Abstract:
Systems and methods employ a guide element that carries a region of energy emitting material. The systems and methods electronically couple the region to a source of energy that, when emitted by the region, ablates tissue. The systems and methods are responsive to user commands for changing the physical characteristics of the lesions being created by electronically altering the energy emitting characteristics of the region itself.

Description:
This is a continuation Ser. No. 08/138,143 filed on Oct. 15, 1993. 
    
    
     FIELD OF THE INVENTION 
     In a general sense, the invention is directed to systems and methods for creating lesions the interior regions of the human body. In a more particular sense, the invention is directed to systems and methods for ablating heart tissue for treating cardiac conditions. 
     BACKGROUND OF THE INVENTION 
     Normal sinus rhythm of the heart begins with the sinoatrial node (or “SA node”) generating an electrical impulse. The impulse usually propagates uniformly across the right and left atria and the atrial septum to the atrioventricular node (or “AV node”). This propagation causes the atria to contract. 
     The AV node regulates the propagation delay to the atrioventricular bundle (or “HIS” bundle). This coordination of the electrical activity of the heart causes atrial systole during ventricular diastole. This, in turn, improves the mechanical function of the heart. 
     Atrial geometry, atrial anisotropy, and histopathologic changes in the left or right atria can, alone or together, form anatomical obstacles. The obstacles can disrupt the normally uniform propagation of electrical impulses in the atria. These anatomical obstacles (called “conduction blocks) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called “reentry circuits,” disrupt the normally uniform activation of the left and right atria. Abnormal, irregular heart rhythm, called arrhythmia, results. This form of arrhythmia is called atrial fibrillation, which is a very prevalent form of arrhythmia. 
     Today, as many as 3 million Americans experience atrial fibrillation. These people experience an unpleasant, irregular heart beat. Because of a loss of atrioventricular synchrony, these people also suffer the consequences of impaired hemodynamics and loss of cardiac efficiency. They are more at risk of stroke and other thromboembolic complications because of loss of effective contraction and atrial stasis. 
     Treatment is available for atrial fibrillation. Still, the treatment is far from perfect. 
     For example, certain antiarrhythmic drugs, like quinidine and procainamide, can reduce both the incidence and the duration of atrial fibrillation episodes. Yet, these drugs often fail to maintain sinus rhythm in the patient. 
     Cardioactive drugs, like digitalis, Beta blockers, and calcium channel blockers, can also be given to control the ventricular response. However, many people are intolerant to such drugs. 
     Anticoagulant therapy also combat thromboembolic complications. 
     Still, these pharmacologic remedies often do not remedy the subjective symptoms associated with an irregular heartbeat. They also do not restore cardiac hemodynamics to normal and remove the risk of thromboembolism. 
     Many believe that the only way to really treat all three detrimental results of atrial fibrillation is to actively interrupt all the potential pathways for atrial reentry circuits. 
     James L. Cox, M. D. and his colleagues at Washington University (St. Louis, Mo.) have pioneered an open heart surgical procedure for treating atrial fibrillation, called the “maze procedure.” The procedure makes a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria, therefore its name. The incisions direct the electrical impulse from the SA node along a specified route through all regions of both atria, causing uniform contraction required for normal atrial transport function. The incisions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. The incisions are also carefully placed to interrupt the conduction routes of the most common reentry circuits. 
     The maze procedure has been found very effective in curing atrial fibrillation. Yet, despite its considerable clinical success, the maze procedure is technically difficult to do. It requires open heart surgery and is very expensive. Because of these factors, only a few maze procedures are done each year. 
     One objective of the invention is to provide catheter-based ablation systems and methods providing beneficial therapeutic results without requiring invasive surgical procedures. 
     Another objective of the invention is to provide systems and methods that simplify the creation of complex lesions patterns in body tissue, such as in the heart. 
     SUMMARY OF THE INVENTION 
     The invention provides systems and methods for ablating tissue within a body to form lesions. The systems and methods employ a guide element that carries a region of energy emitting material. The systems and methods electronically couple the region to a source of energy that, when emitted by the region, ablates tissue. 
     According to the invention, the systems and methods are responsive to user commands for changing the physical characteristics of the lesions being created by electronically altering the energy emitting characteristics of the region itself. 
     The invention thus provides tissue ablating systems and methods that allow the physician to make almost instantaneous changes to the shape, geometry, and type of lesions created during an ablation procedure. 
     In one preferred embodiment, in response to a prescribed input command, the systems and methods electronically configure the region to emit ablating energy either as a zone of uniform polarity or as zones of alternating polarity. In other words, the physician can almost instantaneously select between unipolar and bipolar lesions formation. 
     In another preferred embodiment, in response to a prescribed input command, the systems and methods electronically vary the length of the region where emission occurs. This allows the physician to almost instantaneously select and alter the size of formed lesions. 
     In another embodiment, in response to a prescribed input command, the systems and methods electronically alter the energy emitting characteristics of the region to block emission from a portion of the region, while allowing emission to proceed from another portion of the region. This allows the physician to form complex patterns of interrupted lesions, e.g., alternating lesion areas with lesion-free areas. 
     The invention thus provides new systems and methods that give a physician the flexibility to choose and create specially shaped lesions in body tissue “on the fly.” 
     In a preferred application, the invention provides a catheter-based system and method that create lesions in myocardial tissue. In purpose and effect, the system and method emulate an open heart maze procedure, but do not require costly and expensive open heart surgery. The systems and methods can be used to perform other curative procedures in the heart as well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified and somewhat diagrammatic perspective view of the human heart; 
         FIG. 2  is a diagrammatic plan view of the atrial region of the heart, showing a circuitous path for an electrical impulse to follow between the SA node and the AV node; 
         FIG. 3  is a grid for creating a three-dimensional structure for making curvilinear lesions within the atria of the heart; 
       FIGS.  4 A/ 4 B are splines having electrically conductive and electrically non-conductive regions that, when assembled, emit ablating energy to form curvilinear lesions within the atria of the heart; 
       FIGS.  5 A/ 5 B are the three-dimensional structures formed when the splines shown in FIGS.  4 A/ 4 B are assembled, with the structure shown in  FIG. 5A  being intended for use within the right atrium and the structure shown in  FIG. 5B  being intended for use within the left atrium; 
         FIG. 6  is a perspective, largely diagrammatic view showing the electrical connections that transmit ablating energy to a three-dimensional structure for forming curvilinear lesions within the atria of the heart; 
         FIG. 7  is a perspective view of an alternate three-dimensional structure that can be used to emit ablating energy to form curvilinear lesions within the atria of the heart and that includes, as an integral part, a steerable distal element carried within the open interior area of the structure; 
         FIG. 8  is a perspective view of an alternate three-dimensional structure that can be used to emit ablating energy to form curvilinear lesions within the atria of the heart and that includes, as an integral part, an internal electrode structure that comprises a single length of wire material preshaped to assume a helical array; 
         FIG. 9  is a perspective view of an alternate three-dimensional structure that can be used to emit ablating energy to form curvilinear lesions within the atria of the heart and that includes, as an integral part, an external electrode structure that comprises a single length of wire material preshaped to assume a helical array; 
         FIG. 10  is a perspective view of an alternate three-dimensional structure that can be used to emit ablating energy to form curvilinear lesions within the atria of the heart and that encloses, as an integral part, an internal basket structure; 
         FIG. 11  is a plan view of an ablating probe that carries the three-dimensional basket structure shown in  FIG. 7 ; 
         FIGS. 12A and 12B  are plan views of another ablating probe that carries a three-dimensional basket structure that, in use, forms curvilinear lesions within the atria of the heart; 
         FIG. 13  is a plan view of an alternate ablating element that can be used to emit ablating energy to form curvilinear lesions within the atria of the heart; 
         FIG. 14  is a plan view of an inflatable ablating element that can be used to emit ablating energy to form curvilinear lesions within the atria of the heart; 
         FIGS. 15  to  26  are views of a delivery system that, when used in the manner shown in these Figures, introduces and deploys ablating elements shown in the preceding Figures into the atria of the heart; 
         FIG. 27  is a plan view of a probe that carries a family of flexible, elongated ablating elements that can be used to emit ablating energy to form curvilinear lesions within the atria of the heart; 
         FIGS. 28  to  30  are views of one flexible, elongated ablating element that carries a pattern of closely spaced electrically conductive regions that can be used to emit ablating energy to form curvilinear lesions within the atria of the heart; 
         FIG. 31  shows, in somewhat diagrammatic form, a generally straight adjoining lesion pattern that can be formed by the element shown in  FIGS. 28  to  30 ; 
         FIG. 32  shows, in somewhat diagrammatic form, a curvilinear adjoining lesion pattern that can be formed by the element shown in  FIGS. 28  to  30 ; 
         FIG. 33  show the flexible, elongated ablating element shown in  FIG. 28  that includes an alternating pattern of conductive regions and non-conductive regions that can form an interrupted pattern of lesions in myocardial tissue; 
         FIG. 34  shows, in somewhat diagrammatic form, an interrupted lesion pattern that can be formed by the element shown in  FIG. 33 ; 
         FIG. 35  shows, in somewhat diagrammatic form, an interrupted curvilinear lesion pattern that can be formed by the element shown in  FIG. 33 ; 
         FIGS. 36  to  38  show another embodiment of a flexible, elongated ablating element that comprises a closely wound, single layer spiral winding; 
         FIG. 39  shows, in somewhat diagrammatic form, adjoining lesion patterns, straight and curvilinear, which the element shown in  FIGS. 36  to  38  can form; 
         FIGS. 40  to  45  show a flexible, elongated ablating element that carries elongated strips of conductive material that can form curvilinear patterns of lesions in myocardial tissue; 
         FIG. 46  shows, in somewhat diagrammatic form, adjoining lesion patterns, straight and curvilinear, which the element shown in  FIGS. 40  to  45  can form; 
         FIGS. 47 and 48  show a flexible elongated ablating element that carries a thin, flat ribbon of spirally wound conductive material that can form curvilinear patterns of lesions in myocardial tissue; 
         FIGS. 49 and 50  show a flexible, elongated ablating element that includes an elongated opening that exposes a conductive region that can form curvilinear patterns of lesions in myocardial tissue; 
         FIGS. 51  to  54  show a flexible, elongated ablating element that carries a wound spiral winding with a sliding sheath that can form curvilinear patterns of lesions in myocardial tissue; 
         FIG. 55  shows a handle for the ablating element shown in  FIGS. 51  to  54 ; 
         FIG. 56  shows a flexible, elongated ablation element, generally like that shown in  FIGS. 51  to  54 , with a sheath made of a non rigid material that is less flexible that the underlying element; 
         FIG. 57  shows a flexible, elongated ablation element, generally like that shown in  FIGS. 51  to  54 , with a sheath made of a relatively rigid material; 
         FIG. 58  shows a flexible, elongated alternation element, like that shown in  FIGS. 51  to  54 , except that it can be operated in a bipolar ablation mode to form curvilinear patterns of lesions in myocardial tissue; 
         FIG. 59  is a partially diagrammatic view of a system for supplying ablating energy to the element shown in  FIG. 28 , which includes a controller that electronically adjusts and alters the energy emitting characteristics of the element; 
         FIG. 60  is a schematic view of the controller and associated input panel shown in  FIG. 59 ; 
         FIG. 61  is a schematic view of the toggle carried on the input panel shown in  FIG. 60  in its three operative positions; 
         FIG. 62  is a schematic view of the controller shown in  FIG. 60  electronically configured in its OFF mode; 
         FIG. 63  is a schematic view of the controller shown in  FIG. 60  electronically configured to provide a continuous, unipolar lesion pattern; 
         FIG. 64  is a schematic view of the controller shown in  FIG. 60  electronically configured to provide an interrupted, unipolar lesion pattern; 
         FIG. 65  is a schematic view of the controller shown in  FIG. 60  electronically configured to provide a continuous, bipolar lesion pattern; and 
         FIG. 66  is a schematic view of the controller shown in  FIG. 60  electronically configured to provide an interrupted, bipolar lesion pattern. 
       The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention provides systems and methods for ablating tissue inside a living body. The invention creates elongated lesions, which can be either straight or curvilinear. The invention also creates patterns of lesions, which can be either simple or complex. 
     The invention lends itself to use in many relatively noninvasive catheter-based procedures. In contrast with complex, invasive surgical procedures, these catheter-based procedures introduce ablation elements into interior regions of the body by steering them through a vein or artery. 
     The Specification that follows focuses upon a particular field of use, which is the treatment of cardiac disease. Still, the diverse applicability of the invention in other fields of use will also become apparent. 
       FIG. 1  shows a simplified and somewhat diagrammatic perspective view of the human heart  10 . 
     The views of the heart  10  shown in FIG.  1  and other Figures in this Specification are not intended to be anatomically accurate in every detail. The Figures show views of the heart  10  in diagrammatic form as necessary to show the features of the invention. 
     As will be described in greater detail later, one application of the invention provides systems and methodologies for forming long, curvilinear ablation patterns inside the heart  10 . 
     The Figures focus upon the details of using the invention to form long, curvilinear lesions for the treatment of atrial fibrillation. It should be appreciated, however, that the invention has applicability for use in other regions of the heart to treat other cardiac conditions. The invention also has application in other regions of the body to treat other maladies. 
       FIG. 1  shows the significant heart chambers and the blood vessels that service them.  FIG. 1  shows the right and left right atria, respectively  12  and  14 .  FIG. 1  also shows the right and left ventricles, respectively  16  and  18 . 
       FIG. 1  further shows the atrial septum  20  that separates the right and left atria  12 / 14 .  FIG. 1  also shows the ventricular septum  21  that separates the right and left ventricles  16 / 18 . 
     As  FIG. 1  further shows, the tricuspid valve  22  joins the right atrium  12  with the right ventricle  16 . The mitral (bicuspid) valve  24  joins the left atrium  14  with the left ventricle  18 . 
     The superior vena cava  26  (the “SVC”) and the inferior vena cava  28  (the “IVC”) open into the right atrium  12 . The pulmonary veins  30  (the PV&#39;s”) open into the left atrium  14 . The pulmonary artery  32  leads from the right ventricle  16 . The aorta  34  leads from the left ventricle  18 . 
     During normal sinus rhythm, blood enters the right atrium  12  through the SVC  26  and the IVC  28 , while entering the left atrium  14  through the PV&#39;s  30 . The atria  12 / 14  contract, and the blood enters the ventricles  16 / 18  (through the tricuspid and mitral valves  22  and  24 , respectively). The ventricles  16 / 18  then contract, pumping the blood through the aorta and pulmonary arteries  32  and  34 . 
       FIG. 2  shows a diagrammatic plan view of the atrial region of the heart  10 .  FIG. 2  shows the right atrium  12 , the left atrium  14 , and the atrial septum  20  dividing the right atrium  12  from the left atrium  14 .  FIG. 2  also shows the approximate location of the orifices of the SVC  26  and the IVC  28  entering the right atrium  12 .  FIG. 2  further shows the approximate location of the orifices of the PV&#39;s  30  entering the left atrium  14 . 
       FIG. 2  also shows the atrial electrophysiology pertinent to the generation and treatment of atrial arrhythmias.  FIG. 2  shows the SA node  36  located near the SVC  26 . It also shows the AV node  38 . 
     By folding the left-hand edge of the plan view of  FIG. 2  against the center septum  20 , one forms the three-dimensional contour of the right atrium  12 . By folding the right-hand edge of the plan view of  FIG. 2  against the center septum  20 , one forms the three-dimensional contour of the left atrium  14 . 
       FIG. 2  further shows a maze pattern  40  overlaid upon the plan view of the right and left atria  12  and  14 . The particular maze pattern  40  shown is adopted from one developed by Dr. Cox. See Cox et al., “The Surgical Treatment of Atrial Fibrillation,”  The Journal of Cardiovascular Surgery , Vol. 101, No. 4, pp. 569-592 (1991). 
     The maze pattern  40  directs the sinus impulse from the SA node  36  to the AV node  38  along a specified route. The route that the pattern  40  establishes includes a main conduction route  40 A that leads circuitously from the SA node to the AV node. The route also includes multiple blind alleys  40 B off the main conduction route  40 A. 
     The pattern  40  is laid out to assure that the sinus impulse activates most of the atrial myocardium. Also, the pattern  40  blocks portions of the most common reentry circuits around the SVC  26 , IVC  28 , and the PV&#39;s  30 . The lesion pattern  40  interrupts each of these common reentry circuits to thereby interrupt the generation of reentry circuits in these atrial regions. 
     The invention provides systems and methods for establishing the maze pattern  40 , or one like it, without open heart surgery and without conventional surgical incisions. 
     The systems and methods that embody the invention ablate myocardial tissue in the atria. In the process, they form elongated (i.e., long and thin) and sometimes curvilinear lesions (designated “L” in FIG.  2 ). The lesions L destroy the myocardial tissue in those regions where reentry circuits usually occur. Electrical conduction is interrupted in the regions the lesions L occupy. 
     The presence of the lesions L force electrical impulses emanating in the SA node  36  to follow the open (i.e., not ablated) myocardial regions, which extend between the lesions L. The open regions form a circuitous path leading from the SA node  36  to the AV node  38 , while eliminating reentry pathways. 
     In this way, the lesions L prevent atrial fibrillation from occurring. 
     The lesions L thus serve the same purpose as the incisions made during a surgical maze procedure. However, they do not require an invasive and costly surgical technique. Instead, according to the invention, the physician forms the lesions L without opening the heart. Instead, the physician maneuvers one or more ablation elements through a vein or artery into the atria. 
     For this purpose, the systems and methods that embody the invention provide a family of ablating elements. Numeral  42  generally designates each individual element in  FIGS. 5  to  10  and  25  to  41 . In use, the elements  42  form various curvilinear lesion patterns. 
     In the preferred embodiments, the elements  42  create the lesions L by thermally destroying myocardial tissue by the application of electromagnetic energy. In the particular illustrated embodiments, the elements  42  emit radiofrequency electromagnetic energy. Alternatively, microwave electromagnetic energy or light (laser) energy could be employed for the same purpose. 
     The direct emission of heat energy by an elongated element by resistance heating does not form uniformly long, thin lesion patterns as defined by the invention. Direct heating of an elongated element results in lesion patterns having regions of charring that offer no therapeutic benefit. 
     Still, it is believed the invention can be adapted to other ablation techniques that do not involve the direct contact between a resistance heated element and tissue. For example, it is believed that long, thin, and curvilinear lesions can be formed by destroying myocardial tissue by cooling or by injecting a chemical substance that destroys myocardial tissue. 
       FIGS. 5  to  14  show one preferred category of radiofrequency ablating elements  42 . In this category, the ablating elements  42  make intimate contact against the atrial wall to create an array of adjoining curvilinear lesions L all at once. One of these types of elements  42 , once deployed, can form all or substantially all of desired maze pattern. This category of ablating elements will sometimes be identified as “Category 1 Curvilinear Ablating Elements.” 
     According to another aspect of the invention, the Category 1 Ablating Elements share a common delivery system  44 . The delivery system  44  introduces and deploys a selected Category 1 Ablating Elements in the atria  12 / 14 . 
       FIGS. 27  to  55  show another preferred category of radiofrequency ablating elements  42 . In this category, the ablating elements  42  make intimate contact against the atrial wall to create discrete elongated, curvilinear lesions L, one at a time. The physician individually deploys these ablating elements  42  in succession to form the desired maze pattern. This category of ablating elements will sometimes be identified as “Category 2 Curvilinear Ablating Elements.” 
     Unlike the Category 1 Ablating Elements, the Category 2 Ablating Elements do not require a delivery system  44  for introduction and deployment in the atria  12 / 14 . The Category 2 Ablating Elements are steerable. They can be introduced into the atria  12 / 14  like a conventional steerable catheter. 
     The Delivery System 
       FIGS. 15  to  26  best show the details of common delivery system  44 . 
     Using the delivery system  44 , the physician first introduces a selected ablating element  42  into the right atrium  12  through the femoral vein (as  FIG. 20  generally shows). The physician transmits radiofrequency ablating energy through the ablating element  42  to create the curvilinear lesion L or pattern of lesions L in the myocardium of the right atrium  12 . 
     Once the desired lesion pattern is made in the right atrium, the physician enters the left atrium  14  through the atrial septum  20  (as  FIGS. 25 and 26  generally show). The physician deploys another selected ablating element  42  into the left atrium  14  by puncturing through the atrial septum  20  (as  FIG. 26  generally shows). The physician transmits radiofrequency ablating energy through the ablating element  42  to create the desired curvilinear lesion L or pattern of curvilinear lesions L in the myocardium of the left atrium  14 . 
     To carry out the above sequence of steps, the delivery system  44  includes an introducer  46  and an outer guide sheath  48  (see FIGS.  15  and  16 ). Both the introducer  46  and the guide sheath  48  are made from inert plastic materials, like polyester. 
     As  FIG. 15  shows, the introducer  46  has a skin-piercing cannula  50 . The physician uses the cannula  50  to establish percutaneous access into the femoral vein. 
     The exposed end of the introducer  46  includes a conventional hemostatic valve  52  to block the outflow of blood and other fluids from the access. The valve  52  may take the form of a conventional slotted membrane or conventional shutter valve arrangement (not shown). 
     The hemostatic valve  52  allows the introduction of the outer guide sheath  48  through it, as  FIG. 16  shows. 
     The introducer  46  also preferably includes a flushing port  54  for introducing anticoagulant or other fluid at the access site, if required. 
     In the illustrated and preferred embodiment, the delivery system  44  also includes a guide catheter  60  for directing the outer guide sheath  48  into the right and left atria  12  and  14 . 
     In one embodiment (see FIG.  16 ), the guide catheter  60  takes the form of a conventional steerable catheter with active steering of its distal tip. Alternatively, the guide catheter  60  can take the form of a catheter with a precurved distal tip, without active steering, like a conventional “pig tail” catheter. The catheter with a precurved distal tip is most preferred, because of its simplicity and lower cost. However, for the purposes of this Specification, the details of a catheter with active steering of the distal tip will also be discussed. 
     As  FIG. 16  shows, the steerable catheter  60  includes a catheter body  68  having a steerable tip  70  at its distal end. A handle  72  is attached to the proximal end of the catheter body  68 . The handle  72  encloses a steering mechanism  74  for the distal tip  70 . 
     The steering mechanism  74  can vary. In the illustrated embodiment (see FIG.  17 ), the steering mechanism is the one shown in Copending U.S. application Ser. No. 07/789,260, which is incorporated by reference. 
     As  FIG. 17  shows, the steering mechanism  74  of this construction includes a rotating cam wheel  76  within the handle  72 . An external steering lever  78  rotates the cam wheel. The cam wheel  76  holds the proximal ends of right and left steering wires  80 . 
     The steering wires  80  extend along the associated left and right side surfaces of the cam wheel  76  and through the catheter body  68 . The steering wires  80  connect to the left and right sides of a resilient bendable wire or spring (not shown). The spring deflects the steerable distal tip  70  of the catheter body  68 . 
     As  FIG. 16  shows, forward movement of the steering lever  80  bends the distal tip  70  down. Rearward movement of the steering lever  80  bends the distal tip  70  up. By rotating the handle  70 , the physician can rotate the distal tip  70 . By manipulating the steering lever  80  simultaneously, the physician can maneuver the distal tip  70  virtually in any direction. 
       FIGS. 18 and 19  show the details of using the steerable catheter  60  to guide the outer sheath  48  into position. 
     The outer guide sheath  48  includes an interior bore  56  that receives the steerable catheter body  68 . The physician can slide the outer guide sheath  48  along the steerable catheter body  68 . 
     The handle  58  of the outer sheath  48  includes a conventional hemostatic valve  62  that blocks the outflow of blood and other fluids. The valve  62 , like the valve  52 , may take the form of either a resilient slotted membrane or a manually operated shutter valve arrangement (not shown). 
     Together, the valves  52  and  62  provide an effective hemostatic system. They allow performance of a procedure in a clean and relatively bloodless manner. 
     In use, the steerable catheter body  68  enters the bore  56  of the guide sheath  48  through the valve  62 , as  FIG. 18  shows. The handle  58  of the outer sheath  48  also preferably includes a flushing port  64  for the introduction of an anticoagulant or saline into the interior bore  56 . 
     As  FIG. 18  also shows, the physician advances the catheter body  68  and the outer guide sheath  48  together through the femoral vein. The physician retains the sheath handle  58  near the catheter handle  72  to keep the catheter tip  70  outside the distal end of the outer sheath  48 . 
     In this way, the physician can operate the steering lever  78  to remotely point and steer the distal end  70  of the catheter body  68  while jointly advancing the catheter body  68  through the femoral vein. 
     The physician can observe the progress of the catheter body  68  using fluoroscopic or ultrasound imaging, or the like. The outer sheath  48  can include a radio-opaque compound, such as barium, for this purpose. Alternatively, a radio-opaque marker can be placed at the distal end of the outer sheath  16 . 
     This allows the physician to maneuver the catheter body  68  through the femoral vein into the right atrium  12 , as  FIG. 18  shows. 
     As  FIG. 19  shows, once the physician locates the distal end  70  of the catheter body  68  in the right atrium  12 , the outer sheath handle  58  can be slid forward along the catheter body  68 , away from the handle  72  and toward the introducer  46 . The catheter body  68  directs the guide sheath  48  fully into the right atrium  12 , coextensive with the distal tip  70 . 
     Holding the handle  58  of the outer sheath  48 , the physician withdraws the steerable catheter body  68  from the outer guide sheath  48 . 
     The delivery system  44  is now deployed in the condition generally shown in FIG.  20 . The system  44  creates a passageway that leads through the femoral vein directly into the right atrium  12 . The delivery system  44  provides this access without an invasive open heart surgical procedure. 
     Alternatively, the outer guide sheath  48  can itself be preshaped with a memory. The memory assumes a prescribed curvature for access to the right or left atrium  12  or  14  through venous access, without need for a steerable catheter  60 . 
     To assist passage through the atrial septum  20 , the delivery system  44  includes a transeptal sheath assembly  82 . The delivery system  44  guides the sheath assembly  82  into the right atrium  12  and through the atrial septum  20  (see  FIGS. 25A and 25B ) to open access to the left atrium  14 . 
     The delivery system  44  further includes ablation probes  66  to carry a selected ablating element  42 .  FIG. 20  shows the common structural features shared by the ablation probes  66 . Each ablating probe  66  has a handle  84 , an attached flexible catheter body  86 , and a movable hemostat sheath  88  with associated carriage  90 . Each ablating probe  66  carries at its distal end a particular type of curvilinear ablating element  42 . 
     Category 1 
     Curvilinear Ablating Elements 
       FIGS. 5  to  14  show structures representative of Category 1 Curvilinear Ablating Elements  42  that the probes  66  can carry. Elements  42  in this category take the form of various three-dimensional structures, or baskets  92 . 
     The basket  92  can be variously constructed. In the illustrated and preferred embodiment, the basket  92  comprises a base member  98  and an end cap  100 . An array of generally resilient, longitudinal splines  102  extend in a circumferentially spaced relationship between the base member  98  and the end cap  100 . They form the structure of the basket  92 . The splines  102  are connected between the base member  98  and the end cap  100  in a resilient, pretensed condition. 
     The basket  92  also include one or more transverse bridge splines  108  that periodically span adjacent longitudinal splines  102 . 
     The splines  102 / 108  collapse into a closed, compact bundle in response to an external compression force. This occurs when they are captured within the movable hemostat sheath  88 , as  FIG. 21  shows. As will be described in greater detail later, the splines  102 / 108  are introduced through the delivery system  44  in this collapsed state. 
     Upon removal of the compression force, the splines  102 / 108  resiliently spring open to assume their three-dimensional shape. In this condition, the resilient splines  102 / 108  bend and conform to the tissue surface they contact. The atrial wall is also malleable and will also conform to the resilient splines  102 / 108 . The splines  102 / 108  thereby make intimate contact against the surface of the atrial wall to be ablated, despite the particular contours and geometry that the wall presents. 
     In the embodiment shown in FIGS.  5 A/ 5 B, six longitudinal splines  102  and six transverse bridge splines  108  form the basket  92 . However, additional or fewer splines  102 / 108  could be used, depending upon continuity and complexity of the maze pattern wanted. 
     The splines  102 / 108  can be made of a resilient inert material, like Nitinol metal or silicone rubber. In the illustrated and preferred embodiment, each longitudinal spline  102  is rectangular in cross section and is about 1.0 to 1.5 mm wide. The bridge splines  108  are generally cylindrical lengths of material. 
     As FIGS.  5 A/ 5 B best show, the splines  102  include regions  104  that are electrically conductive (called the “conductive regions”). The splines  102  also include regions  106  that are electrically not conductive (called the “nonconductive regions”). 
     In FIGS.  5 A/ 5 B, the bridge splines  108  comprise conductive regions  104  along their entire lengths. 
     The conductive regions  104  function as radiofrequency emitting electrodes held by the splines  102 / 108  in intimate contact against the atrial wall. These regions  104  emit radiofrequency ablating energy, when applied. The emitted energy forms the curvilinear lesions L in the myocardial tissue that generally conform to the propagation pattern of the emitted energy. 
     The lesions L formed by the conducting electrode regions  104  appear in juxtaposition with normal tissue that the nonconductive regions  106  contact. It is this juxtaposition of ablated tissue with normal tissue that forms the desired maze pattern. 
     The regions  104 / 106  can be variously created on the splines  102 / 108 , depending upon the underlying material of the splines  102 / 108  themselves. 
     For example, when the splines  102 / 108  are made of an electrically conductive material, such as Nitinol, the electrically conductive regions  104  can consist of the exposed Nitinol material itself. In addition, the conductive regions  104  can be further coated with platinum or gold by ion beam deposition and the like to improve their conduction properties and biocompatibility. In this arrangement, insulating material is applied over regions of the Nitinol metal to form the nonconductive regions  106 . 
     When the splines  102 / 108  are not made of an electrically conducting material, like silicone rubber, the conductive regions  104  are formed by coating the exterior surfaces with an electrically conducting material, like platinum or gold, again using ion beam deposition or equivalent techniques. 
     FIGS.  5 A/ 5 B and  4 A/ 4 B purposely exaggerate the diameter difference between the electrically conducting regions  104  and electrically nonconducting regions  106  to illustrate them. Actually, the diameter difference between the two regions  104 / 106  are approximately 0.05 mm to 0.1 mm, which is hard to detect with the naked eye, as  FIGS. 7  to  14  show with greater realism. 
     The relative position of the conductive regions  104  and the nonconductive regions  106  on each spline  102 , and the spaced apart relationship of the splines  102  and the bridge splines  108  take in the basket  92 , depend upon the particular pattern of curvilinear lesions L that the physician seeks to form. 
       FIG. 5A  shows a basket RA. Upon being deployed in the right atrium  12  and used to emit radiofrequency ablating energy, the basket RA creates the pattern of curvilinear lesions L shown in the left hand (i.e., right atrium) side of FIG.  2 . The basket RA forms this pattern of lesions L essentially simultaneously when ablating energy is applied to it. 
       FIG. 5B  shows a basket LA. Upon being deployed in the left atrium  14  and used to emit ablating energy, the basket LA creates the pattern of curvilinear lesions L shown in the right hand (i.e., left atrium) side of FIG.  2 . Like basket RA, the basket LA forms this pattern of lesions L essentially simultaneously when ablating energy is applied to it. 
       FIGS. 3 and 4  generally show the methodology of assembling the splines  102 / 108  into the baskets RA and LA. 
     As  FIG. 3  shows, the splines  102  are first laid out in an equally spaced arrangement upon a template  109 . The template  109  displays the desired lesion pattern for the right and left atria  12  and  14 . 
       FIG. 3  shows splines R 1  to R 6  laid out upon the template  109  where the lesion pattern for the right atrium  12  is displayed.  FIG. 3  shows splines L 1  to L 6  laid out upon the template  109  where the lesion pattern for the left atrium is displayed. 
     The template  109  displays longitudinal lesion areas; that is, lesions L that run generally vertically on the template  109 . The template  109  also displays transverse lesion areas; that is, lesions L that run generally horizontally on the template  109 . The template  109  also displays areas that are to be free of lesions L. 
     Those portions of the splines R 1 -R 6 /L 1 -L 6  that overlay a longitudinal lesion area must be electrically conducting to ablate tissue. These areas of the template  109  identify the electrically conducting regions  104  of the splines R 1 -R 6 /L 1 -L 6 . 
     Those portions of the splines R 1 -R 6 /L 1 -L 6  that do not overlay a desired longitudinal lesion area must not be electrically conducting to create lesion-free areas. These areas of the template  109  identify the electrically nonconductive regions  106  of the splines R 1 -R 6 /L 1 -L 6 . 
     Electrically conducting or electrically insulating material are therefore applied, as appropriate, to the splines to form the regions  104 / 106  the template  109  identifies, as  FIGS. 4A and 4B  show.  FIG. 4A  shows these regions  104 / 106  formed on the splines R 1 -R 6 .  FIG. 4B  shows these regions  104 / 106  formed on the splines L 1 -L 6 . 
     In  FIGS. 4A and 4B , the splines are made from an electrically conducting material (i.e., Nitinol), so an electrically insulating material is applied to form the nonconducting regions  106 . The areas free of the electrically insulating material form the conducting regions  104 . 
     The bridge splines  108  are positioned where the template  109  displays transverse lesion areas (shown in FIG.  3 ). The bridge splines  108  are soldered or otherwise fastened to the adjacent longitudinal splines  102 . The bridge splines  108  are electrically conducting to ablate these transverse regions of tissue. The transverse lesions link the longitudinal lesions to create the circuitous bounds of the maze. 
     The invention therefore forms the template  109  that lays out the desired lesion pattern. The invention then uses the template  109  to identify and locate the conductive and nonconductive regions  104  and  106  on the longitudinal splines R 1 -R 6 /L 1 -L 6 . The template  109  is also used to identify and locate the bridge splines  108  between the longitudinal splines. The baskets RA and LA are then completed by attaching the base members  98  and end caps  100  to opposite ends of the longitudinal splines. 
     As  FIG. 6  shows, each spline  102  is electrically coupled to a signal wire  110  made of an electrically conductive material, like copper alloy. The signal wires  110  extend through the base member  98  and catheter body  86  into the probe handle  84 . Connectors  112  (shown in  FIG. 20 ) attach the proximal ends of the signal wires  110  to an external source  114  of ablating energy. 
     The source  114  applies ablating energy to selectively activate all or some splines  102 . The source  114  applies the ablating energy via the signal wires  110  to create iso-electric paths along the splines  102 / 108  conforming to the desired lesion pattern. Creation of iso-electric paths along the splines  102 / 108  reduces ohmic losses within the probe  66 . 
     As  FIG. 6  shows, the applied energy is transmitted by the conducting regions  104  of the splines  102 / 108 . It flows to an exterior indifferent electrode  116  on the patient. 
       FIG. 20  shows the introduction of the catheter body  86  of the ablation probe  66  and its associated ablating element  42 . The element  42  takes the form of basket RA shown in FIG.  5 A. 
     Before introducing the ablation probe  66 , the physician advances the hemostat sheath  88  along the catheter body  86 , by pushing on the carriage  90 . The sheath  88  captures and collapses the basket RA with it, as  FIG. 21  also shows. 
     As  FIG. 22  shows, the physician introduces the hemostat sheath  88 , with the enclosed, collapsed basket RA, through the hemostatic valve  62  of the outer sheath handle  58 . The sheath  88  and enclosed basket RA enter the guide sheath  48 . The hemostat sheath  88  protects the basket splines  102 / 108  from damage during insertion through the valve  62 . 
     As  FIG. 23  shows, when the catheter body  86  of the ablation probe  66  advances approximately three inches into the guide sheath  48 , the physician pulls back on the sheath carriage  90 . This withdraws the hemostat sheath  88  from the valve  62  along the catheter body  86 . The hemostat valve  62  seals about the catheter body  86 . The interior bore  56  of the guide sheath  48  itself now encloses and collapses the basket RA, just as the sheath  88  had done. 
     As  FIGS. 23 and 24  show, the guide sheath  48  directs the catheter body  86  and attached basket RA of the ablation probe  66  into the right atrium  12 . As the basket RA exits the distal end of the guide sheath  48 , it will spring open within the right atrium  12 , as  FIG. 24  shows. The resilient splines  102 / 108  bend and conform to the myocardial surface of the right atrium  12 . 
     In the illustrated and preferred embodiment (as  FIG. 24  shows), the physician also deploys an ultrasonic viewing probe  118  through the femoral vein into the right atrium  12 , either within our outside the guide sheath  48 . Alternatively, fluoroscopy could be used. The physician operates the viewing probe  118  to observe the basket RA while maneuvering the basket RA to orient it within the right atrium  12 . Aided by the probe  118 , the physician can withdraw the basket RA back into the guide sheath  48 . The physician can rotate the handle  84  to rotate the basket RA, and then redeploy the basket RA within the right atrium  12 , until the physician achieves the desired orientation for the basket RA. 
     The physician now takes steps to ablate the myocardial tissue areas contacted by the conducting regions  104  of the basket RA. In this way, the physician forms the desired pattern of lesions L in the right atrium  12 . 
     Upon establishing the desired lesion pattern, the physician withdraws the ablation probe  66  from the guide sheath  48 , by that removing the basket RA from the right atrium  12 . Aided by the viewing probe  118  (as  FIG. 25A  shows), the physician advances the guide sheath  48  further into the right atrium  12  into nearness with a selected region of the atrial septum  20 . 
     To simplify placement of the guide sheath  48  next to the atrial septum  20 , the physician preferable deploys the steerable catheter body  68  through the guide sheath  48  in the manner generally shown in  FIGS. 18 and 19 . Keeping the steerable tip  70  outside the distal end of the outer sheath  48 , the physician operates the steering lever  78  to remotely point and steer the catheter body  68  across the right atrium toward the atrial septum  20 , aided by the internal viewing probe  118 , or by some external ultrasound or fluoroscopic imaging, or both. 
     Once the physician locates the distal end  70  of the catheter body  68  next to the desired site on the atrial septum  20 , the physician slides the outer sheath  48  forward along the catheter body  68 . The catheter body  68  directs the guide sheath  48  fully across the right atrium  12 , coextensive with the distal tip  70  next to the atrial septum  20 . 
     The physician withdraws the steerable catheter body  68  from the outer guide sheath  48  and (as  FIGS. 25A and 25B  show) advances the transeptal sheath assembly  82  through the now-positioned guide sheath  48  into the atrial septum  20 . The viewing probe  118  can be used to monitor the position of the guide sheath  48  and the advancement of the transeptal sheath assembly  82  toward the atrial septum  20 . 
     As  FIG. 25B  shows, the transeptal sheath assembly  82  includes a cutting edge or dilator  122  that carries a sharpened lead wire  120 . As the physician advances the transeptal sheath assembly  82 , the lead wire  120  forms an initial opening in the septum  20 . The dilator  122  enters this opening, enlarging it and punching through to the left atrium  14  (as  FIG. 25B  shows). 
     The Figures exaggerate the thickness of the atrial septum  20 . The atrial septum  20  comprises a translucent membrane significantly thinner than the Figures show. This transeptal approach is a well known and widely accepted technique used in other left atrium access procedures. 
     The physician then slides the guide sheath  48  along the transeptal sheath assembly  82  and into the left atrium  14 . The physician withdraws the transeptal sheath assembly  82  from the guide sheath  48 . The guide sheath  48  now forms a path through the femoral vein and right atrium  12  into the left atrium  14  (as  FIG. 26  shows) 
     The physician now introduces through the guide sheath  48  the catheter body  86  of another ablation probe  66  and its associated ablating element  42 . At this step in the procedure, the ablating element  42  takes the form of basket LA shown in FIG.  5 B. The physician advances the hemostat sheath  88  along the catheter body  86 , as before described, to capture and collapse the basket LA. The physician introduces the hemostat sheath  88 , with the enclosed, collapsed basket LA, through the hemostatic valve  62  of the outer sheath handle  58 , and then withdraws the hemostat sheath  88 . 
     Just as  FIGS. 23 and 24  show the introduction of the basket RA into the right atrium  12 ,  FIG. 26  shows the guide sheath  48  directing the basket LA into the left atrium  14 . As the basket LA exits the distal end of the guide sheath  48 , it will spring open within the left atrium  14 , as  FIG. 26  shows. 
     As  FIG. 26  also shows, the physician also deploys the viewing probe  118  through the opening made in the atrial septum  20  into the left atrium  14 . The physician operates the viewing probe  118  while maneuvering the basket LA to orient it within the left atrium  14 . Aided by the probe  118 , the physician can withdraw the basket LA back into the guide sheath  48 , rotate the handle  84  to rotate the basket LA, and then redeploy the basket LA within the left atrium  14 . The physician repeats these steps, until the desired orientation for the basket LA is achieved. 
     The physician now takes steps to ablate the myocardial tissue areas contacted by the conducting regions  104  of the basket LA. In this way, the physician forms the desired pattern of lesions L in the left atrium  14 . 
     Upon establishing the desired lesion pattern, the physician withdraws the ablation probe  66  from the guide sheath  48 , removing the basket LA from the left atrium  14 . The physician then withdraws the guide sheath  48  from the heart and femoral vein. Last, the physician removes the introducer  46  to complete the procedure. 
       FIGS. 7  to  14  show alternative embodiments of ablating elements  42 ( 1 ) to  42 ( 7 ) that the ablation probe  66  can carry. The delivery system  44  as just described can be used to introduce and deploy each alternative ablating element  42 ( 1 ) to  42 ( 7 ) in the same way as baskets RA and LA. 
     The alternative ablating elements  42 ( 1 ) to  42 ( 5 ) shown in  FIGS. 7  to  12  share many features that are common to that baskets RA and LA shown in  FIGS. 5A and 5B . Consequently, common reference numerals are assigned. 
     The alternative elements  42 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ) all take the form of a three-dimensional basket, designated  92 ( 1 ),  92 ( 2 ),  92 ( 3 ),  92 ( 4 ), and  92 ( 5 ) respectively. 
     As before described, each basket  92 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ) comprises a base member  98  and an end cap  100 . As also earlier described, an array of generally resilient, longitudinal splines  102  extend in a circumferentially spaced relationship between the base member  98  and the end cap  100 . They form the structure of the baskets  92 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ). 
     As before described, the splines  102  are made of a resilient inert material, like Nitinol metal or silicone rubber. They are connected between the base member  98  and the end cap  100  in a resilient, pretensed condition. 
     Like the baskets RA and LA, the splines  102  of each basket  92 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ) collapse for delivery into the atria  12 / 14  in a closed, compact bundle (as  FIG. 21  generally shows). The splines  102  of each basket  92 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ) also resiliently spring open to assume their three-dimensional shape when deployed in the atria  12 / 14 , bending and conforming to the surrounding myocardial tissue surface. 
     As in the baskets RA and LA (shown in FIGS.  5 A/ 5 B), the splines  102  of each basket  92 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ) include electrically conductive regions  104  juxtaposed with electrically nonconductive regions  106 . These regions  104  and  106  are located and formed on the splines  102  of the baskets  92 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ) using the same template  109  (shown in  FIG. 3 ) and using the same surface alteration techniques (shown in FIGS.  4 A/ 4 B). As previously explained, the diameter differences between the two regions  104 / 106  are hard to detect with the naked eye, as  FIGS. 7  to  10  show. 
     As before described, the conductive regions  104  function as radiofrequency emitting electrodes that form the curvilinear lesions L in the tissue that the conductive regions  104  contact. These lesion areas are juxtaposed with normal tissue that the nonconductive regions  106  contact. 
     Instead of the bridge splines  108  that the basket RA and LA carry, the baskets  92 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ) use alternative assemblies to form the transverse legion regions spanning adjacent transverse splines  102 . 
     The ablating element  42 ( 1 ) shown in  FIGS. 7 and 11  includes, as an integral part, a steerable distal element  124  carried within the open interior area  96  of the basket  92 ( 1 ). As  FIG. 11  shows, the distal element  124  is itself part of a conventional steerable catheter assembly  128  that forms an integral part of the associated ablating probe  66 ( 1 ). 
     The distal element  124  carries an electrode  126  comprising a strip of electrically conducting material, like Nitinol wire. In use, the electrode  126  serves as a single movable bridge electrode. In successive motions controlled by the physician, the single bridge electrode  126  can be positioned and ablating energy applied to it, to thereby make all the transverse lesions that the particular maze pattern requires. The single steerable bridge electrode  126  of the basket  92 ( 1 ) thereby serves the function of the several fixed bridge splines  108  of the baskets RA and LA. 
     The bridge electrode  126  can also be used to “touch up” or perfect incomplete lesions patterns formed by the longitudinal splines  102 . 
     The proximal end of the steering assembly  128  of the probe  66 ( 1 ) includes a handle  130  (as  FIG. 11  shows). A guide tube  132  extends from the handle  130 , through the body  86 ( 1 ) of the probe  66 ( 1 ), and into the interior area  96  of the basket  92 ( 1 ). The steerable distal element  124  and bridge electrode  126  make up the distal end of the guide tube  132 . 
     The handle  130  encloses a steering mechanism  134  for the steerable distal element  124  and associated bridge electrode  126 . The steering mechanism  134  for the assembly  128  is the same as the steering mechanism  74  for the distal tip  70  of the catheter  60  (shown in  FIG. 17 ) and will therefore not be described again. 
     By manipulating the steering assembly  128  (as shown by arrows M 1 , M 2 , and M 3  in FIG.  11 ), the physician can remotely steer the element  124  and the associated bridge electrode  126  in three principal directions inside the basket  92 ( 1 ) (as shown arrows M 1 , M 2  and M 3  in FIG.  7 ). 
     First, by remotely pulling and pushing the handle  130 , the physician moves the element  124  and bridge electrode  126  along the axis of the basket  92 ( 1 ), in the direction of arrows M 1  in  FIGS. 7 and 11 . 
     Second, by remotely rotating the handle  130 , the physician rotates the element  124  and associated bridge electrode  126  about the axis of the basket  92 ( 1 ), in the direction of arrows M 2  in  FIGS. 7 and 11 . 
     Third, by manipulating the steering mechanism  134  by rotating the steering lever  136  (see FIG.  11 ), the physician bends the distal element  124 , and with it, the bridge electrode  126  in a direction normal to the axis of the basket  92 ( 1 ), in the direction of arrows M 3  in  FIGS. 7 and 11 . 
     By coordinating lateral (i.e., pushing and pulling) movement of the handle  130  with handle rotation and deflection of the distal element  124 , it is possible to move the bridge electrode  126  into any desired position, either between any two adjacent longitudinal splines  102  or elsewhere within the reach of the basket  92 ( 1 ). Preferably, the physician deploys the interior viewing probe  118  or relies upon an external fluoroscopic control technique to remotely guide the movement of the bridge electrode  126  for these purposes. 
     The ablating element  42 ( 2 ) shown in  FIG. 8  includes, as an integral part, an internal electrode structure  138  that comprises a single length of wire material, such as Nitinol, preshaped to assume a helical array. 
     In  FIG. 8 , the helical electrode structure  138  extends from the base member  98  and spirals within the interior area  96  of the basket  92 ( 2 ). Along its spiraling path within the basket  92 ( 2 ), the helical electrode structure  138  creates interior points of contact  140  with the longitudinal splines  102 . The structure  138  is slidably attached by eye loops  103  to the splines  102  at these interior points of contact  140 . 
     The helical electrode structure  138  spanning the interior points of contact  140  includes regions  146  that are electrically conducting and regions  148  that are not electrically conducting. The precise location of the regions  146  and  148  along the spiraling path of the electrode structure  138  will depend upon the pattern of transverse lesions required. 
     Where a transverse lesion L is required, the structure  138  will include an electrically conducting region  146  between two points of contact  140  with adjacent splines  102 . The points of contact  140  will also be conducting regions  104 . In this way, the structure  138  serves to conduct ablating energy, when applied, between adjacent splines  102 , just as the presence of the bridge splines  108  did in the baskets RA and LA. 
     Where a transverse lesion is not required, the structure  138  will include an electrically nonconducting region  148  between two points of contact  140  with adjacent splines  102 . The points of contact  140  will also be nonconducting regions  106 . In this way, the structure  138  will not conduct ablating energy between adjacent splines  102 . The structure  138  in these regions  148  serve just as the absence of the bridge splines  108  did in the baskets RA and LA. 
     The electrically conducting regions  146  and electrically nonconducting regions  148  are formed along the helical structure  138  in the same way the comparable conducting and nonconducting regions  104  and  106  of the longitudinal splines  102  are formed. 
     The helical structure  138  captured within the basket  92 ( 2 ) serves the same function as the bridge splines  108  of the baskets RA and LA in creating zones of transverse lesions. 
     The shape of the helical structure  138 , its interior points of contact  140  with the longitudinal splines  102 , and the location of the conducting and nonconducting regions  146  and  148  are, like the location of the regions  104 / 106  on the longitudinal splines  102 , predetermined to create the desired pattern of longitudinal and transverse legions L when ablating energy is applied. 
     As with baskets RA and LA, these considerations for the basket  92 ( 2 ) will require a particular arrangement of elements for use in the right atrium  12  and another particular arrangement of elements for use in the left atrium  14 . 
     The helical electrode structure  138  will collapse laterally upon itself as the basket  92 ( 2 ) itself collapses inward in response to an external compression force. The basket  92 ( 2 ) can thereby be introduced into the atria  12 / 14  in the same manner as the baskets RA and LA. The structure  138  will assume its helical shape when the basket  92 ( 2 ) springs open with the removal of the compression force. The basket  92 ( 2 ) can thereby be deployed for use within the atria  12 / 14  in the same manner as the baskets RA and LA. 
     The ablating element  42 ( 3 ) shown in  FIG. 9  is similar in many respects to the ablating element  42 ( 2 ) shown in FIG.  8 . The ablating element  42 ( 3 ) includes, as an integral part, an internal electrode structure  142 . Like the structure  138  shown in  FIG. 8 , the structure  42 ( 3 ) comprises a single length of wire material, such as Nitinol, preshaped to assume a helical array. 
     In  FIG. 9 , like the structure  138  in  FIG. 8 , the helical electrode structure  142  extends from the base member  98 . However, unlike the structure  138  shown in  FIG. 8 , the structure  142  in  FIG. 9  spirals outside along the exterior surface of the basket  92 ( 3 ). Like the structure  138 , the structure  142  is slidably attached by eye loops  103  to the splines  102  at the exterior points of contact  144 . 
     In other respects, the helical structure  138  and the helical structure  142  are essentially identical. Similar to the structure  138 , the helical structure  142  spanning the points of contact  144  includes regions  146  that are electrically conducting and regions  148  that are not electrically conducting, depending upon the pattern of transverse lesions required. Where a transverse lesion L is required, the structure  142  will include an electrically conducting region  146 . Similarly, where a transverse lesion is not required, the structure  142  will include an electrically nonconducting region  148 . 
     The electrically conducting regions  146  and electrically nonconducting regions  148  are formed along the helical structure  142  in the same way the comparable conducting and nonconducting regions  104  and  106  of the longitudinal splines  102  are formed. 
     The helical structure  138  carried outside the basket  92 ( 3 ) serves the same function as the bridge splines  108  of the baskets RA and LA in creating zones of transverse lesions. 
     As with the structure  138 , the shape of the helical structure  142 , its exterior points of contact  144  with the longitudinal splines  102 , and the location of the conducting and nonconducting regions  146  and  148  are predetermined to create the desired pattern of longitudinal and transverse legions L when ablating energy is applied. 
     As with baskets RA and LA, and the basket  42 ( 2 ), these considerations for the basket  92 ( 3 ) will require a particular arrangement of elements for use in the right atrium  12  and another particular arrangement of elements for use in the left atrium  14 . 
     The helical electrode structure  142 , like the structure  138 , will collapse laterally upon itself and spring back and open into its predetermined shape as the basket  92 ( 3 ) itself collapses and opens. The basket  92 ( 3 ) can be introduced and deployed into the atria  12 / 14  in the same manner as the baskets RA and LA and the basket  92 ( 2 ). 
       FIGS. 12A and B  show an alternative helical electrode structure  150  within a basket  92 ( 4 ). The basket  92 ( 4 ) is essentially identical to the baskets  92 ( 2 ) and  92 ( 3 ) previously described. The helical structure  150 , like the structures  138  and  142 , includes electrically conducting regions  146  and electrically nonconducting regions  148  formed along its length. 
     However, unlike the structures  138  and  142  shown in  FIGS. 8 and 9 , the structure  150  is not integrally attached to the basket  92 ( 4 ). Instead, the structure  150  can be remotely moved by the physician between a retracted position near the base member  98  of the associated basket  92 ( 4 ) (as  FIG. 12A  shows) and a deployed position within the basket  92 ( 4 ) (as  FIG. 12B  shows). 
     The structure  150  occupies its retracted position when the basket  92 ( 4 ) is collapsed within the guide sheath  48  for introduction into the selected atria  12 / 14 , as  FIG. 12A  shows. The structure  150  is deployed for use after the basket  92 ( 4 ) is deployed outside the distal end of the guide sheath  48  for use within the selected atria  12 / 14 , as  FIG. 12B  shows. 
     In this embodiment, the electrode structure  150  comprises a length of memory wire, like Nitinol, that is preshaped into the desired helical shape. The structure  150  is attached to the distal end of a push/pull rod  152  that extends through a bore  153  in the body  154  of an associated probe  156 . The push/pull rod  152  is attached at its proximal end to a slide control lever  158  that extends from the handle  160  of the probe  156 . Fore and aft movement of the slide control lever  158  causes axial movement of rod  152  within the bore  153 . 
     Pulling back upon the slide control lever  158  (as  FIG. 12A  shows) moves the rod  152  aft (i.e., toward the handle  160 ). The aft movement of the rod  152  draws the structure  150  out of the basket  92 ( 4 ) and into the distal end of the probe body  154 . As the structure  150  enters the confines of the bore  153 , it resiliently straightens out, as  FIG. 12A  shows. 
     Pushing forward upon the slide control lever  158  (as  FIG. 12B  shows) moves the rod  152  forward (i.e., away from the handle  160 ). The forward movement of the rod moves the structure  150  out of the confines of the bore  153  and into the interior area  96  of the basket  92 ( 4 ). Since the structure  150  possesses a resilient memory, it will return to its preformed helical shape as it exits the bore  153  and enters the basket  92 ( 4 ), as  FIG. 12B  shows. The resilient memory of the structure  150  generally aligns the conductive and nonconductive regions  146  and  148  of the structure  150  with the conducting and nonconducting regions  104  and  106  of the longitudinal splines  102  to form the desired pattern of longitudinal and transverse lesions L. 
     The ablating element  42 ( 5 ) shown in  FIG. 10  includes an external basket  92 ( 5 ) that encloses, as an integral part, an internal basket structure  212 . The internal basket structure  212  includes several individual splines  214  of wire material, such as Nitinol, preshaped to assume a three-dimension array. The individual splines  214  extend from the base member  98  and transverse prescribed paths within the interior area  96  of the basket  92 ( 5 ). The several paths the interior splines  214  create interior points of contact  216  with the longitudinal splines  102  of the exterior basket  92 ( 5 ). The individual splines  214  are free to move with respect to the splines  102  at these interior points of contact  216 . 
     The interior basket structure  212  spanning the interior points of contact  216  includes regions  218  that are electrically conducting and regions  220  that are not electrically conducting. The precise location of the regions  218  and  220  along the several paths of the interior splines  214  will depend upon the pattern of transverse lesions that is required. 
     Where a transverse lesion L is required, the interior basket structure  212  will include an electrically conducting region  218  between two points of contact  216  with adjacent exterior splines  102 . The points of contact  216  will also be conducting regions  104 . In this way, the interior basket structure  212  serves to conduct ablating energy, when applied, between adjacent splines  102 , just as the presence of the bridge splines  108  did in the baskets RA and LA. 
     Where a transverse lesion is not required, the interior basket structure  212  will include an electrically nonconducting region  220  between two points of contact  216  with adjacent exterior splines  102 . The points of contact will also be nonconducting regions  106 . In this way, the interior basket structure  212  will not conduct ablating energy between adjacent exterior splines  102 . The interior basket structure  212  in these regions  220  serve just as the absence of the bridge splines  108  did in the baskets RA and LA. 
     The electrically conducting regions  218  and electrically nonconducting regions  220  are formed along the interior splines  214  in the same way the comparable conducting and nonconducting regions  104  and  106  of the longitudinal exterior splines  102  are formed. 
     The interior basket structure  212  captured within the exterior basket  92 ( 5 ) serves the same function as the bridge splines  108  of the baskets RA and LA in creating zones of transverse lesions. 
     The shape of the interior basket structure  212 , its interior points of contact  216  with the longitudinal exterior splines  102 , and the location of the conducting and nonconducting regions  218  and  220  are, like the location of the regions  104 / 106  on the longitudinal splines  102 , predetermined to create the desired pattern of longitudinal and transverse legions L when ablating energy is applied. 
     As with baskets RA and LA, these considerations for the basket  92 ( 5 ) and associated interior basket structure  212  will require a particular arrangement of elements for use in the right atrium  12  and another particular arrangement of elements for use in the left atrium  14 . 
     The interior basket structure  212  will collapse upon itself as the exterior basket  92 ( 5 ) itself collapses inward in response to an external compression force. The double basket  92 ( 5 )/ 212  can be introduced into the atria  12 / 14  in the same manner as the baskets RA and LA. The double basket  92 ( 5 )/ 212  will reassume its shape when the baskets  92 ( 5 )/ 212  spring open with the removal of the compression force. The double basket  92 ( 5 )/ 212  can be deployed for use within the atria  12 / 14  in the same manner as the baskets RA and LA. 
       FIG. 13  shows yet another alternative embodiment of an ablating element  42 ( 6 ) that the ablation probe  66  can carry for introduction by the delivery system  44 . 
     The alternative element  42 ( 6 ) differs from the previously described multiple spline baskets  92 ( 1 ) to ( 5 ) in that it forms a single hoop  162 . The hoop  162  allows the physician to form, as part of the lesion pattern, lesions that substantially encircle the orifices of the SVC  26  and the IVC  28  in the right atrium  12  and the PV&#39;s  30  in the left atrium  14  (see FIG.  1 ). Furthermore, by using one or more hoops  162  in succession, the physician can eventually form an entire lesion pattern. 
     As before described, the hoop  162  can be made of a resilient inert material, like Nitinol metal or silicone rubber. It extends from a base member  164  carried at the distal end of the catheter body of the associated ablating probe. 
     The hoop  162  can include electrically conductive regions  104  juxtaposed with electrically nonconductive regions  106 , if needed. Alternatively, the hoop  162  can comprise a single, adjoining conductive region  104 . 
     These regions  104  and  106  are located and formed on the hoop  162  using the same surface alteration techniques as before described. 
     As the baskets  92 ( 1 )/( 2 )/( 3 )/( 4 )/( 5 ), the hoop  162  will resiliently collapse within the guide sheath  48  and resiliently spring open when deployed outside the guide sheath  48 . In this way the hoop  162  can be collapsed for delivery into the atria  12 / 14  and then be deployed within the atria  12 / 14 . 
       FIG. 14  shows yet another alternative embodiment of an ablating element  42 ( 7 ) that the ablation probe  66  can carry for introduction by the delivery system  44 . 
     This alternative element  42 ( 7 ) differs from the previously described multiple spline baskets  92 ( 1 ) to ( 5 ) and hoop  162  in that it comprises an inflatable balloon or bladder  166  made of a thermoplastic polymeric material, such as polyethylene. The bladder  166  is formed by either a free-blown process or a mold process. 
     The bladder  166  carries on its exterior surface a pattern of conduction regions  104  and nonconductive regions  106  to form the desired array of longitudinal and transverse lesions L. 
     In the illustrated and preferred embodiment, the conductive regions  104  are formed by coating the polymeric material of the bladder  166  with a conductive material. The nonconductive regions  106  are preserved free of the conductive material. 
     Coating of the conductive regions  104  may be accomplished by conventional sputter coating techniques. For example, gold can be sputtered onto the exterior surface of the bladder  166 . Alternatively, a two phase sputter coating process may be employed in which an initial layer of titanium is applied followed by an outer coating of gold. The procedure may also use an ion beam assisted deposition (IBAD) process. This process implants the conductive material into the polymer of the bladder  166 . 
     The conductive regions  104  of the bladder  166  are attached to signal wires (not shown) to conduct ablating energy to the conductive regions  104 . 
     As with previously described elements  42 , the difference in patterns in the right and left atria will require a particular pattern of conductive and nonconductive regions  104 / 106  for use in the right atrium  12  and another particular arrangement of conductive and nonconductive regions  104 / 106  for use in the left atrium  14 . 
     As  FIG. 14  shows, the element  42 ( 6 ) includes one or more inflation lumens  168  that communicate with the interior of the bladder  166 . The lumens  168  communicate with a common fluid supply tube  172  that extends through the bore of the catheter body  170  of the associated probe  66 . As shown in phantom lines in  FIG. 20 , the supply tube  172  extends beyond the probe handle  84  to an injection port  174 . 
     In use, the physician connects the port  174  to a source of fluid pressure (not shown), which is preferably a liquid such as water, saline solution, or the like. The bladder  166  is deployed in a collapsed position within the guide sheath  48  using the delivery system  44  already described. After maneuvering the distal end of the guide sheath  48  to the desired location within the right or left atria  12 / 14 , the physician deploys the bladder  166  outside the guide sheath  48 . 
     The physician then conducts positive fluid pressure through the supply tube  172  and lumen(s)  168  into the bladder  166 . The positive fluid pressure causes the bladder  166  to expand or inflate. 
     Preferably, the inflation occurs under relatively low pressures of approximately 3-10 psi. The inflation is conducted to the extent that the bladder  166  is filled and expanded, but not stretched. The electrical conductivity of the conductive regions  104  on the bladder  166  is thus not disturbed or impaired. The inflating bladder  166  assumes a prescribed three-dimension shape, just as the baskets  92 ( 1 ) to  92  ( 5 ). The shape can vary, depending upon the shape of the bladder  166 . In the illustrated embodiment, the bladder  166  assumes a toroidal shape, with an interior central opening to allow blood flow through it. 
     Due to its pliant nature, the bladder  166 , when inflated, naturally conforms to the topography of the surrounding atria  12 / 14  surface, and vice versa, like the baskets  92 ( 1 ) to  92 ( 4 ). 
     By releasing the positive fluid pressure and applying negative pressure through the supply tube  172 , the physician can drain fluid from the bladder  166 . This collapses the bladder  166  for enclosure in the guide sheath  48  for maneuvering within the atria  12 / 14 . 
     As before described, aided by the viewing probe  118  or other means of fluoroscopic or ultrasonic monitoring, the physician can maneuver the bladder  166  within the atria  12 / 14 . Aided by the probe  118 , the physician can repeatedly inflate and deflate the bladder  166  to deploy and withdraw the bladder  166  from and into the guide sheath  48 , while rotating it within the guide sheath  48 , until the desired orientation for the bladder  166  within the atria  12 / 14  is achieved. 
     The physician now takes steps to ablate the myocardial tissue areas contacted by the conducting regions  104  of the bladder  166 . In this way, the physician forms the desired pattern of lesions L in the atria  12 / 14 . 
     Release of the positive fluid pressure and the application of negative pressure through the supply tube  172  collapses the bladder  166  for enclosure in the guide sheath  48  and removal from the atria  12 / 14 . 
     Category 2 
     Curvilinear Ablating Elements 
       FIGS. 27  to  55  show structures representative of Category 2 Curvilinear Ablating Elements  42  that the probes  66  can carry. Elements  42  in this category comprise a family of flexible, elongated ablating elements  176  ( 1 ) to ( 5 ) of various alternative constructions. In the preferred and illustrated embodiments, each element  176  is about 1 to 2.5 mm in diameter and about 1 to 5 cm long. 
     As  FIG. 27  shows, each ablating element  176  is carried at the distal end of a catheter body  178  of an ablating probe  180 . The ablating probe  180  includes a handle  184  at the proximal end of the catheter body  178 . The handle  184  and catheter body  178  carry a steering mechanism  182  for selectively bending or flexing the ablating element  176  along its length, as the arrows in  FIG. 27  show. 
     The steering mechanism  182  can vary. In the illustrated embodiment, the steering mechanism  182  is like that shown in FIG.  13 . The steering mechanism  182  includes a rotating cam wheel  76  with an external steering lever  186 . As  FIG. 13  shows, the cam wheel holds the proximal ends of right and left steering wires  80 . The wires  80  pass through the catheter body  178  and connect to the left and right sides of a resilient bendable wire or spring within the ablating element  176 . 
     As  FIG. 27  shows, forward movement of the steering lever  186  flexes or curves the ablating element  176  down. Rearward movement of the steering lever  186  flexes or curves the ablating element  176  up. 
     In this way the physician can flex the ablating element  176  in either direction along its length. Through flexing, the ablating element  176  is made to assume a multitude of elongated shapes, from a generally straight line to a generally arcuate curve, and all intermediate variable curvilinear shapes between. Through flexing, the ablating element  176  can also be brought into intimate contact along its entire ablating surface against the surface of the atrial wall to be ablated, despite the particular contours and geometry that the wall presents. 
     One or more signal wires (not shown) attached to the ablating element  176  extend through the catheter body  178  and terminate with an external connector  188  carried by the handle  184 . The connector  188  plugs into a source of ablating energy (also not shown) to convey the ablating energy to the element  176 . 
     By first remotely flexing the element  176  into the desired curvilinear shape and then applying ablating energy to it, the physician can form both elongated straight lesions and virtually an infinite variety of elongated, curvilinear lesions. 
     In use, the probe  180  and associated flexible ablating element  176  is introduced into the atria  12 / 14 . Aided by the internal viewing probe  118  or another means of fluoroscopic or ultrasonic monitoring, the physician manipulates the steering lever  186  to steer the probe  180  into the desired atrial region. 
     For entry into the right atrium  12 , the physician can direct the probe  180  through a conventional vascular introducer through the path shown in  FIGS. 18 and 19 , without using the delivery system  44 . For entry into the left atrium  14 , the physician can direct the probe  180  through a conventional vascular introducer retrograde through the aortic and mitral valves. Preferably, however, the physician can use the delivery system  44  to simplify access into the left atrium  14 , in the manner shown in  FIGS. 25 and 26 . 
     Once in the desired region, the physician uses the same steering lever  186  to remotely bend the element  176  into the desired straight or curvilinear shape into intimate contact with the surrounding atrial wall. By then applying ablating energy to the shaped element  176 , the physician forms a lesion that conforms to that shape. 
     By repeating this “shape-and-ablate” process within the atria  12 / 14 , the physician eventually forms a contiguous pattern of straight and curvilinear lesions along the interior atrial surfaces. These lesions form the same desired patterns of longitudinal and transverse lesions that the three dimensional Category 1 Elements form all at once. 
     A single variable curvature ablating element  176  can be deployed within atria of various sizes and dimensions. Furthermore, a single variable curvature ablating element  176  can be used to form a multitude of different lesion patterns for the treatment of atrial fibrillation. Therefore, a single variable curvature ablating element  176  possesses the flexibility to adapt to different atrial geometries and pathologies. 
     The flexible, elongated ablating element  176  can also be used with a Category 1 Element to “touch up” or perfect incomplete lesions patterns formed by the Category 1 Element. 
       FIG. 28  shows one preferred embodiment of a flexible, elongated ablating element  176 ( 1 ). The element  176 ( 1 ) comprises a flexible body  190  made of a polymeric material, such as polyethylene. As shown by solid and phantom lines in  FIG. 28 , the body  190  can be flexed to assumed various curvilinear shapes, as just described. 
     The body  190  carries on its exterior surface a pattern of closely spaced electrically conductive regions  192 . The conductive regions  192  can be formed by coating the polymeric material of the body  190  with a conductive material. The portions  194  of the body  192  between the conductive regions  192  are preserved free of the conductive material. These regions  194  are thereby electrically nonconductive. 
     Coating of the conductive regions  192  may be accomplished by conventional sputter coating techniques, using gold, for example. Alternatively, an initial layer of titanium can be applied followed by an outer coating of gold using an ion beam assisted deposition (IBAD) process. 
     Alternatively, the regions  192  can comprise metallic rings of conductive material, like platinum. In this embodiment, the rings are pressure fitted about the body  190 , which is made from a nonconductive flexible plastic material, like polyurethane or polyethylene. The portions of the body  190  between the rings comprise the nonconductive regions  194 . 
     The conductive regions  192  of the body  190  are attached to signal wires (not shown) to conduct ablating energy to one or more of the conductive regions  192 . 
     The conductive regions  192  can be operated in a unipolar ablation mode, as  FIG. 29  shows, or in a bipolar ablation mode, as  FIG. 30  shows. 
     In the unipolar ablation mode (as  FIG. 29  shows), each conductive region  192  individually serves as an energy transmitting electrode. The energy transmitted by each conductive region  192  flows to an external indifferent electrode on the patient (not shown), which is typically an epidermal patch. In this mode, each conductive region  192  creates its own discrete lesion. However, due to the close spacing of the conductive regions  192 , the lesions overlap to create a single adjoining lesion pattern. 
     In the bipolar ablation mode (as  FIG. 30  shows), the conductive regions  192  are configured as alternating polarity transmitting electrode regions. A first region is designated “+”, and a second region is designated “−”. In this mode, ablating energy flows between the “+” electrode regions and the “−” electrode regions. This mode creates lesions that span adjacent electrode regions. As in the unipolar mode, the lesions overlap to form a single adjoining lesion pattern. 
     When operated in either the unipolar ablation mode or the bipolar ablation mode, the element  176 ( 1 ) forms a contiguous lesion pattern P in myocardial tissue MT along the particular curvature of the body  190 . Depending upon the curvature of the body  190 , the formed lesion pattern P 1  in the tissue MT can be straight (as  FIG. 31  shows), or the formed lesion pattern P 2  in the tissue MT can be curved (as  FIG. 32  shows). Both lesion patterns P 1  and P 2  result from the conformation between the atrial wall and the body  190 . 
     The element  176 ( 1 ) operates with higher impedance, higher efficiencies, and is more sensitive to tissue contact when operated in the bipolar ablation mode than when operated in the unipolar mode. 
     The lesion pattern created is approximately twice as wide as the body  190 . The lesion pattern can be made wider by using wider conductive regions  192 . 
     In a representative embodiment the body  190  is about 2.5 mm in diameter. Each conductive region  192  has a width of about 3 mm, and each nonconductive region  194  also has a width of about 3 mm. When eight conductive regions  192  are present and activated with 30 watts of radiofrequency energy for about 30 seconds, the lesion pattern measures about 5 cm in length and about 5 mm in width. The depth of the lesion pattern is about 3 mm, which is more than adequate to create the required transmural lesion (the atrial wall is generally less than 2 mm). 
     Furthermore, by selectively not activating one or more adjacent regions  192 , one can create a lesion pattern that is not adjoining, but is interrupted along the length of the body  190 . The interruptions in the lesion pattern provide pathways for propagating the activation wavefront and serve to control pulse conduction across the lesion pattern. 
     For example, as  FIG. 33  shows, the body  190  includes an alternating pattern of conductive regions  192  and nonconductive regions  194 , each region  192 / 194  being of equal width. By activating some conductive regions  192  (showed by “A” in FIG.  33 ), while not activation other conductive regions (showed by “N” in FIG.  33 ), an interrupted pattern of lesions PI can be made in myocardial tissue MT, as  FIG. 34  shows. As  FIG. 34  also shows, lesions of different length can be formed along the interrupted pattern PI, depending upon the number of adjacent conductive regions  192  activated. 
     Of course, by varying the curvature of the body  190 , the interrupted pattern PI can assume a generally straight path (as  FIG. 34  shows), or it can assume a generally curved path, as  FIG. 35  shows. 
       FIG. 59  shows a system  298  that couples an ablating energy source  296  to the energy emitting region  192  of the element  176 ( 1 ). In the illustrated embodiment, the source  296  supplies electromagnetic radiofrequency (RF) energy to the region  192 . 
     The system  298  includes a controller  300 . The controller  300  electronically adjusts and alters the energy emitting characteristics of the energy emitting region  192 . 
     The controller  300  can electronically configure the energy emitting region  192  for operation in either a bipolar ablating mode or a unipolar ablating mode. 
     The controller  300  also can electronically configure the energy emitting region  192  to form lesion patterns having differing physical characteristics. In one mode, the controller  300  configures the energy emitting region  192  to form the continuous lesion pattern P 1 /P 2  shown in  FIGS. 31 and 32 . In another mode, controller  300  configures the energy emitting region  192  to form a variety of interrupted lesion patterns PI, one of which is shown  FIGS. 34 and 35 . 
     The controller  300  includes an input panel  302  for governing the operation of the controller  300 . Through the input panel  302 , the physician chooses the ablation mode and physical characteristics of the lesion patterns. In response, the controller  300  electronically configures the energy emitting region  192  to operate in the chosen manner. In this way, the system  298  provides the flexibility to choose and then electronically create specially shaped lesions virtually instantaneously (i.e., “on the fly”) during an ablation procedure. 
     The configuration of the controller  300  and associated input panel  302  can vary.  FIG. 60  diagrammatically shows one preferred arrangement. 
     In  FIG. 60 , the element  176 ( 1 ) includes seven conductive regions, designated E 1  to E 7 , carried on the body  190 . Each conductive region E 1  to E 7  is electrically coupled to its own signal wire, designated W 1  to W 7 . The indifferent electrode, designated EI in  FIG. 60 , is also electrically coupled to its own signal wire WI. 
     In this arrangement, the controller  300  includes a switch S M  and switches S E1  to S E7  that electrically couple the source  296  to the signal wires W 1  to W 7 . The switch S M  governs the overall operating mode of the regions E 1  to E 7  (i.e., unipolar or bipolar). The switches S E1  to S E7  govern the activation pattern of the regions  192 . 
     Each switch S M  and S E1 to E7  includes three leads L 1 ; L 2 ; and L 3 . Electrically, each switch S M  and S E1 to E7  serves as three-way switch. 
     The three-way switches S M  and S E1 to E7  are electrically coupled in parallel to the RF energy. source  296 . The (+) output of the RF source  294  is electrically coupled in parallel by a connector  306  to the leads L 1  of the switches S E1 to E7 . The (−) output of the RF source  294  is electrically directly coupled by a connector  308  to the center lead L 2  of the mode selection switch S M . A connector  310  electrically couples in parallel the leads L 3  of the switches S M  and S E1 to E7 . 
     The center leads L 2  of the selecting switch S E1 to E7  are directly electrically coupled to the signal wires W 1  to W 7  serving the energy emitting regions E 1  to E 7 , so that one switch S E(N)  serves only one energy emitting region E (N) . 
     The lead L 1  of the switch S M  is directly electrically coupled to the signal wire WI serving the indifferent electrode EI. 
     The input panel  302  carries manually operable toggles T M  and T E1 to E7 . One toggle T M  and T E1 to E7  is electrically coupled to one switch, respectively S M  and S E1 to E7 . When manipulated manually by the physician, each toggle T M  and T E1 to E7  can be placed in three positions, designated A, B, and C in FIG.  61 . 
     As  FIG. 61  shows, toggle Position A electrically couples leads L 1  and L 2  of the associated switch. Toggle Position C electrically couples leads L 2  and L 3  of the associated switch. Toggle Position B electrically isolates both leads L 1  and L 3  from lead L 2  of the associated switch. 
     Position B of toggle T M  and toggles T E1 to E7  is an electrically OFF or INACTIVATED Position. Positions A and B of toggle T M  and toggles T E1 to E7  are electrically ON or ACTIVATED Positions. 
     By placing toggle T M  in its Position B (see FIG.  62 ), the physician electronically inactivates the controller  300 . With toggle T M  in Position By the controller  300  conveys no RF energy from the source  296  to any region  192 , regardless of the position of toggles T E1 to E7 . 
     By placing toggle T M  in Position A (see FIG.  63 ), the physician electronically configures the controller  300  for operation in the unipolar mode. With toggle T M  in Position A, the center lead L 2  of switch S M  is coupled to lead L 1 , electronically coupling the indifferent electrode EI to the (−) output of the source  296 . This configures the indifferent electrode EI to receive RF energy. 
     With toggle T M  in Position A, the physician electronically configures the regions E 1  to E 7  to emit RF energy by placing the associated toggle T E1 to E7  in Position A (as  FIG. 63  shows). This electronically couples each region E 1  to E 7  to the (+) output of the source  296 , configuring the regions E 1  to E 7  to emit energy. The indifferent electrode EI receives the RF energy emitted by these regions E 1  to E 7 . 
     With toggle T M  in Position A and all toggles T E1 to E7  in their Positions A, a continuous, unipolar lesion pattern results, as  FIG. 63  shows (like that shown in FIGS.  31  and  32 ). 
     With toggle T M  in Position A, the physician can select to electronically interrupt the flow of RF energy one or more regions E 1  to E 7 , by placing the associated toggles T E1 to E7  in Position B (see  FIG. 64 , where the flow is interrupted to regions E 3  and E 4 ). As  FIG. 64  shows, this configuration forms lesions where the regions E 1 ; E 2 ; and E 5  to E 7  emit RF energy next to lesion-free areas where the selected region or regions E 3  and E 4  emit no RF energy. An interrupted, unipolar lesion pattern results (like that shown in FIGS.  34  and  35 ). 
     Placing toggle T M  in Position C (see  FIG. 65 ) electronically isolates the indifferent electrode EI from the regions E 1  to E 7 . This configures the controller  300  for operation in the bipolar mode. 
     With toggle T M  placed in Position C, the physician can electronically alter the polarity of adjacent energy emitting regions E 1  to E 7 , choosing among energy emitting polarity (+), energy receiving polarity (−), or neither (i.e., inactivated). 
     Toggles T E1 to E7  placed in Position A electronically configure their associated regions E 1  to E 7  to be energy emitting (+). Toggles T E1 to E7  placed in Position C electronically configure their associated regions E 1  to E 7  to be energy receiving (−). Toggles T E1 to E7  placed in Position B electronically inactivate their associated regions E 1  to E 7 . 
     With toggle T M  in Position C, sequentially alternating the toggles T E1 to E7  between Positions A and C (as  FIG. 65  shows) creates a continuous, bipolar lesion pattern. In  FIG. 65 , regions E 1 ; E 3 ; E 5 ; and E 7  are energy transmitting (+), and regions E 2 ; E 4 ; and E 6  are energy receiving (−). 
     With toggle T M  in Position C, moving selected one or more toggles T E1 to E7  to Position B (thereby inactivating the associated regions E 1  to E 7 ), while sequentially alternating the remaining toggles T E1 to E7  between Positions A and C (as  FIG. 66  shows) creates an interrupted, bipolar lesion pattern. In  FIG. 66 , regions E 3  and E 4  are inactivated; regions E 1 ; E 5 ; and E 7  are energy transmitting (+); and regions E 2  and E 6  are energy receiving (−). 
       FIG. 36  shows another preferred embodiment of a flexible, elongated ablating element  176 ( 2 ). The element  176 ( 2 ) comprises a flexible body core  196  made of a polymeric material, such as polyethylene or Teflon plastic. As shown by solid and phantom lines in  FIG. 36 , the core body  196  can be flexed to assumed various curvilinear shapes. 
     In this embodiment, the core body  196  carries a closely wound, spiral winding  198 . 
     The winding  198  can comprise a single length of electrically conducting material, like copper alloy, platinum, or stainless steel. The electrically conducting material of the winding  198  can be further coated with platinum or gold to improve its conduction properties and biocompatibility. 
     The winding  198  can also comprise a single length of an electrically nonconducting material, to which an electrically conducting coating, like platinum or gold, has been applied. 
     The winding  198  can also comprise wound lengths of an electrically conducting material juxtaposed with wound lengths of an electrically nonconducting material. In this way, the winding  198  can form predetermined lesion patterns. 
     When attached to one or more signal wires (not shown), the regions of the winding  198  that comprise electrically conducting materials emit ablating energy. The winding  198  serves as an elongated flexible electrode that can be selectively flexed to form a diverse variety of long, curvilinear or straight lesion patterns. 
     Like the element  176 ( 1 ), the element  176 ( 2 ) can be operated both in a unipolar ablation mode (as  FIG. 37  shows) and in a bipolar ablation mode (as  FIG. 38  shows). 
     In the unipolar ablation mode (as  FIG. 37  shows), the winding  198  is formed from a single length of electrically conductive wire. The winding  198  serves as an energy transmitting electrode (as designated by a positive charge in FIG.  37 ). In this arrangement, the winding  198  transmits energy into the tissue and to an external indifferent electrode on the patient (not shown) to form a lesion. 
     In the bipolar ablation mode (as  FIG. 38  shows), the winding  198  comprises four wrapped lengths of wire (designated  198 ( 1 );  198 ( 2 );  198 ( 3 ); and  198 ( 4 ) in FIG.  38 ). The wires  198 ( 1 ) and  198 ( 3 ) are each electrically conducting. The wire  198 ( 2 ) and  198 ( 4 ) are not electrically conducting. Instead, wires  198 ( 2 ) and  198 ( 4 ) serve to insulate the wires  198 ( 1 ) and  198 ( 3 ) from each other. 
     In the bipolar ablation mode, energy is applied to so that the turns of the wire  198 ( 1 ) serve an energy transmitting regions (designated as “+”), while the turns of the wires  198 ( 3 ) serve as energy receiving electrode regions (designated as “−”). 
     In this mode, ablating energy flows from a transmitting electrode (positive) turn of wire  198 ( 1 ) to an adjacent receiving electrode (negative) turn of wire  198 ( 3 ), across the insulating intermediate wires  198 ( 2 ) and  198 ( 4 ). 
     When operated in either unipolar or bipolar mode, the element  176 ( 2 ), like element  176 ( 1 ), forms a contiguous lesion pattern P in myocardial tissue MT along the curvature of the body  196 . As  FIG. 39  shows, the lesion pattern P 1  can follow a straight path, or the lesion pattern P 2  can follow a curved path, depending upon the shape given to the body  196 . 
     Element  176 ( 2 ) allows the manufacture of a curvilinear ablation element of a smaller diameter than element  176 ( 1 ). The smaller diameter allows for the creation of a contiguous lesion pattern of less width and depth. The small diameter of element  176 ( 2 ) also makes it more flexible and more easily placed and maintained in intimate contact against the atrial wall than element  176 ( 1 ). 
     In a representative embodiment, the element  176 ( 2 ) is about 1.3 mm in diameter, but could be made as small as 1.0 mm in diameter. The element  176 ( 2 ) is about 5 cm in total length. This element  176 ( 2 ), when activated with 40 watts of radiofrequency energy for 30 seconds, forms a contiguous lesion pattern that is about 3 mm in width, about 5 cm in length, and about 1.5 mm in depth. 
       FIGS. 40  to  45  show yet another preferred embodiment of a flexible, elongated ablating element  176 ( 3 ). Like the other elements  176 ( 1 ) and  176 ( 2 ), the element  176 ( 3 ) comprises a flexible body core  200  made of a polymeric material, such as polyethylene. As shown by solid and phantom lines in  FIGS. 40 and 43 , the core body  200  can also be flexed to assumed various curvilinear shapes. 
     In this embodiment, the core body  200  carries one or more elongated, exposed strips  202  of flexible, electrically conducting material. Unlike the circumferential conductive regions  192  of element  176 ( 1 ) and the circumferential winding  198  of the element  176 ( 2 ), the strips  202 ( 1 ) and  202 ( 2 ) of element  176 ( 3 ) run parallel along the axis of the core body  200 . 
     As  FIGS. 40  to  45  show, the parallel strips  202  and the underlying core body  200  can assume different shapes. 
     In  FIGS. 40  to  42 , the core body  200  carries two strips, designated strip  202 ( 1 ) and  202 ( 2 ). These strips  202 ( 1 ) and  202 ( 2 ) are carried close to each other along the same surface region of the core body  200 . 
     In  FIG. 43 , the core body  200  carries a single, elongated strip  200  ( 3 ). This strip  202 ( 3 ) has a larger surface area than the individual strips  202 ( 1 ) and  200 ( 2 ) (shown in  FIGS. 40  to  42 ). However, as will be discussed later, the strip  202 ( 3 ) can be operated only in a unipolar ablation mode (thereby requiring an external indifferent electrode), whereas the closely spaced pair of strips  202 ( 1 )/( 2 ) can be operated in either a unipolar mode or a bipolar ablation mode. 
     As  FIGS. 44 and 45  show, strips  202 ( 4 ) and strip  202 ( 5 ) can occupy all or a significant portion of the core body  200 . 
     In  FIG. 44 , the strip  200 ( 4 ) covers the entire exterior surface of the core body  200 . It therefore becomes an elongated variation of the circumferential regions  192  of element  176 ( 1 ) and the circumferential winding  198  of the element  176 ( 2 ). 
     In  FIG. 45 , multiple strips  200 ( 5 ) segment the core body  200  into elongated conducting and nonconducting regions. 
     The strips  202  shown in  FIGS. 40  to  45  can be affixed by adhesive or thermal bonding to the exterior surface of the core body  196 , as FIGS.  41 A/B and  43  to  45  show. Alternatively, the strips  200  can consist of coextruded elements of the core body  200  (as FIGS.  40  and  42 A/B show). 
     The strips  202  can comprise elongated lengths of an electrically conducting material, like copper alloy. The strips can be further coated with platinum or gold to improve conduction properties and biocompatibility. The strips  202  can also comprise a single length of an electrically nonconducting material to which an electrically conducting coating, like platinum or gold, has been applied. 
     Alternatively, the strips  202  can comprise coatings applied by conventional sputter coating or IBAD techniques. 
     The strips  202  can also have differing cross sectional shapes. In FIGS.  41 A/B, the strips  202 ( 1 ) and  202 ( 2 ) each have a circular cross section and thereby present a generally rounded contact zone with the tissue. The FIGS.  42 A/B;  44 ; and  45 , the strips  202  have a rectilinear cross section and thereby present a generally flat contact zone with the tissue. 
     As FIGS.  41 A/B and  42 A/B also show, the cross sectional shape of the underlying core body  200  can also vary. In FIGS.  41 A/B, the core body  200  has a generally circular cross section. In FIGS.  42 A/B, the core body  200  has a generally flattened region  204 , upon which the strips  202 ( 1 ) and  202 ( 2 ) are laid. The flattened region  204  provides more stable surface contact. 
     The strips  202 ( 1 ) and  202 ( 2 ) can be operated in both a unipolar ablation mode (as  FIGS. 41A and 42A  show) and in a bipolar ablation mode (as  FIGS. 41B and 42B  show), depending upon the efficiencies required, as before discussed. 
     When operated in the unipolar mode (see FIGS.  41 A and  42 A), each strip  202 ( 1 ) and  202 ( 2 ) serves as elongated, flexible energy emitting electrode (designated with positive charges). The strips  202 ( 3 )/( 4 )/( 5 ) ( FIGS. 43  to  45 ) similarly operate as elongated flexible electrodes in the unipolar ablation mode. 
     When operated in the bipolar mode (see FIGS.  41 B and  42 B), one strip  202 ( 1 )/( 2 ) serves as an elongated energy emitting electrode (designated with a positive charge), while the other strip serves as an elongated indifferent electrode (designated with a negative charge). 
     No matter its particular shape, the element  176 ( 3 ) forms a contiguous, elongated lesion P in myocardial tissue MT arrayed along the curvature of the body  200 . 
     As  FIG. 46  shows, the lesion P 1  in the tissue MT can follow a straight path, or the lesion P 2  can follow a curved path, depending upon the shape of the body  200 . In the multiple strip embodiments shown in  FIGS. 40  to  42 , the width of the lesion P 1  or P 2  can be controlled by the spacing between the strips  202 ( 1 )/( 2 ) and  202 ( 5 ). In the single strip embodiments shown in  FIGS. 43  to  45 , the width of the lesion P 1  or P 2  can be controlled by the width of the strips  202 ( 3 )/ 202 ( 4 )/ 202 ( 5 ) themselves. 
       FIGS. 47 and 48  show still another preferred embodiment of a flexible, elongated ablating element  176 ( 4 ). Like the other elements  176 ( 1 )to ( 3 ), the element  176 ( 3 ) comprises a flexible body core  204  made of a polymeric material, such as polyethylene. As shown by solid and phantom lines in  FIG. 40 , the core body  204  can also be flexed to assumed various curvilinear shapes. 
     In this embodiment, a thin, flat ribbon  206  of material is spirally wound about and affixed to the core body  204 . 
     The ribbon  206  comprises a polymeric material to which an electrically conducting coating, like platinum or gold, has been applied. Alternatively, the spiral electrically conductive ribbon  206  can be applied directly on the core body  204  using an ion beam assisted deposition (IBAD) process. 
     The spiral ribbon  206  serves as an elongated flexible electrode. Like the preceding element  176 ( 1 ), the element  176 ( 4 ) can be operated to emit ablating energy to form a pattern P 1  or P 2  of closely spaced lesions arrayed along the curvature of the body  204 , as  FIGS. 31 and 32  show. The element  176 ( 4 ) can be operated only in a unipolar ablation mode in association with an external indifferent electrode. 
       FIGS. 49 and 50  show another preferred embodiment of a flexible, elongated ablating element  176 ( 5 ). Unlike the other elements  176 ( 1 ) to ( 4 ), the element  176 ( 5 ) comprises a flexible body core  208  made of an electrically conducting material. As shown by solid and phantom lines in  FIG. 42 , the core body  208  can be flexed to assumed various curvilinear shapes. 
     In this embodiment, the core body  208  is partially enclosed by a shroud  210  made from an electrically nonconducting material, like polyethylene. The shroud  210  includes an elongated opening  212  that exposes the underlying core body  208 . The shroud  210  electrically insulates the core body  208 , except that portion  214  exposed through the opening  212 . 
     When ablating energy is applied to the core body  208 , only the portion  214  exposed through the window  212  emits energy. The rest of the shroud  214  blocks the transmission of the ablating energy to the tissue. The element  176 ( 5 ) creates a continuous elongated ablation pattern, like that shown in  FIG. 46  as created by the elongated strip  202 ( 3 ) shown in FIG.  37 . 
       FIG. 51  shows an ablation probe  246  that carries another type of flexible, elongated ablating element  176 ( 6 ). In many respects, the probe  246  is like the probe  180  shown in  FIGS. 27 and 36 . 
     The element  176 ( 6 ) comprises a flexible body core  222  made of a polymeric material, such as polyethylene or Teflon plastic. The core  222  is carried at the distal end of the catheter body  248  of the associated probe  246 . 
     The probe  246  includes a handle  250  that carries a steering mechanism  252  for flexing the core body  222  into various curvilinear shapes, as shown by solid and phantom lines in FIG.  51 . As  FIG. 55  shows, the steering mechanism  252  is like the steering mechanism shown in  FIG. 17 , already described. 
     As  FIG. 53  shows, the core body  222  carries a closely wound, spiral winding  224 , like that shown in FIG.  36 . The winding  224  comprises a single length of electrically conducting material, like copper alloy or platinum stainless steel. The electrically conducting material of the winding  224  can be further coated with platinum or gold to improve its conduction properties and biocompatibility. 
     Alternatively, the winding  224  can also comprise a single length of an electrically nonconducting material, to which an electrically conducting coating, like platinum or gold, has been applied. 
     When attached to one or more signal wires (not shown), the winding  224  emits ablating energy into the tissue and to an external indifferent electrode on the patient (not shown). The winding  224  thereby serves as an elongated flexible electrode that can be selectively flexed to form a diverse variety of long, curvilinear or straight lesion patterns, like those shown in FIG.  39 . 
     Unlike the element  176 ( 2 ) shown in  FIG. 36 , the ablating element  176 ( 6 ) includes a sliding sheath  226  carried about the winding  224  (see FIGS.  51  and  52 ). The sheath  226  is made of an electrically nonconducting material, like polyimide. 
     The interior diameter of the sheath  226  is greater than the exterior diameter of the winding  224 , so it can be moved axially fore and aft along the exterior of the winding  224 , as shown by the arrows in FIG.  52 . 
     As  FIG. 53  also shows, the sheath  226  carries a retaining ring  228  on its proximal end. A stylet  230  is attached to the retaining ring  228 . The stylet  230  extends from the retaining ring  228 , through the associated catheter body  248 , and attaches to a sliding control lever  254  carried on the probe handle  250  (see FIG.  55 ). 
     Fore and aft movement of the control lever  254  (as arrows in  FIG. 55  show) imparts, through movement of the stylet  230 , fore and aft movement to the sheath  226  in a one-to-one relationship. 
     The sheath  226  carries a strip  234  of electrically conducting material at its distal end (see FIG.  53 ). The strip  234  includes a contact region  236  that extends through the sheath  226  to contact one or more turns of the underlying winding  224 . 
     A signal wire  238  is electrically connected to the strip  234 . The signal wire  238  conveys ablating energy from the source to the winding  224  through the contact region  236 . The region  236  maintains electrical contact with the winding  224  during movement of the sheath  226 . 
     The signal wire  238  and strip  234  are enclosed upon the sheath  226  by a layer of electrically insulating shrink tubing  240 . A nonconducting adhesive is also used to electrically insulate the signal wire  238  and stylet  230  connections. 
     By moving the sheath  226  forward, the sheath  226  progressively covers more of the winding  224 . Similarly, by moving the sheath  226  rearward, the sheath  226  progressively exposes more of the winding  224 . 
     The impedance of the ablating element  176 ( 6 ) varies with the area of the winding  224  exposed beyond the sheath  226 . As progressively less area of the winding  224  is exposed beyond the sheath  226 , the impedance of the ablating element  176 ( 6 ) becomes progressively greater. Conversely, as progressively more area of the winding  224  is exposed beyond the sheath  226 , the impedance of the ablating element  176 ( 6 ) becomes progressively less. 
     By manipulating the control mechanism  232  on the handle  184 , the physician can thereby remotely adjust the impedance of the ablating element  176 ( 6 ). In this way, the physician gains direct control over the efficiency of the ablation process. 
     By moving the sheath  226  to expose more or less of the winding  224 , the physician also gains direct control over the size of the ablating element  176 ( 6 ) and, thus, over the size of the curvilinear lesion itself. 
     By selecting materials of different stiffness for the sheath  226 , one can also alter the bending characteristics of the winding  224 . 
     As  FIG. 56  shows, when the sheath  226  is made of a non rigid material that less flexible that the underlying core body  222 , movement of the sheath  226  over the core body  222  imparts more total stiffness to the body  222 . In this way, the physician can alter the shape of the curvilinear lesion. The physician can also gain a greater degree of tissue contact with a stiffer flexible body  222 . 
     As  FIG. 57  shows when the sheath  226  is made of a relatively rigid material, movement of the sheath  226  effectively changes the fulcrum point about which the body core  222  curves. The shape of the body  222 , when flexed, therefore changes with movement of the sheath  226 . 
     Further details regarding the concepts of using of a movable sheath to varying the flexing characteristics of a steerable catheter are revealed in copending patent application Ser. No. 08/099,843 filed Jul. 30, 1993, and entitled “Variable Curve Electrophysiology Catheter” and copending patent application Ser. No. 08/100,739 filed Jul. 30, 1993 and entitled “Variable Stiffness Electrophysiology Catheter.” 
     In one preferred construction, the ablating element  176 ( 6 ) is about 1.2 to 2.0 mm in diameter and about 5 cm long. The outer diameter of the catheter body  178  that carries the element  176 ( 6 ) is about 7 French (one French is 0.33 mm). The contact strip  234  measures about 0.05 mm by 0.5 mm by 5 mm. 
       FIG. 58  shows an alternative ablation element  176 ( 6 )′, which can be operated in a bipolar ablation mode. The element  176 ( 6 )′ shares many structural elements with the element  176 ( 6 ) shown in  FIGS. 51  to  54 . The common structural elements are identified with the same reference numbers. 
     Unlike the element  176 ( 6 ) shown in  FIG. 51 , the element  176 ( 6 )′ shown in  FIG. 58  includes an operative electrode  242  at the distal tip  225  of the core body  222 . Also, unlike the element  176 ( 6 ) in  FIG. 51 , the sheath  226  of the element  176 ( 6 ) carries an operative electrode ring  244 . 
     In use, the electrodes  242  and  244  can be maintained at one polarity, while the winding  224  is maintained at the opposite polarity. This arrangement makes operation in a bipolar ablation mode possible. 
     Therefore, along with all the benefits obtained by using the moveable sheath  226  (as already discussed concerning the element  176 ( 6 )), the element  176 ( 6 )′ can also obtain the added benefits that bipolar mode operation provides. 
     The features of the invention are set forth in the following claims.