Abstract:
A method for treating a heart valve of a patient includes inserting into a heart and in contact with a valve surface, an implant including an elongate element and a locking mechanism coupled to the elongate element. The locking mechanism has a resting position that provides a locked state preventing movement of the elongate element with respect to the locking mechanism. The heart valve is treated by facilitating movement of the elongate element with respect to the locking mechanism by maintaining application of a force to the locking mechanism using a tool, and thereby maintaining the locking mechanism in an unlocked state during the facilitating of the movement of the elongate element with respect to the locking mechanism. Subsequently, the locking mechanism is transitioned to the resting position by decoupling the tool from the locking mechanism.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of: (a) US Provisional Patent Application 60/662,616 to Gross et al., filed Mar. 17, 2005, and (b) US Provisional Patent Application 60/700,542 to Gross et al., filed Jul. 18, 2005. Both of these applications are assigned to the assignee of the present application and are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to surgical methods and apparatus, and specifically to methods and apparatus for mitral valve treatment. 
       BACKGROUND OF THE INVENTION 
       [0003]    Mitral valve regurgitation is a disorder in which the mitral valve does not close properly. During systole, a healthy mitral valve prevents oxygenated blood from flowing back (regurgitating) from the left ventricle to the left atrium. Regurgitation caused by a defective mitral valve reduces cardiac output, increasing the risk of progressive heart failure. Treatments for mitral valve regurgitation include valve replacement and strengthening the valve annulus by implanting a mechanical support ring or other structure (generally called valve annuloplasty). 
         [0004]    The chordae tendineae are commonly classified according to their insertion sites on the mitral cusps. The first-order (also called primary or marginal) chordae insert on the cusp free edges, the second-order (also called “strut”) chordae insert on the ventricular surface of the cusps, usually near the junction between the rough and smooth zones, and the third-order (also called tertiary or basal) chordae originate directly from the trabeculae carneae of the left ventricular wall, and attach to the cusps near the annulus of the mitral valve. 
         [0005]    US Patent Application Publication 2005/0010287 to Macoviak et al., which is incorporated herein by reference, describes techniques for supplementing, repairing, or replacing&#39; a native heart valve. The techniques employ an implant that is adapted to extend adjacent a valve annulus. The implant includes a mobile neoleaflet element that occupies the space of at least a portion of one native valve leaflet. The implant mimics the one-way valve function of a native leaflet, to resist or prevent retrograde flow. The implant restores normal coaptation of the leaflets to resist retrograde flow, thereby resisting eversion and/or prolapse, which, in turn, reduces regurgitation. 
         [0006]    US Patent Application Publication 2004/0193191 to Starksen et al., which is incorporated herein by reference, describes methods for treating a cardiac valve annulus, comprising contacting an anchor delivery device with the valve annulus and releasing a plurality of coupled anchors from the anchor delivery device to secure the anchors to the annulus. Anchors, which in some embodiments are super-elastic or shape memory self-securing anchors, are then drawn together to tighten the annulus. The publication also describes devices including an elongate catheter having a housing at or near the distal end for releasably housing a plurality of coupled anchors. The housing may be flexible, may conform to a valve annulus, and in some embodiments may be coupled with an expandable member to enhance contact of the housing with annular tissue. In one embodiment, self-securing anchors lie approximately flat within the delivery device housing, allowing anchors with relatively large deployed shapes to be housed in and deployed from a relatively narrow delivery device. 
         [0007]    US Patent Application Publication 2004/0148020 to Vidlund et al., which is incorporated herein by reference, describes techniques for improving the function of a valve (e.g., a mitral valve) by positioning an implantable device outside and adjacent the heart wall such that the device alters the shape of the heart wall acting on the valve. The implantable device may alter the shape of the heart wall acting on the valve by applying an inward force and/or by circumferential shortening (cinching). The shape change of the heart wall acting on the valve is sufficient to change the function of the valve, and may increase coaptation of the leaflets, for example, to reduce regurgitation. 
         [0008]    US Patent Application Publication 2004/0148019 to Vidlund et al., which is incorporated herein by reference, describes techniques for improving the function of a valve (e.g., a mitral valve) by positioning a spacing filling device outside and adjacent the heart wall such that the device applies an inward force against the heart wall acting on the valve. A substantially equal and opposite force may be provided by securing the device to the heart wall, and/or a substantially equal and opposite outward force may be applied against anatomical structure outside the heart wall. The inward force is sufficient to change the function of the valve, and may increase coaptation of the leaflets, for example. The space filling device may be implanted by a surgical approach, a transthoracic approach, or a transluminal approach, for example. The space filling portion may be delivered utilizing a delivery catheter navigated via the selected approach, and the space filling portion may be expandable between a smaller delivery configuration and a larger deployed configuration. 
         [0009]    US Patent Application Publication 2004/0138745 to Macoviak et al., which is incorporated herein by reference, describes medical devices for improving heart valve function, including leaflet retainers, a neo-annulus, neo-leaflet, and a framework. 
         [0010]    US Patent Application Publication 2004/0127983 to Mortier et al., which is incorporated herein by reference, describes a device for heart valve repair including at least one tension member having a first end and second end. A basal anchor is disposed at the first end of the tension member and a secondary anchor at the second end. The publication describes a method including the steps of anchoring the basal anchor proximate a heart valve and anchoring the secondary anchor at a location spaced from the valve such that the chamber geometry is altered to reduce heart wall tension and/or stress on the valve leaflets. 
         [0011]    U.S. Pat. No. 6,629,534 and US Patent Application Publication 2004/0039442 to St. Goar et al., which are incorporated herein by reference, describe techniques for performing endovascular repair of atrioventricular and other cardiac valves in the heart. Regurgitation of an atrioventricular valve, particularly a mitral valve, is repaired by modifying a tissue structure selected from the valve leaflets, the valve annulus, the valve chordae, and the papillary muscles. These structures are modified by suturing, stapling, snaring, or shortening, using interventional tools which are introduced to a heart chamber. 
         [0012]    US Patent Application Publication 2003/0199974 to Lee et al., which is incorporated herein by reference, describes an annuloplasty system for repairing a heart valve, comprising a surgical implant including a member having first and second end portions. The implant member further is configured and/or adapted to form a partial ring along a portion of one of the valve annulae of a patient&#39;s heart such as the mitral or tricuspid valve annulus. The implant member is axially elastic such that it can axially expand and contract and includes first and second anchors extending from the end portions of the implant member. The anchors are adapted to anchor the implant in tissue such as the mitral or tricuspid valve annulus. The system is described as facilitating tissue plication (e.g., of the posterior annulus of the mitral valve or the annulus of the tricuspid valve) and reinforcement of a valve annulus. 
         [0013]    US Patent Application Publication 2003/0191528 to Quijano et al., which is incorporated herein by reference, describes an expandable annular ring for implantation in a valvular annulus and its percutaneous use. The ring comprises a plurality of stenting elements made of a first shape-memory material having a first shape-transition temperature, wherein the first shape-memory material expands to a preshape when the first shape-memory material is heated to above the first shape-transition temperature; and a plurality of anchoring elements made of a second shape-memory material having a second shape-transition temperature that is higher than the first shape-transition temperature, wherein the second shape-memory material expands to the second preshape when the second shape-memory material is heated to above the second shape-transition temperature. 
         [0014]    US Patent Application Publications 2004/0260393 to Randert et al. and 2004/0127982 to Machold et al., which are incorporated herein by reference, describe techniques using an implant that is sized and configured to attach in, on, or near the annulus of a dysfunctional heart valve. In use, the implant extends either across the minor axis of the annulus, or across the major axis of the annulus, or both. The implant is described as restoring to the heart valve annulus and leaflets a more functional anatomic shape and tension. The more functional anatomic shape and tension are conducive to coaptation of the leaflets, which, in turn, reduces retrograde flow or regurgitation. 
         [0015]    US Patent Application Publication 2004/0260394 to Douk et al., which is incorporated herein by reference, describes a cardiac valve annulus compressor comprising a generally cylindrical main body having plain and barbed ends and an actuator portion. Barbs disposed on the barbed end are engageable with the valve annulus. The length of the circumference of the barbed end is responsive to movement of the actuator portion. The annulus compressor can be delivered percutaneously or surgically. 
         [0016]    US Patent Application Publication 2004/0236419 to Milo, which is incorporated herein by reference, describes methods for reconfiguring an atrioventricular heart valve that use systems comprising a partial or complete annuloplasty rings proportioned to reconfigure a heart valve that has become in some way incompetent, a pair of trigonal sutures or implantable anchors, and a plurality of staples which may have pairs of legs that are sized and shaped for association with the ring at spaced locations along its length. These systems are described as permitting relative axial movement between the staples and the ring, whereby a patient&#39;s heart valve can be reconfigured in a manner that does not deter subtle shifting of the native valve components. Shape memory alloy material staples may have legs with free ends that interlock following implantation. Annuloplasty rings may be complete or partial and may be fenestrated. One alternative method routes a flexible wire, preferably of shape-memory material, through the bights of pre-implanted staples. Other alternative systems use linkers of shape-memory material having hooked ends to interengage with staples or other implanted supports which, following implantation, decrease in effective length and pull the staples or other supports toward one another so as to create desired curvature of the reconfigured valve. These linkers may be separate from the supports or may be integral with them mid may have a variety of shapes and forms. Various of these systems may be implanted non-invasively using a delivery catheter. 
         [0017]    US Patent Application Publication 2004/0243227 to Starksen et al., which is incorporated herein by reference, describes techniques for facilitating positioning of a cardiac valve annulus treatment device. The publication describes methods including advancing an anchor delivery device through vasculature of the patient to a location in the heart for treating the valve annulus, contacting the, anchor delivery device with a length of the valve annulus, delivering a plurality of coupled anchors from the anchor delivery device to secure the anchors to the annulus, and drawing the anchors together to circumferentially tighten the valve annulus. Devices generally include an elongate catheter having at least one tensioning member and at least one tensioning actuator for deforming a distal portion of the catheter to help it conform to a valve annulus. The catheter device may be used to navigate a subannular space below a mitral valve to facilitate positioning of an anchor delivery device. 
         [0018]    Odell J A et al., in an article entitled “Early Results of a Simplified Method of Mitral Valve Annuloplasty,” Circulation 92:150-154 (1995), which is incorporated herein by reference, studied the outcome of three different annuloplasty techniques: commissural annuloplasty, complete ring annuloplasty, and an unmeasured, posterior, partial ring annuloplasty. They concluded that postoperative valve function obtained by unmeasured posterior annuloplasty, as assessed by degree of regurgitation, transvalvular gradient, and valve area, was similar to that obtained by measured, complete ring annuloplasty and superior to that found in patients having commissural annuloplasty. 
         [0019]    US Patent Application Publication 2003/0078465 to Pai et al., which is incorporated herein by reference, describes techniques for treating degenerative, congestive heart disease and related valvular dysfunction. Percutaneous and minimally invasive surgical tensioning structures are implantable within various major coronary blood-carrying conduit structures (arteries, veins and branching vessels), into or through myocardium, or into engagement with other anatomic structures that impact cardiac output to provide tensile support to the heart muscle wall which resists diastolic filling pressure while simultaneously providing a compressive force to the muscle wall to limit, compensate or provide therapeutic treatment for congestive heart failure and/or to reverse the remodeling that produces an enlarged heart. In some embodiments, the tensioning structures are used to apply tension to papillary muscles and/or chordae tendineae to reposition the valve leaflets to reduce/eliminate regurgitation, to limit the motion of the leaflets to improve/restore the function of cardiac valves; and to directly reposition the valve leaflets to prevent prolapse or other abnormalities of the leaflets and to prevent associated deficiencies. 
         [0020]    US Patent Application Publication 2003/0018358 to Saadat, which is incorporated herein by reference, describes techniques for thermally and/or mechanically treating tissue, such as valvular structures, to reconfigure or shrink the tissue in a controlled manner. Mechanical clips are implanted over the leaflets of a valve, e.g., in the heart, either alone or after thermal treatment to cause the valve to close more tightly. The clips are delivered by a catheter and may be configured to traverse directly over the valve itself or to lie partially over the periphery of the valve to prevent obstruction of the valve channel Alternatively, individual anchors with a tensioning element, like a suture, are described as being useful for approximating the valves towards each other. 
         [0021]    U.S. Pat. No. 6,626,899 to Houser et al., which is incorporated herein by reference, describes techniques for thermally and/or mechanically treating tissue, such as valvular structures, to reconfigure or shrink the tissue in a controlled manner. The apparatus comprises a catheter, in communication with an end effector which, induces a temperature rise in an annulus of tissue surrounding the leaflets of a valve or in the chordae tendineae sufficient to cause shrinkage, thereby causing the valves to close more tightly. Mechanical clips can also be implanted over the valve either alone or after the thermal treatment. The clips are delivered by a catheter and may be configured to traverse directly over the valve itself or to lie partially over the periphery of the valve to prevent obstruction of the valve channel. 
         [0022]    US Patent Application Publication 2005/0222678 to Lashinski et al., which is incorporated herein by reference, describes methods and devices for applying pressure to an adjacent tissue structure, such as the annulus of the mitral valve. An adjustable implant is described with an elongate control line having a distal end connected to the implant and a proximal end spaced apart from the implant. The device enables post implantation adjustment, by accessing the proximal end of the control line and manipulating the control line to adjust the implant. 
         [0023]    US Patent Application Publication 2005/0096740 to Langberg et al., which is incorporated herein by reference, describes a mitral annuloplasty and left ventricle restriction device adapted to be transvenously advanced and deployed within the coronary sinus and, in some embodiments, other coronary veins. The device places tension on adjacent structures, reducing the diameter and/or limiting expansion of the mitral annulus and/or limiting diastolic expansion of the left ventricle. These effects may be beneficial for patients with dilated cardiomyopathy. 
       SUMMARY OF THE INVENTION 
       [0024]    In some embodiments of the present invention, a mitral valve treatment device comprises a band, a distal coupling element, and a proximal coupling element. The device is adapted to be placed around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the mitral valve, and (c) a plurality of third-order chordae tendineae. The proximal and distal coupling elements are adapted to be coupled to a first chordae tendinea and a second chordae tendinea, respectively, each of the first and second chordae tendineae selected from the group consisting of: one of the plurality of third-order chordae tendineae, and a first-order chordae tendinea that inserts on a commissural cusp of the mitral valve. Such coupling typically tightens the annulus and thereby treats mitral valve regurgitation. Alternatively or additionally, the space is defined by a plurality of second-order chordae tendineae, and/or the distal and/or proximal end of the band is adapted to be coupled to a second-order chordae tendinea. 
         [0025]    In some embodiments of the present invention, a mitral valve treatment device comprises an inflatable band. The band is adapted to be placed around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the mitral valve, and (c) a plurality of third-order chordae tendineae. After placement, the band is inflated mid sealed, causing the band to press against the posterior cusp, the chordae tendineae, and the ventricular wall, thereby applying pressure to and supporting the posterior cusp. For some applications, inflation of the band additionally holds the band in place. For some applications, the band comprises neither a distal nor a proximal coupling element, or comprises only a single coupling element. 
         [0026]    In some embodiments of the present invention, a method for treating mitral valve regurgitation comprises inserting a band around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the mitral valve, and (c) a plurality of third-order chordae tendineae. The method further comprises coupling a distal end and a proximal end of the band to a first chordae tendinea and a second chorda tendinea, respectively, each of the first and second chordae tendineae selected from the group consisting of: one of the plurality of third-order chordae tendineae, and a first-order chorda tendinea that inserts on a commissural cusp of the mitral valve: Such coupling typically tightens the annulus and, thereby treats mitral valve regurgitation. Alternatively or additionally, the space is defined by a plurality of second-order chordae tendineae, and/or the distal and/or proximal end of the band is coupled to a second-order chorda tendinea. 
         [0027]    In some embodiments of the present invention, apparatus for treating a mitral valve comprises an outward force applicator adapted to be placed around between 90 and 270 degrees of a mitral valve of a heart. The force applicator is configured such that at least two regions thereof (typically end regions) apply force to a wall of a heart chamber in a vicinity of the commissural cusps of the mitral valve. Such outwardly-applied force draws the commissural cusps away from one another, stretching the mitral valve and thereby bringing the posterior and anterior cusps of the valve closer to one another. The device is thus useful for treating mitral valve regurgitation. 
         [0028]    In some embodiments of the present invention, the force applicator is adapted to be placed in a space defined by (a) a ventricular wall, (b) a ventricular surface of at least one of the mitral valve cusps in a vicinity of an annulus of the mitral valve, and (c) a plurality of third-order chordae tendineae. Alternatively or additionally, the space is defined by a plurality of second-order chordae tendineae. Further alternatively, the force applicator is adapted to be placed in a left atrium of the heart, in contact with or in a vicinity of the mitral valve. 
         [0029]    In some embodiments of the present invention, the force applicator comprises one or more coupling elements, which are adapted to hold the force applicator in place after placement. For some applications, the coupling elements comprise one or more protrusions, oriented on the force applicator such that the protrusions contact and grip the wall of the heart. Typically, the protrusions are positioned in a vicinity of the ends of the force applicator, and/or along the length of the force applicator, such as in a vicinity of a middle of the force applicator. For other applications, the coupling elements are adapted to be coupled to the mitral valve, and/or to one or more chordae tendineae, such as third-order chordae tendineae, or second-order chordae tendineae. For these applications, the coupling elements may comprise, for example, hooks, sutures, or staples. 
         [0030]    There is therefore provided, in accordance with an embodiment of the present invention, apparatus for treating mitral valve regurgitation, including: 
         [0031]    a band having distal and proximal ends, the band adapted to be placed:
       around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve,   in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the mitral valve,       
 
         [0034]    and (c) a plurality of third-order chordae tendineae; and 
         [0035]    distal and proximal coupling elements, coupled to the band at the distal and proximal ends thereof, respectively, and adapted to be coupled to a first chorda tendinea and a second chorda tendinea, respectively, each of the first and second chordae tendineae selected from the group consisting of: one of the plurality of third-order chordae tendineae, and a first-order chorda tendinea that inserts on a commissural cusp of the mitral valve. 
         [0036]    In an embodiment, each of the first and second chordae tendineae includes one of the plurality of third-order chordae tendineae, and the distal and proximal coupling elements are adapted to be coupled to the respective ones of the plurality of third order chordae tendineae. 
         [0037]    In an embodiment, the distal and proximal coupling elements are adapted to be coupled to the first and second chordae tendineae such that the band tightens the annulus of the valve. Alternatively or additionally, the distal and proximal coupling elements are adapted to be coupled to the first and second chordae tendineae such that the band applies pressure to the posterior cusp. For some applications, the distal and proximal coupling elements are adapted to be coupled to the first and second chordae tendineae such that the band applies substantially no pressure to an anterior cusp of the valve. For some applications, the distal and proximal coupling elements are adapted to be coupled to the first and second chordae tendineae such that the band does not squeeze an anterior cusp of the valve and the posterior cusp together. 
         [0038]    For some applications, the distal and proximal coupling elements include respective hooks, adapted to be hooked to the first and second chordae tendineae, respectively. 
         [0039]    For some applications, the band is generally elliptical in cross-section. Alternatively, the band is flat. 
         [0040]    For some applications, the band includes at least one sensor selected from the group consisting of: a wireless position sensor, and a navigation sensor. For some applications, the band includes a steering mechanism. 
         [0041]    For some applications, the band includes a shape memory alloy, and the shape memory alloy causes the band to assume a curved shape during placement of the band. 
         [0042]    For some applications, the band includes a tension element, adapted to shorten a length of the band. For some applications, at least a portion of the band includes an elastic material, adapted to shorten a length of the band. 
         [0043]    For some applications, the band is coated with a substance selected from the group consisting of: a drug, and a radiopaque coating. 
         [0044]    For some applications, the band is adapted to be placed around no portion of an anterior cusp of the valve. For some applications, the band is adapted to be placed such that a length of a first portion of the band that surrounds the at least a portion of the posterior cusp is at least 5 times a total length of that portion of the band that surrounds at least a portion of an anterior cusp of the valve. 
         [0045]    For some applications, the band includes a distal stop, and the distal coupling element is adapted to slide along the band until blocked by the distal stop. 
         [0046]    For some applications, the band includes a plurality of bands, the bands adapted to be placed in series around between 90 and 270 degrees of the mitral valve. 
         [0047]    For some applications, the apparatus includes an elongated insertion element, adapted to releasably engage the proximal end of the band. 
         [0048]    In an embodiment, the proximal coupling element is adapted to slide along the band and subsequently be locked to the band. For some applications, a portion of the band in a vicinity of the proximal end is shaped so as to define a first set of teeth, an interior surface of the proximal coupling element is shaped so as to define a second set of teeth, and the teeth are configured to allow distal advancement of the proximal coupling element along the band, and to not allow proximal retraction of the proximal coupling element along the band. 
         [0049]    For some applications, the apparatus includes a crimping mechanism, adapted to be placed around the proximal coupling element and to crimp the proximal coupling element to the band. 
         [0050]    For some applications, a portion of the band in a vicinity of the proximal end is shaped so as to define a first set of teeth, an interior surface of the proximal coupling element is shaped so as to define a second set of teeth, and the crimping element is adapted to crimp the proximal coupling element to the band by crimping at least a portion of the second set of teeth to at least a portion of the first set of teeth. For some applications, the crimping mechanism includes an inflation element, adapted, upon inflation thereof, to crimp the proximal coupling element to the band. 
         [0051]    For some applications, the band is shaped so as to define one or more indentations therein, and the proximal coupling element includes a tension clip, adapted to engage at least one of the indentations, so as to lock the proximal coupling element to the band. 
         [0052]    For some applications, the band is adapted to be placed around between 120 and 240 degrees of the mitral valve, such as between 150 and 210 degrees of the mitral valve. 
         [0053]    There is also provided, in accordance with an embodiment of the present invention, apparatus for treating mitral valve regurgitation, including: 
         [0054]    a band having distal and proximal ends, the band adapted to be placed:
       around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve,   in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the mitral valve,       
 
         [0057]    and (c) a plurality of second-order chordae tendineae; and 
         [0058]    distal and proximal coupling elements, coupled to the band at the distal and proximal ends thereof, respectively, and adapted to be coupled to a first chorda tendinea and a second chorda tendinea, respectively, each of the first and second chordae tendineae selected from the group consisting of: one of the plurality of second-order chordae tendineae, and a first-order chorda tendinea that inserts on a commissural cusp of the mitral valve. 
         [0059]    There is further provided, in accordance with an embodiment of the present invention, apparatus for treating mitral valve regurgitation, including a band adapted to be placed:
       around between 90 and 270 degrees of a mitral valve of a heart, including around at least a portion of a posterior cusp of the valve,   in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the mitral valve, and (c) a plurality of third-order chordae tendineae,       
 
         [0062]    the band configured such that inflation thereof applies pressure to the posterior cusp. 
         [0063]    In an embodiment, the band is configured such that inflation thereof holds the band in place. 
         [0064]    For some applications, the apparatus includes a liquid for inflating the band, the liquid adapted to at least partially solidify after inflation of the band therewith. 
         [0065]    In an embodiment, the band is not configured to be coupled to any portion of the heart, other than by the inflation thereof. 
         [0066]    There is still further provided, in accordance with an embodiment of the present invention, apparatus for treating mitral valve regurgitation, including a band adapted to be placed:
       around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve,   in a space defiled by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the mitral valve,       
 
         [0069]    and (c) a plurality of second-order chordae tendineae, 
         [0070]    the band configured such that inflation thereof applies pressure to the posterior cusp. 
         [0071]    In an embodiment, the band is configured such that inflation thereof holds the band in place. 
         [0072]    There is yet further provided, in accordance with an embodiment of the present invention, apparatus for treating mitral valve regurgitation, including: 
         [0073]    a stent, adapted to be placed while in a contracted state around between 90 and 270 degrees of a mitral valve of a heart, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the valve, and (c) a plurality of third-order chordae tendineae; and 
         [0074]    an inflation element, positioned within the stent, and adapted to expand the stent upon inflation, such that the Stent applies pressure to the posterior cusp. 
         [0075]    In an embodiment, the stent includes at least one coupling element, adapted to be coupled to a chorda tendinea. 
         [0076]    For dome applications, the stent includes a plurality of stents, adapted to be placed in series around between 90 and 270 degrees of the mitral valve. 
         [0077]    There is additionally provided, in accordance with an embodiment of the present invention, a method for treating mitral valve regurgitation, including: 
         [0078]    inserting a band around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the valve, and (c) a plurality of third-order chordae tendineae; and 
         [0079]    coupling a distal end and a proximal end of the band to a first chorda tendinea and a second chorda tendinea, respectively, each of the first and second chordae tendineae selected from the group consisting of: one of the plurality of third order chordae tendineae, and a first-order chorda tendinea that inserts on a commissural cusp of the mitral valve. 
         [0080]    For some applications, inserting includes inserting the band via an ascending aorta. 
         [0081]    For some applications, the band includes at least one sensor selected from the group consisting of: a wireless position sensor, and a navigation sensor, and inserting includes inserting the band at least in part responsively to a signal generated by the sensor. 
         [0082]    For some applications, the band includes a distal stop and a distal coupling element, and coupling the distal end of the band to the first chorda tendinea includes: 
         [0083]    advancing the band until the distal stop reaches a vicinity of the first chorda tendinea; 
         [0084]    advancing the distal coupling element over the band until the distal coupling element reaches the distal stop; and 
         [0085]    coupling the distal coupling element to the first chorda tendinea. 
         [0086]    In an embodiment, the band includes a proximal coupling element, and coupling includes: 
         [0087]    coupling the distal end of the band to the first chorda tendinea; thereafter, sliding the proximal coupling element along the band until the band has a desired length between the distal end and the proximal coupling element; and 
         [0088]    locking the proximal coupling element to the band. 
         [0089]    For some applications, coupling includes, after locking the proximal coupling element, clipping a portion of the band proximal to the proximal coupling element. For some applications, coupling includes, after locking the proximal coupling element, releasing the band from an elongated insertion element, and withdrawing the insertion element from the heart. 
         [0090]    For some applications, a portion of the band in a vicinity of the proximal end includes a first set of teeth, an interior surface of the proximal coupling element includes a second set of teeth, the teeth are configured to allow distal advancement of the proximal coupling element along the band, and to not allow proximal retraction of the proximal coupling element along the band, and locking the proximal coupling element includes advancing the proximal coupling element until the band has the desired length. 
         [0091]    There is yet additionally provided, in accordance with an embodiment of the present invention; a method for treating mitral valve regurgitation, including: 
         [0092]    inserting a band around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the valve, and (c) a plurality of second-order chordae tendineae; and 
         [0093]    coupling a distal end and a proximal end of the band to a first chorda tendinea and a second chorda tendinea, respectively, each of the first and second chordae tendineae selected from the group consisting of: one of the plurality of second-order chordae tendineae, and a first-order chorda tendinea that inserts on a commissural cusp of the mitral valve. 
         [0094]    There is still additionally provided, in accordance with an embodiment of the present invention, a method for treating mitral valve regurgitation, including: 
         [0095]    inserting a band around between 90 and 270 degrees of a mitral valve of a heart, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the valve, and (c) a plurality of third-order chordae tendineae; and 
         [0096]    applying pressure to the posterior cusp by inflating the band. 
         [0097]    There is also provided, in accordance with an embodiment of the present invention, a method for treating mitral valve regurgitation, including: 
         [0098]    inserting a band around between 90 and 270 degrees of a mitral valve, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the valve, and (c) a plurality of second-order chordae tendineae; and 
         [0099]    applying pressure to the posterior cusp by inflating the band. 
         [0100]    There is further provided, in accordance with an embodiment of the present invention, a method for treating mitral valve regurgitation, including: 
         [0101]    inserting a stent in a contracted state around between 90 and 270 degrees of a mitral valve of a heart, including around at least a portion of a posterior cusp of the valve, in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the valve, and (c) a plurality of third-order chordae tendineae; and 
         [0102]    applying pressure to the posterior cusp by expanding the stent by inflating an inflation element positioned within the stent. 
         [0103]    There is still further provided, in accordance with an embodiment of the present invention, apparatus for treating mitral valve regurgitation, including a force applicator adapted to be placed around at least a portion of a mitral valve of a heart, and configured such that at least two regions of the force applicator apply, to a wall of a chamber of the heart in a vicinity of commissural cusps of the mitral valve, force sufficient to bring a posterior cusp and an anterior cusp of the mitral valve closer to one another than a distance therebetween in the absence of the force applicator. 
         [0104]    In an embodiment, the applicator is adapted to be placed in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the valve, and (c) a plurality of third-order chordae tendineae. Alternatively, in an embodiment, the applicator is adapted to be placed in a space defined by (a) a ventricular wall, (b) a ventricular surface of the posterior cusp in a vicinity of an annulus of the valve, and (c) a plurality of second-order chordae tendineae. 
         [0105]    In an embodiment, the applicator is adapted to be placed in a left atrium of the heart, in contact with or in a vicinity of the mitral valve. 
         [0106]    For some applications, the applicator is generally elliptical in cross-section. Alternatively, the applicator is flat. 
         [0107]    For some applications, the applicator is coated with a substance selected from the group consisting of: a drug, and a radiopaque coating. 
         [0108]    For some applications, the applicator is adapted to be placed around no portion of the anterior cusp. For some applications, the applicator is adapted to be placed such that a length of a first portion of the applicator that surrounds at least a portion of the posterior cusp is at least 5 times a total length of that portion of the applicator that surrounds at least a portion of the anterior cusp. 
         [0109]    For some applications, the applicator is configured to enhance fibrosis between at least a portion of the applicator and the wall of the chamber. 
         [0110]    For some applications, the applicator includes at least one sensor selected from the group consisting of: a wireless position sensor, and a navigation sensor. For some applications, the applicator includes a steering mechanism. 
         [0111]    For some applications, the applicator has distal and proximal ends, and the applicator includes an adjustment mechanism, which is configured to change a distance between the distal end and the proximal end of the applicator. 
         [0112]    For some applications, the applicator is shaped so as to define one or more protrusions, oriented such that the protrusions contact the wall of the chamber of the heart upon placement of the applicator. 
         [0113]    In an embodiment, the applicator includes one or more coupling elements, adapted to hold the applicator in place around the at least a portion of the valve. For some applications, the coupling elements are adapted to be coupled to the valve. Alternatively, the coupling elements are adapted to be coupled to respective chordae tendineae. 
         [0114]    In an embodiment, the applicator is adapted to be placed around between 90 and 270 degrees of the mitral valve, such as around between 120 and 240 degrees of the mitral valve, e.g., around between 150 and 210 degrees of the mitral valve. 
         [0115]    In an embodiment, the applicator is configured such that after placement of the applicator, and before the at least two regions apply the force, there is a gap between the applicator and the wall of the chamber. For some applications, the applicator is configured such that the force applied by the at least two regions reduces a distance between the applicator and the wall of the chamber in a vicinity of the gap. For some applications, the applicator is configured such that the force applied by the at least two regions immediately reduces the distance. Alternatively, the applicator is configured such that the force applied by the at least two regions reduces the distance within one month of application of the force. 
         [0116]    In an embodiment, the at least two regions include two end regions of the force applicator, and the force applicator is configured such that at least the two end regions apply the force. For some applications, the applicator includes at least one screw in a vicinity of at least one of the end regions, the screw configured such that rotation thereof adjust a degree of pushing of the at least one end region into the wall of the chamber. 
         [0117]    There is additionally provided, in accordance with an embodiment of the present invention, apparatus for treating mitral valve regurgitation, including a force applicator adapted to be placed around at least a portion of a mitral valve of a heart, and configured to: 
         [0118]    apply force to a wall of a chamber of the heart, so as to change a shape of the heart around the mitral valve, and 
         [0119]    enhance fibrosis between at least a portion of the force applicator and the heart wall, so as to help maintain the changed shape of the heart. 
         [0120]    For some applications, a surface of the at least a portion of the applicator is roughened to enhance fibrosis. Alternatively or additionally, the at least a portion of the applicator is coated with a fibrosis-enhancing substance. 
         [0121]    There is yet additionally provided, in accordance with an embodiment of the present invention, a method for treating mitral valve regurgitation, including placing, around at least a portion of a mitral valve of a heart, a force applicator configured such that at least two regions of the force applicator apply, to a wall of a chamber of the heart in a vicinity of commissural cusps of the mitral valve, force sufficient to bring a posterior cusp and an anterior cusp of the mitral valve closer to one another than a distance therebetween in the absence of the force applicator. 
         [0122]    For some applications, the applicator includes at least one sensor selected from the group consisting of: a wireless position sensor, and a navigation sensor, and placing includes placing the applicator at least in part responsively to a signal generated by the sensor. 
         [0123]    There is also provided, in accordance with an embodiment of the present invention, a method for treating mitral valve regurgitation, including placing, around at least a portion of a mitral valve of a heart, a force applicator configured to apply force to a wall of a chamber of the heart, so as to change a shape of the heart around the mitral valve, and to enhance fibrosis between at least a portion of the force applicator and the heart wall, so as to help maintain the changed shape of the heart. 
         [0124]    The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0125]      FIG. 1  is a schematic illustration of a mitral valve treatment device, in accordance with an embodiment of the present invention; 
           [0126]      FIG. 2  is a schematic illustration of the device of  FIG. 1  placed in a heart, in accordance with an embodiment of the present invention; 
           [0127]      FIG. 3  is a schematic illustration of a portion of the device of  FIG. 1  placed around a portion of a posterior cusp of a mitral valve, in accordance with an embodiment of the present invention; and 
           [0128]      FIG. 4  is a schematic illustration of a procedure for introducing the device of  FIG. 1  into the heart, in accordance with an embodiment of the present invention; 
           [0129]      FIG. 5  is a schematic illustration of a distal end of a catheter for introducing the device of  FIG. 1  into the heart, in accordance with an embodiment of the present invention; 
           [0130]      FIGS. 6A-B  are schematic illustrations of a mitral valve before and after placement of the device of  FIG. 1 , respectively, in accordance with an embodiment of the present invention; 
           [0131]      FIGS. 7A-B  are schematic illustrations of the device of  FIG. 1  during systole and diastole, respectively, in accordance with an embodiment of the present invention; 
           [0132]      FIGS. 8A-B  are schematic illustrations of an over-the-wire implementation of the device of  FIG. 1 , in accordance with an embodiment of the present invention; 
           [0133]      FIGS. 9A-B  are schematic illustrations of a sliding and locking mechanism of the device of  FIG. 1 , in accordance with an embodiment of the present invention; 
           [0134]      FIGS. 10A-C  are schematic illustrations of another sliding and locking mechanism of the device of  FIG. 1 , in accordance with an embodiment of the present invention; 
           [0135]      FIGS. 11A-B  are schematic illustrations of yet another sliding and locking mechanism of the device of  FIG. 1 , in accordance with an embodiment of the present invention; 
           [0136]      FIGS. 12A-B  are schematic illustrations of a band clipping mechanism, in accordance with an embodiment of the present invention; 
           [0137]      FIGS. 13A-B  are schematic illustrations of a band release mechanism, in accordance with an embodiment of the present invention; 
           [0138]      FIGS. 14A-B  are schematic illustrations of an inflation mechanism, in accordance with an embodiment of the present invention; 
           [0139]      FIGS. 15A-B  are schematic illustrations of another inflation technique, in accordance with an embodiment of the present invention; 
           [0140]      FIG. 16  is a schematic illustration of a configuration of the device of  FIG. 1 , in accordance with an embodiment of the present invention; 
           [0141]      FIGS. 17A-B  are schematic illustrations, of a stent adapted for treatment of a mitral valve, in accordance with an embodiment of the present invention; 
           [0142]      FIG. 18  is a schematic illustration of a mitral valve treatment force applicator placed in a heart, in accordance with an embodiment of the present invention; 
           [0143]      FIGS. 19A and 19B  are schematic illustrations of a mitral valve before and after placement of the force applicator of  FIG. 18 , respectively, in accordance with an embodiment of the present invention; 
           [0144]      FIG. 20  is a schematic illustration of a portion of the force applicator of  FIG. 18  placed around a portion of a posterior cusp of the mitral valve, in accordance with an embodiment of the present invention; 
           [0145]      FIGS. 21A and 21B  are schematic illustrations of the mitral valve before and after expansion of the force applicator of  FIG. 18 , respectively, in accordance with an embodiment of the present invention; 
           [0146]      FIGS. 22 and 23  are schematic illustrations of respective configurations of the force applicator of  FIG. 18 , in accordance with respective embodiments of the present invention; 
           [0147]      FIG. 24  is a schematic illustration of a procedure for introducing the force applicator of  FIG. 18  into the heart of a subject, in accordance with an embodiment of the present invention; 
           [0148]      FIG. 25  is a schematic illustration of a distal end of a catheter for introducing the force applicator of  FIG. 18  into the heart, in accordance with an embodiment of the present invention; and 
           [0149]      FIGS. 26 and 27  are schematic illustrations of respective adjustment mechanisms for the force applicator of  FIG. 18 , in accordance with respective embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0150]      FIG. 1  is a schematic illustration of a mitral valve treatment device  20 , in accordance with an embodiment of the present invention. Device  20  typically comprises a flexible band  30 , a distal coupling element  32  (e.g., a hook), and a proximal coupling element  34  (e.g., a hook). For some applications, band  30  is generally elliptical in cross-section (e.g., circular), while for other applications the band is flat, e.g., ribbon-shaped. Band  30  typically comprises a biocompatible material, such as a polymer or metal. For some applications, band  30  is coated with a drug and/or a radiopaque coating. 
         [0151]    Reference is made to  FIG. 2 , which is a schematic illustration of band  30  placed in a heart  50 , which is viewed from above the heart with the atria removed, in accordance with an embodiment of the present invention. Band  30  is adapted to be placed around between 90 and 270 degrees of a mitral valve  58  of a heart  50 , including around at least a portion of a posterior cusp  56  of mitral valve  58 , in a vicinity of an annulus  60  of mitral valve  58 . For some applications, band  30  is adapted to be placed around between 120 and 240 degrees, such as between 150 and 210 degrees, e.g., about 180 degrees, of the mitral valve. For some applications, band  30  is adapted to be placed substantially only around all or a portion of posterior cusp  56 , i.e., substantially not around any portion of an anterior cusp  59  of mitral valve  58 . For example, the length of band  30  surrounding posterior cusp  56  is typically at least about 5 or at least about 10 times the length of any portion of band  30  that may be surrounding anterior cusp  59 . 
         [0152]    For some applications, band  30  is anchored in place by distal coupling element  32  and proximal coupling element  34 , such that the band applies pressure to posterior cusp  56 , thereby tightening annulus  60 , supporting the posterior cusp, and bringing the posterior cusp closer to the anterior cusp. For applications in which a portion of band  30  is placed around a portion of anterior cusp  59 , band  30  typically applies force substantially only to posterior cusp  56 . Furthermore, band  30  is typically configured to apply pressure to posterior cusp  56 , rather than to squeeze the posterior and anterior cusps together. 
         [0153]    Reference is made to  FIG. 3 , which is a schematic illustration of a portion of band  30  placed around a portion of posterior cusp  56 , in accordance with an embodiment of the present invention. Typically, band  30  is placed in the space defined by a ventricular wall  70  of left ventricle  72 , a ventricular surface of posterior cusp  56  in a vicinity of annulus  60 , and third-order chordae tendineae  74  (also called tertiary or basal chordae). (Third-order chordae  74 , of which only two of many are shown in the figure for clarity of illustration, originate directly from the trabeculae carneae of ventricular wall  70 , and attach to posterior cusp  56  in a vicinity of annulus  60 .) Alternatively or additionally, the space is defined by second-order chordae tendineae (not shown in the figure). Typically, distal and proximal coupling elements  32  and  34  are coupled to first and second chordae tendineae, respectively, each of which is selected from the group consisting of: one of third-order chordae  74 , a first-order chorda tendinea that inserts on a commissural cusp  78  of mitral valve  58  (shown in  FIG. 2 ), and a second-order chorda tendinea (not shown in the figures). Typically, when in place, band  30  is in contact with one or more third- or second-order chordae tendineae, and/or the ventricular surface of posterior cup  56  in the vicinity of annulus  60 . 
         [0154]    Alternatively or additionally, band  30  is placed around first-order chordae tendineae  80  that insert on posterior cusp  56 , anterior cusp  59 , and/or commissural cusps  78  (configuration not shown in the figures). Further alternatively or additionally, band  30  is woven between the first-, second-, and/or third-order chordae. 
         [0155]    Reference is made to  FIG. 4 , which is a schematic illustration of a procedure for introducing device  20  into heart  50  of a subject, in accordance with an embodiment of the present invention. Typically, device  20  is introduced into ventricle  72  by a catheter  81 , which is typically introduced into ventricle  72  via an ascending aorta  82 . A surgeon typically guides device  20  to a desired location using images of heart  50  captured using techniques known in the art. For some applications, device  20  comprises, e.g., at a distal end thereof, one or more wireless position sensors, such as those manufactured by Biosense, Inc. (New Brunswick, N.J.), or otherwise known in the art. Alternatively or additionally, device  20  comprises, e.g., at a distal end thereof, one or more sensors for aiding navigation, such as an ultrasound sensor, an infrared sensor, or an optical sensor. For some applications, device  20  comprises a steering mechanism, such as those known in the art of coronary catheter navigation. For some applications, band  30  comprises a shape memory alloy, such as nitinol, which causes the band to assume a curved shape, thereby assisting in navigating the band around the chordae tendineae. For some applications, the surgeon magnetically navigates band  30 , such as using techniques described in U.S. Pat. No. 6,817,364 or 6,522,909 to Garibaldi et al., or U.S. Pat. No. 6,475,223 to Werp et al., which are incorporated herein by reference,  mutatis mutandis.    
         [0156]    Reference is made to  FIG. 5 , which is a schematic illustration of a distal end  84  of catheter  81 , in accordance with an embodiment of the present invention. In this embodiment, the distal end of catheter  81  opens laterally, rather than at its end, so as to guide device  20  towards mitral valve  58  after the catheter is inserted into left ventricle  72 . 
         [0157]    Reference is made to  FIGS. 6A-B , which are schematic illustrations of mitral valve  58  before and after placement of band  30 , respectively, in accordance with an embodiment of the present invention.  FIG. 6A  shows mitral valve regurgitation occurring prior to the placement of band  30 .  FIG. 6A  also shows band  30  as it is being placed around posterior cusp  56 .  FIG. 6B  shows band  30  after it has been anchored in place around posterior cusp  56 , thereby preventing regurgitation. 
         [0158]    Reference is again made to  FIG. 1 . In an embodiment of the present invention, band  30  is adapted to tense, so as to shorten its length. For some applications, band  30  comprises a tension element  88 , such as a spring. Alternatively or additionally, all or a portion of band  30  comprises an elastic material. For some applications, the tension serves to increase the force applied by band  30  to posterior cusp  56  after the band has been coupled to the chordae tendineae. 
         [0159]    Reference is now made to  FIGS. 7A-B , which are schematic illustrations of band  30  during systole and diastole, respectively, in accordance with an embodiment of the present invention. In this embodiment, band  30  comprises tension element  88 , and/or band  30  comprises an elastic material. As shown in  FIG. 7A , during systole tension element  88  contracts, increasing the pressure applied by band  30  to posterior cusp  56 . During diastole, as shown in  FIG. 7B , tension element  88  expands, reducing the pressure applied by band  30  to posterior cusp  56 , and allowing mitral valve  58  to open. 
         [0160]    Reference is now made to  FIGS. 8A-B , which are schematic illustrations of an over-the-wire implementation of device  20 , in accordance with an embodiment of the present invention. In this embodiment, band.  30  comprises a distal stop  100 , which, for example, may be spherical. Distal coupling element  32  is adapted to slide distally along band  30  until blocked by distal stop  100 . During placement, band  30  is advanced until distal stop  100  reaches a vicinity of the chorda tendinea to which the distal end of the band will be coupled. Distal coupling element  32  is then advanced over band  30  until it reaches the distal end of the band. For example, the surgeon may advance catheter  81  over band  30  in order to push distal coupling element  32  to the distal end of the band. The surgeon then couples the coupling element to the chorda tendinea. Typically, the coupling of distal coupling element  32  to the chorda tendinea prevents subsequent proximal sliding of the coupling element. Alternatively, a locking mechanism is provided to hold coupling element  32  in place once it reaches distal stop  100 . The use of distal stop  100  and the techniques described in this paragraph typically enable easier advancement of band  30  than in embodiments in which distal coupling element  32  is fixed to the distal end of band  30  during advancement. 
         [0161]    Reference is again made to  FIG. 1 . In an embodiment of the present invention, proximal coupling element  34  comprises a sliding and locking mechanism  90 . Sliding and locking mechanism  90  is configured to have a locked position and an unlocked position. When in the unlocked position, the mechanism is able to slide along band  30 , and when in the locked position, the mechanism is fixed to the band. Typically, during placement of device  20  a surgeon couples distal coupling element  32  to a chorda tendinea at a desired location, and slides proximal coupling element  34  along band  30  so that band  30  has a desired length between the two coupling elements. The surgeon then locks mechanism  90 , and clips the portion of band  30  proximal to proximal coupling element  34 . For some applications, the surgeon locks and/or clips the excess portion before coupling proximal coupling element to a chorda tendinea, while for other applications the surgeon locks and/or clips the excess portion after coupling proximal coupling element to a chorda tendinea. Alternatively, rather than being clipped, band  30  is released from a release mechanism, as described hereinbelow with reference to  FIGS. 13A-B . 
         [0162]    Typically, the tension of band  30  is determined by the selected length of band  30  and the locations at which coupling elements  32  and  34  are coupled to the chordae. For some applications, the surgeon adjusts the tension of band  30  based on (a) tactile feedback, (b) a force measurement, and/or (c) another measurement, such as an electrocardiographic measurement, and/or a blood flow measurement made in the heart or elsewhere in the body. For some applications, band  30  comprises at least one tension or pressure sensor  86 , which is adapted to measure the tension of band  30 . Alternatively or additionally, device  20  comprises a tension control system  87  proximal to proximal coupling element  34 . 
         [0163]    Reference is made to  FIGS. 9A-B , which are schematic illustrations of another sliding and locking mechanism  120  of band  30 , in accordance with an embodiment of the present invention. Mechanism  120  comprises two interlocking sets of teeth. A first set of teeth  130  is coupled to or integrated into a proximal portion of band  30 , and a second set of teeth  132  is coupled to or integrated into an interior surface of proximal coupling element  34 . The teeth are configured to allow distal advancement of coupling element  34  over band  30 , but to not allow proximal retraction of the coupling element. The surgeon distally advances coupling element  34  over band  30  so that band  30  has a desired length between the two coupling elements. 
         [0164]    Reference is made to  FIGS. 10A-C , which are schematic illustrations of yet another sliding and locking mechanism  140  of band  30 , in accordance with an embodiment of the present invention. Mechanism  140  comprises two interlocking sets of teeth. A first set of teeth  150  is coupled to or integrated into a proximal portion of band  30 , and a second set of teeth  152  is coupled to or integrated into an interior surface of proximal coupling element  34 . When the coupling element is in an unlocked position, the first and second sets of teeth are not engaged with one another, such that the coupling element is able to advance distally over band  30 , as shown in  FIG. 10A . Catheter  81  comprises a crimping mechanism  153  in a vicinity of a distal end of the catheter. Crimping mechanism  153  typically comprises an expansion element  154 , such as a balloon, which is coupled to an external source  156  of fluid (liquid or gas) pressure, via a pressure tube  158 . Crimping mechanism  153  is adapted to be placed around the portion of proximal coupling element  34  having second set of teeth  152 , as shown in  FIG. 10A . Crimping mechanism  153  is configured such that expansion of expansion element  154  pushes second set of teeth  152  into contact with first set of teeth  150 , crimping the first and second sets of teeth together, as shown in  FIG. 10B . Such crimping locks coupling element  34  in place on band  30 . After crimping, catheter  81  and crimping mechanism  153  are retracted, leaving coupling element  34  in place, as shown in  FIG. 10C . 
         [0165]    Reference is made to  FIGS. 11A-B , which are schematic illustrations of still another sliding and locking mechanism  170 , in accordance with an embodiment of the present invention. Mechanism  170  comprises a tension clip  172  that releasably engages one or more indentations  174  in band  30 . Tension clip  172  is configured such that in its resting position, coupling portions  176  of the clip engage respective indentations  174 , preventing movement of the clip, as shown in  FIG. 11A . Applying force to release sites  178  of clip  172  changes the shape of the clip, causing coupling portions  176  to disengage from indentations  174 , as shown in  FIG. 11B . For some applications, release sites  178  also serve as coupling elements for coupling band  30  to the chordae tendineae, while for other applications, clip  172  comprises separate coupling elements (latter configuration not shown). In an embodiment, catheter  81  comprises one or more force application elements  180 , which are configured to apply force to release sites  178 , in order to disengage clip  172  from band  30 . For some applications, force application elements  180  are inflatable, and are configured such that inflation thereof applies force to release sites  178 . 
         [0166]    Reference is made to  FIGS. 12A-B , which are schematic illustrations of a band clipping mechanism  200 , in accordance with an embodiment of the present invention. Clipping mechanism  200  is used to clip the portion of band  30  proximal to proximal coupling element  34 , typically after the proximal coupling element has been locked in place. Clipping mechanism  200  comprises clippers  210 , which are adapted to be introduced through catheter  81  over the proximal portion of band  30 . Clippers  210  clip the band, and the clippers and the proximal portion of the band are withdrawn through catheter  81 , leaving the distal portion of band  30  in place in the heart, as shown in  FIG. 12B . 
         [0167]    Reference is made to  FIGS. 13A-B , which are schematic illustrations of a band release mechanism  220 , in accordance with an embodiment of the present invention. The release mechanism is used to release band  30  from an insertion element  224 , which is subsequently withdrawn through catheter  81 . Therefore, in this embodiment, there is generally no need to clip the band. Release mechanism comprises a grasping element  226 , which is adapted to releasably engage the proximal end of band  30 . For some applications, the proximal end of band  30  comprises or is shaped to as to define a protrusion  228 , such as a spherical protrusion, which grasping element  226  engages. Alternatively, release mechanism  220  comprises another coupling element, such as a screw, which releasably engages the proximal end of band  30 . 
         [0168]    In an embodiment of the present invention, proximal coupling element  34  does not comprise sliding and locking mechanism  90  or any other length-adjusting mechanism, such that the length of band  30  is fixed. In this embodiment, the surgeon may or may not invasively or non-invasively measure or estimate the circumference of annulus  60  prior to choosing which length of band  30  to implant. For some applications of this embodiment, band  30  comprises band release mechanism  220 , described hereinabove with reference to  FIGS. 13A-B . 
         [0169]    In an embodiment of the present invention, band  30  is configured such that distal and proximal coupling elements  32  and  34  push the chordae tendineae to which they are coupled, rather than pull the chordae. In this embodiment, band  30  is typically stiffer than in some other embodiments described herein. 
         [0170]    In an embodiment of the present invention, band  30  comprises one or more supporting members configured to support posterior cusp  56 . For some applications, the supporting members protrude from the band. 
         [0171]    Reference is made to  FIGS. 14A-B , which are schematic illustrations of an inflation mechanism  300 , in accordance with an embodiment of the present invention. Inflation mechanism  300  comprises an inflatable sheath  310 , placed around band  30 , and an external source  312  of liquid (fluid or gas) pressure, which is coupled to an interior of sheath  310  via a pressure tube  314 . During insertion of band  30 , sheath  310  is typically uninflated. After insertion, pressure source  312  inflates sheath  310  by supplying a liquid or gas, such as saline solution, a liquid silicone, a liquid polymer, or a liquid polyurethane. After inflation, sheath  310  is sealed. Such inflation typically increases the support band  30  provides to posterior cusp  56 . For some applications, sheath  310  is inflated with a liquid that completely or partially solidifies after inflation, such as into a flexible material. 
         [0172]      FIGS. 15A-B  are schematic illustrations of another inflation technique, in accordance with an embodiment of the present invention. In this embodiment, band  30  is itself inflatable, and sheath.  310  need not be provided. The interior of band  30  is in fluid communication with external pressure source  312  via pressure tube  314 . This embodiment may employ techniques described hereinabove with reference to  FIGS. 14A-B ,  mutatis mutandis.    
         [0173]      FIG. 16  is a schematic illustration of a configuration of band  30 , in accordance with an embodiment of the present invention. In this embodiment, band  30  is inflatable, such as by using one of the inflation techniques described hereinabove with reference to  FIGS. 14A-B  or  15 A-B. For some applications, inflatable band  30  comprises neither distal coupling element  32  nor proximal coupling element  34 , nor any other anchoring means at either the distal or proximal ends of the band. (Alternatively, for some applications, band  30  comprises anchoring means at only a single one of its ends.) After the band is placed around all or a portion of posterior cusp  56 , the band is inflated and sealed, causing the band to press against posterior cusp  56 , chordae tendineae  74  (or, alternatively, the second-order chordae tendineae), and ventricular wall  70 , thereby applying pressure to and supporting the posterior cusp, and typically holding band  30  in place. 
         [0174]    Reference is made to  FIGS. 17A-B , which are schematic illustrations of a stent  350  adapted for treatment of mitral valve  58 , in accordance with an embodiment of the present invention. Stent  350  is adapted to be placed around between 90 and 270 degrees of mitral valve  58 , including around at least a portion of posterior cusp  56 . For some applications, stent  350  is adapted to be placed around between 120 and 240 degrees, such as between 150 and 210 degrees, e.g., about 180 degrees, of the mitral valve. For some applications, stent  350  is adapted to be placed substantially only around all or a portion of posterior cusp  56 , i.e., substantially not around any portion of anterior cusp  59 . For example, the length of stent  350  surrounding posterior cusp  56  is typically at least about 5 or at least about 10 times the length of any portion of stent  350  that may be surrounding anterior cusp  59 . 
         [0175]    Typically, stent  350 , while in a contracted position, as shown in  FIG. 17A , is placed in the space defined by ventricular wall  70  of left ventricle  72 , a ventricular surface of posterior cusp  56  in a vicinity of annulus  60 , and chordae tendineae selected from third-order chordae tendineae  74  and second-order chordae tendineae. Once hilts desired position, stent  350  is expanded by inflating an inflation element  360  positioned within the stent. Inflation element  360  is removed, leaving stent  350  in place. Expansion of stent  350  applies pressure to and supports posterior cusp  56 , and typically holds the stent in place. 
         [0176]    For some applications, one or both ends of stent  350  are anchored in place by distal and/or proximal coupling elements (not shown in  FIGS. 17A-B , but similar to distal and proximal coupling elements  32  and  34 , as described hereinabove). Typically, the distal and proximal coupling elements are coupled to first and second chordae tendineae, respectively, each of which is selected from the group consisting of: one of third-order chordae  74 , a first-order chorda tendinea that inserts on a commissural cusp  78  of mitral valve  58  (shown in  FIG. 2 ), and a second-order chorda tendinea (not shown in the figures). 
         [0177]    For some applications, a plurality of stents  350  are placed around mitral valve  58 . The plurality of stents arc typically arranged in series, and are optionally coupled to one another. 
         [0178]    In an embodiment of the present invention, a method is provided for removing band  30  after it has been coupled to the chordae tendineae. The method comprises inserting a catheter or other elongated element into the heart, typically via ascending aorta  82 , and navigating the catheter around the chordae tendineae in a direction opposite to the direction in which band  30  was navigated around the chordae during insertion of the band. When the catheter reaches the distal end of band  30 , the catheter is coupled to the distal end. The catheter is then withdrawn, such that band  30  is pulled in the same direction as during the band&#39;s initial insertion. For example, if band  30  is initially inserted in a counterclockwise direction around the mitral valve as viewed from the left atrium, the catheter is inserted in a clockwise direction, and the catheter is withdrawn, pulling band  30 , in a counterclockwise direction. Typically, before removing band  30 , proximal coupling element  34  is removed from the band. For some applications, distal stop  100  is magnetic, and the catheter is magnetically coupled to the distal stop. 
         [0179]    It will be appreciated that whereas band  30  has been generally described herein as comprising a single band, the scope of the present invention is not limited to a single band, and includes the use of multiple bands in series and/or in parallel with one another. 
         [0180]      FIG. 18  is a schematic illustration of a mitral valve treatment outward force applicator  430  placed in heart  50 , which is viewed from above the heart with the atria removed, in accordance with an embodiment of the present invention. Force applicator  430  is typically flexible, and, for some applications, is generally elliptical in cross-section (e.g., circular), while for other applications is flat, e.g., ribbon-shaped. Force applicator  430  typically comprises a biocompatible material, such as a polymer or metal. For some applications, force applicator  430  is coated with a drug and/or a radiopaque coating. 
         [0181]    Force applicator  430  is adapted to be placed around between 90 and 270 degrees of mitral valve  58  of heart  50 , in a vicinity of annulus  60  of mitral valve  58 . The ends of force applicator  430  are typically, but not necessarily, positioned in a vicinity of commissural cusps  78  of mitral valve  58 . Force applicator  430  is configured such that at least two regions thereof (typically end regions  462 ) apply force, symbolically indicated by arrows  464 , to a wall  466  of a heart chamber in a vicinity of commissural cusps  78 . The heart chamber is the left ventricle and/or the left atrium. Such outwardly-applied force draws commissural cusps  78  away from one another, stretching mitral valve  58  and thereby bringing posterior cusp  56  and anterior cusp  59  of mitral valve  58  closer to one another. 
         [0182]    For some applications, force applicator  430  is adapted to be placed around between 120 and 240 degrees, such as between 150 and 210 degrees, e.g., about 180 degrees, of mitral valve  58 . For some applications, force applicator  430  is adapted to be placed substantially only around all or a portion of posterior cusp  56 , i.e., substantially not around any portion of anterior cusp  59 . For example, for these applications, the length of force applicator  430  surrounding posterior cusp  56  may be at least about 5 or at least about 10 times the length of any portion of force applicator  430  that may be surrounding anterior cusp  59 . For other applications, force applicator  430  is adapted to be placed around all or a portion of anterior cusp  59 , and not necessarily around any portion of posterior cusp  56 . 
         [0183]    Reference is made to  FIGS. 19A and 19B , which are schematic illustrations of mitral valve  58  before and after placement of force applicator  430 , respectively, in accordance with an embodiment of the present invention.  FIG. 19A  shows mitral valve  58  during systole, prior to the placement of force applicator  430 . Posterior cusp  56  and anterior cusp  59  are slightly separated from one another, causing mitral valve regurgitation.  FIG. 19B  shows force applicator  430  placed around posterior cusp  56 , and applying outward force (indicated by arrows  464 ) on a wall  468  of a heart chamber. Such outwardly-applied force draws commissural cusps  78  away from one another, stretching mitral valve  58  and thereby forcing posterior cusp  56  and anterior cusp  59  of mitral valve  58  closer to one another, and thereby preventing regurgitation. (Broken lines  469  show the shape of annulus  60  prior to placement of force applicator  430 , for the sake of comparison with  FIG. 19A .) 
         [0184]    Reference is made to  FIG. 20 , which is a schematic illustration of a portion of force applicator  430  placed around a portion of posterior cusp  56 , in accordance with an embodiment of the present invention. For some applications, force applicator  430  is placed in the space defined by ventricular wall  70  of left ventricle  72 , a ventricular surface of posterior cusp  56  in a vicinity of annulus  60 , and third-order chordae tendineae  74  (also called tertiary or basal chordae). (Third-order chordae  74 , of which only two of many are shown in the figure for clarity of illustration, originate directly from the trabeculae carneae of ventricular wall  70 , and attach to posterior cusp  56  in a vicinity of annulus  60 .) Alternatively or additionally, the space is defined by second-order chordae tendineae (not shown in the figure). Further alternatively, force applicator  430  is adapted to be placed in a left atrium of the heart, in contact with or in a vicinity of mitral valve  58  (configuration not shown). 
         [0185]    Reference is made to  FIGS. 21A and 21B , which are schematic illustrations of mitral valve  58  before and after expansion of, force applicator  430 , respectively, in accordance with an embodiment of the present invention.  FIG. 21A  shows mitral valve  58  during systole, immediately after placement of force applicator  430 , but prior to the outward expansion of the force applicator. Force applicator  430  is configured and placed such that there is a gap  490  between the force applicator and dilated wall  468  of the heart chamber. Posterior cusp  56  and anterior cusp  59  are slightly separated from one another, causing mitral valve regurgitation.  FIG. 21B  shows force applicator  430  after outward expansion of ends  462  of the force applicator, as symbolically indicated by arrows  492 . Such outwardly-applied force, in addition to drawing commissural cusps  78  away from one another, draws heart wall  468  closer to force applicator  430  in a vicinity of gap  490 . Such tightening of wall  468  against force applicator  430  may occur immediately upon outward expansion of force applicator  430 , or may occur over time, e.g., within about one month of expansion of force applicator  430 , as the heart adapts to and heals because of the placement of the force applicator. 
         [0186]    In an embodiment of the present invention, a surface of force applicator  430  opposite heart wall  468  is configured to enhance fibrosis between the force applicator and the heart wall. For example, the surface may be roughened, and/or coated with a fibrosis-enhancing substance. The fibrosis holds tissue of the heart wall against the force applicator, thereby helping prevent future dilation of the heart. Thus, force applicator  430  actively changes the shape of the heart around the mitral valve, and the fibrosis helps maintain this new shape. 
         [0187]    Reference is made to  FIG. 22 , which is a schematic illustration of a configuration of force applicator  430 , in accordance with an embodiment of the present invention. In this configuration, force applicator  430  comprises or is shaped to define one or more protruding extensions  94  at one or both ends  462  of the force applicator. The extensions increase the outward pushing of the force applicator on the heart wall. 
         [0188]    Reference is made to  FIG. 23 , which is a schematic illustration of another configuration of force applicator  430 , in accordance with an embodiment of the present invention. In this configuration, force applicator  430  comprises or is shaped to define one or more coupling elements, which are adapted to hold the force applicator in place after placement. For some applications, the coupling elements comprise one or more protrusions  496 , oriented on the force applicator-such that the protrusions contact and grip the wall of the heart. Typically, protrusions  496  are positioned in a vicinity of ends  462  of force applicator  430 , and/or along the length of the force applicator, such as in a vicinity of a middle of the force applicator. For some applications, protrusions  496  are positioned at the ends of protruding extensions  494 , described hereinabove with reference to  FIG. 22  (configuration not shown). For other applications, the coupling elements are adapted to be coupled to the mitral valve, and/or to one or more chordae tendineae, such as third-order chordae tendineae  74 , or second-order chordae tendineae (not shown in the figures). For these applications, the coupling elements may comprise, for example, hooks, sutures, or staples (configuration not shown). 
         [0189]    Reference is made to  FIG. 24 , which is a schematic illustration of a procedure for introducing force applicator  430  into heart  50  of a subject, in accordance with an embodiment of the present invention. Typically, force applicator  430  is introduced into ventricle  72  by a catheter  481 , which is typically introduced into ventricle  72  via ascending aorta  82 . A surgeon typically guides force applicator  430  to a desired location using images of heart  50  captured using techniques known in the art. Alternatively or additionally, the surgeon employs an echocardiogram to determine if placement of force applicator  430  achieves closure of the mitral valve. For some applications, force applicator  430  is adjustable during placement, for example, as described hereinbelow with reference to  FIG. 26  and/or  FIG. 27 . For such applications, if the device does not sufficiently close the valve, the surgeon may adjust the device in situ until the valve is sufficiently closed. 
         [0190]    For some applications, force applicator  430  comprises, e.g., at a distal end thereof, one or more wireless position sensors, such as those manufactured by Biosense, Inc. (New Brunswick, N.J.), or otherwise known in the art. Alternatively or additionally, force applicator  430  comprises, e.g., at a distal end thereof, one or more sensors for aiding navigation, such as an ultrasound sensor, an infrared sensor, or an optical sensor. For some applications, force applicator  430  comprises a steering mechanism, such as those known in the art of coronary catheter navigation. For some applications, the surgeon magnetically navigates force applicator  430 , such as using techniques described in U.S. Pat. No. 6,817,364 or 6,522,909 to Garibaldi et al., or U.S. Pat. No. 6,475,223 to Werp et al., which are incorporated herein by reference,  mutatis mutandis.    
         [0191]    Reference is made to  FIG. 25 , which is a schematic illustration of a distal end  484  of catheter  481 , in accordance with an embodiment of the present invention. In this embodiment, the distal end of catheter  481  opens laterally, rather than at its end, so as to guide force applicator  430  towards mitral valve  58  after the catheter is inserted into left ventricle  72 . 
         [0192]    Reference is made to  FIG. 26 , which is a schematic illustration of an adjustment mechanism  500  for force applicator  430 , in accordance with an embodiment of the present invention. Adjustment mechanism  500  comprises a center wheel  502 , which is configured to move ends  462  of force applicator  430  closer and farther from one another, in a manner similar to a center wheel of a draftsman&#39;s compass. 
         [0193]    Reference is made to  FIG. 27 , which is a schematic illustration of another adjustment mechanism  520  for force applicator  430 , in accordance with an embodiment of the present invention. Adjustment mechanism  520  comprises one or more screws  522  in a vicinity of one or both ends  462  of force applicator  430 . Rotation of screws  522  in one direction increases the pushing of end  462  into the heart wall, while rotation of the screws in the opposite direction decreases such pushing. For some applications, force applicator  430  comprises both adjustment mechanism  520  and adjustment mechanism  500 , described hereinabove with reference to  FIG. 26 . 
         [0194]    It will be appreciated that whereas force applicator  430  has been generally described herein as comprising a single force applicator, the scope of the present invention is not limited to a single force applicator, and includes the use of multiple force applicators in series and/or in parallel with one another. 
         [0195]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.