Abstract:
Methods and apparatus for treating cardiac arrhythmias by ablating myocardial fibers within a pulmonary vein through use of a catheter. For example, the ablative element of the catheter is rotated around an axis to ablate a partial or complete loop of tissue within the pulmonary vein so as to block the transmission into the cardiac tissue of electrical signals originating or propagating from myocardial fibers within a pulmonary vein. In other examples, signals from the catheter are monitored to determine whether the ablative element is in contact with the wall of the pulmonary vein. Additional apparatus allow precise angular positioning of the ablative element within the lumen of the pulmonary vein. Apparatus and methods for detecting the properties of the tissue within the pulmonary vein, locating myocardial fibers, selectively ablating such fibers, and determining if such fibers are ablated are also disclosed.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS  
       [0001]    The present application claims the benefit of U.S. Application No. 60/285,845, filed Apr. 23, 2001, the disclosure of which is hereby incorporated by referenced herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to apparatus and methods for treatment of cardiac arrhythmias such as atrial fibrillation.  
           [0003]    The normal contractions of the heart muscle arrive from electrical impulses generated at a focus within the heart and transmitted through the heart muscle tissue or “myocardial” tissue. In some individuals, fibers of myocardial tissue extend from the wall of the left atrium along the wall of the pulmonary vein. For example, the tissue of the pulmonary vein normally merges with the myocardial tissue of the heart wall at a border near the opening or ostium of the pulmonary vein. In some individuals, however, elongated strands of myocardial tissue extend within the wall of pulmonary vein in the distal direction (away from the heart) so that the strands of myocardial tissue project beyond the normal border. It has been recognized that atrial fibrillation can be caused by an abnormal electrical focus in such strands of myocardial tissue. Electrical signals propagate from such an abnormal focus proximally along one or more strands of myocardial tissue. Because these strains of myocardial tissue merge with myocardial tissue of the heart wall, the abnormal electrical signals propagate through the myocardial tissue in heart wall itself, resulting in abnormal contractions.  
           [0004]    It has been recognized that this condition can be treated by locating the abnormal focus and ablating (i.e., killing or damaging) the tissue at the focus so that the tissue at the focus is replaced by electrically inert scar tissue. However, the focus normally can be found only by a process of mapping the electrophysiological potentials within the heart and in the myocardial fibers of the pulmonary vein. There are significant practical difficulties in mapping the electrical potentials. Moreover, the abnormal potentials which cause atrial fibrillation often are intermittent. Thus, the physician must attempt to map the abnormal potentials while the patient is experiencing an episode of atrial fibrillation.  
           [0005]    Another approach that has been employed is to ablate the tissue of the heart wall, so as to form a continuous loop of electrically inert scar tissue extending entirely around the region of the heart wall which contains the ostium of the pulmonary veins, so that the abnormal electrical impulses do not propagate into the remainder of the atrial wall, outside the loop. In a variant of this approach, a similar loop like scar can be formed around the ostium of a single pulmonary vein or in the wall of the pulmonary vein itself proximal to the focus so as to block propagation of the abnormal electrical impulses. Such scar tissue can be created by forming a surgical incision; by applying energies such as radio frequency energy, electrical energy, heat, intense light such as laser light; cold; or ultrasonic energy. Chemical ablation agents also can be employed. Techniques which seek to form a loop-like lesion to form a complete conduction block between the focus and the major portion of the myocardial tissue are referred to herein as “loop blocking techniques.” 
           [0006]    Loop blocking techniques are advantageous because they do not require electrophysiological mapping sufficient to locate the exact focus. However, if a complete loop is not formed, the procedure can fail. Moreover, ablating complete, closed loops without appreciable gaps presents certain difficulties. Thus, some attempts to form a complete loop of ablated tissue around the entire circumference of the pulmonary vein have left significant unablated regions and thus have not formed a complete conduction block. Other attempts have resulted in burning or scarring of adjacent tissues such as nerves. Moreover, attempts to form the required scar tissue using some types of ablation instruments such as radio frequency ablation and unfocused ultrasonic ablation have caused thromboses or stenosis of the pulmonary vein. The potential for these undesirable side effects varies directly with the amount of tissue ablated. Moreover, the amount of energy which must be applied in an ablation procedure varies directly with the amount of tissue ablated. Particularly where an ablation element must be introduced into the heart through a catheter, the size of the ablation element and hence the energy delivery capacity per unit time of the ablation element is limited. While these difficulties can be alleviated or eliminated by the use of focused ultrasonic ablation as taught, for example, in copending, commonly assigned U.S. Provisional Patent Application No. 60/218,641 filed Jul. 13, 2000, now U.S. patent application Ser. No. 09/905,227 “Thermal Treatment Methods and Apparatus With Focused Energy Application”; Ser. No. 09/904,963 “Energy Application With Inflatable Annular Lens”; and Ser. No. 09/904,620 “Ultrasonic Transducers,” the disclosure of which are incorporated by reference herein, further alternatives would be desirable.  
         SUMMARY OF THE INVENTION  
         [0007]    One aspect of the present invention provides apparatus for treating tissue adjacent a tubular anatomical structure having a lengthwise direction as, for example, for treating tissue of the pulmonary vein wall or tissue of the heart wall in the region surrounding the ostium of the pulmonary vein. The apparatus according to this aspect of the present invention preferably includes a carrier catheter and an anchor. When the device is in an operative condition, the carrier catheter is linked to the anchor so that the carrier catheter is movable with respect to the anchor over a predetermined path of motion. Preferably, the carrier catheter is rotatable with respect to the anchor around a first axis. The carrier catheter may be substantially constrained against movement relative to the anchor transverse to the first axis. The anchor is adapted to engage the wall of the tubular anatomical structure, or another adjacent bodily structure, so that the first axis extends generally in the lengthwise direction of the tubular anatomical structure. The apparatus also includes a local treatment device adapted to confront tissue of the subject at a point and treat tissue at one or more spots adjacent such point. When the device is in an operative condition, the local treatment device is remote from the first axis. The local treatment device desirably projects from the carrier catheter in a direction transverse to the first axis. Thus, the treatment device will trace a generally arcuate path around the first axis when the carrier catheter is rotated relative to the anchor. The local treatment device may include an ultrasonic emitter, RF ablation electrode, optical fiber, chemical applicator or even a mechanical device such as a blade adapted to engage tissue to a controlled depth.  
           [0008]    In a particularly preferred arrangement, the anchor is affixed to an elongated guide structure such as a guide wire. The carrier catheter desirably has a first lumen which receives the guide wire so that the carrier catheter is rotatable about the guide wire. In one arrangement, the local treatment device is carried on a treatment catheter separate from the carrier catheter. The carrier catheter may have a separate carrier catheter lumen extending generally parallel to the guide lumen. A port may be provided in the side wall of the carrier catheter adjacent the distal end thereof. The port communicates with the treatment catheter lumen. In use, the treatment catheter is forced distally within the treatment catheter lumen after the carrier catheter is in place. As the treatment catheter is forced distally, the distal end of the treatment catheter bends outwardly through the hole in the carrier catheter. The local treatment device is carried at or near the distal end of the treatment catheter so that the local treatment device is moved radially outwardly, away from the guide lumen when the treatment catheter is forced distally. In other arrangements, the local treatment device may be carried on a flexible member mounted to the carrier catheter itself and the flexible member may be deformed so as to bend it outwardly, away from the guide lumen.  
           [0009]    The treatment catheter or member carrying the local treatment device desirably is provided with a sensor such an electrode which can be used to detect engagement of the treatment catheter or other member with the tissue. For example, when such an electrode is brought into engagement with cardiac tissue, the electrode will pick up electrophysiological potentials present in the cardiac tissue.  
           [0010]    Most preferably, the apparatus includes a device for controlling or monitoring the rotation of the carrier catheter relative to the anchor or relative to the patient himself. For example, a device for converting linear motion to rotary motion may be connected between the carrier catheter and the guide structure. One such device, commonly referred to as a “Yankee screwdriver” or “New England screwdriver” mechanism includes a generally helical cam surface on one member and a cam follower on the other member so that as the guide catheter is moved distally and proximally along the guide structure, the guide catheter rotates by a known amount per unit movement. In another arrangement, the carrier catheter or treatment catheter is provided with a sensor arranged to detect a magnetic or electromagnetic field and to provide one or more signals which vary depending upon the alignment of the sensor with the field. Provided that a constant field or field varying in known manner is imposed through the patient, the rotation of the carrier catheter can be monitored by monitoring the one or more signals from such a sensor.  
           [0011]    In a particularly preferred arrangement, the apparatus includes a sensor for determining properties of tissue surrounding the tubular anatomical structure. The sensor desirably is linked to the carrier catheter when the sensor is in an operative condition. The sensor may be, for example, an ultrasonic, electrical, optical or other device. Thus, by rotating the first axis while the sensor is operating, the tissue surrounding the tubular anatomical structure can be mapped. In particular, for apparatus intended to be used in treatment of atrial fibrillation, the sensor may be operative to detect differences between regions of a pulmonary vein wall which contain myocardial fibers and other regions which do not contain myocardial fibers. As described in co-pending, commonly assigned U.S. provisional patent application Ser. No. 60/265,480, filed Jan. 31, 2001, now U.S. patent application Ser. No. 10/062,693 “Pulmonary Vein Ablation With Myocardial Tissue Locating,” the disclosure of which is hereby incorporated by reference herein, the myocardial fibers typically are located in only a portion of the pulmonary vein wall. Once the fibers are located, the treatment device can be actuated to ablate or otherwise treat the vein wall only over a portion of the vein wall circumference. The sensor may be a local sensor arranged to detect a property of the tissue in a local region immediately adjacent the sensor. Thus, by actuating the sensor while rotating the carrier catheter, a map of tissue property against rotational position of the carrier catheter can be acquired by plotting the signals acquired from the sensor against rotational position of the carrier catheter. The sensor may be carried on the treatment catheter. Indeed, the elements discussed above with reference to the treatment catheter may also serve as the sensor. For example, where an electrode is provided on the treatment catheter, the electrode can be used to map electrical potentials around the circumference of a pulmonary vein. Alternatively or additionally, the same ultrasonic transducer used in an ultrasonic ablation device can be used as a ultrasonic mapping element.  
           [0012]    Further aspects of the present invention provide methods of treating tissue adjacent a tubular anatomical structure as, for example, the tissue of a pulmonary vein wall or the tissue of the heart surrounding the ostium of the pulmonary vein. Methods according to this aspect of the present invention desirably include the steps of positioning an anchor within the tubular anatomical structure and moving the carrier catheter along a predetermined path of motion relative to the anchor, as, for example, by rotating the carrier catheter with respect to the anchor around a first axis extending generally in the lengthwise direction of the anatomical structure, so that a local treatment device takes a predetermined path along the tissue. For example, a local treatment device projecting from the carrier catheter in a direction transverse to the first axis traces a generally arcuate path centered on the first axis over the tissue surrounding the anatomical structure, and actuating the local treatment device. Methods according to this aspect of the invention may include further steps of monitoring or controlling the position of the carrier catheter relative to the anatomical structure, as by monitoring or controlling the position of the carrier catheter relative to the anchor, such as the rotational position of the carrier catheter, and may also include mapping properties of the tissue along the path as, for example, by using a local sensor linked to the carrier catheter as discussed above in connection with the apparatus. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a cut-away view of the ostium and a portion of a pulmonary vein with an ablation device inserted therein.  
         [0014]    [0014]FIG. 2 is a cross-sectional view of the apparatus in FIG. 1.  
         [0015]    [0015]FIG. 3 is a close-up view of the ablation apparatus according to one embodiment of the invention, positioned inside a pulmonary vein.  
         [0016]    [0016]FIG. 4 is a cross-sectional view of the ablation apparatus according to one embodiment of the invention.  
         [0017]    [0017]FIG. 5 is a graph of the signals received from electrodes of an apparatus according to one embodiment of the invention.  
         [0018]    [0018]FIG. 6 is a diagrammatic view of the ablation apparatus according to one embodiment of the invention.  
         [0019]    [0019]FIG. 7 is a diagrammatic view of a portion of the ablation apparatus according to one embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]    Apparatus according to one embodiment of the invention includes an elongated guide element  10 , which may be a conventional, small diameter guide wire or catheter. Guide element  10  has an expansible anchor  12  mounted adjacent a distal end of the guide element. Anchor  12  may be a balloon or other structure movable between a collapsed condition in which the anchor closely surrounds the guide element  10  and the expanded condition illustrated in FIG. 1, in which the guide element projects radially from the guide element. The anchor has an electrode  14  extending around its circumference. The electrode is connected to one or more leads (not shown) extending in or on the guide element to the proximal end  16  of the guide element. The apparatus further includes a carrier catheter  20  having a guide lumen  22  and a treatment catheter lumen  24  extending in the lengthwise or proximal to distal direction of the carrier catheter. The guide lumen  22  extends to an opening at the distal end  26  of the carrier catheter. The treatment catheter lumen  24  terminates slightly short of the distal end. A port  28  in the side or circumferential wall of the carrier catheter communicates with the treatment catheter lumen at the distal end of this lumen. As best seen in FIG. 4, the carrier catheter desirably has a sloping wall surface  30  at the distal end of lumen  24 . This wall surface slopes outwardly, towards port  28  in the distal direction.  
         [0021]    The apparatus further includes a treatment catheter  36  having a distal end  38  and a small ultrasonic transducer  40  mounted at such distal end. The ultrasonic transducer is a piezoelectric element having a concave emitting surface  42  facing in the distal direction of the treatment catheter, i.e., to the right as seen in FIG. 3. The ultrasonic emitter is connected to leads  44  (FIG. 3) extending on or in the treatment catheter. These leads extend to the proximal end of the treatment catheter.  
         [0022]    An electrode  46  is also mounted at the distal end  38  of the treatment catheter and connected to a further lead  48  extending on or in the treatment catheter.  
         [0023]    In a method according to one embodiment of the invention, guide element  10  and anchor  12  are positioned as illustrated in FIG. 1, with the guide element extending through the subject circulatory system and through the left atrium of the subject&#39;s heart H into a pulmonary vein P through ostium or opening O of the vein. Anchor  12  is expanded to engage the wall of the pulmonary vein. Desirably, anchor  12  has a substantially cylindrical shape, and tends to bring the region of the pulmonary vein adjacent the anchor to a generally cylindrical cross sectional shape as well. In this condition, the axis  50  of the guide element  10 , adjacent the distal end of the guide element lies substantially in the lengthwise direction of the pulmonary vein. Desirably, axis  50  is positioned by balloon  12  at or near the center of the vein. In the expanded condition of the anchor, the electrode  14  on the balloon is engaged with the wall of the vein.  
         [0024]    Before or after expansion of the anchor, carrier catheter  20  is advanced to the position illustrated in FIG. 1. In this position, the guide element  10  extends through the guide lumen  22  of the carrier catheter, and the distal end  26  of the carrier catheter is disposed adjacent the anchor or balloon  12 . For example, the distal end of the carrier catheter may abut the anchor so that the anchor prevents movement of the carrier catheter in the distal direction along the guide element.  
         [0025]    Treatment catheter  36  is advanced within the treatment lumen  24  of the carrier catheter. When the treatment catheter reaches the distal end of lumen  24 , it encounters sloping surface  30  and bends outwardly, through port  28  so that the distal end  38  of the treatment catheter protrudes from the carrier catheter. In this operative condition, the distal end of the treatment catheter is remote from axis  50 . As the treatment catheter is advanced, electrical signals appearing at electrode  46  may be monitored. When the electrode contacts the wall of the pulmonary vein, the characteristics of such signal will change. In particular, the amplitude of naturally occurring electrical signals detected by the electrode will increase. Thus, by detecting this increase using a conventional monitoring device (not shown) connecting through lead  48  to the electrode, the physician can determine when the distal end  38  of the treatment catheter has been engaged with the wall of the pulmonary vein. To enhance this detection, a low voltage marker signal may be applied on electrode  14  at a frequency distinct from the frequencies of naturally occurring electrical signals. The electronic apparatus used to detect the voltage appearing at electrode  46  may be arranged to provide enhanced sensitivity to the marker signal and to suppress response to naturally occurring signals. For example, the detection apparatus may incorporate a frequency selective filter having a relatively narrow pass band centered at the marker frequency, or a synchronous detector locked to the marker signal.  
         [0026]    Once the distal end of the treatment catheter has been engaged with the wall of the pulmonary vein, a drive signal is applied through leads  44  to ultrasonic transducer  40 , causing it to emit ultrasonic waves. The ultrasonic waves converge with one another and mutually reinforce one another within a focal spot F. The position of the focal spot relative to the emitting surface depends, inter alia, on the curvature of the emitting surface. Desirably, this curvature is selected so that the focal spot lies within the wall of the pulmonary vein, beneath the surface of the vein wall lining. The applied ultrasonic energy heats and ablates the tissue of the vein wall. While the ultrasonic energy is being applied, carrier catheter  20  is rotated as, for example, by the physician manually turning the proximal end of the carrier catheter. The distal end of the carrier catheter rotates about axis  50 . Stated another way, the guide element acts as a shaft received within the guide lumen  22 , and the carrier catheter rotates about the shaft. The guide element substantially constrains the carrier catheter against movement transverse to axis  50 . As the carrier catheter rotates, the distal end  38  of the treatment catheter sweeps along an arcuate path  60  substantially concentric with axis  50  on the vein wall. The focal spot F traces a similar path within the vein wall. Thus, the ultrasonic energy ablates tissue within an arcuate zone. A complete, loop like path  60  around the entire pulmonary vein may be ablated by turning the distal end of the carrier catheter through a complete, 360° rotation. Engagement of the treatment catheter distal end with the vein wall may be monitored during this procedure by monitoring the voltage on electrode  46 , and the treatment catheter may be moved relative to the carrier catheter to maintain such engagement. Resilience of the treatment catheter, carrier catheter, the guide element and anchor also help to maintain engagement even if the vein wall is not perfectly circular.  
         [0027]    This procedure provides ablation of a complete circumferential loop using a small, localized ultrasonic treatment element. Moreover, such a loop can be formed without depending entirely upon the physician&#39;s technique in maneuvering the catheter. That is, the distal end of the catheter is guided in its motion around the circumference of the pulmonary vein.  
         [0028]    In the method discussed above, the path  60  of the focal spot extends around the wall of the pulmonary vein itself. However, as is well known in the treatment of atrial fibrillation, a conduction block can be formed at any location proximal to the focus X of the arrhythmia, which is typically located at a point along the pulmonary vein. For example, an effective conduction block can be formed in precisely the same manner along an alternate path  60 ′ in the wall of the ostium, provided that the ablation capabilities of the treatment catheter allow effective ablation through the thickness T of the myocardial tissue in the ostium. Likewise, the same techniques can be used to form a conduction block in the wall of the heart along a path  60 ″. The treatment catheter  38  would extend further from the axis  50  to inscribe a larger circular path. Also, anchor  12  would be positioned proximally from the location shown as, for example, within the ostium of the pulmonary vein rather than deep within the pulmonary vein itself.  
         [0029]    In the techniques discussed above, the conduction block is formed as a complete, closed loop extending 360° around axis  50 . However, as further described in the aforementioned Ser. No. 60/265,480 application, now U.S. patent application Ser. No. 10/062,693, there is a boundary or border  90  between myocardial tissue in the heart wall H and vein wall tissue of the pulmonary vein P. In patients suffering from atrial fibrillation, abnormal fibers  92  of myocardial tissue extend distally from this border along the pulmonary vein P. The abnormal electrical impulses associated with atrial fibrillation are transmitted from the focus X of the arrhythmia along these abnormal fibers  92 . Thus, if ablation is performed at a location between the border  90  and the focus X of the arrhythmia, transmission of the abnormal electrical impulses can be halted by ablating the abnormal myocardial fibers  92 . In this instance, it is only necessary to ablate along a path encompassing the abnormal myocardial fibers; it is not necessary to ablate along a complete, closed loop around the entire circumference of the pulmonary vein. For example, ablation along a path  94  distal to border  90  and encompassing fibers  92  is sufficient to inhibit transmission of the abnormal electrical impulses, assuming that these are the only abnormal myocardial fibers in the particular pulmonary vein.  
         [0030]    Ablation over a limited path is advantageous for several reasons. The degree of damage to normal tissue will be less than with ablation along a complete loop. This tends to reduce the possibility of thrombus formation and stenosis of the pulmonary vein. Also, the procedure can be performed in a shorter time.  
         [0031]    In a further embodiment of the present invention, a sensor  98  is provided on carrier catheter  20  adjacent the distal end thereof. Sensor  98  is arrange to provide a signal which depends upon the alignment between a sensing direction, indicated as vector  100  on the sensor and the direction of a magnetic or electromagnetic field  102  prevailing in the vicinity of the sensor. For example, sensor  102  may be a hall effect sensor, magneto resistive sensor or the like having an output voltage which varies with the component of a magnetic field in the sensing direction  100 . In a method using this sensor, the anchor, guide element, carrier catheter and treatment catheter are positioned as discussed above so that the distal end  38  of the treatment catheter is disposed distal to the border  90  between myocardial tissue and vein wall tissue. In a fiber-locating step, carrier catheter  20  is rotated about axis  50  so it can sweep the distal end of the treatment catheter along path  60 . However, in this stage of operation, the ultrasonic element  40  is not actuated to ablate the tissue. Rather, the ultrasonic element is used as an echo detection device. Thus, the ultrasonic element is actuated intermittently with a low power echo-sounding drive signal. During intervals between such actuations, the transducer serves to convert ultrasonic waves reflected by the tissue in front of the transducer into electrical signals representing the echoes from the tissue. Because the ultrasonic properties of myocardial fibers differ from the ultrasonic properties of vein wall tissue, the electrical signals generated by the transducer when the transducer is aligned with a fiber  92  will differ from those generated when the transducer is not aligned with a fiber. As the carrier catheter and sensor  98  rotate during this step, the voltage from the sensor will vary with the angular position θ of the carrier catheter and hence with the angular position of the treatment catheter distal end  38 . For example, as indicated in FIG. 5, the voltage will be at a maximum at point  106  where the sensing direction  100  (FIG. 1) is most nearly co-directional with the field direction  102  and at a minimum at another value of θ at  108 , where the sensing direction  100  is most nearly opposite (counter-directional) to the field direction  102 . This variation will occur for any field direction  102 , provided that the field direction is not exactly parallel to axis  50 . Thus, the angular position θ of the carrier catheter can be monitored by monitoring the signal voltage from sensor  98 . Although the angular position is not a unique function of signal voltage, the angular position can be determined from the signal voltage. For example, a particular value f signal voltage occurs at two points: θ 111  and θ 112  within 360° of rotation. However, at point  111  the signal voltage increases with rotation in a particular direction, whereas at point  110  the signal voltage decreases with rotation in this direction. Only point  110  exhibits the combination of the same voltage and this trend or slope in the voltage versus rotation curve.  
         [0032]    The results of the ultrasonic monitoring step plotted against rotational position. Those rotational positions associated with ultrasonic results indicating the presence of myocardial fibers are identified. For example, assume that the distal end  38  of the treatment catheter is aligned with myocardial fibers  92  at rotational positions θ 110  and θ 112 .  
         [0033]    Once the rotational positions associated with myocardial fibers have been identified, the carrier catheter and treatment catheter are rotated through a range of rotational positions encompassing the rotational positions associated with the myocardial fibers as, for example, the range  94 ′ (FIG. 5) encompassing rotational positions θ 110  and θ 112 , so as to sweep the distal end of the treatment catheter over the path  94  encompassing the myocardial fibers  92  (FIG. 1). During this step, the transducer  40  is actuated to ablate the vein wall tissue in the manner discussed above and thus ablate the abnormal myocardial fiber  92 .  
         [0034]    In a variant of the procedure discussed above, the fiber locating step can be performed using electrode  46  rather than transducer  40  as the sensing element. Thus, a marker signal as discussed above is applied through electrode  14 . Because myocardial fibers  92  will conduct electrical signals differently than the normal tissue of the vein wall, the marker signal will appear at greater amplitudes when the electrode  46  (FIG. 3) on the distal end of the treatment catheter is aligned with a myocardial fiber.  
         [0035]    In a further variant of the procedures discussed above, the sensor can be carried on treatment catheter  38 , rather than on the carrier catheter. Indeed, treatment catheter  38  may be a commercially available electrophysiological ablation catheter equipped with a position sensor. In yet another variant, the fiber locating step can be performed using a locating catheter (not shown) inserted through treatment lumen  24 . The locating catheter may carry any type of sensor capable of identifying the presence of myocardial fibers, including the ultrasonic and electrode sensors discussed above. After the locating step, the locating catheter is withdrawn and the treatment catheter is inserted into the treatment lumen of the carrier catheter as discussed above.  
         [0036]    There is a repeatable association between the position of the treatment catheter and the rotational position of the carrier catheter distal end. Because the rotational position of the carrier catheter distal end is monitored either directly using a sensor on the carrier catheter itself or indirectly using a sensor on the treatment catheter, the procedure does not depend upon accurate transmission of rotation between the proximal end of the carrier catheter and the distal end. However, translational movement of the carrier catheter relative to the guide element typically can be transmitted from the proximal ends of these devices to their distal ends with good accuracy and repeatability.  
         [0037]    As shown in FIG. 6, in an apparatus according to a further embodiment of the invention, the distal end  226  of carrier catheter  220  and the adjacent portion of guide element  210  are interconnected by a translation to rotation conversion mechanism including a helical cam  201  on the guide element and a mating follower surface  202  on the carrier catheter. The opposite arrangement (helical surface on carrier catheter with follower on guide element) can also be used. Any other mechanical elements are capable of converting translation of the distal end  226  relative to the guide element  210  into a rotation of the carrier catheter distal end relative to the guide element can be used. Thus, the distal end  226  of the carrier catheter can be brought to a repeatable rotational position relative to the anchor  212  and relative to the adjacent tissues (not shown) by controlling the position of the proximal end  221  of the carrier catheter relative to the proximal end  216  of the guide element.  
         [0038]    A conventional position controlling mechanism such as a screw mechanism  203  interconnects the proximal ends  221  and  216  so that the distance  217  between these ends may be varied as desired in a controlled manner. A conventional indicating device such as a knob  205  associated with screw mechanism  203  and a scale  207  associated with a pointer  206  on the knob is provided for indicating the distance  217 . Each value of distance  217  corresponds to a particular value of the angular position θ of the distal end  226  relative to anchor  212  and guide element  210 . Thus, there is no need to detect the angular position relative to a field as discussed above. The myocardial fiber locating step can be performed as discussed above, and the linear positions on scale  207  corresponding to the locations of myocardial fibers can be recorded. In the ablation step, the carrier catheter is moved relative to the guide element through a range of linear positions sufficient to encompass the linear positions associated with the myocardial fibers, thus sweeping the ablation element over a range of angular positions which encompass the myocardial fibers during the ablation step. The same apparatus can be used to perform a full-loop, 360° ablation as discussed above, without the need for a locating step, by moving the carrier catheter relative to the guide catheter through a range of linear positions corresponding to a full 360° rotation.  
         [0039]    Any other form of mechanical positioning device may be substituted for screw mechanism  203 . Also, the dial and scale  205  and  207  may be replaced by any other conventional device for monitoring the relative positions of the two elements as, for example, a mechanical dial indicator or an optical or electronic position measuring device.  
         [0040]    In the apparatus of FIG. 6, the ablation element  240  is not carried on a separate treatment catheter. Rather, the ablation element is mounted on a deformable element such as a strip  219 . In the extended position depicted in FIG. 6, the leaf-life element projects in the radial direction from the carrier catheter so that the ablation element  240  is removed from the axis  250  of the guide board  222  in the carrier catheter and hence remote from the axis of rotation of the carrier catheter around guide element  210 . In the collapsed condition (not shown) leaf element  219  lies against the side wall of carrier catheter  220  to facilitate threading. The resilience of leaf element  219  normally biases to the collapsed condition. A sleeve or other axially moveable element  227  carried on the carrier catheter can be actuated from the proximal end of the carrier catheter to move the leaf element to the extended condition. Any other type of radially expansible structure as, for example, a balloon, can be used instead of the leaf element.  
         [0041]    Apparatus according to a further embodiment of the invention (FIG. 7) incorporates a carrier catheter  320  and guide element  310  similar to the corresponding elements discussed above with reference to FIG. 1. However, the treatment catheter  336  has distal end  338  adapted to form a generally J-shaped configuration when the treatment catheter is extended through the port  328  on the carrier catheter. The ablation element  340  includes a series of sub-elements  341  such as electrodes for RF application or ultrasonic transducers encircling the distal end of the treatment catheter. The side wall of the treatment catheter distal end in the vicinity of ablation element  340  is engaged with the wall of the pulmonary vein, ostium or heart when the treatment catheter is in the extended position illustrated.  
         [0042]    In yet another variant, the sensor  98  discussed above with reference to FIG. 1 can be replaced by a rotary position encoder having one element linked to the distal end  26  of carrier catheter  20  and another element linked to anchor  12 . Such a rotary position encoder is arranged to provide a signal representing the angular position of the carrier catheter with respect to the anchor. Because the anchor remains in a fixed position relative to the pulmonary vein, this angular position can be used in the same manner as the angular position of the carrier catheter with respect to a field.  
         [0043]    The particular ablation elements discussed above are merely exemplary. For example, the treatment catheter may include an optical fiber for transmitting intense light from a source such as a laser from the proximal end of the catheter so that the light ablates the tissue. Alternatively, the treatment catheter may be a tubular catheter adapted to conduct a chemical ablation agent to an outlet at the distal end. In yet another alternative, the treatment catheter may carry a blade or other mechanical device for mechanically ablating (cutting) the tissues to a controlled depth.  
         [0044]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.