Abstract:
Devices and methods are provided for tissue approximation and repair. Fixation devices comprise a pair of elements each having a first end, a free end opposite the first end, and an engagement surface therebetween for engaging the tissue, the first ends being moveable between an open position wherein the free ends are spaced apart and a closed position wherein the free ends are closer together with the engagement surfaces generally facing each other. The fixation devices also include a locking mechanism coupled to the elements for locking the elements in place. The devices and methods find use in a variety of therapeutic procedures, including endovascular, minimally-invasive, and open surgical procedures, and can be used in various anatomical regions. The invention is particularly useful in procedures requiring minimally-invasive or endovascular access to remote tissue locations, where the instruments utilized must negotiate long, narrow, and tortuous pathways to the treatment site.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of U.S. patent application Ser. No. 11/130,818 (Attorney Docket 020489-001420US), filed May 16, 2005, which claims the benefit and priority of U.S. Provisional Patent Application No. 60/571,217 (Attorney Docket 020489-001410US), filed May 14, 2004, and is a continuation-in-part of U.S. patent application Ser. No. 10/441,531 (Attorney Docket 020489-001400US), filed May 19, 2003 which is a continuation-in-part of, and claims the benefit of priority from U.S. Pat. No. 6,752,813 (Attorney Docket 020489-000400US), filed Jun. 27, 2001, which is a continuation-in-part of U.S. Pat. No. 6,629,534 (Attorney Docket 020489-00011US), filed Apr. 7, 2000, which claims the benefit of prior Provisional Application No. 60/128,690, filed on Apr. 9, 1999 under 37 CFR § 1.78(a), the full disclosures of which are hereby incorporated herein by reference. 
         [0002]    In addition, U.S. patent application Ser. No. 10/441,531 (Attorney Docket 020489-001400US) is related to U.S. patent application Ser. No. 10/441,753 (Attorney Docket No. 020489-001200US), U.S. patent application Ser. No. 10/441,508 (Attorney Docket No. 020489-001500US), and U.S. patent application Ser. No. 10/441,687 (Attorney Docket No. 020489-001700US), all of which were filed on the same day (May 19, 2003), the full disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates generally to medical methods, devices, and systems. In particular, the present invention relates to methods, devices, and systems for the endovascular, percutaneous or minimally invasive surgical treatment of bodily tissues, such as tissue approximation or valve repair. More particularly, the present invention relates to repair of valves of the heart and venous valves. 
         [0005]    Surgical repair of bodily tissues often involves tissue approximation and fastening of such tissues in the approximated arrangement. When repairing valves, tissue approximation includes coapting the leaflets of the valves in a therapeutic arrangement which may then be maintained by fastening or fixing the leaflets. Such coaptation can be used to treat regurgitation which most commonly occurs in the mitral valve. 
         [0006]    Mitral valve regurgitation is characterized by retrograde flow from the left ventricle of a heart through an incompetent mitral valve into the left atrium. During a normal cycle of heart contraction (systole), the mitral valve acts as a check valve to prevent flow of oxygenated blood back into the left atrium. In this way, the oxygenated blood is pumped into the aorta through the aortic valve. Regurgitation of the valve can significantly decrease the pumping efficiency of the heart, placing the patient at risk of severe, progressive heart failure. 
         [0007]    Mitral valve regurgitation can result from a number of different mechanical defects in the mitral valve or the left ventricular wall. The valve leaflets, the valve chordae which connect the leaflets to the papillary muscles, the papillary muscles or the left ventricular wall may be damaged or otherwise dysfunctional. Commonly, the valve annulus may be damaged, dilated, or weakened limiting the ability of the mitral valve to close adequately against the high pressures of the left ventricle. 
         [0008]    The most common treatments for mitral valve regurgitation rely on valve replacement or repair including leaflet and annulus remodeling, the latter generally referred to as valve annuloplasty. A recent technique for mitral valve repair which relies on suturing adjacent segments of the opposed valve leaflets together is referred to as the “bow-tie” or “edge-to-edge” technique. While all these techniques can be very effective, they usually rely on open heart surgery where the patient&#39;s chest is opened, typically via a sternotomy, and the patient placed on cardiopulmonary bypass. The need to both open the chest and place the patient on bypass is traumatic and has associated high mortality and morbidity. 
         [0009]    For these reasons, it would be desirable to provide alternative and additional methods, devices, and systems for performing the repair of mitral and other cardiac valves. Such methods, devices, and systems should preferably not require open chest access and be capable of being performed either endovascularly, i.e., using devices which are advanced to the heart from a point in the patient&#39;s vasculature remote from the heart or by a minimally invasive approach. Further, such devices and systems should provide features which allow repositioning and optional removal of a fixation device prior to fixation to ensure optimal placement. Still further, the fixation devices should be able to be locked in a fixed position and left behind for implantation. Still more preferably, the methods, devices, and systems would be useful for repair of tissues in the body other than heart valves. At least some of these objectives will be met by the inventions described hereinbelow. 
         [0010]    2. Description of the Background Art 
         [0011]    Minimally invasive and percutaneous techniques for coapting and modifying mitral valve leaflets to treat mitral valve regurgitation are described in PCT Publication Nos. WO 98/35638; WO 99/00059; WO 99/01377; and WO 00/03759. 
         [0012]    Maisano et al. (1998)  Eur. J. Cardiothorac. Surg.  13:240-246; Fucci et al. (1995)  Eur. J. Cardiothorac. Surg.  9:621-627; and Umana et al. (1998)  Ann. Thorac. Surg.  66:1640-1646, describe open surgical procedures for performing “edge-to-edge” or “bow-tie” mitral valve repair where edges of the opposed valve leaflets are sutured together to lessen regurgitation. Dec and Fuster (1994)  N. Engl. J. Med.  331:1564-1575 and Alvarez et al. (1996)  J. Thorac. Cardiovasc. Surg.  112:238-247 are review articles discussing the nature of and treatments for dilated cardiomyopathy. 
         [0013]    Mitral valve annuloplasty is described in the following publications. Bach and Bolling (1996)  Am. J. Cardiol.  78:966-969; Kameda et al. (1996)  Ann. Thorac. Surg.  61:1829-1832; Bach and Bolling (1995)  Am. Heart J.  129:1165-1170; and Bolling et al. (1995) 109:676-683. Linear segmental annuloplasty for mitral valve repair is described in Ricchi et al. (1997)  Ann. Thorac. Surg.  63:1805-1806. Tricuspid valve annuloplasty is described in McCarthy and Cosgrove (1997)  Ann. Thorac. Surg.  64:267-268; Tager et al. (1998)  Am. J. Cardiol.  81:1013-1016; and Abe et al. (1989)  Ann. Thorac. Surg.  48:670-676. 
         [0014]    Percutaneous transluminal cardiac repair procedures are described in Park et al. (1978)  Circulation  58:600-608; Uchida et al. (1991)  Am. Heart J.  121: 1221-1224; and Ali Khan et al. (1991)  Cathet. Cardiovasc. Diagn.  23:257-262. 
         [0015]    Endovascular cardiac valve replacement is described in U.S. Pat. Nos. 5,840,081; 5,411,552; 5,554,185; 5,332,402; 4,994,077; and 4,056,854. See also U.S. Pat. No. 3,671,979 which describes a catheter for temporary placement of an artificial heart valve. 
         [0016]    Other percutaneous and endovascular cardiac repair procedures are described in U.S. Pat. Nos. 4,917,089; 4,484,579; and 3,874,338; and PCT Publication No. WO 91/01689. 
         [0017]    Thoracoscopic and other minimally invasive heart valve repair and replacement procedures are described in U.S. Pat. Nos. 5,855,614; 5,829,447; 5,823,956; 5,797,960; 5,769,812; and 5,718,725. 
       BRIEF SUMMARY OF THE INVENTION 
       [0018]    The invention provides devices, systems and methods for tissue approximation and repair at treatment sites. The devices, systems and methods of the invention will find use in a variety of therapeutic procedures, including endovascular, minimally-invasive, and open surgical procedures, and can be used in various anatomical regions, including the abdomen, thorax, cardiovascular system, heart, intestinal tract, stomach, urinary tract, bladder, lung, and other organs, vessels, and tissues. The invention is particularly useful in those procedures requiring minimally-invasive or endovascular access to remote tissue locations, where the instruments utilized must negotiate long, narrow, and tortuous pathways to the treatment site. In addition, many of the devices and systems of the invention are adapted to be repositionable or reversible and removable from the patient at any point without interference with or trauma to internal tissues. 
         [0019]    In preferred embodiments, the devices, systems and methods of the invention are adapted for fixation of tissue at a treatment site. Exemplary tissue fixation applications include cardiac valve repair, septal defect repair, patent foramen ovale repair, vascular ligation and clamping, laceration repair and wound closure, but the invention may find use in a wide variety of tissue approximation and repair procedures. In a particularly preferred embodiment, the devices, systems and methods of the invention are adapted for repair of cardiac valves, and particularly the mitral valve, as a therapy for regurgitation. The invention enables two or more valve leaflets to be coapted using an “edge-to-edge” or “bow-tie” technique to reduce regurgitation, yet does not require open surgery through the chest and heart wall as in conventional approaches. 
         [0020]    Using the devices, systems and methods of the invention, the mitral valve can be accessed from a remote surgical or vascular access point and the two valve leaflets may be coapted and fixed together using endovascular or minimally invasive approaches. The devices of the present invention include a fixation device having a locking mechanism which allows the user to “lock” the fixation devices in a desired position to fix the leaflets together. In some embodiments, the locking mechanism locks the fixation device in a single predetermined configuration or in one of a few predetermined configurations. In other embodiments, the locking mechanism allows locking at any point along a continuum of points on the device so that the user may choose the desired position for fixing the leaflets together during the procedure. The desired position for fixing the leaflets may vary due to variability in the thickness and amount of tissue captured by the fixation device, the presence or absence of disease (e.g. calcification, hypertrophy), the age of the patient and other factors potentially unknown to the user prior to the procedure. For example, if more tissue is captured or coapted by the fixation device, the fixation device may not be able to close as far than if less tissue is captured. Therefore, in some circumstances it may be advantageous that the locking mechanism of the fixation device be lockable at a specific, non-predetermined point desired by the user even though that point may not be able to be determined prior to the procedure. 
         [0021]    In some circumstances the invention may also find application in open surgical approaches as well. According to the invention, the mitral valve may be approached either from the atrial side (antegrade approach) or the ventricular side (retrograde approach), and either through blood vessels or through the heart wall. 
         [0022]    In a first aspect of the present invention, a fixation device is provided having a pair of distal elements (or fixation elements), each distal element having a free end and an engagement surface for engaging the tissue, wherein the distal elements are moveable between a first position for capturing the tissue and a second position for fixing the tissue. Preferably, the engagement surfaces are spaced apart in the first position and are closer together and generally face toward each other in the second position. The fixation device is preferably delivered to a target location in a patient&#39;s body by a delivery catheter having an elongated shaft, a proximal end and a distal end, the delivery catheter being configured to be positioned at the target location from a remote access point such as a vascular puncture or cut-down or a surgical penetration. In a preferred embodiment, the target location is a valve in the heart. 
         [0023]    In a second aspect of the present invention, the fixation device further includes a locking mechanism that maintains the distal elements in a selected position relative to each other. While a variety of locking mechanisms may be used. In some embodiments, the fixation device includes a moveable stud coupled to the fixation elements wherein movement of the stud moves the fixation elements between the positions. In such embodiments, the locking mechanism may comprise an engagement element engageable with the moveable stud wherein engagement restricts movement of the stud. In some instances, the engagement element comprises at least one wedging element which frictionally engages the moveable stud to restrict movement of the stud. In other embodiments, the engagement element has at least one protrusion which mates with at least one external groove on the stud so as to restrict movement of the stud. 
         [0024]    Alternatively, the locking mechanism may comprises an interference element which is positionable along the moveable stud so that the interference element prevents movement of the moveable stud in at least a first direction by contacting a stationary surface of the fixation device. In some embodiments, the interference element comprises a locking sheath advanceable over the moveable stud so that the locking sheath prevents movement of the stud in the at least first direction by abutting against the stationary surface. In other embodiments, the moveable stud includes external grooves and the interference element comprises a lock nut mateable with the external grooves of the moveable stud so that the mated lock nut prevents movement of the stud in at least the first direction by abutting against the stationary surface. 
         [0025]    It may be appreciated that the moveable stud may be comprised of a rigid material, such as a metal or plastic, or the moveable stud may be comprised of a flexible line, such as a suture. When the moveable stud comprises a flexible line, the locking mechanism may comprise an interference element which is positionable along the flexible line so that the interference element prevents movement of the flexible line in at least a first direction by contacting a stationary surface of the fixation device. 
         [0026]    In still other embodiments, the locking mechanism comprises gears, wherein movement of the gears moves the fixation elements between the positions while locking the fixation elements in place at each position. 
         [0027]    Further, in other embodiments, the locking mechanism comprises a biasing member which biases the fixation elements toward one of the positions. The biasing member may comprise a pair of spring loaded support sleeves positionable against a portion of the fixation device so as to bias the fixation elements toward one of the positions. Or, the biasing member may comprise a cinching band positionable around the fixation elements so as to bias the fixation elements toward one of the positions. In some embodiments, the cinching band comprises an elastic cinching band positionable around the fixation elements in a stretched configuration so as to apply biasing force to the fixation elements. In other embodiments, the cinching band comprises a cinching line positionable around the fixation elements in a lasso configuration so as to apply biasing force to the fixation elements when tightened. 
         [0028]    Typically, the fixation further comprises at least one leg joined with the fixation elements so that movement of the at least one leg moves the fixation elements between the positions. In such embodiments, the at least one leg may have a spring loaded configuration so as to bias the fixation elements toward one of the positions. Alternatively or in addition, the locking mechanism may comprise a structure joinable with the at least one leg so as to prevent movement of the fixation elements. In some embodiments, the structure comprises a barb engagable with the at least one leg. 
         [0029]    In a third aspect of the present invention, the fixation devices include an unlocking mechanism for disengaging the locking mechanism. In some embodiments, the unlocking mechanism comprises a harness, the harness adapted to disengage or reduce engagement of an engaging element from the moveable stud. For example, the harness may reduce frictional engagement a wedging element against the moveable stud. 
         [0030]    In other aspect of the present invention, a locking mechanism coupled to the fixation elements is provided for locking the fixation elements in place along a continuum of positions between the open position and the closed position. Again, the fixation device may include a moveable stud coupled to the fixation elements wherein movement of the stud moves the fixation elements between the positions. In such embodiments, the locking mechanism may comprise at least one wedging element for frictionally engaging the stud to restrict movement thereof. For example, the at least one wedging element may comprise a binding plate having a first end, a second end and a portion therebetween shaped to engage the stud, the binding plate positioned so that the portion is disposed near the stud. The portion shaped to engage the stud may at least partially surround the stud and the binding plate may be positioned so that the portion at least partially surrounds the stud. In some embodiments, the portion shaped to at least partially surround the stud comprises an aperture, wherein the binding plate is positioned so that the stud passes through the aperture. The locking mechanism may further comprise a spring which forces the aperture against the stud to restrict movement of the stud through the aperture. 
         [0031]    In some embodiments, the at least one wedging element comprises at least one cam, the at least one cam pivotable to frictionally engage the stud to restrict movement thereof. The at least one cam may have an inward surface engageable with the stud and an outward surface connected with a spring which forces the inward surface against the stud to restrict movement of the stud. Embodiments including an unlocking mechanism for disengaging the locking mechanism, may include at least one actuator attached to a pivot point on each of the at least one cams, the at least one actuator adapted to pivot the at least one cam about its pivot point to reduce frictional engagement of the inner surface with the stud. Sometimes, the at least one cam comprises two cams, each cam disposed on opposite sides of the stud. 
         [0032]    In another aspect of the present invention, a locking mechanism coupled to the fixation elements is provided for locking the fixation elements in a position which allows movement of the fixation elements within a sub-range of the range. For example, in embodiments having a moveable stud coupled to the fixation elements wherein movement of the stud moves the fixation elements between the positions within the range, the stud may have may have at least one external groove for engagement by at least one wedging element wherein the at least one external groove is sized to allow shifting of the at least one wedging element within the at least one external groove which allows movement of the fixation elements within the sub-range. In other embodiments having such a moveable stud, the locking mechanism comprises at least one wedging element for frictionally engaging the stud to restrict movement thereof. In some instances, the at least one wedging element comprises an at least partially flexible material wherein flexing of the material allows movement of the fixation elements within the sub-range. In other instances, the at least one wedging element comprises a binding plate having a first end, a second end and a portion therebetween shaped to at least partially surround the stud, the binding plate positioned so that the portion at least partially surrounds the stud. In some embodiments, the portion shaped to at least partially surround the stud comprises an aperture and the binding plate is positioned so that the stud passes through the aperture. 
         [0033]    It may be appreciated that the fixation elements may be configured for engaging valve leaflets of a valve within a heart, and movement of the fixation elements within the sub-range is achievable by force caused by dynamic fluid flow through the valve. 
         [0034]    In another aspect of the present invention, a locking mechanism is provided comprising a moveable stud coupled to a device, wherein movement of the stud actuates movement of a portion of a device to a desired position in a range from a first position to a second position, at least one element configured to engage the stud to restrict movement of the stud which locks the device in the desired position, and an unlocking mechanism configured to disengage the at least one element from the stud which allows movement of the stud. In some instances, the at least one element comprises a binding plate having a first end, a second end and a portion therebetween shaped to at least partially surround the stud, the binding plate positioned so that the portion at least partially surrounds the stud. The portion shaped to at least partially surround the stud may comprise an aperture, the binding plate positioned so that the stud passes through the aperture. In some embodiments, the locking mechanism further comprising a spring configured to force the aperture against the stud to restrict movement of the stud through the aperture. The unlocking mechanism may comprise a harness, the harness adapted to move the second end while the first end remains substantially stationary so as to reduce frictional engagement of the at least partially surrounding portion with the stud. 
         [0035]    In some embodiments, the at least one element comprises at least one cam, the at least one cam pivotable to frictionally engage the stud to restrict movement thereof. The at least one cam may have an inward surface engageable with the stud and an outward surface connected with a spring which forces the inward surface against the stud to restrict movement of the stud. In some embodiments, the unlocking mechanism comprises at least one actuator attached to a pivot point on each of the at least one cams, the at least one actuator adapted to pivot the at least one cam about its pivot point to reduce frictional engagement of the inner surface with the stud. 
         [0036]    In still other embodiments, the moveable stud may have at least one external groove for engagement with the at least one element to restrict movement of the stud. Thus, the at least one element may comprise at least one component having at least one protrusion which mates with the at least one external groove of the stud wherein the at least one component is moveable to engage the at least one protrusion with the at least one external groove of the stud to restrict movement of the stud. In many of these embodiments, the unlocking mechanism comprises a hinge component which moves the at least one component to disengage the at least one protrusion from the at least one external groove. It may be appreciated that the at least one external groove may comprise threads and the at least one component comprise a split nut. 
         [0037]    The desired position typically includes any position between the first position and the second position. Likewise, the desired position may includes one of a series of predetermined positions between the first position and the second position. 
         [0038]    In another aspect of the present invention, a lockable system is provided comprising a device having a portion which is moveable to a desired position, and a locking mechanism coupled to the device. The locking mechanism comprises a moveable stud configured so that movement of the stud actuates movement of the portion of the device to the desired position, at least one element configured to engage the stud to restrict movement of the stud which locks the device in the desired position, and an unlocking mechanism configured to disengage the at least one element from the stud which allows movement of the stud. 
         [0039]    In some embodiments, the device comprises a catheter. The catheter may include at least one pullwire fixedly attached to the stud so that movement of the stud moves the at least one pullwire which actuates movement of the portion of the catheter to the desired position. In other embodiments, the device comprises a grasper. The grasper may include at least one pullwire fixedly attached to the stud so that movement of the stud moves the at least one pullwire which actuates movement of the portion of the grasper to the desired position. And, in still other embodiments, the device comprises a retractor. 
         [0040]    As mentioned, the locking mechanism of the present invention may be employed in catheter shafts, retractors, or other medical instruments such as graspers or biopsy forceps, where it is desirable to lock a device in a particular position prior to, during, or following a medical procedure. Such procedures can include biopsies or ablation procedures, wherein it is desired to navigate and hold catheter position, and retrieval procedures (e.g. of polyps, foreign objects). 
         [0041]    Other objects and advantages of the present invention will become apparent from the detailed description to follow, together with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]      FIG. 1  illustrates an embodiment of a fixation device having an embodiment of a locking mechanism. 
           [0043]      FIG. 2  illustrates another embodiment of a fixation device having an embodiment of a locking mechanism. 
           [0044]      FIG. 3  provides a front view of the locking mechanism of  FIG. 1 . 
           [0045]      FIGS. 4A-4C  illustrate the locking mechanism of  FIG. 3  in unlocked and locked positions. 
           [0046]      FIGS. 5-7  illustrate elements of an embodiment of a locking mechanism which includes a binding plate. 
           [0047]      FIGS. 8A-8B  illustrate an embodiment of a locking mechanism having a one-sided release harness. 
           [0048]      FIGS. 9A-9C  illustrate an embodiment of a locking mechanism having wedging elements comprising binding structures. 
           [0049]      FIGS. 10A-10C  illustrate an embodiment of a locking mechanism having wedging elements comprising interdigitating structures. 
           [0050]      FIGS. 11A-11B  illustrate an embodiment of a locking mechanism comprising a pair of cams. 
           [0051]      FIGS. 12A-12D  illustrate elements of an embodiment of a locking mechanism which includes mateable components having at least one protrusion and groove which engage for locking. 
           [0052]      FIGS. 13A-13C  illustrate an embodiment of a locking mechanism comprising gears. 
           [0053]      FIGS. 14A-14D ,  15 A- 15 B illustrate an embodiment of a locking mechanism which works against biasing forces that advance the stud of the fixation device. 
           [0054]      FIGS. 16A-16B  illustrate a fixation device having a flexible line replacing the stud, and wherein the locking mechanism works against biasing forces that advance the flexible line. 
           [0055]      FIG. 17A  illustrates an embodiment of a fixation device having legs spring biased toward a closed position. 
           [0056]      FIGS. 17B-17C  illustrate the application of support sleeves to bias the distal elements of the fixation device toward a closed position. 
           [0057]      FIGS. 18A-18C  illustrate an embodiment of a biasing member comprising a cinching band. 
           [0058]      FIGS. 19A-19C  illustrate an embodiment of a biasing member comprising a cinching line. 
           [0059]      FIG. 20  illustrates a locking mechanism comprising barbs which attach to the legs, holding the legs in a fixed position. 
           [0060]      FIGS. 21A-21C  illustrate attachment of the barbs to the legs. 
           [0061]      FIG. 22  illustrates a catheter having an embodiment of a locking mechanism of the present invention. 
           [0062]      FIG. 23  illustrates a grasper having an embodiment of a locking mechanism of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0063]    The fixation devices of the present invention provide for grasping, approximating and fixating tissues such as valve leaflets to treat cardiac valve regurgitation, particularly mitral valve regurgitation. In preferred embodiments, the fixation devices provide features that allow repositioning and removal of the device if so desired. Such removal would allow the practitioner to reapproach the valve in a new manner if so desired. Once the tissue has been satisfactorily approximated, the grasped tissue is typically fixed in place by maintaining grasping with the fixation device which is left behind as an implant. 
         [0064]    The fixation device is releasably attached to a shaft of an interventional tool at its distal end. When describing the devices of the invention herein, “proximal” shall mean the direction toward the end of the device to be manipulated by the user outside the patient&#39;s body, and “distal” shall mean the direction toward the working end of the device that is positioned at the treatment site and away from the user. With respect to the mitral valve, proximal shall refer to the atrial or upstream side of the valve leaflets and distal shall refer to the ventricular or downstream side of the valve leaflets. 
         [0065]    Referring to  FIG. 1 , a fixation device  14  typically comprises proximal elements  16  (or gripping elements) and distal elements  18  (or fixation elements) which protrude radially outward and are positionable on opposite sides of tissue, such as leaflets, so as to capture or retain the leaflets therebetween at a single location or along a continuum or range of positions as desired by the user. The fixation device  14  is coupleable to the shaft of the interventional tool (not shown) by a coupling mechanism, a portion of which is shown as coupling member  19 . The coupling mechanism allows the fixation device  14  to detach and be left behind as an implant to hold the leaflets together in the coapted position. The coupling member  19  is either formed with or connected to housing  3  which typically houses locking mechanism  106 . 
         [0066]    It may be appreciated that the fixation device  14  may have a variety of forms, of which  FIG. 1  is an example.  FIG. 2  illustrates another embodiment of a fixation device  14 . Here, the fixation device  14  comprises distal elements  18  (or fixation elements) which protrude radially outward and are positionable on opposite sides of tissue, such as leaflets, so as to capture or retain the leaflets therebetween along a continuum as desired by the user. Here the distal elements  18  are formed from a continuous piece of material that is flexed to open and close by movement of the legs  68 , however it may alternatively be hinged at the midpoint thereof. Again the fixation device  14  is coupleable to the shaft of the interventional tool (not shown) by a coupling mechanism, a portion of which is shown as coupling member  19 . The coupling mechanism allows the fixation device  14  to detach and be left behind as an implant to hold the leaflets together in the coapted position. 
         [0067]    In these embodiments, the fixation device  14  includes a locking mechanism for locking the device  14  in a particular position, such as an open, closed or inverted position or any position therebetween. It may be appreciated that the locking mechanism includes an unlocking mechanism which allows the device to be both locked and unlocked.  FIGS. 1-3 ,  4 A- 4 C illustrate an embodiment of a locking mechanism  106 . Referring to  FIG. 1 , in this embodiment, the locking mechanism  106  is disposed between the coupling member  19  and the base  69  of the actuation mechanism  58 . The base  69  is connected to the legs  68  of the actuation mechanism  58  which are in turn connected to the distal elements  18 . Thus, movement of the legs  68  moves the distal elements  18  through open, closed and inverted positions. The base  69  is also fixedly attached to a stud  74  which extends through the locking mechanism  106 . The stud  74  is releasably attached to an actuator rod which passes through the coupling member  19  and the shaft of the interventional tool. Release of the stud  74  from the actuator rod allows the fixation device  14  to be detached and left behind as an implant. 
         [0068]      FIG. 1  also illustrates the proximal elements  16 , which in this embodiment straddle the locking mechanism and join beneath the locking mechanism  106 . The proximal elements  16  are shown supported by proximal element lines  90 . The proximal elements  16  are raised and lowered by manipulation of the proximal element lines  90 . 
         [0069]    The proximal element lines  90  may be connected with the proximal elements  16  by threading the lines  90  in a variety of ways as described and illustrated in U.S. patent Ser. No. 10/441,531 (Attorney Docket No. 020489-001400US), incorporated herein by reference for all purposes. As described and illustrated, a line loop  48  may be present on a proximal element  16  through which a proximal element line  90  may pass and double back. Such a line loop  48  may be useful to reduce friction on proximal element line  90  or when the proximal elements  16  are solid or devoid of other loops or openings through which the proximal element lines  90  may attach. Line loops  48  may be comprised of any suitable material, may be formed into the proximal element  16  itself or may be formed from a material tied onto or attached to the proximal element  16 . For example, the line loop  48  may be comprised of a suture loop which is tied to the proximal element  16 , such as through an opening in the proximal element  16 . In embodiments which include a covering, such as a fabric, mesh, textured weave, felt, looped or porous structure, as described and illustrated in U.S. patent Ser. No. 10/441,531 (Attorney Docket No. 020489-001400US), incorporated herein by reference for all purposes, the proximal element lines  90  may be connected to the proximal elements  16  by attachment to the covering itself or by passage of the proximal element lines  90  through the covering and attaching to the proximal elements  16  in any manner described. 
         [0070]    In addition, lock lines  92  are shown in  FIG. 1  connected with a release harness  108  of the locking mechanism  106 . The lock lines  92  are used to lock and unlock the locking mechanism  106  as will be described below. The proximal element lines  90  and lock lines  92  may be comprised of any suitable material, typically wire, nitinol wire, cable, suture or thread, to name a few. In addition, the proximal element lines  90  and/or lock lines  92  may include a coating, such as Parylene®. Parylene® is a vapor deposited pinhole free protective film which is conformal and biocompatible. It is inert and protects against moisture, chemicals, and electrical charge. 
         [0071]      FIG. 3  provides a front view of the locking mechanism  106  of  FIG. 1 . However, here the proximal elements  16  are supported by a single proximal element line  90  which is through both of the proximal elements  16 . In this arrangement both of the elements are raised and lowered simultaneously by action of a single proximal element line  90 . Whether the proximal elements  16  are manipulated individually by separate proximal element lines  90  or jointly by a single proximal element line  90 , the proximal element lines  90  may extend directly through openings in the proximal elements and/or through a layer or portion of a covering on the proximal elements, or through a suture loop above or below a covering. 
         [0072]      FIGS. 4A-4C  illustrate the locking mechanism  106  showing the locking mechanism  106  in the unlocked and locked positions respectively. Referring to  FIG. 4A , the locking mechanism  106  includes one or more engagement elements, such as wedging elements or rolling elements. In this embodiment, the wedging elements comprise a pair of barbells  110  disposed on opposite sides of the stud  74 , each barbell having a pair of generally cylindrical caps and a shaft therebetween. The barbells  110  and the stud  74  are preferably comprised of cobalt chromium or stainless steel, however any suitable material may be used. 
         [0073]    In some embodiments, each barbell  10  has a higher hardness than the stud  74 . This hardness difference can enhance the grip or friction of the surfaces by allowing one element to “dig into” or invaginate into the other surface, even if only slightly. In addition, to improve engagement of the barbells  110  with the stud  74 , the stud  74  may include one or more surface treatments and/or the stud  74  may have a particular composition and/or geometry, such as roughened surfaces, raised protrusions formed on the surface, frictional elements embedded in the surface, etc., to enhance surface friction and thereby increase the engagement strength. 
         [0074]    The barbells  110  are manipulated by hooked ends  112  of the release harness  108 . A perspective view of an embodiment of the release harness  108  is illustrated in  FIG. 4B . When an upwards force is applied to the harness  108  by the lock line  92  (illustrated in  FIG. 1 ), the hooked ends  112  raise the barbells  110  against a spring  114 , as shown in  FIG. 4A . This draws the barbells  110  up along a sidewall or sloping surface  116  which unwedges the barbells  110  from against the stud  74 . In this position, the stud  74  is free to move. Thus, when the lock line  92  raises or lifts the harness  108 , the locking mechanism  106  is in an unlocked position wherein the stud  74  is free to move the actuation mechanism  58  and therefore the distal elements  18  to any desired position. Release of the harness  108  by the lock line  92  transitions the locking mechanism  106  to a locked position, illustrated in  FIG. 4C . By releasing the upwards force on the barbells  110  by the hooked ends  112 , the spring  114  forces the barbells  110  downwards and wedges the barbells  110  between the sloping surface  116  and the stud  74 . This restricts motion of the stud  74 , which in turn locks the actuation mechanism  58  and therefore distal elements  18  in place. 
         [0075]    In addition, the stud  74  may include one or more grooves  82  or indentations which receive the barbells  110 . This may provide more rapid and positive locking by causing the barbells  110  to settle in a definite position, increase the stability of the locking feature by further preventing movement of the barbells  110 , as well as tangible indication to the user that the barbell has reached a locking position. In addition, the grooves  82  may be used to indicate the relative position of the distal elements  18 , particularly the distance between the distal elements  18 . For example, each groove  82  may be positioned to correspond with a 0.5 or 1.0 mm decrease in distance between the distal elements  18 . As the stud  74  is moved, the barbells  110  will contact the grooves  82 ; by counting the number of grooves  82  that are felt as the stud  74  is moved, the user can determine the distance between the distal elements  18  and can provide the desired degree of coaptation based upon leaflet thickness, geometry, spacing, blood flow dynamics and other factors. Thus, the grooves  82  may provide tactile feedback to the user, and may also be visible on fluoroscopy or an echocardiogram to provide visual feedback. Further, the grooves  82  may be sized to allow shifting or movement of each barbells  110  within each groove  82 . Such shifting allows the stud  74  to move slightly in the proximal and distal direction, therefore allowing slight movement of the distal elements  18  when the locking mechanism is in the locked position. This may allow the fixation device  14  to open slightly in response to dynamic cardiac forces. 
         [0076]    As mentioned, the locking mechanism  106  allows the fixation device  14  to remain in an unlocked position when attached to the interventional tool  10  during grasping and repositioning and then maintain a locked position when left behind as an implant. It may be appreciated, however, that the locking mechanism  106  may be repeatedly locked and unlocked throughout the placement of the fixation device  14  if desired. Further, the locking mechanism  106  depicted in  FIGS. 1-3 ,  4 A- 4 C allows the fixation device  14  to be incrementally moved toward the closed position while locked. As mentioned, movement toward the closed position is achieved by retracting or pulling the stud  74  in the proximal direction so that the distal elements  18  approach each other. Retraction of the stud  74  draws the barbells  110  upward. Since the sloping surfaces  116  widen in the proximal direction, the barbells  110  are allowed to unwedge in this direction. In contrast, extension or pushing of the stud  74  in the distal direction is resisted by further wedging of the barbells  110  between the sloping surfaces  116  and the stud. Once the final placement is determined, the lock line  92  and proximal element lines  90  are removed and the fixation device is left behind. 
         [0077]      FIG. 5  illustrates another embodiment of a locking mechanism  106 . In this embodiment, the locking mechanism  106  also includes an engagement element comprising a wedging element. Here the wedging element comprises a binding lever or binding plate  450 . In this embodiment, as shown in  FIG. 6 , the binding plate  450  has an oblong shape extending between a first end  452  and a second end  454  with a bottom planar surface  456  and a top planar surface  458 . An aperture  460  is formed between the first and second ends  452 ,  454  extending from the top planar surface  458  through to the bottom planar surface  456 . Referring back to  FIG. 5 , the binding plate  450  is positioned within the locking mechanism  106  so that the stud  74  passes through the aperture  460 .  FIG. 7  provides a closer view of the binding plate  450  within the locking mechanism  106 . As shown, the first end  452  is positioned within a notch  462  which prevents axial movement of the first end  452 . However, the second end  454  is free to move in an axial direction thus creating a lever type movement of the binding plate  450 . Movement of the second end  454  is controlled by the associated hooked end  112  of the release harness  108 . When an upwards force is applied to the harness  108  by the lock line  92 , the hooked end  112  raises the second end  454  of the plate  450  against a spring  114  so that the planar surfaces  456 ,  458  are substantially perpendicular to the stud  74 . This aligns the aperture  460  with the stud  74  allowing free movement of the stud  74 . Thus, in this state, the locking mechanism  106  is unlocked wherein the stud  74  is free to move the actuation mechanism  58  and therefore the distal elements  18  to any desired position. 
         [0078]    Release of the harness  108  by the lock line  92  transitions the locking mechanism  106  to a locked position. By releasing the upwards force on the second end  452  of the binding plate  450 , the spring  114  forces the second end  452  downwards and wedges the aperture  460  against the stud  74 , as illustrated in  FIG. 5  and  FIG. 7 . This restricts motion of the stud  74 , which in turn locks the actuation mechanism  58  and therefore distal elements  18  in place. It may be appreciated that the binding plate  450  may have any suitable form to function as described above. For example, the plate  450  may have a variety of shapes with or without planar surfaces  456 ,  458  and/or the aperture  460  may be of a variety of shapes and positioned in a variety of locations, to name a few. Further, it may be appreciated that any number of binding plates  450  may be present. Each binding plate  450  provides an additional binding location which may enhance lock performance. 
         [0079]    It may be appreciated that although the above described embodiment of the binding plate  450  includes an aperture  460  for passing of the stud  74  therethrough, the binding plate  450  may be shaped so as to not include such an aperture  460 . In such embodiments, the binding plate  450  may be shaped to at least partially surround the stud  74 , such as having a notch, inlet or hook-shape through which the stud  74  passes. Thus, the binding plate  450  would function in the same manner as above wherein the portion at least partially surrounding the stud  74  would engage the stud  74  for locking and disengage the stud  74  for unlocking. 
         [0080]    The binding plate  450  and the stud  74  may be comprised any suitable material. In some embodiments, the binding plate  450  has a higher hardness than the stud  74 . In other embodiments, the binding plate  450  is comprised of a flexible or semi-flexible material. Such flexibility allows slight movement of the stud  74  in the proximal and distal directions, therefore allowing slight movement of the distal elements  18  when the locking mechanism is in the locked position. This may allow the fixation device  14  to adjust in response to dynamic cardiac forces. 
         [0081]    To improve engagement of the binding plate  450  with the stud  74 , the stud  74  may include one or more surface treatments and/or the stud  74  may have a particular composition and/or geometry as set forth above. 
         [0082]    In this embodiment the stud  74  may include one or more grooves  82  or indentations which receive the binding plate  450 , similar to the grooves of the locking mechanism of  FIGS. 1-3 ,  4 A- 4 C. Again, this may provide more rapid and positive locking by causing the binding plate  450  to settle in a definite position, increase the stability of the locking feature by further preventing movement of the binding plate  450 , as well as tangible indication to the user that the binding plate  450  has reached a locking position. In addition, the grooves  82  may be used to indicate the relative position of the distal elements  18 , particularly the distance between the distal elements  18 . 
         [0083]    The locking mechanism  106  depicted in  FIG. 5  allows the fixation device  14  to be incrementally moved toward the closed position while locked. Movement toward the closed position is achieved by retracting or pulling the stud  74  in the proximal direction so that the distal elements  18  approach each other. Retraction of the stud  74  draws the binding plate  450  towards a horizontal position, aligning the aperture with the stud  74  and thus allowing movement. In contrast, extension or pushing of the stud  74  in the distal direction is resisted by further wedging of the binding plate  450  against the stud  74 . Once the final placement is determined, the lock line  92  and proximal element lines  90  are removed and the fixation device is left behind. 
         [0084]      FIGS. 8A-8B  illustrate a similar embodiment of a locking mechanism. Again, the wedging element comprises a binding plate  450  positioned within the housing  3  so that the stud  74  passes through the aperture  460 .  FIG. 8B  provides a closer view of the binding plate  450  within the housing  3 . As shown, the first end  452  of the lever  450  is positioned within a notch  462  which prevents axial movement of the first end  452 . However, the second end  454  of the binding plate  450  is free to move in an axial direction thus creating a lever type movement of the binding plate  450 . Movement of the second end  454  is controlled by the associated hooked end  112  of the release harness  108 . Here, the release harness  108  is “one-sided” in comparison to the release harness of  FIG. 5 , i.e. only one hooked end  112  is present. When an upwards force is applied to the harness  108  by the lock line  92 , the hooked end  112  raises the second end  454  of the plate  450  against a spring  114  so that plate  450  is substantially perpendicular to the stud  74 . This aligns the aperture  460  with the stud  74  allowing free movement of the stud  74 . Thus, in this state, the locking mechanism  106  is unlocked wherein the stud  74  is free to move the actuation mechanism  58  and therefore the distal elements  18  to any desired position. The “one-sided” harness improves ease of use and unlocking consistency throughout various fixation device positions. 
         [0085]    Release of the harness  108  by the lock line  92  transitions the locking mechanism  106  to a locked position. By releasing the upwards force on the second end  452  of the binding plate  450 , the spring  114  forces the second end  452  downwards and wedges the aperture  460  against the stud  74 . This restricts motion of the stud  74 , which in turn locks the actuation mechanism  58  and therefore distal elements  18  in place. 
         [0086]      FIGS. 9A-9C  illustrate another embodiment of a locking mechanism  106 . Referring to  FIG. 9A , in this embodiment, the locking mechanism  106  is again disposed between the coupling member  19  and the base  69  of the actuation mechanism  58 . The base  69  is connected to the stud  74  which extends through the locking mechanism  106 , and connects to an actuator rod which extends through the coupling member  19  and the shaft  12  of the interventional tool  10 . The base  69  is also connected to the legs  68  of the actuation mechanism  58  which are in turn connected to the distal elements  18 .  FIG. 9A  also illustrates proximal elements  16  which manipulate the locking mechanism  106  in this embodiment. The locking mechanism  106  includes wedging elements comprising folded leaf or binding structures  124  having overlapping portions  124   a ,  124   b . Each folded binding structure  124  is attached to or continuously formed with a proximal element  16 , as shown. In  FIG. 9A  and  FIG. 9B , the folded structures  124  are shown without the remainder of the locking mechanism  106  (housing) for clarity. The proximal elements  16  are flexible, resilient and biased outwardly. The binding structures  124  include holes  125  ( FIG. 9C ) in each overlapping portion  124   a ,  124   b  so that the stud  74  passes through the holes  125  of the portions  124   a ,  124   b  as shown. The locking mechanism includes slots into which ends  123  of the binding structures  124  are fixed. When the proximal elements  16  are in an undeployed position, as in  FIG. 9A , the binding structures  124  lie substantially perpendicular to the stud  74  so that the holes  125  in each overlapping portion are vertically aligned. This allows the stud  74  to pass freely through the holes and the locking mechanism  106  is considered to be in an unlocked position. 
         [0087]    Deployment of the proximal elements  16 , as shown in  FIG. 9B , tilts the binding structures  124  so as to be disposed in a non-perpendicular orientation relative to the stud  74  and the holes  125  are no longer vertically aligned with one another. In this arrangement, the stud  74  is not free to move due to friction against the holes of the binding structure  124 .  FIG. 9C  provides a larger perspective view of the folded structures  124  in this position. Thus, the locking mechanism  106  is considered to be in a locked position. This arrangement allows the fixation device  14  to maintain an unlocked position during grasping and repositioning and then maintain a locked position when the proximal elements  16  are deployed and the fixation device  14  is left behind as an implant. This arrangement also allows locking to be achieved automatically by releasing of the proximal elements  16 . Therefore, there is no need for a separate actuator for the locking mechanism. Such as combined function of grasping and locking, thereby eliminating the need for separate actuation elements, may reduce the profile and complexity of the fixation device, simplifying the user interface. It may also be appreciated, that the locking mechanism  106  may be repeatedly locked and unlocked throughout the placement of the fixation device  14  if desired. 
         [0088]      FIGS. 10A-10C  illustrate a similar embodiment of a locking mechanism  106 . Referring to  FIG. 10A , in this embodiment, the locking mechanism  106  is again disposed between the coupling member  19  and the base  69  of the actuation mechanism  58 . And, the base  69  is connected to the stud  74  which extends through the locking mechanism  106  and connects to an actuator rod which extends through the coupling member  19  and the shaft of the interventional tool  10 .  FIG. 10A  illustrates the proximal elements  16  which manipulate the locking mechanism  106  in this embodiment. The locking mechanism  106  includes wedging elements comprising interdigitating structures  128 , such as in the shape of a “C” as illustrated, each interdigitating structure  128  attached to a proximal element  16 . The interdigitating structures  128  hook around the stud  74  so that the stud  74  passes through the “C” of each structure  128  as shown in  FIGS. 10B-10C . As shown, the structures  128  cross each other and the “C” of each structure  128  faces each other. A spring  130  biases the interdigitating structures into engagement with one another. When the proximal elements are in an undeployed position, as in  FIG. 10B , the interdigitating structures  128  are urged into an orientation more orthogonal to the axial direction defined by stud  74 , thus bringing the “C” of each structure  128  into closer axial alignment. This allows the stud  74  to pass freely through the “C” of each structure  128 . Deployment of the proximal elements  16  outwardly urges the interdigitating structures into a more angular, non-orthogonal orientation relative to stud  74  causing the sidewalls of the “C” of each structure  128  to engage stud  74  more forcefully. In this arrangement, the stud  74  is not free to move due to friction against the interdigitating structures  128 . 
         [0089]      FIGS. 11A-11B  illustrate another embodiment of a locking mechanism  106 . In this embodiment, the locking mechanism  106  also includes at least one wedging element. Here each wedging element comprises a cam  480 .  FIG. 11A  illustrates a pair of cams  480  disposed on opposite sides of the stud  74 , each cam  480  having an inward surface  482  and an outward surface  484 . Each cam  480  is connected to a wall of the locking mechanism  106  by a spring  486  or other mechanism which applies force to the outward surface  484  of the cam  480 . Such force wedges the inward surface  482  of the cam  480  against the stud  74 , as shown in  FIG. 11A , when in the locked position. Thus, when the cams  480  are wedged against the stud  74  the stud  74  is not free to move and therefore the distal elements  18  are locked in place. 
         [0090]    Each cam  480  is coupled with a actuator  488  at a pivot point  490 . By applying an upwards force on actuator  488 , the associated cam is pivoted around pivot point  490  so that its inward surface  482  is unwedged from the stud  74 , as illustrated in  FIG. 11B . In this position, the stud  74  is free to move. Thus, when the cams  480  are pivoted the locking mechanism  106  is in an unlocked position wherein the stud  74  is free to move the actuation mechanism  58  and therefore the distal elements  18  to any desired position. It may be appreciated that any number of cams  480  may be present and each cam  480  may have any suitable form to function as described above. 
         [0091]      FIGS. 12A-12D  illustrate another embodiment of a locking mechanism  106  having at least one engagement element. In this embodiment, the at least one engagement element has at least one protrusion which engages at least one groove on the stud  74  to lock the stud  74  in place.  FIG. 12A  illustrates an embodiment of a stud  74  of the present invention having external grooves along its surface, in this instance external threads  500 . Here, the stud  74  is shown attached at one end to base  69  and having a threaded free end  502  which is coupleable with shaft  12  of the tool  10 . It may be appreciated that the external grooves or threads  500  may extend along any distance of the surface of the stud  74  and may have any depth or spacing. Also it may be appreciated that the external grooves may comprise a series of cuts, indentations or threading which may or may not extend around the circumference of the stud  74 .  FIG. 12B  illustrates an embodiment of the at least one engagement element having grooves, in this instance a split nut  506 . The split nut  506  has a curved threaded surface  508  sized to mate with the external threads  500  of the stud  74 . Each split nut  506  also has at least one hinge component  510  which is used to rotate or translate each split nut  506  within the locking mechanism  106  to engage or disengage the external threads  500  of the stud  74 . 
         [0092]      FIG. 12C  illustrates a pair of split nuts  506  disposed on opposite sides of the stud  74 , each split nut  506  having its curved threaded surface  508  facing the external threads  500  of the stud  74 . The split nuts  506  are rotated or translated so that the threaded surfaces  508  are not engaging the external threads  500 . In this position, the stud  74  is free to move. Thus, when the split nuts  506  are rotated or translated outward the locking mechanism  106  is in an unlocked position wherein the stud  74  is free to move the actuation mechanism  58  and therefore the distal elements  18  to any desired position. Rotation or translation of the split nuts  506  inward engages the curved threaded surfaces  508  with the external threads  500 . Such engagement prevents motion of the stud  74 , locking the distal elements  18  in place. It may be appreciated that any number of components may be present and each component may have any suitable form to function as described above. 
         [0093]    Many of the locking mechanisms of the present invention may be adapted for locking the fixation device  14  in a single predetermined position. Thus, rather than closing the distal elements  18  and locking the distal elements  18  in place at one of a multitude of optional locations, the distal elements  18  may be closed and locked at a single predetermined position, such as at a 15, 30, 45 or 60 degree angle. For example, as mentioned above, the stud  74  may include a single groove  82  or indentation which receives the barbells  110 . This may provide more rapid locking by causing the barbells  110  to settle in a single position, as well as indicating to the user that the fixation device  14  is locked in a known configuration. Likewise,  FIG. 12D  illustrates a locking embodiment similar to the embodiment of  FIG. 12C . Here, a split ring  507 , rather than a split nut, is disposed on opposite sides of the stud  74 . The split ring  507  has a curved projection  509  sized to mate with a groove  501  on the stud  74 . Each split ring  507  also has at least one hinge component  510  which is used to rotate or translate each split ring  507  within the locking mechanism  106  to engage or disengage the groove  501  of the stud  74 . For example, the split rings  507  may be rotated or translated so that the projections  509  are not engaging the groove  501 . In this position, the stud  74  is free to move. Thus, when the split rings  507  are rotated or translated outward the locking mechanism  106  is in an unlocked position wherein the stud  74  is free to move the actuation mechanism  58  and therefore the distal elements  18 . Rotation or translation of the split rings  507  inward engages the curved projections  507  with the groove  501 . Such engagement prevents motion of the stud  74 , locking the distal elements  18  in the predetermined position. It may be appreciated that any number of components may be present and each component may have any suitable form to function as described above. 
         [0094]    In some embodiments, the locking mechanism comprises gears. Such gears are used to incrementally translate the stud  74  in a forward or reverse direction which opens and closes the distal elements  18 . Since translation of the stud  74  is controlled by the gears, the stud  74  is locked in place when the gears are not moving. Thus, no additional locking mechanism may be desired.  FIGS. 13A-13C  illustrate an embodiment of a fixation device  14  of the present invention having gears. Here, the stud  74  extends through the locking mechanism  106  as in previous embodiments. Advancement and retraction of the stud  74  moves the distal elements  18  (not show, for clarity) which are attached to the base  69 . In this embodiment, the locking mechanism  106  comprises bevel gears. Referring to  FIG. 13B , the bevel gears include a driving component  600  and a driven component  602 . The driving component  600  has a pedestal  604  connectable with the housing  3  and a meshing surface  606  having gear teeth  607 . The meshing surface  606  of the driving component  600  meshes with gear teeth  609  of a meshing surface  608  of the driven component  602  at an approximate angle of 90 degrees, or other suitable angle. The driven component  602  has a threaded interior  610  which mates with external threads  500  on the stud  74 . Thus, rotation of the driven component  602  causes advancement or retraction of the stud  74 . The driving component  600  may be rotated by any suitable mechanism, including a gear belt or gear line  612 . In this embodiment, two gear lines  612 ,  612 ′ are attached to the base  604  of the driving component  600 . Each gear line  612 ,  612 ′ is wound in the opposite direction so that pulling one gear line  612  rotates the driving component  600  in a clockwise direction and pulling the other gear line  612 ′ rotates the driving component  600  in a counterclockwise direction. Alternatively, one gear line may be employed and operated in a clockwise or counterclockwise direction. The gear lines  612 ,  612 ′ extend from the locking mechanism  106  through the coupling mechanism  19 , as shown in  FIG. 13A , and through the delivery catheter so as to be manipulable by the user outside of the body. In other embodiments, illustrated in  FIG. 13C , two driving components  600 ,  600 ′ may be present, each driving component  600 ,  600 ′ meshed with the driven component  602 . One gear line  612  is connected with one driving component  600  and the other gear line  612 ′ is connected with the other driving component  600 ′. Pulling the gear line  612  rotates driving component  600  which rotates the driven component  602  causing advancement of the stud  74 . Pulling the other gear line  612 ′ rotates the other driving component  600 ′ which rotates the driven component  602  in the opposite direction causing retraction of the stud  74 . It may be appreciated that a variety of gear mechanisms may be used including spur gears, helical and herringbone gears, miter gears, worms and worm gears, hypoid gears and rack and pinions, to name a few. 
         [0095]    In some embodiments, the locking mechanism works against biasing forces, either inherent in the fixation device or created by the grasped tissue. As mentioned, the fixation device  14  includes a stud  74  for moving the distal elements between open, closed, and inverted positions. In a “pull to close/push to open” embodiment, the distal elements  18  are pivotably coupled to the stud  74  by a pair of legs or link members, whereby pushing the stud  74  pivots the distal elements  18  inwardly toward the closed position. Once tissue has been grasped in a desired configuration (such as leaflets in a desired coapted arrangement), it may be desired to hold the stud  74  in place by a locking mechanism. In this embodiment, the grasped tissue biases the fixation toward the open position since it requires force to hold the tissues in place. Thus, the stud  74  is biased toward advancing (“pushing” to open).  FIG. 14A  illustrates the stud  74  extending through housing  3  and holding the distal elements in a desired position wherein the fixation device  14  is biased towards opening, i.e. the stud  74  is biased towards advancing. To lock or hold the stud  74  in place, an interference element, such as a locking sheath  640 , is advanced over the stud  74 , as illustrated in  FIG. 14B . The locking sheath  640  fits snuggly over the stud  74  to prevent movement of the stud  74  relative to the sheath  640  by, for example, friction or by interlocking an internal threaded surface with threads  500  on the stud  74 . The sheath  640  is advanced so that its distal end  642  abuts the housing  3  which is a stationary surface of the fixation device, as shown. Since the stud  74  is biased towards advancing, the distal end  642  of the sheath  640  is held against the housing  3  preventing advancement of the stud  74  and hence locking the stud  74  in place. Upon decoupling of the fixation device  14  for implantation, as illustrated in  FIG. 14C , the distal end  642  of the sheath  640  may also be decoupled from its proximal end  644  for leaving behind with the fixation device  14 . The distal end  642  may be removably joined with the proximal end  644  by any suitable mechanism. In one embodiment, illustrated in  FIG. 14D , the proximal and distal ends  642 ,  644  each have projections  646  which are press-fit together in an alternating fashion. Thus, the proximal and distal ends  642 ,  644  may be decoupled by pulling the ends  642 ,  644  apart, disengaging the projections  646 . 
         [0096]    In a similar embodiment, illustrated in  FIGS. 15A-15B , the interference element comprises a lock nut  650  which holds the stud  74  in place.  FIG. 15A  illustrates the stud  74  extending through housing  3  and holding the distal elements (not shown for clarity) in a desired position wherein the fixation device  14  is biased towards opening, i.e. the stud  74  is biased towards advancing. A lock nut  650  is screwed down over threads  500  by means of a torqueable sleeve  652  which is advanced over the stud  74 . The torqueable sleeve  652  is joined with the lock nut  650  by any suitable means to provide torqueable attachment, such as projections into the lock nut  650 , etc. The sleeve  652  is advanced until the lock nut  650  abuts the housing  3 , as shown in  FIG. 15B . Since the stud  74  is biased towards advancing, the lock nut  650  is held against the housing  3  preventing advancement of the stud  74  and hence locking the stud  74  in place. The sleeve  652  may then be removed and the fixation device  14  decoupled for implantation. It may be appreciated that the distal end  642  of the locking sheath  640  of  FIGS. 14A-14D  may also be considered a lock nut utilized in the same fashion. It may also be appreciated that the lock nut  650  may have external threads which mate with threads on housing  3 . By screwing the lock nut  650  into the housing, the stud  74  may be prevent from advancing or retracting. Thus, such a locking feature may be used with fixation devices  14  which are not biased toward opening or closing. 
         [0097]    In another embodiment, illustrated in  FIGS. 16A-16B , the stud comprises a suture line  75  or other flexible line.  FIG. 16A  illustrates the line  75  extending through housing  3  and allowing the distal elements (not shown for clarity) to move to a desired position wherein the fixation device  14  is biased towards opening, i.e. the line  75  is biased towards advancing. A suture fastener  698  is advanced down the line  75  until the fastener  698  abuts the housing  3  as shown in  FIG. 16B . Since the line  75  is biased towards advancing, the fastener  698  is held against the housing  3  preventing advancement of the line  75  and hence locking the distal elements in place. The line  75  may then be cut proximal to the fastener  698  and the fixation device  14  decoupled for implantation. 
         [0098]    As mentioned above, in many embodiments the distal elements  18  are pivotably coupled to the stud  74  by legs  68 , whereby retracting the stud  74  pivots the distal elements  18  inwardly toward the closed position. In some embodiments, as illustrated in  FIG. 17A , the legs  68  are spring biased toward the closed position. This may be achieved by forming the legs  68  from a continuous flexible material, such as cobalt chromium, stainless steel, Nitinol, Elgiloy® and the like. Opening of the distal elements  18  flexes the legs  68  outward, storing potential energy therein. Once the fixation device  14  has been desirably positioned, grasping tissue therebetween, the distal elements  18  are released and the legs  68  recoil toward the closed position, holding the distal elements  18  against the grasped tissue, thereby locking the distal elements  18  in place. 
         [0099]    In other embodiments, the distal elements  18  are biased toward the closed position by the application of a biasing member. For example, as shown in  FIGS. 17B-17C , the biasing member  670  may be comprised of a pair of support sleeves  672  mounted on a rod  674 . The rod  674  may be advanced through the stud  74  so that the sleeves  672  are disposed distally of the fixation device  14 . This allows the fixation device  14  to open, close, and/or invert as desired. Once the distal elements  18  have satisfactorily grasped the tissue, the distal elements  18  may be locked in place by retracing the rod  674  which slides the support sleeves  672  over the legs  68 , as illustrated in  FIG. 17C . The support sleeves  672  are comprised of a flexible material, such as cobalt chromium, stainless steel, Nitinol, Elgiloy® and the like, so that opening of the support sleeves  672  flexes the support sleeves  672  outward, spring loading the sleeves  672  and storing potential energy therein. The stored spring force then biases the sleeves  672  toward the closed position, holding the distal elements  18  against the grasped tissue, thereby locking the distal elements  18  in place. 
         [0100]    In other embodiments, the biasing member  670  comprises a cinching band. The cinching band may be elastic or substantially inelastic. An embodiment of an elastic cinching band  680  is illustrated in  FIGS. 18A-18C . During positioning of the fixation device  14 , the elastic cinching band  680  may be disposed distally of the distal elements  18 , such as around the legs  68 , as illustrated in  FIG. 18A . This allows the distal elements  18  to be moved between open, closed and/or inverted positions as desired while grasping the tissue in a desired configuration. Once the tissue has been satisfactorily grasped, the distal elements  18  may be locked in place by repositioning of the band  680 . The band  680  may be repositioned with the use of an adjustment line  682 , such as a suture or wire, which is joined with the band  680 . As illustrated in  FIG. 18B , the band  680  may be pulled in the proximal direction by retracting the adjustment line  682 . This draws the band  680  over the distal elements  18  in a stretched configuration, as illustrated in  FIG. 18C . Stretching of the elastic cinching band  680  stores potential energy therein. The stored spring force then biases the distal elements  18  toward the closed position, holding the distal elements  18  against the grasped tissue, thereby locking the distal elements  18  in place. The distal elements  18  may also include grooves  684  into which the band  680  may be placed. Such grooves  684  may reduce possible slippage of the band  680  and indicate to the user a desired position along the distal elements  18  for placement. The adjustment line  682  is then removed and the fixation device  14  left in place. It may be appreciated that an inelastic cinching band would function similarly. One difference is that the inelastic band may hang loosely around the legs  68  and would be taut when positioned around the distal elements  18 . The distal elements  18  are locked at a position based on the length of the inelastic cinching band whereas the distal elements  18  would be held a position based on the stored potential energy of the elastic cinching band. 
         [0101]    In other embodiments, the cinching band comprises a cinching line  690 , as illustrated in  FIGS. 19A-19C . The cinching line  690  is typically comprised of a substantially inelastic material, such as a suture, thread or filament. The cinching line  690  is wrapped around the fixation device  14  in a “lasso”-type configuration. Typically, the cinching line  690  has a loop  692  at one end through which the line  690  passes so that pulling on the line  690  tightens the lasso. In one embodiment, illustrated in  FIG. 19A , the cinching line  690  is wrapped loosely around the distal elements  18 . This allows the distal elements  18  to be moved between open, closed and/or inverted positions as desired while grasping the tissue in a desired configuration. The line  690  may be adhered to the distal elements  18  (or other parts of the fixation device) at various locations  694  to assist in keeping the line  690  in place. Once the tissue has been satisfactorily grasped, the distal elements  18  may be locked in place by tightening the cinching line  690 . The cinching line  690  may be tightened by pulling the line  690  in the proximal direction so the lasso tightens around the distal elements  18 , as illustrated in  FIG. 19B . Such tightening allows the line  690  to break from the adhered locations  694 . The cinching line  690  biases the distal elements  18  toward the closed position, holding the distal elements  18  against the grasped tissue, thereby locking the distal elements  18  in place. The distal elements  18  may be held at any desired position by applying more or less force to the cinching line  690 . It may be appreciated that the distal elements  18  may also include grooves into which the line  690  may be placed. Such grooves may reduce possible slippage of the line  690  and indicate to the user a desired position along the distal elements  18  for placement. Referring to  FIG. 19C , a suture fastener  698  is then advanced along the cinching line  690  and positioned against the loop  692  to hold the line  690  in place. The line  690  is then cut proximal to the suture fastener  698  and the fixation device  14  left in place. 
         [0102]    In some embodiments, the locking mechanism is comprised of structures, such as barbs, which attach to the legs, holding the legs in a fixed position.  FIG. 20  illustrates an embodiment of such a locking mechanism. Here, barbs  700  extend outwardly from the housing  3  toward the legs  68 . The barbs  700  are segmented so that the barbs  700  can be extended through the legs  68  to variable extents which in turn allows the distal elements  18  to be locked at various positions.  FIGS. 21A-21C  illustrate such attachment to the legs  68 .  FIG. 21A  illustrates a barb  700  approaching a leg  68 . The leg  68  has a hole  702  which is covered by a flap  703 . As the distal element  18  rotates toward the closed position, the leg  68  is drawn toward the barb  700 . Referring to  FIG. 21B , the barb  700  then advances through the hole  702 , pushing the flap  703  open.  FIG. 21C  illustrates a first segment  706  of the barb  700  extending through the hole  702  wherein the flap  703  recoils and wedges against the barb  700 . This holds the barb  700  in attachment with the leg  68 . The leg  68  is now locked in place, thereby locking the associated distal element  18  in place. Additional segments of the barb  700  may be advanced through the leg  68  to lock the distal elements  18  in more closed positions. It may also be appreciated that the barb  700  may only include a first segment  706  wherein the leg  68  may be locked in a single position, rather than allowing variable positions. 
         [0103]    It is further within the scope of the present invention that the locking mechanism be a wedge contacting a sloped surface, a threaded engagement, a spring, a groove engaging protrusion, a ratchet mechanism, a pin engaging a hole, a magnet attracting to a dipole magnet, a geared mechanism pulley or belt mechanism and the like. Further, the lock mechanism may include use of epoxy resin, energy (such as radiofrequency or ultrasonic welding) to bind the stud relative to the housing. 
         [0104]    It may be appreciated that the locking mechanisms of the present invention may be utilized in a variety of fixation devices having any number and combination of proximal and/or distal elements. For example, the locking mechanisms may be used in combination with a device having a single distal element or a single pair comprising one proximal element and one distal element wherein a leaflet or other tissue is grasped between the proximal and distal element of the pair. In another example, the locking mechanisms may be used in combination with a device having multiple distal elements, such as three distal elements. In general, the locking mechanisms of the present invention may be used to lock any moveable elements in place. 
         [0105]    It may further be appreciated that the locking mechanism of the present invention may also be utilized in other devices and systems, such as to lock catheters, retractors, or other medical instruments such as graspers or biopsy forceps in a particular position prior to, during, or following a medical procedure. Examples of catheters include steerable guide catheters, such as described in U.S. patent Ser. No. 10/441,753 (Attorney Docket Number 020489-001200US) incorporated herein by reference, and inner and/or outer guide catheters, such as described in U.S. patent Ser. No. 10/441,531 (Attorney Docket Number 020489-001400US) incorporated herein by reference. In these examples, the locking mechanism of the present invention function as the locking actuators. 
         [0106]      FIG. 22  illustrates a proximal end of a catheter  1600  having an embodiment of a locking mechanism  106  of the present invention. Here, the stud  74  is fixedly attached to a pullwire  1602  which extends along the catheter  1600 , typically within a lumen  1604  in the wall of the catheter  1600 . In this embodiment, a knob  1606  is connected with the stud  74  and extends radially outwardly through an opening  1608  in the catheter  1600 . The opening  1608  is shaped to allow axial movement of the knob  1606  along the length of a portion of the proximal end of the catheter  1600 . Axial movement of the knob  1606  in turn moves the stud  74  and attached pullwire  1602  which in turn steers the catheter  1600 . The pullwire  1602  can be locked in any desired axial position by the locking mechanism  106 . The locking mechanism includes one or more wedging elements  1610  which wedge against the stud  74  to hold the stud  74  and attached pullwire  1602  in a desired axial position.  FIG. 22  illustrates the locking mechanism of  FIGS. 4A-4C , however it may be appreciated that any of the locking mechanism disclosed herein may be used. When in the unlocked position, the stud  74  is free to move. When in the locked position, a spring forces the wedging elements  1610  downwards and wedges the wedging elements  1610  between a sloping surface and the stud  74 . This restricts motion of the stud  74 , which in turn locks the pullwire  1602  in place. 
         [0107]      FIG. 23  illustrates an endoscopic grasper  1620  having an embodiment of a locking mechanism  106  of the present invention. The grasper  1620  comprises an elongate shaft  1622  rotateably coupled at its distal end with a pair of jaws  1624 . The jaws  1624  are spring loaded so that the jaws  1624  are in a closed position unless tension is applied to a pair of pullwires  1626  which draw the jaws  1624  toward an open position. The shaft  1622  and pullwires  1626  extend through a tubular sheath  1628  as shown. The jaws  1624  may be locked in any position including the closed position, a fully open position and any position therebetween. This may be achieved with a locking mechanism  106  of the present invention. Here, the stud  74  is fixedly attached to the pullwires  1626  which extend along the shaft  1622  to the proximal end of the sheath  1628 . In this embodiment, a knob  1606  is connected with the stud  74  and extends radially outwardly through an opening  1608  in the sheath  1628 . The opening  1608  is shaped to allow axial movement of the knob  1606  along the length of a portion of the proximal end of the sheath  1628 . Axial movement of the knob  1606  in turn moves the stud  74  and attached pullwires  1626  which in turn steers the catheter  1600 . The pullwire  1602  can be locked in any desired axial position by the locking mechanism  106 . The locking mechanism includes one or more wedging elements  1610  which wedge against the stud  74  to hold the stud  74  and attached pullwires  1626  in a desired axial position. 
         [0108]      FIG. 23  also illustrates an additional grasper  1650  advanceable through a lumen in the shaft  1622  of the endoscopic grasper  1620 . Here, the additional grasper  1650  has an elongate shaft  1652  coupled with a stud  74  of a locking mechanism  1610 . Advancement and retraction of the stud  74  opens and closes a pair of jaws  1654  so that the jaws  1654  are moveable in a manner similar to the distal elements of the above described fixation devices. Thus, the jaws  1654  may be locked in place by the locking mechanism  1610  as described above. It may be appreciated that the jaws  1624  of the endoscopic grasper  1620  may be locked in this manner as an alternative to the locking mechanism disposed near its distal end. 
         [0109]      FIG. 23  illustrates the locking mechanism of  FIGS. 4A-4C , however it may be appreciated that any of the locking mechanism disclosed herein may be used. When in the unlocked position, the stud  74  is free to move. When in the locked position, a spring forces the wedging elements  1610  downwards and wedges the wedging elements  1610  between a sloping surface and the stud  74 . This restricts motion of the stud  74 , which in turn locks the pullwire  1602  in place. 
         [0110]    It may be appreciated that locking mechanisms of the present invention may be disposed within or near a distal portion of a device where space is limited, along an elongate portion of the device (particularly if multiple locking mechanisms are desired), or within or near a proximal end of the device (such as illustrated in  FIGS. 22-23 ). Multiple locking mechanisms may be desired when multiple pullwires are used to steer a sheath or catheter. Thus, the multiple locking mechanisms can assist in positioning instruments in tortuous body paths or locations. 
         [0111]    Although the foregoing invention has been described in some detail by way of illustration and example, for purposes of clarity of understanding, it will be obvious that various alternatives, modifications and equivalents may be used and the above description should not be taken as limiting in scope of the invention which is defined by the appended claims.