Patent Publication Number: US-2009240248-A1

Title: Methods and Apparatus for Ablation of Cardiac Tissue

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 60/755,753, filed Dec. 30, 2005, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This application relates to electrophysiology procedures and medical devices therefor. 
     BACKGROUND OF THE INVENTION 
     The human heart is a very complex organ, which relies on both muscle contraction and electrical impulses to function properly. The electrical impulses travel through the heart walls, first through the atria and then the ventricles, causing the corresponding muscle tissue in the atria and ventricles to contract. Thus, the atria contract first, followed by the ventricles. This order is essential for proper functioning of the heart. 
     Over time, the electrical impulses traveling through the heart can begin to travel in improper directions, thereby causing the heart chambers to contract at improper times. Such a condition is generally termed a cardiac arrhythmia, and can take many different forms. When the chambers contract at improper times, the amount of blood pumped by the heart decreases, which can result in premature death of the person. 
     Techniques have been developed which are used to locate cardiac regions responsible for the cardiac arrhythmia, and also to disable the short-circuit function of these areas. According to these techniques, electrical energy is applied to a portion of the heart tissue to ablate that tissue and produce scars which interrupt the reentrant conduction pathways or terminate the focal initiation. The regions to be ablated are usually first determined by endocardial mapping techniques. Mapping typically involves percutaneously introducing a catheter having one or more electrodes into the patient, passing the catheter through a blood vessel (e.g. the femoral vein or artery) and into an endocardial site (e.g., the atrium or ventricle of the heart), and deliberately inducing an arrhythmia so that a continuous, simultaneous recording can be made with a multichannel recorder at each of several different endocardial positions. When an arrythormogenic focus or inappropriate circuit is located, as indicated in the electrocardiogram recording, it is marked by various imaging or localization means so that cardiac arrhythmias emanating from that region can be blocked by ablating tissue. An ablation catheter with one or more electrodes can then transmit electrical energy to the tissue adjacent the electrode to create a lesion in the tissue. One or more suitably positioned lesions will typically create a region of necrotic tissue which serves to disable the propagation of the errant impulse caused by the arrythromogenic focus. Ablation is carried out by applying energy to the catheter electrodes. The ablation energy can be, for example, RF, DC, ultrasound, microwave, or laser radiation. 
     Atrial fibrillation together with atrial flutter are the most common sustained arrhythmias found in clinical practice. 
     Current understanding is that atrial fibrillation is frequently initiated by a focal trigger from the orifice of or within one of the pulmonary veins. Though mapping and ablation of these triggers appears to be curative in patients with paroxysmal atrial fibrillation, there are a number of limitations to ablating focal triggers via mapping and ablating the earliest site of activation with a “point” radiofrequency lesion. One way to circumvent these limitations is to determine precisely the point of earliest activation. Once the point of earliest activation is identified, a lesion can be generated to electrically isolate the trigger with a lesion; firing from within those veins would then be eliminated or unable to reach the body of the atrium, and thus could not trigger atrial fibrillation. 
     Another method to treat focal arrhythmias is to create a continuous, annular lesion around the ostia (i.e., the openings) of either the veins or the arteries leading to or from the atria thus “corralling” the signals emanating from any points distal to the annular lesion. Conventional techniques include applying multiple point sources around the ostia in an effort to create such a continuous lesion. Such a technique is relatively involved, and requires significant skill and attention from the clinician performing the procedures. 
     Another source of arrhythmias may be from reentrant circuits in the myocardium itself. Such circuits may not necessarily be associated with vessel ostia, but may be interrupted by means of ablating tissue either within the circuit or circumscribing the region of the circuit. It should be noted that a complete ‘fence’ around a circuit or tissue region is not always required in order to block the propagation of the arrhythmia; in many cases simply increasing the propagation path length for a signal may be sufficient. Conventional means for establishing such lesion ‘fences’ include a multiplicity of point-by-point lesions, dragging a single electrode across tissue while delivering energy, or creating an enormous lesion intended to inactivate a substantive volume of myocardial tissue. 
     SUMMARY OF THE INVENTION 
     One embodiment of the invention is directed to a method of treating a cardiac arrhythmia. The method comprises forming a first lesion about a source of an electrical signal in the heart, the first lesion having an open first perimeter, and forming a second lesion about the source of the electrical signal in the heart. The second lesion has an open second perimeter and is located closer to the source of the electrical signal than the first lesion. The first lesion is discontinuous from the second lesion, and at least the first and second lesions together form a closed, at least substantially complete conduction block. 
     Another embodiment of the invention is directed to a catheter comprising a shaft portion having a central longitudinal axis; and a conductive member coupled to the shaft portion, the conductive member formed of a plurality of filaments. The conductive member comprises an insulated portion and at least first and second uninsulated portions. The first uninsulated portion has an open first perimeter and the second uninsulated portion has an open second perimeter and is located closer to the central longitudinal axis of the shaft. Each uninsulated portion of the at least the first and second uninsulated portions spans a respective angle, a sum of the respective angles spanned by each uninsulated portion of the at least the first and second uninsulated portions exceeds 360°, and at least the first and second uninsulated portions collectively span an angle of 360° on the conductive member. 
     A further embodiment of the invention is directed to a catheter comprising a shaft portion having a central longitudinal axis; and means, coupled to the shaft portion, for simultaneously forming first and second lesions about a source of an electrical signal in the heart. The first lesion has an open first perimeter and the second lesion has an open second perimeter and is located closer to the source of the electrical signal than the first lesion. The first lesion is discontinuous from the second lesion, and at least the first and second lesions together form a closed, at least substantially complete conduction block. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are incorporated herein by reference and in which like elements have been given like references characters, 
         FIG. 1  illustrates an overview of a mapping and ablation catheter system in accordance with the present invention; 
         FIGS. 2 and 3  illustrate further details of the catheter illustrated in  FIG. 1 ; 
         FIGS. 4-7  illustrate further details of the braided conductive member illustrated in  FIGS. 2 and 3 ; 
         FIGS. 8-11  illustrate, among other things, temperature sensing in the present invention; 
         FIGS. 12-13  illustrate further details of the steering capabilities of the present invention; 
         FIGS. 14-17  illustrate further embodiments of the braided conductive member; 
         FIGS. 18-19  illustrate the use of irrigation in connection with the present invention; 
         FIGS. 20A-20E  illustrate the use of shrouds in the present invention; 
         FIG. 21  illustrates a guiding sheath that may be used in connection with the present invention; 
         FIGS. 22-24  illustrate methods of using the present invention; 
         FIG. 25  is an exploded view of a handle that may be used with the catheter system of  FIG. 1  according to another embodiment of the invention; 
         FIG. 26  is a schematic cross sectional view of a slide actuator for the handle of  FIG. 25  in a neutral or unloaded state; 
         FIG. 27  is a schematic cross sectional view of a slide actuator for the handle of  FIG. 25  in a deployed or loaded state; 
         FIG. 28  is a cross sectional end view of the slide actuator of  FIG. 26  taken along line  28 - 28  in  FIG. 26 ; 
         FIG. 29  is an exploded perspective view of the left section of the handle of  FIG. 25 ; 
         FIG. 30  is a schematic cross sectional view of a thumbwheel actuator for the handle of  FIG. 25  in a neutral or unloaded state; 
         FIG. 31  is a schematic cross sectional view of the thumbwheel actuator for the handle of  FIG. 25  in a deployed or loaded state; 
         FIGS. 32-33  illustrate aspects of a handle configuration according to another embodiment of the invention; 
         FIGS. 34-40  illustrate aspects of a catheter having a retractable distal tip portion; 
         FIGS. 41-42  illustrate a modified version of the catheter illustrated in  FIGS. 34-40  having a lumen for the delivery of fluids or devices; and 
         FIG. 43  illustrates a first embodiment of a lesion pattern that may be formed to create a complete or substantially complete conduction block; 
         FIG. 44  illustrates an exemplary implementation of a braided conductive member that that may be used to form the lesion pattern of  FIG. 43 ; 
         FIG. 45  illustrates another embodiment of a lesion pattern that may be formed to create a complete or substantially complete conduction block; 
         FIG. 46  illustrates an exemplary implementation of a braided conductive member that that may be used to form the lesion pattern of  FIG. 45 ; 
         FIG. 47  illustrates a further embodiment of a lesion pattern that may be formed to create a complete or substantially complete conduction block; 
         FIG. 48  illustrates an exemplary implementation of a braided conductive member that that may be used to form the lesion pattern of  FIG. 48 ; and 
         FIG. 49  illustrates a side view of a catheter including the braided conductive member of  FIG. 44 . 
     
    
    
     DETAILED DESCRIPTION 
     System Overview 
     Reference is now made to  FIG. 1 , which figure illustrates an overview of a mapping and ablation catheter system in accordance with the present invention. The system includes a catheter  10  having a shaft portion  12 , a control handle  14 , and a connector portion  16 . A controller  8  is connected to connector portion  16  via cable  6 . Ablation energy generator  4  may be connected to controller  8  via cable  3 . A recording device  2  may be connected to controller  8  via cable  1 . When used in an ablation application, controller  8  is used to control ablation energy provided by ablation energy generator  4  to catheter  10 . When used in a mapping application, controller  8  is used to process signals coming from catheter  10  and to provide these signals to recording device  2 . Although illustrated as separate devices, recording device  2 , ablation energy generator  4 , and controller  8  could be incorporated into a single device. In one embodiment, controller  8  may be a QUADRAPULSE RF CONTROLLER™ device available from CR Bard, Inc., Murray Hill, N.J. 
     In this description, various aspects and features of the present invention will be described. The various features of the invention are discussed separately for clarity. One skilled in the art will appreciate that the features may be selectively combined in a device depending upon the particular application. Furthermore, any of the various features may be incorporated in a catheter and associated method of use for either mapping or ablation procedures. 
     Catheter Overview 
     Reference is now made to  FIGS. 2-7 , which figures illustrate one embodiment of the present invention. The present invention generally includes a catheter and method of its use for mapping and ablation in electrophysiology procedures. Catheter  10  includes a shaft portion  12 , a control handle  14 , and a connector portion  16 . When used in mapping applications, connector portion  16  is used to allow signal wires running from the electrodes at the distal portion of the catheter to be connected to a device for processing the electrical signals, such as a recording device. 
     Catheter  10  may be a steerable device.  FIG. 2  illustrates the distal tip portion  18  being deflected by the mechanism contained within control handle  14 . Control handle  14  may include a rotatable thumbwheel  21  and/or a slide actuator  5  which can be used by a user to deflect the distal end of the catheter. The thumbwheel (or any other suitable actuating device) is connected to one or more pull wires which extend through shaft portion  12  and are connected to the distal end  18  of the catheter at an off-axis location, whereby tension applied to one or more of the pull wires causes the distal portion of the catheter to curve in a predetermined direction or directions U.S. Pat. Nos. 5,383,852, 5,462,527, and 5,611,777, which are hereby incorporated by reference, illustrate various embodiments of control handle  14  that may be used for steering catheter  10 . 
     Shaft portion  12  includes a distal tip portion  18 , a first stop  20  and an inner member  22  connected to the first stop portion  20 . Inner member  22  may be a tubular member. Concentrically disposed about inner member  22  is a first sheath  24  and a second sheath  26 . Also concentrically disposed about inner member  22  is a braided conductive member  28  anchored at respective ends  30  and  32  to the first sheath  24  and the second sheath  26 , respectively. 
     In operation, advancing the second sheath  26  distally over inner member  22  causes the first sheath  24  to contact stop  20 . Further distal advancement of the second sheath  26  over inner member  22  causes the braided conductive member  28  to expand radially to assume various diameters and/or a conical shape.  FIG. 3  illustrates braided conductive member  28  in an unexpanded (collapsed or “undeployed”) configuration.  FIGS. 2 and 4  illustrate braided conductive member  28  in a partially expanded condition.  FIG. 1  illustrates braided conductive member  28  radially expanded (“deployed”) to form a disk. 
     Alternatively, braided conductive member  28  can be radially expanded by moving inner member  22  proximally with respect to the second sheath  26 . 
     As another alternative, inner member  22  and distal tip portion  18  may be the same shaft and stop  20  may be removed. In this configuration, sheath  24  moves over the shaft in response to, for example, a mandrel inside shaft  22  and attached to sheath  24  in the manner described, for example, in U.S. Pat. No. 6,178,354, which is incorporated herein by reference. 
     As illustrated particularly in  FIGS. 4 and 5  a third sheath  32  may be provided. The third sheath serves to protect shaft portion  12  and in particular braided conductive member  28  during manipulation through the patient&#39;s vasculature. In addition, the third sheath  32  shields braided conductive member  28  from the patient&#39;s tissue in the event ablation energy is prematurely delivered to the braided conductive member  28 . 
     The respective sheaths  24 ,  26 , and  32  can be advanced and retracted over the inner member  22 , which may be a tubular member, in many different manners. Control handle  14  may be used. U.S. Pat. Nos. 5,383,852, 5,462,527, and 5,611,777 illustrate examples of control handles that can control sheaths  24 ,  26 , and  32 . As described in these incorporated by reference patents, control handle  14  may include a slide actuator which is axially displaceable relative to the handle. The slide actuator may be connected to one of the sheaths, for example, the second sheath  26  to control the movement of the sheath  26  relative to inner member  22 , to drive braided conductive member  28  between respective collapsed and deployed positions, as previously described. Control handle  14  may also include a second slide actuator or other mechanism coupled to the retractable outer sheath  32  to selectively retract the sheath in a proximal direction with respect to the inner member  22 . 
     Braided conductive member  28  is, in one embodiment of the invention, a plurality of interlaced, electrically conductive filaments  34 . Braided conductive member  28  may be a wire mesh. The filaments are flexible and capable of being expanded radially outwardly from inner member  22 . The filaments  34  are preferably formed of metallic elements having relatively small cross sectional diameters, such that the filaments can be expanded radially outwardly. The filaments may be round, having a dimension on the order of about 0.001-0.030 inches in diameter. Alternatively, the filaments may be flat, having a thickness on the order of about 0.001-0.030 inches, and a width on the order of about 0.001-0.030 inches. The filaments may be formed of Nitinol type wire. Alternatively, the filaments may include non metallic elements woven with metallic elements, with the non metallic elements providing support to or separation of the metallic elements. A multiplicity of individual filaments  34  may be provided in braided conductive member  28 , for example up to 300 or more filaments. 
     Each of the filaments  34  can be electrically isolated from each other by an insulation coating. This insulation coating may be, for example, a polyamide type material. A portion of the insulation on the outer circumferential surface  60  of braided conductive member  28  is removed. This allows each of the filaments  34  to form an isolated electrode, not an electrical contact with any other filament, that may be used for mapping and ablation. Alternatively, specific filaments may be permitted to contact each other to form a preselected grouping. 
     Each of the filaments  34  is helically wound under compression about inner member  22 . As a result of this helical construction, upon radial expansion of braided conductive member  28 , the portions of filaments  34  that have had the insulation stripped away do not contact adjacent filaments and thus, each filament  34  remains electrically isolated from every other filament.  FIG. 6 , in particular, illustrates how the insulation may be removed from individual filaments  34  while still providing isolation between and among the filaments. As illustrated in  FIG. 6 , regions  50  illustrate regions, on the outer circumferential surface  60  of braided conductive member  28 , where the insulation has been removed from individual filaments  34 . In one embodiment of the invention, the insulation may be removed from up to one half of the outer facing circumference of each of the individual filaments  34  while still retaining electrical isolation between each of the filaments  34 . 
     The insulation on each of the filaments  34  that comprise braided conductive member  28  may be removed about the outer circumferential surface  60  of braided conductive member  28  in various ways. For example, one or more circumferential bands may be created along the length of braided conductive member  28 . Alternatively, individual sectors or quadrants only may have their insulation removed about the circumference of braided conductive member  28 . Alternatively, only selected filaments  34  within braided conductive member  28  may have their circumferentially facing insulation removed. Thus, an almost limitless number of configurations of insulation removal about the outer circumferential surface  60  of braided conductive member  28  can be provided depending upon the mapping and ablation characteristics and techniques that a clinician desires. 
     The insulation on each of the filaments  34  may be removed at the outer circumferential surface  60  of braided conductive member  28  in a variety of ways as long as the insulation is maintained between filaments  34  so that filaments  34  remain electrically isolated from each other. 
     The insulation can be removed from the filaments  34  in a variety of ways to create the stripped portions  50  on braided conductive member  28 . For example, mechanical means such as ablation or scraping may be used. In addition, a water jet, chemical means, or thermal radiation means may be used to remove the insulation. 
     In one example of insulation removal, braided conductive member  28  may be rotated about inner member  22 , and a thermal radiation source such as a laser may be used to direct radiation at a particular point along the length of braided conductive member  28 . As the braided conductive member  28  is rotated and the thermal radiation source generates heat, the insulation is burned off the particular region. 
     Insulation removal may also be accomplished by masking selected portions of braided conductive member  28 . A mask, such as a metal tube may be placed over braided conducive member  28 . Alternatively, braided conductive member  28  may be wrapped in foil or covered with some type of photoresist. The mask is then removed in the areas in which insulation removal is desired by, for example, cutting away the mask, slicing the foil, or removing the photoresist. Alternatively, a mask can be provided that has a predetermined insulation removal pattern. For example, a metal tube having cutouts that, when the metal tube is placed over braided conductive member  28 , exposes areas where insulation is to be removed. 
       FIG. 6  illustrates how thermal radiation  52  may be applied to the outer circumferential surface  56  of a respective filament  34  that defines the outer circumferential surface  60  of braided conductive member  28 . As thermal radiation  52  is applied, the insulation  54  is burned off or removed from the outer circumference  56  of wire  34  to create a region  58  about the circumference  56  of filament  34  that has no insulation. 
     The insulation  54  can also be removed in a preferential manner so that a particular portion of the circumferential surface  56  of a filament  34  is exposed. Thus, when braided conductive member  28  is radially expanded, the stripped portions of filaments may preferentially face the intended direction of mapping or ablation. 
     With the insulation removed from the portions of filaments  34  on the outer circumferential surface  60  of braided conductive member  28 , a plurality of individual mapping and ablation channels can be created. A wire runs from each of the filaments  34  within catheter shaft  12  and control handle  14  to connector portion  16 . A multiplexer or switch box may be connected to the conductors so that each filament  34  may be controlled individually. This function may be incorporated into controller  8 . A number of filaments  34  may be grouped together for mapping and ablation. Alternatively, each individual filament  34  can be used as a separate mapping channel for mapping individual electrical activity within a blood vessel at a single point. Using a switch box or multiplexer to configure the signals being received by filaments  34  or ablation energy sent to filaments  34  results in an infinite number of possible combinations of filaments for detecting electrical activity during mapping procedures and for applying energy during an ablation procedure. 
     By controlling the amount of insulation that is removed from the filaments  34  that comprise braided conductive member  28 , the surface area of the braid that is in contact with a blood vessel wall can also be controlled. This in turn will allow control of the impedance presented to an ablation energy generator, for example, generator  4 . In addition, selectively removing the insulation can provide a predetermined or controllable profile of the ablation energy delivered to the tissue. 
     The above description illustrates how insulation may be removed from a filaments  34 . Alternatively, the same features and advantages can be achieved by adding insulation to filaments  34 . For example, filaments  34  may be bare wire and insulation can be added to them. 
     Individual control of the electrical signals received from filaments  34  allows catheter  10  to be used for bipolar (differential or between filament) type mapping as well as unipolar (one filament with respect to a reference) type mapping. 
     Catheter  10  may also have, as illustrated in  FIGS. 2 and 3 , a reference electrode  13  mounted on shaft  12  so that reference electrode  13  is located outside the heart during unipolar mapping operations. 
     Radiopaque markers can also be provided for use in electrode orientation and identification. 
     One skilled in the art will appreciate all of the insulation can be removed from filaments  34  to create a large ablation electrode. 
     Although a complete catheter steerable structure has been illustrated, the invention can also be adapted so that inner tubular member  22  is a catheter shaft, guide wire, or a hollow tubular structure for introduction of saline, contrast media, heparin or other medicines, or introduction of guidewires, or the like. 
     Temperature Sensing 
     A temperature sensor or sensors, such as, but not limited to, one or more thermocouples may be attached to braided conductive member  28  for temperature sensing during ablation procedures. A plurality of thermocouples may also be woven into the braided conductive member  28 . An individual temperature sensor could be provided for each of the filaments  34  that comprise braided conductive member  28 . Alternatively, braided conductive member  28  can be constructed of one or more temperature sensors themselves. 
       FIG. 8  illustrates braided conductive member  28  in its fully expanded or deployed configuration. Braided conductive member  28  forms a disk when fully expanded. In the embodiment illustrated in  FIG. 8 , there are sixteen filaments  34  that make up braided conductive member  28 . 
     Temperature monitoring or control can be incorporated into braided conductive member  28 , for example, by placing temperature sensors (such as thermocouples, thermistors, etc.) on the expanded braided conductive member  28  such that they are located on the distally facing ablative ring formed when braided conductive member  28  is in its fully expanded configuration. “Temperature monitoring” refers to temperature reporting and display for physician interaction. “Temperature control” refers to the capability of adding an algorithm in a feedback loop to titrate power based on temperature readings from the temperature sensors disposed on braided conductive member  28 . Temperature sensors can provide a means of temperature control provided the segment of the ablative ring associated with each sensor is independently controllable (e.g., electrically isolated from other regions of the mesh). For example, control can be achieved by dividing the ablative structure into electrically independent sectors, each with a temperature sensor, or alternatively, each with a mechanism to measure impedance in order to facilitate power titration. The ablative structure may be divided into electrically independent sectors so as to provide zone control. The provision of such sectors can be used to provide power control to various sections of braided conductive member  28 . 
     As illustrated in  FIG. 8 , four temperature sensors  70  are provided on braided conductive member  28 . As noted previously, since the individual filaments  34  in braided conductive member  28  are insulated from each other, a number of independent sectors may be provided. A sector may include one or more filaments  34 . During ablation procedures, energy can be applied to one or more of the filaments  34  in any combination desired depending upon the goals of the ablation procedure. A temperature sensor could be provided on each filament  34  of braided conductive member  28  or shared among one or more filaments. In mapping applications, one or more of the filaments  34  can be grouped together for purposes of measuring electrical activity. These sectoring functions can be provided in controller  8 . 
       FIG. 10  illustrates a side view of braided conductive member  28  including temperature sensors  70 . As shown in  FIG. 10 , temperature sensors  70  emerge from four holes  72 . Each hole  72  is disposed in one quadrant of anchor  74 . The temperature sensors  70  are bonded to the outside edge  76  of braided conductive member  28 . Temperature sensors  70  may be isolated by a small piece of polyimide tubing  73  around them and then bonded in place to the filaments. The temperature sensors  7  may be woven and twisted into braided conductive member  28  or they can be bonded on a side-by-side or parallel manner with the filaments  34 . 
     There are several methods of implementing electrically independent sectors. In one embodiment, the wires are preferably stripped of their insulative coating in the region forming the ablative ring (when expanded). However, sufficient insulation may be left on the wires in order to prevent interconnection when in the expanded state. Alternatively, adjacent mesh wires can be permitted to touch in their stripped region, but can be separated into groups by fully insulated (unstripped) wires imposed, for example, every 3 or 5 wires apart (the number of wires does not limit this invention), thus forming sectors of independently controllable zones. Each zone can have its own temperature sensor. The wires can be “bundled” (or independently attached) to independent outputs of an ablation energy generator. RF energy can then be titrated in its application to each zone by switching power on and off (and applying power to other zones during the ‘off period’) or by modulating voltage or current to the zone (in the case of independent controllers). In either case, the temperature inputs from the temperature sensors can be used in a standard feedback algorithm to control the power delivery. 
     Alternatively, as illustrated in  FIG. 10A , braided conductive member  28  may be used to support a ribbon-like structure which is separated into discrete sectors. As shown in  FIG. 10A , the ribbon-like structure  81  may be, for example, a pleated copper flat wire that, as braided conductive member  28  expands, unfolds into an annular ring. Each of the wires  83   a - 83   d  lie in the same plane. Although four wires are illustrated in  FIG. 10A , structure  81  may include any number of wires depending upon the application and desired performance. Each of wires  83   a - 83   d  is insulated. Insulation may then be removed from each wire to create different sectors  85   a - 85   d . Alternatively, each of wires  83   a - 83   d  may be uninsulated and insulation may be added to create different sectors. The different sectors provide an ablative zone comprised of independently controllable wires  83   a - 83   d . Temperature sensors  70  may be mounted on the individual wires, and filaments  34  may be connected to respective wires  83   a - 83   d  to provide independent control of energy to each individual sector. One skilled in the art will appreciate that each of wires  83   a - 83   d  can have multiple sectors formed by removing insulation in various locations and that numerous combinations of sectors  85   a - 85   d  and wires  83   a - 83   d  forming ribbon-like structure  81  can be obtained. 
       FIGS. 11A-D  illustrate further exemplary configurations that include a temperature sensor within braided conductive member  28 . In each configuration, the temperature sensor is formed using one thermocouple wire  75  and one filament  34  of braided conductive member  28 , which are coupled via a junction  77  to form a thermocouple  71 . Advantageously, since only one dedicated thermocouple wire is required to form the thermocouple  71 , the size of a braided conductive member  28  in  FIGS. 11A-C  may be smaller than it would be if a pair of dedicated thermocouple wires were required to form each thermocouple  71 . In addition, the filament  34  that is used to form a portion of the thermocouple  71  may be used for ablation and/or mapping purposes while signals indicative of temperature are supplied by the thermocouple  71 . 
     In the configurations described in connection with  FIGS. 11B-D , the temperature sensors may be formed on an outward-facing or exterior portion of the braided conductive member  28 , or an inward-facing or interior portion of the braided conductive member  28 .  FIG. 11A  illustrates an exterior portion  84   a  and an interior portion  84   b  of a braided conductive member  28 , which is concentrically disposed about inner member  22  and anchored to the first sheath  24  and second sheath  26 , respectively. It should be appreciated that temperature sensors disposed on an exterior portion  84   a  of the braided conductive member  28  may be formed anywhere along the length or circumference of the braided conductive member  28  on an exterior portion thereof. Similarly, temperature sensors disposed on an interior portion  84   b  of the braided conductive member  28  may be formed anywhere along the length or circumference of the braided conductive member  28  on an interior portion thereof. 
       FIG. 11B  illustrates an exterior portion of the braided conductive member  28 , while  FIG. 11C  illustrates a interior portion of the braided conductive member  28 . According to one implementation of the thermocouple  71 , the junction  77  may be formed on an exterior portion of the braided conductive member  28 , as shown in  FIG. 11B . Thus, the junction  77  may be formed on a portion of the braided conductive member  28  that may come into contact with tissue during an electrophysiology procedure. According to another implementation of the thermocouple  71 , the junction  77  may be formed on an interior portion of the braided conductive member  28 , as shown in  FIG. 11C . Thus, the junction  77  may be formed on a surface of the braided conductive member  28  that does not come into contact with tissue during an electrophysiology procedure. In each case, the junction  77  may be formed so as to avoid interference with filaments of the braided conductive member  28  during deployment of the braided conductive member  28 . 
       FIG. 11D  illustrates an configuration in which the filament  34  and the thermocouple wire  75  that form thermocouple  71  are coupled together via a sheath  79  to form a unitary strand that may be woven into braided conductive member  28 . Junction  77  is formed on a portion of the filament  34  and the thermocouple wire  75  that is not covered by sheath  79 , and where insulation of the filament  34  and the thermocouple wire  75  has been removed. Thus, the filament  34  and the thermocouple wire  75  are in electrical contact at the location of junction  77 . It should be appreciated that while the sheath  79  is shown as removed around an entire circumference thereof at the location of junction  77 , alternatively, only a portion of the circumference of the sheath  79  may be removed. Thus, the junction  77  may be formed on an exterior-facing portion of the braided conductive member  28 , an interior-facing portion of the braided conductive member  28 , or both. The configuration of  FIG. 11D  secures the thermocouple wire  75  from movement during deployment of the braided conductive member. In addition, by coupling the filament  34  and the thermocouple wire  75  along their length, the size of the thermocouple  71  may be minimized. 
     It should be appreciated that while sheath  79  that couples filament  34  and thermocouple wire  75  is shown as having a generally tubular shape, many other implementations are possible. For example, the sheath may be constructed as tubes that are connected along adjacent surfaces thereof such that a cross-section of the tube would have a figure-eight configuration. Other exemplary alternative configurations are a spiral configuration and an oval tubular configuration. It should be appreciated that the sheath need not be continuous and may be perforated or cover only portions of the filament  34  and the thermocouple wire  75 . It should further be appreciated that the sheath  79  may have a solid core with the filament  34  and thermocouple wire  75  molded within the sheath  79 . 
     Thermocouple wire  75  and filament  34  may be formed of different electrically conductive materials such that an electric current will flow between the wires when the thermocouple wire  75  and filament  34  are at different temperatures. In one example, thermocouple wire  75  may be formed of constantan and filament  34  may be formed of copper-beryllium, with the beryllium comprising approximately 2% of the filament composition. However, it should be appreciated that a number of alternative materials may be used for thermocouple wire  75  and filament  34 . 
     Junction  77  may be formed on an uninsulated portion of filament  34  and thermocouple wire  75 . In one example, filament  34  and thermocouple wire  77  are at least partially insulated, but are uninsulated where the filament  34  and thermocouple wire  75  contact junction  77 . Thus, if junction  77  is formed on an exterior portion of the braided conductive member  28 , the portions of filament  34  and thermocouple wire  75  that face the interior of braided conductive member  28  and are opposite junction  77  may be insulated. Correspondingly, if junction  77  is formed on an interior portion of the braided conductive member  28 , the portions of filament  34  and thermocouple wire  75  that face the exterior of braided conductive member  28  and are opposite junction  77  may be insulated. 
     Junction  77  may be formed of a material that is electrically conductive and capable of forming a mechanical bond between the thermocouple wire  75  and filament  34 . According to one example, the junction  77  is formed of a metal such as silver solder. According to another example, the junction  77  is formed of a material resistant to corrosion. If it is not resistant to corrosion, a junction may corrode when it is exposed to blood or another electrolyte. This corrosion could weaken the mechanical strength of the bond and serve as a source of electrical noise that can interfere with electrogram signal quality. According to one example, an electrically conductive epoxy such as silver epoxy, which is resistant to corrosion, may be used to form a junction  77 . 
     It should be appreciated that although the above features of an epoxy junction and a single dedicated thermocouple wire may be advantageously employed together, these features may also be employed separately. It should further be appreciated that although only a single temperature sensor is shown on braided conductive member  28  in  FIGS. 11B-D , a plurality of temperature sensors may be included on the braided conductive member  28  as described in the foregoing discussion of temperature sensing. The features described in connection with  FIGS. 11B-D  may be combined with other catheter features described herein to provide temperature sensing capabilities to a catheter. 
     Steering 
     Reference is now made to  FIGS. 12-13  which illustrate aspects of the steering capabilities of the present invention. As illustrated in  FIGS. 1-2 , catheter  10  is capable of being steered using control handle  14 . In particular,  FIG. 1  illustrates steering where the steering pivot or knuckle is disposed on catheter shaft  12  in a region that is distal to the braided conductive member  28 . 
       FIG. 12A  illustrates catheter  10  wherein the pivot point or steering knuckle is disposed proximal to braided conductive member  28 . 
       FIG. 12B  illustrates catheter  10  having the capability of providing steering knuckles both proximal and distal to braided conductive member  28 . 
       FIGS. 1-2 , and  12 A- 12 B illustrate two dimensional or single plane type steering. The catheter of the present invention can also be used in connection with a three dimensional steering mechanism. For example, using the control handle in the incorporated by reference &#39;852 patent, the catheter can be manipulated into a three-dimensional “lasso-like” shape, particularly at the distal end of the catheter. As shown in  FIG. 13 , the catheter can have a primary curve  80  in one plane and then a second curve  82  in another plane at an angle to the first plane. With this configuration, the catheter can provide increased access to difficult to reach anatomical structures. For example, a target site for a mapping or ablation operation may be internal to a blood vessel. Thus, the increased steering capability can allow easier access into the target blood vessel. In addition, the additional dimension of steering can allow for better placement of braided conductive member  28  during an ablation or mapping procedure. Catheter  10  can be inserted into a site using the steering capabilities provided by primary curve  80 . Thereafter, using the secondary curve  82 , braided conductive member  28  can be tilted into another plane for better orientation or contact with the target site. 
     Conductive Member Configurations and Materials 
     Reference is now made to  FIGS. 14-17  which figures illustrate other configurations of braided conductive member  28 . As has been described above and will be described in more detail, braided conductive member  28  can include from one to 300 or more filaments. The filaments may vary from very fine wires having small diameters or cross-sectional areas to large wires having relatively large diameters or cross-sectional areas. 
       FIG. 14  illustrates the use of more than one braided conductive member  28  as the distal end of catheter  10 . As shown in  FIG. 14 , three braided conductive members  28 A,  28 B, and  28 C are provided at the distal end of catheter  10 . Braided conductive members  28 A,  28 B, and  29 C may be, in their expanded conditions, the same size or different sizes. Each of the braided conductive members  28 A,  28 B, and  28 C can be expanded or contracted independently in the manner illustrated in  FIGS. 1-4  via independent control shafts  26 A,  26 B, and  26 C. The use of multiple braided conductive members provides several advantages. Rather than having to estimate or guess as to the size of the blood vessel prior to starting a mapping or ablation procedure, if braided conductive members  28 A,  28 B, and  28 C are of different expanded diameters, than sizing can be done in vivo during a procedure. In addition, one of the braided conductive members can be used for ablation and another of the braided conductive members can be used for mapping. This allows for quickly checking the effectiveness of an ablation procedure. 
     Reference is now made to  FIGS. 15A and 15B , which figures illustrate other shapes of braided conductive member  28 . As described up to this point, braided conductive member  28  is generally symmetrical and coaxial with respect to catheter shaft  12 . However, certain anatomical structures may have complex three-dimensional shapes that are not easily approximated by a geometrically symmetrical mapping or ablation structure. One example of this type of structure occurs at the CS ostium. To successfully contact these types of anatomical structures, braided conductive member  28  can be “preformed” to a close approximation of that anatomy, and yet still be flexible enough to adapt to variations found in specific patients. Alternatively, braided conductive member  28  can be “preformed” to a close approximation of that anatomy, and be of sufficient strength (as by choice of materials, configuration, etc.) to force the tissue to conform to variations found in specific patients. For example  FIG. 15A  illustrates braided conductive member  28  disposed about shaft  12  in an off-center or non concentric manner. In addition, braided conductive member  28  may also be constructed so that the parameter of the braided conductive member in its expanded configuration has a non-circular edge so as to improve tissue contact around the parameter of the braided conductive member.  FIG. 15B  illustrates an example of this type of configuration where the braided conductive member  28  is both off center or non concentric with respect to catheter shaft  12  and also, in its deployed or expanded configuration, has an asymmetric shape. The eccentricity of braided conductive member  28  with respect to the shaft and the asymmetric deployed configurations can be produced by providing additional structural supports in braided conductive member  28 , for example, such as by adding nitinol, ribbon wire, and so on. In addition, varying the winding pitch or individual filament size or placement or deforming selective filaments in braided conductive member  28  or any other means known to those skilled in the art may be used. 
       FIGS. 16A-16C  illustrate another configuration of braided conductive member  28  and catheter  10 . As illustrated in  FIGS. 16A-16C , the distal tip section of catheter  10  has been removed and braided conductive member  28  is disposed at the distal end of catheter  10 . One end of braided conductive member  28  is anchored to catheter shaft  12  using an anchor band  90  that clamps the end  32  of braided conductive member  28  to catheter shaft  12 . The other end of braided conductive member  28  is clamped to an activating shaft such as shaft  26  using another anchor band  92 .  FIG. 16A  illustrates braided conductive member  28  in its undeployed configuration. As shaft  26  is moved distally, braided conductive member  28  emerges or everts from shaft  12 . As shown in  FIG. 16B , braided conductive member  28  has reached its fully deployed diameter and an annular tissue contact zone  29  can be placed against an ostium or other anatomical structure. As illustrated in  FIG. 16C , further distal movement of shaft  26  can be used to create a concentric locating region  94  that can help to provide for concentric placement within an ostium of a pulmonary vein, for example. Concentric locating region  94  may be formed by selective variations in the winding density of filaments  34  in braided conductive member  28 , preferential predeformation of the filaments, additional eversion of braided conductive member  28  from shaft  12 , or by other means known to those skilled in the art. 
     Reference is now made to  FIG. 17 , which figure illustrates a further embodiment of braided conductive member  28 . As illustrated in  FIG. 17 , braided conductive member  28  is composed of one or several large wires  96  rather than a multiplicity of smaller diameter wires. The wire or wires can be moved between the expanded and unexpanded positions in the same manner as illustrated in  FIG. 1 . In addition, a region  98  may be provided in which the insulation has been removed for mapping or ablation procedures. The single wire or “corkscrew” configuration provides several advantages. First, the wire or wires do not cross each other and therefore there is only a single winding direction required for manufacture. In addition, the risk of thrombogenicity may be reduced because there is a smaller area of the blood vessel being blocked. In addition, the connections between the ends of the large wire and the control shafts may be simplified. 
     The catheter  10  of the present invention can be coated with a number of coatings that can enhance the operating properties of braided conductive member  28 . The coatings can be applied by any of a number of techniques and the coatings may include a wide range of polymers and other materials. 
     Braided conductive member  28  can be coated to reduce its coefficient of friction, thus reducing the possibility of thrombi adhesion to the braided conductive member as well as the possibility of vascular or atrial damage. These coatings can be combined with the insulation on the filaments that make up braided conductive member  28 , these coatings can be included in the insulation itself, or the coatings can be applied on top of the insulation. Examples of coating materials that can be used to improve the lubricity of the catheter include PD slick available from Phelps Dodge Corporation, Ag, Tin, BN. These materials can be applied by an ion beam assisted deposition (“IBAD”) technique developed by, for example, Amp Corporation. 
     Braided conductive member  28  can also be coated to increase or decrease its thermal conduction which can improve the safety or efficacy of the braided conductive member  28 . This may be achieved by incorporating thermally conductive elements into the electrical insulation of the filaments that make up braided conductive member  28  or as an added coating to the assembly. Alternatively, thermally insulating elements may be incorporated into the electrical insulation of the filaments that make up braided conductive member  28  or added as a coating to the assembly. Polymer mixing, IBAD, or similar technology could be used to add Ag, Pt, Pd, Au, Ir, Cobalt, and others into the insulation or to coat braided conductive member  28 . 
     Radioopaque coatings or markers can also be used to provide a reference point for orientation of braided conductive member  28  when viewed during fluoroscopic imaging. The materials that provide radiopacity including, for example, Au, Pt, Ir, and other known to those skilled in the art. These materials may be incorporated and used as coatings as described above. 
     Antithrombogenic coatings, such as heparin and BH, can also be applied to braided conductive member  28  to reduce thrombogenicity to prevent blood aggregation on braided conductive member  28 . These coatings can be applied by dipping or spraying, for example. 
     As noted above, the filament  34  of braided conductive member  28  may be constructed of metal wire materials. These materials may be, for example, MP35N, nitinol, or stainless steel. Filaments  34  may also be composites of these materials in combination with a core of another material such as silver or platinum. The combination of a highly conductive electrical core material with another material forming the shell of the wire allows the mechanical properties of the shell material to be combined with the electrical conductivity of the core material to achieve better and/or selectable performance. The choice and percentage of core material used in combination with the choice and percentage of shell material used can be selected based on the desired performance characteristics and mechanical/electrical properties desired for a particular application. According to one implementation, the core material and shell material may be covalently bonded together. 
     Irrigation 
     It is known that for a given electrode side and tissue contact area, the size of a lesion created by radiofrequency (RF) energy is a function of the RF power level and the exposure time. At higher powers, however, the exposure time can be limited by an increase in impedance that occurs when the temperature at the electrode-tissue interface approaches a 100° C. One way of maintaining the temperature less than or equal to this limit is to irrigate the ablation electrode with saline to provide convective cooling so as to control the electrode-tissue interface temperature and thereby prevent an increase in impedance. Accordingly, irrigation of braided conductive member  28  and the tissue site at which a lesion is to be created can be provided in the present invention.  FIG. 18  illustrates the use of an irrigation manifold within braided conductive member  28 . An irrigation manifold  100  is disposed along shaft  22  inside braided conductive member  28 . Irrigation manifold  100  may be one or more polyimid tubes. Within braided conductive member  28 , the irrigation manifold splits into a number of smaller tubes  102  that are woven into braided conductive member  28  along a respective filament  34 . A series of holes  104  may be provided in each of the tubes  102 . These holes can be oriented in any number of ways to target a specific site or portion of braided conductive member  28  for irrigation. Irrigation manifold  100  runs through catheter shaft  12  and may be connected to an irrigation delivery device outside the patient used to inject an irrigation fluid, such as saline, for example, such as during an ablation procedure. 
     The irrigation system can also be used to deliver a contrast fluid for verifying location or changes in vessel diameter. For example, a contrast medium may be perfused prior to ablation and then after an ablation procedure to verify that there have been no changes in the blood vessel diameter. The contrast medium can also be used during mapping procedures to verify placement of braided conductive member  28 . In either ablation or mapping procedures, antithrombogenic fluids, such as heparin can also be perfused to reduce thrombogenicity. 
       FIG. 19  illustrates another way of providing perfusion/irrigation in catheter  10 . As illustrated in  FIG. 19 , the filaments  34  that comprise braided conductive member  28  are composed of a composite wire  110 . The composite wire  110  includes an electrically conductive wire  112  that is used for delivering ablation energy in an ablation procedure or for detecting electrical activity during a mapping procedure. Electrical wire  112  is contained within a lumen  114  that also contains a perfusion lumen  116 . Perfusion lumen  116  is used to deliver irrigation fluid or a contrast fluid as described in connection with  FIG. 18 . Once braided conductive member  28  has been constructed with composite wire  110 , the insulation  118  surrounding wire filament  112  can be stripped away to form an electrode surface. Holes can then be provided into perfusion lumen  116  to then allow perfusion at targeted sites along the electrode surface. As with the embodiment illustrated in  FIG. 18 , the perfusion lumens can be connected together to form a manifold which manifold can then be connected to, for example, perfusion tube  120  and connected to a fluid delivery device. 
     Shrouds 
     The use of a shroud or shrouds to cover at least a portion of braided conductive member  28  can be beneficial in several ways. The shroud can add protection to braided conductive member  28  during insertion and removal of catheter  10 . A shroud can also be used to form or shape braided conductive member  28  when in its deployed state. Shrouds may also reduce the risk of thrombi formation on braided conductive member  28  by reducing the area of filament and the number of filament crossings exposed to blood contact. This can be particularly beneficial at the ends  30  and  32  of braided conductive member  28 . The density of filaments at ends  30  and  32  is greatest and the ends can therefore be prone to blood aggregation. The shrouds can be composed of latex balloon material or any material that would be resistant to thrombi formation durable enough to survive insertion through an introducer system, and would not reduce the mobility of braided conductive member  28 . The shrouds can also be composed of an RF transparent material that would allow RF energy to pass through the shroud. If an RF transparent material is used, complete encapsulation of braided conductive member  28  is possible. 
     A shroud or shrouds may also be useful when irrigation or perfusion is used, since the shrouds can act to direct irrigation or contrast fluid to a target region. 
       FIGS. 20A-20E  illustrate various examples of shrouds that may be used in the present invention.  FIG. 20A  illustrates shrouds  130  and  132  disposed over end regions  31  and  33 , respectively, of braided conductive member  28 . This configuration can be useful in preventing coagulation of blood at the ends of braided conductive member  28 .  FIG. 20B  illustrates shrouds  130  and  132  used in conjunction with an internal shroud  134  contained inside braided conductive member  28 . In addition to preventing blood coagulation in regions  31  and  32 , the embodiment illustrated in  FIG. 20B  also prevents blood from entering braided conductive member  28 . 
       FIG. 20C  illustrates shrouds  130  and  132  being used to direct and irrigation fluid or contrast medium along the circumferential edge of braided conductive member  28 . In the embodiment illustrated in  FIG. 20C , perfusion can be provided as illustrated in  FIGS. 18 and 19 . 
       FIG. 20D  illustrates the use of an external shroud that covers braided conductive member  28 . Shroud  136  completely encases braided conductive member  28  and thereby eliminates blood contact with braided conductive member  28 . Shroud  136  may be constructed of a flexible yet ablation-energy transparent material so that, when used in an ablation procedure, braided conductive member  28  can still deliver energy to a targeted ablation site. 
       FIG. 20E  also illustrates an external shroud  137  encasing braided conductive member  28 . Shroud  137  may also be constructed of a flexible yet ablation-energy transparent material. Openings  139  may be provided in shroud  137  to allow the portions of braided conductive member  28  that are exposed by the opening to come into contact with tissue. Openings  139  may be elliptical, circular, circumferential, etc. 
     Guiding Sheaths 
     There may be times during ablation or mapping procedures when catheter  10  is passing through difficult or tortuous vasculature. During these times, it may be helpful to have a guiding sheath through which to pass catheter  10  so as to allow easier passage through the patient&#39;s vasculature. 
       FIG. 21  illustrates one example of a guiding sheath that may be used in connection with catheter  10 . As illustrated in  FIG. 21 , the guiding sheath  140  includes a longitudinal member  142 . Longitudinal member  142  may be constructed of a material rigid enough to be pushed next to catheter shaft  12  as the catheter is threaded through the vasculature. In one example, longitudinal member  142  may be stainless steel. Longitudinal member  142  is attached to a sheath  144  disposed at the distal end  146  of longitudinal member  142 . The split sheath  144  may have one or more predetermined curves  148  that are compatible with the shapes of particular blood vessels (arteries or veins) that catheter  10  needs to pass through. Split sheath  144  may extend proximally along longitudinal member  142 . For example, sheath  144  and longitudinal member  142  may be bonded together for a length of up to 20 or 30 centimeters to allow easier passage through the patient&#39;s blood vessels. Sheath  144  includes a predetermined region  150  that extends longitudinally along sheath  144 . Region  150  may be, for example, a seam, that allows sheath  144  to be split open so that the guiding sheath  140  can be pulled back and peeled off catheter shaft  12  in order to remove the sheath. 
     In another embodiment, longitudinal member  142  may be a hypotube or the like having an opening  152  at distal end  146  that communicates with the interior of sheath  144 . In this embodiment, longitudinal member  142  can be used to inject irrigation fluid such as saline or a contrast medium for purposes of cooling, flushing, or visualization. 
     Methods of Use 
     Reference is now made to  FIGS. 22 ,  23 , and  24 , which figures illustrate how the catheter of the present invention may be used in endocardial and epicardial applications. 
     Referring to  FIG. 22 , this figure illustrates an endocardial ablation procedure. In this procedure, catheter shaft  12  is introduced into a patient&#39;s heart  150 . Appropriate imaging guidance (direct visual assessment, camera port, fluoroscopy, echocardiographic, magnetic resonance, etc.) can be used.  FIG. 22  in particular illustrates catheter shaft  12  being placed in the left atrium of the patient&#39;s heart. Once catheter shaft  12  reaches the patient&#39;s left atrium, it may then be introduced through an ostium  152  of a pulmonary vein  154 . As illustrated, braided conductive member  28  is then expanded to its deployed position, where, in the illustrated embodiment, braided conductive member  28  forms a disk. Catheter shaft  12  then advanced further into pulmonary vein  154  until the distal side  156  of braided conductive member  28  makes contact with the ostium of pulmonary vein  154 . External pressure may be applied along catheter shaft  12  to achieve the desired level of contact of braided conductive member  28  with the ostium tissue. Energy is then applied to the ostium tissue  152  in contact with braided conductive member  28  to create an annular lesion at or near the ostium. The energy used may be RF (radiofrequency), DC, microwave, ultrasonic, cryothermal, optical, etc. 
     Reference is now made to  FIG. 23 , which figure illustrates an epicardial ablation procedure. As illustrated in  FIG. 23 , catheter shaft  12  is introduced into a patient&#39;s thoracic cavity and directed to pulmonary vein  154 . Catheter  10  may be introduced through a trocar port or intraoperatively during open chest surgery Using a steering mechanism, preformed shape, or other means by which to make contact between braided conductive member  128  and the outer surface  158  of pulmonary vein  154 , braided conductive member  28  is brought into contact with the outer surface  158  of pulmonary vein  154 . Appropriate imaging guidance (direct visual assessment, camera port, fluoroscopy, echocardiographic, magnetic resonance, etc.) can be used. As illustrated in  FIG. 23 , in this procedure, braided conductive member  28  remains in its undeployed or unexpanded condition. External pressure maybe applied to achieve contact between braided conductive member  28  with pulmonary vein  154 . Once the desired contact with the outer surface  158  of pulmonary vein  154  is attained, ablation energy is applied to surface  158  via braided conductive member  28  using, for example, RF, DC, ultrasound, microwave, cryothermal, or optical energy. Thereafter, braided conductive member  28  may be moved around the circumference of pulmonary vein  154 , and the ablation procedure repeated. This procedure may be used to create, for example, an annular lesion at or near the ostium. 
     Use of the illustrated endocardial or epicardial procedures may be easier and faster than using a single “point” electrode since a complete annular lesion may be created in one application of RF energy. 
     Reference is now made to  FIG. 24  which figure illustrates an endocardial mapping procedure. In the procedure illustrated in  FIG. 24 , catheter shaft  12  is introduced into pulmonary vein  154  in the manner described in connection with  FIG. 22 . Once braided conductive  28  has reached a desired location within pulmonary vein  154 , braided conductive member  28  is expanded as described in connection with, for example,  FIGS. 2-5  until filaments  34  contact the inner wall  160  of pulmonary vein  154 . Thereafter, electrical activity within pulmonary vein  154  may be detected, measured, and recorded by an external device connected to the filaments  34  of braided conductive member  28 . 
     Access to the patient&#39;s heart can be accomplished via percutaneous, vascular, surgical (e.g. open-chest surgery), or transthoracic approaches for either endocardial or epicardial mapping and/or mapping and ablation procedures. 
     The present invention is thus able to provide an electrophysiology catheter capable of mapping and/or mapping and ablation operations. In addition, the catheter of the invention may be used to provide high density maps of a tissue region because electrocardiograms may be obtained from individual filaments  34  in braided conductive member  28  in either a bipolar or unipolar mode. 
     Furthermore, the shape of the electrode region can be adjusted by controlling the radial expansion of braided conductive member  28  so as to improve conformity with the patient&#39;s tissue or to provide a desired mapping or ablation profile. Alternatively, braided conductive member  28  may be fabricated of a material of sufficient flexural strength so that the tissue is preferentially conformed to match the expanded or partially expanded shape of the braided conductive member  28 . 
     The catheter of the present invention may be used for mapping procedures, ablation procedures, and temperature measurement and control on the distal and/or proximal facing sides of braided conductive member  28  in its fully expanded positions as illustrated in, for example,  FIG. 1 . In addition, the catheter of the present invention can be used to perform “radial” mapping procedures, ablation procedures, and temperature measurement and control. That is, the outer circumferential edge  76 , illustrated, for example, in  FIG. 8 , can be applied against an inner circumferential surface of a blood vessel. 
     Furthermore, being able to use the same catheter for both mapping and ablation procedures has the potential to reduce procedure time and reduce X-ray exposure. 
     The ability to expand braided conductive member  28  in an artery or vein against a tissue structure such as a freewall or ostium can provide good contact pressure for multiple electrodes and can provide an anatomical anchor for stability. Temperature sensors can be positioned definitively against the endocardium to provide good thermal conduction to the tissue. Lesions can be selectively produced at various sections around the circumference of braided conductive member  28  without having to reposition catheter  10 . This can provide more accurate lesion placement within the artery or vein. 
     Braided conductive member  28 , in its radially expanded position as illustrated in particular in  FIGS. 1 and 8  is advantageous because, in these embodiments, it does not block the blood vessel during a mapping or ablation procedure, but allows blood flow through the braided conductive member thus allowing for longer mapping and/or ablation times, which can potentially improve accuracy of mapping and efficacy of lesion creation. 
     Handle Assembly 
     An exemplary implementation of handle  14  ( FIG. 1 ) will now be described in connection with  FIGS. 25-31 . The handle configuration shown uses linear movement of the slide actuator  124  ( FIG. 26 ), formed of slider  232  and slider grip  252 , to selectively control the tension applied to pull cables  162   a  and  162   b , which may for example control the radius of curvature of the distal end of the catheter. The handle configuration further uses rotational movement of the thumbwheel actuator  122  to selectively control the tension applied to pull cables  162   c  and  162   d  coupled thereto. These pull cables may control the orientation of the distal end of the catheter of the catheter relative to the longitudinal axis of the shaft  12 . 
     Referring to  FIG. 25 , the handle  201  comprises a housing having a left section  200 L and a right section  200 R. These two sections  200 L and  200 R are somewhat semicircular in cross section and have flat connecting surfaces which may be secured to each other along a common plane to form a complete housing for the handle  201 . The outer surfaces of the handle  201  are contoured to be comfortably held by the user. 
     A wheel cavity  210  is formed within the right section  200 R of the handle  201 . The wheel cavity  210  includes a planar rear surface  211  which is generally parallel to the flat connecting surface of the handle  201 . The thumbwheel actuator  122  is a generally circular disc having a central bore  216 , an integrally formed pulley  218 , and upper and lower cable anchors  220 . Upper and lower cable guides  221  serve to retain the cables  162   c  and  162   d  within a guide slot or groove  223  formed in a surface of the integrally formed pulley  218 . In the embodiment illustrated, the thumbwheel  122  rotates about a sleeve  228  inserted in the central bore  216 . The thumbwheel  122  is held in position by a shoulder nut  224  that mates with a threaded insert  229  in the planar rear surface  211  of the right section  200 R of the handle  201 . To provide friction that permits the thumbwheel to maintain its position even when tension is applied to one of the cables  162   c ,  162   d , a friction disk  226  is provided between the shoulder nut  224  and the thumbwheel  122 . Tightening of the shoulder nut  224  increases the amount of friction applied to the thumbwheel  122 . 
     A peripheral edge surface  222  of the thumbwheel  122  protrudes from a wheel access opening so that the thumbwheel  122  may be rotated by the thumb of the operator&#39;s hand which is used to grip the handle  201 . To ensure a positive grip between the thumbwheel  122  and the user&#39;s thumb, the peripheral edge surface  222  of the thumbwheel  122  is preferably serrated, or otherwise roughened. Different serrations on opposite halves of thumbwheel  122  enable the user to “feel” the position of the thumbwheel. 
     The left section  200 L supports part of the mechanism for selectively tensioning each of the two pull cables  162   a  and  162   b  that control the radius of curvature of the distal end the catheter. To accommodate the protruding portion of the thumbwheel  122 , the left handle section  200 L includes a wheel access opening similar in shape to the wheel access opening of the right handle section  200 R. It also includes an elongated slot  230  in its side surface. 
     A slider  232  is provided with a neck portion  242  which fits snugly within the slot  230 . The slider  232  includes a forward cable anchor  235  and a rear cable anchor  236  for anchoring the pull cables  162   a  and  162   b . Pull cable  162   b  is directly attached to the forward cable anchor  235  and becomes taught when the slider  232  is moved toward the distal end of the handle  201 . Pull cable  162   a  is guided by a return pulley  238  prior to being attached to the rear cable anchor  236  and becomes taught when the slider  232  is moved toward the proximal end of the handle  201 . The return pulley  238  is rotatably attached to a pulley axle  239  which is supported in a bore (not shown) in the flat surface of the right handle section  200 R. The return pulley  238  may include a groove (not shown) to guide pull cable  162   a . In the illustrated embodiment, a cable guide  205  is attached to the right handle section  200 R to guide the cables  162   a - 162   d  and prevent their entanglement with one another. As shown, cables  162   a  and  162   b  are routed up and over the cable guide  205 , while cables  162   c  and  162   d  are routed through a gap  206  in the cable guide  205 . Grooves may be formed in a top surface of the cable guide  205  to keep cables  162   a  and  162   b  in position, although they could alternatively be routed through holes formed in the cable guide  205 , or by other suitable means. 
     A slider grip  252  is attached to the neck portion  242  of the slider  232  and positioned externally of the handle  201 . The slider grip  252  is preferably ergonomically shaped to be comfortably controlled by the user. Preload pads  254  are positioned between the outer surface of the left handle section  200 L and the slider grip  252  (shown in  FIGS. 25 and 28 ). By tightening the screws  260  that attach the slider grip  252  to the slider  232 , friction is applied to the slider  232  and thus, to the pull cables  162   a ,  162   b . Preload pads  237  may also be placed on a surface of the slider  232  for a similar purpose. 
     A dust seal  234  ( FIGS. 25 and 28 ) having an elongated slit and preferably made from latex is bonded along the slot  230  within the left handle section  200 L. The neck portion  242  of the slider  232  protrudes through the slit of the dust seal  234  so that the slit only separates adjacent to the neck portion  242 . Otherwise, the slit remains “closed” and functions as an effective barrier preventing dust, hair and other contaminants from entering the handle  201 . Further details of the handle  201  are described in U.S. Pat. Nos. 5,383,852, 5,462,527, and 5,611,777, which are hereby incorporated herein by reference. 
     According to a further aspect of the present invention, each of the thumbwheel actuator and the slide actuator may include means for imparting a first amount of friction on at least one pull cable to which the actuator is attached when the actuator is in a first position, and for imparting a second and greater amount of friction on the at least one pull cable when the actuator is moved away from the first position. According to this aspect of the present invention, the first position may correspond to a neutral position of the actuator wherein the tip assembly is aligned with the longitudinal axis of the shaft, or a neutral position of the actuator wherein the radius of curvature of the distal end of the tip assembly is neither being actively reduced or increased, and the second position may correspond to a position of the actuator that is other than the neutral or rest position. 
     As should be appreciated by those skilled in the art, it is desirable that the actuators for changing the orientation of the tip assembly and for controlling the radius of curvature of the distal end of the tip assembly remain in a fixed position, once actuated. Conventionally, this has been achieved by providing a sufficient amount of friction between the actuator and another surface on the handle  201  to resist movement of the actuator unless a certain amount of force is applied to the actuator. For example, in  FIG. 25 , by tightening shoulder nut  224  that holds the thumbwheel in position, a greater amount of force must be applied to the thumbwheel to rotate the thumbwheel from one rotational position to another. Similarly, and with respect to the slide actuator, by tightening the two screws  260  that hold the slider grip  252  in position against an undersurface of the handle section, a greater amount of force must be applied to the slider grip  252  to move the slider  232  from one position to another. 
     Although this conventional approach is straightforward, it results in the same amount of friction being applied to the actuator(s) in all positions, and not merely those positions that deviate from a neutral or rest position. Thus, in use, it can be difficult to ascertain whether the orientation of the tip assembly or the radius of curvature of the distal end of the tip assembly is in a neutral state, without visually looking at the handle. This can be problematic, as the user of the catheter would need to divert his or her attention to visually inspect the position of the actuator(s). Further, Applicants have determined that the frictional force imparted by the mechanisms that maintain the cables and actuators in a fixed position can significantly decrease over time, for example, while stacked on the shelf, oftentimes requiring that the mechanisms used to impart such friction (e.g., the shoulder nut and the screws) be tightened prior to use. It is believed that this phenomena is due to material creep associated with the various materials used to form the actuator mechanisms. This decrease in frictional force is especially apparent where the catheter has been brought to elevated temperatures during a sterilization cycle, as the materials from which the handle and the control mechanisms are formed have a tendency to yield at elevated temperatures. Although the various mechanisms may be tightened after sterilization, such tightening may contaminate the sterile nature of the catheter, and is undesirable in a clinical setting. 
     According to a further aspect of the present invention, each of the thumbwheel actuator and the slide actuator may include means for imparting a first amount of friction on at least one pull cable to which the actuator is attached when the actuator is in a first position, and for imparting a second and greater amount of friction on the at least one pull cable when the actuator is moved away from the first position. This difference in the frictional force can be perceived by the user to alert the user as to when the actuator is in a neutral or rest position, without visually inspecting the actuator. Further, because the frictional forces on the actuating mechanisms are reduced in a neutral or rest position, the catheter may be sterilized with the actuator(s) in a neutral or rest position, thereby reducing yielding of the actuation mechanism during sterilization. 
     According to one embodiment that is directed to the thumbwheel actuator, the means for imparting different amounts of friction may include a plurality of detents formed in the planar rear surface of the handle housing that cooperate with corresponding plurality of detents in a lower surface of the thumbwheel. In this embodiment, each of the plurality of detents in the lower surface of the thumbwheel receives a ball or bearing that sits partially within the respective detent. In a first neutral position, each of the balls also rest within a respective detent in the rear surface of the handle and exert a first amount of friction on the thumbwheel and the pull cables attached thereto. But, as the thumbwheel is rotated, the balls ride outside the detent in the rear surface of the handle onto the elevated surface above, thereby exerting a second and greater amount of friction on the thumbwheel and the pull cables attached thereto. According to one embodiment, this second amount of friction is sufficient to prevent the thumbwheel from returning to its neutral position.  FIGS. 25 ,  29 ,  30 , and  31  illustrate one implementation of a means for imparting different amounts of friction for a thumbwheel actuator  122  according to this embodiment of the present invention. 
     As shown in  FIGS. 25 ,  29 ,  30 , and  31 , the planar rear surface  210  of the right section  200 R includes a plurality of detents  212  formed therein. A corresponding number of detents  215  are provided in an undersurface of the thumbwheel  122  ( FIGS. 29-31 ). Within each of the plurality of detents  215  in the undersurface of the thumbwheel is a ball or bearing  214 . The balls or bearings may be made from any suitable material, such as stainless steel, or may alternatively be made from a hard plastic. The balls or bearings  214  may be fixed in position for example, with an epoxy, or permitted to rotate within the detents  215 . It should be appreciated that the balls or bearings  214  may alternatively be seated within the detents  212  in the planar rear surface  211  of the right section of the handle  200 R. In a neutral or rest position, for example, corresponding to an orientation of the tip assembly that is parallel to the longitudinal axis of the shaft, each of the plurality of balls rests within a corresponding detent  212  in the planar rear surface  211 . Such a resting or neutral state is depicted in  FIG. 30  which is a schematic cross sectional view of the thumbwheel of  FIG. 25 . As may be appreciated, this neutral or rest position corresponds to a position of reduced friction on the thumbwheel  122  in which the friction disk  226  is compressed to only a small degree, and thus, to a reduced frictional force on the pull cables that are attached to the thumbwheel. 
     As the thumbwheel  122  is rotated from this neutral or rest position, the balls  214  ride up and out of their respective detents  212  and along the path  265  indicated in  FIG. 25 . In this second position wherein each of the balls contacts the elevated planar rear surface  211 , a second and greater amount of friction is imparted to the thumbwheel, and thus, the pull cables attached thereto, that tends to prevent the thumbwheel from moving to another position without further rotational force applied to the thumbwheel.  FIG. 31  is a schematic cross sectional view of the thumbwheel of  FIG. 25  illustrating a state in which the thumbwheel is in a position other than the neutral or rest position. As can be seen in  FIG. 31 , each of the balls  214  rests upon the elevated planar rear surface  211  and the friction disk  226  is compressed relative to that shown in  FIG. 30 . As shown best in  FIG. 22 , each of the detents  212  in the planar rear surface  211  may include lead in/lead out sections  267  that are gradually tapered to the level of the planar rear surface  211  to facilitate smooth movement of the balls  214  out of and into the detents  212 . 
     Although the present invention is not limited to the number of detents  212 ,  215  incorporated into the handle and the thumbwheel, Applicants have found that three detents spaced equally about a circumference of the planar rear surface  211  and the thumbwheel  122  distributes stress evenly about the thumbwheel  122  and permits a sufficient amount of rotation before another detent  212  is encountered. Furthermore, although the present invention is not limited to the amount of force applied to the thumbwheel to change the position of the thumbwheel, Applicants have empirically determined that a force of approximately 4 to 8 pounds is sufficient to resist any forces on the pull cables. Moreover, this amount of force is sufficient so that the thumbwheel cannot be moved inadvertently, and does not require great strength by the user. This amount of force also accounts for any yielding during storage and/or sterilization. 
     Although this embodiment of the present invention has been described in terms of a plurality of detents in a surface of the handle and a corresponding number of detents that hold a ball or bearing in an undersurface of the thumbwheel, the present invention is not so limited. For example, and as discussed above, the detents in the planar surface  211  of the handle  201  may hold the balls or bearings  214  and not the thumbwheel. Moreover, it should be appreciated that other means of imparting different frictional forces on the thumbwheel may be readily envisioned. For example, rather than detents, the rear planar surface  211  may be contoured to include a plurality of ramps (for example, three ramps). The undersurface of the thumbwheel  122  may include a corresponding plurality of complementary shaped ramps such that when the thumbwheel  122  is in a neutral or rest position, a minimum of friction is imparted, and as the thumbwheel  122  is rotated, the heightened surface of the ramps on the undersurface of the thumbwheel  122  contacts a heightened surface of the ramps in the planar surface. As the thumbwheel  122  is rotated further, addition friction is imparted. 
     According to another embodiment that is directed to the slide actuator, the means for imparting different amounts of friction may include a ramp disposed on or formed within the handle  201 . In this embodiment, the apex of the ramp corresponds to a neutral position of the slider  232 . In this neutral position, a minimum amount of friction is applied to the slider  232  and the pull cables  162   a ,  162   b  attached thereto. As the slider  232  is moved forward or backward away from the neutral position, the slider  232  is pushed toward the thumbwheel and an interior surface of the housing to impart a great amount of friction on the slider and the pull cables attached thereto. As with the thumbwheel, this second amount of friction is sufficient to prevent the slider from returning to its neutral position. 
       FIGS. 26 ,  27 , and  28  illustrate one implementation of a means for imparting different amounts of friction for a slide actuator  124 . As shown in these figures, the undersurface of the left section  200 L includes a ramp  164 . The ramp may be integrally formed within the left section  200 L of the handle  201 , or alternatively, the ramp  164  may be separate from the handle and attached thereto. As illustrated in  FIG. 28 , which is a schematic cross sectional view of the slide actuator  124  shown in  FIG. 26 , the ramp  164  includes a central section of decreased thickness and proximal and distal sections that increase in thickness away from the central section until flush with the undersurface of the left section. The top surface of the slider  232  that contacts the undersurface of the left section  200 L of the handle may have a complementary shape to the ramp as shown in  FIGS. 26 and 27 . In the position shown in  FIG. 26 , the slide actuator is in a neutral or rest position corresponding to a first radius of curvature of the distal end of the tip assembly. The two screws  260  force the slider grip  252  and the slider  232  closer to one another and compress the preload pads  254  therebetween. In the neutral or rest position shown in  FIGS. 26 and 28 , the preload pads  254  are compressed to only a minimal extent. However, as the slider  232  is moved away from the neutral or resting position, the shape of the ramp  164  (and the slider  232 ) imparts an additional frictional force that tends to separate the slider  232  from the slider grip  252 , thereby compressing the preload pads  254  to a greater extent, as illustrated in  FIG. 27 . This additional frictional force resists the slide actuator  124  from changing position, absent further force on the slide actuator  124 . 
     Although this embodiment of the present invention has been described in terms of a ramp formed within or disposed on an undersurface of the handle  201 , the present invention is not so limited. For example, the ramp may alternatively be formed on an outer surface of the handle and provide similar functionality. Other means for imparting different frictional forces on the slide actuator may be readily envisioned by those skilled in the art. 
       FIGS. 32-33  illustrates a variation of the handle  201  described in connection with  FIG. 25 . In particular,  FIGS. 32-33  illustrate a thumbwheel assembly  165  that omits the friction disk  226  of  FIG. 25 , and instead includes a compression spring  170  to provide the friction that permits the thumbwheel  122  to maintain its position even when tension is applied to a cable coupled to one of cable anchors  220 . 
     Compression spring  170  is provided between shoulder nut  168  and thumbwheel  122 . The shoulder nut  168  is held in place by a screw  166  that mates with the threaded insert  229  in the planar rear surface  211  of the right section  200 R of the handle. Compression of the spring  170  against the thumbwheel  122  increases the rotational friction imparted on the thumbwheel  122  such that thumbwheel  122  will maintain its position even when a tensioned cable coupled thereto exerts a rotational force on the thumbwheel  122 . 
     As with the thumbwheel  122  of  FIG. 25 , balls or bearings  214  and corresponding detents  212  are provided for imparting a first amount of rotational friction on the thumbwheel  122  when the balls or bearings  214  rest within detents  212 , and a second, greater amount of friction on thumbwheel  122  when the balls or bearings  214  are moved from the detents  212 . Although not shown in  FIGS. 32-33 , detents  215  are also provided in an undersurface of the thumbwheel  122  ( FIGS. 29-31 ) to receive balls or bearings  214 . When balls or bearings  214  rest within detents  212 , compression spring  170  is slightly compressed and a first frictional force is imparted on the thumbwheel  122 . When the thumbwheel  122  is then rotated such that balls or bearings  214  are moved from the detents  212  as described in connection with  FIG. 25 , the compression spring  170  is compressed to a greater degree. Accordingly, a second greater frictional force is imparted in the thumbwheel  122 . 
     Anchors  220 , which may anchor pull cables secured thereto, may be adapted to allow selective tensioning of the pull cables. In particular, when the handle is opened to expose an anchor  220 , an anchor  220  may be rotated (e.g., using a wrench) such that the cable coupled thereto may be looped around the anchor one or more times. The cable may be bent at an approximately ninety degree angle, and partially inserted into a hole  172  of the anchor  220  to secure the cable during rotation of the anchor  220 . Accordingly, the tension on a cable attached to the anchor  220  may be increased by decreasing the slack in the cable. Tensioning of the cable may be desirable, for example, when the cable become slack after some period of time or after some period of use. 
     Pulley  218  may be formed with a smaller diameter than conventional thumbwheel pulleys so as to reduce the force necessary to turn thumbwheel  122 . For example, pulley  218  may have a smallest diameter (e.g., the diameter of the pulley  218  at groove  223 ) of between ⅛ in. and ½ in. According to one embodiment, pulley  218  may have a smallest diameter of approximately ¼ in. According to another embodiment, pulley  218  may have a diameter that is approximately one third the size of the thumbwheel  122 . 
     Although the above described embodiments for imparting a varying amount of friction on an actuator have been described with respect to actuators adapted to change the diameter of curvature or orientation of the distal end of a catheter, the present invention is not so limited. For example, the actuator may instead be coupled to a push/pull cable connected to a movable electrode, or a cable or rod used to deploy a braided conductive member as described in connection with  FIGS. 34A-B . Accordingly, it should be appreciated that this embodiment of the present invention may be used to impart varying amounts of friction on any cable or other mechanism that controls movement of a portion of a catheter with respect to another. 
     Retractable Tip 
     The catheter  300  shown in  FIGS. 34A-34B  addresses one drawback that may be experienced when using a catheter such as shown in  FIG. 1 . When a catheter having a long distal end is used in an electrophysiology procedure involving the heart, the distal end may hinder the ability to maneuver the catheter within the heart. For example, certain pulmonary veins of the heart may branch to form smaller veins close to the heart. If the portion of the catheter that is distal to the braided conductive member is sufficiently long, the physician may have difficulty introducing the distal end of the catheter into a desired vessel and therefore may have difficulty positioning the braided conductive member. 
     As shown in  FIGS. 34A-B , a distal tip portion  302  of catheter  300  may be retracted proximally in the direction of the shaft  304  using a mandrel  306  that is slidably disposed within the shaft  304 , which results in the radial expansion of braided conductive member  28 . Thus, the overall length of catheter  300  may be shortened when the braided conductive member  28  is deployed, which may aid the insertion of the distal tip portion of the catheter into a vessel during an electrophysiology procedure. 
     Catheter  300  comprises a distal tip portion  302 , a shaft  304 , and a braided conductive member  28  coupled therebetween. A mandrel  306  is fixedly attached to the distal tip portion  302  and slidably disposed within the shaft  304 . A strain relief portion  305  is secured to shaft  304  to provide support for mandrel  306 , which is slidable within a lumen of the strain relief portion  305 . Plugs  307  may be secured to a distal portion of strain relief portion  305  to enable retraction of the mandrel within shaft  304 , while preventing liquids or debris from entering the catheter  300 . Accordingly, the plugs  307  may help to ensure that the interior of the catheter remains sterile. According to one example, plugs  307  may be formed of silicone or another elastomeric material. 
     Distal tip portion  302  comprises a distal cap  308  and an anchor portion  310 . The anchor portion  310  performs two primary functions. First, the anchor portion  310  helps to secure the distal end  312  of braided conductive member  28  to distal cap  308 . Second, the anchor portion  310  secures a distal end of the mandrel  306  to the distal tip portion  302 . 
     As will be discussed in more detail below, mandrel  306  is movable with respect to the shaft  304  of the catheter  300 . Advantageously, mandrel  306  may be used to transmit pulling forces as well as pushing forces. Thus, mandrel  306  may be used both the deploy and undeploy braided conductive member  28 . It should be appreciated that mandrel  306  may comprise any actuating mechanism that is capable of transmitting both pulling and pushing forces. For example, mandrel  306  may comprise a rod, a wire, or other actuating member having sufficient rigidity to enable transmission of pushing forces. In one example, mandrel  306  may be formed of nitinol or another material exhibiting superelasticity, although the invention is not limited in this respect. 
     Mandrel  306  may include a coating, which may for example enhance the operating properties of the mandrel. For example, the mandrel  306  may be coated to reduce the possibility of thrombi adhesion to the mandrel  306  and/or to provide a reference a radio-opaque point on mandrel  306  when viewed during fluoroscopic imaging. According to another example, the mandrel  306  may be coated with a high dielectric coating for safety when using ablation energy, as a portion of the mandrel  306  may be exposed to blood during an electrophysiology procedure. One exemplary high dielectric coating that may be used is parylene. According to a further example, the mandrel  306  may be coated to reduce the coefficient of friction of the mandrel  306 . Such a coating may reduce the friction that may result between mandrel  306  and plugs  307  or between mandrel  306  and braided cable  390 , an external portion of which forms the braided conductive member  28  at the distal end of the catheter  300 . A parylene coating may act to reduce this friction when applied to the mandrel  306 , and may therefore may serve dual functions of acting as a dielectric and acting as a lubricant. Braided conductive member  28  may include any of the features described in connection with other braided conductive members. In particular, braided conductive member  28  may be partially insulated, and may include an uninsulated portion  309  around a circumference thereof ( FIG. 34A ). The insulated portion may be preferentially disposed on a distal face of the braided conductive member  28 , such that a larger area of the braided conductive member  28  is uninsulated on its distal face. 
     The actuation of braided conductive member  28  using mandrel  306  will now be described. Sliding the mandrel  306  within the shaft  304  of catheter  300  changes the configuration of the braided conductive member  28 . In particular, when the mandrel  306  is slid distally within the shaft  304 , the braided conductive member  28  assumes an undeployed configuration. The undeployed configuration may be generally cylindrical. The diameter of the diameter of the braided conductive member  28  in this configuration may approximate that of the shaft  304 . When the mandrel  306  is slid proximally within the shaft  304 , the braided conductive member  28  assumes a deployed configuration. The deployed configuration may have a disk-like shape. The braided conductive member  28  in this configuration has a larger diameter than in the undeployed configuration. Thus, deploying the braided conductive member  28  expands the braided conductive member  28  radially. 
       FIG. 35  illustrates an enlarged view of the distal tip portion  302  shown in  FIG. 34B . As shown, anchor portion  310  includes a central opening  314 , within which mandrel  306  is disposed. Mandrel  306  is secured within anchor portion  310  via first and second collets  316   a  and  316   b . In one example, the first collet  316   a  may be secured to the mandrel  306  using solder and the second collet  316   b  may be secured to the mandrel  306  using a bonding agent such as epoxy, although the invention is not limited in this respect. Collets  316   a  and  316   b  anchor the mandrel  306  with respect to the anchor portion  310 . As may be appreciated from  FIG. 35 , any motion of mandrel  306  with respect to anchor portion  310  when mandrel  306  is slid within the shaft of the catheter is inhibited by the interface of collets  316   a  and  316   b  with edges  318   a  and  318   b , respectively. For example, if mandrel  306  is slid within the shaft in a proximal direction, the interface of first collet  316   a  with edge  318   a  inhibits motion of the mandrel  306  with respect to anchor portion  310 . Similarly, if mandrel  306  is slid within the shaft in a distal direction, the interface of second collet  316   b  with edge  318   b  inhibits motion of the mandrel  306  with respect to anchor portion  310 . 
     Anchor portion  310  also includes features that interface with distal cap  308 . First, a collar  320  of anchor portion  310  is configured to mechanically “lock” the anchor portion  310  in distal cap  308 . When anchor portion  310  is properly positioned within distal cap  308 , collar  320  is adjacent to a corresponding collar  322  of distal cap  308 . Hence, when collar  320  is positioned at a distal end of distal cap  308 , collar  322  is proximal to and adjacent collar  320 , which thereby inhibits proximal motion of anchor portion  310  with respect to distal cap  308 . In addition, when collar  320  is positioned at a distal end of distal cap  308 , collar  320  is adjacent to a distal interior wall  324  of distal cap  308 . The interface therebetween inhibits distal motion of anchor portion  310  with respect to distal cap  308 . 
     Second, anchor portion  310  includes a plurality of grooves  326  on an outer surface thereof that may provide a suitable surface for a bonding agent, e.g., epoxy, disposed between anchor portion  310  and distal cap  308  to adhere. A distal end  312  of braided conductive member  28  ( FIG. 34B ) may be secured in a recess  328  between anchor portion  310  and distal cap  308 . A bonding agent disposed within the recess  328  secures the braided conductive member  28  within the distal cap  308 . If desired, anchor portion  310  may include a ramp  332  of approximately fifteen degrees at proximal end thereof to maintain the distal end of the braided conductive member  28  in a conical shape. 
     One exemplary process for the assembly of the distal tip portion  302  will now be described. First, the first collet  316   a  may be secured to the mandrel  306 , for example using solder or epoxy. Next, the anchor portion  310  may be slid over the first collet  316   a  and mandrel  306 , and second collet  316   b  may be secured to the mandrel  306 , for example using solder or epoxy. The anchor portion  310 , which is secured to collets  316   a - b  and mandrel  306 , may then be inserted into distal cap  308 . Anchor portion  310  may be formed by machining, or another suitable process. A chamfer  330  may be provided at the distal end of anchor portion  310  to aid the insertion of anchor portion  310  past the collar  322  of distal cap  308 . The individual wires of the braided conductive member  28  may be cut and then separately insulated at their distal ends with an ultraviolet cure adhesive. A potting material may be included between anchor portion  310  and distal cap  308  to secure the distal end of the braided conductive member  28  therebetween. 
     Because distal tip position  302  may be maneuvered through vasculature and the heart during the course of an electrophysiology procedure, it may be desirable that distal tip portion  302  be constructed so as to reduce trauma to tissue it may contact. Accordingly,  FIG. 36  illustrates an exemplary embodiment of a portion of catheter  336  having a distal tip portion  338  that includes material selected to provide a gentle interaction with tissue. Distal tip portion  338  comprises a distal cap  340  and an anchor portion  342 . Anchor portion  342  is similar to and performs the same function as the anchor portion  342  of  FIG. 35 . Distal cap  340  includes two sub-portions: a proximal portion  340   a  and a distal portion  340   b . Proximal portion  340   a  is similar to and performs the same function as the distal cap  308  of  FIG. 35 , but includes a protrusion  346  adapted to mate with a recess  344  of distal portion  340   b . A bonding agent such as epoxy, or alternate coupling means, may be included in grooves  348  in proximal portion  340   a  to secure the proximal portion  340   a  to distal portion  340   b . Distal portion  340   b  may be constructed to provide a more gentle interaction with tissue than occurs with conventional catheter tips. For example, distal portion  340   b  may be formed of an elastomeric material such as polyurethane or silicone, or another material having a low durometer. Accordingly, distal cap  340  may be used, for example, to locate vein entrances in the walls of the atria without damaging the tissue of the wall. It should be appreciated that a number of variations are possible for the distal cap portion  340  described above. For example, a unitary cap portion may be formed with the “atraumatic” properties described for the distal portion  340   b , or both proximal portion  340   a  and distal portion  340   b  may be formed with atraumatic properties. In addition, distal portion  340   b  can assume a number of different configurations and need not have the shape and dimensions shown in  FIG. 36 . 
     Referring again to  FIG. 34A-B , a steering arrangement that may be used in connection with catheter  300  according to another embodiment of the invention will now be described. Steering cables  360  may be provided within catheter  300  to enable the catheter to be bent or curved via actuation of one or more of the steering cables  360 . Steering cables  360  may be anchored at steering anchor  362 , which is located at a distal end of shaft  304 . Actuation of one or more steering cables  360  may cause a bend or curve at a location proximal to steering anchor  362 , for example at a junction  364  between distal shaft portion  304   a  and proximal shaft portion  304   b . In one example, distal shaft portion  304   a  may be formed of a less rigid material than proximal shaft portion  304   b  so that a bend or curve is formed at a portion of the distal shaft portion  304   a  near the junction  364  between the distal shaft portion  304   a  and the proximal shaft portion  304   b . As should be appreciated from the foregoing, according to one embodiment of the invention, steering anchor  362  may be provided proximal to braided conductive member  28 . Further, a steering “knuckle” (e.g., a location of a bend or curve) may be formed by actuation of a steering cable  360  anchored at steering anchor  362  at a location proximal to the steering anchor. 
     In the example shown in  FIGS. 34A-34B , steering anchor  3249  comprises a plurality of loops formed by steering cables  360  around an exterior surface of catheter  300 , wherein the steering cables  360  form a continuous length of cable. The loops may be formed in a recess  366  in the exterior surface of the catheter  300 , and may be potted in place and sealed with silicone. In one example, an uncoated section of the steering cables  360  is looped around the catheter shaft  304  two and a half times and then potted to provide sufficient tensile forces for the cables  360 . 
     Although the configuration shown in  FIGS. 34A-B  provides suitable anchoring of steering cables  360 , certain drawbacks exist. For example, an opening is needed via which steering cables  360  may exit the catheter shaft  304  so that they may be looped around the exterior surface of the catheter  300 . The opening in the catheter shaft  304  may result in fluid leakage into the catheter  300 , or may cause other undesirable results. 
       FIG. 37  illustrates an alternative configuration of a steering anchor that may be used in accordance with catheter  300  and other embodiments described herein. In the configuration shown in  FIG. 37 , steering cables  370  are provided with anchors  372  having a width or diameter that is greater than the diameter of steering cables  370 . The anchors  372  may be integrally formed with the steering cables  370  or may be securely attached thereto. Steering cables  370  are at least partially disposed in lumens  374  having a larger width or diameter region  374   a  and a smaller width or diameter region  374   b . Anchors  372  may be disposed in larger width or diameter region  374   a  and may be sized such that the anchors  372  do not fit within smaller width or diameter region  374   b . In other words, each anchor  372  may have a diameter or width that is larger than a diameter or width of smaller with or diameter region  374   b  and smaller than a diameter or width of larger width or diameter region  374   a . Accordingly, steering cables  360  may be anchored at the junction of regions  374   a - b . A bonding agent such as epoxy may be provided to secure the anchors  372  at this location. 
       FIG. 38  illustrates an exemplary implementation of a control handle for use with the catheter  300  shown in  FIGS. 34A-B . The handle  380  includes a housing  382 , and a slide actuator  384  and thumbwheel  386  coupled to the housing  382 . The slide actuator  384  is coupled to the mandrel  306  to actuate the mandrel. Slide actuator  384  includes a lumen  392  in which a distal portion of mandrel  306  is disposed. The mandrel  306  may be fixedly attached to the slide actuator  384 , for example using an adhesive disposed in the lumen  392  between the mandrel  306  and the slide actuator  384 . The thumbwheel  386  may be coupled to one or more steering cables, such as steering cables  360  discussed in connection with  FIGS. 34A-B . Thus, thumbwheel may be use to actuate steering cables  360  to control an orientation of catheter  300  ( FIGS. 34A-B ). 
     Handle  380  is coupled to the catheter shaft  304  at a distal end thereof and a connector  388  at a proximal end thereof. A braided cable  390 , an external portion of which forms braided conductive member  28  at a distal end of the catheter  300  ( FIGS. 34A-B ), travels from the shaft  304  to the connector  388  through the handle  382 . In the catheter shaft, the braided cable  390  may be concentrically disposed around mandrel  306 . In the handle  380 , the mandrel  306  may exit through an opening in braided cable  390  such that the braided cable  390  is no longer disposed around mandrel  306 . It should be appreciated however, that braided cable  390  need not be concentrically disposed about mandrel  306  in shaft  304  and that the configuration shown is merely exemplary. In addition, braided cable  390  need not be braided along an entire length thereof. For example, braided cable  390  may comprise a plurality of unbraided filaments that are braided only at a distal end thereof where braided conductive member  28  is formed. 
     Mandrel  306  should be sufficiently stable in the region of handle  380  to transmit the pushing force applied by slide actuator  384  to more distal portions of mandrel  306 . Thus, it is preferable that the mandrel  306  have a sufficient diameter in the region of handle  380  to provide such stability. However, if this diameter of mandrel  306  were used along the entire length of the mandrel, the distal end of the catheter  300  may be excessively stiff. Excessive stiffness at the distal end of the catheter is undesirable as it may result in trauma to the heart and/or vasculature.  FIGS. 39-40  illustrate an exemplary implementation of mandrel  306  that addresses these considerations. In particular, the mandrel of  FIGS. 39-40  may have increased flexibility at a distal end thereof such that a catheter that incorporates the mandrel will also have increased flexibility at its distal end. Thus, trauma to the heart and/or vasculature may be reduced because the distal tip may yield when it contacts tissue due to its flexibility. In addition, the increased flexibility of the distal end of the catheter may enhance the maneuverability of the catheter, which may also reduce undesirable contact with the heart and/or vasculature. 
       FIG. 39  illustrates a mandrel  400  having three tiers: a first tier  402 , a second tier  404 , and a third tier  406 . The first tier  402  and second tier  404  are connected via a first transition region  408 , and the second tier  404  and third tier  406  are connected via a second transition region  410 . The transition regions may have a gradual and linear profile. The first tier  402  has the largest diameter of the three tiers, which may be approximately 0.038 inches according to one example. The second tier  404  has a diameter that is smaller than that of the first tier  402  but larger than that of the third tier  406 . According to one example, the second tier has a diameter of approximately 0.028 inches. The third tier  406  has the smaller diameter of the three tiers, which may be approximately 0.0175 inches according to one example. One exemplary material for mandrel  400  is nitinol, or another superelastic material. Nitinol has the benefit of being more resistant to kinking than other materials that may be used for mandrel  400 , such as stainless steel. 
       FIG. 40  illustrates exemplary locations for the first, second, and third tiers within catheter  300 . The first tier  402  may extend from slide actuator  384 , where the distal end of the mandrel is coupled, to a location  412  at the distal end of the handle  380 . Thus, the first transition  408  ( FIG. 39 ) may occur at location  412 . The second tier  404  may extend from location  412  to a location  414  located in shaft  304 . Thus, the second transition  410  ( FIG. 39 ) may occur at location  414 . The third tier  406  may extend from location  414  to distal tip portion  302 . 
     It should be appreciated that a number of variations are possible on the mandrel  400  described in connection with  FIGS. 39-40 . For example, the mandrel  400  may comprise two tiers, four tiers, or some greater number of tiers. Alternatively, the mandrel  400  may be constructed to have a continuous taper along an entire or substantial length thereof. It should also be appreciated that the transition regions  408  and  410  need not be gradual. For example, the transitions may be perpendicular relative to tiers of the mandrel  400 . 
       FIGS. 41A-E  illustrate a modified version of the catheter  300  illustrated in  FIGS. 34A-B . Most notably, catheter  416  includes a mandrel  418  having an interior lumen  420 . As will be discussed in detail below, lumen  420  may provide a passage for fluids or devices used during an electrophysiology procedure. 
     As shown in  FIG. 41A , catheter  416  includes a catheter shaft  422 , a braided conductive member  28 , and a distal tip portion  424 . The catheter shaft  422  includes a distal shaft portion  422   a , a proximal shaft portion  422   b , and an anchor portion  422   c  coupled between distal shaft portion  422   a  and braided conductive member  28 . A counterbore  426  is coupled between the proximal shaft portion  422   b  and the distal shaft portion  422   a . Steering cables  428   a  and  428   b  are respectively anchored via anchors  430   a  and  430   b , which are secured within anchor section  422   c . A seal  432  is provided at a distal end of anchor section  422   c  to prevent or substantially avoid admitting fluid or debris into the interior of shaft  422 . 
     According to one implementation, the lumen  420  of mandrel  418  has a diameter of approximately 2.5 French, while catheter shaft  422  has a diameter of approximately 10 French when no steering cables are used and approximately 12.5 French when two steering cables are used. However, it should be appreciated that the dimensions provided above are merely exemplary, and that alternative dimensions may be suitable. 
       FIG. 41B  illustrates an enlarged view of a portion of catheter  416  including counterbore  426 . Counterbore  426  is located at a junction between the distal shaft portion  422   a  and the proximal shaft portion  422   b  and provides an interface between the two portions. The counterbore  426  may be formed of plastic, and may be substantially rigid to reduce the strain on the junction between the distal shaft portion  422   a  and the proximal shaft portion  422   b . According to an embodiment of the invention, a bending point (or “knuckle”) may be formed at the junction upon actuation of steering cables  428   a - b.    
       FIG. 41C  illustrates an enlarged view of a portion of catheter  416  including seal  432  and steering anchors  430   a - b . The seal  432  includes a first portion  432   a  and a second portion  432   b . The second portion  432   b  is anchored to the anchor section  422   c , for example using a bonding agent such as epoxy, a locking mechanism, or another mechanical connection. Alternatively, the second potion  432   b  may be integrally formed with a portion of the catheter  416 . The second portion  432   b  may be formed of a plastic such as polyurethane, or another material suitable for forming a mechanical connection between the first portion  432   a  and the anchor section  422   c . The first portion  432   a  is coupled to the second portion  432   b , for example using a bonding agent. The first portion  432   a  may be formed of silicone, or another material suitable for forming a seal around mandrel  418 . The seal formed may be wholly or substantially fluid-tight. In one example, the first and second portions  432   a - b  include inner surfaces constructed to allow the mandrel  418  to be slidably received therein. For example, the surfaces may be smooth and/or generate little friction when slid against a surface. However, it should be appreciated that the invention is not limited in this respect. For example, a lubricant or coating may be disposed on the inner surfaces to reduce the friction between the first and second portions  432   a - b  and the mandrel  418 . It should also be appreciated that the seal  432  described above may have a number of alternate implementations. For example, the seal  432  may be formed of a single element and/or have a shape or configuration other than shown in  FIGS. 41A and 41C . 
     Steering anchors  430   a - b  and steering cables  428   a - b  are configured in a manner similar to those shown in  FIG. 37 . In particular, anchors  430   a - b  have a width or diameter that is greater than the diameter of steering cables  428   a - b . The anchors  430   a - b  may be integrally formed with the steering cables  428   a - b  or may be securely attached thereto. Steering cables  428   a - b  pass through lumens  436   a - b , respectively, which extend along at least a portion of catheter  416 . Lumens  436   a - b  respectively include larger width or diameter regions  438   a - b  and a smaller width or diameter regions  440   a - b . Anchors  430   a - b  may be disposed in larger width or diameter regions  438   a - b  and may be sized such that the anchors do not fit within smaller width or diameter regions  440   a - b . Accordingly, steering cables  428   a - b  may be anchored at the junction between regions  438   a - b  and  440   a - b , respectively. A bonding agent such as epoxy may be provided to further inhibit movement of the anchors  430   a - b.    
       FIG. 41E  illustrates an enlarged view of a portion of distal shaft portion  422   a , including mandrel  418 , steering cables  428   a - b , and wires  434  used to form braided conductive member  28 . As shown, steering cables  428   a - b  are disposed in lumens  436   a - b  formed in the wall of the distal shaft portion  422   a . Mandrel  434  is disposed along a central longitudinal axis of shaft  422 , and is surrounded by wires  434 . The wires  434 , which may be braided in the same manner as braided conductive member  28 , are disposed in an opening between mandrel  418  and lumens  436   a - b . It should be appreciated that the internal configuration of distal shaft portion  422   a  shown in  FIG. 41E  is merely exemplary, and that other configurations are possible. For example, lumens  436   a - b  may be absent, and both steering cables  428   a - b  and wires  434  may be disposed in an opening between mandrel  418  and an outer wall of the catheter shaft  422 . In one implementation, steering cables  428   a - b  may be disposed at an inner radial position with respect to wires  434 . 
     Mandrel  418  extends the length of the catheter  416  to a handle of the catheter. As shown in  FIG. 41D , distal tip portion  424  includes a distal cap  444  coupled to the mandrel  418  at its most distal end. A distal end of braided conductive mesh  28  is circumferentially disposed about the mandrel  418  in a recess  446  between mandrel  418  and distal cap  444 . In addition, a sleeve  448  is included between braided conductive member  28  and mandrel  418  in distal tip portion  424  to help to anchor the braided conductive member  28  within the distal cap  444 . The sleeve  448  may be bonded to the mandrel  418 , and the braided conductive member  28  may be bonded to the sleeve  448 . In addition, a bonding agent may be included in recess  446  to provide additional fixation. Distal cap  444  may include an opening  450  in its distal tip to receive a distal opening of mandrel  418 . As will be described in more detail below, the opening  450  in distal cap  444  may serve as a passageway for fluids or devices that passed to or from a patient&#39;s body during an electrophysiology procedure. 
     The mandrel  418  may be slidably disposed within the shaft  422 , and may be moved along a longitudinal axis of the catheter  416  to actuate the braided conductive member  28 . As described in connection with  FIG. 41D , mandrel  418  and braided conductive member  28  are secured, at distal ends thereof, to distal cap portion  444 . Hence, when the distal end of mandrel  418  is slid in a proximal direction within shaft  422 , the distal tip portion  424  is moved towards shaft  422 . The retraction motion of the distal tip portion  424  laterally compresses braided conductive member  28  and radially expands the outer diameter of the braided conductive member  28 , thereby causing the braided conductive member  28  to assume a deployed configuration. Conversely, when the distal end of mandrel  418  is slid in a distal direction within shaft  422 , the distal tip portion  424  is moved away from shaft  422 . This causes braided conductive member  28  to radially compress and laterally expand so as to assume an undeployed configuration. In one example that will be described in connection with  FIG. 42 , the movement of mandrel  418  may be controlled using an actuator on a handle of the catheter  416 . It should be appreciated that braided conductive member  28  may include any of the features described in connection with other braided conductive members disclosed herein. 
     According to one implementation, mandrel  418  has a substantially tubular shape and is formed of a plastic such as high durometer polyurethane. However, it should be appreciated that mandrel  418  may assume any shape that may extend along catheter  416  and accommodate an internal lumen. Further, mandrel  418  may be formed of alternative materials, such as nitinol or other alloys, and may be formed of or coated with a biocompatible material. Preferably, the mandrel  418  is constructed to resist kinking upon actuation of the mandrel in the distal direction. Accordingly, the stiffness of the mandrel material and the shape and thickness of the mandrel  418  itself may be selected so that the mandrel  418  is not susceptible to kinking. However, it is preferable that mandrel  418  be constructed to not unduly limit any steering capabilities of the catheter. Accordingly, the mandrel  418  may be bendable in a direction transverse to the longitudinal axis of the catheter under a force imposed by steering cables of the catheter. 
     Mandrel  418  may also be a multi-tiered mandrel, similar to the multi-tiered mandrel  400  of  FIG. 39 . For example, mandrel  418  may comprise two tiers having different outer diameters that join at a transition region. The diameter of lumen  420 , however, may remain substantially constant. 
     Lumen  420  of mandrel  418  may be used to transport fluids or devices to or from the heart or vasculature of a patient during an electrophysiology procedure. For example, lumen  420  may be used to deliver an irrigation fluid such as saline to provide convective cooling during an ablation procedure. In another example, example, lumen  420  may be used to deliver a contrast fluid, such as a fluoroscopic contrast agent, to verify the placement of braided conductive member  28  or changes in vessel diameter. In either ablation or mapping procedures, antithrombogenic fluids, such as heparin, may be delivered via lumen  420  to reduce thrombogenicity. Other medicines may also be delivered via lumen  420  for other treatment purposes. The fluids described above may be released from catheter  416  via the opening  450  discussed previously, or via one or more openings that may be formed in the sidewalls of mandrel  418 . Fluids released via opening  450  may advantageously enter the blood flow of the patient upstream with respect to the mapping and/or ablating site, which aids in the visualization of the vascular structure where the catheter is to be placed and deployed. 
     In addition to, or as an alternative to being adapted for the transport of fluids, the lumen  420  of mandrel  418  may be adapted for the passage of medical devices. For example, lumen  420  may be used to introduce catheters, guidewires, and/or sensors (e.g., a blood pressure sensor, a pH sensor, a blood flow sensor, or an ultrasonic imaging device) into a patient. When catheter  416  is used in connection with a guidewire, the guidewire may be positioned first at a target site so that the catheter may follow the guidewire to the site. Alternatively, the guidewire may be inserted within mandrel  418  after the catheter  416  is introduced into the patient. 
       FIG. 42  illustrates an exemplary handle  460  that may be used to actuate mandrel  418 . The handle  460  operates in the same manner as handle  380  discussed in connection with  FIG. 38 , with slide actuator  384  being coupled to mandrel  418  to actuate the mandrel. However, in this configuration, mandrel  418  extends out of handle housing  462  so that devices and/or fluids may be introduced into the lumen  420  of the mandrel  418 . Channel  471 , which is coupled to and partially disposed within housing  462 , provides an opening through which mandrel  418  may slide. 
     Port  464  is coupled to the handle  460  to provide fluid or device access to the lumen  420  of mandrel  418 . Fluids may be introduced via fluid opening  466 , which is coupled to port  464  via tube  468 . The port  464  may form a seal with the mandrel  418  to ensure the sterility of the injected fluids, and may be equipped with a valve (not shown) to control the passage of fluid. To provide device access to lumen  420 , a device opening  470  is also provided in port  464 . A silicone seal  472  may seal the device opening  470  such that fluids will not escape from device opening  470  if fluids and a device are simultaneously introduced via port  464 . 
     Because mandrel  418  may be movable along a longitudinal axis of the catheter, the port  464  coupled to the handle  460  may also be movable. Alternatively, the port may be fixed with respect to the handle, and may not move in response to movement of the mandrel  418 . Although many implementations are possible to achieve a fixed port,  FIG. 42  shows an example in which port  464  has a lumen  474  to receive mandrel  418 . Because the proximal end of mandrel  418  is slidably disposed within lumen  474 , lumen  474  may have a length that is greater than a length  476  that slide actuator  384  may cause mandrel  418  to move. 
     Lesion Formation 
     One method for treating arrhythmia described herein involves the creation of a continuous, annular lesion at or near the ostium of a pulmonary vein. Such a lesion serves to block the propagation of the arrhythmia. However, as also described herein, a complete ‘fence’ around a circuit or tissue region is not always required in order to block the propagation of the arrhythmia. Rather, propagation of the arrhythmia may be halted or sufficiently diminished by one or more lesions, each only partially circumscribing an area of tissue traversed by errant signals. 
     For example, Applicants have appreciated that a complete or substantially complete conduction block may result when two or more generally arcuately shaped lesions are formed about a pulmonary vein or ostium thereof. According to one implementation, the lesions are concentrically formed about the pulmonary vein or ostium, although the invention is not limited in this respect. Preferably, the lesions are oriented such that at least one lesion intersects every direct path from the inside of the pulmonary vein to the atrium of the heart. For example, two or more discrete lesions may be formed that generally surround the pulmonary vein. One exemplary lesion pattern that may be formed to create a complete or substantially complete conduction block using concentrically formed lesions is illustrated in  FIG. 43 . 
       FIG. 43  illustrates two lesions  434  and  436  formed in a region of cardiac tissue  438  that surrounds a pulmonary vein  432 . Region  438  may be an ostium of pulmonary vein  432 , for example, or a portion of the atrium of the heart that surrounds the ostium of the pulmonary vein. Lesions  434  and  436  are generally concentric, both with each other and with pulmonary vein  432 . First lesion  434 , which has a larger radius than second lesion  436 , is located outside of lesion  436  and at a greater distance from pulmonary vein  432 . Lesions  434  and  436  are arcuately shaped, and do not form, either individually or together, a closed circle. In the example of  FIG. 43 , first lesion  434  spans approximately 270° (i.e., its arc angle is 270°), and second lesion  436  spans greater than 90°. Second lesion  436  is located adjacent the opening of lesion  434 , and has an arc angle that is larger than that of the opening of lesion  434 . Thus, lesions  434  and  436  eliminate direct pathways for electrical signals traveling between the tissue of the pulmonary vein  432  and atrial tissue  430 , as signals cannot cross region  438  without being diverted by lesion  434  or lesion  436 . Thus, lesions  434  and  436  effect a complete or substantially complete conduction block that is sufficient to halt or sufficiently diminish the propagation of an arrhythmia. 
     It should be appreciated that the number, placement, size, and shape of the lesions shown in  FIG. 43  is merely exemplary, as many configurations of discontinuous lesions may be envisioned that would similarly eliminate direct pathways for electrical signals traveling between the tissue of the pulmonary vein  432  and atrial tissue  430 , such that a complete or substantially complete conduction block between the pulmonary vein  432  and atrial tissue  430  would be formed. For example, the angles specified for arcuate lesions  434  and  436  are merely exemplary, as other angles may alternatively be used. According to a preferred implementation, the angles of arcuate lesions forming the conduction block are selected so that the sum of the angles is greater than 360°. For example, one lesion may span approximately 180° and another adjacent lesion may span greater than 180°. To minimize damage to tissue, in another example, the sum of the angles of the lesions is greater than 360°, but less than 450°. It should also be appreciated that more than two lesions may be used, and that the configuration of the lesions may also be varied without departing from the invention. Further, although a pulmonary vein is illustrated and described, the method may be applied to other orifices or regions within the heart. 
       FIG. 44  illustrates an exemplary implementation of a braided conductive member  440  that that may be used to form the lesion pattern of  FIG. 43 . Braided conductive member  440  has the same structure as braided conductive member  28  described herein, but has a different pattern of uninsulated regions. Accordingly, braided conductive member  440  may be used in connection with any of the various catheter embodiments disclosed herein (e.g., catheter  10  of  FIG. 1  and catheter  300  of  FIGS. 34A and 34B ). 
     As in braided conductive member  20 , braided conductive member  440  comprises a plurality of interlaced, electrically conductive filaments  34  surrounding a distal cap  308 . Regions  442  and  444  designate areas where insulation has been removed on the outer circumferential surface  60  (see  FIG. 7 ) or the entire circumferential surface of filaments  34  of braided conductive member  440 . When braided conductive member  440  is fully energized with ablation energy, the ablation energy is transmitted to the tissue in a pattern that corresponds to the shape and orientation of regions  442  and  444 . Other lesion patterns may be created by exposing areas of insulation on filaments  34  in a manner corresponding with the desired lesion pattern. For example,  FIG. 46  illustrates a braided conductive mesh  460  having regions  462  and  464  of exposed insulation. Regions  462  and  464  are shaped like concentric horseshoes, and will form a corresponding lesion pattern when energized.  FIG. 45  illustrates an exemplary implementation of a lesion pattern that may be formed using braided conductive member  460  to create a complete or substantially complete conduction block  46 . Lesions  452  and  454  correspond in configuration and arrangement to uninsulated regions  462  and  464 , respectively, of braided conductive member  460 . 
       FIG. 47  illustrates another exemplary lesion pattern that may be formed to create a complete or substantially complete conduction block. Four lesions  472 ,  474 ,  476  and  478  are formed in a region of cardiac tissue  438  that surrounds pulmonary vein  432 . Lesions  472 ,  474 ,  476  and  478  are generally concentric, both with each other and with pulmonary vein  432 . First and second lesions  472  and  474  each have a larger radius than third and forth lesions  476  and  478 , are located at a greater distance from pulmonary vein  432 . Lesions  472 ,  474 ,  476  and  478  are arcuately shaped, and do not form, either individually or together, a closed circle. In the example of  FIG. 47 , each of lesions  472 ,  474 ,  476  and  478  spans approximately 50° and spans a different respective quadrant in the region of cardiac tissue  438  that surrounds pulmonary vein  432 . Collectively, the lesions are sized and arranged to eliminate direct pathways for electrical signals traveling between the tissue of the pulmonary vein  432  and atrial tissue  430 , as signals cannot cross region  438  without being diverted by at least one of lesions  472 ,  474 ,  476  and  478 . Thus, lesions  472 ,  474 ,  476  and  478  effect a complete or substantially complete conduction block that is sufficient to halt or sufficiently diminish the propagation of an arrhythmia. 
       FIG. 48  illustrates an exemplary implementation of a braided conductive member  480  that that may be used to form the lesion pattern of  FIG. 47 . Braided conductive member  480  has the same structure of interlaced conductive filaments  34  as braided conductive member  28 , but has a different pattern of uninsulated regions. Uninsulated regions  482 ,  484 ,  486  and  488  designate areas where insulation has been removed on the outer circumferential surface or the entire circumferential surface of filaments  34  of braided conductive member  480 . When braided conductive member  480  is fully energized with ablation energy, the ablation energy is transmitted to the tissue in a pattern that corresponds to the shape and orientation of regions  482 ,  484 ,  486  and  488 . Thus, uninsulated regions  482 ,  484 ,  486  and  488  correspond in configuration and arrangement to lesions  472 ,  474 ,  476  and  478 , respectively. 
     The principles described herein for providing zone control in braided conductive member  28  may also be applied to the braided conductive members of  FIGS. 44 ,  45  and  48 . In particular, braided conductive members  440 ,  450  and  480  may be divided into electrically independent sectors if desired. In the context of  FIG. 44 , one exemplary method of creating electrically independent sectors involves selecting a portion of the filaments  34  of braided conductive member  440  to deliver energy to the first region  444  and a different portion of the filaments  34  of braided conductive member  440  to deliver energy to the second region  442 . Only those filaments that are delivering energy to a given region will have insulation exposed in that region. Thus, according to this exemplary method, not all of the filaments that pass through a region will have insulation exposed in that region. Further, exposed portions of filaments that deliver energy to first region  444  can be insulated from filaments that deliver energy to second region  442  to avoid shorting the different sectors together. Similar principles may be applied to the braided conductive member  450  of  FIGS. 45 and 48  to create electrically independent sectors. 
     One potential benefit of providing electrically independent sectors is that it allows energy to be delivered to just one region (e.g., first region  444  or second region  442 ). This may be desirable because, in some instances, ablation of a smaller portion of heart tissue than would be ablated if both regions were energized may be sufficient to treat an arrhythmia. If ablation of a smaller region is effective, it is desirable to ablate only the smaller region so as to minimize the area of tissue death. Another potential benefit of providing electrically independent sectors is that it allows energy to be delivered to regions (e.g., first region  444  or second region  442 ) at different levels. Controlling the energy applied to the different regions allows the amount of ablation energy delivered to more closely approximate the amount of energy necessary to achieve a satisfactory conduction block. 
       FIG. 49  illustrates a side view of a catheter  490 , which is similar to the catheter of  FIG. 34   a , but has been modified to include the braided conductive member  440  shown in  FIG. 44 . 
     According to one exemplary implementation, the first and second regions  444 ,  442  of braided conductive member  440  may energized simultaneously, such that the lesion pattern shown in  FIG. 43  may be formed by a single application or multiple applications of RF energy to regions  444  and  442 . 
     According to another exemplary implementation, the first and second regions  444 ,  442  of braided conductive member  440  may energized individually, such that the lesion pattern shown in  FIG. 43  is formed by at least two applications of RF energy. To energize the first and second regions  442 ,  444  individually, the principles described above for providing zone control may be applied. Thus, a first group of filaments having insulation exposed within the second region  442  may be energized independently from a second group of filaments having insulation exposed within the first region  444 . For example, to energize first region  444  independently from second region  442 , filaments in regions  444   a - c  are energized. Region  444   c  does not include any filaments common to region  442 ; thus, all of the filaments that traverse region  444   c  may have insulation exposed in region  444   c  and may be energized. Regions  444   a  and  444   b , on the other hand, include filaments common to regions  442   a  and  442   b , respectively. To make region  444   a  independently energizable with respect to region  442   a , a first group of filaments traversing regions  444   a  and  442   a  may have their insulation exposed only in region  444   a ; a second group of filaments traversing regions  444   a  and  442   a , different from the first group, may have their insulation exposed only in region  442   a . Similarly, to make region  444   b  independently energizable with respect to region  442   b , a first group of filaments traversing regions  444   b  and  442   b  may have their insulation exposed only in region  444   b ; a second group of filaments traversing regions  444   a  and  442   b , different from the first group, may have their insulation exposed only in region  442   b . According to one example, the first groups of filaments may comprise filaments that are interleaved with filaments of the second groups of filaments. In view of the foregoing, it may be appreciated that to energize only first region  444 , filaments in region  444   c  may be energized, along with the first groups of filaments in regions  444   a  and  444   b.    
     It should be appreciated that any combination of the features described in connection with  FIGS. 43-49  may be advantageously employed with other catheter features or electrophysiology procedures described herein. 
     Having thus described at least one illustrative embodiment of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. For example, one skilled in the art will appreciate that each of the above described features may be selectively combined into a method of use and/or a device depending on, for example, the function desired to be carried out. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.