Patent Publication Number: US-6669687-B1

Title: Apparatus and methods for treating tissue

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit from the filing date of provisional U.S. patent application Ser. No. 60/141,077 filed Jun. 25, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to treatment of tissue. More particularly, the present invention provides methods and apparatus for treating valvular disease with a catheter inserted into a patient&#39;s cardiac chambers, the catheter having an end effector for modifying cardiac structures, including valve leaflets and support structure. 
     BACKGROUND OF THE INVENTION 
     Degenerative valvular disease is the most common cause of valvular regurgitation in human beings. Regurgitation is typically characterized by an expanded valve annulus or by lengthened chordae tendineae. In either case, an increase in the geometry of a valve or its supporting structure causes the valve to become less effective, as it no longer fully closes when required. 
     Loose chordae tendineae may result, for example, from ischemic heart disease affecting the papillary muscles. The papillary muscles attach to the chordae tendineae and keep the leaflets of a valve shut. Some forms of ischemic cardiac disease cause the papillary muscles to lose their muscle tone, resulting in a loosening of the chordae tendineae. This loosening, in turn, allows the leaflets of the affected valve to prolapse, causing regurgitation. 
     It therefore would be desirable to provide methods and apparatus for treatment of tissue that modify the geometry and operation of a heart valve. 
     It would also be desirable to provide methods and apparatus that are configured to thermally treat chordae tendineae, the annulus of a valve, or valve leaflets. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide methods and apparatus for the treatment of tissue that modify the geometry and operation of a heart valve. 
     It is another object of the present invention to provide methods and apparatus that are configured to thermally treat chordae tendineae, the annulus of a valve, or valve leaflets. 
     These and other objects of the present invention are accomplished by providing apparatus and methods for thermally or mechanically treating tissue, such as valvular structures, to reconfigure or shrink the tissue in a controlled manner, thereby improving or restoring tissue function. Embodiments of the present invention advantageously may be employed to modify flow regulation characteristics of a cardiac valve or its component parts, as well as to modify flow regulation in other lumens of the body, including, for example, the urinary sphincter, digestive system valves, leg vein valves, etc., where thermal shrinkage or mechanical reconfiguration of tissue may provide therapeutic benefit. 
     In a first family of embodiments of the present invention, apparatus is provided having an end effector that induces a temperature rise in an annulus of tissue surrounding the leaflets of a valve sufficient to cause shrinkage of the tissue, thereby reducing a diameter of the annulus and causing the valves to close more tightly. In a second family of embodiments, apparatus is provided having an end effector that selectively induces a temperature rise in the chordae tendineae sufficient to cause a controlled degree of shortening of the chordae tendineae, thereby enabling the valve leaflets to be properly aligned. In yet a third family of embodiments, apparatus is provided having an end effector comprising a mechanical reconfigurer configured to attach to a longitudinal member, such as the chordae tendineae. The reconfigurer forces the longitudinal member into a tortuous path and, as a result, reduces the member&#39;s effective overall or straight length. 
     Any of these embodiments may employ one or more expanding members that serve to stabilize the end effector in contact with the tissue or structure to be treated. In addition, where it is desired to preserve the interior surface of a lumen or structure, the instrument may include means for flushing the surface of the tissue with cooled saline. Where it is desired to achieve a predetermined degree of heating at a depth within a tissue or structure, the end effector may comprise a laser having a wavelength selected to penetrate tissue to the desired depth, or the end effector may comprise a plurality of electrically conductive needles energized by an RF power source, as is known in the electrosurgical arts. The end effector may alternatively comprise an acoustic heating element, such as an ultrasonic transducer. 
     Methods of using apparatus according to the present invention are also provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like parts throughout, and in which: 
     FIG. 1 is a side-sectional view of a human heart showing major structures of the heart, including those pertaining to valvular degeneration; 
     FIG. 2 is a side view of apparatus of a first family of embodiments constructed in accordance with the present invention; 
     FIGS. 3A-3C are, respectively, a side view of an end effector for use with the apparatus of FIG. 2 and a sectional view through its catheter along sectional view line A—A, a side view of an alternative end effector and a sectional view of its catheter along view line B—B, and a side view of a still further alternative end effector; 
     FIG. 4 is a sectional view through the human heart, depicting a method of using the apparatus of FIG. 2 to shrink tissue in an annulus surrounding the leaflets of a regurgitating valve; 
     FIGS. 5A and 5B are schematic views of alternative embodiments of the apparatus of FIG. 2; 
     FIGS. 6A-6D are views of a still further alternative embodiment of the apparatus of FIG. 2 having barbs, and illustrating a method of use; 
     FIGS. 7A-7C are schematic views showing, respectively, an alternative embodiment of the end effector of FIGS. 6 having electrically insulated barbs, a method of using the end effector to thermally treat tissue, and a temperature profile within the tissue during treatment; 
     FIGS. 8A and 8B are side views of another alternative embodiment of the apparatus of FIG. 6 having multipolar, individual electrodes; 
     FIG. 9 is a side view of an alternative embodiment of the apparatus of FIG. 8 having individual ultrasonic transducers; 
     FIG. 10 is a side-sectional view of another alternative embodiment of the apparatus of FIG. 8 having individual laser fibers; 
     FIG. 11 is a side-sectional view of an alternative embodiment of the apparatus of FIGS. 8-10 having individual barb members that may comprise multipolar electrodes, ultrasonic transducers, or laser fibers; 
     FIG. 12 is a sectional view through the human heart, illustrating an alternative method of introducing apparatus of the first family of embodiments to a treatment site; 
     FIGS. 13A and 13B are views of an alternative embodiment of the apparatus of FIG. 2 shown, respectively, in schematic side view and in use shrinking an annulus of tissue; 
     FIGS. 14A and 14B are, respectively, a side view of an alternative embodiment of the apparatus of FIG. 2, and a method of using the embodiment via the introduction technique of FIG. 12; 
     FIGS. 15A and 15B are isometric views of an alternative end effector for use with the apparatus of FIGS. 14; 
     FIG. 16 is a top view of apparatus of a second family of embodiments constructed in accordance with the present invention; 
     FIGS. 17A-17C are views of end effectors for use with the apparatus of FIG. 16; 
     FIG. 18 is a sectional view of the human heart, illustrating a method of using the apparatus of FIG. 16 to selectively induce a temperature rise in the chordae tendineae sufficient to cause a controlled degree of shortening of the tendineae; 
     FIGS. 19A-19C show a section of chordae tendineae and illustrate a method of shrinking the tendineae in a zig-zag fashion using the end effector of FIG. 17C with the apparatus of FIG. 16; 
     FIGS. 20A-20C show, respectively, a side view of an intact tendineae, a side view of the tendineae after treatment by a shrinkage technique, and a cross section through the tendineae along sectional view line C—C of FIG. 20A after treatment by an alternative shrinkage technique; 
     FIGS. 21A and 21B are side views of apparatus of a third family of embodiments, constructed in accordance with the present invention, shown in a collapsed delivery configuration and in an expanded deployed configuration; 
     FIGS. 22A and 22B are schematic views depicting a method of using the apparatus of FIGS. 21 to mechanically shorten an effective length of chordae tendineae; and 
     FIG. 23 is a side view, partially in section, illustrating a method and apparatus for non-invasive coagulation and shrinkage of scar tissue in the heart, or shrinkage of the valve structures of the heart. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, a sectional view through human heart H is presented. Major structures labeled include the right atrium RA, left atrium LA, right ventricle RV, left ventricle LV, superior vena cava SVC, inferior vena cava IVC, and ascending aorta AA. Structures that may be involved in valvular degeneration and regurgitation are also labeled, including the papillary muscles PM, chordae tendineae CT, valve leaflets L, and annuluses of tissue surrounding the leaflets A, as well as the tricuspid valve TV, the bicuspid or mitral valve MV, and the aortic valve AV. The pulmonary valve PV is not seen in the cross section of FIG. 1, but may also experience valvular degeneration. As discussed previously, degenerative valvular disease often leads to valvular regurgitation, which is typically characterized by an expanded valve annulus A or by lengthened chordae tendineae CT. Loose chordae tendineae may result from ischemic heart disease affecting the papillary muscles PM, which attach to the chordae tendineae and act to regulate flow through leaflets L. 
     The present invention therefore provides apparatus and methods for shrinking or reconfiguring tissue, such as annulus A or chordae tendineae CT. Embodiments of the present invention advantageously may be employed to modify flow regulation characteristics of a cardiac valve or its component parts, as well as to modify flow regulation in other lumens of the body, including, for example, the urinary sphincter, digestive system valves, leg vein valves, etc., where thermal shrinkage or mechanical reconfiguration of tissue may provide therapeutic benefit. 
     FIGS. 2-15 illustrate apparatus of a first family of embodiments of the present invention. The first family of embodiments have an end effector that induces a temperature rise in an annulus of tissue surrounding the leaflets of a valve sufficient to cause shrinkage of the tissue, thereby reducing a diameter of the annulus and causing the valve to close more tightly. 
     Referring to FIG. 2, apparatus  30  comprises catheter  32  having end effector  34  in a distal region of the catheter. End effector  34  may be collapsible within and extendable beyond the distal end of catheter  30  to permit percutaneous delivery to a treatment site. End effector  34  has an annular shape to facilitate treatment of an annulus of tissue, as well as stabilization against the walls of a treatment site. 
     With reference to FIGS. 3A-3C, alternative embodiments of end effector  34  and catheter  32  are described. In FIG. 3A, end effector  34  comprises expandable balloon  40 . Balloon  40  comprises bipolar electrodes  42   a  and  42   b  that may be attached to a radiofrequency (“RF”) voltage or current source (not shown). Balloon  40  further comprises lumen  44  to facilitate unimpeded blood flow or fluid transport therethrough, and temperature sensors  46  to monitor shrinkage of tissue caused by current flow between bipolar electrodes  42   a  and  42   b . Sensors  46  may comprise, for example, standard thermocouples, or any other temperature sensor known in the art. 
     The end effector of FIG. 3A is thus capable of achieving controlled luminal shrinkage while allowing blood to pass through the center of balloon  40 . Electrodes  42   a  and  42   b  are disposed as bands on the periphery of balloon  40  and may inject an RF electrical current into the wall of a treatment site, such as an annulus or lumen, to shrink collagen contained therein. Furthermore, balloon  40  may be inflated with a circulating coolant C, such as water, to cool the surface of balloon  40  and thereby minimize thermal damage at the surface of the treatment site. Thermally damaged tissue may be thrombogenic and may form thrombus on its surface, leading to potentially lethal complications. 
     FIG. 3A also provides a cross section through an embodiment of catheter  32 , along sectional view line A—A, for use in conjunction with the balloon embodiment of end effector  34 . Catheter  32  comprises coolant lumens  48   a  and  48   b  that may circulate coolant C into and out of balloon  40 , respectively. It further comprises wires  49   a - 49   c , electrically coupled to electrode  42   a , electrode  42   b , and temperature sensors  46 , respectively. 
     In FIG. 3B, an alternative embodiment of end effector  34  and catheter  32  is presented. Instead of RF energy, the heating element in this embodiment is a laser source (not shown) coupled to fiber optic cable  50  having side firing tip  51 . The laser source injects light energy into the wall of a treatment site via fiber optic cable  50 , thereby thermally shrinking the tissue. The wavelength of the laser may be selected to penetrate tissue to a desired depth. Furthermore, a plurality of fiber optic cables  50 , coupled to the laser source and disposed about the circumference of balloon  40 , may be provided. 
     Balloon  40  is substantially transparent to the laser energy, and coolant C may again serve to cool the surface of balloon  40 , thereby minimizing damage at the surface of the treatment site. The circulating stream of coolant C maintains the temperature of surface tissue layers at a sufficiently low level to prevent thermal damage, and thus, to prevent formation of thrombus. Temperature sensor  46  optionally may also be provided. 
     As seen in FIG. 3C, end effector  34  may alternatively comprise wrapped sheet  52  incorporating one or more electrodes on its surface. Sheet  52  may be advanced to a treatment site in a collapsed delivery configuration within a lumen of catheter  32 , and may then be unfurled to an expanded deployed configuration wherein it contacts the interior wall of the treatment site and may be energized to shrink tissue. 
     Referring now to FIG. 4, a method of using apparatus  30  to thermally shrink an annulus of tissue is described. End effector  34  is placed in intimate contact with the inner wall of a blood vessel or other body lumen. In the valvular regurgitation treatment technique of FIG. 4, end effector  34  is percutaneously delivered just proximal of aortic valve AV within ascending aorta AA at annulus of tissue A supporting leaflets L, using well-known techniques. Aortic valve AV suffers from valvular degeneration, leading to regurgitation. End effector  34  delivers energy to annulus A sufficient to heat and shrink the annulus, thus enhancing function of the degenerative valve. Collagen within annulus A shrinks and reduces a diameter of the annulus. Leaflets L are approximated towards one another, as seen in dashed profile in FIG. 4, and valvular regurgitation is reduced or eliminated. In addition to valvular regurgitation, the technique is expected to effectively treat aortic insufficiency. 
     End effector  34  stabilizes apparatus  30  against the wall of a body passageway. Once stabilized, a source of energy may be applied to the wall to thermally shrink the tissue contained in the wall. In addition to the application of FIG. 4, treatment may be provided, for example, to the annulus of mitral valve MV, to the urinary sphincter for treatment of incontinence, to digestive system valves for treatment of acid reflux, to leg vein valves, and to any other annulus of tissue where treatment is deemed beneficial. 
     With reference to FIGS. 5A and 5B, alternative embodiments of the apparatus of FIG. 2 are described. In FIG. 5A, apparatus  60  comprises catheter  62  having a lumen, in which end effector  64  is advanceably disposed. End effector  64  comprises monopolar electrode  66 , which is fabricated in an arc from a shape memory alloy, such as spring steel or nitinol, to approximate the shape of an annulus of tissue at a treatment site within a patient. Electrode  66  may be retracted within the lumen of catheter  62  to facilitate transluminal, percutaneous delivery to the treatment site. Once in position, electrode  66  may be advanced out of a distal region of catheter  62 . The electrode resumes its arc shape and approximates the wall of the treatment site. 
     Monopolar electrode  66  is electrically coupled to RF source  68 , which is positioned outside of the patient. RF source  68  is, in turn, coupled to reference electrode  69 . When RF source  68  is activated, current flows between monopolar electrode  66  and reference electrode  69 , which may, for example, be attached to the exterior of the patient in the region of the treatment site. RF current flows into the wall of the treatment site, thereby effecting annular tissue shrinkage, as described previously. 
     In FIG. 5B, a bipolar embodiment is provided. Apparatus  70  comprises catheter  72  and end effector  74 . End effector  74  comprises a plurality of atraumatic tipped legs  76  that are electrically coupled by a plurality of current carrying wires  78  to an RF source (not shown). The plurality of legs contact the wall of a treatment site and inject current into the wall. The current flows between the tips of the legs. Alternatively, the plurality of legs may comprise a monopolar electrode coupled by a single wire to the RF source, and current may flow between the plurality of legs and a reference electrode, as in FIG.  5 A. 
     Referring to FIGS. 6A-6D, another alternative embodiment of the apparatus of FIG. 2 is described. FIG. 6A shows apparatus  80  in side-sectional view in a retracted delivery configuration. Apparatus  80  comprises catheter  82  and end effector  84 . Catheter  82  further comprises central bore  86 , a plurality of side bores  88 , and optional temperature sensors  90 . End effector  84  may, for example, be fabricated from nitinol or spring steel, and comprises conductive shaft  92  having a plurality of radially extending electrodes  94  with optional barbs  96 . Conductive shaft  92  is electrically coupled to RF source  98 , which is electrically coupled to reference electrode  99 . Conductive shaft  92  is disposed within central bore  86 , while electrodes  94  are disposed within side bores  88 . 
     End effector  84  is advanceable with respect to catheter  82 . When advanced distally, apparatus  80  assumes the expanded deployed configuration of FIG. 6B, wherein electrodes  94  extend through side bores  88  beyond the surface of catheter  82 . Apparatus  80  is also configured such that its distal region may approximate the shape of an annulus of tissue, as described hereinbelow with respect to FIG. 6D, and is thus suited for both linear and circular subsurface tissue coagulation and shrinkage. 
     FIGS. 6C and 6D provide a method of using apparatus  80  to treat annulus of tissue A surrounding a heart valve. Apparatus  80  is percutaneously advanced to the surface of a heart valve in the delivery configuration of FIG.  6 C. Once positioned at annulus A, the distal region of apparatus  80  approximates the shape of the annulus, as seen in FIG.  6 D. This may be accomplished, for example, with a steering mechanism comprising two purchase points or a pre-shaped tip that is retracted within a straight guiding catheter to allow insertion into the vascular system, as described in U.S. Pat. No. 5,275,162, which is incorporated herein by reference. Once inserted, the pre-shaped tip is advanced out of the guide catheter and recovers its preformed shape. 
     With apparatus  80  approximating annulus A, end effector  84  is distally advanced with respect to catheter  82 , thereby selectively advancing electrodes  94  into the annulus. RF source  98  then provides RF current, which flows between electrodes  94  and reference electrode  99 . The annulus of tissue shrinks, bringing valve leaflets into proper position and minimizing or eliminating regurgitation through the valve. 
     Catheter  82  insulates conductive shaft  92  from annulus A, thereby protecting surface tissue and only allowing coagulation at depth in treatment zones surrounding electrodes  94 . To further ensure that coagulation only occurs at depth, a coolant, such as saline, may be introduced through central bore  86  and side bores  88  of catheter  82  to the surface of annulus A, thereby cooling and flushing the area where electrodes  94  penetrate the tissue. It is expected that such liquid infusion will keep the surface of the annulus clean and will prevent thrombus formation in response to thermal damage. 
     Referring now to FIGS. 7A-7C, an alternative embodiment of end effector  84  of FIGS. 6 is described. The end effector of FIGS. 7 is equivalent to the end effector of FIGS. 6 except that it is coated with electrically insulating layer I. Insulation layer I covers the entire exterior of end effector  84 , except at the distal ends of the plurality of electrodes  94 . The layer is preferably sufficiently thin to allow insertion of electrodes  94  into tissue T without impediment. The exposed distal ends of the electrodes are configured to deliver energy into subsurface tissue at treatment zones Z. The zones may be ideally modeled as spheres of subsurface tissue. Tissue shrinks within treatment zones Z without damaging surface tissue, as seen in FIG.  7 B. 
     The size of treatment zones Z may be controlled to ensure that tissue remodeling only occurs at depth. Assuming a temperature T 1 , at which tissue damage is negligible, the magnitude of current passed through tissue T may be selected (based on the material properties of the tissue and the depth of insertion of electrodes  94  within the tissue) such that the temperature decays from a temperature T 0  at a position D 0  at the surface of an electrode  94  to the benign temperature T 1  at a distance D 1  from the surface of the electrode. The distance D 1  may be optimized such that it is below the surface of tissue T. An illustrative temperature profile across a treatment zone Z is provided in FIG.  7 C. 
     With reference to FIGS. 8A and 8B, another alternative embodiment of the apparatus of FIG. 6 is described. Apparatus  100  comprises catheter  102  and end effector  104 . End effector  104  further comprises a plurality of individual, multipolar electrodes  106 , which are electrically coupled to an RF or other current source (not shown) by a plurality of current carrying wires  108 . As with the embodiments of FIGS. 6 and 7, apparatus  100  is configured such that end effector  104  may approximate an annulus, as seen in FIG.  8 B. 
     Referring to FIGS. 9-11, alternative embodiments of the apparatus of FIGS. 8 are described. In FIG. 9, apparatus  110  comprises catheter  112  and end effector  114 . End effector  114  comprises a plurality of acoustic heating elements  116 . Acoustic elements  116  may, for example, comprise ultrasonic transducers. The acoustic energy may further be focused by appropriate means, for example, by lenses, such that a tissue damage threshold sufficient to cause shrinkage is only attained at a specified depth within treatment site tissue, thereby mitigating surface tissue damage and thrombus formation. Acoustic elements  116  are connected to appropriate controls (not shown). Apparatus  110 , and any other apparatus described herein, may optionally comprise temperature sensors  118 . 
     In FIG. 10, apparatus  120  comprises catheter  122  and end effector  124 . Catheter  122  comprises a plurality of central bores  126  and a plurality of side bores  128 , as well as a plurality of optional temperature sensors  130 . End effector  124  comprises a plurality of side-firing fiber optic laser fibers  132  disposed within central bores  126  of catheter  122 . The fibers are aligned such that they may deliver energy through side bores  128  to heat and induce shrinkage in target tissue. Fibers  132  are coupled to a laser source (not shown), as discussed with respect to FIG.  3 B. Suitable wavelengths for the laser source preferably range from visible (488-514 nm) to infrared (0.9-10.6 microns), wherein each wavelength has an ability to heat tissue to a predetermined depth. As an example, a preferred laser source comprises a continuous wave laser having a 2.1 micron wavelength, which will shrink and heat tissue to a depth of 1-2 mm. 
     In FIG. 11, apparatus  140  comprises catheter  142  and end effector  144 . Catheter  132  comprises central bores  146  and side bores  148 . Catheter  132  further comprises temperature sensors  150  that are configured to penetrate superficial tissue layers to measure temperature at depth. Temperature sensors  150  may be retractable and extendable to facilitate percutaneous delivery of apparatus  140 . End effector  144  comprises fibers  152  disposed within central bores  146 . Fibers  152  are retractable within and extendable beyond side bores  148 . Fibers  152  are preferably sharpened to facilitate tissue penetration and energy delivery to subsurface tissue, thereby inducing shrinkage of the tissue. 
     Fibers  152  may comprise any of a number of energy delivery elements. For example, fibers  152  may comprise a plurality of optical fibers coupled to a laser (not shown). The wavelength of the laser may be selected as described hereinabove, while the energy deposited by the fibers may be controlled responsive to the temperature recorded by sensors  150 . Thus, for example, a controller (not shown) may be provided to switch off the laser once a preset temperature, for example, 45° C.-75° C., is attained, thereby ensuring that a sufficiently high temperature is achieved to cause tissue shrinkage without inadvertently damaging surrounding tissues. 
     Fibers  152  may alternatively comprise a plurality of multipolar electrodes. Each electrode may be capable of injecting RF energy into tissue independently. Alternatively, current may be passed between a pair of adjacent or non-adjacent electrodes to heat intervening tissue. 
     Referring now to FIG. 12, an alternative method of introducing apparatus of the first family of embodiments to a treatment site is described. Apparatus  30  of FIG. 2 is been introduced to the annulus of tissue A surrounding mitral valve MV via the venous circulatory system. Catheter  32  is transluminally inserted via the jugular vein and superior vena cava SVC. The distal end of the catheter or a separate instrument then penetrates atrial septum AS using a procedure known as septostomy. Once the septum is perforated, end effector  34  may be inserted into left atrium LA and positioned over mitral valve annulus A to effect the thermal treatment described hereinabove. The tricuspid valve in the right ventricle, and the pulmonic valve, may also be treated in the same manner using a venous approach. 
     Referring to FIGS. 13A and 13B, a further alternative embodiment of the apparatus of FIG. 2 is described that may be introduced using the technique of FIG. 4, the technique of FIG. 12, or by another suitable technique. Apparatus  160  comprises catheter  162  and end effector  164 . End effector  164  comprises adjustable, heatable loop  166 , which is configured for dynamic sizing to facilitate positioning next to tissue at a treatment site. The size of loop  166  is adjusted so as to lie contiguous with annulus of tissue A at a treatment site, as seen in FIG.  13 B. The loop may be collapsible within catheter  162  to facilitate percutaneous delivery and is electrically coupled to RF source  168 , which is electrically coupled to reference electrode  170 . Loop  166  may be fabricated from nitinol, copper, or any other suitably conductive and ductile material. 
     Referring to FIGS. 14A and 14B, a still further alternative embodiment of the apparatus of FIG. 2, and a method of using the embodiment with the introduction technique of FIG. 12, is described. Apparatus  170  comprises catheter  172  and end effector  174 . End effector  174  is capable of grabbing and penetrating tissue, as well as delivering RF energy into tissue. End effector  174  comprises jaws  176   a  and  176   b , which are spring-biased against one another to a closed position. By pushing a knob on the handpiece (not shown), the jaws may be actuated to an open position configured to grab tissue at a treatment site. RF energy may then be deposited in the tissue in a monopolar or bipolar mode. Jaws  176  may optionally be coated with electrically insulating layer I everywhere except in a distal region, such that tissue is only treated at depth, as described hereinabove. End effector  174  has temperature sensor  178  to control power delivered to the tissue, again as described hereinabove. 
     With reference to FIG. 14B, a method of using apparatus  170  via a septostomy introduction technique to treat mitral valve regurgitation is described. In particular, jaws  176  of end effector  174  are actuated to engage individual sections of valve annulus A so as to penetrate into the collagenous sublayers and to thermally shrink those sublayers. The procedure may be repeated at multiple locations around the perimeter of annulus A until regurgitation is minimized or eliminated. 
     FIGS. 15A and 15B show an alternative end effector for use with apparatus  170  of FIGS.  14 . End effector  180  is shown in an open position and in a closed position, respectively, and comprises jaws  182   a  and  182   b . End effector  180  is similar to end effector  174 , except that jaws  182  are configured to engage tissue with a forceps grasping motion wherein bent tips  184   a  and  184   b  of the jaws are disposed parallel to one another and contact one another when closed. 
     With reference now to FIGS. 16-20, apparatus of a second family of embodiments of the present invention are described. These embodiments are provided with an end effector that selectively induces a temperature rise in the chordae tendineae sufficient to cause a controlled degree of shortening of the chordae tendineae, thereby enabling valve leaflets to be properly aligned. 
     A preferred use for apparatus of the second family is in treatment of mitral valve regurgitation. Mitral valve regurgitation has many causes, ranging from inherited disorders, such as Marphan&#39;s syndrome, to infections and ischemic disease. These conditions affect the macromechanical condition of the mitral valve and prevent the valve from closing completely. The resulting gap in the leaflets of the valve permit blood to regurgitate from the left ventricular chamber into the left atrium. 
     Mechanically, the structural defects characterizing mitral valve regurgitation include: (1) the chordae tendineae are too long due to a given disease state; (2) papillary muscle ischemia changes the shape of the papillary muscle, so that attached chordae tendineae no longer pull the leaflets of the mitral valve completely shut; (3) the annulus of the mitral valve becomes enlarged, resulting in the formation of a gap between the leaflets when closed; and (4) there is an inherent weakness in the leaflets, leaving the leaflets floppy and dysfunctional. 
     In accordance with the principles of the present invention, a temperature rise is induced in the support structure of the mitral valve to cause shrinkage that modifies the geometry of the valve to restore proper stopping of blood backflow and thereby regurgitation. This process is depicted in FIGS. 18-20 using the apparatus of FIGS. 16 and 17 to selectively shrink portions of the chordae tendineae, thereby bringing leaflets of the mitral valve leaflets into alignment. Apparatus of the second family may also be used in treatment of aortic valve regurgitation, and in treatment of a variety of other ailments that will be apparent to those of skill in the art. 
     Referring to FIG. 16, apparatus  200  comprises catheter  202  and end effector  204 . Catheter  204  optionally comprises collapsible and expandable stabilizer  206 , configured to stabilize apparatus  200  in a body lumen. Stabilizer  206  may comprise, for example, struts or an inflatable balloon. 
     End effector  204  may be collapsible to a delivery configuration within catheter  202 , and may expand to a delivery configuration beyond a distal end of the catheter. End effector  204  is configured to engage, heat, and shrink chordae tendineae. Various sources of energy may be used to impart heat to the collagenous tissue and thereby shrink it, including RF energy, focused ultrasound, laser energy, and microwave energy. In addition, chemical modifiers, such as aldehydes, may be used. For laser embodiments, a preferred laser is a continuous wave Holmium:Yag laser, with application of visible or infrared laser energy in the wavelength range of 400 nanometers to 10.6 micrometers. 
     With reference to FIGS. 17A-17C, embodiments of end effector  204  are described. In FIG. 17A, the end effector comprises a gripping mechanism that carries the heating element. Arms  210   a  and  210   b  are opposing and spring-biased against each other. The arms may be actuated to an open position using a handpiece (not shown) coupled thereto. Arms  210   a  and  210   b  may alternatively be vertically displaced with respect to one another to allow the arms to criss-cross and tightly grasp tissue. Heating elements  212  and temperature sensors  214  are attached to the arms. Heating elements  212  may comprise electrodes, acoustic transducers, side-firing laser fibers, radioactive elements, etc. It may be desirable to employ a saline flush with heating elements  212  to prevent coagulation of blood caught between arms  210 . 
     FIG. 17B shows an embodiment of end effector  204  with fixed, straight arms  220   a  and  220   b . The arms are configured to engage and disengage chordae tendineae simply by being positioned against the tendineae. FIG. 17C shows an embodiment of the end effector having arms  230   a  and  230   b . Multiple heating elements  212  are disposed on arm  230   a . When heating elements  212  comprise bipolar electrodes, current flow through the tendineae using the embodiment of FIG. 17C may be achieved primarily along a longitudinal axis of the tendineae, as opposed to along a radial axis of the tendineae, as will be achieved with the embodiment of FIG.  17 A. These alternative heating techniques are described in greater detail hereinbelow with respect to FIGS. 19 and 20. 
     Referring to FIG. 18, a method of using apparatus of the second family of embodiments to induce shrinkage of chordae tendineae CT is described. Catheter  202  of apparatus  200  is advanced percutaneously, using well-known techniques, through the ascending aorta AA and aortic valve AV into the left ventricle LV, with end effector  204  positioned within the catheter in the collapsed delivery configuration. Stabilizer  206  is then deployed to fix catheter  202  in ascending aorta AA, thereby providing a stationary leverage point. 
     End effector  204  is expanded to the deployed configuration distal of catheter  202 . The end effector is steerable within left ventricle LV to facilitate engagement of chordae tendineae CT. End effector  204 , as well as any of the other end effectors or catheters described herein, may optionally comprise one or more radiopaque features to ensure proper positioning at a treatment site. End effector  204  is capable of moving up and down the chordae tendineae to grab and selectively singe certain sections thereof, as illustrated in dotted profile in FIG. 18, to selectively shorten chordae tendineae CT, thereby treating valvular regurgitation. 
     When energy is transmitted through tissue utilizing one of the embodiments of this invention, the tissue absorbs the energy and heats up. It may therefore be advantageous to equip the end effector with temperature or impedance sensors, as seen in the embodiments of FIGS. 17, to output a signal that is used to control the maximum temperature attained by the tissue and ensure that the collagen or other tissues intended to be shrunk are heated only to a temperature sufficient for shrinkage, for example, a temperature in the range of 45° C.-75° C., and even more preferably in the range of 55° C.-65° C. Temperatures outside this range may be so hot as to turn the tissue into a gelatinous mass and weaken it to the point that it loses structural integrity. A closed loop feedback system advantageously may be employed to control the quantity of energy deposited into the tissue responsive to the output of the one or more sensors. In addition, the sensors may permit the clinician to determine the extent to which the cross-section of a chordae has been treated, thereby enabling the clinician to heat treat only a portion of the cross-section. 
     This technique is illustrated in FIGS. 19 and 20, in which alternating bands, only a single side, or only a single depth of the chordae is shrunk to leave a “longitudinal intact fiber bundle.” This method may be advantageous in that, by avoiding heat treatment of the entire cross section of the chordae, there is less risk of creating mechanical weakness. 
     FIGS. 19A-19C depict a method of shrinking a section of chordae tendineae CT in a zig-zag fashion using the embodiment of end effector  204  seen in FIG.  17 C. In FIG. 19A, the tendineae has an initial effective or straight length L 1 . Arms  230  engage chordae tendineae CT, and heating elements  212  are both disposed on the same side of the tendineae on arm  230   a . The heating elements may comprise bipolar electrodes, in which case the path of current flow through tendineae CT is illustrated by arrows in FIG.  19 A. 
     Collagen within the tendineae shrinks, and chordae tendineae CT assumes the configuration seen in FIG.  19 B. Treatment zone Z shrinks, and the tendineae assumes a shorter effective length L 2 . Treatment may be repeated on the opposite side of the tendineae, as seen in FIG. 19C, so that the tendineae assumes a zig-zag configuration of still shorter effective length L 3 . In this manner, successive bands of treatment zones Z and intact longitudinal fiber bundles may be established. 
     An additional pair of bipolar electrodes optionally may be disposed on arm  230   b  of the end effector to facilitate treatment in bands on opposite sides of chordae tendineae CT. The depth of shrinkage attained with apparatus  200  is a function of the distance between the electrodes, the power, and the duration of RF energy application. If, laser energy is applied, the wavelengths of energy application may be selected to provide only partial penetration of the thickness of the tissue. For example, continuous wave Holmium:YAG laser energy having a wavelength of 2.1 microns penetrates a mere fraction of a millimeter and may be a suitable energy source. 
     FIGS. 20A-20C illustrate additional shrinkage techniques. Intact chordae tendineae CT is seen in FIG.  20 A. FIG. 20B demonstrates shrinkage with apparatus  200  only on one side of the chordae, using the technique described with respect to FIGS.  19 . FIG. 20C demonstrates shrinkage with, for example the end effector of FIG. 17A or  17 B, wherein, for example, bipolar current flows across the tendineae and treats the tendineae radially to a certain preselected depth. When viewed in cross-section along sectional view line C—C of FIG. 20A, chordae tendineae CT has an intact longitudinal fiber bundle core C surrounded by treatment zone Z. 
     With reference to FIGS. 21-22, apparatus of a third family of embodiments of the present invention are described. These embodiments are provided with an end effector comprising a mechanical reconfigurer configured to engage a longitudinal member, such as the chordae tendineae. The reconfigurer forces the longitudinal member into a tortuous path and, as a result, reduces the member&#39;s effective overall or straight length. 
     Referring to FIGS. 21A and 21B, apparatus  300  comprises catheter  302  and end effector  304 . End effector  304  comprises mechanical reconfigurer  306 , adapted to mechanically alter the length of a longitudinal member, for example, chordae tendineae. Reconfigurer  306  comprises a preshaped spring fabricated from a shape memory alloy, for example, nitinol, spring steel, or any other suitably elastic and strong material. Reconfigurer  306  is preshaped such that there is no straight path through its loops. Overlap between adjacent loops is preferably minimized. The shape of reconfigurer  306  causes longitudinal members, such as chordae tendineae, passed therethrough to assume a zig-zag configuration and thereby be reduced in effective length. Reconfigurer  306  is collapsible to a delivery configuration within catheter  302 , as seen in FIG. 21A, and is expandable to a deployed configuration, as seen in FIG.  21 B. The reconfigurer optionally may be selectively detachable from catheter  302 . 
     With reference to FIGS. 22A and 22B, a method of using apparatus  300  to mechanically shorten chordae tendineae CT is described. Apparatus  300  is advanced to the chordae tendineae, for example, using the technique described hereinabove with respect to FIG.  18 . End effector  304  is then expanded from the delivery configuration seen in FIG. 22A to the deployed configuration of FIG.  22 B. Mechanical reconfigurer  306  regains its preformed shape, and chordae tendineae CT is passed through a tortuous path that reduces its effective length, thereby treating valvular regurgitation. Reconfigurer  306  may then be detached from apparatus  300  and permanently implanted in the patient, or the reconfigurer may be left in place for a limited period of time to facilitate complementary regurgitation treatment techniques. 
     Other embodiments of the third family in accordance with the present invention will be apparent to those of skill in the art in light of this disclosure. 
     Referring now to FIG. 23, apparatus in accordance with the present invention is described that may be used as either an embodiment of the first family or of the second family. Apparatus and methods are provided for noninvasively coagulating and shrinking scar tissue around the heart, or valve structures inside the heart, using energy delivered via high intensity, focused ultrasound. Apparatus  350  comprises catheter  352  and end effector  354 . End effector  354  comprises ultrasonic transducer  356  and focusing means  358 , for example, a lens. Focused ultrasound is propagated and directed with a high level of accuracy at the chordae CT, the annuluses A of the valves or at a section of bulging wall of the heart, using, for example, echocardiography or MRI for guidance. As with the previous embodiments, the shrinkage induced by energy deposition is expected to reduce valvular regurgitation. Apparatus  350  may also be used to reduce ventricular volume and shape, in cases where there is bulging scar tissue on the wall of the left ventricle LV secondary to acute myocardial infarction. 
     All of the above mentioned methods and apparatus may be used in conjunction with flow-indicating systems, including, for example, color Doppler flow echocardiography, MRI flow imaging systems, or laser Doppler flow meters. Application of energy from the end effector may be selected such that regurgitation stops before the procedure is completed, as verified by the flow-indicating system. Alternatively, the procedure may be “overdone” to compensate for expected tissue relapse, without compromising the ultimate outcome of the procedure. 
     Additionally, all of the foregoing apparatus and methods optionally may be used in conjunction with ECG gating, thereby ensuring that tissue is at a specified point in the cardiac cycle before energy is deposited into the tissue. ECG gating is expected to make treatment more reproducible and safer for the patient. 
     Although preferred illustrative embodiments of the present invention are described above, it will be evident to one skilled in the art that various changes and modifications may be made without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.