Patent Publication Number: US-2020275974-A1

Title: Devices and methods for remodeling tissue

Description:
FIELD OF THE PRESENT TECHNOLOGY 
     The present technology relates to RF devices used to remodel tissue. The device and methods disclosed herein have broad applicability to shrink collagenous tissue, and in particular they are well suited for remodeling cardiac tissue (e.g., a cardiac valve annulus and the chordae tendineae) to reduce regurgitation though the valve and enhance valve competency. 
     BACKGROUND 
     Mitral annular dilatation is a common feature of mitral valve disease, especially in functional or secondary mitral valve disease. As the annulus dilates, the leaflets are pulled apart until the edges no longer coapt in systole resulting in regurgitation. Reducing the overall circumference of the annulus is one of the most common elements of successful surgical mitral valve repair. This can be surgically performed by sewing the mitral annulus to an annuloplasty ring having a smaller diameter than the annulus. This permanently reduces the mitral annular circumference, but it entails an open or minimally-invasive surgical procedure involving significant trauma, morbidity, and recovery time. 
     Many different catheter-based mitral annuloplasty concepts have been pursued. For example, devices have been placed in the coronary sinus paralleling the mitral annulus, or a number of anchors have been placed in the annulus and then pulled together. 
     Several techniques to perform mitral annuloplasty using radiofrequency (RF) energy have been attempted. For example, a ring of electrodes has been applied against the atrial surface of the annulus, and then RF energy is delivered between pairs of electrodes to heat and shrink the tissue. Another technique involves driving a pair of spaced-apart electrodes into the annular tissue and delivering RF energy between the electrodes to shrink the annular tissue. 
     Other techniques deliver RF energy via catheters to reshape tissue to perform other valve modifications, such as shrinking the length of chordae tendineae and shrinking heart valve leaflet tissue itself. However, these techniques have drawbacks, such as controlling the extent of shrinkage. For example, the mitral valve has delicate and carefully sculpted tissue features, which may need to be shrunk in only certain directions. 
     Chemically induced ablation has also been applied to the mitral valve. One such attempt is disclosed in the American Journal of Physiology and is entitled “Ablation of mitral annular and leaflet muscle: effects on annular and leaflet dynamics”, Tomasz A. Timek et al., 1 Oct. 2003, https://doi.org/10.1152/ajpheart.00179.2003, PubMed12969884. 
     Given the difficulties associated with current procedures, there remains the need for simple, effective, and less invasive devices and methods for treating dysfunctional heart valves. 
     SUMMARY OF THE PRESENT TECHNOLOGY 
     A minimally invasive method for reducing the size of a cardiac valve annulus in a beating heart, comprising:
         a. advancing an energy delivery catheter into the heart proximate a cardiac valve annulus, the energy delivery catheter having at least two electrodes;   b. advancing the two electrodes such that the two electrodes pierce into the cardiac valve annulus at a distance from one another;   c, applying an approximating force to at least one of the two electrodes, thereby reducing the distance between the two electrodes; and   d. applying energy between the at least two electrodes, thereby heating and shrinking the annulus in a direction of the approximating force.       

     In the previous method, further comprising extending the two electrodes from the catheter by increasing a spacing between the two electrodes from a compact spacing to an extended spacing, wherein a spacing between the two electrodes in the extended spacing is greater than the spacing between the two electrodes in the compact spacing. 
     In any of the previous methods, the at least two electrodes may be configured to self-extend away from each other when unconstrained, and wherein increasing a spacing between the two electrodes includes allowing the two electrodes to self-extend away from each other. 
     In any of the previous methods, wherein increasing a spacing between the two electrodes includes inflating a bladder interposed between the two electrodes, 
     In any of the previous methods, wherein increasing a spacing between the two electrodes includes actuating a mechanism to actively increase the spacing between the two electrodes. 
     In any of the previous methods, the two electrodes include a first electrode and a second electrode, and the method includes:
         a. withdrawing the first electrode from the annulus while leaving the second electrode embedded in the annulus;   b. pivoting the energy delivery catheter about the second electrode;   c, advancing the first electrode into the cardiac annulus;   d. applying an approximating force biasing at least one of the first or second electrodes toward the other; and   e. applying an energy between the first and second electrodes thereby heating and shrinking the annulus in a direction of the approximating force.       

     In any of the preceding methods, further comprising:
         a. terminating delivery of the energy and allowing the valve annulus time to cool; and   b. removing the two electrodes from the annulus.       

     In any of the previous methods, wherein applying an approximating force includes advancing a sheath catheter toward the at least two electrodes. 
     In any of the previous methods, wherein applying an approximating force includes deflating the bladder between the electrodes, 
     In any of the previous methods, applying an approximating force includes actuating an approximating mechanism to actively decrease the spacing between the two electrodes. 
     Also disclosed is a minimally invasive method for selectively reducing the dimensions of a cardiac valve tissue in a beating heart, comprising:
         a. advancing a delivery catheter into the heart, the delivery catheter having at least two engagement members and an energy delivery mechanism;   b. advancing the engagement members into the cardiac valve tissue such that engagement members are spaced apart from one another by a distance;   c. applying an approximating force to the engagement members; and   d. applying energy between the engagement members using the energy delivery member thereby shrinking the annulus cardiac tissue in a direction of the approximating force.       

     In the preceding method for selectively reducing the dimensions of cardiac tissue, further comprising extending the engagement members from the catheter by increasing a spacing between the engagement members from a compact spacing to an extended spacing, wherein the extended spacing is greater than the compact spacing. 
     In any of the preceding methods for selectively reducing the dimensions of cardiac tissue, wherein the engagement members are configured to self-extend away from each other when unconstrained, and wherein increasing a spacing between the engagement members includes allowing the engagement members to self-extend away from each other. 
     In any of the preceding methods for selectively reducing the dimensions of cardiac tissue, wherein increasing a spacing between the engagement members includes inflating a bladder interposed between the engagement members. 
     In any of the preceding methods for selectively reducing the dimensions of cardiac tissue, wherein increasing a spacing between the engagement members includes actuating an approximating mechanism to actively increase the spacing between the engagement members. 
     In any of the preceding methods for selectively reducing the dimensions of cardiac tissue, wherein the engagement members include a first engagement member and second engagement member, and the method further comprises:
         a. withdrawing the first engagement member from the annulus cardiac tissue while leaving the second engagement member embedded in the cardiac tissue;   b. pivoting the energy delivery catheter about the second engagement member;   c. advancing the first engagement member into the cardiac tissue;   d. moving at least one of the engagement members toward the other along an approximating path; and   e. applying at least one of energy and chemical agent between the engagement members thereby shrinking the cardiac tissue annulus in the direction of the approximating path.       

     In any of the preceding methods for selectively reducing the dimensions of cardiac tissue, wherein moving at least one of the engagement members along an approximating path includes advancing the catheter toward the engagement members. 
     In any of the preceding methods for selectively reducing the dimensions of cardiac tissue, wherein moving at least one of the engagement members along an approximating path includes deflating the bladder between the engagement members. 
     In any of the preceding methods for selectively reducing the dimensions of cardiac tissue, wherein moving at least one of the engagement members along an approximating path includes actuating an approximating mechanism to actively decrease the spacing between the engagement members. 
     In any of the preceding methods, wherein applying energy includes applying an energy modality selected from the group of (bipolar, monopolar, resistive heating, ultrasound, laser, and microwave). 
     In any of the preceding methods for selectively reducing the dimensions of cardiac tissue; wherein the chemical agent is selected from the group of (phenol, and glutaraldehyde). 
     Also disclosed is a minimally invasive device for reducing the diameter of a cardiac valve annulus in a beating heart; comprising:
         a. an elongate delivery catheter;   b. at least two engagement members carried by the delivery catheter, wherein the engagement members and catheter have a retracted position in which the engagement members are fully contained within the catheter and an extended position in which the engagement members extend beyond a distal end of the catheter;   c. a tissue shrinking component configured to deliver at least one of energy and a chemical agent between the two engagement members; and   d. an approximation mechanism configured to apply a force to the engagement members, wherein the force is selected from the group of an approximating force and a separating force.       

     In the above-described device, the tissue shrinking component comprises an energy delivery mechanism configured to deliver an energy modality selected from the group (bipolar, resistive heating, ultrasound, laser, and microwave). 
     In any of the above-described devices, the tissue shrinking component comprises a chemical agent is selected from the group of (phenol, and glutaraldehyde). 
     In any of the above-described devices, the tissue shrinking component is operably connected to the engagement members. 
     In any of the above-described devices, the approximation mechanism includes a linkage connecting the engagement members. 
     In the above-described device, the linkage may include a hinge. 
     In the above-described device, the approximation mechanism includes a pull-wire connected to the linkage such that pulling on the pull-wire applies an approximation force to the engagement members. 
     In any of the above-described devices, the approximation mechanism includes a sleeve surrounding at least a portion of the engagement members, and wherein advancing the sleeve biases the engagement members together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an energy delivery device; 
         FIG. 2  depicts an energy delivery device; 
         FIG. 3  depicts an energy delivery device; 
         FIGS. 4A-4D  depict an energy delivery device and a method for shrinking cardiac tissue in a selective direction; 
         FIGS. 5A-5D  depict a method for shrinking cardiac tissue in a selective direction; 
         FIG. 6  depicts an energy delivery device; 
         FIGS. 7A-7C  depict optional features of the energy delivery device of  FIGS. 1-3 ; and 
         FIG. 8  depicts an energy delivery device. 
     
    
    
     DETAILED DESCRIPTION 
     The present technology is useful for shrinking collagenous tissue in general, and it is particularly useful for shrinking cardiac tissue; such as the annulus of a cardiac valve and/or the chordae tendineae, in a controlled, predictable manner to reduce regurgitation through the valve. 
     Annuloplasty 
     Several existing mitral annuloplasty techniques shrink collagen fibers by heating the fibers to a transition temperature. It is known that applying energy to heat collagenous tissue in a relaxed state causes it to shrink, and the shrinkage typically occurs in all directions. In general, the rate of shrinkage is greater in the direction of the fiber orientation. However; heating collagenous tissue while it is under a certain degree of tension often results in the collagen shrinking in dimensions other than the direction of the tension. This presents particular challenges for mitral valve procedures because the effect of ventricular pressure on the mitral annulus induces significant tension in the mitral annulus. The general stiffness of the mitral annulus and the tendency of the surrounding tissues, including muscular ventricular tissue, also tends to hold the collagen in its original shape even after applying energy. Moreover, the collagenous tissue in the annulus is surrounded by other tissue, such as muscle, which is not as likely to shrink when heated. As a result, existing mitral annuloplasty techniques may not shrink the collagen fibers in a desired manner. 
     The present technology is expected to overcome the drawbacks of existing mitral annuloplasty techniques by grasping the cardiac tissue and approximating it in the desired direction of shrinkage. Energy is applied to the tissue either during or after approximating the tissue. The desired shrinkage may be in a circumferential direction (e.g., around the cardiac valve annulus), or it may be in another direction. Approximating the tissue reduces the tension experienced by the cardiac tissue thereby preferentially shrinking the collagenous tissue in the desired direction. The force approximating the tissue may be maintained briefly after terminating energy delivery. The tissue will shrink further in the desired direction than it would without pre-approximation, and it will retain more of the shrinkage in the desired direction after the energy has been applied and the device is removed. 
       FIG. 1  depicts an energy delivery device  100  having a delivery catheter  120  and an optional guide catheter  122 . The device  100  has a plurality of pin-shaped electrodes  102  (identified individually as a first electrode  102   a  and a second electrode  102   b ) at the distal end. The electrodes  102  can be independently advanced and/or retracted to insert them into and/or remove them from the annular tissue. For example, the electrodes  102  may be advanced using a pushing motion (e.g., a push rod or push wire), and/or the electrodes  102  may have threaded surface  104  that engages and advances them into the annular tissue by rotation. The electrodes  102  may have an electrically conductive non-stick coating  106  so that they can be easily retracted from the tissue after heating the tissue. The electrodes  102  may be relatively stiff so that they resist bending when an approximating force is applied to pull the two electrodes together. 
     The first and second electrodes  102   a  and  102   b  can be contained in individual guide tubes  108   a  and  108   b , respectively, and the catheter  100  can further include an approximating mechanism  110  which can pull the guide tubes  108   a - b  together. For example, the approximating mechanism can draw the guide tubes  108   a - b  together (i.e., approximate the guide tubes  108   a - b ) with sufficient force to overcome the naturally occurring tension in the tissue. In some embodiments, the approximating mechanism  110  includes a pull-wire  111 W that extends through the catheter and a hinge  112  proximal of the distal tip as shown in  FIG. 1 . These embodiments produce an arcuate approximating motion between the first and second electrodes  102   a  and  102   b  (indicated by arrows A A ). In some embodiments, as shown in  FIG. 2 , the approximating mechanism  110  is connected by a linkage  114  configured to produce a linear approximating motion (indicated by arrows A L ) between the first and second electrodes  102   a  and  102   b  to maintain a constant orientation between the first and second electrodes  102   a  and  102   b  as they are approximated. For example, the approximating mechanism  110  in  FIG. 2  can maintain a parallel relationship between the first and second electrodes  102   a  and  102   b  throughout the operational portion of the approximating motion. In some embodiments, such as shown in  FIG. 2 , the approximating mechanism  110  is a threaded mechanism  111 S having a worm gear (not illustrated), or the like. The embodiments illustrated in  FIG. 2 , however, can substitute the pull-wire  111 W for the threaded mechanism  111 S to operate the linkage  114 . 
       FIG. 3  illustrates the device  100  in which the approximating mechanism  110  includes a contraction member  116  around the first and second electrodes  102   a - b  and an expansion member  118  interposed between first and second electrodes  102   a - b . The contraction member  116  pulls the two electrodes  102   a - b  together (approximated), while the expansion member  118  drives the electrodes  102   a - b  apart from each other. In some embodiments, the contraction member  116  is an elastic sleeve and the expansion member  118  is a balloon  118  or the like. The expansion member  118  is configured to overcome the biasing force of the contraction member  116  for driving the electrodes  102   a - b  apart from each other. For example, when the expansion member  118  is a balloon, inflating the balloon with a fluid such as saline or the like will overcome the approximation force of the contraction member  116  and thereby further separate the electrodes  102   a - b  from each other. Deflating the balloon by withdrawing some of the fluid from the balloon allows the approximation force from the contraction member  116  to overcome the expansion force of the balloon and thereby approximate the electrodes  102 . The contraction member  116  can comprise one or more biasing members such as springs, elastomeric members, a worm gear or the like interconnecting the electrodes  102   a - b  and/or the tubes  108   a - b  instead of an elastic sleeve. One of ordinary skill in the art will appreciate that many alternative mechanisms may be used to adjust the spacing between the electrodes  102 . 
     The catheters  100  shown in  FIGS. 1-3  can further include a first sensor  130   a  at the first electrode  102   a  and a second sensor  130   b  at the second electrode  102   b  (collectively “sensors  130 ”). The sensors  130  can be impedance sensors or thermistors embedded into one or both of the electrodes  102 . The sensors  130  can monitor the temperature or impedance of the tissue to determine the status of the tissue before, during and/or after applying energy to the tissue via the electrodes  102   a - b , The sensors  130  can send signals to a controller for ensuring electrode operation, ensuring electrode contact, controlling the extent of shrinkage, avoiding overtreatment, etc. For example, the signals from the sensors  130  can be used to determine the total energy delivered to the tissue based on the relative spacing of the electrodes or estimate the distance between the electrodes. 
     The electrodes  102   a - b  may be solid members (e.g., solid wires), or they may be tubes having a longitudinal lumen (e.g., hollow wires—not shown) and distal side-apertures (not shown), The lumens, for example, may extend through the full longitudinal length of the electrodes  102   a - b , and the side-apertures may be in fluid communication with the lumens such that fluid introduced into the lumens exits through the apertures. A saline or hypertonic saline can be infused via the lumen and apertures while applying energy via the electrodes  102   a - b  to expand the effective area of heating and to control the extent of tissue desiccation at the electrodes  102   a - b . Alternatively, the electrodes  102   a - b  can be cooled via circulation of fluid through them to prevent overheating of the electrodes while the intervening tissue is being heated. 
       FIGS. 4A-4D  illustrate an example of the operation of the device  100  shown in  FIG. 1 . A person skilled in the art will understand that the devices  100  shown in  FIGS. 2 and 3  operate in an analogous manner. In use, the distal end of the energy delivery catheter  120  is first positioned near or against cardiac tissue such as the mitral valve annulus. (See  FIG. 4A .) The energy delivery catheter  120  may be introduced to the left atrial surface of the annulus via a trans-septal or a trans-atrial approach, or it may be delivered against the ventricular surface of the annulus via a trans-aortic or a trans-apical approach. The energy catheter  120  or the guide catheter  122  may be manipulated to position the tip  120   a  of the catheter  120  near or in contact with appropriate annular tissue. The first electrode  102   a  is then advanced into the annular tissue, as shown in  FIG. 4A , The first or second electrodes  102   a - b  can be advanced into the annular tissue independently of each other, or they can be advanced into the tissue together. The electrodes  102  are exposed by unsheathing the energy delivery catheter  120  from the guide catheter  122  or extending the energy delivery catheter  120  from the guide catheter  122 , and then withdrawing the energy delivery catheter  120  with respect to the tubes  108   a - b . As the energy delivery catheter  120  is withdrawn, the electrodes  102   a - b  can be self-biased to move further apart. The second electrode  102 B can then be advanced into the tissue. (See  FIG. 4B .) An approximating force is applied to pull the two electrodes  102   a - b  together, which cinches the annulus tissue between the electrodes  102   a - b  and thereby reduces the overall diameter of the annulus. (See  FIG. 4C .) For example, the electrodes  102   a - b  might be inserted into the annular tissue spaced 10 mm apart, and then pulled together to a separation of 2 mm-8 mm, or 3 mm-7 mm, or about 5 mm. The device  100  shown in  FIGS. 4A-40  pulls the electrodes  102   a - b  together using the pull-wire  111 W described above with reference to  FIG. 1 , but the approximating mechanism can use a worm gear, linkage or the like as described above with reference to  FIGS. 2 and 3  to approximate the two electrodes. 
     After the electrodes  102   a - b  are spaced apart by a desired distance, energy is then applied between the electrodes  102   a ,  102   b  to heat the tissue for a desired time, (e.g., 15 seconds) until the collagen is adequately denatured so that the annulus retains the new smaller circumference. The energy may be bipolar RF energy, monopolar RF energy, laser energy, ultrasonic energy, resistive heating of the electrodes, microwave energy, or other energy modalities. The energy is applied based on the power and time to cause the desired amount of shrinkage without undesired disruption of the tissue. For example, the energy can be applied at 10 W-100 W, or 15 W-85 W, or 20 W-70 W, or 25 W-55 W, or 10 W, 15 W, 20 W, 25 W, 30 W, 40 W, 45 W, 50 W, 55 W, 60 W, 65 W, 70 W, 75 W, 80 W, 85 W, 90 W, 95 W or 100 W, or any suitable wattage therebetween. 
     Additionally, the energy can be applied for 5 s-300 s, or 10 s-240 s, or 10 s-60 s, or 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, 55 s, or 60 s. A chemical agent (e.g., phenol, glutaraldehyde or other fixative chemicals) may be applied to the cardiac tissue between the two electrodes in addition to or in substitution of delivering electromagnetic or mechanical energy via the first and second electrodes  102   a - b.    
     Although bipolar RF energy has the advantage of being naturally directed between the two electrodes for heating the tissue so that it shrinks in the desired area, other energy modalities could also be applied. For example, monopolar RF energy, laser energy, ultrasonic energy, resistive heating of the electrodes, microwave energy, or other energy modalities can be used with any of the catheters  100  described above in addition to or in lieu of RF energy. Additionally, chemical methods could also be used to form the tissue into a desired shape, such as the injection of small amounts of phenol, glutaraldehyde or other fixative chemicals. 
     The process described above with reference to  FIGS. 4A-4C  can be repeated at different areas of the annulus to further reduce the circumference of the annulus in selected regions and thereby selectively reshape the annulus to promote coaptation. Referring to  FIG. 4D , for example, after the tissue has been approximated, heated, shrunk, and sufficiently cooled in a first region of the annulus, at least one of the electrodes  102   a - b  can be withdrawn from the tissue and moved to another section of annular tissue. If it is desired to treat the adjacent tissue on one side or the other of the first region of the annulus, the first electrode  102   a  can be removed from the tissue while the second electrode  102   b  remains in the tissue, and then the energy delivery catheter  120  can be (pivoted) rotated 180 degrees around the second electrode  102   b  such that the first electrode  102   a  is on the other side of the second electrode  102   b . The first electrode  102   a  can then be advanced into the tissue at the new location such that the first and second electrodes  102   a - b  span a second region of the annulus adjacent to the first region. The treatment can then continue by applying energy to the second region of the annulus via the first and second electrodes  102   a - b . In this manner, the catheter can be “walked” from one region of the annulus tissue to an adjacent region while remaining attached to the annulus at all times. This is expected to make re-positioning the electrodes  102   a - b  much faster and simpler. 
     In any of the foregoing embodiments, the guide catheter  122  can be used to position the energy delivery catheter  120  on or near the mitral annulus. For example, the guide catheter  120  can be inserted into the femoral vein and advanced across the interatrial septum of the heart until a tip  122   a  of the guide catheter  122  is positioned in the left atrium. The energy delivery catheter  120  can be inside the guide catheter  122  at this point. The guide catheter  122  can then be flexed until the tip  122   a  is open towards a location on the mitral annulus. The energy delivery catheter  120  can then be advanced distally through the guide catheter  122  until the electrodes  102  are at or near the mitral annulus. One or both of the electrodes  102   a - b  can be advanced into the annular tissue as described above with respect to  FIG. 4A . For example, once the first electrode  102   a  is fixed in position, the guide catheter  122  can be withdrawn to allow the two electrodes to move laterally apart from each other. The energy delivery catheter  120  can be rotated until the second electrode  102   b  is positioned over the mitral annulus, and the second electrode  102   b  can be advanced into the annulus as described above with respect to  4 B. The two electrodes  102   a - b  can be pulled toward each other until they are spaced apart by a distance that places the tissue in a desired tensile state. Energy can then be delivered to the tissue via the first and second electrodes  102   a - b . After a sufficient amount of energy is delivered to the tissue between the first and second electrodes  102   a - b , the first electrode  102   a  can be removed and repositioned at an adjacent section of the annulus for sequential treatment.  FIG. 4D  shows an example of the resulting annular shrinkage of the annulus. 
     Several of the foregoing embodiments can be modified to use a single electrode and/or a chemical delivery device instead of requiring two electrodes. For example, instead of having the two active electrodes  102   a  and  102   b , the catheters  100  described above with reference to  FIGS. 1-3  can have electrically inactive arms configured to extend from the guide tubes  108   a - b  and a monopolar electrode and/or a chemical injection needle configured to extend between the arms. In operation, the approximating mechanism  110  can draw the guide tubes  108   a - b  toward each other to move the electrically inactive arms closer together, as described above, and then (a) electrical energy can be applied to the tissue between the arms using the monopolar electrode and/or (b) a chemical shrinking agent can be applied to the tissue between the arms via the chemical injection needle. 
     This concept has been described for performing mitral annuloplasty, but it can similarly be applied to the tricuspid annulus. The elasticity of the tricuspid annulus is even more pronounced than the mitral annulus, so each segment might be compressed more before delivering energy. For example, each segment might be compressed to one-third of its pre-treatment length before delivering energy. 
     Chordae Tendineae Shortening 
     Mitral prolapse or regurgitation may be attributable to overly long chordae tendineae. The chordae tendineae are taut and linear during systole and become limp and tortuous during diastole. It has been previously proposed to shorten chordae by applying energy to heat and shrink the chordae. Previous techniques involved placing an electrode against the chordae tendineae and applying energy until the chord shrinks appropriately. This is an uncontrolled method which may easily result in excessive shrinkage of a chord, which could end up “tethering” the leaflets and preventing closure of the valve. Moreover, it may be difficult to control the chords and to visualize how much shrinkage is occurring. 
       FIGS. 5A-5D  show a procedure for selectively and controllably heating and shrinking the chordae tendineae using a device  500  having energy delivery mechanisms  501  (identified individually as first energy delivery mechanism  501   a  and second energy delivery mechanism  501   b ). The first and second energy delivery mechanisms  501   a - b  are configured to grasp one or more chordae in two places a certain distance apart. The energy delivery mechanisms  501   a - b  can then be approximated by the desired length of shrinkage, and energy is then delivered between the energy delivery mechanisms  501   a - b  to shrink the portion of the chordae between the energy delivery mechanisms  501   a - b . For example, the first energy delivery mechanism  501   a  could be biased at one polarity and the second energy delivery mechanism  501   b  could be biased at the opposite polarity such that the current flows through the region of the chordae between the first and second energy delivery mechanisms  501   a - b.    
     Grasping a chord or group of chords in a beating heart may be challenging. For example, it may be hard to maneuver existing catheter-based systems to grasp the same chord such that the electrodes are spaced apart by a desired distance. One solution to this challenge is shown in  FIGS. 5A-5D . Referring to  FIG. 5A , the first and second energy delivery mechanisms  501   a - b  are initially close together, possibly at an oblique angle to the axis of the catheter to minimize their cross-sectional profile for delivery through a guide catheter  530 . The energy delivery elements  501   a - b  can have jaws  502   a - b , respectively, configured to be; (a) open for receiving a chord; (b) partially closed to retain the chord while being able to slide along the chord; and (c) fully closed to grasp the chord to prevent the chord from sliding with respect to the jaws  502   a - b . Referring to  FIGS. 5A and 5B  together, the first and second energy delivery mechanisms  501   a - b  can be placed near each other at first region of a chord ( FIG. 5A ), and then the first energy delivery mechanism  501   a  can be moved apart from the second energy delivery mechanism  501   b  to space the first and second energy delivery mechanisms  501   a - b  apart from each other along the chord ( FIG. 5B ). The first and second jaws  502   a - b  can then be firmly clamped against the chord and the moved closer together (approximated) such that a certain amount of slack S is induced in the chord, as shown in  FIG. 5 a    Energy can then be applied between the first and second energy delivery mechanisms  501   a - b  to preferentially and controllably shrink the chord in the longitudinal direction of the chord, as shown in  FIG. 5D . After the chord has achieved a desired length, the jaws  502   a - b  can be released (e.g.; opened) to release the chord. Valve performance can then be re-assessed and, if needed, energy can be reapplied to further shrink the chord or other chords can be shrunk. 
     The device  500  can be placed at the chords using a trans-apical; trans-aortic, trans-atrial, or trans-septal approach. In this setting, ultrasonic imaging, especially 3-dimensional trans-esophageal imaging, will be very helpful in managing the procedure. This device could also be used in a surgical setting, with visual confirmation of the chord grasping and length to be shortened. 
     The energy may be bipolar RF energy applied between the first and second jaws  502   a - b , monopolar RF energy, laser energy, ultrasonic energy, resistive heating of the electrodes, microwave energy; or other energy modalities. Bipolar energy may have the advantage of directing energy to the tissue between the two jaws. A chemical agent (e.g., phenol, glutaraldehyde or other fixative chemicals) may be applied to the cardiac tissue between the two jaws  502   a - b  in addition to or in substitution of the energy delivery. 
       FIG. 6  illustrates some embodiments of the energy delivery mechanism  501  of the device  500  described above with reference to  FIGS. 5A-50 . In some embodiments, the energy delivery mechanism  501  has a jaw  502  with a first jaw portion  503   a  and a second jaw portion  503   b , and the first and second jaw portions  503   a - b  include first and second electrical contacts  504   a - b , respectively, (identified collectively as “contacts  504 ”). Each of the first and second jaw portions  503   a - b  can have a shaft  506   a - b , respectively, and a grasping portion  508   a - b , respectively. The shafts  506   a - b  are configured to extend longitudinally along the length of the device and be manipulated to move the grasping portions  508   a - b  toward/away from each other. The shafts  506   a - b  and grasping portions  508   a - b  can be electrically conductive and coated with a dielectric material except for the areas of the contacts  504   a - b . Alternatively, the shafts  506   a - b  and grasping portions  508   a - b  can be made from a dielectric material with separate electrically conductive contacts  504   a - b  and wires in or on the shafts  506   a - b . The energy delivery mechanism  501  can further include a coiled sleeve  522  through which the shafts  506   a - b  and grasping portions  508   a - b  can extend. In operation, the grasping portions  508   a - b  can be closed (e.g., clamped together) by sliding advancing the coiled sleeve  522  distally toward the grasping portions  508   a - b  or opened (e.g., moved apart) by sliding (retracting) the coiled sleeve proximally away from the grasping portions  508   a - b . The grasping portions  508   a - b  can accordingly extend from the shafts  506   a - b  along a smooth bend  509   a - b , respectively, to facilitate the closing and opening of the grasping portions  508   a - b  via movement of the coiled sleeve  522 . The energy delivery mechanism may have only one of the electrical contacts  504   a - b  in some embodiments. 
     In operation, a common polarity can be applied to both contacts  504   a - b  in a single jaw  502  of one energy delivery mechanism  501 . As such, two energy delivery mechanisms  501  can be used as described above with respect to  FIGS. 5A-5D  to apply bipolar RF energy through a chord. Or, a common electrode can be used instead of one of the energy delivery mechanisms  501   a - b . Additionally, the contacts  504   a - b  of a single energy delivery element  501  may by biased at opposite polarities to focus the energy in the region of a chord between the contacts  504   a - b,    
     Leaflet Re-Shaping 
     Mitral valve regurgitation often happens because there is excess loose tissue in the posterior leaflet. Dr. Dwight McGoon of the Mayo Clinic developed a technique of excising a V-shaped section of the P 2  section of the posterior leaflet free edge and sewing the cut edges together. More recently, surgeons have simply folded the excess tissue into the ventricle and sewed the edges of that section together without cutting the leaflets, a technique sometimes called a “foldoplasty” or “dunkoplasty.” Several attempts have been made to use RF energy to shrink the leaflets, but the existing techniques do not provide appropriate control of the directionality of the shrinkage. For most patients with mitral prolapse due to excessive posterior leaflet tissue, it is desired to shrink the leaflet along the lateral-medial direction of its free edge, but not in the direction from the edge to the annulus (anterior-posterior). The present technology provides a mechanism to prevent shrinkage in the anterior-posterior direction, while encouraging shrinkage in the lateral-medial direction. Moreover, RF energy may modify the elastic modulus of the leaflet (e.g., make it stiffer) in a manner that may reduce the amount of prolapse. 
       FIGS. 7A-70  show a device  600  for controlled shrinkage of leaflets via application of energy and/or through the application of a chemical agent. As shown in  FIG. 7A , the device  600  includes a catheter  620  that can be introduced into the left atrium and two energy delivery arms  601  (identified individually as first and second arms  601   a  and  601   b ) having energy delivery elements  602  (identified individually as first and second energy delivery elements  602   a  and  602   b ). The energy delivery elements  602   a - b  can be configured to be pressed against a native leaflet of a heart valve, such as the posterior leaflet of a mitral valve, and each of the energy delivery elements  602   a - b  can include an electrode  604  and an aperture  606 . The energy delivery elements  602   a - b  can be individually secured against the leaflet with suction transmitted through aperture  606 . The energy delivery elements  602   a - b  can optionally include an extension  608  configured to wrap over the free edge of the leaflet and press the leaflet against the energy delivery element  602 . The electrodes  604  can be flexible, such as an electrically conductive mesh, so that they can be securely held against the leaflet. (See,  FIG. 7B .). The electrodes  604  can alternatively be a more rigid electrically conductive element. The energy delivery elements  602  may further include a face  609  having surface features  609   a  such as roughness, serrations, small spikes, or the like which engage the tissue and prevent it from shrinking along the length of the electrode  604  while energy is delivered, as shown in  FIG. 7B , The device  600  can further include an approximating mechanism  610  having a pull-wire system  611  designed to pull the two arms  601  together before applying energy, or to freely allow the arms  601  to move closer together as the tissue shrinks. The approximating mechanism can alternatively be any of the approximating mechanisms  110  described above with reference to  FIGS. 2 and 3 . The energy may be bipolar RF energy, monopolar RF energy, laser energy, ultrasonic energy, resistive heating of the electrodes, microwave energy, or other energy modalities. A chemical agent (e.g., phenol, glutaraldehyde or other fixative chemicals) may be applied to the cardiac tissue between the two energy delivery elements  602  in addition to or in substitution for the energy delivery. (See,  FIG. 7C .) 
     Surgical Applications of these Concepts 
     The annuloplasty, chordal shortening, and leaflet re-shaping techniques described above in accordance with the present technology can also be applied to open surgical and minimally-invasive surgical techniques. For example,  FIG. 8  shows a device  700  having a pair of surgical forceps with pointed electrodes  702  on the tips which the surgeon can insert into the annular tissue. The electrodes  702  are used to approximate the tissue and to deliver energy. Electrodes  702  are electrically isolated from the forceps body  704  so that energy can be delivered between the electrodes  702 . Alternatively, the electrodes  702  and arms  706  can be attached to a catheter or single-shafted instrument or the like (not illustrated), perhaps with a covering sleeve. This allows insertion through a thoracoscopic port for “Port-Access” surgery, and/or insertion through a purse-string incision in the wall of the left atrium for beating-heart surgery. The catheter or instrument shaft may be designed to be flushed to prevent the introduction of air into the bloodstream, and to prevent the backflow of blood out of the device. In some embodiments, the catheter may have an overall shaft diameter of 3-10 mm, and the shaft might be made flexible to accommodate varying surgical angles. The catheter can also be a disposable device or a reusable device. Similarly, the other concepts described above could be adapted to use in the surgical setting. The energy may be bipolar RF energy, monopolar RF energy, laser energy, ultrasonic energy, resistive heating of the electrodes, microwave energy, or other energy modalities, A chemical agent (e.g., phenol, glutaraldehyde or other fixative chemicals) may be applied to the cardiac tissue between the two electrodes in addition to or in substitution for the energy delivery. 
     Combination of these Concepts with Other Technologies 
     It should be noted that in performing mitral valve repair, it is often desirable to perform several different repair techniques in the same procedure. For example, the cardiac tissue shrinkage techniques described in this disclosure could be combined with a chordal shrinking procedures, an edge-to-edge repair with a MitraClip® device (Abbott Vascular) or other device, or other procedures.