a discrete electrically conductive area on the surface of the patch so that the assembly may function as a bi-polar electrode, with a voltage applied between the discrete conductive areas. 
         [0005]    An applicator is also disclosed that comprises a hand piece, an elongated shaft sized to be passed through a trocar, and a delivery mechanism in the form of a spring-loaded push rod for dispensing the clips of the marker. 
         [0006]    A housing is also disclosed that is adapted to be received on the distal end of the shaft of the applicator, and may be pre-loaded with the marker. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a marker in accordance with one embodiment in the present disclosure. 
           [0008]      FIG. 2  is a perspective view of a first embodiment of a clip suitable for use in the marker/electrode assembly described herein. 
           [0009]      FIG. 3  is a plan view of the clip of  FIG. 2 . 
           [0010]      FIG. 4  is an end view of the clip of  FIG. 2 . 
           [0011]      FIG. 5  is a side view of the clip of  FIG. 2 . 
           [0012]      FIG. 6  is a plan view of a second embodiment of a clip suitable for use in the marker assembly described herein. 
           [0013]      FIG. 7  is a side view of the clip of  FIG. 6 . 
           [0014]      FIG. 8  is a plan view of a patch electrode forming part of the marker. 
           [0015]      FIG. 9  is a plan view of the patch material for forming the patch electrode prior to being incorporated into the marker. 
           [0016]      FIG. 10  is a further pre-assembly view of the patch electrode material. 
           [0017]      FIG. 11  is a perspective view showing an applicator for use in deploying a marker that is described in the present disclosure. 
           [0018]      FIG. 12  is an exploded perspective view of the distal end of the applicator assembly showing the details of the push rod, in conjunction with the clip housing and two clips, the patch and leads forming the marker. 
           [0019]      FIG. 13  is a perspective view of the push rod forming part of the applicator. 
           [0020]      FIG. 14  is an end view of the push rod of  FIG. 15 . 
           [0021]      FIG. 15  is a perspective view of the housing for use in conjunction with the applicator assembly and marker. 
           [0022]      FIG. 16  is a top or proximal end view of the housing of  FIG. 17 . 
           [0023]      FIG. 17  is a bottom or distal end view of the housing of  FIG. 17 . 
           [0024]      FIG. 18  is a cross-sectional view of the housing showing the camming surfaces on the interior thereof for engaging the legs of the clip members. 
       
    
    
     DESCRIPTION 
       [0025]    In keeping with the disclosure, a marker for application to tissue is provided that comprises a patch with an electrically conductive surface for contacting the target tissue. At least one retainer is associated with the patch for securing the electrically conductive surface in contact with the target tissue. A conductive lead is in conductive contact with the conductive surface of the patch for transmitting and receiving electrical impulses 
         [0026]    Turning to the figures of the drawings, there is seen in  FIG. 1  a perspective view of one embodiment of a marker  10  in accordance with the present disclosure. The marker  10  has an electrically conductive surface adapted to contact the target tissue in the form of a patch  12 . Preferably, the patch  12  has two discrete electrically conductive areas or surfaces  14   a,    14   b  that are insulated from one another so that a voltage can be applied between them, thus permitting the patch  12  to serve as a bi-polar electrode. However, the patch  12  may have a single, continuous electrically-conductive surface if a mono-polar electrode is desired. 
         [0027]    The electrically conductive surfaces  14   a,    14   b  may be a metal/metal chloride film that is applied to the patch  12  by, e.g., printing or other suitable way such as soldering, adhesive or using techniques known in the manufacture of microprocessors, such as lithography and the like. Alternatively, the electrode surface may be formed by interweaving into the patch  12  strands of an electrically-conductive, biocompatible material, such as stainless steel. As shown in  FIG. 1 , the tissue contacting areas  14   a,    14   b  are on both the upper and lower surfaces of the patch  12 . To provide a tissue contacting surface sufficiently large for conducting pacing and sensing impulses, each electrically-conductive surface  14   a,    14   b  on the patch preferably has a tissue-contacting surface area of at least about 2 mm 2 , but smaller or larger areas may be used depending on the particular arrangement of the conductive areas or members. 
         [0028]    In the illustrated embodiment, a clip member  16  is associated with each conductive area  14   a,    14   b  of the patch  12  for securing the patch  12  to the target tissue. A conductive contact or lead  18  is also associated with each of the electrically conductive surface  14   a,    14   b  of the patch  12  to transmit electrical impulses to and from the patch  12 . The lead  18  may comprise stainless steel, copper, gold, silver, or other conductive materials. The lead is preferably braided and is insulated except for the portion containing the clip and/or patch. If the patch  12  has a single continuous electrically conductive surface, only a single clip  12  and lead  18  are required. 
         [0029]    With reference to  FIGS. 2-5 , a first embodiment of a clip  16  for use in the marker of the present disclosure is seen. The clip  16  is generally U-shaped with a pair of legs  20  depending from a base or bridging segment  22 . When the target tissue for the marker  10  is the heart, the legs  20  of the clip  16  are sized in length so as to not completely penetrate through the myocardium. For such an application, the clip  16  is, preferably, on the order of approximately 5 mm in overall length, with the legs  20  of the clip being on the order of approximately 3.5 mm in length and the bridge/base  22  being on the order of approximately 3.3 mm in length. The legs  20  of the clip may optionally include a barb (not shown) to more securely fix the clip  16  to the target tissue. 
         [0030]    The base/bridge portion  22  of the clip  16  is configured to receive the electrically conductive lead  18 . This may take any suitable form, such as apertures  24  through which the conductive lead  18  is threaded. In the embodiment of  FIGS. 2-5 , the base member includes a pair of brackets  26 , each having an aperture  24  therein through which the lead  18  may be threaded. Alternatively, as shown in  FIGS. 6 and 7 , the base/bridging portion  22  of the clip  16  may be formed with a series of three apertures  24 . In either case, the conductive lead  18  is preferably threaded through apertures  24  so that both ends of the lead  18  extend out of the surgical field for attachment to a pacing/sensing generator. As a further option, the bridge portion  22  of the clip  16  may be formed without any apertures, and the lead  18  may be simply threaded between the bridge portion  22  of the clip  16  and the upper surface of the patch  12 . If, at the end of a procedure the leads  18  need to be removed, this may be simply done by pulling on one end of the lead  18 . 
         [0031]    Suitable material for the clips  16  include any biocompatible implantable material that exhibits the requisite closure force to prevent inadvertent dislodgment, such as titanium, stainless steel, plated copper, platinum, or any other conductive biocompatible material. The clip materials are also preferably radiopaque, so that, if the marker  10  is permanently implanted, the clip  16  may serve to enhance visibility of the clip through fluoroscopy. 
         [0032]    As illustrated, the clips  16 /leads  18  are associated with the patch electrode  12  through which the legs  20  of the clips  16  extend. The patch  16  serves to optimize the electrode surface area and epicardial contact. Further, the patch  12  provides for immediate wound closure and minimizes the risk of the marker  10  migrating or dislodging once deployed. The patch  12  also facilitates long-term tissue regeneration. 
         [0033]    With reference to  FIGS. 8-10 , the illustrated patch  12  electrode is generally oval in shape and is made of a material such as knit braid polyester. A mesh material is preferred for the patch  12  in order to promote tissue ingrowth. The electrically conductive coating  14   a,    14   b,  is applied to two discrete areas of the patch  12  electrically isolated from the other, each area having a clip  16  and lead  18  associated therewith. The electrode surfaces  14   a,    14   b  are preferably spaced apart approximately 2 mm. The overall length of the patch  12  is preferably no more than about 5 mm and the width is preferably no more than approximately 3 mm. 
         [0034]    Both the top and bottom surfaces of the patch  12  are preferably coated with the electrically conductive material to ensure good conduct between the leads  18  and the electrode surface  14   a,    14   b.  To this end, the patch  12  may be formed as shown in  FIG. 9  with ends  28  that fold back onto the back side of the patch  12  so as to present two discrete conductive surfaces for engagement with the leads  18 . As shown in  FIG. 10 , the ends  28  may be secured to the back side of the patch by an adhesive  30 , which is preferably an electrically conductive pressure sensitive adhesive. The adhesive  30  is applied to the upper surface of the patch by, e.g., printing, and then the ends  28  of the patch  12  are folded back onto the top side (as shown in  FIG. 10 ). 
         [0035]    An applicator  32  for applying markers  10  in accordance with the present disclosure is seen in  FIGS. 11-18 . The tool  32  includes an elongated shaft  34  that is preferably sized to fit through a 5 mm trocar and slidably mounts a push rod  36  therein (best seen in  FIG. 12-14 ). A marker  10  is associated with the distal end of the applicator  32 . The distal end of the push rod  36  includes a driver segment  38  that is received on the interior of a clip housing  40  upon actuation of the applicator  32  to eject the clips  16  from the housing  40  and secure the marker  10  to the target tissue. 
         [0036]    One or more markers  10  as described above are pre-loaded onto the housing  40 . With reference to  FIGS. 15-18 , the housing  40  receives the proximal portion of the clips  16  in spaced-apart parallel slots  42 . The slots  42  narrow in width from the proximal side  44  of the housing  40  to the distal side  46  of the housing  40 , thus providing a camming surface  48  (best seen in  FIG. 18 ). The camming surface  48  acts to close the legs  20  of the clips  16  toward each other when the clip is ejected from the housing  40 , thus securing the marker to the target tissue. The clip housing  40  has a further slot  50  transverse to the slots  42  into which the driving segment  38  of the push rod  36  is slidably received. As can be appreciated, the driving segment  38  of the push rod  36  engages the bridge portions  22  of the clips  16 . When axially extended, the push rod  36  pushes the clips out of the housing  90 . Preferably, when a marker is loaded into the housing  40 , the legs  20  of the clip extend at least partially out of the housing  40  and the leads are accessible such that the marker is fully functional. Thus, electrical readings may be taken before the device is deployed to assist in the optimally locating the marker  10  on the target tissue before it is affixed thereto. 
         [0037]    In order to apply a marker  10  according to the present disclosure to the surface of a heart or other target tissue, the distal end of the applicator  32  is brought into contact with the target tissue in proximity to the line of ablation or lesion, and then the applicator  32  is activated to discharge the clips and secure the marker  10  to the target tissue. A single marker  10  may be used with the two conductive surfaces of the patch being on opposite sides of the line of ablation. Alternatively, two markers may be applied to the target tissue, with one being on each side of the line of ablation. As noted above, if ends of the legs  20  of the clips  16  extend out from the housing  40  so that they are able to contact the target tissue prior to attachment, readings may be taken or pulses delivered to confirm the positioning of the marker  10  prior to being fixed to the target tissue. Although disclosed for contacting the epicardial surface, the marker may also be used in contact with the endocardial surface, although such may require a different delivery system. 
         [0038]    Once a marker has been fixed with one electrically conductive surface  14   a,    14   b  on each side of a line of ablation (or, e.g., a monopolar marker is secured on each side of a line of ablation), the efficacy of the line of ablation can be determined by using one of the conductive surfaces to transmit pacing pulses to the cardiac tissue, and the other conductive surface as an EKG sensor. Pacing signals are then transmitted to the cardiac tissue through the pacing electrode. If the pacing signals are detected by the EKG electrode, then the line of ablation is not complete or transmural. Conversely, if the pacing pulses are not sufficiently detected by the EKG electrode, the line of ablation may be deemed transmural. 
         [0039]    Having shown and described various examples of an embodiment according to the present disclosure, further adaptations of the methods, components and systems described herein may be accomplished by appropriate modifications by one of ordinary skill in the art without departing from the scope of the disclosure. Several of such potential modifications have been mentioned, and still others will be apparent to those skilled in the art. For instance, the examples, embodiments, geometries, materials, dimensions, steps, and the like discussed above are illustrative and are not necessarily required. Accordingly, the scope of the present disclosure should be considered in terms of the following claims and is understood not to be limited to the details of structure and operation shown and described in the specification and drawings.