Abstract:
An ablation catheter assembly includes an elongate catheter body having a proximal portion, a distal portion and a lumen therethrough. A helical structure associated with the catheter distal portion carries a plurality of independently operable electrodes and is transformable between a low-profile configuration wherein a straightening element is positioned in the lumen and an expanded configuration wherein the straightening element is at least partially retracted from the spiral structure. When the helical structure is in the expanded configuration, a laterally offset tip portion extends distally therefrom.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/760,807, filed Apr. 15, 2010, now U.S. Pat. No. ______, which is a divisional of U.S. patent application Ser. No. 10/655,197, filed Sep. 4, 2003, now U.S. Pat. No. 7,771,421, which is a divisional of U.S. patent application Ser. No. 09/848,555, filed May 3, 2001, now U.S. Pat. No. 6,702,811, which is a continuation-in-part of U.S. patent application Ser. No. 09/733,356, filed Dec. 8, 2000, now abandoned, which is a continuation-in-part of U.S. Pat. No. 6,325,797, filed Apr. 5, 1999. All of the foregoing applications are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an ablation catheter for treatment of cardiac arrhythmia, for example atrial fibrillation. More particularly, it relates to an ablation catheter configured to electrically isolate portions or an entirety of a vessel, such as a pulmonary vein, from a chamber, such as the left atrium, with a lesion pattern and a method for forming such a lesion pattern. 
         [0003]    The heart includes a number of pathways that are responsible for the propagation of signals necessary to produce continuous, synchronized contractions. Each contraction cycle begins in the right atrium where a sinoatral node initiates an electrical impulse. This impulse then spreads across the right atrium to the left atrium, stimulating the atria to contract. The chain reaction continues from the atria to the ventricles by passing through a pathway known as the atrioventricular (AV) node or junction, which acts as an electrical gateway to the ventricles. The AV junction delivers the signal to the ventricles while also slowing it, so the atria can relax before the ventricles contract. 
         [0004]    Disturbances in the heart&#39;s electrical system may lead to various rhythmic problems that can cause the heart to beat irregularly, too fast or too slow. Irregular heart beats, or arrhythmia, are caused by physiological or pathological disturbances in the discharge of electrical impulses from the sinoatrial node, in the transmission of the signal through the heart tissue, or spontaneous, unexpected electrical signals generated within the heart. One type of arrhythmia is tachycardia, which is an abnormal rapidity of heart action. There are several different forms of atrial tachycardia, including atrial fibrillation and atrial flutter. With atrial fibrillation, instead of a single beat, numerous electrical impulses are generated by depolarizing tissue at one or more locations in the atria (or possibly other locations). These unexpected electrical impulses produce irregular, often rapid heartbeats in the atrial muscles and ventricles. Patients experiencing atrial fibrillation may suffer from fatigue, activity intolerance, dizziness and even strokes. 
         [0005]    The precise cause of atrial fibrillation, and in particular the depolarizing tissue causing “extra” electrical signals, is currently unknown. As to the location of the depolarizing tissue, it is generally agreed that the undesired electrical impulses often originate in the left atrial region of the heart. Recent studies have expanded upon this general understanding, suggesting that nearly 90% of these “focal triggers” or electrical impulses are generated in one (or more) of the four pulmonary veins (PV) extending from the left atrium. In this regard, as the heart develops from an embryotic stage, left atrium tissue may grow or extend a short distance into one or more of the PVs. It has been postulated that this tissue may spontaneously depolarize, resulting in an unexpected electrical impulse(s) propagating into the left atrium and along the various electrical pathways of the heart. 
         [0006]    A variety of different atrial fibrillation treatment techniques are available, including drugs, surgery, implants, and catheter ablation. While drugs may be the treatment of choice for some patients, drugs typically only mask the symptoms and do not cure the underlying cause. Implantable devices, on the other hand, usually correct an arrhythmia only after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem by ablating the abnormal tissue or accessory pathway responsible for the atrial fibrillation. The catheter-based treatments rely on the application of various destructive energy sources to the target tissue, including direct current electrical energy, radiofrequency electrical energy, laser energy, and the like. The energy source, such as an ablating electrode, is normally disposed along a distal portion of a catheter. 
         [0007]    Most ablation catheter techniques employed to treat atrial fibrillation focus upon locating the ablating electrode, or a series of ablating electrodes, along extended target sections of the left atrium wall. Because the atrium wall, and thus the targeted site(s), is relatively tortuous, the resulting catheter design includes multiple curves, bends, extensions, etc. In response to recent studies indicating that the unexpected electrical impulses are generated within a PV, efforts have been made to ablate tissue within the PV itself. Obviously, the prior catheter designs incorporating convoluted, multiple bends are not conducive to placement within a PV. Instead, a conventional “straight ended” ablation catheter has been employed. While this technique of tissue ablation directly within a PV has been performed with relatively high success, other concerns may arise. 
         [0008]    More particularly, due to the relatively small thickness of atrial tissue formed within a PV, it is likely that ablation of this tissue may in fact cause the PV to shrink or constrict. Because PV&#39;s have a relatively small diameter, a stenosis may result. Even further, other vital bodily structures are directly adjacent each PV. These structures may be undesirably damaged when ablating within a PV. 
         [0009]    In light of the above, an alternative technique has been suggested whereby a continuous ablation lesion pattern is formed in the left atrium wall about the ostium associated with the PV in question. In other words, the PV is electrically isolated from the left atrium by forming an ablation lesion pattern that surrounds the PV ostium. As a result, any undesired electrical impulse generated within the PV could not propagate into the left atrium, thereby eliminating unexpected atria contraction. 
         [0010]    Unfortunately, while PV isolation via a continuous ablation lesion pattern about the PV ostium appears highly viable, no acceptable ablation catheter configuration exists. Most atrial fibrillation ablation catheters have linear distal ends, designed for manipulation in a sliding fashion along the atrial wall. That is to say, the distal, electrode-carrying end of the catheter is typically slid along (or parallel to) the atrial wall. With this generally accepted configuration in mind, it may be possible to shape the distal, electrode-carrying end into a small ring sized in accordance with the PV ostium. For example, U.S. Pat. No. 5,617,854 discloses one such possibility. More particularly, the described ablation catheter includes a substantially ring-shaped portion sized to contact the ostium of the coronary sinus. Pursuant to conventional designs, the ring extends linearly from the catheter body. In theory, the ring-shaped portion may be placed about a PV ostium. However, proper positioning would be extremely difficult and time consuming. More particularly, it would be virtually impossible to locate and then align the ring about a PV ostium when sliding the catheter along the atrium wall. The ring must be directed toward the ostium in a radial direction (relative to a central axis of the ostium). Even if the electrophysiologist were able to direct the ring to the ostium, the periodic blood flow through the PV would likely force the ring away from the atrium wall, as the catheter body would not provide any support. 
         [0011]    A related concern entails mapping of a PV prior to ablation. In cases of atrial fibrillation, it is necessary to identify the origination point of the undesired electrical impulses prior to ablation. Thus, it must first be determined if the electrical impulse originates within one or more PVs. Once the depolarizing tissue has been identified, necessary ablation steps can be taken. Mapping is normally accomplished by placing one or more mapping electrodes into contact with the tissue in question. In order to map tissue within a PV, therefore, a relatively straight catheter section maintaining two or more mapping electrodes must be extended axially within the PV. Ablation catheters configured to slide along the atrial wall cannot include a separate, distal extension for placement within the PV. Instead, an entirely separate mapping catheter must be provided and then removed for subsequent replacement with the ablation catheter. Obviously, these additional steps greatly increase the overall time required to complete the procedure. 
         [0012]    Electrical isolation of a pulmonary vein via an ablation lesion pattern surrounding the pulmonary vein ostium presents a potentially revolutionary technique for treatment of atrial fibrillation. However, the unique anatomical characteristics of a pulmonary vein and left atrium render currently available ablation catheters minimally useful. Therefore, a substantial need exists for an ablation catheter designed for consistent positioning of one or more ablation electrodes about a pulmonary vein ostium, as well as for providing pulmonary vein mapping information. 
       SUMMARY 
       [0013]    One aspect of the present invention provides a catheter assembly for treatment of cardiac arrhythmia. The catheter assembly includes a catheter body and an ablative energy source. The catheter body includes a proximal portion, an intermediate portion, and a distal portion. The intermediate portion extends from the proximal portion and defines a longitudinal axis. The distal portion extends from the intermediate portion and includes an ablation section and a tip. The ablation section forms a loop defining a diameter greater than an outer dimension of a pulmonary vein ostium. The tip extends distally from the ablation section and is configured to locate a pulmonary vein. Finally, the ablative energy source is associated with the ablation section. With this configuration, upon activation of the energy source, the ablation section ablates a desired lesion pattern. In one preferred embodiment, the ablation section forms a distally decreasing radius helix, whereas the tip includes a relatively linear leader section. With this one preferred configuration, the tip readily locates a pulmonary vein and guides the ablation section to a seated relationship about a pulmonary vein ostium. 
         [0014]    Another aspect of the present invention relates to a catheter assembly for electrically isolating a vessel from a chamber for treatment of cardiac arrhythmia. The catheter assembly includes a catheter body and an ablative energy source. The catheter body includes a proximal portion, an intermediate portion, and a distal portion. The intermediate portion extends from the proximal portion and defines a longitudinal axis. The distal portion extends from the intermediate portion and includes an ablation section and a tip. The ablation section forms a loop. The tip extends distally from the ablation section and is configured to locate a vessel. Further, the tip is characterized has having a feature different from that of the ablation section. In particular, the tip has either a different shape, material, durometer, or porosity as compared to the ablation section. Finally, the ablative energy source is associated with the ablation section. With this configuration, upon activation of the energy source, the ablation section ablates a desired lesion pattern. By forming the tip to have a feature different from that of the ablation section, the catheter assembly more readily locates a vessel, such as a pulmonary vein, and seats the ablation section about the vessel ostium, thereby promoting a properly located and uniform ablation pattern. In one preferred embodiment, the ablation section is formed of a microporous polymer, whereas the tip is impervious to fluid flow. With this configuration, fluid is irrigated to an exterior of the ablation section and then energized to ablate the tissue. 
         [0015]    Yet another aspect of the present invention relates to a catheter assembly for electrically isolating a vessel from a chamber for treatment of cardiac arrhythmia. The catheter assembly includes a catheter body and an ablative energy source. The catheter body includes a proximal portion, an intermediate portion, and a distal portion. The intermediate portion extends from the proximal portion and defines a longitudinal axis. The distal portion extends from the intermediate portion and includes an ablation section and a tip. The ablation section forms a loop transverse to the longitudinal axis. The tip extends distally from the ablation section and defines a shape different from a shape defined by the ablation section. Finally, the ablative energy source is associated with the ablation section. With this configuration, upon activation of the energy source, the ablation section ablates a desired lesion pattern. In one preferred embodiment, the ablation section and the tip define different distally decreasing radius helixes. 
         [0016]    Yet another aspect of the present invention relates to a method of electrically isolating a vessel from a chamber for treatment of cardiac arrhythmia. In this regard, the vessel forms an ostium at a wall of the chamber. With this in mind, the method includes selecting a catheter assembly including a catheter body and an ablative energy source. The catheter body includes a proximal portion and a distal portion, with the distal portion including an ablation section and a tip. The ablation section forms a loop and the tip extends distally from the ablation section. Further, the ablative energy source is associated with the ablation section. The distal portion of the catheter body is then guided into the chamber. The vessel is located with the tip. The distal portion is then advanced such that the ablation section contacts the chamber wall about the vessel ostium. In this regard, interaction between the tip and the vessel properly positions the ablation section relative to the vessel ostium as the distal portion is advanced. Finally, the ablative energy source is activated to ablate a desired lesion pattern about at a portion of at least a portion of the ostium to electrically isolate the vessel from the chamber. In one preferred embodiment, the tip is prevented from ablating the vessel during activation of the ablative energy source. 
     
    
     
       SUMMARY OF THE INVENTION 
         [0017]      FIG. 1A  is a side-elevational view of a catheter assembly in accordance with the present invention; 
           [0018]      FIG. 1B  is a perspective view of a portion of the catheter assembly of  FIG. 1A ; 
           [0019]      FIG. 1C  is an end view of a portion of the catheter assembly of  FIG. 1A ; 
           [0020]      FIG. 1D  is an end view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0021]      FIGS. 2A-2D  illustrates use of the catheter assembly of  FIG. 1A  within a heart; 
           [0022]      FIG. 3A  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0023]      FIG. 3B  is an end view of the catheter assembly of  FIG. 3A ; 
           [0024]      FIG. 3C  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0025]      FIG. 3D  is a simplified cross-sectional view of a portion of the heart and a portion of the catheter assembly of  FIGS. 3A and 3B ; 
           [0026]      FIG. 4A  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0027]      FIG. 4B  illustrates placement of the catheter assembly of  FIG. 4A  within the left atrium of a heart; 
           [0028]      FIG. 5A  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0029]      FIG. 6  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0030]      FIG. 7  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0031]      FIG. 8  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0032]      FIG. 9A  is a side view of a portion of an alternative catheter assembly in accordance with the present invention, in a deployed position; 
           [0033]      FIG. 9B  is a side view of the catheter assembly of  FIG. 9A  in a retracted position; 
           [0034]      FIG. 10  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0035]      FIG. 11  is a side view of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0036]      FIGS. 12A and 12B  are side views of a portion of an alternative catheter assembly in accordance with the present invention; 
           [0037]      FIG. 13A  is a side view of an alternative catheter assembly in accordance with the present invention; 
           [0038]      FIG. 13B  is a cross section of a catheter assembly of  FIG. 13A  along the line B-B; 
           [0039]      FIG. 13C  is a cross-sectional view of the catheter assembly of  FIG. 13A  along the line C-C; 
           [0040]      FIG. 13D  is a cross-sectional view of the catheter assembly of  FIG. 13A  along the line D-D; 
           [0041]      FIG. 13E  is a cross-sectional view of an alternative embodiment catheter assembly; 
           [0042]      FIG. 14A  is a side view of a catheter body of the catheter assembly of  FIG. 13A  in uncoiled position; 
           [0043]      FIG. 14B  is a side view of an alternative catheter body portion of the catheter assembly of  FIG. 13A ; 
           [0044]      FIG. 15A  is a side view of a shaping wire of the catheter assembly of  FIG. 13A  in a straightened position; 
           [0045]      FIG. 15B  is a side view of the shaping wire of  FIG. 15A  in a helical position; 
           [0046]      FIG. 15C  is a side view of an alternative shaping wire in a straightened position; 
           [0047]      FIGS. 16A and 16B  are side views of an alternative catheter assembly in accordance with the present invention; 
           [0048]      FIGS. 17A-17D  illustrate use of the catheter assembly of  FIG. 13A  within a heart; 
           [0049]      FIG. 18A  is an end view of the catheter assembly of  FIG. 13A  in an axially compressed position; 
           [0050]      FIG. 18B  is a simplified view of an ablation pattern formed with the catheter assembly of  FIG. 13A ; 
           [0051]      FIG. 19  illustrates use of an alternative catheter assembly within a heart; 
           [0052]      FIG. 20A  is a simplified, side-sectional view of a pulmonary vein and associated ostium; 
           [0053]      FIG. 20B  is a simplified, side-view of a shaping wire in accordance with the present invention in an axially compressed position; 
           [0054]      FIG. 20C  is a simplified, side view of the shaping wire of  FIG. 20B  applied to the pulmonary vein of  FIG. 20A ; 
           [0055]      FIG. 21A  is a simplified, side-sectional view of a pulmonary vein and associated ostium; 
           [0056]      FIG. 21B  is a simplified, side view of an alternative shaping wire in an axially compressed position; 
           [0057]      FIG. 21C  is a simplified, side view of the shaping wire of  FIG. 21B  applied to the pulmonary vein of  FIG. 21A ; 
           [0058]      FIG. 22  is a simplified, perspective view of an alternative embodiment catheter assembly in accordance with the present invention; 
           [0059]      FIG. 23  is a side view of a delivery catheter portion of the catheter assembly of  FIG. 22 ; 
           [0060]      FIG. 24A  is a cross-sectional view of the delivery catheter of  FIG. 23  along the line  24 A- 24 A; 
           [0061]      FIG. 24B  is a cross-sectional view of the delivery catheter of  FIG. 23  along the line  24 B- 24 B; 
           [0062]      FIG. 24C  is an enlarged, side view of a portion of the delivery catheter of  FIG. 23 ; 
           [0063]      FIG. 24D  is a cross-sectional view of the delivery catheter of  FIG. 23  along the line  24 D- 24 D; 
           [0064]      FIG. 25  is an end view of the catheter assembly of  FIG. 22 ; 
           [0065]      FIG. 26  is a side view of another alternative catheter assembly in accordance with the present invention; 
           [0066]      FIG. 27  is an enlarged, front elevational view of a portion of the catheter assembly of  FIG. 26 ; 
           [0067]      FIG. 28  illustrates use of the catheter assembly of  FIG. 26  within a heart, the heart being represented diagrammatically; 
           [0068]      FIG. 29A-29C  are simplified views of ablation patterns formed by the catheter assembly of  FIG. 26 ; 
           [0069]      FIG. 30  is a side view of a portion of another alternative catheter assembly in accordance with the present invention; 
           [0070]      FIG. 31  illustrates use of the catheter assembly of  FIG. 30  within a heart; and 
           [0071]      FIG. 32  is a side view of a portion of another alternative catheter assembly in accordance with the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0072]    One preferred embodiment of a catheter assembly  20  in accordance with the present invention is shown in  FIGS. 1A-1C . The catheter assembly  20  is comprised of a catheter body  22 , a handle  24  and electrodes  26 . As described in greater detail below, the catheter body  22  extends from the handle  24 , and the electrodes  26  are disposed along a portion of the catheter body  22 . 
         [0073]    The catheter body  22  is defined by a proximal portion  28 , an intermediate portion  30  and a distal portion  32 , and includes a central lumen (not shown). Although not specifically shown, the catheter body may be configured for over-the-wire or rapid exchange applications. In one preferred embodiment, the proximal portion  28 , the intermediate  30  and the distal portion  32  are integrally formed from a biocompatible material having requisite strength and flexibility for deployment within a heart. Appropriate materials are well known in the art and include polyamide. 
         [0074]    The intermediate portion  30  extends from the proximal portion  28 . The proximal portion  28  and the intermediate portion  30  are preferably flexible, so as to facilitate desired articulation during use. In general terms, however, the intermediate portion  30  defines a longitudinal axis L 1 . It should be recognized that in one position (shown in  FIG. 1A ), the longitudinal axis L 1  extends linearly through the intermediate portion  30  and the proximal portion  28 . Upon deployment, it may be that the proximal portion  28  and/or the intermediate portion  30  is forced to a curved or curvilinear orientation. With this in mind, the longitudinal axis L 1  is more specifically defined as a center of the intermediate portion  30  adjacent a point of intersection between the distal portion  32  and the intermediate portion  30 , as best shown in  FIG. 1C . 
         [0075]    The distal portion  32  extends from the intermediate portion  30  and forms a loop  34 . In one preferred embodiment, the loop  34  is circular, formed in a plane transverse to the longitudinal axis L 1 . To this end, the distal portion  32  preferably includes a lateral segment  36 . The lateral segment  36  extends in a generally lateral fashion from the intermediate portion  30 . The loop  34  extends from the lateral segment  36  in an arcuate fashion, turning or revolving about a central loop axis C 1  (shown best in  FIG. 1B ). While the loop  34  is shown in  FIG. 1A  as forming a single revolution about the central loop axis C 1 , the loop  34  may instead include a plurality of revolutions to define a spiral or coil. In the one preferred embodiment depicted in  FIGS. 1A-1C , the central loop axis C 1  is aligned with the longitudinal axis L 1 . Alternatively, however, the lateral segment  36  may be eliminated such that the loop  34  extends directly from the intermediate portion  30 . Even further, the lateral segment  36  may be configured such that the central loop axis C 1  is offset from the longitudinal axis L 1 . Regardless of the exact construction, however, the central loop axis C 1  is preferably substantially parallel to the longitudinal axis L 1 . 
         [0076]    As best shown in  FIG. 1C , the loop  34  preferably extends to form a circle in a frontal plane. Alternatively, a variety of other shapes may also be useful. For example, as shown in  FIG. 1D , a square-shaped loop is depicted. The loop  34  may further assume a triangular, rectangular, octagonal, or other closed shape. Returning to  FIGS. 1A-1C , regardless of the exact shape, the loop  34  is preferably substantially closed and can be defined by a proximal end  40  and a distal end  42 . To effectuate the preferred “closed” configuration of the loop  34 , the distal end  42  is preferably adjacent the proximal end  40 . In fact, the distal end  42  may contact the proximal end  40 , although this relationship is not required. Alternatively, the distal end  42  may be longitudinally spaced from the proximal end  40 . With this configuration, the distal portion  32  is preferably sufficiently flexible such that upon contact with a tissue wall, the distal end  42  will deflect proximally to a position adjacent the proximal end  40 . 
         [0077]    Regardless of the exact shape, the loop  34  preferably defines an enclosed area A greater than a size of an ostium (not shown) associated with a particular vessel to be isolated, as described in greater detail below. In one preferred embodiment, the catheter assembly  20  is configured to electrically isolate a pulmonary vein from the left atrium. With this one preferred application, where the loop  34  is circular, the loop  34  has a diameter in the range of approximately 10-20 mm, more preferably 15 mm, although other sizes, either greater or smaller, are acceptable. 
         [0078]    The loop  34  may be formed in a variety of ways, such as by incorporating a preformed section of super elastic, shape memory material, such as Nitinol, with a loop configuration. To facilitate guiding of the distal portion  32  into a heart (not shown), the catheter assembly  20  may include a stylet (not shown) internally disposed within the catheter body  22 . In an extended position, the stylet would extend through the distal portion  32 , so as to render the loop  34  straight. Upon retraction of the stylet, the distal portion  32  would form the loop  34 . Alternatively, the catheter assembly  20  may include a sheath (not shown) slidably receiving the catheter body  22 . Prior to deployment, the distal portion  32  would be retracted within the sheath, rendering the loop  34  straight. Upon deployment from the sheath, the distal portion  32  would form the loop  34 . Other similar approaches for providing the loop  34  are similarly acceptable. 
         [0079]    The handle  24  is preferably sized to be grasped by a user and includes an electrical connector  44 . The electrical connector provides electrical connections to the electrodes  26  carried by the distal portion  32 . To this end, wire(s) (not shown) may extend within the central lumen (not shown) from the distal portion  32  to the handle  24 . 
         [0080]    The electrodes  26  are preferably of a type known in the art and are preferably a series of separate band electrodes spaced along the loop  34 . Instead of, or in addition to, separate band electrodes, the electrodes  26  may include one or more spiral or coil electrodes, or one or more counter-electrodes. Additionally, the electrodes  26  are preferably non-thrombogenic, non-coagulum or char forming. The electrodes  26  may be cooled by a separate source (not shown), such as a saline source. The electrodes  26  may be electrically isolated from one another, or some or all of the electrodes  26  may be electrically connected to one another. Preferably, however, at least one electrode  26  is provided. The electrodes  26  are preferably shaped and positioned such that during an ablation procedure, a continuous, closed therapeutically-effective lesion pattern is created. Preferably, the length of each of the electrodes  26  is about 4-12 mm, more preferably about 7 mm. The spacing between each of the electrodes  26  is preferably about 1-3 mm, and more preferably about 2 mm. Finally, to effectuate a continuous, closed lesion pattern, preferably one of the electrodes  26  is disposed at the proximal end  40  of the loop  34 , and another of the electrodes  26  is disposed at the distal end  42 . As previously described, it is not necessary that the loop segment  38  be formed such that the proximal end  40  and the distal end  42  are integral. Instead, a slight spacing may exist. With this in mind, the spacing or gap between the electrode  26  at the proximal  40  and the electrode  26  at the distal end  42  is preferably less than about 5 mm. 
         [0081]      FIGS. 2A and 2B  illustrate use of the catheter assembly  20  shown in  FIGS. 1A-1C  within a heart  50 . As a point of reference, the heart  50  includes a right atrium RA, a left atrium LA, a right ventricle RV and a left ventricle LV. An inferior vena cava IVC and a superior vena cava SVC lead into the right atrium RA. The right atrium RA is separated from the left atrium LA by an interarterial septum (not shown). Finally, four pulmonary veins PV extend from the left atrium LA. Each of the pulmonary veins PV forms an ostium PVO in the left atrium LA wall. As previously described, during formation of the heart  50 , it is possible that tissue of the left atrium LA may grow upwardly into one or more of the pulmonary veins PV. This left atrium LA tissue may spontaneously depolarize, resulting in atrial fibrillation. Notably, the heart  50  may be formed such that a separate ostium PVO is not formed for each individual pulmonary vein PV. In other words, a single pulmonary vein ostium PVO may be formed for two pulmonary veins PV. For example, a single pulmonary vein ostium PVO may be formed for both the left inferior pulmonary vein PV and the left superior pulmonary vein PV, with the two pulmonary veins PV bifurcating from the single ostium PVO. 
         [0082]    As shown in  FIG. 2A , electrical isolation of a pulmonary vein PV begins by directing the distal portion  32  of the catheter body  22  through the inferior vena cava IVC, into the right atrium RA through a puncture in the interarterial septum (not shown) and into the left atrium LA. Alternatively, the introduction of the distal portion  32  of the catheter body  22  into the right atrium RA is also suggested by passage of the distal portion  32  into the right atrium RA through the superior vena cava SVC. The loop  34  is positioned slightly spaced from the ostium PVO associated with the pulmonary vein PV to be treated. More particularly, the loop  34  is positioned such that the central loop axis C 1  ( FIG. 1B ) is approximately aligned with a center of the pulmonary vein ostium PVO. The catheter body  22  is then advanced distally such that the loop  34  contacts the left atrium LA wall about the pulmonary vein ostium PVO in question, as shown in  FIG. 2B . In other words, the catheter body  22  is advanced in a direction parallel with the central loop axis C 1  such that the loop  34  contacts the left atrium LA wall, surrounding the pulmonary vein ostium PVO. Importantly, because the central loop axis C 1  is parallel to the longitudinal axis L 1 , the catheter body  22  longitudinally supports advancement of the loop  34 . In other words, the longitudinal axis L 1  is effectively aligned with the pulmonary vein ostium PVO such that blood flow from the pulmonary vein PV acts along the longitudinal axis L 1 . Thus, the catheter body  22  limits deflection of the loop  34  otherwise caused by blood flow from the pulmonary vein PV. 
         [0083]    The electrodes  26  (shown best in  FIGS. 1A-1C ) are then energized to a sufficient level to ablate the contacted tissue, for example with an RF source. In one preferred embodiment, the electrodes  26  ablate the left atrium LA tissue for 30-120 seconds at a temperature in the range of approximately 60-70 degree C. As a result, a continuous, closed lesion pattern is formed around the pulmonary vein ostium PVO as shown in  FIG. 2C . Pursuant to the above described catheter assembly  20  configuration, the lesion pattern is formed in a plane substantially perpendicular to the longitudinal axis L 1 . Notably, while the lesion pattern is shown as being only slightly larger than the pulmonary vein ostium PVO, the loop  34  ( FIG. 1A ) may be sized to produce an even larger ablation lesion pattern. To this end, where a single pulmonary vein ostium PVO is formed for two pulmonary veins PV, the resulting pulmonary vein ostium PVO may be elongated. As shown in  FIG. 2D , then, the loop  34  ( FIG. 1A ) is configured to form a continuous, closed lesion pattern about the elongated-shaped pulmonary vein ostium PVO. 
         [0084]    The continuous, closed lesion pattern electrically isolates the pulmonary vein PV from the left atrium LA. Any undesired electrical impulses generated in the pulmonary vein are effectively “stopped” at the lesion pattern, and will not propagate into the left atrium LA. 
         [0085]    An alternative catheter assembly  60  is shown in  FIGS. 3A and 3B . The catheter assembly  60  includes a catheter body  62 , a handle (not shown) and electrodes  64 . The catheter body  62  includes a proximal portion (not shown), an intermediate portion  66  and a distal portion  68 . For ease of illustration, the handle and the proximal portion of the catheter body  22  are not shown in  FIGS. 3A and 3B , it being understood that these components are similar to the handle  24  and the proximal portion  28  shown in  FIG. 1A . 
         [0086]    Similar to the catheter body  22 , the intermediate portion  66  extends from the proximal portion and defines a longitudinal axis L 2 . The distal portion  68  extends from the intermediate portion  66  and forms a loop or coil  70  substantially transverse to the longitudinal axis L 2  and includes a plurality of loop segments  72 A- 72 C. The coil  70  is formed such that each of the loop segments  72 A- 72 C revolves about a central loop axis C 2 . In one preferred embodiment, the central loop axis C 2  is aligned with the longitudinal axis L 2  defined by the intermediate portion  66 . Alternatively, the central loop axis C 2  may be offset from the longitudinal axis L 2 . Regardless, the central loop axis C 2  is preferably substantially parallel with the longitudinal axis L 2 . 
         [0087]    Each of the loop segments  72 A- 72 C preferably defines a different diameter. For example, the first loop segment  72 A defines a diameter slightly larger than that of the second loop segment  72 B; whereas the second loop segment  72 B defines a diameter slightly greater than that of the third loop segment  72 C. In this regard, while each of the loop segments  72 A- 72 C are depicted as being longitudinally spaced (such that the loop  70  forms a multi-lane spiral or coil), the loop segments  72 A- 72 C may instead be formed in a single plane (such that the loop  70  forms a unitary plane spiral or coil). While the loop segments  72 A- 72 C extend distal the intermediate portion  66  so as to define a descending or decreasing diameter, an opposite configuration may also be employed. For example,  FIG. 3C  depicts a coil  70 ′ having loop segments distally increasing in diameter. 
         [0088]    Returning to  FIGS. 3A and 3B , the electrodes  64  are similar to the electrodes  26  ( FIG. 1A ) previously described, and preferably are band electrodes disposed along the loop segments  72 A- 72 C. In this regard, each of the loop segments  72 A- 72 C includes electrodes  64 A- 64 C, respectively. In one preferred embodiment, a power source (not shown) associated with the electrodes  64  is configured to individually energize the electrodes  64  to varying levels. Further, the electrodes  64  are preferably configured to provide feedback information indicative of tissue contact, such as by including a thermocouple. 
         [0089]    The catheter assembly  60  is used in a fashion highly similar to the method previously described for the catheter assembly  20  (as shown, for example, in  FIGS. 2A-2C ). Thus, for example, the distal portion  68  of the catheter body  62  is directed within the left atrium LA ( FIG. 2A ) such that the loop  70  is disposed about a pulmonary vein ostium PVO. It should be understood that one or more of the loop segments  72 A- 72 C may define a diameter (or area) that is less than a diameter (or area) of the pulmonary vein ostium PVO in question. For example, in the simplified cross-sectional view of  FIG. 3D , the electrodes  64 C associated with the third loop segment  72 C ( FIG. 3A ) are not in contact with the left atrium LA wall, but instead are within the area defined by the pulmonary vein ostium PVO. Conversely, the electrodes  64 B associated with the second loop segment  72 B ( FIG. 3A ) and the electrodes  64 A associated with the first loop segment ( FIG. 3A ) are in contact with the left atrium LA wall. To avoid potential collateral damage caused by full energization of the electrodes  64 C not in contact with the left atrium LA wall, each of the electrodes  64 A- 64 C are selectively energized with a low energy supply. The energy level is not sufficient to ablate contacted tissue, but provides a low energy measurement, such as through a thermocouple or other sensing device associated with each of the electrodes  64 A- 64 C. If the sensing device detects a temperature rise, an indication is given that the particular energized electrode  64 A,  64 B or  64 C is in contact with tissue of the left atrium LA. Following the low energy measurement procedure, only those electrodes determined to be in contact with the left atrium LA (for example, electrodes  64 A and  64 B) are powered to ablate a continuous, closed lesion pattern about the pulmonary vein ostium PVO, as previously described. 
         [0090]    Another alternative embodiment of a catheter assembly  80  is shown in  FIG. 4A . The catheter assembly  80  includes a catheter body  82 , an electrode  84  and a locating device  86 . For ease of illustration, only a portion of the catheter assembly  80  is shown, and catheter assembly  80  may further include a handle similar to the handle  24  associated with the catheter assembly  20  ( FIG. 1A ) previously described. 
         [0091]    Catheter body  82  is defined by a proximal portion (not shown), an intermediate portion  88  and a distal portion  90 . The intermediate portion  88  extends from the proximal portion and is defined by a proximal segment  92  and a distal segment  94 . In a preferred embodiment, the distal segment  94  is preferably more flexible than the proximal segment  92 . With this configuration, the distal segment  94  can more easily deflect relative to the proximal segment  92 , thereby facilitating desired positioning of the distal portion  90  during deployment. In this regard, an internal pull wire (not shown) may be provided to effectuate desired deflection of the distal segment  94 . Even further, an anchor  96  is preferably included for facilitating a more radical displacement of the distal portion  90  relative to the intermediate portion  88 . 
         [0092]    As with previous embodiments, the intermediate portion  88  defines a longitudinal axis L 3 . Once again, where the intermediate portion  88  is axially aligned with the proximal portion (not shown), the longitudinal axis L 3  is linear along the intermediate portion  88  and the proximal portion. However, because the intermediate portion  88  is preferably bendable relative to the proximal portion, and further because the distal segment  94  may bend relative to the proximal segment  92 , the longitudinal axis L 3  is more succinctly defined by the intermediate portion  88  at the point of intersection between the intermediate portion  88  and the distal portion  90 . 
         [0093]    Similar to the catheter assembly  20  ( FIG. 1A ) previously described, the distal portion  90  preferably forms a loop  98 . The loop  98  may include one or more loop segments (one is shown in  FIG. 4A ), with each loop segment revolving around a central loop axis C 3 . The loop  98  is formed substantially transverse to the longitudinal axis L 3 , with the central loop axis C 3  preferably aligned with the longitudinal axis L 3 . Alternatively, the central loop axis C 3  may be slightly offset from the longitudinal axis L 3 . Regardless, the central loop axis C 3  is preferably parallel with the longitudinal axis L 3 . 
         [0094]    The electrode  84  is shown in  FIG. 4  as being a continuous coil electrode. Alternatively, a plurality of spaced, band electrodes or counter-electrodes may be used. 
         [0095]    Finally, the locating device  86  includes a tip  104  configured to extend distal the loop  98 . In one preferred embodiment, the locating device  86  is integrally formed with the catheter body  82 , extending from the distal portion  90 . Alternatively, the locating device  86  may be a separate body. Regardless, the tip  104  extends distal the distal portion  90 , and is aligned with the central loop axis C 3  defined by the loop  98 . The tip  104  preferably has a diameter less than a diameter of a pulmonary vein, and a length in the range of approximately 1-15 mm. Further, as shown in  FIG. 4 , the tip  104  may include a series of mapping electrodes  102 . The mapping electrodes  102  are electrically connected to an external recording system (not shown) for providing information indicative of tissue polarization. 
         [0096]    As shown in  FIG. 4B , during use, the catheter assembly  80  is directed into the left atrium LA as previously described. The locating device  86 , and in particular the tip  104 , is then used to locate the pulmonary vein ostium PVO. Once located, the tip  104  is inserted into the pulmonary vein PV, effectively centering the loop  98  around the pulmonary vein ostium PVO. Where the tip  104  includes the mapping electrodes  102 , a mapping procedure can be performed, whereby information indicative of tissue activity nearby the mapping electrodes  102  is provided. During this mapping procedure, a determination can be made as to whether the particular pulmonary vein PV is generating undesired electrical impulses. Where it is determined that, in fact, tissue in the pulmonary vein PV is spontaneously depolarizing, the electrode  84  is energized to form the continuous, closed lesion pattern about the pulmonary vein ostium PVO as previously described. 
         [0097]    Yet another alternative embodiment of a catheter assembly  110  in accordance with the present invention is shown in  FIG. 5 . The catheter assembly  110  is highly similar to the catheter assembly  80  ( FIG. 4A ) and includes a catheter body  112 , electrodes  114  and a locating device  116 . The catheter body  112  includes a proximal portion (not shown) an intermediate portion  88  defining a longitudinal axis L 4  and a distal portion  120 . The distal portion  120  extends from the intermediate portion  118  and forms a loop  122  substantially transverse to the longitudinal axis L 4 . In this regard, the loop  122  revolves about a central loop axis C 4 . In one preferred embodiment, the central loop axis C 4  is aligned with the longitudinal axis L 4 . Alternatively, the central loop axis C 4  is offset from, but substantially parallel with, the longitudinal axis L 4 . The electrodes  114  (shown as spaced band electrodes) are disposed along the loop  122  for forming a continuous, closed lesion pattern. 
         [0098]    The locating device  116  includes a tip  124  that extends distal the loop  122 . In one preferred embodiment, the locating device  116  is integrally formed with the catheter body  112  and includes mapping electrodes  126  connected to an external recording device (not shown). Alternatively, the locating device  116  may be a separate body. As shown in  FIG. 5 , the tip  124  forms a descending diameter coil, generally aligned with the central loop axis C 4 . By providing a coil configuration for the tip  124 , the tip  124  facilitates a more positive centering of the loop  122  about a pulmonary vein ostium PVO ( FIG. 4B ). In one preferred embodiment, the tip  124  defines a maximum diameter approximating a diameter of a pulmonary vein. When inserted within a pulmonary vein, then, the tip  124  effectively lodges along the pulmonary vein wall. This, in turn, positions the loop  122  in a more central fashion about the associated ostium. Further, by providing the mapping electrodes  126 , the locating device  116  additionally serves as a mapping device for evaluating a particular pulmonary vein. 
         [0099]    It should be recognized that other devices can be provided to assist in centering the ablation loop about the pulmonary vein ostium. For example, yet another alternative embodiment of a catheter assembly  130  is depicted in  FIG. 6 . The catheter assembly includes a catheter body  132 , electrodes  134 , a balloon  136  and a locating device  138 . The catheter body  132  is similar to those previously described, and includes a proximal portion (not shown) an intermediate portion  140  defining a longitudinal axis L 5  and a distal portion  142 . The distal portion  142  extends from the intermediate portion  140  and forms a loop  144  substantially transverse to the longitudinal axis L 5 . The loop  144  revolves about a central loop axis C 5 , that, in one preferred embodiment, is aligned with the longitudinal axis L 5 . The balloon  136  is disposed along the distal portion  142  distal the loop  144 . In one preferred embodiment, the balloon  136  is fluidly connected to a fluid source (not shown), such as a pressurized reservoir of saline, by a lumen (not shown) formed within the catheter body  132 . Finally, the locating device  138  includes a tip  146  extending distal the loop  144 . In one preferred embodiment, as shown in  FIG. 6 , the locating device  138  is integrally formed with the catheter body  132 , with the tip  146  extending distal the balloon  136 . Alternatively, the locating device  138  may be a separate body, and the tip  146  may be positioned between the loop  144  and the balloon  136 . Regardless, the tip  146  preferably includes mapping electrodes  148 . 
         [0100]    During use, the locating device  138  is used to locate a pulmonary vein PV ( FIG. 4B ) via the tip  146 . The tip  146  axially inserted into the pulmonary vein PV. The mapping electrodes  148  may then be used to ascertain whether tissue in the pulmonary vein PV is spontaneously generating unexpected electrical impulses. Upon determining that the pulmonary vein PV requires electrical isolation, the catheter body  132  is deployed such that the loop  144  contacts the left atrium LA ( FIG. 4B ) wall (as previously described). The balloon  136  is inflated such that it engages the pulmonary vein PV wall. Once inflated, the balloon  136  positively centers the loop  144  about the pulmonary vein ostium PVO ( FIG. 4B ). 
         [0101]    Yet another alternative embodiment of a catheter assembly  160  is shown in  FIG. 7 . The catheter assembly  160  includes a catheter body  162 , electrodes  164 , a wire basket  166  and a locating device  168 . As with previous embodiments, the catheter body  162  includes a proximal portion (not shown), an intermediate portion  170  defining a longitudinal axis L 6  and a distal portion  172 . The distal portion  172  extends from the intermediate portion  170  and forms a loop  174  transverse to the longitudinal axis L 6 . In this regard, the loop  174  revolves around a central loop axis C 6  that, in one preferred embodiment, is aligned with the longitudinal axis L 6 . 
         [0102]    The wire basket  166  is maintained by the distal portion  172  distal the loop  174 . The wire basket  166  may be radially extended and retracted via a pull wire or similar activation device extending through a lumen (not shown) formed within the catheter body  162 . 
         [0103]    Finally, the locating device  168  includes a tip  176  positioned distal the loop  174 . In one preferred embodiment, the locating device  168  is integrally formed with the catheter body  162  and includes mapping electrodes  178 . Alternatively, the locating device  168  may be a separate body, and the tip  176  may be disposed between the wire basket  166  and the loop  174 . 
         [0104]    During use, the catheter assembly  160  functions in a fashion highly similar to the catheter assembly  130  ( FIG. 6 ) previously described. The locating device  168 , and in particular the tip  176 , is used to locate and map a pulmonary vein PV ( FIG. 4B ). The loop  174  is maneuvered into contact with the left atrium LA ( FIG. 4B ) wall. The wire basket  166  is then radially deployed so as to engage the pulmonary vein PV wall. In this deployed position, the wire basket  166  serves to positively center the loop  174  about the pulmonary vein ostium PVO ( FIG. 4B ). 
         [0105]    Yet another alternative embodiment of a catheter assembly  190  is shown in  FIG. 8 . The catheter assembly  190  includes a catheter body  192  (shown partially in  FIG. 8 ), electrodes  194 , a locating device  196  and a guide catheter or sheath  198 . As described in greater detail below, the sheath  198  coaxially maintains the catheter body  192  and the locating device  196  such that each of the catheter body  192  and the locating device  196  are slidable between a retracted position and a deployed position (shown in  FIG. 8 ). 
         [0106]    The catheter body  192  is virtually identical to the catheter body  62  ( FIG. 3A ) previously described and includes a proximal portion (not shown), an intermediate portion  200  defining a longitudinal axis L 7  and a distal portion  202 . The distal portion  202  extends from the intermediate portion  200  and forms a coil or plurality of loops  204  substantially transverse to the longitudinal axis L 7 . Alternatively, the coil  204  may form a single loop. The coil  204  revolves around a central loop axis C 7 , that, in one preferred embodiment, is aligned with the longitudinal axis L 7 . The distal portion  202 , and in particular the coil  204 , is preferably sufficiently flexible so as to assume a relatively straight configuration when refracted within the sheath  198 . Further, the distal portion  202  includes a shape memory characteristic such that when deployed from the sheath  198 , the distal portion  202  forms the coil  204  as shown in  FIG. 8 . 
         [0107]    The electrodes  194  are identical to those previously described and preferably comprise band electrodes disposed along the coil  204 . Alternatively, a continuous coil electrode or counter-electrode may be provided. 
         [0108]    The locating device  196  is relatively rigid and includes a shaft  206  defining a tip  208  that preferably maintains mapping electrodes  210 . The shaft  206  is sized to be slidably received within a lumen (not shown) in the sheath  198 . As shown in  FIG. 8 , the tip  208  preferably assumes a coil shape with decreasing diameter. Alternatively, the tip  208  may be substantially straight. Preferably, however, the tip  208  is sufficiently flexible such that upon retraction into the sheath  198 , the tip  208  assumes a relatively straight form. Additionally, the tip  208  has a shape memory characteristic such that upon deployment from the sheath  198 , the tip  208  assumes the coiled shape shown in  FIG. 8 . For example, the tip  208  may include stainless steel or Nitinol core wires. Further, the tip  208  may be formed from a shape memory alloy of Nitinol that forms the coil shape when heated above a certain temperature. The heat may be achieved through resistive heating of the wire directly, or by surrounding the wire with a tubular heater. 
         [0109]    The sheath  198  includes a proximal end (not shown) and a distal end  212 , and forms at least one central lumen (not shown) sized to maintain the catheter body  192  and the locating device  196 . Alternatively, a separate lumen may be provided for each of the catheter body  192  and the locating device  196 . Regardless, the sheath  198  is configured to slidably maintain each of the catheter body  192  and the locating device  196  in a relatively close relationship. In one preferred embodiment, the sheath  198  is formed of a relatively soft material such as 35D or 40D polyether block amide copolymer sold under the trademark PEBAX. 
         [0110]    As described above, each of the catheter body  192  and the locating device  196  are slidable relative to the sheath  198 . In a deployed position (depicted in  FIG. 8 ), the distal portion  202  of the catheter body  192  and the tip  208  of the locating device  196  extend distally from the sheath  198 . More particularly, the locating device  196  is positioned such that the tip  208  is distal the coil  204 . In this extended position, the tip  208  is essentially aligned with the central loop axis L 7 . 
         [0111]    During use, the catheter body  192  and the locating device  196  are retracted within the sheath  198 . The sheath  198  is then guided to the left atrium LA ( FIG. 4B ). The catheter body  192  and the locating device  196  are deployed from the sheath  198 . More particularly, the distal portion  202  of the catheter body  192  and the tip  208  of the locating device  196  are extended from the distal end  212  of the sheath  198  (as shown in  FIG. 8 ). A locking device (not shown) is preferably provided to secure the catheter assembly  190  in the deployed position. As previously described, upon deployment, the distal portion  202  forms the coil  204 , whereas the tip  208  preferably assumes a coil shape. The tip  208  locates and is directed axially into a pulmonary vein PV as previously described. The mapping electrodes  210  sample electrical activity of the pulmonary vein tissue. If the mapping procedure determines that the pulmonary vein PV requires electrical isolation, the sheath  198  is guided in a direction along the central loop axis C 7  until the coil  204  contacts the left atrium LA ( FIG. 4B ) wall about the pulmonary vein ostium PVO ( FIG. 4B ). Because the catheter body  192  and the locating device  196  are directly connected by the sheath  198 , the tip  208  effectively positively centers the loop  204  about the pulmonary vein ostium PVO. The electrodes  194  may be selectively energized with a low energy supply to determine which of the electrodes  194  are in contact with tissue of the left atrium LA. Some or all of the electrodes  194  are then energized to ablate a continuous, closed lesion pattern about the pulmonary vein ostium PVO, thereby electrically isolating the pulmonary vein PV from the left atrium LA. 
         [0112]    While the catheter assembly  190  has been described as including the sheath  198  to maintain the catheter body  192  and the locating device  196 , the sheath  198  may be eliminated for example, the catheter body  192  may alternatively be configured to include lumen (not shown) sized to slidably receive the locating device  192 . In this regard, the locating device  192  may serve as a guide wire, with the catheter body  192  riding over the locating device  192  much like an over-the-wire catheter configuration commonly known in the art. Even further, the catheter body  192  may include a rapid exchange design characteristic for quick mounting to removal from the locating device  190 . 
         [0113]    Yet another alternative embodiment of a catheter assembly  220  is shown in  FIGS. 9A and 9B . The catheter assembly  220  includes a catheter body  222  (shown partially in  FIGS. 9A and 9B ), electrodes  224 , stylets  226  and a locating device  228 . The electrodes  224  are disposed along a portion of the catheter body  222 . The stylets  226  are slidably maintained within the catheter body  222 . Finally, the locating device  228  is slidably maintained by the catheter body  222 . 
         [0114]    The catheter body  222  is similar to those previously described and includes a proximal portion (not shown), an intermediate portion  230 , defining a longitudinal axis L 8 , and a distal portion  232 . The distal portion  232  forms a loop  234  substantially transverse to the longitudinal axis L 8 . The loop  234  revolves around a central loop axis C 8  which, in one preferred embodiment, is aligned with the longitudinal axis L 8 . The distal portion  232  is preferably sufficiently flexible so as to be relatively straight in a retracted position ( FIG. 9B ). Further, the distal portion  232  has a shape memory characteristic such that the distal portion  232  forms the loop  234  in a deployed position ( FIG. 9A ). For example, the catheter body  222  may be formed of a super elastic, shape memory Nitinol alloy. 
         [0115]    Each of the stylets  226  are relatively rigid shafts sized to be slidably received within lumens (not shown) formed by the catheter body  222 . To this end, as shown in  FIG. 9A , in a deployed position, the stylets  226  are proximal the distal portion  232  such that the distal portion  232  is allowed to form the loop  234 . Conversely, in a retracted position ( FIG. 9B ) the stylets  226  extend into the distal portion  232 , thereby rendering the distal portion  232  substantially straight. 
         [0116]    The electrodes  224  are identical to those previously described and preferably comprise band electrodes disposed along the loop  234 . Alternatively, a continuous coil electrode or counter electrode may be provided. 
         [0117]    The locating device  228  includes a shaft  236  having a tip  238 . Similar to previous embodiments, the tip  238  is preferably coil shaped, and includes mapping electrodes  240 . In this regard, the tip  238  is preferably sufficiently flexible such that in the refracted position ( FIG. 9B ), the tip  238  is rendered relatively straight by the catheter body  222 . Conversely, in the deployed position ( FIG. 9A ), the tip  238  assumes the coiled shape. Alternatively, the tip  238  may be substantially straight in the deployed position. 
         [0118]    The catheter assembly  220  is used in a manner highly similar to that previously described. The catheter assembly  220  is initially placed in the retracted position ( FIG. 9B ), whereby the stylets  226  are maneuvered distally to straighten the distal portion  232 . Further, the locating device  228  is retracted within the catheter body  222  such that tip  238  is proximal the distal portion  232  and is rendered relatively straight. In this retracted position, the catheter assembly  222  can more easily be directed into the left atrium LA ( FIG. 4B ) as previously described. Once in the left atrium LA, the catheter assembly  220  is maneuvered to the deployed position ( FIG. 9A ), whereby the stylets are moved proximally such that the distal portion  232  forms the loop  234 . Further, the locating device  228  is maneuvered distally relative to the catheter body  222  such that the tip  238  extends distal the loop  234 . In the deployed position, the locating device  228  is maneuvered in a generally axial fashion to locate and extend into a pulmonary vein PV. The mapping electrodes  240  map the pulmonary vein tissue ( FIG. 4B ). Where the mapping procedure indicates that the pulmonary vein PV requires electrical isolation, the catheter assembly  220  is advanced such that the loop  234  surrounds the pulmonary vein ostium PVO ( FIG. 4B ). More particularly, the catheter assembly  220  is advanced in the direction of the central loop axis C 8 . Once again, the unique configuration of the catheter assembly  220  facilitates movement in an axial direction (relative to the pulmonary vein ostium PVO) as opposed to a radial, sliding direction required by previous ablation catheter designs. Notably, because the locating device  228  is directly connected to the catheter body  222 , the locating device  228  facilitates positive centering of the loop  234  about the pulmonary vein ostium PVO. The electrodes  224  are then energized to ablate a continuous, closed lesion pattern about the pulmonary vein ostium PVO, thereby electrically isolating the pulmonary vein PV. 
         [0119]    Yet another alternative embodiment of the catheter assembly  250  in accordance with the present invention is shown in  FIG. 10 . The catheter assembly  250  includes a catheter body  252  (shown partially in  FIG. 10 ), electrodes  254 , a locating device  256  and a guide catheter or sheath  258 . As described in greater detail below, the sheath  258  coaxially maintains the catheter body  252  and the locating device  256  such that each of the catheter body  252  and the locating device  256  are slidable between a retracted position and a deployed position (shown in  FIG. 10 ). 
         [0120]    The catheter body  252  is virtually identical to the catheter body  62  ( FIG. 3A ) previously described and includes a proximal portion (not shown), an intermediate portion  260  defining a longitudinal axis L 9  and a distal portion  262 . The distal portion  262  extends from the intermediate portion  260  and forms a coil or loops  264  substantially transverse to the longitudinal axis L 9 . Alternatively, the coil  264  may form a single loop. The coil  264  revolves around a central loop axis C 9 , that, in one preferred embodiment, is aligned with the longitudinal axis L 9 . The distal portion  262 , and in particular the coil  264 , is preferably sufficiently flexible so as to assume a relatively straight configuration when retracted within the sheath  258 . Further, the distal portion  262  includes a shape memory characteristic such that when deployed from the sheath  258 , the distal portion  262  forms the coil  264  as shown in  FIG. 10 . 
         [0121]    The electrodes  254  are identical to those previously described and preferably comprise band electrodes disposed along the coil  264 . Alternatively, a continuous coil electrode or counter-electrode may be provided. 
         [0122]    The locating device  256  includes a shaft  266  and a balloon  268 . The shaft  266  includes a distal portion  270  and a tip  272 . The distal portion  270  preferably forms an expansion joint  274 . The tip  272  is distal the expansion joint  274  and preferably maintains mapping electrodes  276 . The balloon  268  is sealed to the distal portion  270  of the shaft  266  about the expansion joint  274 . In this regard, the expansion joint  274  is configured to be manipulated between a contracted position ( FIG. 10 ) and an expanded position. In the expanded position, the expansion joint  274  extends axially so as to collapse the balloon  268 . When collapsed, the balloon  268  can more easily be refracted within the sheath  258 . 
         [0123]    The sheath  258  includes a proximal end (not shown) and a distal end  278 , and forms at least one central lumen (not shown) sized to maintain the catheter body  252  and the locating device  256 . Alternatively, a separate lumen may be provided for each of the catheter body  252  and the locating device  256 . Regardless, the sheath  258  is configured to slidably maintain each of the catheter body  252  and the locating device  256  in relatively close relationship. In one preferred embodiment, the sheath  258  is formed of a relatively soft material such as 35D or 40D PEBAX. 
         [0124]    As described above, each of the catheter body  252  and the locating device  256  are slidable relative to the sheath  258 . In a deployed position (depicted in  FIG. 10 ), the distal portion  262  of the catheter body  252  and the distal portion  270  of the locating device  256  extend distally from the sheath  258 . More particularly, the coil  264  is positioned distal the distal end  278  of the sheath  258 . Further, the distal portion  270 , including the balloon  268 , of the locating device  256  is positioned distal the coil  264 . In this position, the distal portion  270  is essentially aligned with the central loop axis L 9 . 
         [0125]    Prior to use, the catheter body  252  and the locating device  256  are retracted within the sheath  258 . The sheath  258  is then guided to the left atrium LA ( FIG. 4B ). The catheter body  252  and the locating device  256  are deployed from the sheath  258 . More particularly, the distal portion  262  of the catheter body  252  and the distal portion  270  of the locating device  256  are extended from the distal end  278  of the sheath  258  (as shown in  FIG. 10 ). A locking device (not shown) is preferably provided to secure the catheter assembly  250  in the deployed position. As previously described, upon deployment, the distal portion  262  of the catheter body  252  forms the coil  264 . The distal portion  270  of the locating device  256 , including the balloon  268 , is positioned distal the coil  264 . The tip  272  locates and is directed axially into a pulmonary vein PV ( FIG. 4B ) as previously described. The mapping electrodes  276  sample electrical activity of the pulmonary vein tissue. If the mapping procedure determines that the pulmonary vein PV requires electrical isolation, the sheath  258  is guided in a direction along the central loop axis C 9  until the coil  264  contacts the left atrium LA wall about the pulmonary vein ostium PVO ( FIG. 4B ). The expansion joint  274  is contracted and the balloon  268  inflated. Once inflated, the balloon  268  engages the pulmonary vein PV. Because the catheter body  252  and the locating device  256  are directly connected by the sheath  258 , the balloon  268  effectively positively centers the coil  264  about the pulmonary vein ostium PVO. The electrodes  254  may be selectively energized with a low-energy supply to determine which of the electrodes  254  are in contact with the tissue of the left atrium LA. Some or all of the electrodes  254  are then energized to ablate a continuous, closed lesion pattern about the pulmonary vein ostium PVO, thereby electrically isolating the pulmonary vein PV from the left atrium LA. 
         [0126]    Yet another alternative embodiment of a catheter assembly  290  is shown in  FIG. 11 . The catheter assembly  290  is highly similar to the catheter assembly  250  ( FIG. 10 ) previously described, and includes a catheter body  292 , electrodes  294 , a locating device  296  and a guide catheter or sheath  298 . The sheath  298  coaxially maintains the catheter body  292  and the locating device  296  such that each of the catheter body  292  and the locating device  296  are slidable between a refracted position and a deployed position (shown in  FIG. 11 ). 
         [0127]    The catheter body  292  includes a proximal portion (not shown), an intermediate portion  300  defining a longitudinal axis L 10  and a distal portion  302 . The distal portion  302  extends from the intermediate portion  300  and forms a coil or plurality of loops  304  substantially transverse to the longitudinal axis L 10 . Alternatively, the coil  304  may form a single loop. The coil  304  revolves around a central loop axis C 10 , that, in one preferred embodiment, is aligned with the longitudinal axis L 10 . The distal portion  302 , and in particular the coil  304 , is preferably sufficiently flexible so as to assume a relatively straight configuration when retracted within the sheath  298 . Further, the distal portion  302  includes a shape memory characteristic such that when deployed from the sheath  298 , the distal portion  302  forms the coil  304  as shown in  FIG. 11 . 
         [0128]    The electrodes  294  are identical to those previously described and preferably comprise band electrodes disposed along the coil  304 . Alternatively, a continuous coil electrode or counter-electrode may be provided. 
         [0129]    The locating device  296  includes a shaft  306  and a wire basket  308 . The shaft  306  includes a distal portion  310  and a tip  312 . The distal portion  310  forms an expansion joint  314 . The tip  312  preferably maintains mapping electrodes  316 . The wire basket  308  is secured to the distal portion  310  about the expansion joint  314 . With this configuration, the expansion joint  314  can be manipulated between an expanded position in which the wire basket  308  is relatively flat and a contracted position ( FIG. 11 ) in which the wire basket  308  expands radially. 
         [0130]    The sheath  298  is highly similar to previous embodiments and includes a proximal end (not shown) and a distal end  318 , and forms at least one central lumen (not shown) sized to maintain the catheter body  292  and the locating device  296 . Alternatively, a separate lumen may be provided for each of the catheter body  292  and the locating device  296 . Regardless, the sheath  298  is configured to slidably maintain each of the catheter body  292  and the locating device  296  in a relatively close relationship. 
         [0131]    As described above, each of the catheter body  292  and the locating device  296  are slidable relative to the sheath  298 . In a deployed position (depicted in  FIG. 11 ), the distal portion  302  of the catheter body  292  and the distal portion  310  of the locating device  296  extend distally from the sheath  298 . More particularly, the catheter body  292  is positioned such that the coil  304  is distal the distal end  318 . Further, the distal portion  310  of the locating device  296  is distal the coil  304 . 
         [0132]    During use, the catheter assembly  290  functions in a manner highly similar to the catheter assembly  250  ( FIG. 10 ) previously described. However, the wire basket  308  is used to positively center the coil  304  about a pulmonary vein ostium PVO instead of the balloon  268  ( FIG. 10 ) previously described. 
         [0133]    Yet another alternative embodiment of the catheter assembly  330  is shown in  FIGS. 12A and 12B . The catheter assembly  330  includes a catheter body  332  (shown partially in  FIGS. 12A and 12B ), a wire basket  334 , a locating device  336  and a stylet or guide wire  338 . The wire basket  334  is secured to the catheter body  332 . The locating device  336  is preferably integrally formed with the catheter body  332  and includes a balloon  340 . Finally, the guide wire  338  is slidably disposed within a central lumen (not shown) in the catheter body  332  and the locating device  336 . 
         [0134]    The catheter body  332  includes a proximal portion (not shown), an intermediate  342  defining a longitudinal axis L 11  and a distal portion  344 . The distal portion  344  maintains a proximal collar  346  and a distal collar  348 . In a preferred embodiment, the proximal collar  346  is slidable relative to the distal collar  348 . 
         [0135]    The wire basket  334  is secured to the distal portion  344  by the proximal collar  346  and the distal collar  348 . Further, the wire basket  334  includes a plurality of individual wire struts  350  each maintaining an electrode  352 . In a preferred embodiment, the wire struts  350  are preferably tubular and are fluidly connected to a cooling source. The electrodes  352  are preferably disposed along the wire struts  350 , respectively, slightly distal of a central position. With this configuration, the wire basket  334  can be maneuvered between a refracted position ( FIG. 12A ) and an expanded position ( FIG. 12B ) with movement of the proximal collar  346  relative to the distal collar  348 . Notably, in the expanded position of  FIG. 12B , the wire basket  334  positions the electrodes  352  so as to form a loop transverse to the longitudinal axis L 11 . More particularly, the loop formed in the expanded position revolves around a central loop axis C 11 , that, in one preferred embodiment, is aligned with the longitudinal axis L 11 . 
         [0136]    The electrodes  352  are identical to those previously described and preferably comprise band electrodes disposed along the wire basket  334 . 
         [0137]    The locating device  336  extends distal the distal collar  348 , and maintains the balloon  340  and mapping electrodes  354 . The balloon  340  is fluidly connected to an inflation source (not shown) by a lumen (not shown) formed within the catheter body  332 . As shown in  FIGS. 12A and 12B , the balloon  340  is preferably positioned distal the wire basket  334 . Further, the mapping electrode  354  is positioned distal the balloon  340 . 
         [0138]    Prior to use, the catheter assembly  330  is positioned in the retracted position shown in  FIG. 12A . The guide wire  338  is guided to the left atrium LA ( FIG. 4B ) and into a pulmonary vein PV ( FIG. 4B ). The catheter body  332 , including the locating device  336 , are guided over the guide wire  338  to a point adjacent the pulmonary vein. The catheter body  332  is then advanced such that the locating device  336  enters the pulmonary vein PV. The mapping electrodes  354  sample electrical activity of the pulmonary vein tissue. If the mapping procedure determines that the pulmonary vein PV requires electrical isolation, the catheter assembly  330  is maneuvered to the expanded position shown in  FIG. 12B , whereby the wire basket  334  expands radially. The catheter body  332  is then advanced axially toward the pulmonary vein such that the wire basket  334  contacts the left atrium LA about the pulmonary vein ostium PVO ( FIG. 4B ). The balloon  340  is then inflated so as to engage the pulmonary vein PV. Once inflated, the balloon  340  effectively centers the wire basket  334 , and thus the electrodes  352 , about the pulmonary vein ostium PVO. The electrodes  352  are then energized to ablate a continuous, closed lesion pattern about the pulmonary vein ostium PVO, thereby electrically isolating the pulmonary vein PV from the left atrium LA. If necessary, the individual wire struts  350  are cooled, such as by forcing a cooling liquid through the wire struts  350 . The balloon  340  is deflated and the wire basket  334  maneuvered to the contracted position ( FIG. 12A ). The entire catheter assembly  330  may then be removed from the patient. Alternatively, the catheter body  332  may be retracted from the patient along the guide wire  338  and replaced with a separate catheter device (not shown). To this end, the catheter body  332  may be configured to provide a rapid exchange feature, as would be apparent to one of ordinary skill. 
         [0139]    Yet another alternative embodiment of a catheter assembly  400  is shown in  FIGS. 13A-13E . With reference to  FIG. 13A , the catheter assembly  400  includes a catheter body  402 , a fluid source  404 , a shaping wire  406  (hidden in  FIG. 13A ), a guide wire  408  and first and second sensing electrode pairs  410   a  and  410   b . The fluid source  404  is fluidly connected to a lumen formed by the catheter body  402 . The shaping wire  406  and the guide wire  408  are coaxially and slidably maintained by the catheter body  402  such that each of the shaping wire  406  and the guide wire  408  are slidable between a retracted position and a deployed position (shown in  FIG. 13A ). Finally, the sensing electrodes  410   a ,  410   b  are secured to a portion of the catheter body  402 . 
         [0140]    The fluid source  404  is shown schematically in  FIG. 13A , and can assume a wide variety of forms. The fluid source  404  maintains an appropriate volume of a conductive liquid or ionic fluid, such as a hypertonic saline solution, and includes a pump (not shown). The pump is controllable to provide a desired flow rate of the liquid to the catheter body  402 . 
         [0141]    The catheter body  402  includes a proximal portion  416 , an intermediate portion  418 , and a distal portion  420 . Construction of the catheter body  402  is described in greater detail below. In general terms, and as shown in  FIG. 13A , the distal portion  420  extends from the intermediate portion  418  and forms, or is formed to, a coil or helix (e.g., conical or cylindrical). Further, the distal portion  420  defines an ablation section  422 . The ablation section  422  forms, or is formed to, a loop of at least one revolution. As with previous embodiments, the loop formed at or by the ablation section  422  revolves around a central loop axis C 12 , that is substantially parallel with, preferably aligned with, a longitudinal axis L 12  defined by the intermediate portion  418 . Alternatively stated, the loop formed at or by the ablation section  422  extends transversely relative to the longitudinal axis L 12 . 
         [0142]    With additional reference to  FIG. 13B , the catheter body  402  preferably defines a first lumen  428  and a second lumen  430 . The first lumen  428  extends from the proximal portion  416  through the distal portion  420 , including the ablation section  422 , and is preferably closed or terminates at a distal end  432  of the catheter body  402 . As described in greater detail below, the first lumen  428  is sized to slidably receive the shaping wire  406  as depicted in  FIG. 13B , and preferably has a diameter slightly greater than that of the shaping wire  406  and any other elements carried by the shaping wire  406 , such as a coil electrode. With this configuration, the first lumen  428  provides sufficient spacing about the shaping wire  406  to allow passage of the conductive liquid or ionic fluid (not shown) from the fluid source  404 . Thus, the first lumen  428  is fluidly connected to the fluid source  404  and directs liquid from the fluid source  404  to at least the ablation section  422 . By closing the first lumen  428  at the distal end  432 , a back pressure can be generated within the first lumen  428  to promote fluid irrigation through the ablation section  422  as described below. 
         [0143]    The second lumen  430  extends from the proximal portion  416  to the distal portion  420 , preferably terminating at an opening  434  located proximal the ablation section  422 . This relationship is illustrated in  FIG. 13C . The second lumen  430  is sized to slidably maintain the guide wire  408 . In this regard, the catheter body  402  is preferably configured such that in the deployed position of  FIG. 13A , the guide wire  408  extends from the opening  434  in a substantially concentric fashion relative to the helix formed in or by the distal portion  420 . 
         [0144]    The catheter body  402  is described in greater detail with reference to  FIG. 14A . For ease of illustration, only a portion of the catheter body  402  is provided in  FIG. 14A , including the intermediate portion  418  and the distal portion  420 . Further, the distal portion  420  is shown in a straightened or uncoiled state, as compared to the helical configuration of  FIG. 13A . As previously described, the catheter body  402  includes the ablation section  422  formed along the distal portion  420 . In one preferred embodiment, the ablation section  422  is formed of a material different from a remainder of the catheter body  402 , including the distal portion  420 . More particularly, the ablation section  422  is tubular, formed of a flexible, microporous, surgically-safe material, whereas a remainder of the catheter body  402 , and in particular the distal portion  420 , is formed of a flexible, fluid impermeable material. In one preferred embodiment, the ablation section  422  is a microporous polymer, preferably microporous, high density, expanded polytetrafluoroethylene (PTFE), whereas a remainder of the distal portion  420  is a fluid impermeable polymer, such as polyethylene, polyurethane, or PEBAX. A remainder of the catheter body  402  is similarly formed from a fluid impermeable, polymeric, electrically non-conductive material but can be more rigid than the distal portion  420 . Alternatively, other known materials useful in catheter applications are equally acceptable. 
         [0145]    Use of a porous material for the ablation section  422  establishes a plurality of pores  440  extending from an interior surface  442  to an exterior surface  444 . As shown in  FIG. 13D , the pores  440  are in fluid communication with the first lumen  428 . It should be noted that a size of the pores  440  has been greatly exaggerated in  FIG. 13D  for purposes of illustration. Further, the pores  440  need not be continuous from the exterior surface  444  to the interior surface  442 . Instead, a plurality of interconnected interstitial spaces can be formed by the ablation section  422  so as to establish fluid communication between the interior surface  442  and the exterior surface  444 . As a point of reference, a porosity of the ablation section  422  is preferably in the range of approximately 5-25 microns. Regardless of the exact construction, the ablation section  422  formed with microporous material irrigates liquid (and contained ions) from the first lumen  428  to the exterior surface  444  in a uniform fashion along an entirety of the exterior surface  444 , or at least along an entire length of the ablation section  422  (and thus into contact with targeted tissue (not shown)). With this construction, then, where the conductive fluid has been energized (such as by an electrode), a continuous electrode is effectively established along an entire length of the ablation section  422 , in direct contrast to “compartmentalized” ablation electrodes typically employed. By way of example, use of a high density, expanded PTFE material for the ablation section  422  having a straightened length of approximately 3.2 inches (81.3 mm) and wall thickness of approximately 0.010 inch (0.25 mm) exhibited virtually uniform liquid distribution of a preferably isotonic, alternatively hypertonic, saline solution along the exterior surface  444  at flow rates as low as 1 ml/min. 
         [0146]    While the ablation section  422  has been preferably described as being formed of a microporous polymer, other constructions are equally acceptable. For example, as shown in  FIG. 14B , an alternative ablation section  450  is initially formed as a non-porous sleeve. During manufacture, a series of small passages  452  are created in the sleeve, such as with a laser, to facilitate generally uniform irrigation of a conductive liquid for an interior to an exterior of the sleeve. Once again, the passages  452  are minute, preferably having a diameter in the range of 5-100 microns. A wide variety of materials are useful for the sleeve, including polyethylene (high or low density), nylon, polyamide block co-polymer, PTFE, polyurethane, fluoropolymers, etc. 
         [0147]    Regardless of exact construction, in a preferred embodiment the distal portion  420 , including the ablation section  422 , is preferably compliant, and can readily be manipulated to a desired shape. To this end, the shaping wire  406  is preferably employed to selectively direct the distal portion  420  to the helical or coiled configuration of  FIG. 13A . Thus, in one preferred embodiment, the distal portion  420 , including the ablation section  422 , defines the first lumen  428  for receiving the shaping wire  406  along with an electrode (not shown) for applying an ablation energy to fluid irrigated through the ablation section  422 . This relationship is depicted in  FIG. 13D . Alternatively, and with reference to  FIG. 13E , an additional lumen, such as a third lumen  460 , can be formed in the distal portion  420  (and extending to the proximal portion  418 ). With this configuration, the first lumen  428  is available to direct fluid to the ablation section  422 , while the third lumen  460  is available to maintain the shaping wire  406  and/or an electrode for applying an ablation energy. Even further, the material selected for the distal portion  420  can have an elasticity or shape memory characteristic such that the helix configuration is independently achieved by the distal portion  420  without requiring the separate shaping wire  406 . 
         [0148]    Returning to  FIG. 14A , regardless of the exact construction, the ablation section  422  is preferably sized so as to provide a relatively large ablation area when formed as a loop (as otherwise depicted in  FIG. 13A ). In one preferred embodiment, the ablation section  422  has a straightened length in the range of approximately 2-8 inches (51-203 mm), more preferably approximately 5 inches (127 mm). Alternatively, other dimensions are equally acceptable. 
         [0149]    The shaping wire  406  is shown in greater detail in  FIGS. 15A and 15B . The shaping wire  406  includes a proximal segment (not shown), an intermediate segment  464  and a distal segment  466 . In addition, a metal wire  470  is preferably provided and secured to the shaping wire  406  as described below. As a point of reference, the distal segment  466  is shown in a straightened or uncoiled state in  FIG. 15A , whereas  FIG. 15B  depicts a helical (or coiled) state. 
         [0150]    The shaping wire  406 , and in particular the distal segment  466 , is preferably formed of a thin material having a super elasticity or shape memory characteristic. For example, in one preferred embodiment, the shaping wire  406  is formed from spring-like material such as super elastic or pseudo-elastic nickel titanium (commercially available as Nitinol material), having a diameter in the range of approximately 0.010-0.020 inch (0.25-0.5 mm). With this or other resilient material (such as stainless steel or resilient plastic), the desired helical configuration of the distal segment  466  is imparted during formation of the shaping wire  406 . As a result, the distal segment  466  has a highly resilient, spring-like attribute whereby the distal segment  466  can be “forced” to the straightened state of  FIG. 15A , but will readily revert to the helical configuration of  FIG. 15B  (it being understood that the super elastic Nitinol or other material has a phase transition temperature well below normal human body temperature). 
         [0151]    The metal wire  470  is wound about a portion of the distal segment  466  to form a coil electrode  474  and is secured to the shaping wire  406 , such as by a weld  472 . Further, the metal wire  470  extends to the proximal segment (not shown) where it is electrically connected to a power source (not shown), for example a source of radio frequency (RF) energy. The location and length of the coil electrode  474  relative to the shaping wire  406  corresponds with a location and length of the ablation section  422  ( FIG. 14A ) relative to the catheter body  402  ( FIG. 14A ). Thus, upon final assembly and activation of the power source, the coil electrode  474  serves to provide an ablation energy to the ablation section  422 , and in particular, the conductive fluid (not shown) otherwise supplied to the ablation section  422 . Notably, a winding density and thickness of the coil electrode  474  does not impede the ability of the distal segment  466  to revert to the helical state of  FIG. 15B . In the straightened state of  FIG. 15A , the coil electrode  474  preferably has a length slightly greater than a length of the ablation section  422 , in the range of approximately 2.5-8.5 inches (63-216 mm). In one preferred embodiment, with the ablation section  422  length of approximately 5 inches (127 mm), the coil electrode  474  has a length of approximately 5.5 inches (140 mm). A wide variety of known, electrically conductive materials are available for use as the metal wire  470 . Preferably, however, the metal wire  470  is comprised of platinum, copper, copper-silver alloy, nickel-cobalt alloy, etc. 
         [0152]    While the shaping wire  406  has been described as carrying a single metal wire  470 , and thus a single coil electrode  474 , multiple wires/coil electrodes can be provided. For example, in a more preferred embodiment, depicted in  FIG. 15C , six metal wires  470   a - 470   f  forming six coil electrodes  474   a - 474   f  are each secured to the distal segment  466  (depicted in a straightened state for ease of illustration) as previously described. The coil electrodes  474   a - 474   f  are preferably longitudinally spaced by approximately 1-2 mm. For ease of illustration, only one of the metal wires  470   a  is shown as extending proximally, it being understood that all of the metal wires  470   a - 470   f  extend proximally, and are connected to a power source and/or control box (not shown). The coil electrodes  474   a - 474   f  are sized such that when the shaping wire  406  assumes the helical shape, (e.g.,  FIG. 15B ) each of the coil electrodes  474   a - 474   f  have a length less a full revolution defined by the distal segment  466 . While the coil electrodes  474   a - 474   f  may have varying lengths, the coil electrodes  474   a - 474   f  are sized such that a combined length is slightly greater than one revolution (or of a length of the ablation section  422  ( FIG. 13A )). With this configuration, a user can selectively ablate quadrants or portions of a complete circle (or other closed shape) by selectively energizing less than all of the coil electrodes  474   a - 474   f . For example, a user may wish to ablate only muscle tissue (determined by electrogram analysis). By providing multiple, relatively short coil electrodes  474   a - 474   f , this desired procedure is available. Once again, however, only a single coil electrode is necessary. 
         [0153]    Returning to  FIG. 13A , the guide wire  408  is of a type known in the art, and is preferably constructed of a rigid metal material. In this regard, the guide wire  408  includes a proximal section  480  and a distal section  482 . Further, the guide wire  408  is sized to be slidably received within the second lumen  430  of the catheter body  402 . With this relationship, the guide wire  408  is selectively moveable from a refracted position in which the distal section  482  is proximal the distal portion  420 , and a deployed position in which the distal section  482  is distal the distal portion  420  (as shown in  FIG. 13A ). 
         [0154]    Finally, the distal section  482  can be formed to include a J-shaped or floppy tip to facilitate placement within a vein. As described below with reference to an alternative embodiment, the guide wire  408  is not a necessary element, and can be replaced with an alternative locating device. 
         [0155]    Finally, the sensing electrode pairs  410   a ,  410   b  are preferably band electrodes capable of providing feed back information indicative of electrical activity. As described below, the sensing electrode pairs  410   a ,  410   b  are useful for evaluating the “completeness” of an ablation pattern formed by the catheter assembly  400 . To this end, the sensing electrode pairs  410   a ,  410   b  are strategically located along the distal portion  420  relative to the ablation section  422 . It will be noted that the distal portion  420  is preferably helically-shaped, having a decreased diameter proximal the ablation section  422 , and an increased diameter distal the ablation section  422 . With this in mind, the first sensing electrode pair  410   a  is preferably located proximal the ablation section  422  for evaluating electrical activity “within” the loop pattern defined by the ablation section  422 . Conversely, the second sensing electrode pair  410   b  is distal the ablation section  422  for evaluating electrical activity “outside” the loop. With alternative embodiments, one or both of the sensing electrode pairs  410   a ,  410   b  can be eliminated; or additional sensing electrodes provided. Even further, additional sensors, such as a thermocouple, can be included along the distal portion  420 . 
         [0156]    The catheter assembly  400  of  FIG. 13A  is deployed to a desired area of a heart as described below, preferably in a straightened or uncoiled state. To facilitate this arrangement, and in a more preferred embodiment, the catheter assembly  400  further includes a guide catheter or sheath  486  as shown in  FIGS. 16A and 16B . For ease of illustration, only a distal region of the catheter assembly  400  is shown in  FIGS. 16A and 16B . The guide catheter  486  forms a lumen  488  sized to slidably maintain the catheter body  402  (including the shaping wire  406  and the guide wire  408 ), and terminates at an open tip  490 . With this configuration, the catheter assembly  400  is selectively maneuverable between the retracted position of  FIG. 16A  in which entireties of the catheter body  402 , the shaping wire  406 , and the guide wire  408  are proximal the tip  490 , and the deployed position of  FIG. 16B  in which portions of the various components  402 ,  406 ,  408  are distal the tip  490 . As described in greater detail below, then, the catheter assembly  400  is initially directed to a desired area in the retracted position. Subsequently, the catheter body  402 , the shaping wire  406  and the guide wire  408  are directed to the deployed position of  FIG. 16B . 
         [0157]      FIG. 17A-17D  illustrate use of the catheter assembly  400  within the heart  50 , and in particular the left atrium (LA). Prior to deployment of the catheter assembly  400 , the left atrium LA anatomy is preferably evaluated using an available 3-D imaging device, such as a fluoroscope, CT scanner, MRI or ultrasound, to determine the geometry and orientation of the various pulmonary veins (PV). The fluid source  404  ( FIG. 13A ) is activated to provide a continuous flow of conductive liquid, (e.g., isotonic saline solution) to the first lumen  428  ( FIG. 13A ), and in particular the ablation section  422  ( FIG. 13A ). For example, a continuous flow rate in the range of 1-4 ml/min is established to purge air from the first lumen  428 . 
         [0158]    Following the preparatory steps, and with reference to  FIG. 17A , electrical isolation of a left pulmonary vein (LPV) begins by directing the catheter assembly  400  of  FIG. 16A  in a retracted position through the inferior vena cava (IVC), into the right atrium (RA) through a puncture in the interatrial septum (not shown) and into the left atrium LA. Alternatively, the introduction of the catheter assembly  400  into the right atrium RA is also suggested by passage of the catheter body  402  into the right atrium RA through the superior vena cava (SVC). The tip  490  of the guide catheter  486  is positioned slightly spaced from the pulmonary vein ostium PVO associated with the left pulmonary vein (LPV) to be isolated. The catheter body  402  is then deployed as shown in  FIG. 17B . More particularly, the distal portion  420  is extended distal the tip  490  of the guide catheter  486 . In this regard, the distal segment  466  ( FIG. 13A ) of the shaping wire  406  ( FIG. 13A ) is within the distal portion  420  of the catheter body  402  such that the distal portion  420  forms the helical shape shown in  FIG. 17B . 
         [0159]    Following deployment of the catheter body  402 , the guide wire  408  is then deployed as illustrated in  FIG. 17C . By preferably performing deployment of the catheter assembly  400  in this order, the opportunity for damage to the catheter body  402  is minimized. Once deployed, the distal section  482  of the guide wire  408  is substantially concentric with, and extends distally beyond, the helix formed at the distal portion  420 . 
         [0160]    Once deployed, the guide wire  408  is utilized to locate the left pulmonary vein LPV to be treated. In this regard, a fluoroscope is preferably employed to provide visual confirmation that the guide wire  408  is positioned within the left pulmonary vein LPV to be isolated. 
         [0161]    The catheter body  402  is advanced over the guide wire  408  and into contact with the left atrium LA tissue wall/material surrounding the pulmonary vein ostium PVO as shown in  FIG. 17D . In particular, the distal portion  420  is pressed against the tissue wall such that the helix formed in or by the distal portion  420  compresses onto itself and the loop formed by the ablation section  422  is in complete contact with the chamber wall about the pulmonary vein ostium PVO. To this end, fluoroscopic visualization is preferably utilized to confirm relatively continuous contact between the ablation section  422  and the chamber wall. In addition, bipolar electrograms can be recorded from the electrode pairs  410   a ,  410   b  to assess LA endocardial wall contact. 
         [0162]    The fluid flow rate from the fluid source (not shown) to the ablation section  422  is then increased to approximately 4-10 ml/min. After waiting for a short period to ensure increased fluid flow to, and irrigation through, the ablation section  422 , the coil electrode  472  ( FIG. 16A ) is energized, for example with RF energy. This energy is transferred via the fluid irrigated along the ablation section  422  to the tissue contacted by the ablation section  422 . The conductive fluid establishes a conductive path from the coil electrode  472  to the contacted tissue, thereby ablating the targeted tissue. As previously described, a porosity associated with the ablation section  422  is such that the conductive fluid irrigates or “weeps” or “sweats” to the exterior surface  444  ( FIG. 13D ) of the ablation section  422 . This weeping attribute serves to cool the coil electrode  472  and, because the fluid contacts the targeted tissue, minimizes the opportunity for thrombosis formation. In one preferred embodiment, the coil electrode  472  is energized for two minutes at 40-50 watts, although other ablation energies and times are equally acceptable. The endpoint of energy delivery can be determined by the reduction in electrogram amplitude at the discretion of the physician. 
         [0163]    Following application of the ablation energy, the catheter assembly  400  is preferably operated to determine whether a closed, electrically isolating ablation pattern has been established in the chamber wall, about or outside of the ostium PVO. More particularly, and as shown in  FIGS. 18A and 18B , the sensing electrode pairs  410   a ,  410   b  are simultaneously interrogated to evaluated isolation of the PV ostium PVO from the left atrium LA wall. As a point of reference,  FIG. 18A  provides an end view of the distal portion  420  compressed against a chamber wall (not shown), including the ablation section  422  and the sensing electrode pairs  410   a ,  410   b . Conversely,  FIG. 18B  depicts an ablation pattern  494  formed on a tissue wall  496 , as well as locations of the sensing electrode pairs  410   a ,  410   b  relative to the ablation pattern  494  when the distal portion  420  (not shown in  FIG. 18B ) is compressed against the tissue wall  496 . With these orientations in mind, the first sensing electrode pair  410   a  is located within the ablation pattern  494 , whereas the second sensing electrode pair  410   b  is located outside of the ablation pattern  494 . This configuration is further exemplified by reference to  FIG. 18A  in which the first sensing electrode pair  410   a  is located within loop defined by the ablation section  422 , whereas the second sensing electrode pair  410   b  is outside of the loop. Following application of the ablation energy, the sensing electrode pairs  410   a ,  410   b  are operated to observe and sense electrical activity inside and outside of the ablation pattern  494 . If it is determined that electrical activity continues to traverse the ablation pattern  494 , an ablation energy can again be applied to the coil electrode  472  ( FIG. 13A ) to further ablate the tissue wall about the pulmonary vein ostium PVO. Once sufficient ablation has been achieved, the catheter body  402  and the guide wire  408  are retracted from the pulmonary vein ostium PVO. Subsequently, additional ablation patterns can be formed about other ones or all of the pulmonary vein ostia PVOs. 
         [0164]    As should be evident from the views of  FIG. 17A-17D , proper positioning of the catheter assembly  400  relative to the left pulmonary veins LPVs is straightforward in that the catheter assembly  400  is essentially axially aligned with the left pulmonary veins LPVs upon passage into the left atrium LA. However, the right pulmonary veins RPVs are normally obliquely orientated relative to the catheter assembly  400  upon guidance into the left atrium LA. Thus, in one preferred embodiment, and as shown in  FIG. 19 , the catheter assembly  400  is preferably provided with a steering capability so that the right pulmonary veins RPVs are more easily accessed. For example, the guide catheter  486  can be configured such that the tip  490  is deflectable relative to remainder of the guide catheter  486 , and therefore maneuverable by a user to the position shown in  FIG. 19 . 
         [0165]    Controls and structures useful in providing this steering capability are well-known in the art, and can include a stiffening wire or pulling wire extending along the guide catheter  486 . Alternatively and/or in addition, the catheter body  402  may be provided with a steering device to facilitate selective deflection of the distal portion  420  relative to a remainder of the catheter body  402 . 
         [0166]    The preferred implementation of the shaping wire  406  ( FIG. 16A ) to dictate the axially compressible, helical shape of the distal portion  420  of the catheter body  402  provides several advantages. First, because the distal portion  420 , and in particular the ablation section  422 , need not have a rigid characteristic necessary to maintain the helical shape, a compliant, microporous material can be used for the ablation section  422 , such as high density, expanded PTFE. The microporous material facilitates uniform perfusion of conductive fluid that cools the ablation section  422 , thereby minimizing the opportunity for thrombus formation. In addition, a wide variety of differently shaped and sized shaping wires  406  can be made available to a user, who can then select the size and shape most appropriate for achieving desired ablation. In other words, upon evaluating the pulmonary vein and associated ostium, the user can select an appropriate shaping wire that in turn dictates an optimal size and shape of the distal portion  420  and the ablation section  422 . In this regard, not only can an overall size of the ostium (e.g., larger or smaller) be properly accounted for, but also the associated shape. For example, as shown in  FIG. 20A , a simplified, side-sectional view of a pulmonary vein PV is shown, including the chamber wall tissue T surrounding and forming the pulmonary vein ostium PVO. As is evident from the illustration, the chamber wall tissue T is relatively planar adjacent the pulmonary vein ostium PVO. As such, the selected shaping wire  500  of  FIG. 20B  includes a coil segment  502  that axially compresses to a relatively planar loop or series of loops. During use, then, and as shown in  FIG. 20C , the relatively planar, axially compressed configuration of the shaping wire  500  readily conforms with the relatively planar configuration of the chamber wall tissue T, so that an optimal ablation pattern is formed on the chamber wall tissue T outside of the pulmonary vein ostium PVO. 
         [0167]    Alternatively, as shown in  FIG. 21A , the pulmonary vein ostium PVO and associated chamber wall tissue T can have a non-planar shape. More particularly, pulmonary vein ostia are often formed to have a “saddle” shape. When so identified, a user will select a correspondingly-shaped shaping wire, such as the shaping wire  504  depicted in  FIG. 21B . The shaping wire  504  includes a coiled segment  506  that, when axially compressed, assumes a non-planar shape. During use, and when axially compressed against the chamber wall tissue T, the coiled segment  506  assumes a “saddle” shape corresponding generally with the chamber wall tissue outside of (or surrounding) the pulmonary vein ostium PVO, as depicted in  FIG. 21C . In practice, by providing a number of interchangeable, but uniquely sized and shaped shaping wires, a user can quickly ablate and electrically isolate all of the pulmonary vein ostia PVOs without removing the catheter body  402  from the left atrium LA. 
         [0168]    Another alternative, more preferred embodiment of a catheter assembly  550  is shown in  FIG. 22 . For ease of illustration, only a distal region of the catheter assembly  550  is depicted. The catheter assembly  550  is similar to the catheter assembly  400  ( FIGS. 13A-13E ) previously described, and includes a delivery catheter  552  and an ablation catheter  554 . The delivery catheter  552  includes a distal locator  556  and forms a delivery lumen  558  (shown partially in  FIG. 22 ) terminating at an opening  560  proximal the delivery locator  556 . The ablation catheter  552  is slidably disposed within the delivery lumen  558  such that the ablation catheter  552  is selectively deployable and retractable relative to the delivery catheter  552  via the opening  560 . 
         [0169]    The delivery catheter  552  is shown in greater detail in  FIG. 23 . For ease of illustration, the ablation catheter  554  ( FIG. 22 ) has been omitted from the view of  FIG. 23 . The delivery catheter  552  includes a proximal region  570 , an intermediate region  572 , and the distal locator  556 . The intermediate region  572  extends from the proximal region  570  and terminates in the opening  560 . The distal locator  556 , in turn, extends from the intermediate region  572  distal the opening  560 . As described in greater detail below, the delivery catheter  552  is preferably steerable both proximal and distal the opening  560 . 
         [0170]    In light of the preferred steerable attribute of the delivery catheter  552 , the proximal region  570  includes a Y-connector  574  coupled to a handpiece  576  and a guide piece  578 . The handpiece  576  is of a type known in the art and provides control devices  580 , the operation of which effectuates desired bending of the delivery catheter  552  via pull wires (not shown) described in greater detail below. The guide piece  578  is fluidly connected to the delivery lumen  558  ( FIG. 22 ) and preferably is a hemostatic valve forming a first port  582  and a second port  584 . The first port  582  is available for receiving and directing a separate body, such as the ablation catheter  554  ( FIG. 22 ) or a dilator (not shown), to the delivery lumen  558 . Further, the second port  584  is also fluidly connected to the delivery lumen  558 , and is available for directing fluid thereto. For example, the second port  584  can be fluidly connected to a stop cock valve (not shown) that in turn facilitates flushing of a liquid, such as saline, through the delivery lumen  558  while preventing back flow of other liquids, such as blood. 
         [0171]    With further reference to  FIG. 24A , the proximal region  570  forms the delivery lumen  558  within which the ablation catheter  554  ( FIG. 22 ) is slidably disposed. In addition, the proximal region  570  forms a passage  588  surrounding the delivery lumen  558  and maintaining, as depicted in  FIG. 24A , a first pull wire  590 , a second pull wire  592 , and a cluster of electrode wires  594 . In one preferred embodiment, the delivery lumen  558  is defined by a tube  596  disposed within the passage  588 . Alternatively, the proximal region  570  can be configured to integrally form the delivery lumen  558 . The first pull wire  590  extends from the handpiece  576  to the intermediate region  572  for effectuating steering or bending of the delivery catheter  552  proximal the opening  560  ( FIG. 23 ). The second pull wire  592  extends from the handpiece  576  to the distal locator  556  for effectuating steering or bending of the delivery catheter  552  distal the opening  560 . Finally, the cluster of electrode wires  594  are electrically connected to an auxiliary energy source (not shown) for energizing various electrodes associated with the delivery catheter  552 . 
         [0172]    The proximal region  570  is preferably formed of a reinforced, braided material such as a tubular shaft constructed of amorphous thermoplastic polyetherimide (PEI) materials sold under the trademark ULTEM, polyamide, or other high temperature polymer covered with a reinforcing braid wire or high strength filament and jacketed by a flexible polymer such as nylon, polyurethane, or PEBAX. With this preferred material, the proximal region  570  exhibits enhanced torqueability, such that a user can more easily steer or guide the delivery catheter  552  to a target site. 
         [0173]    The intermediate region  572  forms the opening  560  and preferably maintains an electrode  600 . With additional reference to  FIG. 24B , the intermediate region  572  defines first, second, and third lumens  602 - 606 , in addition to the delivery lumen  558 . Once again, the delivery lumen  558  is preferably defined by the tube  596  otherwise carried within the intermediate region  572 . Alternatively, the delivery lumen  558  can be integrally formed by the intermediate region  572 . The delivery lumen  558  is available to slidably maintain the ablation catheter  554  ( FIG. 22 ) or other body, and terminates at the opening  560 . The first pull wire  590  extends through the first lumen  602  and is secured to the intermediate region  572  adjacent the opening  560 . The second pull wire  592  extends through the second lumen  604 . Finally, the cluster of electrode wires  594  are maintained within the third lumen  606 . 
         [0174]    The electrode  600  is preferably a band electrode electrically connected to one or more of the cluster of electrode wires  594 . With this configuration, the electrode  600  serves as a mapping electrode. Notably, however, the electrode  600  is not a necessary element for use of the delivery catheter  552 . 
         [0175]    The intermediate region  572  is preferably formed of a material different from that of the proximal region  570 . More particularly, unlike the preferably reinforced, torqueable composition of the proximal region  570 , the intermediate region  572  is preferably comprised of a softer material such as nylon, polyurethane, or PEBAX. With this configuration, the intermediate region  572  is highly amenable to bending via tensioning of the first pull wire  590 . To this end, a length of the intermediate region  572  (i.e., longitudinal distance proximal the opening  560 ) dictates the focal point at which bending of the intermediate region  572  occurs, as well as an available bend radius. In a preferred embodiment, the intermediate region  572  has a longitudinal length in the range of 5-25 cm, more preferably 15 cm. 
         [0176]    The opening  560  is shown more clearly in  FIG. 24C , and preferably includes rounded or curved edges  608 . This preferred configuration minimizes possible tissue damage as the delivery catheter  552  is passed through bodily lumens, for example veins. Alternatively, however, the opening  560  may assume a wide variety of other forms. As described below, a rounded-tip dilator (not shown) is preferably extended into and/or through the opening  560  to further minimize the opportunity for tissue damage during delivery through bodily lumens. 
         [0177]    The distal locator  556  extends distally beyond the opening  560  and preferably includes electrode pairs  610   a  and  610   b . Further, the distal locator  556  preferably terminates at a tip  612  that, in one preferred embodiment, incorporates a thermocouple and serves as an electrode pair with an electrode  614 . With additional reference to  FIG. 24D , the distal locator  556  defines the second lumen  604 , maintaining the second pull wire  592 , and the third lumen  606 , maintaining the cluster of electrode wires  594 . The second pull wire  592  is attached to the distal locator  556  adjacent the tip  612 . The cluster of electrode wires  594  are connected to the pairs of electrodes  610   a  and  610   b , as well as the tip  612  and the electrode  614 . With this configuration, the electrode pairs  610   a  and  610   b , as well as the tip  612  and the electrode  614 , are available for mapping and/or ablation functions. 
         [0178]    The distal locator  556  is preferably formed from a soft material similar to the intermediate region  572 , preferably nylon, polyurethane, or PEBAX. With this configuration, the distal locator  556  is bendable or steerable via tensioning of the second pull wire  592 . In a preferred embodiment, the distal locator  556  has a length in the range of 5-20 cm, more preferably 15 cm; and a diameter in the range of 5-7 French, more preferably 6 French. 
         [0179]    Returning to  FIG. 22 , the ablation catheter  554  includes a distal portion  620  forming an ablation section  622 . In one preferred embodiment, the ablation catheter  554  is highly similar to the catheter body  402  ( FIGS. 13A-13C ) previously described, such that the ablation section  622  is formed from a microporous material that is fluidly connected to a fluid source (not shown) by a lumen (not shown). Further a shaping wire (not shown) similar to that previously described is slidably disposed within the ablation catheter  554  for selectively forming the distal portion  620 , and in particular the ablation section  622 , to the helical or loop configuration, and an electrode(s) is associated with the ablation section  622 . Alternatively, the ablation catheter  554  can be formed in accordance with any other of the embodiments disclosed herein. 
         [0180]    To facilitate deployment of the ablation catheter  554 , a distal end  624  of the distal portion  620  extends radially outwardly relative to a curvature defined by the ablation section  622 . This relationship is shown most clearly in  FIG. 25 . The angle of deflection defined by the distal end  624  relative to the ablation section  622  is preferably in the range of approximately 5-45°, more preferably 10°. As described in greater detail below, as the distal portion  620  is initially deployed relative to the distal locator  556  ( FIG. 23 ) of the delivery catheter  552  ( FIG. 23 ), the offset or deflected orientation of the distal end  624  assists in guiding the distal portion  620  about the distal locator  556 . 
         [0181]    Returning to  FIG. 22 , in a preferred embodiment the ablation catheter  554  further includes mapping electrodes  626 ,  628 , proximal and distal the ablation section  622 , respectively. As with previous embodiments, the electrodes  626 ,  628  are available to assist a user in evaluating a target site prior to and following ablation. 
         [0182]    The delivery catheter  552  can further include an additional anchoring device (not shown), such as the balloon  136  ( FIG. 6 ) or the wire cage  166  ( FIG. 7 ) previously described. 
         [0183]    During use, the delivery catheter  552  is first directed toward the target site (e.g., pulmonary vein ostium). In one preferred embodiment, prior to placement in the patient, the ablation catheter  554  is replaced with a rounded-tip dilator (not shown) known in the art that extends through the delivery lumen  558  and partially out of the opening  560 . By providing the dilator, the delivery catheter  552  can be fed through bodily lumens, such as veins, without damaging the tissue walls at the opening  560 . Once the intermediate region  572  and the distal locator  556  of the delivery catheter  552  have been guided to the general area of interest (e.g., the left atrium LA), the rounded-tip dilator is removed from the delivery lumen  558 , and the ablation catheter  554  inserted therein. The distal portion  620  of the ablation catheter  554  is then deployed through the opening  560 . In particular, as the distal portion  620  is directed distally through the opening  560 , the ablation catheter  554  is rotated such that the distal end  624  passes around the distal locator  556 . The preferred deflected or tangential orientation of the distal end  624  relative to a curvature of a remainder of the distal portion  620  facilitates guiding of the distal end  624  around the distal locator  556 . Continued rotation of the ablation catheter  554  positions the distal locator  556  within the circle or spiral defined by the distal portion  620 . 
         [0184]    With the ablation catheter  554  deployed to the position depicted in  FIG. 22 , the distal locator  556  is then maneuvered to locate the orifice in question, for example one of the pulmonary vein ostia. In this regard, a user can steer the delivery catheter  552  both proximal and distal the opening  560 . For example, the first pull wire  590  ( FIG. 25A ) can be manipulated or tensioned to bend the delivery catheter  552  at the intermediate region  572  (proximal the opening  560 ). This first bend serves to “aim” or direct the distal locator  556  generally toward the orifice (or ostium) of interest. As the distal locator  556  is then maneuvered or directed toward the ostium, the distal locator  556  itself can steered via tensioning of the second pull wire  592  ( FIG. 24A ) so as to facilitate exact, desired positioning of the distal locator  556  within the ostium. 
         [0185]    Once the distal locator  556  has been positioned within the ostium in question, the ablation catheter  554  is advanced, with the distal locator  556  effectively “guiding” the distal portion  620 , and in particular the ablation section  622 , to the target site. In other words, the distal portion  620  “rides” along the distal locator  556  and is thereby properly positioned about the pulmonary vein ostium. Once positioned, the ablation catheter  554  is available to form a continuous ablation pattern on the chamber wall outside of/around the pulmonary vein ostium as previously described. If other of the pulmonary vein ostia require electrical isolation, the distal locator  556  can readily be aligned with the desired ostium by steering or bending of the delivery catheter  552  both proximal and distal the opening  560  as previously described. 
         [0186]    Yet another alternative, even more preferred, embodiment of a catheter assembly  700  is shown in  FIG. 26 . In a preferred embodiment, the catheter assembly  700  includes input components  702 , a catheter body  704 , and a shaping wire  706  (shown partially in  FIG. 26 ). In general terms, the input components  702  are connected to the catheter body  704 , and control functioning of the catheter assembly  700 . As with several previous embodiments, the shaping wire  706  is slidably disposed within a lumen (not shown) of the catheter body  704  to selectively form the catheter body to a desired shape. 
         [0187]    The input components can assume a wide variety of forms relating to desired functioning of the catheter assembly  700 . For example, in one preferred embodiment, the input components  702  include a hand piece  708 , a fluid input port  710  and an ablative energy source  712  (only a portion of which is depicted in  FIG. 26 ). As previously described, the catheter assembly  700  is preferably configured to ablate tissue by energizing fluid irrigated from a portion of the catheter body  704 . With this in mind, then, the hand piece  708  provides fluid flow to the catheter body  704  via the fluid input port  710 . For example, a saline or other fluid source can be connected to the fluid input port  710 . Similarly, the ablative energy source  712  includes an electrical connector (shown in  FIG. 26 ) electrically connecting an energy source (not shown) to corresponding components of the catheter assembly  700  (such as internally disposed coil electrode(s) not otherwise illustrated) via the hand piece  708 . In this regard, electrical connectors are well known in the art. 
         [0188]    Alternatively, and as described below, where the catheter assembly  700  is designed to make use of a differing ablation energy technique, one or both of the fluid input port  710  and/or the electrical connector  712  can be eliminated, modified or replaced with an appropriate component. For example, the catheter assembly  700  can be configured to ablate tissue via energized band or coil electrodes, ultrasound, RF energy, microwave energy, laser, cryogenic energy, thermal energy, etc., as is known in the art. 
         [0189]    The catheter body  704  includes a proximal portion  716 , an intermediate portion  718  and a distal portion  720 . As with previous embodiments, the intermediate portion  718  extends from the proximal portion  716  and defines a longitudinal axis. The distal portion  720 , in turn, extends from the intermediate portion  718 , and includes an ablation section  722  and a tip  724 . The tip  724  extends distally from the ablation section  722 , and, in one preferred embodiment, terminates in a leader section  726 . 
         [0190]    The shape of the distal portion  720  is an important feature of the catheter body  704 . In particular, at least a segment of the distal portion  720  defines a distally decreasing radius helix. In this regard, the ablation section  722  generally forms at least one loop that is preferably transverse to the longitudinal axis defined by the intermediate portion  718 . With the one preferred embodiment of  FIG. 26 , the ablation section  722  forms a plurality of loops that define a distally decreasing radius helix. This configuration has surprisingly been found to greatly enhance positioning and ablation about a pulmonary vein ostium (not shown). The ablation section  722  most preferably defines a plurality of loops curving approximately 540°. Alternatively, any other degree of circumferential extent is acceptable, ranging from 90°-720°. It has surprisingly been found that curving the ablation section approximately 540° ensures a complete, closed lesion pattern with minimal power requirements. Further, the frontal diameter defined by the ablation section  722  is sized to be larger than a pulmonary vein ostium. For example, in one preferred embodiment, a maximum outer diameter defined by the ablation section  722  is approximately 35 mm. Alternatively, other maximum outer diameters corresponding with pulmonary vein ostiums are acceptable. Preferably, however, the maximum frontal outer diameter defined by the ablation section  722  is in the range of 10 mm-35 mm. 
         [0191]    The tip  724  includes a proximal section  728  that continues the distally decreasing radius helix otherwise defined by the ablation section  722 . That is to say, a relatively uniform decreasing radius helix is defined by the ablation section  722  and the proximal section  728  of the tip  724 . However, the proximal section  728  of the tip  724  is preferably not capable of ablating tissue during an ablative procedure at the ablation section  722 , as described below. The proximal section  728  of  FIG. 26  defines a maximum frontal outer diameter approximating a diameter of a pulmonary vein, +/−10 mm. With this configuration, the proximal section  728  is sized for placement within a pulmonary vein (not shown). 
         [0192]    Finally, the leader section  726  extends distally from the proximal section  728  and is preferably relatively linear. To this end, the leader section  726  can be coaxially aligned with, or angled with respect to, a central axis defined by the intermediate portion  718 . Stated otherwise, the relatively linear leader section  726  is preferably angled with respect to, alternatively aligned with, a central axis defined by the helix of the ablation section  722 /proximal section  728 . Regardless, by employing a relatively linear or straight design, the leader section  726  more readily locates a pulmonary vein, and is easily maneuvered within a pulmonary vein. Further, the relatively linear design is easily identified on an appropriate viewing device, such as a fluoroscope, such that the leader section  726  serves as an indicator of venous branching. 
         [0193]    In addition to the varying shapes defined by the ablation section  722  and the tip  724 , other differing features are preferably provided. For example, in a most preferred embodiment, the catheter body  704  is highly similar to the catheter body  402  ( FIGS. 13A-13C ) previously described, such that the ablation section  722  is formed from a microporous material, preferably expanded PTFE, that is fluidly connected to the fluid input port  710  by a lumen (not shown). Further, the shaping wire  706 , similar to that previously described, is slidably disposed within the catheter body  704  for selectively forming the distal portion  720  to the shape illustrated in  FIG. 26 . In one preferred embodiment, and as previously described, the shaping wire  706  positions a coil electrode(s) at the ablation section  722 . Alternatively, the coil electrode(s) can be independently maintained within the ablation section  722  apart from the shaping wire  706 . Regardless, this one preferred configuration, the ablation section  722  is porous, whereas the tip  724  is impermeable to fluid flow. Even more preferably, the tip  724 , and in particular the leader section  726 , is formed of a soft, atrumatic material such as low durometer polyurethane. Thus, the tip  724 , and in particular the leader section  726 , has a lower durometer than a remainder of the catheter body  704 , and will not cause trauma to contacted tissue (e.g., pulmonary vein). To further soften the leader section  726 , the distal-most section of the shaping wire  706  (otherwise disposed within and “shaping” the leader section  726 ) is preferably taper ground to a smaller diameter than a remainder of the wire  706 . 
         [0194]    An additional preferred feature of the catheter assembly  700  is the inclusion of an electrode  729  on the leader section  726 ; spaced electrodes  730  (referenced generally in  FIG. 26 ) along the proximal section  728  (i.e., distal the ablation section  722  and proximal the leader section  726 ); electrodes  732  adjacent, but proximal, the ablation section  722 ; and an electrode  734  along the intermediate portion  718 . In a preferred embodiment, each of the electrodes  729 - 734  is a band electrode capable of sensing electrical activity, as known in the art. As such, each of the electrodes  729 - 734  is electrically connected to a device (not shown) otherwise associated with the catheter assembly  700  for analyzing signals generated by the electrodes  729 - 734 , and is preferably an ECG reference electrode. Thus, the electrodes  729 - 734  serve as reference electrodes, available for confirming complete ablation as described below. Alternatively, or in addition, one or more of the electrodes  729 - 734 , and in particular the electrodes  730 , serve as pacing electrodes. Even further, one or more of the electrodes  729 - 734  is preferably formed from a radio opaque material (e.g., platinum-iridium) or other material viewable using available devices, such as a fluoroscope. 
         [0195]    In a most preferred embodiment, the electrodes  730  along the proximal section  728  of the tip  724  are located at specific radial locations of the formed helix. The location of each of the electrodes  730  correlates with a radial location of respective ones of the preferred coil electrodes (not shown) relative to the helix of the ablation section  722 . This relationship is best illustrated by the diagrammatic view of  FIG. 27  in which a frontal representation of the decreasing radius helix otherwise defined by the ablation section  722  and proximal section  728  is provided.  FIG. 27  includes, by way of example, five coil electrodes  736   a - e  disposed along the ablation section  722 , and five of the reference electrodes  730   a - e  disposed along the proximal section  728 . The coil electrodes  736   a - e  are preferably platinum-iridium, although a wide variety of other conductive materials are equally acceptable. Each of the reference electrodes  730   a - e  are radially aligned with a respective one of the coil electrodes  736   a - e . Of course, any other number of coil electrodes  736  and reference electrodes  730  is equally acceptable, and more than one reference electrode  730  can be provided along the helix of the proximal section  728  and correlated with one of the coil electrodes  736 . Regardless, as described in greater detail below, the spatially spaced and correlated nature of the coil electrodes  736  and the reference electrodes  730  facilitates selective ablation of specific portions of tissue (i.e., extra-ostial), as opposed to complete, “closed” ablation pattern. 
         [0196]    Returning to  FIG. 26 , as is clear from the above, though the tip  724  extends directly from the ablation section  722 , several differences exist. More particularly, and in the most preferred embodiment, the ablation section  722  and the tip  724  have a number of differing features, including shape, material, porosity, and durometer. Alternatively, the catheter body  704  can be configured such that the ablation section  722  and the tip  724  differ only in terms of shape, material, porosity, or durometer. Thus, for example, the catheter body  704  need not be configured to form the ablation section  722  with a microporous material. Instead, any of the other configurations previously disclosed herein can be incorporated. Along these same lines, the ablation section  722  can be configured to accommodate a variety of different ablative energy sources other than energize irrigated fluid. In a preferred embodiment, the ablation section  722  delivers an RF energy, and is a single electrical element or multiple elements each defining a portion of the circumference of the ablation section  722 , each in the range of 10°-540°, more preferably each in the range of 45°-180°. 
         [0197]    Use of the catheter assembly  700  is highly similar to that previously described with respect to  FIGS. 17A-17D . With further reference to  FIG. 28 , the distal portion  720  is, following previously described preparatory and deployment steps, positioned within the left atrium (LA). As a point of reference,  FIG. 28  generally illustrates a portion of the left atrium LA and includes an atrium wall (W) and a pulmonary vein (PV). The pulmonary vein PV forms a pulmonary vein ostium (PVO) at the wall W. With this general description in mind, the tip  724  is employed to locate the pulmonary vein PV. The relatively linear leader section  726  is easily positioned within the pulmonary vein PV. Once the pulmonary vein has been located, the distal portion  720  is advanced until the ablation section  722  contacts the tissue wall W about the pulmonary vein ostium PVO. In this regard, the tip  724  readily slides along and within the pulmonary vein PV. The tip  724  is preferably formed of an atrumatic material such that contact between the tip  724  and the pulmonary vein PV does not damage the pulmonary vein PV tissue. Further, the preferred distally decreasing radius helix formed by the proximal section  728  of the tip  724  contacts the pulmonary vein PV wall, effectively seating the distal portion  720  within the pulmonary vein PV. Once seated, the ablation section  722  is essentially centered about the pulmonary vein ostium PVO. Subsequently, as the ablation section  722  is compressed (not illustrated in  FIG. 28 ) against the wall W, a complete ablation perimeter is consistently defined about (proximal) the pulmonary vein ostium PVO (or extra-ostial). 
         [0198]    Once properly positioned, extra-ostial ablation via the ablation section  722  is initiated. For example, with the one most preferred embodiment and as previously described, an appropriate fluid is irrigated through the ablation section  722 , and is then energized via the coil electrode(s) (not shown), for example with RF energy. This energy is transferred, via the fluid irrigated along the ablation section  722 , to the tissue contacted by the ablation section  722 . The conductive fluid establishes a conductive path from the coil electrode(s) to the contacted tissue, thereby ablating the targeted tissue. Depending upon operator preference and indications of electrical activity recorded from the electrodes  730 , it is possible to selectively ablate only specific portions of the extra-ostial perimeter by applying energy only to specific ones of the coil electrodes. In some instances, the atrial tissue fibers extend into the pulmonary vein PV along only a portion of the pulmonary vein ostium PVO circumference. The operator may desire to only ablate at this specific location, as opposed to forming a complete, closed ablation pattern. The catheter assembly  700  of the present invention promotes this procedure. In particular, and with additional reference to  FIG. 27 , the various reference electrodes  730   a - e  can be interrogated to determine where electrical activity is occurring relative to a circumference of the pulmonary vein ostium PVO. The corresponding coil electrode(s)  736   a - e  are then energized to effectuate partial, or quadrant ablation. 
         [0199]    Following application of the ablation energy, the catheter assembly  700  is preferably operated to determine whether a closed, electrically isolating ablation pattern has been established in the chamber wall W, about or outside of the pulmonary vein ostium PVO. More particularly, one or more of the electrodes  729 - 734  are interrogated to evaluate electrical isolation of the pulmonary vein PV from the atrium wall W. The electrodes  729  along the tip  724  provide information relating electrical activity within the pulmonary vein PV, whereas the electrodes  732 ,  734  provide information relating to electrical activity within the left atrium LA. Thus, where the electrodes  729 - 734  are ECG reference electrodes, a comparison can be made between the electrical activity within the pulmonary vein PV (via the electrodes  730 ) and the electrical activity with the left atrium LA (via the electrodes  732 ,  734 ) or electrical activity sensed from a catheter placed in the coronary sinus. If it is determined that electrical activity within the pulmonary vein PV is similar or otherwise related to electrical activity at the left atrium LA, further ablation of the tissue wall W is required. Ablation energy can again be applied to further ablate the tissue wall W about the pulmonary vein ostium PVO. Once sufficient ablation has been achieved, the distal section  720  is retracted from the pulmonary vein PV. Subsequently, additional ablation patterns can be formed about other ones or all of the pulmonary vein ostia PVOs. 
         [0200]    To best illustrate the ablation pattern capabilities of the catheter assembly  700 , reference is made to the diagrammatic ablation illustrations of  FIGS. 29A-C . In  FIG. 29A , a full, circumferential, extra-ostial ablation pattern has been formed. In theory, where the individual loops of the ablation section  722  ( FIG. 26 ) are aligned upon compression, the relatively continuous circle ablation pattern is formed. Conversely, the ablation pattern of  FIG. 29B  is generally spiral-shaped, a result of the individual loops of the ablation section  722  not being perfectly aligned. However, the radial spacing between individual turns of the spiral ablation pattern is so small such that the ablative effect extends across adjacent turns. As a result, an extra-ostial ablation pattern is again achieved. Finally,  FIG. 29C  illustrates a partial or quadrant ablation pattern as previously described, electrically isolating muscular tissue M extending into the pulmonary vein ostium PVO. 
         [0201]    As previously described, the catheter assembly  700  can assume a wide variety of forms beyond the specific embodiment of  FIG. 26 . For example, the catheter assembly  700  can be configured to provide the distally decreasing helical shape of the ablation section  722  and the tip  724  via a component other than the shaping wire  706 . Alternatively and/or in addition, a delivery catheter or sheath can be provided. Even further, the catheter assembly  700  can be provided with one or more pull wires as previously described to effect directional deflection. 
         [0202]    Yet another alternative embodiment catheter assembly  740  is shown in  FIG. 30 . For ease of illustration, only a distal region of the catheter assembly  740  is depicted. The catheter assembly  740  is similar to the catheter assembly  700  ( FIG. 26 ) previously described, and includes a catheter body  742 . The catheter body  742  includes a proximal portion  744 , an intermediate portion  746  and a distal portion  748 . The proximal portion  744  is connected to an ablative energy source (not shown), such as that previously described. The intermediate portion  746  extends from the proximal portion  744  and defines a longitudinal axis. Finally, the distal portion  748  extends from the intermediate portion  746  and forms an ablation section  750  and a tip  752 . 
         [0203]    The ablation section  750  forms a loop substantially transverse to the longitudinal axis. In the embodiment of  FIG. 30 , the loop formed by the ablation section  750  is greater than a single revolution, preferably curving approximately 360°-540° but is not a radius decreasing helix. The tip  752  extends distally from the ablation section  750  and preferably forms a slightly distally decreasing radius helix. With this configuration, an outer diameter defined by the ablation section  750  is greater than an outer dimension of a pulmonary vein ostium (not shown), whereas a maximum outer diameter defined by the tip  752  approximates a diameter of a pulmonary vein (not shown). Though not illustrated, the tip  752  can form a distal leader, similar to the leader section  726  ( FIG. 26 ) previously described. 
         [0204]    As with the catheter assembly  700  ( FIG. 26 ) previously described, the ablation section  750  and the tip  752  define differing shapes. In addition, and in accordance with a most preferred embodiment, the ablation section  750  is formed by microporous material as previously described, whereas the tip  752  is fluid impermeable. Thus, the catheter body  742 , and in particular the ablation section  750 , is configured to ablate tissue by irrigating energized conductive fluid, whereas ablation will not occur along the tip  752 . Also, as with the catheter assembly  700  previously described, the catheter body  742  preferably includes electrodes  754  positioned along the tip  752 ; electrodes  756  positioned adjacent, but proximal, the ablation section  750 ; and an electrode  758  positioned along the intermediate portion  746 . 
         [0205]    In a preferred embodiment, a shaping wire  760  (shown partially in  FIG. 30 ) is provided to selectively form the distal portion  748  to the shape illustrated in  FIG. 30 , similar to previously described embodiments. Though not illustrated, one or more coil electrodes are positioned within or along the ablation section  750  at various radial positions. Once again, the coil electrodes energize fluid irrigated through the ablation section  750  during use, and their radial location is preferably correlated with radial locations of respective ones of the electrodes  754  along the tip  752 . Alternatively, and as previously described, a wide variety of other configurations can be employed to form the distal portion  748  to the shape shown in  FIG. 30  and/or to provide ablative energy. 
         [0206]    During use, and with reference to  FIG. 31 , following various preparatory steps, the distal portion  748  is deployed within the left atrium LA as previously described. As a point of reference,  FIG. 31  depicts the catheter body  740 , and in particular the ablation section  750 , compressed against the chamber wall W. With this in mind, the tip  752  is first used to locate the pulmonary vein PV. Once again, the distally decreasing radius helix form of the tip  752  promotes placement within the pulmonary vein PV with minimal trauma to the pulmonary vein PV tissue. Once located, the distal portion  748 , and in particular, the tip  752  is advanced within the pulmonary vein PV until the ablation section  750  contacts the tissue wall W. In this regard, the tip  752  essentially seats within the pulmonary vein PV, such that the ablation section  750  is substantially centered about the pulmonary vein ostium PVO and seats against the wall W in an extra-ostial position. 
         [0207]    Once properly positioned, an ablative energy is applied to the tissue wall W via the ablation section  750 . Following application of the ablation energy, the electrodes  754 - 758  are operated to sense electrical activity inside and outside of the pulmonary vein, as previously described. If it is determined that electrical activity continues to traverse the ablated lesion or selected portion(s) of the circumference, an ablation energy can again be applied to further ablate the tissue wall W about the entire pulmonary vein ostium PVO or only about selected portions of the pulmonary vein ostium as previously described. 
         [0208]    Yet another alternative embodiment catheter assembly  770  is depicted in  FIG. 32 . For ease of illustration, only a distal region of the catheter assembly  770  is shown. The catheter assembly  770  is similar to the catheter assemblies  700  ( FIG. 26) and 740  ( FIG. 30 ) previously described, and includes a catheter body  772  having a proximal portion  774 , an intermediate portion  776 , and a distal portion  778 . The proximal portion  774  is connected to an ablative energy source (not shown). The intermediate portion  776  extends from the proximal portion  774  and defines a longitudinal axis. Finally, the distal portion extends from the intermediate portion  778  and includes an ablation section  780  and a tip  782 . 
         [0209]    The tip  782  extends distally from the ablation section  780 . Further, the ablation section  780  and the tip  782  combine to define a distally decreasing radius helix for the distal portion  778 . Thus, unlike the catheter bodies  704 ,  742  previously described, the ablation section  780  and the tip  782  define a continuous shape. However, the ablation section  780  and the tip  782  have other varying features. For example, in the preferred embodiment, the ablation section  780  is formed of a microporous material, preferably expanded PTFE, previously described; whereas the tip  782  is formed of a fluid impermeable material. Further, the tip  782  is formed of an atraumatic material such as low durometer elastomer or thermoplastic and/or utilizing a smaller diameter shaping wire  784 , and is thus softer than the ablation section  780 . 
         [0210]    As with previous embodiments, the catheter assembly  770  preferably incorporates a shaping wire  784  to selectively dictate the distally decreasing helical shape of the distal section  778 . Once again, the shaping wire  784  preferably carries one or more coil electrodes (not shown) positioned within the ablation section  780 . The coil electrodes serve to energize, via an ablative energy source (not shown), fluid irrigated through the ablation section  780 . Alternatively, the distally decreasing helical shape of the distal portion  778  can be achieved with something other than the shaping wire  784 , for example thermally formed thermoplastics or mechanically manipulated torque and puller wires that create a helical shape. Further, an ablation technique other than energized conductive fluid irrigated through the ablation section  780  can be incorporated into the catheter body  772 . Regardless, the catheter body  772  preferably carries an electrode  786  along the tip  782  and an electrode  788  along the intermediate portion  776 . 
         [0211]    During use, the distal portion  778  is deployed similar to the embodiments previously described with respect to  FIGS. 27 and 31 . Once again, the tip  782  is uniquely configured to optimally locate and seat within a pulmonary vein (not shown). This relationship essentially ensures that the ablation section  780 , once compressed against the tissue wall is centered about the pulmonary vein ostium (not shown), more particularly, in an extra-ostial location. Finally, the electrodes  786 ,  788  provide a means for evaluating electrical activity both inside and outside of the pulmonary vein. 
         [0212]    The catheter assembly of the present invention provides a highly viable tool for electrically isolating a vessel, such as a pulmonary vein or coronary sinus, from a chamber, such as the left atrium. With respect to one preferred embodiment in which the distal portion of the catheter body forms a distally decreasing radius helix, the ablation section is readily and consistently positioned about a pulmonary vein ostium. In this regard, by forming the distal portion to include both an ablation section and a distally extending tip, the pulmonary vein in question is easily located. Further, the tip is preferably formed to seat within the pulmonary vein, thereby providing a user with a tactile confirmation of proper positioning. Finally, reference electrodes are preferably provided both inside and outside of the pulmonary vein to confirm electrical isolation thereof following ablation. 
         [0213]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the preferred embodiment has described electrical isolation of a pulmonary vein from the left atrium for treatment of atrial fibrillation. Alternatively, the method and apparatus of the present invention may be utilized in the treatment of other cardiac arrhythmias, such as isolating the coronary sinus from the right atrium, the superior vena cava, or isolating the outflow tract (or pulmonary valve) from the right ventricle. Further, with respect to the preferred embodiments described with reference to  FIGS. 26-32 , certain features can be altered or eliminated while still providing a viable device. For example, the ablation section and tip need not be made of differing materials. Further, a variety of ablative energy sources are available, including ultrasound, RF energy, microwave energy, laser, cryogenic energy, thermal energy, etc. Further, while a shaping wire has preferably been employed, the catheter body itself can be made of a shape memory material able to achieve the desired shape. In addition, the shaping wire may be taper ground to reduce its diameter near the distal end thereof (corresponding to the tip or leader section of the catheter body), thereby reducing the stiffness of the catheter body tip upon final assembly. Even further, the catheter body can be provided with various pull wires, the maneuvering of which selectively forms the distal portion to the desired shape. Finally, other features associated with different embodiments can be incorporated into the catheter assembly of  FIGS. 26-32 . Even further, other features not specifically disclosed can be employed. For example, the catheter assembly may include a rapid exchange feature for quick placement over, and removal from, a guidewire.