Abstract:
Methods and apparatus for an ablation device used in the treatment of atrial fibrillation comprise an elongate shaft and a positioning mechanism adjacent the distal end of the shaft. The positioning mechanism is adapted to facilitate location of an anatomic structure and also to anchor the elongate shaft adjacent the anatomic structure. The positioning mechanism comprises an electrode for stimulating the anatomic structure as well as sensing electrical signals. Also, an energy delivery element is adjacent the distal end of the shaft and is adapted to stimulate the anatomic structure and create a zone of ablation that blocks abnormal electrical activity thereby reducing or eliminating atrial fibrillation in the patient.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional of, and claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 61/061,362 (Attorney Docket No. 027680-000200US) filed Jun. 13, 2008, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to medical devices and methods, and more specifically to improved devices and methods for positioning an ablation device in a human or animal patient. The device may be used to treat atrial fibrillation. 
         [0004]    The condition of atrial fibrillation is characterized by the abnormal (usually very rapid) beating of left atrium of the heart which is out of synch with the normal synchronous movement (“normal sinus rhythm”) of the heart muscle. In normal sinus rhythm, the electrical impulses originate in the sino-atrial node (“SA node”) which resides in the right atrium. The abnormal beating of the atrial heart muscle is known as fibrillation and is caused by electrical impulses originating instead in the pulmonary veins (“PV”) [Haissaguerre, M. et al., Spontaneous Initiation of Atrial Fibrillation by Ectopic Beats Originating in the Pulmonary Veins, New England J Med., Vol. 339: 659-666]. 
         [0005]    There are pharmacological treatments for this condition with varying degrees of success. In addition, there are surgical interventions aimed at removing the aberrant electrical pathways from PV to the left atrium (“LA”) such as the Cox-Maze III Procedure [J. L. Cox et al., The development of the Maze procedure for the treatment of atrial fibrillation, Seminars in Thoracic &amp; Cardiovascular Surgery, 2000; 12: 2-14; J. L. Cox et al., Electrophysiologic basis, surgical development, and clinical results of the maze procedure for atrial flutter and atrial fibrillation, Advances in Cardiac Surgery, 1995; 6: 1-67; and J. L. Cox et al., Modification of the maze procedure for atrial flutter and atrial fibrillation. II, Surgical technique of the maze III procedure, Journal of Thoracic &amp; Cardiovascular Surgery, 1995; 2110: 485-95]. This procedure is shown to be 99% effective [J. L. Cox, N. Ad, T. Palazzo, et al. Current status of the Maze procedure for the treatment of atrial fibrillation, Seminars in Thoracic &amp; Cardiovascular Surgery, 2000; 12: 15-19] but requires special surgical skills and is time consuming. 
         [0006]    There has been considerable effort to copy the Cox-Maze procedure for a less invasive percutaneous catheter-based approach. Less invasive treatments have been developed which involve use of some form of energy to ablate (or kill) the tissue surrounding the aberrant focal point where the abnormal signals originate in PV. The most common methodology is the use of radio-frequency (“RF”) electrical energy to heat the muscle tissue and thereby ablate it. The aberrant electrical impulses are then prevented from traveling from PV to the atrium (achieving conduction block within the heart tissue) and thus avoiding the fibrillation of the atrial muscle. Other energy sources, such as microwave, laser, and ultrasound have been utilized to achieve the conduction block. In addition, techniques such as cryoablation, administration of ethanol, and the like have also been used. 
         [0007]    There has been considerable effort in developing the catheter based systems for the treatment of AF using radiofrequency (RF) energy. One such method is described in U.S. Pat. No. 6,064,902 to Haissaguerre et al. In this approach, a catheter is made of distal and proximal electrodes at the tip. The catheter can be bent in a J shape and positioned inside a pulmonary vein. The tissue of the inner wall of the PV is ablated in an attempt to kill the source of the aberrant heart activity. Other RF based catheters are described in U.S. Pat. Nos. 6,814,733 to Schwartz et al., 6,996,908 to Maguire et al., 6,955,173 to Lesh; and 6,949,097 to Stewart et al. 
         [0008]    Another source used in ablation is microwave energy. One such device is described by Dr. Mark Levinson [(Endocardial Microwave Ablation: A New Surgical Approach for Atrial Fibrillation; The Heart Surgery Forum, 2006] and Maessen et al. [Beating heart surgical treatment of atrial fibrillation with microwave ablation.  Ann Thorac Surg  74: 1160-8, 2002]. This intraoperative device consists of a probe with a malleable antenna which has the ability to ablate the atrial tissue. Other microwave based catheters are described in U.S. Pat. Nos. 4,641,649 to Walinsky; 5,246,438 to Langberg; 5,405,346 to Grundy, et al.; and 5,314,466 to Stem, et al. 
         [0009]    Another catheter based method utilizes the cryogenic technique where the tissue of the atrium is frozen below a temperature of −60 degrees C. This results in killing of the tissue in the vicinity of the PV thereby eliminating the pathway for the aberrant signals causing the AF [A. M. Gillinov, E. H. Blackstone and P. M. McCarthy, Atrial fibrillation: current surgical options and their assessment, Annals of Thoracic Surgery 2002; 74:2210-7]. Cryo-based techniques have been a part of the partial Maze procedures [Sueda T., Nagata H., Orihashi K., et al., Efficacy of a simple left atrial procedure for chronic atrial fibrillation in mitral valve operations, Ann Thorac Surg 1997; 63: 1070-1075; and Sueda T., Nagata H., Shikata H., et al.; Simple left atrial procedure for chronic atrial fibrillation associated with mitral valve disease, Ann Thorac Surg 1996; 62: 1796-1800]. More recently, Dr. Cox and his group [Nathan H., Eliakim M., The junction between the left atrium and the pulmonary veins, An anatomic study of human hearts, Circulation 1966; 34: 412-422, and Cox J. L., Schuessler R. B., Boineau J. P., The development of the Maze procedure for the treatment of atrial fibrillation, Semin Thorac Cardiovasc Surg 2000; 12: 2-14] have used cryoprobes (cryo-Maze) to duplicate the essentials of the Cox-Maze III procedure. Other cryo-based devices are described in U.S. Pat. Nos. 6,929,639 and 6,666,858 to Lafintaine and 6,161,543 to Cox et al. 
         [0010]    More recent approaches for the AF treatment involve the use of ultrasound energy. The target tissue of the region surrounding the pulmonary vein is heated with ultrasound energy emitted by one or more ultrasound transducers. One such approach is described by Lesh et al. in U.S. Pat. No. 6,502,576. Here the catheter distal tip portion is equipped with a balloon which contains an ultrasound element. The balloon serves as an anchoring means to secure the tip of the catheter in the pulmonary vein. The balloon portion of the catheter is positioned in the selected pulmonary vein and the balloon is inflated with a fluid which is transparent to ultrasound energy. The transducer emits the ultrasound energy which travels to the target tissue in or near the pulmonary vein and ablates it. The intended therapy is to destroy the electrical conduction path around a pulmonary vein and thereby restore the normal sinus rhythm. The therapy involves the creation of a multiplicity of lesions around individual pulmonary veins as required. The inventors describe various configurations for the energy emitter and the anchoring mechanisms. 
         [0011]    Yet another catheter device using ultrasound energy is described by Gentry et al. [Integrated Catheter for 3-D Intracardiac Echocardiography and Ultrasound Ablation, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 51, No.7, pp 799-807]. Here the catheter tip is made of an array of ultrasound elements in a grid pattern for the purpose of creating a three dimensional image of the target tissue. An ablating ultrasound transducer is provided which is in the shape of a ring which encircles the imaging grid. The ablating transducer emits a ring of ultrasound energy at 10 MHz frequency. In a separate publication [Medical Device Link, Medical Device and Diagnostic Industry, February 2006], in the description of the device, the authors assert that the pulmonary veins can be imaged. 
         [0012]    While these devices and methods are promising, improved devices and methods for positioning a device relative to an anatomic structure such as the pulmonary vein are needed. Furthermore, it would also be desirable if such devices could create single or multiple ablation zones to block abnormal electrical activity in the heart in order to lessen or prevent atrial fibrillation. Such devices and methods should be easy to use, cost effective and simple to manufacture. 
         [0013]    2. Description of Background Art 
         [0014]    Other devices based on ultrasound energy to create circumferential lesions are described in U.S. Pat. Nos. 6,997,925; 6,966,908; 6,964,660; 6,954,977; 6,953,460; 6,652,515; 6,547,788; and 6,514,249 to Maguire et al.; 6,955,173; 6,052,576; 6,305,378; 6,164,283; and 6,012,457 to Lesh; 6,872,205; 6,416,511; 6,254,599; 6,245,064; and 6,024,740; to Lesh et al.; 6,383,151; 6,117,101; and WO 99/02096 to Diederich et al.; 6,635,054 to Fjield et al.; 6,780,183 to Jimenez et al.; 6,605,084 to Acker et al.; 5,295,484 to Marcus et al.; and WO 2005/117734 to Wong et al. 
         [0015]    In all above approaches, the inventions involve the ablation of tissue inside a pulmonary vein or at the location of the ostium. The anchoring mechanisms engage the inside lumen of the target pulmonary vein. In all these approaches, the anchor is placed inside one vein, and the ablation is done one vein at a time. 
       BRIEF SUMMARY OF THE INVENTION 
       [0016]    The present invention generally relates to medical devices and methods and more particularly relates to devices and methods for positioning an ablation device used in the treatment of atrial fibrillation. 
         [0017]    In a first aspect of the present invention, an ablation device for treating atrial fibrillation in a patient comprises an elongate shaft having a proximal end and a distal end. A positioning mechanism is adjacent the distal end of the shaft and is adapted to facilitate location of an anatomic structure and also adapted to anchor the elongate shaft adjacent the anatomic structure. The positioning mechanism comprises an electrode for stimulating the anatomic structure and also for sensing electrical signals from the anatomic structure. An energy delivery element is adjacent the distal end of the shaft and is adapted to stimulate the anatomic structure and create a zone of ablation that blocks abnormal electrical activity thereby reducing or eliminating atrial fibrillation in the patient. 
         [0018]    The elongate shaft may comprise a lumen extending between the proximal and distal ends of the shaft. The shaft may be rotatable around the positioning mechanism. The shaft may also have a sidewall with a window therethrough, and the energy delivery element may be adapted to stimulate the anatomic structure through the window. 
         [0019]    The positioning mechanism may be slidably disposed in the lumen, and it may be in a substantially linear configuration while disposed in the lumen. The positioning mechanism may exit the shaft via an aperture in a sidewall of the shaft. The positioning mechanism may comprises a coil or a plurality of wires expandable from a contracted configuration to an expanded configuration. In the expanded configuration, the plurality of wires may form a cage-like structure. The plurality of wires may also be biased to flare radially outward when unconstrained. The positioning mechanism may be adapted to exert an outward biasing force against an interior surface of the anatomical structure thereby anchoring the elongate shaft thereto. The anatomic structure may be a pulmonary vein and the positioning mechanism may be adapted to indicate an angle of entry of the elongate shaft into the pulmonary vein. In still other embodiments, the positioning mechanism may comprise a proximal wire and a distal wire, both proximal and distal wires at least partially encircling the elongate shaft. 
         [0020]    The electrode may operate in a monopolar mode or the electrode may comprise a plurality of electrodes operating in a bipolar mode. 
         [0021]    The energy delivery element may comprise an ultrasound transducer. The energy delivery element may also be adapted to deliver radiofrequency energy, microwaves, light energy, thermal energy, or cryogenic cooling to the anatomic structure. The zone of ablation may be a linear region, an annular region, or an arcuate. The zone of ablation may encircle one or more than one pulmonary veins or the zone of ablation may be outside of and adjacent a pulmonary vein. The energy delivery element often may remain unobstructed by the positioning mechanism. 
         [0022]    In another aspect of the present invention, a method of ablating an anatomic structure in a patient as a treatment for atrial fibrillation comprises providing an elongate shaft having a proximal end and a distal end and locating the anatomic structure with a positioning mechanism disposed adjacent the distal end of the shaft. The shaft is anchored adjacent the anatomic structure with the positioning mechanism and an electrode adjacent a distal portion of the positioning mechanism is used to electrically stimulate or sense electrical signals from the anatomic structure. Energy is delivered to the anatomic structure with an energy delivery element near the distal end of the shaft, thereby creating a zone of ablation that blocks abnormal electrical activity in order to reduce or eliminate atrial fibrillation in the patient. 
         [0023]    The elongate shaft may comprise a lumen extending between the proximal and distal ends and the method may further comprise delivering a fluid from the lumen to the anatomic structure. The step of locating the anatomic structure may comprise visualizing the anatomic structure, or tactile or audible feedback. The positioning mechanism may be advanced from or retracted into the elongate shaft during the step of locating. The positioning mechanism may comprise a plurality of wires and the anatomic structure may be located by deflecting at least some of the plurality of wires. Locating the anatomic structure may also comprise determining an entry angle of the elongate shaft into the anatomic structure. 
         [0024]    The step of anchoring the shaft may comprise engaging the positioning mechanism against the anatomical structure and exerting an outward biasing force against an interior surface of the anatomical structure. Anchoring may also comprise forming and engaging a cage-like structure on the positioning mechanism with the anatomic structure. 
         [0025]    The step of stimulating the anatomic structure may comprise stimulating in a monopolar or bipolar mode. Stimulating may also comprise pacing the patient&#39;s heart. The stimulating step may be performed before, during or after creation of the ablation zone. 
         [0026]    Delivering energy to the anatomic structure may comprise delivering one of ultrasound energy, radiofrequency energy, microwave, light, and thermal energy. The step of creating the zone of ablation may comprise creating a linear or arcuate ablation path such as when the zone of ablation encircles one or more than one pulmonary vein. Sometimes the elongate shaft may be rotated around the positioning mechanism while delivering energy. The energy may be delivered through a window in the elongate shaft and the energy may be directed at an angle between 65 and 115 degrees to the anatomic structure. Delivering energy may comprise adjusting power, frequency, bandwidth, or amplitude of the energy delivered to the anatomic structure. The method may further comprise cooling the anatomic structure with cooling fluid. 
         [0027]    These and other embodiments are described in further detail in the following description related to the appended drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0028]      FIGS. 1A and 1B  are drawings of the system of the preferred embodiment of the invention; 
           [0029]      FIGS. 2-4  are drawings of three rotation variations of the system of the preferred embodiment of the invention; 
           [0030]      FIGS. 5-8C  are drawings of a first variation of the positioning mechanism of the system of the preferred embodiment of the invention; 
           [0031]      FIGS. 9A and 9B  are drawings of a second variation of the positioning mechanism of the system of the preferred embodiment of the invention; 
           [0032]      FIGS. 10A and 10B  are drawings of a third variation of the positioning mechanism of the system of the preferred embodiment of the invention; 
           [0033]      FIG. 11  is a drawing of a fourth variation of the positioning mechanism of the system of the preferred embodiment of the invention; and 
           [0034]      FIG. 12  is a drawing of a fifth variation of the positioning mechanism of the system of the preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    The following description of preferred embodiments of the invention is not intended to limit the invention to these embodiments, but rather to enable any person skilled in the art to make and use this invention. 
         [0036]    As shown in  FIGS. 1A and 2 , the system  10  of the preferred embodiments includes an elongate member  12  and a positioning mechanism  14  coupled to the elongate member  12 . The elongate member  12  may be radiopaque to allow it to be seen during fluoroscopy. This may be achieved with radiopaque marker bands or by including radiopaque filler materials in the elongate member such as barium sulfate or titanium dioxide. The positioning mechanism  14  performs one or more of the following functions: (a) facilitate locating an anatomical structure (preferably a pulmonary vein  3000  in a left atrium of a heart  3002 , but alternatively any other suitable anatomical structure), (b) anchor the elongate member  12  with respect to the anatomical structure, and (c) electrically stimulate and/or sense electrical signals from the anatomical structure. The system  10  is preferably designed for positioning an elongate member within a patient and, more specifically, for positioning a therapy and/or navigation catheter with respect to a pulmonary vein in the left atrium of the heart of a patient. The system  10 , however, may be alternatively used in any suitable environment and for any suitable reason. 
         [0037]    The Elongate Member. The elongate member  12  of the preferred embodiments is a catheter made of a flexible multi-lumen tube, but may alternatively be a cannula, tube or any other suitable elongate structure having one or more lumens. The elongate member  12  preferably has a separate lumen that houses the positioning mechanism  14 , but may alternatively house the positioning mechanism  14  in any other suitable configuration. The elongate member  12  preferably houses a single positioning mechanisms  14  (as shown in  FIG. 1A ), but may house more than one positioning mechanisms (as shown in  FIG. 2 ). The elongate member  12  of the preferred embodiments functions to accommodate pull members, fluids, gases, energy delivery structures, electrical connections, therapy catheters, navigation catheters, pacing catheters, and/or any other suitable device or element. As shown in  FIG. 2 , the elongate member  12  preferably includes a distal tip assembly  16  positioned at a distal portion of the elongate member  12 . The distal tip assembly  16  preferably houses an energy delivery structure  18  that functions to deliver energy  20  to tissue, such as tissue of a heart  3002 . The energy delivery structure  18  preferably includes an ultrasound transducer subassembly, but may alternatively include any other suitable source of ablation energy such as radio frequency (RF) energy, microwaves, photonic energy, and thermal energy. Ablation could alternatively be achieved using cooled fluids (e.g., cryogenic fluid). 
         [0038]    The Positioning Mechanism. As shown in  FIGS. 1A and 1B , the positioning mechanism  14  of the preferred embodiments is coupled to a distal portion of the elongate member  12 . As shown in  FIG. 1A , the positioning mechanism  14  is preferably coupled to the distal tip of the elongate member  12 . The positioning mechanism  14  is preferably coupled to the distal tip of the elongate member  14  such that fluid (for cooling the energy delivery system  18  or for cooling the tissue, for example) is able to flow through a lumen in the elongate member  12  and exit out of the elongate member as necessary. Alternatively, as shown in  FIG. 1B , the positioning mechanism  14  is preferably coupled to the side of the elongate member  12  near the distal end of the elongate member  12 . In some variations, the positioning member  14  is retractable into and exits from the elongate member  12  through the distal end or through a notch  22  near the distal end of the elongate member  12 . In these variations, the positioning member  14  preferably is held in or moves to a smaller configuration (by folding, straightening, etc.) such that it fits within the elongate member  12 . The positioning member, when residing completely inside a lumen of the elongate member  12 , is preferably held in a generally straight shape, conforming to confines of the lumen. As the positing member  14  is advanced outwards, and/or as it exits the notch  22 , it preferably takes on a predetermined shape, for example as shown in  FIGS. 1B ,  5 , and  11 . 
         [0039]    As shown in  FIG. 2 , the positioning mechanism  14  of the preferred embodiments performs one or more of the following functions: (a) facilitate locating an anatomical structure, (b) anchor the elongate member  12  with respect to the anatomical structure, and (c) electrically stimulate and/or sense electrical signals from the anatomical structure. Regarding the first function, the positioning mechanism  14  facilitates locating an anatomical structure by providing an indication of where the positioning mechanism  14  is with respect to the anatomical structure. The indication is preferably a visual indication (via a medical imaging system such as a fluoroscope), but is alternatively or additionally a tactile or audible indication. Additionally, the elongate member  12  and/or the positioning mechanism  14  may include indicia, such as markings indicating distance, that indicate the location of the anatomical structure and/or to indicate the depth of insertion of the system  10  where the anatomical structure was located. 
         [0040]    Regarding the second function, the positioning mechanism  14  anchors the elongate member  12  with respect to the anatomical structure by coupling to a portion of an anatomical structure (for example a pulmonary vein  3000  and/or a left atrium  3002  of a heart) and by providing stabilization of the elongate member  12  when manipulating at least a portion of the elongate member  12  and/or by providing an axis of rotation to the elongate member  12  as it is rotated. The elongate member  12  is preferably manipulated to position the energy delivery structure  18  within the left atrium of the heart  3002  (or in any other suitable location) and, once positioned there, is preferably manipulated to move the energy delivery structure  18  along an ablation path and to direct the energy delivery structure  18  towards tissue to provide a partial or complete zone of ablation along the ablation path. The ablation path preferably has any suitable geometry or geometries to provide a conduction block—isolation and/or block of conduction pathways of abnormal electrical activity, which typically originate from the pulmonary veins in the left atrium—for treatment of atrial fibrillation in a patient, but may alternatively provide any other suitable therapy. A linear ablation path is preferably created by moving and bending the elongate member  12  in an X, Y, and/or Z direction. A generally circular or elliptical ablation path  30  is preferably created by rotating the elongate member  12  about an axis. The elongate member  12  is preferably rotated in one of several variations. In a first variation, as shown in  FIG. 2 , the elongate member is rotated, as shown by arrow  3010 , around the two positioning mechanisms  14 , the energy delivery structure  18  preferably sweeps a generally circular ablation path  30 . The two positioning mechanisms  14  preferably assure that the rotation of the elongate member  12  and therefore the energy delivery structure  18  will occur in an ablation path  30  outside of the pulmonary veins  3000  and  3000 ′. The ablation path  30  may alternatively encircle a single pulmonary vein or encircle any other suitable number of pulmonary veins. 
         [0041]    In a second variation, as shown in  FIG. 3 , the elongate member is rotated, as shown by arrow  3012 , within the pulmonary vein  3000  such that the energy delivery structure  18  preferably sweeps a generally circular ablation path  30 , generally perpendicular to the axis of the pulmonary vein  3000 . In an alternative version of this second variation, the elongate member may alternatively be located outside of and adjacent to the pulmonary vein while still generally perpendicular to the axis of the pulmonary vein  3000 . The elongate member is preferably rotated such that the energy delivery structure  18  preferably sweeps a generally circular ablation path  30  around at least one ostium of a pulmonary vein. In this version of the second variation, the energy delivery structure  18  is preferably angled such that it is preferably at an acute angle with respect to the axis of the elongate member and such that the energy delivery structure preferably points and delivers energy  20  substantially towards the atrial wall and around the pulmonary vein ostium. In the second variation, the energy delivery structure  18  preferably rotates within the distal tip assembly  16 , delivering ablation energy though a window that runs around the circumference of the distal tip assembly  16 . The window is preferably made of a material that is transparent to ultrasound waves such as a poly 4-methyl, 1-pentene (PMP) material or may alternatively be an open window. Alternatively, the elongate member  12  and/or distal tip assembly  16  may rotate, rotating the energy delivery structure within. The positioning mechanism  14  preferably does not rotate along with the elongate member  12  and/or the distal tip assembly  16 . 
         [0042]    In a third variation, as shown in  FIG. 4 , the positioning mechanism  14  is pressed against a portion of a heart chamber (such as the ceiling wall of the left atrium), or in any other suitable location and the elongate member  12  is rotated, as shown by arrow  3014 , around the axis created by the positioning mechanism  14 , the energy delivery structure  18  preferably sweeps a generally circular ablation path outside of the pulmonary veins  3000  and  3000 ′. The ablation path may alternatively encircle a single pulmonary vein or any other suitable number of pulmonary veins. 
         [0043]    In all variations, the energy delivery structure is preferably positioned with respect to the tissue at an appropriate angle. The energy delivery system is preferably directed towards the target tissue at an angle between 20 and 160 degrees to the tissue, more preferably at an angle between 45 and 135 degrees to the tissue, and most preferably at an angle of 65 and 115 degrees to the tissue. 
         [0044]    Regarding the third function, the positioning mechanism  14  electrically stimulates and/or senses electrical signals from the anatomical structure by electrically coupling to the anatomical structure and sending and/or receiving electrical signals to the tissue. The positioning mechanism  14  preferably includes an even number of electrodes or electrically active portions such that a bipolar electrical system may be used, wherein each pair of electrodes or electrically active portions has an opposite polarity. The positioning mechanism  14  may alternatively include a single electrode or electrically active portion and use a monopolar electrical system, or may include any other suitable number of electrodes or electrically active portions. The positioning mechanism  14  functions to map the tissue by sensing the electrical conduction between the pulmonary veins and the other parts of the atrial wall on the endocardial side. The positioning mechanism  14  functions to pace the tissue and maintain an artificial heart rate (preferably temporarily) by sending electrical pulses to the tissue. The positioning mechanism  14  preferably paces the tissue located in a position distal from the energy delivery structure  18  and/or the ablation path  30 , such that the energy delivery structure  18  and/or the ablation path  30  are between the positioning mechanism  14  that is pacing and the beating heart. The positioning mechanism may alternatively pace tissue in any other suitable location. The recording and sensing signals received and sent by the positioning mechanism are preferably compatible with conventional navigation and mapping systems such as CARTO XP EP Navigation System (Biosense Webster, Diamond Bar, Calif.), EnSite System (St. Jude Medical, St. Paul, Minn.), and/or any other suitable mapping, navigation, or visualization system. 
         [0045]    As mentioned above, the positioning mechanism  14  of the preferred embodiments performs one or more of the following functions: (a) facilitate locating an anatomical structure, (b) anchor the elongate member  12  with respect to the anatomical structure, and (c) electrically stimulate and/or sense electrical signals from the anatomical structure. Although the positioning mechanism  14  is preferably one of the several variations described below, the positioning mechanism  14  may be any suitable mechanism to perform one or more of these functions. 
         [0046]    First Variation of the Positioning Mechanism. In a first variation, as shown in  FIGS. 5 ,  6 A, and  6 B, the positioning mechanism  14 ′ includes a plurality of wires each having a first end  24  and a second end  26 . The plurality of wires are preferably flexible wires, but may alternatively be movable in any other suitable fashion. The first end  24  is preferably coupled to the distal tip of the elongate member  12 , but may alternatively be attached in any other suitable location (shown in  FIG. 4 ). The second end  26  preferably extends from the distal tip of the elongate member and is positioned in a fully extended position, as shown in  FIG. 5 . The second end  26  preferably deflects due to contact with a surface, as shown in  FIGS. 6A and 6B . The second end  26  is preferably biased towards the fully extended position, but may alternatively be biased towards any other suitable position. The first end  24  is preferably slidably coupled to the elongate member  12  such that it is partially or fully retractable into the elongate member  12 . For example, the plurality of wires may be pushed or pulled through the distal tip of the elongate member  12  by a wire that extends through the elongate member  12 . The plurality of wires may be pulled back through the distal tip of the elongate member  12  in order to return the wires to the fully extended position, as shown in  FIG. 5 . The plurality of wires may alternatively be fixed to the distal tip of the elongate member  12  or coupled to the elongate member  12  in any other suitable fashion. The wires are preferably made from a conductive material and/or a material with shape memory such as nickel/titanium or a shape memory polymer. The material is preferably flexible so as not to cause injury to the tissue of the heart where the positioning mechanism  14 ′ might contact and move against it. At least a portion of each wire is preferably made from a fluoro-opaque material, such as platinum or gold, such that it may be seen while positioned inside the internal structures of a patient through the use of a fluoroscope. The fluoro-opaque portion  28  is preferably located at the second end  26  of a wire, but may alternatively be located in any suitable position such that it may be seen while positioned inside the internal structures of a patient through the use of a fluoroscope. The fluoro-opaque portion is preferably flush with the wire, but may alternatively have a round or any other suitable shape such that it will not damage the tissue. Additionally, the plurality of wires preferably includes at least one electrically active portion and/or at least one insulated portion (e.g. an insulating coating on a portion of each wire). The electrically active portion is preferably located at the second end  26  of a wire, but may alternatively be located in any suitable position, such as the center portion, such that it conies in contact with tissue. 
         [0047]    The plurality of wires preferably has any suitable geometry such that positioning mechanism  14 ′ may perform any combination of functions described. Additionally, the plurality of wires preferably have a length and/or geometry such that when they deflect, they do not cover, block, or lay in front of the energy delivery structure  18 , or any portion thereof. Therefore, they preferably do not block any portion of the energy delivered by the energy delivery structure  18  and cause a “shadow” effect. In a first version, as shown in  FIG. 5 , the wires are substantially straight. In a second version, as shown in  FIG. 8A , the wires are curved or bent such that they are biased away from the elongate member  12 . In a third version, as shown in  FIG. 8B , the plurality of wires includes six wires circumferentially disposed around the elongate member  12 . The plurality of wires preferably includes an even number of wires, but may alternatively include a single wire or any other suitable number of wires. In a fourth version, as shown in  FIG. 8C , the plurality of wires includes multiple tiers or layers of wires. Each tier or layer may include any suitable number of wires and each tier or level may include a different number of wires from any other tier or level. 
         [0048]    As shown in  FIGS. 6A and 6B , the plurality of wires function to facilitate locating an anatomical structure by flexing as they come in contact with the anatomical structure. For example, the wires will remain fully extended from the elongate member  12  when they are unobstructed in the left atrium of the heart  3002 , as shown in  FIG. 4 . As the system  10  is moved within the left atrium of the heart  3002  and begins to contact the ostium (opening) of a pulmonary vein  3000 , the plurality of wires will begin to deflect partially, as shown in  FIG. 6A . As the system  10  is moved into the pulmonary vein  3000 , the wires will deflect more dramatically as shown in  FIG. 6B . As the system is moved deeper into the pulmonary vein, the wires will not deflect as much, if at all, and an operator of the system  10  will be able to determine when the positioning mechanism  14  of the system  10  is correctly located within the pulmonary vein. 
         [0049]    Furthermore, as shown in  FIG. 7 , the angle  3004  at which the system  10  enters the pulmonary vein  3000  with respect to the longitudinal axis of the pulmonary vein  3000  is determined. For example, if the system  10  is entering the pulmonary vein  3000  at angle  3004 , a wire to the left of the elongate member  12  will deflect to an angle  3006  with respect to the elongate member  12  while a wire to the right of the elongate member  12  will deflect to an angle  3008  with respect to the elongate member  12 . Therefore, the angle  3004  at which the system  10  is entering the pulmonary vein  3000  is preferably determined from the size of angles  3006  and  3008 . These angles  3006  and  3008  are preferably detected visually under fluoroscopic guidance by the operator of the system  10 , but may alternatively be detected and processed by a processor in order to determine angle  3004 . Upon the detection of the angle  3004 , an operator of the system  10  is alerted of an off-center entry, the operator adjusts and centers the system  10  and/or is instructed on how to do so. The system  10  may alternatively be adjusted automatically through a motor drive system or any other suitable system. The ablation path  30  is preferably altered such that energy delivery structure will be located substantially the same distance from each point of tissue along the ablation path  3  and/or the energy delivery structure is preferably adjusted to accommodate an off-center entry. The energy delivery structure is preferably adjusted by changing the power and/or frequency, bandwidth, and amplitude of the sound wave propagated into the tissue along certain portions of an ablation path  30 . Due to an off-center entry, the energy delivery structure will be closer to some tissue along the ablation path  30  and further away from other tissue. In one example, the energy delivery structure is adjusted to use less power for the portions of the tissue that are closer to the energy delivery structure. 
         [0050]    The plurality of wires function to anchor the elongate member  12  with respect to the anatomical structure, preferably a pulmonary vein  3000 , by coupling to the anatomical structure. The outward biasing force of the plurality of wires against the interior wall of the pulmonary vein will preferably hold the positioning mechanism  14 ′ within the pulmonary vein due to friction. Alternatively, the tips of the plurality of wires may function as barbs such that the plurality of wires are preferably advanced into the pulmonary vein, but the tips of the wires will prevent the positioning mechanism  14  from being pulled out of the pulmonary vein. In this version, the wires may be manually retracted upon completion of the procedure to allow for the removal of the positioning mechanism  14 ′. The positioning mechanism may alternatively function to anchor the elongate member  12  with respect to the anatomical structure in any other suitable fashion. 
         [0051]    Second Variation of the Positioning Mechanism. In a second variation, as shown in  FIGS. 9A and 9B , the positioning mechanism  14 ″ includes a plurality of wires, a first end cap  32 , a second end cap  34 , and a pull member  36 . The plurality of wires are circumferentially disposed around the elongate member  12 . The plurality of wires preferably includes an even number of wires such as two, four, six, eight, or more, but may alternatively include a single wire or any other suitable number of wires. The first end cap  32  is preferably coupled to the distal tip of the elongate member  12 , but may alternatively be attached in any other suitable location, as shown in  FIG. 4 . The second end cap  34  preferably extends from the distal tip of the elongate member  12  along the longitudinal axis of the elongate member  12  and transitions between a fully extended position, as shown in  FIG. 9A , and a retracted position, as shown in  FIG. 9B . When the second end cap  34  is in the fully extended position, the wires are preferably substantially straight. When the second end cap  34  is in the retracted position, the wires preferably flex and bend at one location along the wire to form a basket or cage-like structure. The second end cap  34  preferably transitions between a fully extended position and a retracted position by pulling the pull member  36 . The pull member  36  is preferably coupled to the second end cap  34  and runs through the first end cap  32  such that the first end cap  32  is slidably coupled to the pull member  36 . Preferably, the pull member  36  is attached to the second end cap  34  with an adhesive band, but may alternatively be coupled to the second end cap  34  with any other suitable chemical and/or mechanical connection such as adhesive, welding, pins and/or screws. The pull member is preferably disposed within a lumen of the first end cap and the elongate member  12 , but may alternatively be held in any suitable location. The pull member preferably terminates at a slider in a proximal housing (not shown) that preferably includes various actuating mechanisms to transition the second end cap from the fully extended position to the retracted position. The second end cap preferably returns to the fully extended position by the spring force of the plurality of wires (they are preferably biased towards the substantially straight position), but may alternatively return to the fully extended position in any other suitable fashion. 
         [0052]    The wires may alternatively flex or bend in multiple locations and each wire may bend in a different location. The wires are preferably biased towards the substantially straight position, but may alternatively be biased towards the bent position or any other suitable position. The wires are preferably made from a conductive material and/or a material with shape memory such as nickel/titanium alloys or a shape memory polymer, but may alternatively be made from any suitable material such as plastic. The material is preferably flexible so as not to cause injury to the tissue of the heart where the positioning mechanism  14  might contact and move against it. At least a portion of each wire is preferably made from a fluoro-opaque material (also referred to herein using the term “radiopaque”), such as platinum or gold, such that it may be seen while positioned inside the internal structures of a patient through the use of a fluoroscope. The fluoro-opaque portion is preferably located in any suitable position such that it may be seen while positioned inside the internal structures of a patient through the use of a fluoroscope. The fluoro-opaque portion is preferably flush with the wire, but may alternatively have a round or any other suitable shape such that it will not damage the tissue. Additionally, the plurality of wires preferably includes at least one electrically active portion and/or at least one insulated portion (e.g. an insulating coating on a portion of each wire). The electrically active portion is preferably located towards the center portion of each wire, but may alternatively be located in any suitable position such that it comes in contact with tissue. 
         [0053]    The positioning mechanism  14 ″ functions to facilitate locating an anatomical structure by the plurality of wires flexing as they come in contact with the anatomical structure. For example, when the wires are flexed or bent as shown in  FIG. 9B , and as the system  10  is moved within the left atrium of the heart  3002  and begins to contact the ostium (opening) of a pulmonary vein  3000 , the plurality of wires will begin to deflect inward or away from the adjacent wires due to contact with a tissue surface. As the system is moved deeper into the pulmonary vein, the wires will not deflect as much if at all, and an operator of the system  10  will be able to determine when the positioning mechanism  14 ″ of the system  10  is correctly located within the pulmonary vein. 
         [0054]    The plurality of wires of the positioning mechanism  14 ″ function to anchor the elongate member  12  with respect to the anatomical structure, preferably a pulmonary vein  3000 , by coupling to the anatomical structure. Preferably, the outward force of the plurality of wires in the flexed or bent position, as shown in  FIG. 9B , against the interior wall of the pulmonary vein will hold the positioning mechanism  14 ″ within the pulmonary vein due to friction. In this version, the second end cap  34  will be returned to the fully extended position upon completion of the procedure, straightening the plurality of wires, to allow for the removal of the positioning mechanism  14 ″. The positioning mechanism  14 ″ may alternatively function to anchor the elongate member  12  with respect to the anatomical structure in any other suitable fashion. 
         [0055]    Third, Fourth, and Fifth Variation Positioning Mechanism. In a third variation, as shown in  FIGS. 10A and 10B , the positioning mechanism is a combination of the first and second variations of the positioning mechanisms  14 ′ and  14 ″. In this variation, the positioning mechanism preferably includes two pluralities of wires. The first plurality of wires has a first end  24  and a second end  26  as described above, and the second plurality of wires has a first end cap  32 , a second end cap  34 , and a pull member  36  also as described above. When the second end cap  34  is in the retracted position, as shown in  FIG. 10B , the second plurality of wires preferably flex and bend in one location to form a basket or cage-like structure. The first plurality of wires deflect due to contact with a surface and will preferably deflect down and in between the second plurality of wires such that they will not obstruct the function of the second plurality of wires. 
         [0056]    In a fourth variation, as shown in  FIG. 11 , the positioning mechanism  14 ″′ is a coil. The coil is preferably made from a conductive material and/or a material with shape memory such as nickel/titanium alloys or a shape memory polymer. The material is preferably flexible so as not to cause injury to the tissue of the heart where the positioning mechanism  14  might contact and move against it. At least a portion of the coil is preferably made from a fluoro-opaque material, such as platinum or gold, such that it may be seen while positioned inside the internal structures of a patient through the use of a fluoroscope. The fluoro-opaque portion is preferably located in any suitable position such that it may be seen while positioned inside the internal structures of a patient through the use of a fluoroscope. The fluoro-opaque portion is preferably flush with the wire, but may alternatively have a round or any other suitable shape such that it will not damage the tissue. Additionally, the coil preferably includes at least one electrically active portion and/or at least one insulated portion (e.g. an insulating coating on a portion of each wire). The electrically active portion is preferably located in any suitable position such that it comes in contact with tissue. 
         [0057]    The positioning mechanism  14 ″′ functions to facilitate locating an anatomical structure by the coil flexing as it comes in contact with the anatomical structure. For example, as the system  10  is moved within the left atrium of the heart  3002  and begins to contact the wall of the atrium or the ostium (opening) of a pulmonary vein  3000 , the coil will begin to deflect. As the system is moved deeper into the pulmonary vein, the wires will not deflect as much if at all, and an operator of the system  10  will be able to determine when the positioning mechanism  14 ″′ of the system  10  is correctly located within the pulmonary vein. 
         [0058]    The coil of the positioning mechanism  14 ″′ functions to anchor the elongate member  12  with respect to the anatomical structure, preferably a pulmonary vein  3000 , by coupling to the anatomical structure. Preferably, the outward force of the coil against the interior wall of the pulmonary vein will hold the positioning mechanism  14 ″′ within the pulmonary vein due to friction. The positioning mechanism  14 ″′ may alternatively function to anchor the elongate member  12  with respect to the anatomical structure in any other suitable fashion. 
         [0059]    In a fifth variation, as shown in  FIG. 12 , the positioning mechanism includes at least one distal wire  38  and at least one proximal wire  40 , each wrapped around at least a portion of the elongate member  12 . The wires are preferably made from a conductive material and/or a material with shape memory such as nickel/titanium alloys or a shape memory polymer. The material is preferably flexible so as not to cause injury to the tissue of the heart where the wires might contact and move against it. At least a portion of each of the wires is preferably made from a fluoro-opaque material, such as platinum or gold, such that it may be seen while positioned inside the internal structures of a patient through the use of a fluoroscope. The fluoro-opaque portion is preferably located in any suitable position such that it may be seen while positioned inside the internal structures of a patient through the use of a fluoroscope. The fluoro-opaque portion is preferably flush with the wire, but may alternatively have a round or any other suitable shape such that it will not damage the tissue. Additionally, each of the wires preferably includes at least one electrically active portion  42  and/or at least one insulated portion (e.g. an insulating coating on a portion of each wire). The wires each preferably include an even number of electrically active portions  42  such that a bipolar electrical system may be used, wherein each pair of electrodes or electrically active portions has an opposite polarity. For clarity, only a single electrically active portion  42  per wire has been shown in  FIG. 12 . The wires may alternatively include a single electrode or electrically active portion and use a monopolar electrical system, or may include any other suitable number of electrodes or electrically active portions. The electrically active portion  42  is preferably located in any suitable position such that it comes in contact with tissue. The distal wire  38  is preferably located distally from the energy delivery structure  18 , and the proximal wire is preferably located proximally from the energy delivery structure. The wires are preferably each coupled to the elongate member  12  at one end of the wire and then the other end is preferably wrapped around at least a portion of the elongate member  12  such that the other ends unwind towards the tissue once the distal tip assembly  16  is placed within the pulmonary vein  3000  or any other suitable structure. The wires preferably unwind such that the electrically active portion  42  of each wire is in contact with the tissue. The wires are preferably wrapped around the elongate member such that as the elongate member  12  and/or distal tip assembly are rotated (as shown by arrow R in  FIG. 12 ), the electrically active portions  42  of the wires sweep along the tissue. The wires are further preferably wrapped around at least a portion of the elongate member such that they are biased away from one another. For example, the distal wire  38  may be wrapped such that the end is biased towards the distal end of the catheter. This will encourage the wires to not block the energy delivery structure and to not contact one another. There is preferably at least one distal wire and at least one proximal wire such that, as the energy delivery structure  18  delivers energy to the tissue to form an ablation path and/or conduction block, there will be at least one wire distal to the conduction block and at least one wire proximal to the ablation path and/or conduction block. 
         [0060]    Although omitted for conciseness, the preferred embodiments include every combination and permutation of the various elongate members  12  and positioning mechanism  14 . 
         [0061]    While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting in scope of the invention which is defined by the appended claims.