Abstract:
A catheter introduction apparatus provides an optical assembly for emission of laser light energy. In one application, the catheter and the optical assembly are introduced percutaneously, and transseptally advanced to the ostium of a pulmonary vein. An anchoring balloon is expanded to position a mirror near the ostium of the pulmonary vein, such that light energy is reflected and directed circumferentially around the ostium of the pulmonary vein when a laser light source is energized. A circumferential ablation lesion is thereby produced, which effectively blocks electrical propagation between the pulmonary vein and the left atrium.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to methods and apparatus for the medical treatment of disease of the heart. More particularly, this invention relates to a method and apparatus for treating cardiac arrhythmias by ablating in a vicinity of pulmonary venous tissue.  
           [0003]    2. Description of the Related Art  
           [0004]    Tissue ablation from the inner walls of hollow viscera of the body generally, and the vascular system in particular, has been found to be useful in the treatment of various medical conditions. Technological developments in intravascular catheters, manipulative instruments adapted to intravascular catheters, and catheter localization techniques have especially benefited the field of cardiology. Percutaneous transcatheter ablation has been used successfully in the treatment of conduction defects and arrhythmias of various types. Today, atrial tachyarrhythmias are a common application for ablative therapy.  
           [0005]    Various ablative modalities have been employed in the past, such as ablation by direct heating. Energy can be conducted to the target tissue using various modalities, such as ultrasound, laser, resistive heating, and radiofrequency energy.  
           [0006]    One ablative approach is the so-called “maze” technique. In general, the maze procedure attempts to block abnormal conduction patterns in the left atrium by establishing a maze-like pattern of linear lesions in the left atrial wall.  
           [0007]    Atrial arrhythmias are known to be associated with abnormal electrical activity of tissue foci in the vicinity of the pulmonary veins, especially the superior pulmonary veins. Various ablative treatments of such foci have been attempted. For example, the production of linear atrial lesions by radiofrequency ablation, in combination with ablation of suspected arrhythmogenic foci has been performed using transcatheter techniques.  
           [0008]    More recently, circumferential lesions at or near the ostia of the pulmonary veins have been created to treat atrial arrhythmias. U.S. Pat. Nos. 6,012,457 and 6,024,740, both to Lesh, disclose a radially expandable ablation device, which includes a radiofrequency electrode. Using this device, it is proposed to deliver radiofrequency energy to the pulmonary veins in order to establish a circumferential conduction block, thereby electrically isolating the pulmonary veins from the left atrium.  
           [0009]    U.S. Pat. No. 5,468,239 to Tanner et al. describes a circumferential laser assembly, adapted, for example, to be placed in the urethral canal such that a transurethral resection of benign prostatic hypertrophy may be performed.  
           [0010]    Radiofrequency ablation using multiple contiguous circumferential points, guided by electro-anatomical mapping is proposed in the document,  Circumferential Radiofrequency Ablation of Pulmonary Vein Ostia: A New Anatomic Approach for Curing Atrial Fibrillation , Pappone C, Rosanio S, Oreto G, Tocchi M, Gugliotta F, Vicedomini G, Salvati A, Dicandia C, Mazzone P, Santinelli V, Gulletta S, Chierchia S, Circulation 102:2619-2628 (2000). It is emphasized that particular care must be exercised to ensure that the ablation sites are indeed contiguous; otherwise irregular electrical activity in the pulmonary vein may continue to contribute to atrial arrhythmia.  
           [0011]    It has also been proposed to produce circumferential ablative lesions using ultrasound energy delivered via a cylindrical ultrasound transducer through a saline-filled balloon. This technique is described in the document,  First Human Experience With Pulmonary Vein Isolation Using a Through - the - Balloon Circumferential Ultrasound Ablation System for Recurrent Atrial Fibrillation , Natale A, Pisano E, Shewhik J, Bash D, Fanelli R, M D; Potenza D; Santarelli P; Schweikert R; White R; Saliba W; Kanagaratnam L; Tchou P; Lesh M, Circulation 102:1879-1882 (2000). Ablation times in the order of 2 minutes are reported.  
           [0012]    A known drawback in the use of ultrasound energy for cardiac tissue ablation is the difficulty in controlling the local heating of tissue. There are tradeoffs between the clinical desire to create a sufficiently large lesion to effectively ablate an abnormal tissue focus, or block an aberrant conduction pattern, and the undesirable effects of excessive local heating. If the ultrasound device creates too small a lesion, then the medical procedure could be less effective, or could require too much time. On the other hand, if tissues are heated excessively then there could be local charring effects due to overheating. Such overheated areas can develop high impedance, and may form a functional barrier to the passage of heat. The use of slower heating provides better control of the ablation, but unduly prolongs the procedure.  
           [0013]    In consideration of these, and other factors, it is appropriate, in designing a practical energy emitter, to consider the amplitude of the energy signal, the amount of time required for the energy application, the size of the emitter, and the contact area, as well as ease of positioning, withdrawal, and repositioning of the device so as to be able to conveniently produce multiple lesions during the same medical procedure.  
           [0014]    Previous approaches to controlling local heating include the inclusion of thermocouples within the electrode and feedback control, signal modulation, local cooling of the catheter tip, and fluid assisted techniques, for example perfusion of the target tissue during the energy application, using chilled fluids. Typical of the last approach is Mulier, et al. U.S. Pat. No. 5,807,395.  
           [0015]    Publications which describe various medical techniques of interest include:  
           [0016]    Scheinman M M, Morady F. Nonpharmacological Approaches to Atrial Fibrillation. Circulαtion 2001; 103:2120-2125.  
           [0017]    Wang P J, Homoud M K, Link M S, Estes III N A. Alternate energy sources for catheter ablation.  Curr Cardiol Rep  1999 July;1(2):165-171.  
           [0018]    Fried N M, Lardo A C, Berger R D, Calkins H, Halperin H R. Linear lesions in myocardium created by Nd:YAG laser using diffusing optical fibers: in vitro and in vivo results.  Lasers Surg Med  2000;27(4):295-304.  
           [0019]    Keane D, Ruskin J, Linear atrial ablation with a diode laser and fiber optic catheter.  Circulation  1999; 100:e59-e60.  
           [0020]    Ware D, et al., Slow intramural heating with diffused laser light: A unique method for deep myocardial coagulation.  Circulation; Mar.  30, 1999; pp. 1630-1636.  
           [0021]    Other medical technologies of interest are described in U.S. Pat. No. 5,891,134 to Goble et al., U.S. Pat. No. 5,433,708 to Nichols et al., U.S. Pat. No. 4,979,948 to Geddes et al., U.S. Pat. No. 6,004,269 to Crowley et al., U.S. Pat. No. 5,366,490 to Edwards et al., U.S. Pat. Nos. 5,971,983, 6,164,283, and 6,245,064 to Lesh, U.S. Pat. No. 6,190,382 to Ormsby et al., U.S. Pat. Nos. 6,251,109 and 6,090,084 to Hassett et al., U.S. Pat. No. 5,938,600 to Swartz et al., U.S. Pat. No. 6,064,902 to Haissaguerre et al., and U.S. Pat. No. 6,117,101 to Diederich et al.  
           [0022]    All of the patents and publications cited in this disclosure are incorporated herein by reference.  
         SUMMARY OF THE INVENTION  
         [0023]    It is therefore a primary object of some aspects of the present invention to provide improved apparatus and method for electrically isolating the pulmonary vein by accomplishing a circumferential conduction block surrounding the pulmonary vein ostium in a single ablation application of laser light energy.  
           [0024]    It is another object of some aspects of the present invention to reduce the time required to perform isolation of the pulmonary veins using a laser.  
           [0025]    A catheter introduction apparatus provides an optical assembly for emission of laser light energy. In one application, the catheter and the optical assembly are introduced percutaneously, and transseptally advanced to the ostium of a pulmonary vein. An anchor such as an anchoring balloon is expanded to center a mirror in front of the ostium of the pulmonary vein, such that light energy is reflected from the mirror circumferentially onto the wall of the pulmonary vein when a laser light source is energized. A circumferential ablation lesion is produced around the ostium of the pulmonary vein, which effectively blocks electrical propagation between the pulmonary vein and the left atrium.  
           [0026]    The invention provides a method for electrically isolating a cardiac chamber, including the steps of introducing an optical assembly at a pulmonary vein proximate its ostium, anchoring the optical assembly at the pulmonary vein, and thereafter conducting laser light energy in a path extending from the optical assembly to a circumferential ablation region of the pulmonary vein.  
           [0027]    According to an aspect of the method, the path avoids the anchor.  
           [0028]    According to another aspect of the method, conducting the laser light energy is performed by directing the laser light energy into a circumferential line that intersects the ablation region.  
           [0029]    In another aspect of the method, the anchor is a balloon, and anchoring is performed by expanding the balloon to engage the pulmonary vein.  
           [0030]    In a further aspect of the method, the optical assembly is introduced via the fossa ovalis, and preliminary laser light energy is directed onto the fossa ovalis to ablate tissue thereof to facilitate passage of the optical assembly therethrough.  
           [0031]    In yet another aspect of the method, conducting the laser light energy is performed in exactly one application.  
           [0032]    In still another aspect of the method, conducting the laser light energy is performed in a series of pulses.  
           [0033]    According to another aspect of the method, the duration of each of the pulses is less than 100 milliseconds.  
           [0034]    In an additional aspect of the method, introducing the optical assembly is performed by disposing the optical assembly on an intravascular catheter, and passing the distal portion of the intravascular catheter through a blood vessel into the heart.  
           [0035]    In one aspect of the method, conducting the laser light energy also includes reflecting the laser light energy.  
           [0036]    According to a further aspect of the method, reflecting the laser light energy includes disposing a mirror in a path of the laser light energy external to the anchor.  
           [0037]    According to yet another aspect of the method, reflecting the laser light energy includes disposing a light-reflective coating on an external surface of the anchor and reflecting the laser light energy from the light-reflective coating.  
           [0038]    According to still another aspect of the method, the laser light energy has a wavelength of about 13,000 nm.  
           [0039]    The invention provides an apparatus for electrically isolating a cardiac chamber, including an intravascular catheter adapted for introduction into a pulmonary vein proximate an ostium thereof, an anchor disposed at a distal end of the catheter for fixation of the catheter tip at the pulmonary vein, and an optical assembly for conducting laser light energy in a path extending to a circumferential ablation region of the pulmonary vein.  
           [0040]    According to an aspect of the apparatus, the optical assembly is in a non-contacting relationship with the anchor.  
           [0041]    According to yet another aspect of the apparatus, the path avoids the anchor.  
           [0042]    According to an additional aspect of the apparatus, the optical assembly includes an optical fiber for conducting the laser light energy from a light source, a lens disposed at an exit face of the optical fiber, and a reflector disposed in the path external to the anchor for directing the laser light energy into a circumferential line that intersects the ablation region.  
           [0043]    According to an additional aspect of the apparatus, the lens is a graded index lens.  
           [0044]    According to one aspect of the apparatus, the reflector is a parabolic mirror.  
           [0045]    According to another aspect of the apparatus, the reflector is a light reflecting external surface of the anchor.  
           [0046]    According to one aspect of the apparatus, the anchor includes a balloon that inflates to engage the pulmonary vein.  
           [0047]    According to an additional aspect of the apparatus, the balloon is bilobate.  
           [0048]    According to one aspect of the apparatus, a proximal portion of the balloon is more expanded than a distal portion of the balloon in an inflated state thereof.  
           [0049]    According to another aspect of the apparatus, the laser light energy is applied to the ablation region in exactly one application.  
           [0050]    According to a further aspect of the apparatus, the laser light energy is applied to the ablation region in a series of pulses.  
           [0051]    According to yet another aspect of the apparatus, the duration of each of the pulses is less than 100 milliseconds.  
           [0052]    According to still another aspect of the apparatus, the laser light energy has a wavelength of about 13 microns. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0053]    For a better understanding of these and other objects of the present invention, reference is made to the detailed description of the invention, by way of example, which is to be read in conjunction with the following drawings, wherein:  
         [0054]    [0054]FIG. 1 illustrates a therapeutic catheter that is constructed and operative in accordance with a preferred embodiment of the invention;  
         [0055]    [0055]FIG. 2 is an enlarged schematic illustration of the distal end of the catheter shown in FIG. 1 with an inflation balloon expanded, and an optical fiber and associated optics in place, in accordance with respective preferred embodiments of the present invention;  
         [0056]    [0056]FIG. 3 is a schematic sectional view of a laser subassembly employing a parabolic mirror, taken along the axis of a catheter in accordance with a preferred embodiment of the invention;  
         [0057]    [0057]FIG. 4 is a schematic sectional view of a laser subassembly employing a light-reflective coating taken along the axis of a catheter in accordance with an alternate embodiment of the invention;  
         [0058]    [0058]FIG. 5 is a flow chart of a method for electrically isolating pulmonary veins, which is operative in accordance with a preferred embodiment of the invention;  
         [0059]    [0059]FIG. 6 schematically illustrates certain aspects of a method of intracardiac catheter access during a first phase of the method shown in FIG. 5;  
         [0060]    [0060]FIG. 7 schematically illustrates certain aspects of a method of intracardiac catheter access during a second phase of the method shown in FIG. 5; and  
         [0061]    [0061]FIG. 8 schematically illustrates certain aspects of a method of intracardiac catheter access during a third phase of the method shown in FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0062]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art, however, that the present invention may be practiced without these specific details. In other instances, well known circuits, control logic, and other apparatus have not been shown in detail in order not to unnecessarily obscure the present invention.  
         [0063]    Turning now to the drawings, reference is made to FIG. 1, which illustrates a medical device that is constructed and operative in accordance with a preferred embodiment of the invention. An intravascular catheter  10  has a proximal end  12  and a distal end  14 . The distal end  14  is provided with at least one seal  16 , and optionally a second seal  18 . The seals  16 ,  18  are preferably inflatable balloons, made from rubber, polyurethane, or a similar elastic material. The catheter  10  has one or more lumens, which conduct fluid for inflating and deflating the seals  16 ,  18 . One of the lumens terminates in a port  20 , and is useful for injection of fluids and withdrawal of blood as may be required during use. Other lumens are provided for passage of guidewires and instruments therethrough. An inflatable anchoring balloon  22 , shown in a deflated condition, is located distal to the seals  16 ,  18 . The catheter  10  also has a coaxial guidewire lumen  24 .  
         [0064]    Reference is now made to FIG. 2, which is a schematic enlarged view of the distal end  14  of a catheter that is constructed and operative in accordance with a preferred embodiment of the invention, similar to the catheter  10  (FIG. 1), in which like elements are given like reference numerals. Disposed near the distal end  14  of the catheter  10  is a laser subassembly  26 , which includes an optical fiber  28 , shown in a position proximate the lumen  24 , which conveys laser light through a lens  30  to a mirror (FIG. 3) or a light-reflective coating (FIG. 4), which in turn reflects the laser light circumferentially onto a target. The laser subassembly  26  is preferably disposed external to and in a non-contacting relationship with the anchoring balloon  22 . Thus in many embodiments, the anchoring balloon  22  need not directly support the laser subassembly  26 , and is excluded from the laser light path. An advantage of this arrangement is that standard catheter balloons can be used in the catheter  10 .  
         [0065]    Introduced slidably via the lumen  24 , the optical fiber  28  extends to and is connected proximally to a suitable external laser light source  32 . For some applications, a mirror  34  is rigidly fixed in position with respect to the catheter body or a structural component thereof. It will be appreciated that whereas the mirror  34  is shown by way of illustration, other optical elements known in the art (e.g., lenses) may also be configured for use with some embodiments of the invention.  
         [0066]    In a preferred embodiment, the active sites to be ablated are identified using the location and mapping system disclosed in commonly assigned U.S. Pat. No. 5,840,025, which is herein incorporated by reference. Certain components of the location and mapping system are incorporated into the distal end  14  of the catheter  10 , namely a sensor  36  and a transmitting antenna  38  (FIG. 1), which can be a dipole antenna. The sensor  36  detects local electrical activity of the heart, and the antenna  38  transmits signals to a plurality of receiving antennae (not shown) which are placed on the body surface of a patient during use. The distal end  14  can be radio-opaque, in order to facilitate its localization by conventional radiographic techniques, alternatively or in addition to the system disclosed in the above-noted U.S. Pat. No. 5,840,025.  
         [0067]    In embodiments in which the system disclosed in the above-noted U.S. Pat. No. 5,840,025 is not used, the sensor  36  performs conventional monitoring of local electrical activity, and the antenna  38  can be omitted.  
         [0068]    The anchoring balloon  22  is inflated, and preferably has a large-radius proximal lobe or segment  40 , and a small-radius distal lobe or segment  42 . Typically the anchoring balloon  22  measures 1 cm in length and has a caliber of about 2.7 mm. (8 French) when uninflated, expanding to 3-4 cm when inflated. The bilobate configuration of the anchoring balloon  22  aids in securely positioning the anchoring balloon  22  within the ostium of a pulmonary vein. Alternatively the anchoring balloon  22  can be pyriform, ellipsoidal, or otherwise constructed, preferably such that its proximal portion is more radially expanded than its distal portion. The anchoring balloon  22  is constructed of conventional materials. Proximally, a connection between the optical fiber  28  and the laser light source  32  is illustrated.  
         [0069]    In some embodiments, the anchoring balloon  22  is coated with a light-reflective coating (FIG. 4), and is positioned so as to reflect the light from the laser subassembly  26  to the endocardial wall and thereby facilitate the circumferential ablation around the pulmonary vein. In these embodiments, the mirror  34  is typically omitted, and a light-reflective coating directs the laser light circumferentially and directly towards the ablation zone.  
         [0070]    Reference is now made to FIG. 3, which is a schematic sectional view of the laser subassembly  26  (FIG. 2) taken along the axis of the optical fiber  28  in accordance with a preferred embodiment of the invention. The description of FIG. 3 should be read in conjunction with FIG. 2, in which like elements are given like reference numerals. The optical fiber  28  is coupled at its exit face to a graded index (GRIN) rod lens  44 , which serves as a relay lens for light passing through the optical fiber  28 . As shown by an exemplary ray  46 , light exiting the lens  44  strikes a mirror  48  that is disposed between the lens  44  and the anchoring balloon  22 , and is then reflected. The mirror  48  is a 360 degree parabolic mirror, which is symmetric about the axis of the catheter  10  (FIG. 1), so that when the apparatus is positioned, the reflected light strikes the ablation zone as a circumferential beam.  
         [0071]    Reference is now made to FIG. 4, which is a schematic sectional view of a laser subassembly taken along the axis of the optical fiber  28  in accordance with an alternate embodiment of the invention. The description of FIG. 4 should be read in conjunction with FIG. 2 and FIG. 3, in which like elements are given like reference numerals. The arrangement shown in FIG. 4 is similar to that of FIG. 3, except that the mirror is omitted. Instead a light-reflective coating  50  is disposed on the external surface of the anchoring balloon  22 . As shown by an exemplary ray  52 , light exiting the lens  44  strikes the light-reflective coating  50 , and is then reflected. When the apparatus is positioned, the reflected light strikes the ablation zone as a circumferential beam.  
         [0072]    Reference is now made to FIG. 5, which is a flow chart of a method for electrically isolating pulmonary veins, which is operative in accordance with a preferred embodiment of the invention. The description of FIG. 5 should be read in conjunction with FIG. 1, FIG. 3, and FIG. 4.  
         [0073]    In initial step  54  routine preparation of a subject (not shown) and equipment are accomplished. This includes attachment of various monitoring and grounding leads, as may be required for electrophysiological monitoring of the procedure and for the operation of the above-noted location and mapping system.  
         [0074]    Next, at step  56 , a series of events begins, ultimately leading to the positioning of the catheter  10  and the laser subassembly  26  at the ostium of a pulmonary vein. Step  56  is typically conventional. In a preferred approach, the venous system is accessed using the well-known Seldinger technique, in which an introducer sheath is positioned in a peripheral vein, typically a femoral vein. A guiding sheath is introduced through the introducer sheath, and is advanced via the inferior vena cava into the right atrium. Then, using a Brockenbrough needle, the fossa ovalis of the interatrial septum is punctured, and the puncture dilated if necessary. The Brockenbrough needle is withdrawn, and the guiding sheath placed in the left atrium. Alternatively, the ablation catheter is energized as it contacts the interatrial septum, usually at the fossa ovalis, in order to ablate a portion of the fossa ovalis. Ablation of septal tissue eases the passage of the catheter through the septum, reduces the amount of hardware used, and shortens the procedure, as it is not necessary to pass a dilator through the fossa ovalis. Ablation of septal tissue typically requires a power output of less than 70 watts. It is also possible to access the left atrium via the superior vena cava, or to use a retrograde intra-arterial technique.  
         [0075]    Next, in step  58  a guidewire is advanced through the guiding sheath, through the left atrial chamber, into a pulmonary vein.  
         [0076]    The order in which the specific pulmonary veins are visited and treated is arbitrary, but it is preferable to concentrate first on the two superior pulmonary veins, in which the muscular sleeves are more prominent than in the inferior pulmonary veins. Thereafter the inferior pulmonary veins may be isolated. Typically, an ablation procedure involves the isolation of all four pulmonary veins.  
         [0077]    Reference is now made to FIG. 6, which schematically illustrates certain aspects of the method of electrical pulmonary vein isolation in accordance with a preferred embodiment of the invention. The description of FIG. 6 should be read in conjunction with FIG. 5. FIG. 6 represents the status at the completion of step  58  (FIG. 5). A cutaway view of a left atrial chamber  60  includes a right superior pulmonary vein  62  and a left superior pulmonary vein  64 , whose ostium  66  is indicated. The view of FIG. 6 also includes a right inferior pulmonary vein  68 , and a left inferior pulmonary vein  70 . A conventional guiding sheath  72  has a distal end  74  which has been positioned on the left atrial side of an interatrial septum  76 . A conventional guidewire  78  extends through the lumen of the guiding sheath  72 , into the lumen of the left superior pulmonary vein  64 . It will be understood that while the guidewire  78  is shown in relation to the left superior pulmonary vein  64 , the technique is equally applicable to the other pulmonary veins.  
         [0078]    Referring again to FIG. 5, at step  80  the guiding sheath is withdrawn, and an ablation catheter is slidably tracked over the guidewire, using the guidewire lumen of the catheter. The catheter is advanced into the left atrium. While maneuvering the catheter in the heart, its position is preferably monitored by the location and mapping system disclosed in the above-noted U.S. Pat. No. 5,840,025, or alternatively by conventional imaging modalities. The anchoring balloon of the catheter is deflated during the positioning maneuver. The tip of the catheter is advanced until it is located at the ostium of a pulmonary vein, such that a first segment of the catheter&#39;s anchoring balloon, which is substantially the balloon&#39;s proximal third, is disposed in the left atrium, and a second segment of the anchoring balloon, composed of its remaining distal portion, lies within the lumen of the pulmonary vein.  
         [0079]    Reference is now made to FIG. 7, which schematically illustrates certain aspects of the method of electrical pulmonary vein isolation in accordance with a preferred embodiment of the invention. The description of FIG. 7 should be read in conjunction with FIGS. 5 and 6. FIG. 7 represents the status at the completion of step  80  (FIG. 5). Structures in FIG. 7 which are identical to corresponding structures in FIG. 6 have been given like reference numerals. The shaft of the catheter  10  extends through the interatrial septum  76 . A portion of the anchoring balloon  22  is disposed across the ostium  66  of the left superior pulmonary vein  64 . The guidewire  78  is still in position. The optical fiber  28  has not yet been introduced. During placement, the anchoring balloon  22  is deflated.  
         [0080]    Referring again to FIG. 5, at step  82  the anchoring balloon  22  is inflated to fix the catheter  10  in position. The guidewire  78  is withdrawn, and the optical fiber  28  is introduced into the catheter  10  via the lumen  24 , or is pre-fixed to the distal end of the catheter  10 . The mirror  34  is positioned proximal to the anchoring balloon, to be in a position to reflect the laser output of the optical fiber  28 , such that the light essentially simultaneously impinges upon an entire ring in or adjacent to the inner lining of the pulmonary vein. Perfusion of the area through one of the catheter ports may be employed during step  82  to minimize stasis of blood in the region.  
         [0081]    In step  84 , once the position of the mirror  34  is confirmed, the laser light source  32  is energized, and light energy is conducted from the optical fiber  28  to the target tissue.  
         [0082]    Reference is now made to FIG. 8, which schematically illustrates certain aspects of the method of electrical pulmonary vein isolation in accordance with a preferred embodiment of the invention. The description of FIG. 8 should be read in conjunction with FIGS. 5 and 7, in which like reference numbers denote the same element throughout. FIG. 8 represents the status at step  84  (FIG. 5). The anchoring balloon  22  is inflated, and the optical fiber  28  has been introduced such that its distal end is at the distal end  14  of the catheter  10 . The mirror  34  is positioned in readiness for reception of laser light from the optical fiber  28 .  
         [0083]    Referring again to FIG. 5, the transfer of laser light energy from the optical fiber  28  to the pulmonary vein in step  84  preferably occurs in a single, relatively short application. The output of the laser light source  32  (FIG. 2) is preferably infrared light at about 13 microns. This wavelength has a low absorption coefficient in water and is therefore suitable for transfer of energy to the ablation zone. It is recommended to deliver short pulses of energy of a few milliseconds each. Pulses less than 100 milliseconds are most preferred. The energy application may be controlled in response to continuous electrophysiological monitoring, an end point being reached when conduction block is confirmed across the line of ablation. Alternatively, it may continue for a duration predetermined to cause conduction block, substantially without feedback. In this latter case, electrophysiological data recorded while the catheter is still in position are preferably analyzed, so as to determine whether a second period of energy application is desired.  
         [0084]    Upon completion of the ablation, in step  86  the anchoring balloon is deflated and the mirror  34  retracted. The tip of the catheter is withdrawn into the left atrial chamber. The optical fiber  28  is also withdrawn from the catheter  10 , if appropriate.  
         [0085]    Next, at decision step  88 , a test is made to determine if more pulmonary veins remain to be electrically isolated. If the determination is affirmative then control proceeds to step  90 , where the next pulmonary vein is selected. Control then returns to step  58 .  
         [0086]    If the determination at decision step  88  is negative, then control proceeds to final step  92 . The anchoring balloon is deflated, and the entire apparatus withdrawn from the patient. The procedure thereupon terminates.  
         [0087]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art which would occur to persons skilled in the art upon reading the foregoing description.