Patent Publication Number: US-10779829-B2

Title: Tissue compression device for cardiac valve repair

Description:
BACKGROUND 
     The mitral valve controls blood flow from the left atrium to the left ventricle of the heart, preventing blood from flowing backwards from the left ventricle into the left atrium so that it is instead forced through the aorta for distribution throughout the body. A properly functioning mitral valve opens and closes to enable blood flow in one direction. However, in some circumstances the mitral valve is unable to close properly, allowing blood to regurgitate back into the atrium. Such regurgitation can result in shortness of breath, fatigue, heart arrhythmias, and even heart failure. 
     Mitral valve regurgitation has several causes. Functional mitral valve regurgitation (FMR) is characterized by structurally normal mitral valve leaflets that are nevertheless unable to properly coapt with one another to close properly due to other structural deformations of surrounding heart structures. Other causes of mitral valve regurgitation are related to defects of the mitral valve leaflets, mitral valve annulus, or other mitral valve tissues. In some circumstances, mitral valve regurgitation is a result of infective endocarditis, blunt chest trauma, rheumatic fever, Marfan syndrome, carcinoid syndrome, or congenital defects to the structure of the heart. Other cardiac valves, in particular the tricuspid valve, can similarly fail to properly close, resulting in undesirable regurgitation. 
     Heart valve regurgitation is often treated by repairing the faulty valve through an interventional procedure. In some circumstances, adjacent leaflets of the faulty valve are grasped and brought together using an interventional clip. The interventional clip is intended to remain deployed at the repaired valve to promote better coaptation of the grasped leaflets and to thereby reduce regurgitant flow through the valve. Although such a procedure may be beneficial, residual regurgitation can sometimes remain. A need therefore exists for solutions which further improve cardiac valve repair and associated patient outcomes. 
     The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced. 
     BRIEF SUMMARY 
     The present disclosure is directed to devices, systems, and methods for treating regurgitant leaks in cardiac valve tissue, including leaks along the cardiac valve line of coaptation. In some implementations, interventional device embodiments described herein may be deployed at gaps disposed between two previously deployed implants, or between a previously deployed implant and a valve commissure. 
     In one embodiment, an interventional device for compressing cardiac valve tissue at a targeted gap includes a distal member and a pair of opposing arms flexibly joined to the distal member. Each arm extends proximally from the distal member to a free end. The pair of opposing arms define an interior space between the arms for holding cardiac valve tissue. The arms have a default position and are flexibly moveable apart from one another away from the default position to increase the size of the interior space and to enable grasping of cardiac valve tissue within the interior space. The arms are configured to be biased toward the default position when moved apart from one another. In this manner, the arms provide a compressive force upon cardiac valve tissue held within the interior space. 
     In some embodiments, the interventional device is configured in size and shape for deployment at a targeted gap measuring about 2 mm to about 8 mm, or about 2 mm to about 5 mm. The interventional device may therefore be used in anatomical locations and/or under circumstances where deployment of a conventional clip (typically measuring 15 mm in length and 5 mm in width when closed) is improper. For example, an interventional device as described herein may be deployed between two conventional clips or between a conventional clip and a valve commissure. Such gaps may not provide sufficient space for deployment of another conventional clip, or may not provide sufficient space for the required articulation and maneuvering of a conventional clip. 
     In some embodiments, one or both of the free ends may flare outwardly. Some embodiments include an attachment point at the distal member for attaching to a delivery device. In some embodiments, one or both of the arms include a force-distributing pattern. In some embodiments, the device is formed from a shape-memory material such that the free ends, when deployed distally, sweep around proximally to grasp targeted cardiac valve tissue. 
     Some embodiments include an anchor configured to couple to the distal member. The anchor extends through the interior space and has a width greater than the distal member or the arms. The anchor may be positioned on the atrial side of a targeted cardiac valve while the distal member and arms are positioned on the ventricular side of the targeted valve. The anchor may include a textured surface for encouraging tissue ingrowth. The anchor may have a width of about 5 mm to about 8 mm. 
     In one embodiment, the interventional device includes a first arm which extends proximally from the distal member to form an inner member, and a second arm which extends proximally from the distal member and loops back distally to form a pair of outer members. The inner member is laterally offset from each of the outer members to avoid compressing tissue directly between any two of the arm members. 
     The interventional device may be deployed using a self-centering delivery catheter. The self-centering delivery catheter includes a pair of laterally extending fins extending from a distal section of the delivery catheter. The fins are configured to enable alignment of the delivery catheter with a line of coaptation at the targeted gap. In some embodiments, the self-centering delivery catheter is intra-procedurally adjustable in width. In one embodiment, the self-centering delivery catheter includes a pair of skives and a corresponding pair of wires laterally extendable through the skives to form the fins. The wires may extend through a lumen of the delivery catheter such that width of the fins is controllable via translation of the wires within the lumen. 
     One embodiment is directed to a method of reducing regurgitation through a cardiac valve by compressing leaflet tissue at a targeted gap of the cardiac valve. The method includes the steps of delivering an interventional tissue compression device to the targeted gap, and deploying the compression device at the targeted gap to compress the leaflet tissue and reduce regurgitant flow through the targeted gap. The targeted gap may be located at a mitral valve. The compression device may be delivered to the ventricular side of the mitral valve, then retracted proximally to enable the arms to grasp the leaflet tissue at the ventricular side of the mitral valve. 
     Additional features and advantages will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the embodiments disclosed herein. The objects and advantages of the embodiments disclosed herein will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing brief summary and the following detailed description are exemplary and explanatory only and are not restrictive of the embodiments disclosed herein or as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe various features and concepts of the present disclosure, a more particular description of certain subject matter will be rendered by reference to specific embodiments which are illustrated in the appended drawings. Understanding that these figures depict just some example embodiments and are not to be considered to be limiting in scope, various embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  illustrates an embodiment of a delivery system which may be utilized to deliver an interventional device to a targeted cardiac valve; 
         FIG. 2  illustrates a human heart and shows an exemplary intravascular approach by which a guide catheter of the delivery system of  FIG. 1  may be routed to the heart to deploy the interventional device; 
         FIGS. 3A and 3B  illustrate, in side view, deployment of a conventional clip device at a mitral valve; 
         FIG. 4  illustrates a superior view of the mitral valve showing placement of conventional clip devices and showing gaps where residual regurgitation may occur; 
         FIGS. 5A through 5C  illustrate an embodiment of a tissue tensioning device configured to be positioned within a targeted gap and to tension leaflet tissue at the gap along the line of coaptation to aid in closing the gap; 
         FIGS. 6A and 6B  illustrate another embodiment of a tissue tensioning device; 
         FIGS. 7A and 7B  illustrate deployment of a tissue compression device configured to grasp leaflet tissue at a targeted gap on the ventricular side of the mitral valve and to compress the tissue to aid in closing the gap; 
         FIG. 8  illustrates alternative embodiments of tissue compression devices; 
         FIGS. 9A and 9B  illustrate an embodiment of a tissue compression device having an attached anchor member configured for placement on the atrial side of the mitral valve to prevent displacement of the tissue compression device; 
         FIGS. 10A and 10B  illustrate an embodiment of a tissue compression device formed with a clip-like construction and having an inner member offset from two outer members to avoid compressing leaflet tissue directly between two arm members; 
         FIGS. 11A through 11C  illustrate deployment of an embodiment of a tissue compression device having shape memory, showing initial distal deployment of the free ends of the device followed by the arms sweeping around and extending proximally to engage leaflet tissue; 
         FIGS. 12A through 12D  illustrate an embodiment of a combination tissue tensioning and tissue compression device configured to tension leaflet tissue along the line of coaptation and to compress leaflet tissue to aid in closing a targeted gap; 
         FIGS. 13A through 13D  illustrate various embodiments of a force-distributing feature which may be utilized at portions of a tissue tensioning and/or compression device; 
         FIG. 14  illustrates an embodiment of a self-centering delivery catheter and/or sizer having a pair of fins for aligning the delivery catheter with cardiac valve anatomy; 
         FIGS. 15A and 15B  illustrate another embodiment of a self-centering delivery catheter having adjustable-width fins; and 
         FIGS. 16A through 16C  illustrate various embodiments of attachment/detachment mechanisms which may be used with the interventional devices described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Introduction 
     The present disclosure is directed to devices, systems, and methods for treating regurgitant leaks in cardiac valve tissue, including leaks along the cardiac valve line of coaptation. In some implementations, interventional device embodiments described herein may be deployed at gaps disposed between two previously deployed implants, or between a previously deployed implant and a valve commissure. The interventional devices may be deployed to apply a tensioning force along the line of coaptation and/or to compress captured leaflet tissue along a line orthogonal to the line of coaptation to assist in closing a targeted gap and reducing regurgitant flow through the gap. 
     Throughout this disclosure, many examples are described in the context of guiding a delivery system to a mitral valve. One of skill in the art will understand, however, that the described components, features, and principles may also be utilized in other applications. For example, at least some of the embodiments described herein may be utilized for guiding a delivery system to a pulmonary, aortic, or tricuspid valve. 
     Delivery System Overview 
       FIG. 1  illustrates a delivery system  100  which may be utilized to deliver an interventional device to a targeted cardiac valve. The illustrated delivery system  100  includes a handle  102  and a guide catheter  104  coupled to the handle  102 . The handle  102  is connected to the proximal end  108  of the guide catheter  104  and may be configured to be operatively connected to one or more lumens of the guide catheter  104  to provide steering control over the guide catheter  104 . 
     An interventional device  106  may be passable through an inner lumen of the guide catheter  104  to the distal end  110 . The interventional device  106  generically represents any of the tensioning devices and/or compression devices described herein, such as those illustrated in  FIGS. 5A through 13D . The interventional device  106  may be attached to a suitable delivery member  109  (e.g., delivery catheter, sheath, and/or push rod such as those illustrated in  FIGS. 14 through 16C ) for delivery through the guide catheter  104 . One or more controls  112  may be included at the handle  102 . The one or more controls  112  may be operatively coupled to the guide catheter  104  to provide steering control (e.g., by tensioning one or more control wires). 
       FIG. 2  illustrates a schematic representation of a patient&#39;s heart and a delivery procedure that may be conducted using the illustrated delivery system  100 . The guide catheter  104  may be inserted into the patient&#39;s vasculature and directed to the inferior vena cava  12 . The guide catheter  104  is passed through the inferior vena cava  12  toward the heart. Upon entering the heart from the inferior vena cava  12 , the guide catheter  104  enters the right atrium  14 . For procedures associated with repair of the mitral valve  20 , the guide catheter  104  must further pass into the left atrium  18 . As shown, the guide catheter  104  may reach the left atrium  18  through a puncture in the intra-atrial septum  16 . 
     In other implementations, such as for procedures associated with a tricuspid valve, the guide catheter  104  may be passed through the inferior vena cava  12  into the right atrium  14 , where it may then be positioned and used to perform the procedure related to the tricuspid valve. As described above, although many of the examples described herein are directed to the mitral valve, one or more embodiments may be utilized in other cardiac procedures, including those involving the tricuspid valve. 
     Although  FIG. 2  and many of the other examples described herein illustrate a transfemoral approach for accessing a targeted cardiac valve, it will be understood that the embodiments described herein may also be utilized where alternative approaches are used. For example, embodiments described herein may be utilized in a transjugular approach, transapical approach, or other suitable approach. For repair procedures related to the mitral valve or tricuspid valve, delivery of the interventional device  106  is preferably carried out from an atrial aspect (i.e., with the distal end of the guide catheter  104  positioned within the atrium superior to the targeted valve). The illustrated embodiments are shown from such an atrial aspect. However, it will be understood that the interventional device embodiments described herein may also be delivered from a ventricular aspect. 
     In some embodiments, a guidewire  107  is utilized in conjunction with the guide catheter  104 . For example, the guidewire  107  (e.g., 0.014 in, 0.018 in, 0.035 in) may be routed through the guide catheter  104  to the targeted cardiac valve. Once the guidewire has been properly positioned, the guide catheter  104  may be removed. The guidewire  107  may then remain in position so that one or more interventional devices  106  can travel over the guidewire to the targeted cardiac valve (e.g., via a suitable delivery catheter, sheath, and/or push rod). 
     Conventional Clip Deployment 
       FIGS. 3A and 3B  schematically illustrate, in side view, deployment of a conventional tissue clip  114  at the mitral valve  20 . The clip  114  includes a pair of proximal arms  116  and an opposing pair of distal arms  118 , with each proximal arm  116  corresponds to an opposing distal arm  118 . The clip  114  configured so that an operator can control articulation of the arms to grasp leaflet tissue between the proximal arms  116  and distal arms  118 , as shown. When the clip  114  is deployed and the leaflet tissue is grasped, the proximal arms  116  are positioned on the superior side of the valve leaflets (facing toward the left atrium  18 ) and the distal arms  118  are positioned on the inferior side of the valve leaflets (facing toward the left ventricle  22 ). Once the leaflet tissue has been sufficiently grasped, the clip  114  is moved to a closed, lower profile configuration, and the actuator rod  120  is detached and removed, as shown in  FIG. 3B . The deployed and closed configuration is intended to affix the grasped leaflet tissue to promote improved leaflet coaptation and reduced regurgitation at the mitral valve  20 . 
     An example of a conventional tissue clip  114  is the MitraClip® device available from Abbott Vascular. A typical clip  114  has a closed clip length of about 15 mm. The typical clip  114  has an open clip width of about 20 mm and a closed clip width of about 5 mm. 
       FIG. 4  illustrates the mitral valve  20  from a superior aspect. As shown, a set of conventional clips  114  have been deployed and implanted at the mitral valve  20 . In some circumstances, use of such conventional clips  114  does not completely reduce regurgitation through the mitral valve  20 , and an amount of residual regurgitation remains. For example, residual regurgitation may occur at a gap  26  located between two implanted clips  114  and/or may occur at a gap  28  located between a commissure  24  and an implanted clip  114 . 
     In some circumstances, it may not be clinically appropriate to deploy another such conventional clip  114  at a gap where residual regurgitation is occurring. For example, the targeted gap may be too small to fit another clip  114 . Further, even if the targeted gap is large enough to fit another clip  114  in a closed and deployed position (e.g., with a closed clip width of about 5 mm), there may be insufficient space to safely maneuver, articulate, and deploy the clip  114  at the targeted gap without entangling nearby tissues, damaging clip components, and/or displacing a previously placed clip. In other circumstances, use of an additional clip  114  may be inappropriate because the clip  114  would grasp too much of the relatively narrow gap and would risk causing stenosis of the valve. In such circumstances, the residual regurgitation, while not ideal, is often allowed to continue because it is preferable to risking valve stenosis. 
     Accordingly, there are many situations in which valve leakage exists but conventional repair devices and procedures are inappropriate. The devices, systems, and methods described below may be utilized in such circumstances to provide effective reduction of regurgitation. Although many of the examples illustrated and described herein relate to deployment of an interventional device between two previously deployed tissue clips, it will be readily understood that the described features and components may be readily utilized in other applications where leakage occlusion is intended. For example, one or more of the embodiments described below may be utilized to treat a paravalvular leakage (e.g., in a mitral valve, aortic valve, or other cardiac valve), other vascular leakages, or to treat leakage between an implanted device and a naturally occurring structure, such as between an implanted device and a valve commissure. 
     Embodiments described below may be deployed to effectively treat gaps of about 1 mm to about 10 mm, or about 2 mm to about 8 mm. Included in the foregoing ranges, gaps of about 5 mm or less (e.g., about 2 mm to 5 mm) may be effectively treated using one or more of the embodiments described below. Further, although the examples shown below illustrate treatment of a single gap, it will be understood that in at least some applications, a plurality of gaps may be treated. For example, as shown by the dashed-line conventional clip  114  of  FIG. 4 , there may be circumstances where multiple treatable gaps exist, where one or more may be located between two implanted clips and one or more may be located between an implanted clip and a valve commissure. 
     Tissue Tensioning Devices 
       FIGS. 5A through 5C  illustrate deployment of an interventional device configured as a tissue tensioning device  200  configured to apply a tensioning force along the line of coaptation of a targeted gap in a cardiac valve. The views of  FIGS. 5A through 5C  show the mitral valve  20  from the ventricular side. As shown in  FIG. 5A , a gap  26  may exist between two clips  114  previously deployed at the mitral valve  20 .  FIG. 5B  shows insertion of the tensioning device  200  within the targeted gap  26 . The illustrated tensioning device  200  includes a distal section  202 , an intermediate section  206 , and a proximal section  204 . In the illustrated embodiment, the tensioning device  200  is formed as wire having free ends at the proximal section  204  which extend to form opposing members of the intermediate section  206  before meeting and closing at the distal section  202 . 
     The tensioning device  200  is configured so that at least the intermediate section  206  may be biased laterally outwardly. As shown in  FIG. 5C , after positioning the tensioning device  200  within the gap  26 , the intermediate section  206  is allowed to laterally expand along the line of coaptation. The laterally expanding structure of the intermediate section  206  abuts against the implanted clips  114  and forces them further away from one another to thereby assist in closing the gap  26 . 
     The tensioning device  200  is preferably formed with a width that is allows the device to fit within the targeted gap and provide the laterally outward tensioning force. For example, the tensioning device  200  may have a default, expanded width of about 1 to 3 mm greater than the targeted gap. In this manner, the tensioning device  200  can be positioned within the gap in the laterally compressed state which provides the outward lateral tensioning force. The tensioning device  200  is preferably sized for deployment at a gap of approximately 1 to 10 mm, or about 2 to 8 mm in width, including relatively small gaps of about 2 to 5 mm in width. The length of the device may be up to about 9 mm, such as about 5 to 9 mm. 
     The tensioning device  200  may be deployed, for example, by routing a delivery catheter carrying the tensioning device  200  through the targeted gap  26  from the atrial side to the ventricular side, and unsheathing the tensioning device  200  to allow it to expand along the line of coaptation from the more compressed, smaller width profile shown in  FIG. 5B  to the expanded, larger width profile shown in  FIG. 5C . 
     In the illustrated embodiment, the proximal section  204  of the tensioning device  200  includes free ends that extend or flare outwardly to provide a greater overall width to the proximal section  204  relative to the intermediate section  206 . This feature may aid in preventing the tensioning device  200  from being forced distally through mitral valve  20  and carried downstream into the ventricle. The illustrated embodiment is configured with a closed distal section  202  and an open proximal section  204 . The proximal section  204  may alternatively be closed in a manner similar to the distal section  202 . In some embodiments, the proximal section  204  is closed and the distal section  202  is open. In each embodiment, however, it is preferred that at least the proximal section  204  have a width greater than the intermediate section  206 . 
     The illustrated tensioning device  200  is shown as a simple wire structure. In other embodiments, the tensioning device may include an interior wireframe assembly, elastomer film cover, and/or other interior structural elements. The tensioning device  200  may be formed from any suitable biocompatible material, including biocompatible metals, alloys, polymers, and combinations thereof. In some embodiments, the tensioning device  200  is formed at least partially from a superelastic material such as nitinol. The tensioning device  200  may also be formed from a cobalt-chromium-nickel alloy (e.g., Elgiloy®), polypropylene, polyester, polylactide (e.g., PLLA or PLA), polyglycolide (PGA). 
       FIGS. 6A and 6B  illustrate another embodiment of a tissue tensioning device  300  which may be delivered to a targeted gap to reduce regurgitation/leakage through the gap.  FIG. 6A  illustrates a perspective view of the tensioning device  300 , and  FIG. 6B  illustrates the tensioning device  300  in a deployed position at the mitral valve  20 . The tensioning device  300  may be configured in some aspects (e.g., materials, size) similar to tissue tensioning device  200  described above. 
     The illustrated tensioning device  300  includes a proximal section  304 , an intermediate section  306 , and a distal section  302 . When deployed, the tensioning device  300  is positioned such that the distal section  302  extends through the mitral valve  20  and into the ventricle, while the proximal section  304  remains on the atrial side of the mitral valve  20 . The intermediate section  306  is positioned at the gap between the implanted clips  114 . In a manner similar to the tensioning device  200  of  FIGS. 5B and 5C , the intermediate section  306  of the tensioning device  300  biases laterally outward along the line of coaptation and against the implanted clips  114  to assist in closing the gap between the implanted clips  114 . 
     The illustrated tensioning device  300  may be deployed at the mitral valve  20  in a manner similar to the tensioning device  200  of  FIGS. 5B and 5C . For example, the tensioning device  300  may be delivered to the mitral valve  20  in a sheathed, low profile configuration. The distal section  302  may be unsheathed first to open at the ventricular side of the targeted gap. Further unsheathing then exposes the intermediate section  306  and proximal section  304 . 
     In the illustrated embodiment, the distal section  302  and the proximal section  304  are formed with deployed widths that are greater than the deployed width of the intermediate section  306 . This substantially flat “hourglass” shape can beneficially prevent the tensioning device  300  from translating away from the valve  20  and embolizing downstream. The tensioning device  300  may be formed as a braided or mesh wire structure. In some embodiments, the perimeter  308  of the device is formed as a solid wire to which the interior wire mesh attaches. 
     The tensioning device may be formed using any suitable biocompatible material. The tensioning device  300  may also be formed from a cobalt-chromium-nickel alloy (e.g., Elgiloy®), polypropylene, polyester, polylactide (e.g., PLLA or PLA), polyglycolide (PGA), for example. In some embodiments, a nitinol wireframe structure is shape set in the desired flat hourglass shape to form the tensioning device  300 . The interior mesh may provide a textured surface which beneficially encourages tissue ingrowth. Alternatively, the interior mesh may be omitted. 
     Tissue Compression Devices 
       FIGS. 7A and 7B  illustrate an embodiment of a tissue compression device  400  which may be delivered to a targeted gap to reduce regurgitation/leakage through the gap. The tissue compression device  400  is configured to compress captured tissue along a line orthogonal to the line of coaptation of the targeted cardiac valve tissue. The illustrated compression device  400  includes a distal member  401  and a pair of opposing arms  404  that extend proximally from the distal member  401 . The compression device  400  is configured to grasp and hold leaflet tissue within an interior space between the opposing arms  404 . The compression device  400  may thereby aid in closing the gap and reducing regurgitation by compressing the grasped tissue. The illustrated compression device  400  also includes frictional elements  412  for improving the engagement of the arms  404  with the leaflet tissue. The compression device  400  is configured to provide sufficient compression of grasped tissue for a desired period of time to enable tissue bridging/fusion without overly compressing the tissue and causing necrosis or damage during delivery. 
     A delivery member  410  detachably couples to the distal member  401  at the attachment point  414 . The compression device  400  may be deployed by passing the delivery member  410  through the mitral valve  20  from the atrial side (the bottom side in  FIGS. 7A and 7B ) to the ventricular side (the upper side in  FIGS. 7A and 7B ). The delivery member  410  may then be retracted proximally to bring the interior side of the arms  404  into engagement with the leaflet tissue on the ventricular side of the mitral valve  20 , as shown in  FIG. 7A . The delivery member  410  is then detached from the distal member  401  and removed, leaving the compression device  400  in place on the ventricular side of the mitral valve  20  with the leaflet tissue affixed between the opposing arms  404  as shown in  FIG. 7B . 
     The illustrated compression device  400  is preferably formed from a flexible material capable of flexing sufficiently to allow the arms  404  to position over and grasp the leaflets. The flexible compression device  400  may therefore be deployed without requiring articulation of the arms  404  or relatively complex operator control over arm position relative to the valve  20 . The illustrated compression device  400  is flexible such that when the arms  404  are moved apart and away from the default position—such as when they are positioned over the leaflet tissue—the arms  404  will be biased back toward the default position, in a direction orthogonal to the line of coaptation, to provide a compressive force upon the grasped leaflet tissue. 
     The compression device  400  may also be formed from a cobalt-chromium-nickel alloy (e.g., Elgiloy®), polypropylene, polyester, polylactide (e.g., PLLA or PLA), polyglycolide (PGA). In some embodiments, the compression device  400  is formed from a bioabsorbable material. Such embodiments may provide for natural tissue bridging and fusion at the targeted gap. The compression device  400  is preferably sized for deployment at a gap of approximately 1 to 10 mm, or about 2 to 8 mm in width. The compression device  400  may have a width of about 5 mm or less, such as about 2 to 5 mm. The length of the arms  404  may be up to about 9 mm, such as about 5 to 9 mm. 
       FIG. 8  illustrates alternative embodiments of tissue compression devices  450  and  460 . The compression devices  450  and  460  (as well as the additional compression device embodiments described below) may be configured in some aspects (e.g., materials, size) similar to compression device  400  described above. As shown by compression device  450 , the distal section  452  may be substantially rounded rather than angular. As shown by compression device  460 , the distal section  462  may include a neck  466  configured to act as a flexible, living hinge from which the extending arms  464  can flex. Both the compression device  450  and the compression device  460  include arms  454  and  464  which flare outwardly at their proximal ends. The flared construction may assist in capturing leaflet edges and bringing leaflets into the interior space between the opposing arms as the device is retracted proximally over the leaflets. 
       FIGS. 9A and 9B  illustrate use of the compression device  460  in conjunction with an atrial anchor  468 .  FIG. 9A  is a view from the ventricular side, while  FIG. 9B  is a cross-sectional side view. As shown in  FIG. 9B , the atrial anchor  468  is attached to the compression device  460  at attachment point  470 . The compression device  460  may be deployed on the ventricular side of the valve  20  in the manner described above with respect to compression device  460 . The atrial anchor  468  is positioned on the atrial side, and is sized with a width that is greater than the width of the compression device  460  and preferably also exceeds the width of the gap so as to prevent movement of the atrial anchor  468  and attached compression device  460  downstream from the valve  20 . The atrial anchor  468  may be formed from a mesh, latticed, or otherwise textured material that encourages ingrowth of the compressed leaflet tissue affixed against the atrial anchor  468 . 
     The compression device  460  and the atrial anchor  468  may be delivered in one piece as an integral device. Alternatively, the compression device  460  and atrial anchor  468  may be delivered sequentially and then locked together at the attachment point  470 . For example, the atrial anchor  468  may be unsheathed or otherwise delivered to the atrial side of the targeted gap. The compression device  460  may then be routed through the targeted gap to the ventricular side, then retracted back until mechanically engaged with the atrial anchor  468 . In alternative embodiments, a suture or other suitable connection member may be used to connect the compression device  460  and atrial anchor  468 . Although the particular compression device  460  is illustrated here, it will be understood that other compression device embodiments described herein may also be utilized with an atrial anchor in a similar manner. 
       FIGS. 10A and 10B  illustrate another embodiment of a tissue compression device  500  which may be delivered to a targeted gap to reduce regurgitation/leakage through the gap.  FIG. 10A  is a view of the mitral valve  20  from the ventricular side and  FIG. 10B  is a cross-sectional view taken along the line of coaptation. The compression device  500  includes a distal member  501  and two arms which extend proximally from the distal member  501 . A first arm loops back distally to form two extended outer members  502  and  504 . The second arm extends proximally to form an inner member  506 . The inner member  506  extends between the outer members  502  and  504 . The outer members  502  and  504  and the inner member  506  are connected in a clip configuration such that when deployed at the targeted gap, the outer members  502  and  504  may be positioned on one side of the captured leaflets while the inner member  506  is positioned on the opposite side of the captured leaflets. 
     As shown in  FIG. 10B , the inner member  506  is laterally offset to extend between the outer members  502  and  504 . With this configuration, when the compression device  500  is deployed, the captured leaflet tissue is not compressed directly between any two hard structures. The offset lines of compression may prevent over-compression of tissue to avoid injury and necrosis. Some embodiments may include barbs or other frictional elements (not shown) to promote engagement with captured tissue. 
     The compression device  500  may be delivered in a manner similar to the compression device  400  as described in relation to  FIGS. 7A and 7B . For example, a delivery member may attach to the distal member  501 . The compression device  500  may be delivered to the ventricular side of the valve  20 , and then retracted proximally to bring the outer members  502  and  504  and inner member  506  into position on opposite sides of the grasped leaflets. 
       FIGS. 11A through 11C  illustrate in cross-sectional side view an embodiment of a tissue compression device  600  having self-closing features. A delivery catheter  610  is shown with a distal end delivered through the mitral valve  20  to the ventricular side (the upper side in the Figures). The compression device  600  is unsheathed and deployed from the delivery catheter  610  with the proximal free ends  604  extending first out of the delivery catheter. An inner push rod (not shown), for example, may extend within the delivery catheter  610  to enable pushing of the compression device  600  distally out of the delivery catheter  610 . As shown in  FIG. 11B , further deployment of the compression device  600  out of the delivery catheter  610  allows the proximal free ends  604  to sweep laterally outwardly and rotate back toward the axis of the delivery catheter  610 . As shown in  FIG. 11C , further deployment allows the proximal free ends  604  to wrap around proximally on opposite sides of the leaflets of the mitral valve  20  and to engage with the outer surfaces of the leaflets. The compression device  600  may then be detached from the delivery catheter  610  and the delivery catheter  610  removed. 
     The compression device  600  is formed from a suitable shape memory material (e.g., nitinol) processed at a transition temperature to set the desired final deployed shape. The compression device  600  is preferably processed at a suitably low temperature to allow straightening and installation into the lower profile shape within the delivery catheter  610  without exceeding the strain properties and causing plastic deformation. Once exposed to the relatively elevated temperature within the body, the unsheathed or extruded device will progressively transition in shape to the final position capable of grasping leaflet tissue. 
     Combination Compression/Tensioning Devices 
       FIGS. 12A through 12D  illustrate an exemplary embodiment of a device  700  configured to both tension and compress tissue at a targeted gap. As described below, the device  700 , when deployed at a targeted gap of a cardiac valve, provides tension along the line of coaptation of the gap while simultaneously providing compression of grasped tissue along a line orthogonal to the line of coaptation. 
     As shown in  FIG. 12A , the combination device  700  includes a pair of free ends  704  which each angle at bend  706  and then extend as a lateral member  712 . Each lateral member  712  then loops at bend  708  and extends as a longitudinal member  710 . The opposing longitudinal members  710  meet and close at a proximal end  702 . Although not shown, the combination device  700  may optionally include a mesh or webbing to encourage tissue ingrowth. 
     As shown in  FIG. 12B , the combination device  700  may be flexed so that the longitudinal members  710  move inwardly and the overall width of the device  700  is reduced. From such a constrained position, the device will provide an outward lateral force toward the default, wider position shown in  FIG. 12A . 
       FIGS. 12C and 12D  illustrate the combination device  700  in a deployed position at a targeted gap between two conventional clips  114 .  FIG. 12C  is a side view showing the ventricular side of the valve  20  and  FIG. 12D  is a view from a position inferior to the valve  20 . When positioned within the gap, the lateral outward tensioning force  730  provided by the opposing longitudinal members  710  can cause the device  700  to abut against and force the clips  114  apart from one another. This will bring leaflets of the gap into contact with one another to assist in closing the gap. In addition to the tensioning force  730 , the combination device provides a compressive force  720  against the grasped leaflet tissue. The lateral members  712  are positioned on opposite sides of the grasped leaflets and are biased toward one another to compress the tissue held between. 
     The combination device  700  may be deployed in a manner similar to the deployment of compression device  600  shown and described in relation to  FIGS. 11A through 11C . For example, the combination device  700  may be formed from a suitable shape memory material (e.g., nitinol) and deployed by unsheathing the device  700  at the targeted gap. The free ends  704  may be unsheathed first and allowed to sweep around on opposite sides of the leaflets to form the lateral members  712 . The remainder of the device  700 , including the longitudinal members  710  and proximal end  702 , may then be unsheathed at the desired position within the targeted gap. 
     Force-Distributing Features 
       FIGS. 13A through 13D  illustrate embodiments of tissue compression devices having force-distributing features.  FIGS. 13A through 13C  show various exemplary wire patterns which may be utilized at one or more sections of a compression device to provide greater effective surface area. The relatively high effective surface area better distributes compressive forces upon the grasped tissue while also providing effective contact and tissue engagement.  FIG. 13A  illustrates a portion of a compression device  800  having a looping or spiraling pattern.  FIG. 13B  illustrates a portion of a compression device  802  having a serpentine or winding pattern of extensions  808 .  FIG. 13C  illustrates a portion of a compression device  804  having a forked pattern with a plurality of extensions  812  radiating from a common point  810 . 
     Force-distributing features such as those illustrated may be included with any of the compression or combination compression/tensioning devices described above. For example, any of the illustrated force distributing patterns, or combinations thereof, may be used at the free ends of the embodiments shown in  FIGS. 10A through 12D . 
       FIG. 13D  illustrates the compression device  800  as deployed at a targeted gap of the mitral valve  20 . As shown, the force-distributing spiral pattern is employed on one side of the grasped tissue and an inner member  806  is disposed on the opposite side of the grasped tissue. The spiral pattern functions to distribute applied forces and prevent overly compressing tissue grasped between the spiral pattern and the inner member  806 . Alternative embodiments may include one or more force-distributing features on both sides. 
     Self-Centering Delivery Catheter and Sizer 
       FIGS. 14 through 15B  illustrate exemplary embodiments of delivery catheters having a self-centering feature that provides desired alignment to the cardiac valve anatomy. As shown in  FIG. 14 , a delivery catheter  900  includes a pair of fins  906  extending laterally from the longitudinal axis of the delivery catheter  900  (the leaflets of the mitral valve  20  are shown here as transparent to better illustrate the delivery catheter  900 ). The fins  906  are positioned near the distal end of the delivery catheter  900  so that when the distal end of the delivery catheter  900  is positioned at the targeted gap, the fins  906  will cause the delivery catheter  900  to rotate as needed to align with the line of coaptation of the mitral valve  20 . 
     For example, if the projected fins  906  are not aligned to the line of coaptation during the approach to the mitral valve  20 , the fins  906  will abut against the atrial facing surfaces of the leaflets. Because the leaflets slope closer to each other in the ventricular direction toward the leaflet edges, further movement of the delivery catheter  900  in the ventricular direction will cause the delivery catheter  900  to rotate so that the fins  906  will better fit within the wedge shape of the leaflets. The delivery catheter  900  may travel over a previously positioned guidewire  901 , as shown. 
     The self-centering feature can beneficially ensure that an interventional device passed through the delivery catheter  900  is properly aligned to the line of coaptation of the valve  20 . For example, the interventional device carried within the delivery catheter  900  may be rotationally keyed to the delivery catheter such that by ensuring alignment of the delivery catheter  900  also ensures alignment of the interventional device. 
     The fins  906  are shown here in a symmetric arrangement with each opposing fin having a substantially equal width. When used, such an embodiment will operate to position the distal end of the delivery catheter  900  at the center of the targeted gap (e.g., between the two implanted clips  114 ). Alternative embodiments may have fins with a non-symmetric arrangement to offset from the center of the gap the position the distal end of the catheter. Such an offset, non-symmetric embodiment may be used where particular patient anatomy and/or procedural requirements require deployment of an interventional device off from the center of a targeted gap. 
       FIGS. 15A and 15B  illustrate an embodiment of a delivery catheter  1000  having adjustable-width fins.  FIG. 15A  shows a distal end  1002  of the delivery catheter  1000  with the fins  1004  in a retracted position. Wires  1004  (or strips, ribbons, or other suitable structures) pass through the interior of the delivery catheter  1000  and are attached near the distal end  1002 . A pair of skives  1006  are also included near the distal end  1002 . As shown in  FIG. 15B , the wires  1004  may be translated distally such that portions extend laterally out of skives  1006 . The laterally extended wires  1004  may then function as the self-centering fins which align the delivery catheter  1000  to the line of coaptation when delivered to the cardiac valve. In some embodiments, the distal portion of the delivery catheter  1000  includes a coating of an elastomer material or other suitable material covering at least the skives  1006 . In this configuration, the extending wires  1004  which form the fins are covered and there is no gap between the extended wires  1004  and the skives  1006 . 
     The width of the fins is controllable by translating the wires  1004  relative to the body of the delivery catheter  1000 . For example, moving the wires  1004  distally will force greater lengths out of the skives  1006  to increase the effective width of the fins. Likewise, retracting the wires  1004  proximally will pull more wire length in through the skives  1006  to shorten the width of the fins. The wires  1004  may extend proximally to a handle and may be operatively coupled to one or more controls so that an operator can control fin adjustment through manipulation at the handle (see, e.g.,  FIG. 1 ). In some embodiments, the wires  1004  are independently controllable, and the widths of each opposing fin may be adjusted to a symmetric or non-symmetric configuration. 
     Although embodiments of  FIGS. 14 through 15B  are described above in the context of their use as delivery catheters, it will be understood that they may also be utilized as sizers for informing an operator as to the size of the targeted gap. Determining the size of a targeted gap may therefore inform the selection and/or sizing of the interventional device to deploy at the gap. An operator may pass the fins into the targeted gap and use the width of the fins to determine the size of the gap. For example, if real-time monitoring (e.g., via echo/Doppler) confirms that regurgitation is sufficiently reduced while the fins are positioned within the gap, the properly coapted gap will be determined to be about the same width as the fins. When configured as sizers, the sizers need not necessarily also be capable of delivering an interventional device to the targeted gap. In some implementations, a separate sizer or set of sizers may be utilized to determine gap size, and a separate delivery catheter may then be used to delivery an interventional device. 
     Attachment/Detachment Mechanisms 
       FIGS. 16A through 16C  illustrate various exemplary mechanisms for attaching and detaching at least some of the interventional devices described herein. For example, the illustrated interventional device  1100  may generically represent any of the tensioning devices and/or compression devices illustrated in  FIGS. 5A through 13D . In  FIG. 16A , an interventional device  1100  is shown sheathed within a delivery catheter  1110 . An inner member  1128  (formed as a push rod or other suitable structure) couples to the interventional device  1100  at attachment point  1102 . 
       FIG. 16B  illustrates various attachment/detachment mechanisms that may be utilized, including a hook member  1120 , a fitting member  1122 , a threaded member  1124 , or a clamp member  1126 . The interventional device  1100  is configured so that the attachment point  1102  matches the particular construction of the of the attachment/detachment mechanism of the inner member  1128 . Other embodiments may include one or more alternative locking mechanisms suitable for detachably coupling the interventional device  1100  to the inner member  1128 . For example, an irreversible shearing feature may be designed to fail at a given stress to detach the inner member  1128  from the interventional device  1100 . 
       FIG. 16C  shows retraction of the delivery catheter  1110  relative to the inner member  1128  and resulting unsheathing of the interventional device  1100 . Following unsheathing and deployment, the inner member  1128  may be detached from the interventional device  1100  and removed. In preferred embodiments, the delivery catheter  1110  functions as a single outer sheath, however additional (e.g., telescoping) sheaths may be utilized if staged deployment is desired. 
     The terms “approximately,” “about,” and “substantially” as used herein represent an amount or condition close to the stated amount or condition that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount or condition that deviates by less than 10%, or by less than 5%, or by less than 1%, or by less than 0.1%, or by less than 0.01% from a stated amount or condition. 
     Elements described in relation to any embodiment depicted and/or described herein may be substituted for or combined with elements described in relation to any other embodiment depicted and/or described herein. For example, any of the interventional device embodiments illustrated in  FIGS. 5A to 13D  may be utilized with any of the delivery catheter or attachment/detachment mechanism embodiments illustrated in  FIGS. 14 through 16C .