Abstract:
Device, system and method for evaluating the effectiveness of tissue ablations of a heart of a patient. The tissue is clamped between a pair of opposing jaws. A portion of the tissue is ablated at a first generally linear position on the tissue by applying ablative energy to two of a plurality of elongate electrodes, each of the two of the plurality of elongate electrodes being coupled in opposing relationship to each other and the pair of opposing jaws, respectively. An effectiveness of the ablation is sensed at a second generally linear position on the tissue with at least one of the plurality of elongate electrodes positioned on one of the pair of opposing jaws. The second linear position on the tissue is laterally distal to the first linear position on the tissue with respect to the atrium of the heart.

Description:
FIELD 
       [0001]    This disclosure relates to an ablation device and method for creating a lesion and, more particularly, and to such an ablation device and method for creating an elongate lesion. 
       BACKGROUND 
       [0002]    The action of the heart depends on electrical, and cardiac muscle cell contractile conduction within the heart tissue. In certain people at certain times, electrical signals within heart tissue may not function properly and can create cardiac arrhythmias. Ablation of cardiac conduction pathways in the region of tissue where the signals are malfunctioning may reduce or eliminate such faulty signals. Ablation involves creating lesions on tissue during surgery. To provide effective therapy, surgically created lesions may block the transmission of cardiac contractions. 
         [0003]    Ablation may be accomplished in several ways. Sometimes ablation is necessary only at discrete positions along the tissue, is the case, for example, when ablating accessory pathways, such as in Wolff-Parkinson-White syndrome or AV nodal reentrant tachycardias. At other times, however, ablation is desired along a line (either straight or curved), called linear ablation. (In contrast to linear ablation, ablations at discrete positions along the tissue are called non-linear or focal ablations.) One way is to position a tip portion of the ablation device so that an ablation electrode is located at one end of the target lesion line. Then energy is applied to the electrode to ablate the tissue adjacent to the electrode. The tip portion of the electrode is then dragged or slid along the tissue while delivering energy to a new position at the other and of the target lesion line. A second way of accomplishing linear ablation is to use an ablation device having a series of spaced-apart band or coil electrodes that, after the electrode portion of the ablation device has been properly positioned, are energized simultaneously or one at a time to create the desired lesion. If the discrete electrodes are positioned adequately close together, a continuous lesion may be formed. 
         [0004]    In addition, electrical pathways through tissue are often not merely or primarily in the surface of the tissue, but rather may run throughout the depth of the tissue. As such, in order to block or cut an adequate number of electrical pathways in order to reduce or prevent electrical propagation, the lesion may need to reach a particular depth in the tissue. In the past, the need to create relatively deep lesions has been addressed by applying ablation energy for relatively long periods of time. In addition, some ablation elements have been developed which allow for a focal zone for ablation energy to be adjusted. When the focal point may be adjusted, relatively deep lesions may be formed by adjusting the focal point to be relatively deeper in the tissue. 
         [0005]    Common areas of the heart that are treated using surgically created continuous linear lesions are located in the atria. This may be the case for atrial fibrillation, which is a common form of arrhythmia. The aim of linear ablation in the treatment of atrial fibrillation may be to reduce the total mass of electrically connected atrial tissue below a threshold believed to be needed for sustaining multiple reentry wavelets. Linear transmural lesions may be created between electrically non-conductive anatomic landmarks to reduce the contiguous atrial mass. Transmurality is achieved when the full thickness of the target tissue is ablated. 
         [0006]    Before the procedure is complete, the area of the heart may be tested to confirm a conduction block or see if the ablation is effective and eliminates the undesired electrical signals. Present methods to confirm conduction block include the use of electrophysiology catheters to evaluate pulmonary vein isolation lesions and monopolar and bipolar focal probes using pacing or electrogram techniques, and are described below. 
       SUMMARY 
       [0007]    An ablation system has been developed which may improve the ability to create a transmural lesion in tissue while reducing the time required and avoiding damage to tissue which is undesirable to ablate. In particular, the ablation system may utilize ultrasonic monitoring to monitor the elasticity and/or hydration of the tissue. The less the elasticity and hydration of the tissue, the less time may be required to achieve a transmural lesion. This may reduce the time spent ablating the tissue, as well as reduce the likelihood of excessive ablation being delivered. In addition, the impedance, inductance and/or capacitance of the tissue may be monitored in the target tissue. Based on changes in these electrical characteristics, the effectiveness of the lesion may be determined. In addition, a sensing lead may monitor an amplitude or waveform of an electrogram in the tissue. Based on changes in the amplitude or waveform, further determinations may be made as to the effectiveness of the ablation process so far, as well as further deliveries of ablation energy which may be required. 
         [0008]    A controller may factor in the electrical characteristics to make a determination of the effectiveness or completeness of a lesion at a particular location. Based on the determination, the controller may automatically adjust the focal zone of the ablation element to a new depth and continue forming the lesion. The refocusing of the ablation element may continue automatically until the controller determines that the lesion is adequately transmural. In this way, user input may be reduced, as well as time. 
         [0009]    Moreover, the controller may be sensitive to tissue which may be undesirable to ablate because the tissue does not naturally propagate electrical energy and because the tissue may be utilized for other, potentially important purposes. Such tissue which may be undesirable to ablate may include blood vessels, nerves and the like. Based on the sensed electrical and physical parameters, the controller may automatically control the focal zone of the ablation element to prevent ablation of tissue which is undesirable to ablate. Such sensed parameters may include Doppler flow detection of coronary arteries or the coronary sinus flow, for example. The controller may direct, focus, focal heating to occur around any such regions of high linear blood flow. 
         [0010]    In an embodiment, the present invention provides an ablation device for creating an elongate lesion along a path in tissue of a patient having a controller and a source of ablation energy. An actuatable transducer operatively coupled to the controller and the source of ablation energy, the actuable transducer being movable with respect to the tissue of the patient. A sensor operatively coupled to the controller, the sensor producing an output indicative of at least partial completion of at least a portion of the elongate lesion. The controller controls delivery of ablation energy to a particular portion of the tissue along the path by controlling a position of the actuable transducer along the path based at least partially upon the output of the sensor indicative of a degree of the at least partial completion of at least a portion of the lesion along the path. 
         [0011]    In an embodiment, the controller controls the position of the actuable transducer along the path by moving the actuable transducer with respect to the path based at least partially upon a degree of completion of at least a portion of the lesion along the indicated by the output of the sensor. 
         [0012]    In an embodiment, a positioning mechanism, the controller controls the position of the actuable transducer on the path by moving the actuable transducer with the positioning mechanism based at least partially upon a degree of completion of at least a portion of the lesion along the indicated by the output of the sensor. 
         [0013]    In an embodiment, the positioning mechanism comprises a track positioned with respect to the path and wherein the controller moves the actuable transducer along the track based at least partially upon a degree of completion of at least a portion of the lesion along the path indicated by the output of the sensor. 
         [0014]    In an embodiment, the positioning mechanism moves the actuable transducer to one of a plurality of selectable locations on the track based at least partially upon the completion of the lesion indicated by the output of the sensor. 
         [0015]    In an embodiment, the controller additionally controls delivery of ablation energy by controlling an amount of the ablation energy delivered by the actuable transducer at a particular location along the path. 
         [0016]    In an embodiment, the actuatable transducer has a focal point and wherein the controller controls a distance of the focal point based at least partially upon the completion of the lesion indicated by the output of the sensor. 
         [0017]    In an embodiment, the actuable transducer comprises an array of selectively actuable transducer elements. 
         [0018]    In an embodiment, the controller controls delivery of ablation energy to a particular portion of the tissue along the path by selectively activating the selectively actuable transducer elements based at least partially upon the completion of the lesion by the output of the sensor. 
         [0019]    In an embodiment, the sensor is an ultrasound sensor. 
         [0020]    In an embodiment, the condition of the tissue indicated by the ultrasound sensor is indicated by an ultrasound image. 
         [0021]    In an embodiment, the sensor is a sensor which senses an acoustical impedance of the tissue by transmitting a sound wave into the tissue and measuring a resistance of the tissue to the sound wave. 
         [0022]    In an embodiment, the acoustical impedance of the tissue indicates a hydration of the tissue. 
         [0023]    In an embodiment, the acoustical impedance of the tissue indicates an elasticity of the tissue. 
         [0024]    In an embodiment, the present invention provides a method for creating an elongate lesion along a path of tissue of a patient using an ablation device having an actuatable transducer operatively coupled to a controller and a source of ablation energy, and a sensor operatively coupled to the controller. The actuable transducer is positioned with respect to the path of the tissue. Ablation energy is delivered to a portion of the path of the tissue with the actuatable transducer. A degree of completion of the lesion in the tissue proximate the portion of the path of the tissue is sensed. The position of the actuable transducer along the path is moved when the degree of completion indicates the lesion proximate the portion of the path of the tissue is complete. Then repeat by returning to deliver ablation energy step until the elongate lesion is complete along an entirety of the path. 
         [0025]    In an embodiment, the moving step is controlled by the controller. 
         [0026]    In an embodiment, the moving step comprises the controller controls a positioning mechanism coupled to the actuatable transducer. 
         [0027]    In an embodiment, the moving step further comprises the positioning mechanism moving the actuable transducer to one of a plurality of selectable locations on a track based on the degree of completion of the lesion indicated by the sensor. 
         [0028]    In an embodiment, the delivering ablation energy step further comprises the controller controlling an amount of the ablation energy delivered by the actuable transducer at a particular location along the path. 
         [0029]    In an embodiment, the actuatable transducer has a focal point and wherein the delivering ablation energy step further comprises the controller adjusting a distance of the focal point based on the degree of completion of the lesion indicated by the sensor. 
         [0030]    In an embodiment, the controller is operatively coupled to the positioning mechanism and where the moving step further comprises the controller controlling the positioning mechanism to position the transducer array based on the degree of completion of the lesion indicated by the sensor. 
         [0031]    In an embodiment, the sensor is an ultrasound sensor. 
         [0032]    In an embodiment, the sensing step senses a degree of completion of the lesion in the tissue proximate the portion of the path of the tissue based on an ultrasound image generated by the ultrasound sensor. 
         [0033]    In an embodiment, the sensor senses an acoustical impedance of the tissue by transmitting a sound wave into the tissue and measuring a resistance of the tissue to the sound wave. 
         [0034]    In an embodiment, the acoustical impedance indicates a hydration of the tissue, and wherein the sensing step senses a degree of completion of the lesion in the tissue proximate the portion of the path of the tissue based on the hydration of the tissue. 
         [0035]    In an embodiment, the acoustical impedance indicates an elasticity of the tissue, and wherein the sensing step senses a degree of completion of the lesion in the tissue proximate the portion of the path of the tissue based on the elasticity of the tissue. 
         [0036]    In an embodiment, the present invention provides a method for creating an elongate lesion along a path of tissue of a patient using an ablation device comprising an actuatable transducer operatively coupled to a controller and a source of ablation energy, and a sensor operatively coupled to the controller. The actuable transducer is selectively actuated at a first selected location along the path. First, a degree of completion of the lesion in the tissue proximate the first selected location along the path of the tissue is sensed. The actuable transducer at the first selected location along the path is deactivated based at least partially upon the degree of completion of the lesion proximate the first selected location obtained in the sensing step. The actuable transducer is selectively actuated at a new selected location along the path based at least partially upon the degree of completion. Then a degree of completion of the lesion in the tissue proximate the new selected location along the path of the tissue is sensed. The actuable transducer is selectively deactivated at the new selected location along the path based at least partially upon the degree of completion of the lesion proximate the first selected location. Then returning to the selectively actuating the actuable transducer at the new selected location step until the elongate lesion is complete along an entirety of the path. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a schematic drawing of a heart with surgically created lesions; 
           [0038]      FIG. 2  is an ablation device for creating a lesion; 
           [0039]      FIG. 3  is a side-view of an ablation member of the ablation device of  FIG. 2 ; 
           [0040]      FIGS. 4A-4D  are front-views of different embodiments of the ablation member of  FIG. 3 ; 
           [0041]      FIG. 5  is a block diagram a controller of the ablation device of  FIG. 2 ; 
           [0042]      FIGS. 6A and 6B  are side-views of an ablation device; and 
           [0043]      FIG. 7  is a flowchart of a method of using an ablation device. 
       
    
    
     DESCRIPTION 
       [0044]      FIG. 1  illustrates a portion of heart  10  as viewed from facing the back of a patient. Heart  10  includes tissue  11  forming left superior pulmonary vein  12 , left inferior pulmonary vein  14 , right superior pulmonary vein  16  and right inferior pulmonary vein  18 . Newly oxygenated blood returns from the lungs into the left atrium through right and left pulmonary veins  12 ,  14 ,  16 ,  18 . Heart  10  further includes left atrial myocardium and myocardial extensions  20  onto pulmonary veins  12 ,  14 ,  16 ,  18 . In order to treat atrial fibrillation, transmural lesion  22  may be formed on the left atrium (LA), proximal to the left pulmonary veins  12 ,  14  and transmural lesion  24  may be formed on the left atrium (LA), proximal to the right pulmonary veins  16 ,  18 . 
         [0045]      FIG. 2  is an illustration of an embodiment of ablation device  26  (not including a microprocessor  66  nor function generator/amplifier  64 ) incorporating ablation member  28  positioned on head  30  of neck  32 . In an embodiment, neck  32  is flexible, and both head  30  and neck  32  are sized to permit insertion of head  30  and neck  32  through an incision and into the thoracic cavity to a point proximate heart  10 . Source of ablation energy  34  is operatively coupled to ablation member  28  by hard-wired connection down neck  32 . In alternative embodiments, ablation device  26  does not incorporate neck  32 , with ablation member  28  operatively coupled to source of ablation energy  34  by way of other modes known in the art. 
         [0046]    In various embodiments, source of ablation energy  34  is a source of ultrasound energy, and ablation member  28  is configured to deliver ultrasound energy. In an embodiment, source of ultrasound energy  34  is a source of high intensity focused ultrasound, known in the art as “HIFU”, and ablation member  28  is configured to deliver high intensity focused ultrasound energy. 
         [0047]      FIG. 3  is a side-view of an embodiment of ablation member  28 . In this embodiment, ablation member  28  is a HIFU transducer configured to focus ultrasound energy at adjustable focus zones  36 ,  38 ,  40 . Focus zones  36 ,  38 ,  40  increase in distance from surface  41  of ablation member  28 . In various embodiments, ablation member  28  is configured to focus ultrasound energy to discrete focal zones. In such embodiments, the discrete focal zones may have two or more focal zones. In various alternative embodiments, ablation member  28  does not have discrete focal zones, instead allowing a user to adjust the focal point to a variable desired distance from the ablation member. 
         [0048]    In the illustrated embodiment, ablation member  28  is an ultrasonic parabolic transducer. The parabolic configuration permits relatively easier focusing of ultrasound energy. In alternative embodiments, ablation member  28  may incorporate alternative profiles as appropriate, including planar, conic and “half-pipe” configurations, half-pipe being related to planar but with two opposing edges curved. In the illustrated embodiment, focal points may be determined on the basis of their distance from surface  41 . 
         [0049]      FIGS. 4A-4D  are front views of various embodiments of ablation member  28  incorporating multiple independently steerable transducer elements. The perspective drawings of  FIGS. 4A-4D  are directly perpendicular to surface  41 . As such,  FIGS. 4A-4D  may be utilized in parabolic, planar, “half-pipe” and conic transducers, or any other appropriate transducer. 
         [0050]      FIG. 4A  is an array of square elements  44 . As depicted, square elements  44  are formed into a larger square  46 , but may, in alternative embodiments, be formed into any desirable shape comprised of multiple squares. Alternatively, square elements  44  may be rectangles of desirable size. 
         [0051]      FIGS. 4B-4D  are circular arrays  48  of wedge elements  50 . In the embodiment of  FIG. 4B , wedge elements  50  extend to center point  52 . In the embodiment of  FIG. 4C , wedge elements  50  extend only to mid-point  56 . In an embodiment, mid-point is two-thirds of the way from edge  58  and center point  52 . In alternative embodiments, mid-point is between one-third of the distance from edge  58  to center point  52  and three-quarters of the distance from edge  58  to center point  52 . In further alternative embodiments, mid-point  56  is anywhere between edge  58  and center point  52 . In an alternative embodiment of  FIG. 4C , circular element  60  is positioned in the middle of circular array  48 . In the embodiment of  FIG. 4D , related to  FIG. 4C , wedge elements  50  extend only part-way to center point  52 , while center wedge elements  62  occupy the remainder of circular array  48 , in general the same area occupied by circular element  60  in  FIG. 4C . 
         [0052]    All of the embodiments of  FIG. 4A-4D  may be configured so that transducer elements may be focused at various distances from surface  41  or primary focal point  38 . While the various embodiments of  FIGS. 4A-4D  may be utilized in many different shapes of transducers, as detailed above, certain embodiments of  FIGS. 4A-4D  may be particularly advantageous in certain circumstances. For instance, while square elements  44  of  FIG. 4A  may be advantageous in a planar or half-pipe transducer, wedge elements  54  combined with center wedge elements  62  of  FIG. 4D  may be advantageous in a parabolic transducer. 
         [0053]      FIG. 5  is a block diagram of ablation device  26 . Ablation element  28  is coupled to function generator/amplifier  64 , which supplies ablation energy to ablation element  28 . In an embodiment, function generator/amplifier  64  is a source of ablation energy and supplies high intensity focused ultrasound energy to transducer  28 . Microprocessor  66  (controller) is coupled to both function generator/amplifier  64  and transducer  28 . In an alternative embodiment, microprocessor is coupled only to transducer  28 . Microprocessor  66  is operable to control both the delivery of ablation energy from function generator/amplifier  64  and the configuration of ablation element  28 , in particular the focal zone. Sensor  68  is coupled to microprocessor  66 . Microprocessor may control function generator/amplifier  64  and ablation element  28  on the basis of internal programming and on the basis of feedback from sensor  68 . 
         [0054]    In various embodiments, pulse-echo sensor  68  senses various acoustic characteristics of the tissue  11  of heart  10  which is being ablated by ablation device  26 . In an embodiment, sensor  68  senses elasticity and hydration of the tissue. In alternative embodiments, sensor  68  senses impedance, inductance and/or capacitance of the tissue. In such an embodiment, sensor  68  may incorporate conventional features of commercial frequency analyzers and multi-meters. In further alternative embodiments, sensor  68  senses an electrogram generated by the heart of the patient. In such an embodiment, sensor  68  may incorporate conventional electrogram detection electrodes and hardware well known in the art. 
         [0055]    In various embodiments, sensor  68  may incorporate various ones of the above-described detection elements. In such an embodiment, all of the sensor information may be provided to microprocessor  66 , which may utilize various combinations of the information in order to control ablation element  28  and function generator/amplifier  64 . In an embodiment, sensor  68  may combine a hydration detector, an impedance detector and an electrogram detector, and microprocessor  66  may control the delivery of ablation energy on the basis of the information provided by those detectors. 
         [0056]    Data provided to microprocessor  66  by sensor  68  may give microprocessor information regarding the nature of the tissue of heart  10  which is to be ablated. On the basis of that information, ablation energy may be delivered at various intensities and for various lengths of time. For instance, it is possible that it may be desirable in tissue with relatively high hydration and/or relatively high elasticity to ablate at relatively high power for relatively short periods of time. In tissue with relatively low hydration and/or elasticity it may be desirable to ablate at relatively low power for relatively long periods of time. 
         [0057]    In addition, microprocessor  66  may determine a thickness of the tissue of heart  10  to be ablated on the basis of data from sensor  68 . For instance, atrial tissue which is relatively thick may be greater than five millimeters (5 mm) in thickness may characterize thick tissue. By contrast, tissue which is relatively thin may be less than one millimeter (1 mm) in thickness. Information provided by sensor  68  may be utilized to determine a relatively precise estimate of the thickness of the tissue. On the basis of this determination, microprocessor  66  may thus select an appropriate number of focal zones for ablation element  28  to ablate in order to attain transmurality in the tissue. 
         [0058]    In addition, sensor  68  may provide microprocessor  66  information relating to the process towards ablating tissue during an ablation procedure. In particular, when sensor  68  measures impedance and electrogram data, microprocessor  66  may determine progress in forming the lesion. As the lesion becomes relatively more complete, impedance in the tissue tends to rise while the amplitude of the sensed electrograms tends to decrease. As such, in various embodiments, microprocessor  66  may determine that a lesion is complete in a particular location when the measured impedance rises above a certain threshold and the measured electrogram amplitude falls below a certain threshold. In various alternative embodiments, other sensed factors may be utilized in determining that a lesion is complete at a particular location. 
         [0059]    Moreover, on the basis of sensed characteristics of the tissue, microprocessor  66  may determine that particular tissue should not be ablated at all. Ablation device  26  may be utilized in locations other than heart  10 . Particularly in such circumstances, the tissue to be ablated may include, for instance, blood vessels and nerves, which may be undesirable to ablate due to the physiological impact on the patient. In addition, blood vessels and nerves may be unable to propagate the kinds of electrical signals which are desired to be blocked in ablation. Because tissue such as blood vessels and nerves may possess different characteristics than tissue to be ablated, sensor  68  may provide data to microprocessor  66  which may be utilized by microprocessor  66  to determine that ablation energy should not be applied in certain locations. 
         [0060]    In various embodiments, microprocessor  66  may determine that blood vessels or nerves are at particular depths within the target tissue. In such circumstances, microprocessor  66  may control the focal zones at which ablation element  28  delivers ablation energy to ablate tissue, for instance, above and below a blood vessel or nerve, but not ablate the blood vessel or nerve itself. 
         [0061]    As illustrated in  FIG. 1 , it may be desirable to create an elongate lesion  22 ,  24  in tissue  11  of heart  10 . In circumstances where lesion  22 ,  24  need not be elongate, ablation device  26  may be positioned once and microprocessor  66  may control the delivery of ablation energy and the focal zone of ablation element  28  in order to create a discrete transmural lesion. In circumstances where an elongate lesion may be desirable, various embodiments of ablation device  26  may provide it without a user having to manually move ablation device  26 . In an embodiment incorporating an array of square elements  44 , square elements  44  may be configured in an elongate configuration sized to create the desired lesion. In an embodiment, square elements  44  may be formed in the “half-pipe” configuration to enhance the creation of a focal zone. 
         [0062]      FIGS. 6A and 6B  show an alternative embodiment of ablation device  26  which incorporates ablation element  28  attached to automatic repositioning system  70 . In such embodiments, ablation element  28  may be an ablation element  28  of many different sizes and configurations, and may be moved to different linear positions in order to create a linear transmural lesion. 
         [0063]    In  FIG. 6A  ablation element  28  is coupled to screw drive  72 . Screw drive  72  functions in a manner common to screw drives known in the art. By actuating screw  74  clockwise and counterclockwise, ablation element  28  moves up and down screw  74 . Screw  74  is coupled to motor  76  which provides motive power to turn screw  74 . In an embodiment, motor  76  is coupled to microprocessor  66 , which may initiate movement of screw  74  and thus ablation element  28  on the basis of data from sensor  68 . 
         [0064]    In  FIG. 6B  ablation element  28  is connected to cable drive  78 . Cable drive  78  functions in a manner common to cable drives known in the art. Cable  80  is wound around pulley  82  and is coupled to motor  84 . When motor  84  moves cable  80  ablation element  28  moves with respect to pulley  82 . As with motor  76 , motor  84  is, in an embodiment, coupled to and controlled by microprocessor  66 . 
         [0065]    Alternative embodiments of devices which may move ablation element  28  to different locations are contemplated. In cases involving automatic repositioning, ablation element  28  may be positioned at a first location, at which a transmural lesion may be created by varying the focal zone until transmurality is achieved. Once transmurality is achieved in the first location, ablation element  28  is repositioned to a second location, where a second transmural location is created. Additional transmural locations may be created at additional locations, such that ultimately, once all transmural lesions have been created, the transmural lesions are in contact with each other in order to create a single elongate transmural lesion. In alternative embodiments, ablation element  28  may be steadily moved among various locations, repeating visits to various locations as a transmural lesion is gradually formed over the length of the elongate lesion. In automatic repositioning embodiments, a user of ablation device  26  may program microprocessor  66  with a desired length of the elongate transmural lesion. 
         [0066]    In various alternative embodiments, ablation device may be configured to curvilinear lesions. In an embodiment, cable drive  78  may be adapted to curve, with cable  80  pulling ablation element  28  in a curved pattern. In such an embodiment, the curved elongate lesion may be formed in the same manner as described with respect to the linear elongate lesion described above. In various embodiments, ablation device  26  may be reconfigurable by attaching a new automatic repositioning system  70 . Alternatively, automatic reposition system  70  may be capable of having its shape changed. In such an embodiment, automatic repositioning system  70  may be flexed or otherwise adjusted into various shapes. 
         [0067]    In various further embodiments, repositioning system  70  is not automatic but manually controlled by a user. In such an embodiment, ablation device  26  may provide a prompt to a use to manipulate repositioning system  70  to reposition ablation element  28 . The user prompt may be any conventional prompt known in the art, including but not limited to a tone or other sound, a light or other visual indicator, or a vibration or other mechanical output. 
         [0068]      FIG. 7  is a flowchart of a method for ablating tissue utilizing ablation device  26 . Tissue thickness is determined ( 700 ) at a tissue location. Ablation element  28  is focused ( 702 ) by microcontroller  66  to a focal zone and ablation energy is delivered ( 704 ) from function generator/amplifier  64 . Sensor  68  measures ( 706 ) characteristics of tissue  11 , and microcontroller  66  determines ( 708 ) if an appropriate lesion has been formed at the current focal zone. If not, ablation energy is delivered ( 704 ). If the lesion has been fanned at the focal zone, microcontroller  66  determines ( 710 ) if the lesion is transmural by referencing data from sensor  68 . If the lesion is not transmural the focal zone is adjusted ( 712 ) to a new focal zone and ablation energy is delivered ( 704 ). If the lesion is transmural then microcontroller  66  determines ( 714 ) if the lesion is complete. If the lesion is not complete then ablation element  28  is repositioned ( 716 ) to a new location and ablation energy is delivered ( 704 ). If the lesion is complete then the ablation procedure terminates ( 718 ). 
         [0069]    In various alternative embodiments, the above procedure may be varied dependent on the circumstances. For instance, it may be desirable to first reposition ( 716 ) ablation element  28  rather than adjusting ( 712 ) the focal zone. In such an embodiment, repositioning ( 716 ) may be swapped with adjusting ( 712 ), and the flowchart followed normally. In further alternative embodiments, ablation element  28  could be mounted on a robotically controlled manipulator for minimally invasive access. 
         [0070]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present invention.