Abstract:
Devices for supporting diagnostic or therapeutic elements and assemblies for creating curves in the distal regions thereof. The assemblies are adapted to create compound curves such that respective portions of the distal region have distinct curvatures.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 08/645,456, filed May 13, 1996, now U.S. Pat. No. 5,820,591, which is a continuation-in-part of application Ser. No. 08/625,724, filed Mar. 29, 1996, now abandoned, which is itself a continuation of application Ser. No. 08/099,603, filed Jul. 30, 1993, now U.S. Pat. No. 5,395,327, which is itself a continuation of application Ser. No. 07/991,474, filed Dec. 16, 1992, now U.S. Pat. No. 5,254,088, which is itself a continuation of application Ser. No. 07/736,384, filed Jul. 26, 1991, now abandoned, which is itself a divisional of application Ser. No. 07/473,667, filed Feb. 2, 1990, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to catheters that can by steered by external controls. More particularly the invention relates to such catheters that can assume complex three dimensional curves. In addition, the invention relates to the use of such complex curves to ablate arrhythmia substrates in body tissue. 
     BACKGROUND OF THE INVENTION 
     Cardiac mapping is used to locate aberrant electrical pathways and currents emanating within the heart. Such aberrant pathways cause irregular contractions of the heart muscle resulting in life-threatening patterns or disrhythmias. 
     Ablation of cardiac tissue to create long curvilinear lesions within the heart is also desired for treatment of various disorders such as atrial fibrillation. Various steering mechanisms for catheters carrying such electrodes have heretofore been developed and used. 
     To access various endocardial sites, physicians have used a number of different catheters and techniques, each of which provides a different characteristic. The use of catheters having limited steering characteristics increases the risk inherent in any catheterization procedure and limits the accessibility of many potential ablation sites. 
     Site access using standard distal tip steerable catheters is less of a problem because those catheters position a single electrode into contact with the endocardium and a specific electrode orientation is not required. Problems of endocardial site access are accentuated when trying to simultaneously position multiple electrodes into intimate tissue contact. In this scenario, standard steerable catheter configurations orient multiple electrodes in planes emanating about the axis of the introduction vessel. 
     A need has thus existed for catheters which, in the nonlinear environment found within the heart as well as other body cavities, are capable of being steered to place ablation elements at a number of locations while creating intimate tissue contact throughout the length of all active ablation elements. 
     Particularly, a need has existed for a catheter which could effectively and accurately form curves in more than one plane for better access or tissue contact. Previous attempts to provide such devices are represented by U.S. Pat. No. 5,383,852 wherein there was suggested the use of steering wire extending from a central lumen of a catheter radially outward to the periphery of a distal end component. Another suggestion in represented by U.S. Pat. No. 5,358,479 wherein a single pull cable is attached to the distal end of a shim which has two flat sections that are twisted relative to each other. This arrangement, however limits the device to bending, first, of the more distal portion of the shim followed by subsequent bending of the more proximal section, thus limiting the procedures using the device. 
     SUMMARY OF THE INVENTION 
     The present inventions provides a catheter, usable in both diagnostic and therapeutic applications, that enables a physician to swiftly and accurately steer the distal section of the catheter containing the ablation and/or mapping element(s) in multiple planes or complex curves within the body of a patient. The catheters that embody the invention allows physicians to better steer a catheter to access various endocardial sites. In its broadest aspect, the invention provides catheters which enable a physician to position ablation and/or mapping electrodes inserted within a living body by manipulation of external controls into intimate contact with an interior body surface that curves in more than one plane. 
     One aspect of the invention provides a catheter having more than one steering mechanism for bending the distal section by external manipulation into more than one curvilinear direction. Movement of the individual controls results in bending of the distal section at more than one location and in more than one direction. Thus the ease of accessing and measuring electrical activity in all portions of the heart is increased. 
     In accordance with another embodiment, the catheter steering assembly may include a proximal section containing a preformed portion in conjunction with a distal steering mechanism which enables steering in a different plane that is non-parallel to the bending plane of the preformed proximal section, and/or improving tissue contact by moving the focal point of the steering mechanism to increase the angle of steering capable of applying force against the endocardial surface. This configuration may be accomplished by preforming the proximal section of the catheter into the desired curve or manipulating a preformed wire or other support structure which, when freed from the constraints of a sheath such as the catheter main body, causes the proximal section to assume the preformed shape. 
     In accordance with a further embodiment of the invention, a loop catheter has a preformed proximal end and a moveable wire attached to the distal end of the spline housing the ablation element(s). The preformed proximal end enables the loop to access varying planes relative to the catheter axis. 
     Further, objects and advantages of the invention will become apparent from the following detailed description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a catheter having a distal region with a compound steering assembly that embodies features of the invention; 
     FIG. 2 is a fragmentary side view of the handle portion of the catheter shown in FIG. 1; 
     FIG. 3 is a perspective view of one embodiment of a compound steering assembly that embodies features of the invention; 
     FIG. 4 is a side section view of another embodiment of a compound steering assembly that embodies features of the invention; 
     FIGS. 5A to  5 C are side views, with portions broken away and in section, of the compound steering assembly shown in FIG. 4 in use; 
     FIGS. 6A to  6 C are side views, with portions broken away and in section, of an alternative embodiment of a compound steering assembly that embodies features of the invention being used; 
     FIG. 7 is an exploded perspective view of a two piece offset spring assembly that forms a part of an alternative embodiment of a compound steering assembly that embodies feature of the invention; 
     FIGS. 8 and 9 are side perspective views of the compound steering assembly that incorporates the two piece offset spring assembly shown in FIG. 7; 
     FIG. 10A is a side view of another embodiment of a compound steering assembly that embodies features of the invention; 
     FIG. 10B is a top sectional view of the compound steering assembly shown in FIG. 10A, taken generally along line  10 B— 10 B in FIG. 10A; 
     FIG. 11 is a side view of another embodiment of a compound steering assembly that embodies features of the invention; 
     FIGS. 12 and 13 are side views of another embodiment of a compound steering assembly that embodies features of the invention; 
     FIGS. 14 and 15 are side views of another embodiment of a compound steering assembly that embodies features of the invention; 
     FIG. 16 is a side view of a complex curve that a compound steering assembly made in accordance with the invention can assume; 
     FIGS. 17 and 18 are side views of another embodiment of a compound steering assembly that embodies features of the invention; and 
     FIGS. 19A to  19 C are side views of another embodiment of a compound steering assembly that embodies features of the invention. 
    
    
     The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     This Specification discloses electrode-carrying structures that can be bent in compound and complex manners for greater maneuverability within the body and enhanced contact with tissue. The illustrated and preferred embodiments discuss these structures, systems, and techniques in the context of catheter-based cardiac ablation. That is because these structures, systems, and techniques are well suited for use in the field of cardiac ablation. 
     Still, it should be appreciated that the invention is applicable for use in other tissue ablation applications. For example, the various aspects of the invention have application in procedures for ablating tissue in the prostrate, brain, gall bladder, uterus, and other regions of the body, using systems that are not necessarily catheter-based. 
     FIG. 1 shows a catheter  10 , which embodies features of the invention. The catheter  10  includes a handle  12  and a flexible catheter body  14 . The distal region  16  of the catheter body  14  carries at least one electrode  18 . In the illustrated and preferred embodiment, the distal region  16  carries an array of multiple electrodes  18 . 
     The electrodes  18  can serve to monitor electrical events in heart tissue, or transmit electrical energy to ablate heart tissue, or both. Signal wires (not shown)are electrically coupled to the electrodes  18  in conventional fashion. The signal wires extend through the catheter body  14  into the handle  12 . The signal wires electrically connect to an exterior plug  22 , which can be connected to signal processing equipment or a source of electrical ablation energy, or both. 
     The catheter  10  shown in FIG. 1 includes a steering mechanism  20 . The mechanism  20  includes two control knobs  24  and  26  on the handle  12 , which can be individually manipulated by the physician. 
     As will be described in greater detail later, the steering mechanism  20  is coupled to a compound steering assembly  28 , which is carried within the distal region  16  of the catheter body  14 . Operation of the control knobs  24  and  26  bend the steering assembly  28  to flex the distal region  16  (as FIG. 1 generally shows) in ways that aid in orienting the ablation element  18  in intimate contact with tissue. 
     FIG. 3 shows one embodiment of a compound steering assembly, designated by reference numeral  28 ( 1 ), that embodies features of the invention. The compound steering assembly  28 ( 1 ) includes a spring element formed as a single piece in two bendable sections  30  and  32 . The bendable section  30  is distal to the bendable section  32 . 
     In the illustrated embodiment, the bendable sections  30  and  32  are arranged essentially orthogonally relative to each other, being offset by about 90°. Different offset angles between 0° and 180° may be used. 
     The proximal end of the proximal bendable section  32  is secured within a guide tube  34 . In the illustrated embodiment, the guide tube  34  takes the form of a coiled stainless steel spring. The guide tube  34  extends from the steering assembly  28 ( 1 ) rearward within the catheter body  14  to the handle  12 . The guide tube  34  serves to stiffen the catheter body  14  and to help impart twisting motion from the handle to the steering assembly  28 ( 1 ). 
     As FIG. 3 shows, a distal steering wire  36  is attached by soldering or adhesive to one surface of the distal bendable section  30 . The steering wire  36  extends from the bendable section  30  through a guide tube  38  secured by soldering or adhesive to a surface  40  of the proximal bendable section  32 . From there, the steering wire  36  extends through the guide tube  34  into the handle  12 . The steering wire  36  is coupled to the control knob  24  within the handle  12 , as will be described in greater detail later. 
     A proximal steering wire  42  is attached by soldering or adhesive to the surface  44  of the proximal bendable section  32  opposite to the surface  40 . From there, the steering wire  42  extends through the guide tube  34  into the handle  12 . The steering wire  42  is coupled to the control knob  26  within the handle  12 , as will be described in greater detail. 
     Flexible heat shrink tubing  56  (shown in FIG.  1  and in phantom lines in FIG. 3) encloses the compound steering assembly  28 ( 1 ). 
     As FIG. 2 shows, the control knobs  24  and  26  are individually coupled by shafts, respectively  45  and  46 , to rotatable cam wheels, respectively  48  and  50 , within the handle  12 . Rotation of the respective knob  24  and  26  serves to rotate its respective cam wheel  48  and  50 . The steering wire  36  is attached to the cam wheel  48 , and the steering wire  42  is attached to the cam wheel  50 . 
     Further details of the structure of the cam wheels  48  and  50  and their attachment to the steering wires  36  and  42  are not essential to the invention and can be found in U.S. Pat. No. 5,254,088, which is incorporated herein by reference. 
     Rotation of the cam wheel  48  (by manipulation of the knob  24 ) pulls upon the distal steering wire  36 . This, in turn, pulls upon the distal bendable section  30 , flexing the bendable section  30  in the direction of the wire  36  (shown by arrow  52  in FIG.  3 ). The guide tube  38  facilitates movement of the steering wire  36  and the transmission of the pulling force from the cam wheel  48  to the bendable section  30 . In the absence of the pulling force upon the wire  36 , the bendable section  30  resiliently returns to its normal unbent condition (shown in FIG.  3 ). 
     Likewise, rotation of the cam wheel  50  (by manipulation of the knob  26 ) pulls upon the steering wire  42 . This, in turn, pulls upon the proximal bendable section  32 , flexing the bendable section  32  in the direction of the wire  42  (as arrow  54  shows in FIG.  3 ). In the absence of the pulling force upon the wire  42 , the bendable section  32  resiliently returns to its normal unbent condition (as FIG. 3 shows). 
     In the illustrated and preferred embodiment, the guide tube  38  comprises a stainless steel coil. As a steel coil, the guide tube  38  provides bending resistance and bias for the assembly  28 ( 1 ) to return to the unbent orientation after deflection. 
     The compound steering assembly  28 ( 1 ) makes possible the formation of complex curves in the distal region  16 . Pulling on the distal wire  36  bends the distal region  16  in the direction  52 . Pulling on the proximal steering wire  42  further bends the distal region  16  in a different direction  55 . 
     FIG. 3 shows a single steering wire  36  and  42  attached to each bendable section  30  and  32  to provide unidirectional bending of each section  30  and  32 . Of course, either or both bendable sections  30  and  32  may include an opposing pair of steering wires (not shown) to provide bidirectional bending action. If bidirectional bending of the distal section  30  is desired, a guide tube  38  is preferably provided for each steering wire attached to the section  30 . In this arrangement, the guide tubes should preferably comprise a material at least as flexible as the proximal section  32  itself, so as to not impede the desired bending action. 
     FIG. 4 shows an alternative embodiment of a compound steering assembly, designated  28 ( 2 ). The compound steering assembly  28 ( 2 ) includes a spring element formed as a single piece in two bendable sections  58  and  60 . The bendable section  58  is distal to the bendable section  60 . 
     Like the embodiment shown in FIG. 3, the proximal end of the bendable section  60  is secured within a guide tube  34 . Unlike the embodiment shown in FIG. 3, the bendable sections  58  and  60  are not offset from each other, but extend in the same plane. 
     A pair of steering wires  62  and  64  are attached to opposite surfaces of the distal bendable section  58 . The steering wires  62  and  64  extend rearward through the guide tube  34  within the catheter body  14  for attachment to opposite sides of a rotatable cam wheel (not shown) within the handle  12 . U.S. Pat. No. 5,254,088 shows the details of this construction, which is incorporated herein by reference. Rotation of the cam wheel in one direction pulls on the steering wire  62  to bend the distal section  58  in one direction (shown by arrow  66 A in FIG.  4 ). Rotation of the cam wheel in the opposite direction pulls on the steering wire  64  to bend the distal section  58  in the opposite direction (shown by arrow  66 B in FIG.  6 ). Bidirectional steering of the distal section  58  is thereby achieved. 
     The compound steering assembly  28 ( 2 ) shown in FIG. 4 further includes a preformed wire  68  secured by soldering or adhesive to the proximal bendable section  60 . The preformed wire  68  is biased to normally curve. The preformed wire  68  may be made from stainless steel  17 / 7 , nickel titanium, or other memory elastic material. It may be configured as a wire or as a tube with circular, elliptical, or other cross-sectional geometry. 
     The wire  68  normally imparts its curve to the attached bendable section  60 , thereby normally bending the section  60  in the direction of the curve. The direction of the normal bend can vary, according to the functional characteristics desired. The wire  68  can impart to the section a bend in the same plane as the distal bendable section  58  (as shown by arrow  66 C in FIG.  4 ), or in a different plane. 
     In this arrangement, the steering assembly  28 ( 2 ) further includes a main body sheath  70 . The sheath  70  slides along the exterior of the catheter body  14  between a forward position overlying the junction between the wire  68  and proximal bendable section  60  and an aft position away from the proximal bendable section  68 . In its forward position, the sheath  70  retains the proximal bendable section  60  in a straightened configuration against the normal bias of the wire  68 , as FIG. 4 shows. The sheath  70  may include spirally or helically wound fibers to provide enhanced tensile strength to the sheath  70 . Upon movement of the sheath  70  to its aft position, the proximal bendable section  60  yields to the wire  68  and assumes its normally biased bent position. The slidable sheath  70  is attached to a suitable control mechanism on the handle  12 . 
     As FIG. 5A shows, during introduction of the proximal catheter region  16  into the body, the sheath  70  is retained in its forward position. This retains the proximal bendable section  60  in a substantially straight orientation (as FIG. 4 also shows). After introduction of the distal catheter region  16  into a desired heart chamber, the sheath  70  is withdrawn (as shown in a stepwise fashion by FIGS.  5 B and  5 C). The wire  68  urges the proximal bendable section  60  to assume a curvature in the direction indicated by arrow  66 C. 
     The embodiment of FIGS.  4  and  5 A/B/C provides compound curves. The amount of curvature of the preshaped wire  68  is selected in accordance with the projected shape of the body chamber into which the catheter is introduced. Further bending of the distal section  58  is accomplished by pulling on the steering wires  62  and  64 . 
     It should be appreciated that, instead of a stationary preshaped wire  68  and movable sheath  70 , the steering assembly  28 ( 2 ) can include a precurved stylet  72  (see FIGS. 6A to  6 C) moveable along the proximal bendable section  60  within a stationary sheath  74 . A mechanism (not shown) mounted in the handle affects movement of the stylet  72  under the control of the physician. The stationary sheath  74  extends about the catheter body  14  up to distal region  16 . 
     When located within the region of the sheath  74  (as FIG. 6A shows), the stylet  72  is retained by the sheath  74  in a straight condition. When the preshaped stylet  72  is advanced beyond the sheath  74  (as FIGS. 6B and 6C show, the stylet  72  imparts its normal curve to the proximal section  60 , causing it to assume a curvature determined by the stylet  72 . 
     FIGS. 7 to  9  show another alternative embodiment for a compound steering assembly, designated  28 ( 3 ), embodying features of the invention. The compound steering assembly  28 ( 3 ) includes a composite spring  76  formed from two individual spring sections  78  and  80  (see FIG.  7 ). The spring sections  78  and  80  include mating central notches  82  and  84 , which nest one within the other to assemble the spring sections  78  and  80  together. Soldering or brazing secures the assembled sections  78  and  80  to complete the composite spring  76 . 
     The resulting composite spring  76 , like the spring shown in FIG. 3, comprises a bendable distal section  30  (spring section  78 ) and a bendable proximal section  32  (spring section  80 ). The bendable proximal section  32  is secured to a guide coil in the catheter body in the same manner shown in FIG.  3 . 
     As FIGS. 8 and 9 further show, the compound steering assembly  28 ( 3 ) preferably includes two steering wires  86  and  88  attached by soldering or adhesive to opposite surfaces of the distal bendable section  30 . The steering wires  86  and  88  each extend from the distal bendable section  30  through a guide tube  90  secured by soldering or adhesive to one surface  92  of the proximal bendable section  32 . From there, the steering wires  86  and  88  extend through the main guide tube  34  within the catheter body  14  into the handle  12  for attachment to a control mechanism in the handle, as already described. 
     As FIGS. 8 and 9 also show, the compound steering assembly  28 ( 3 ) preferably includes one steering wire  94  attached by soldering or adhesive to the proximal bendable section  32  on the surface opposite to the surface to which the guide tubes  90  are attached. The steering wire  94  likewise passes through guide tube  34  within the catheter body  14  for attachment to a second control mechanism in the handle, as already described. 
     As also previously described, the guide tubes  90  preferable take the form of metal coils. As coils, the guide tubes  90  provide increased spring bias to aid the return of the proximal bendable section  32  to the straightened position in the absence of pulling force on the steering wire. 
     The compound steering assembly  28 ( 3 ) shown in FIGS. 8 and 9 permits flexing the distal bendable section  30  in opposite directions normal to the surface of spring section  78 . The compound steering assembly  28 ( 3 ) also permits independent flexing of the proximal bendable section  32  in a single direction normal to the surface of spring section  80  to which the steering wire  94  is attached. 
     While the illustrated and preferred embodiment of the proximal bendable section  32  shown in FIGS. 8 and 9 does not permit bidirectional bending, it should be appreciated that two oppositely attached steering wires may be attached to the proximal section  32  to allow bidirectional steering. In this arrangement, the guide tubes  90  should be made of materials no less flexible than the proximal section itself. 
     FIGS. 10A and 10B show another alternate embodiment of a compounding steering assembly, designated  28 ( 4 ). The compound steering assembly  28 ( 4 ) includes two separate steering assemblies  96  and  98  radially offset from each other within the catheter body  14  (see FIG.  10 B). Each steering assembly  96  and  98  includes a bendable spring, respectively  100  and  102 , carried by relatively small diameter spring coils, respectively  104  and  106 . The bendable spring  100  extends distally to the bendable spring  102 . 
     A pair of steering wires  108  and  110  are attached to the opposite sides of the distal steering spring  100  to enable bending in a first plane (shown by arrows  112  in FIG.  10 A). A second pair of steering wires  114  and  116  are attached to opposite sides of the proximal steering spring  102  to enable bending in a second plane (shown by arrows  118  in FIG.  10 A). As FIG. 10A shows, the small diameter wire coils  104  and  106  may themselves be contained within the larger diameter steering coil  34  within the catheter body  14 . 
     Instead of steering wires  108 / 110  and  114 / 116 , either or both springs  100  and  102  could be attached to preshaped wires (not shown) to assume a desired curvature, to thereby bend the respective spring in the manner shown in FIG.  4 . Alternatively, the compound steering assembly  28 ( 4 ) may includes a third, preshaped wire section (not shown), like that shown in FIG. 4 located, either proximally or distally to the bendable springs  100  and  102 . In these arrangements, an external slidable sleeve (not shown) is used to selectively straighten the preshaped wire when desired. In this way, complex bends can be formed in the distal region in at least 3 different planes, or, alternatively, two bending locations can be provided in a single plane with another bending location being provided in an orthogonally separate plane. 
     FIG. 11 shows an alternative embodiment of a compound steering assembly, designated  28 ( 5 ), that reduces stiffness of the proximal section. The compound steering assembly  28 ( 5 ) includes two side-to-side guide coils  120  and  122 . A distal element  124  is soldered between the distal ends of the guide coils  120  and  122 , thereby collectively forming a distal bendable section  30 . A PET retaining sleeve  126  preferably holds the guide coils  120  and  122  together orthogonal to plane of the distal element  124 . 
     Distal steering wires  128  and  130  are attached to opposite sides of the distal element  124 . The steering wires  128  and  130  pass through the guide coils  120  and  122  and into the main guide coil  34  within the catheter body  14  for attachment to a control element on the handle. By applying tension to a steering wire  128  and  130 , the distal element  124  and guide coils  120  and  22  bend as a unified structure in the direction of the tensioned steering wire. 
     A proximal steering wire  132  is soldered to a transverse edge  134  of the distal element  124 . The proximal steering wire  132  also extends into the main guide coil  34  within the catheter body  14  for attachment to another control element on the handle. By applying tension to the proximal steering wire  132 , the distal element  124  and guide coils  120  and  122  bend as a unified structure in a direction orthogonal to the direction controlled by the distal steering wires  128  and  130 . A second proximal steering wire (not shown) could be soldered to the opposite transverse edge of the distal element  124  for bi-directional steering. 
     FIGS. 12 and 13 show another embodiment of a compound steering assembly, designated  28 ( 6 ) that embodies features of the invention. The steering assembly  28 ( 6 ) includes a preformed proximal section  136 , which maintains a predefined curve, thereby forming a bend in the distal region  16 . The distal end of the preformed proximal section  136  carries a ferrule  138 . The ferrule  138  includes a notch  140 . A bendable distal spring  142  fits within the notch  140 . 
     The distal spring  142  includes two oppositely attached steering wires  144  and  146 . Bidirectional bending of the spring  142  is thereby provided. Alternatively, a single steering wire could be provided for single directional bending. 
     A sleeve (not shown) made of Kevlar polyester or Kevlar Teflon or plain polyester preferable encircles the junction of the distal spring  142  and the ferrule  138  to strengthen the junction. Further details concerning the sleeve and the attachment of the spring to the distal end of the proximal section are contained in U.S. Pat. No. 5,257,451, which is incorporated herein by reference. 
     As shown in FIGS. 12 and 13, the notched ferrule  138  holds the distal spring  142  in a plane that is generally orthogonal to the plane of the preshaped bend of the preformed proximal section  136 . The distal spring  142  therefore bends in two cross-plane directions, to the right and to the left of the proximal section  136  (as arrows  148  in FIG. 13 show). Still, it should be appreciated that the notched ferrule  138  can be rotated to hold the distal spring  142  in any desired angular relationship with the preshaped proximal section  136 . 
     For example, FIGS. 14 and 15 show the notch  140  of the ferrule  138  has been rotated to orient the distal spring  142  in generally the same plane as the preformed proximal section  136 . In this arrangement, the distal spring  142  is supported for bi-directional, in-plane bending, upward and downward of the preformed proximal section (as arrows  150  in FIG. 15 show). 
     The proximal section  136  may be preformed into any desired curve, simple (as FIGS. 12 and 13 and FIGS. 14 and 15 show) or complex (as FIG. 16 shows, without a distal spring  142  attached). 
     In the illustrated simple and complex curve embodiments, the proximal section  136  preferably comprises a braid tube  152  made of polyamide with wire braid, which is thermally formed into the desired shape. The preshaped proximal tube  152  preferably contains within it a guide coil  154 , through which the steering wires  144 / 146  for the distal spring  142  pass. The steering wires  144 / 146  may also be preshaped like the proximal section to prevent straightening the preformed proximal section. 
     In the illustrated and preferred embodiments shown in FIGS. 12 and 13 and FIGS. 14 and 15, a flatwire  156  lends additional support to the preformed proximal section  136 . The flatwire  156  is formed in a preshaped curve matching corresponding to the proximal section  136 . The flatwire  156  is preferably bonded to the exterior of the proximal tube  152 . Also preferably, an exterior polyester shrink tube  158  encloses the flatwire  156  and proximal tube  152  to hold them intimately together. The polyester shrink tube  158  can also serve this purpose without first bonding the flatwire  156  to the proximal tube  152 . The assembly of the flatwire  156  and shrink tube  158  as just described can also be used in association with the complex curve shown in FIG.  16 . 
     In an alternative embodiment (see FIGS.  17  and  18 ), a compound steering assembly, designated  28 ( 7 ) includes a proximal section  160  comprising a guide coil  166  that does not have a preset curvature. In this embodiment, the steering assembly  28 ( 7 ) includes a flatwire  162  preshaped into the desired curve. The precurved flatwire  162  includes a bracket  164  at its distal end designed to receive and support the guide coil  166 . The bracket  164  is spot welded to the guide coil  166 , thereby holding the guide coil  166  in a bent condition corresponding to the curve of the flatwire  162 . A heat shrink polyester tube (not shown) preferably encircles the flatwire  162  and guide coil  166  to hold them together. The preformed proximal section  136  is thereby formed. 
     The compound steering assembly  28 ( 7 ) includes a notched ferrule  138  like that shown in the preceding FIGS. 12 to  16 . The ferrule  138  is spot welded to the distal end of the guide coil  166  (see FIG. 18) to receive and support a distal bendable spring  142  and steering wires  144  and  146 , in the manner previously shown in FIGS. 12 to  16 . As before described, the notch  140  of the ferrule  138  can be rotated to orient the distal spring  142  in any desired orientation, either orthogonal to the curve axis of the preformed proximal section (as FIG.  18  and preceding FIGS. 12 and 13 show), or in plane with the curve axis of the preformed proximal section (as preceding FIGS. 14 and 15 show), or any desired angular relationship in between. 
     Instead of using a preformed braid tube  152  and/or a flatwire  156 / 162  to preform the proximal section  136  in the manner above described, the proximal section  136  may take the form of a malleable tube, which can be bent by the physician into the desired simple or complex curvature. 
     As FIG. 16 represents, the preformed proximal section  136  may be shaped in any simple 2-dimensional or complex 3-dimensional shape. Virtually any curvature can be selected for the proximal section end, provided that the curvature permits unimpeded movement of the steering wires  144 / 146  for the bendable distal spring  142 . Furthermore, the stiffness of the preformed proximal section  136  is controlled so that it readily yields for straightening during introduction, either through the vasculature or a guide sheath. 
     In vivo experiments demonstrate that the walls of the vasculature themselves provide enough force to straighten the proximal section  136  made according to the invention, to thereby enable easy advancement of the distal region  16  of the catheter body  14  through the vasculature. Guide sheaths may also be used, if desired. 
     Entry of the distal region  16  of the catheter body  14  into the desired body cavity frees the proximal section  136 , and it assumes its predefined shape as previously described. The physician may now further manipulate the distal region  16  by rotating the catheter body  14  and/or bending the distal spring  142  to locate the ablation and/or sensing element(s)  18  at the desired tissue location(s). 
     The various compound steering assemblies  28 ( 1 ) to  28 ( 7 ) that the invention provides make it possible to locate the ablation and/or mapping electrode(s) at any location within the body cavity. With prior conventional catheter designs, various awkward manipulation techniques were required to position the distal region, such as prolapsing the catheter to form a loop within the atrium, or using anatomical barriers such as the atrial appendage or veins to support one end of the catheter while manipulating the other end, or torquing the catheter body. While these techniques can still be used in association with the compound assemblies  28 ( 1 ) to  28 ( 7 ), the compound bendable assemblies  28 ( 1 ) to  28 ( 7 ) significantly simplify placing electrode(s) at the desired location and thereafter maintaining intimate contact between the electrode(s) and the tissue surface. The compound assemblies  28 ( 1 ) to  28 ( 7 ) make it possible to obtain better tissue contact and to access previously unobtainable sites, especially when positioning multiple electrode arrays. 
     Compound bendable assemblies  28 ( 1 ) to  28 ( 7 ) which provide a proximal curved section orthogonal to the distal steering plane allow the physician to access sites which are otherwise difficult and often impossible to effectively access with conventional catheter configurations, even when using an anatomic barrier as a support structure. For example, to place electrodes between the tricuspid annulus and the cristae terminalis perpendicular to the inferior vena cava and superior vena cava line, the distal tip of a conventional the catheter must be lodged in the right ventricle while the catheter is torqued and looped to contact the anterior wall of the right atrium. Compound bendable assemblies  28 ( 1 ) to  28 ( 7 ) which can provide a proximal curved section orthogonal to the distal steering plane greatly simplify positioning of electrodes in this orientation. Compound bendable assemblies  28 ( 1 ) to  28 ( 7 )which provide a proximal curved section orthogonal to the distal steering plane also maintain intimate contact with tissue in this position, so that therapeutic lesions contiguous in the subepicardial plane and extending the desired length, superiorly and/or inferiorly oriented, can be accomplished to organize and help cure atrial fibrillation. 
     A transeptal approach will most likely be used to create left atrial lesions. In a transeptal approach, an introducing sheath is inserted into the right atrium through the use of a dilator. Once the dilator/sheath combination is placed near the fossa ovalis under fluoroscopic guidance, a needle is inserted through the dilator and is advanced through the fossa ovalis. Once the needle has been confirmed to reside in the left atrium by fluoroscopic guidance of radiopaque contrast material injected through the needle lumen, the dilator/sheath combination is advanced over the needle and into the left atrium. At this point, the dilator is removed leaving the sheath in the left atrium. 
     A left atrial lesion proposed to help cure atrial fibrillation originates on the roof of the left atrium, bisects the pulmonary veins left to right and extends posteriorly to the mitral annulus. Since the lesion described above is perpendicular to the transeptal sheath axis, a catheter which can place the distal steering plane perpendicular to the sheath axis and parallel to the axis of the desired lesion greatly enhances the ability to accurately place the ablation and/or mapping element(s) and ensure intimate tissue contact with the element(s). To create such lesions using conventional catheters require a retrograde procedure. The catheter is advanced through the femoral artery and aorta, past the aortic valve, into the left ventricle, up through the mitral valve, and into the left atrium. This approach orients the catheter up through the mitral valve. The catheter must then be torqued to orient the steering plane parallel to the stated lesion and its distal region must be looped over the roof of the left atrium to position the ablation and/or mapping element(s) bisecting the left and right pulmonary veins and extending to the mitral annulus. This awkward technique often fails to create adequate tissue contact necessary for therapeutic lesions. 
     Preformed guiding sheaths have also been employed to change catheter steering planes. However, preformed guiding sheaths have been observed to straighten in use, making the resulting angle different than the desired angle, depending on the stiffness of the catheter. Furthermore, a guiding sheath requires a larger puncture site for a separate introducing sheath, if the guiding sheath is going to be continuously inserted and removed. Additional transeptal punctures increase the likelihood for complications, such as pericardial effusion and tamponade. 
     While various preferred embodiments of the invention have been shown for purposes of illustration it will be understood that those skilled in the art may make modifications thereof without departing from the true scope of the invention as set forth in the appended claims. 
     For example, as FIGS. 19A to  19 C show a compound loop assembly  168  carried at the distal end of a catheter body  14 . The loop assembly  168  comprises at least two loop splines  168  and  170 . 
     The loop spline  168  carries an array of ablation elements  172 . According to the features of the invention described above, the loop spline  168  includes a proximal section  174  that is preformed into a desired curvature to access additional planes. 
     Since the loop spline  168  may be formed from memory elastic materials, the spline  168  may be preformed into any desired shape through mechanically forming the spline  168  and thermally forming the spline  168  in that shape. Preshaped braid tubing or other support may also be included to help maintain the shape of the proximal spline bend  174 , as previously described. 
     As FIGS. 19B and 19C show, the other spline  170  of the loop structure  168  may be retracted or advanced to decrease or increase the loop diameter to affect desired tissue contact and ablation element location. 
     The two splines  168  and  170  may be fabricated from a single wire made of nickel titanium or other memory elastic material. Alternatively, the two splines  168  and  170  may be fabricated from two or more wires which are connected by a distal tip at a common point. One spline may be attached to the catheter body, or two splines may be attached to the catheter body with another stylet to manipulate the preshaped loop, or both splines may be maneuvered. 
     Various features of the invention are set forth in the following claims.