Patent Publication Number: US-2021162178-A1

Title: Catheter with improved loop contraction and greater contraction displacement

Description:
CROSS-REFERENCE TO CO-PENDING APPLICATION 
     The present application is a Continuation application under 35 U.S.C. § 120 of U.S. patent application Ser. No. 15/470,291, filed Mar. 27, 2017. The entire contents of this application is incorporated by reference herein in its entirety. 
    
    
     FIELD OF INVENTION 
     This invention relates generally to methods and devices for invasive medical treatment, and specifically to catheters, in particular, catheters having distal sections adapted for mapping and ablating selected anatomy. 
     BACKGROUND 
     Ablation of myocardial tissue is well known as a treatment for cardiac arrhythmias. In radio-frequency (RF) ablation, for example, a catheter is inserted into the heart and brought into contact with tissue at a target location. RF energy is then applied through an electrode on the catheter in order to create a lesion for the purpose of breaking arrhythmogenic current paths in the tissue. 
     Circumferential ablation of the ostia of the pulmonary vein is now accepted as a treatment for atrial arrhythmias, and particularly for atrial fibrillation. For example, U.S. Pat. No. 6,064,902, whose disclosure is incorporated herein by reference, describes a catheter for ablating tissue on the inner wall of a blood vessel, such as a pulmonary vein. The tip portion of the catheter is deflectable from a first, generally straight, configuration, in which the proximal and distal sections are substantially co-linear, to a second, J-shaped, configuration in which the proximal and distal sections are generally parallel with a separation therebetween substantially corresponding to the inside diameter of the blood vessel. The distal end portion of the catheter is rotated about the longitudinal axis of the catheter to cause a circumferential displacement of proximal and distal ablation electrodes on the catheter along the inner wall of the pulmonary vein. In this way, the electrode catheter may be used to ablate a number of circumferentially-spaced sites on the inner wall of the pulmonary vein by ablating one or two sites at each circumferential position. 
     U.S. Pat. No. 6,973,339, whose disclosure is incorporated herein by reference, describes a lasso for pulmonary vein mapping and ablation. A catheter for circumferentially mapping a pulmonary vein (PV) includes a curved section shaped to generally conform to the shape of the interior surface of the PV. The curved section is connected to catheter by a generally straight axial base section that is in an “on edge” configuration where the base axial section connects to the curved section on the circumference of the curved section. The curved section comprises one or more sensing electrodes, and its proximal end is joined at a fixed or generally known angle to a base section of the catheter. Position sensors are fixed to the curved section of the catheter and to the distal end of the base section. The catheter is inserted into the heart, and the curved section is positioned in contact with the wall of the PV, while the base section remains within the left atrium, typically positioned such that the joint with the curved section is at the ostium of the vein. The information generated by the three position sensors is used to calculate the locations and orientations of the sensing electrodes, which enables mapping of the surface of the PV. The sensing electrodes may additionally perform ablation of selected sites, or the catheter may further comprise ablation elements. 
     U.S. Pat. No. 7,008,401, whose disclosure is incorporated herein by reference, describes compound steering assemblies, usable in both diagnostic and therapeutic applications, for steering the distal section of a catheter in multiple planes or complex curves. These assemblies are said to enable a physician to swiftly and accurately position and maintain ablation and/or mapping electrodes in intimate contact with an interior body surface. U.S. Pat. No. 5,820,591, whose disclosure is incorporated herein by reference, similarly describes compound steering assemblies of this sort. 
     U.S. Pat. No. 8,608,735 whose disclosure is incorporated herein by reference, describes a medical device, including an insertion shaft, having a longitudinal axis and having a distal end adapted for insertion into a body of a patient. A resilient end section is fixed to the distal end of the insertion shaft and is formed so as to define, when unconstrained, an arc oriented obliquely relative to the axis and having a center of curvature on the axis. One or more electrodes are disposed at respective locations along the end section. 
     However, because human anatomy varies between individuals, the shape and size of an ostium vary, and the arcuate distal section may not always fit the particular target ostium. Moreover, it may be desirable to use the same catheter for a target ostium of a certain diameter and also the PV of that ostium which may have a significantly lesser diameter. Additionally, where a lasso catheter may have a variable arcuate distal assembly, contraction of the arcuate distal assembly may misshapen the generally circular form of the arcuate distal assembly because one or more of the components thereof are too stiff for tighter coiling in a desirable manner. 
     Current circular loop catheters are constructed utilizing a support member, e.g., a nitinol spine, with a constant uniform cross-section that fails to consistently maintain a circular configuration during loop contraction. Such current circular loop catheters also are limited in its contraction and deflection characteristics in requiring more pound contraction wire tensile force for less loop contraction. Moreover, current circular loop catheters may lack reliable attachment between the contraction wire and the support member that would eliminate possible breakage or release of the contraction wire from the support member. Current circular loop catheters have nitinol spines with the same uniform area moments of inertia along their entire length and the nitinol spines have the same cross-sectional area. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a catheter having a variable arcuate distal with improved contraction and bending radius characteristics, along with greater durability. The variable arcuate distal section includes a shape-memory support member, a contraction wire, and a radially-constrictive tubing or sleeve to greatly increase the degree of contraction of a generally circular catheter loop while decreasing the forces on the contraction wire and all other structural support portions of the loop and providing operators of the catheter with a repeatable and more truthful round contraction for circular diagnostic and therapeutic catheters. 
     In some embodiments, the radially-constrictive tubing is transparent or at least translucent so that the contraction wire under the tubing is visible, especially during assembly of the variable arcuate distal section. 
     In some embodiments, the radially-constrictive tubing has a braided construction so that its radial constriction is increased when tension is applied to the tubing in a longitudinal direction. 
     In some embodiments, the radially-constrictive tubing is constructed of a manufactured fiber, spun from a liquid crystal polymer (LCP), for example, manufactured fiber sold under the trademark VECTRAN®, created by Celanese Acetate LLC and now manufactured by Kuraray Co., Ltd. 
     In some embodiments, an electrophysiology catheter includes an elongated catheter body, a contraction wire, and a distal assembly configured for contraction by actuation of the contraction wire. The distal assembly has a shape-memory support member having a 3-D configuration with a distal portion defined by a distal radius. 
     In more detailed embodiments, the support member has an inner side facing an inner circumference of the 3-D configuration, wherein a coextensive portion of the contraction wire extending through the distal assembly is aligned with the inner side. 
     In some detailed embodiments, the distal assembly includes a radially constrictive tubing surrounding the support member and a coextensive portion of the contraction wire with the support member. 
     In some detailed embodiments, the support member and the coextensive segment of the contraction wire jointly define a cross-sectional profile, and the radially constrictive tubing surrounds the support member and the coextensive segment generally in conformity to the cross-sectional profile. 
     In some detailed embodiments, the coextensive portion of the contraction wire is aligned with a flat side of the support member and configured to maintain the coextensive segment of the contraction wire generally in align the flat side during contraction of the distal assembly. 
     In some embodiments, an electrophysiology catheter has an elongated catheter body defining a longitudinal axis, a contraction wire, and a 3-D distal assembly movable between a neutral configuration and a contracted configuration in response to longitudinal movement of the contraction wire. The 3-D distal assembly has at least an elbow defined by a proximal diameter and a distal portion defined by a distal diameter, and a radially constrictive tubing that extends generally between the elbow junction and the distal portion. For the neutral configuration, the proximal diameter is less than the distal diameter. For the contracted configuration, the distal diameter is about equal to or less than the proximal diameter. 
     In some detailed embodiments, the elbow junction has a twist configured to support the distal portion generally transversal to the longitudinal axis such that the longitudinal axis extends through a center of the distal portion. 
     In some detailed embodiments, the distal assembly has an elongated support member having an inner flat side and an opposing flat side, and wherein the contraction wire has a distal segment coextensive with the inner flat side along its entire length. 
     In some detailed embodiments, the inner side of the support member is on or near an inner circumference of the distal portion of the 3-D distal assembly. 
     In some embodiments, the distal assembly further includes a radially-constrictive tubing circumferentially surrounding at least a portion of the elongated support member and a friction-reducing tubing surrounding a portion of the contraction wire. 
     In some embodiments, the radially-constrictive tubing is circumferentially constrictive around the support member and the friction-reducing tubing in minimizing lateral movement of the contraction wire relative to the support member. 
     In other embodiments, an electrophysiology catheter has an elongated catheter body defining a longitudinal axis, a contraction wire, and a distal assembly with a 3-D arcuate form, the distal assembly movable between a neutral configuration and a contracted configuration in response to longitudinal movement of the contraction wire. The distal assembly has a support member providing the 3-D arcuate form, the 3-D arcuate form having an elbow junction and a distal portion, the elbow junction defined by at least a proximal diameter and the distal portion defined by a distal diameter, and a radially constrictive tubing surrounding the support member and a coextensive portion of the contraction wire. For the neutral configuration, the proximal diameter is less than the distal diameter. For the contracted configuration, the distal diameter is decreased to a diameter about less than the distal diameter. 
     In some detailed embodiments, the 3-D arcuate form defines an inner circumference, the distal assembly includes a tubing with multiple lumens including a lumen closest to the inner circumference, and the support member and the coextensive portion of contraction wire are in the lumen closest to the inner circumference. 
     In some detailed embodiments, the support member has a generally-rectangular cross-section, the support member having a distal portion wherein a width dimension and a height dimension of the generally rectangular cross-section varies along the length of the distal portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. It is understood that selected structures and features have not been shown in certain drawings so as to provide better viewing of the remaining structures and features. 
         FIG. 1  is a top plan view of a catheter of the present invention, according to one embodiment. 
         FIG. 2A  is a detailed view of a 3-D arcuate distal assembly of the catheter of  FIG. 1 , in a neutral, unconstrained configuration. 
         FIG. 2B  is the detailed view of the 3-D arcuate distal assembly of  FIG. 2 , in a contracted configuration. 
         FIG. 3  is an end cross-sectional view of a catheter body of the catheter of  FIG. 1 , taken along line A-A. 
         FIG. 4  is an end cross-sectional view of a deflectable intermediate section of the catheter of  FIG. 1 , taken along line B-B. 
         FIG. 5A  is an end cross-sectional view of a connector section of the catheter of  FIG. 1 , taken along line C-C. 
         FIG. 5B  is a side cross-sectional view of the connector section of  FIG. 1 , taken along area D-D. 
         FIG. 6A  is a perspective view of a support member and a coextensive contraction wire, along with a radially-constrictive tubing. 
         FIG. 6B  is a detailed top view of an assembled structure of distal ends of the support member and the contraction wire of  FIG. 6A . 
         FIG. 6C  is a perspective view of a radially-constrictive tubing, in accordance with an embodiment of the present invention. 
         FIG. 6D  is a perspective view of a radially-constrictive tubing, in accordance with another embodiment of the present invention. 
         FIG. 7  is an end view of the distal assembly of  FIG. 1 . 
         FIG. 8  is an end cross-sectional view of the distal assembly of  FIG. 2A , taken along line E-E. 
         FIG. 9  is a side cross-sectional view of the distal assembly of  FIG. 2A , taken along line F-F. 
         FIG. 10  is a perspective view of an irrigated ablation electrode with lead wire attachments, according to one embodiment. 
         FIG. 11  is a side cross-sectional view of a control handle, in accordance with one embodiment. 
         FIG. 12  is a partial top cross-sectional view of the control handle of  FIG. 11 . 
         FIG. 13A  is an end cross-sectional view of the support member of  FIG. 6A , before reshaping. 
         FIG. 13B  is an end cross-sectional view of the support member of  FIG. 6A , taken along line G-G. 
         FIG. 13C  is an end cross-sectional view of the support member of  FIG. 6A , taken along line J-J. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention that are described hereinbelow provide probes, such as catheters, with improved arcuate distal electrode-carrying structures, to facilitate maneuvering and positioning in the heart and especially tubular regions of different sizes in a patient&#39;s body and different circumferential locations within the tubular regions. Such catheters can be used to produce generally circular or helical ablation paths, as well as sensing electrical activity along a generally curve or helical pattern for electrical potential and anatomical mapping. 
     Referring to  FIG. 1 , a catheter  10  according to the disclosed embodiments comprises an elongated body that may include a flexible insertion shaft or catheter body  12  having a longitudinal axis  13 , and an intermediate section  14  distal of the catheter body that can be uni- or bi-directionally deflected off-axis from the longitudinal axis  13 . As shown in  FIG. 2A , extending from the intermediate section  14  is a resilient three-dimensional (3-D) arcuate distal assembly  17  which is advantageously constructed for significantly greater and more uniform loop contraction. As explained below in further detail, the distal assembly  17  is responsive to operator manipulation of a control handle  16  in decreasing its radius and increasing its coiling, as shown in  FIG. 2B . 
     In the depicted embodiment of  FIG. 1  and  FIG. 3 , the catheter body  12  comprises an elongated tubular construction having a single, axial or central lumen  18 . The catheter body  12  is flexible, i.e., bendable, but substantially non-compressible along its length. The catheter body  12  can be of any suitable construction and made of any suitable material. In some embodiments, the construction comprises an outer wall  20  made of polyurethane or PEBAX. The outer wall  20  comprises an imbedded braided mesh of stainless steel or the like, as is generally known in the art, to increase torsional stiffness of the catheter body  12  so that, when the control handle  16  is rotated, the intermediate section  14  will rotate in a corresponding manner. 
     The outer diameter of the catheter body  12  is not critical, but in some embodiments is no more than about 8 french, more preferably 7 french. Likewise the thickness of the outer wall  20  is not critical, but is thin enough so that the central lumen  18  can accommodate any desired wires, cables and/or tubes. The inner surface of the outer wall  20  is lined with a stiffening tube  22  to provide improved torsional stability. The outer diameter of the stiffening tube  22  is about the same as or slightly smaller than the inner diameter of the outer wall  20 . The stiffening tube  22  can be made of any suitable material, such as polyimide, which provides very good stiffness and does not soften at body temperature. 
     The deflectable intermediate section  14  comprises a shorter section of tubing  23  having multiple lumens, most of which are occupied by the various components passing from the catheter  12  and into the intermediate section  14 . In the illustrated embodiment of  FIG. 4 , there are six lumens. Coupled to the ring electrodes  19 , respective lead wire/thermocouple pairs  40 ,  41  pass through a first lumen  31 . A nonconductive protective sheath  39  may be provided to surround the wire pairs  40 / 41 . An irrigation tubing  43  for delivering irrigation fluid to the distal assembly  17  passes through a second lumen  32 . For enabling deflection of the intermediate section  14 , a deflection puller wire  44  passes through a third lumen  33 . A position sensor cable assembly  48 , including one or more single axis sensors (SAS) carried in the distal assembly  17 , passes through a fourth lumen  34 . To render an arcuate distal portion  15  of the distal assembly  17  variable in shape and size, e.g., curvature radii, in response to manipulation of the control handle by a user, a contraction wire  24  passes through a sixth lumen  36 . As described below, the contraction wire  24  acts on an elongated shape-memory support member  50  that provides the 3-D shape of the distal assembly  17 . 
     The multi-lumened tubing  23  of the intermediate section  14  is made of a suitable non-toxic material that is preferably more flexible than the catheter body  12 . A suitable material is braided polyurethane or PEBAX, i.e., polyurethane or PEBAX with an embedded mesh of braided stainless steel or the like. The plurality and size of the lumens are not critical, provided there is sufficient room to house the relevant components. In the illustrated embodiment, the third and sixth lumens  33  and  36  for the deflection puller wire  44  and contraction wire  24  are off-axis and diametrically opposed to each other, and the fifth lumen  35  for the support member  50  is on-axis. 
     The useful length of the catheter, i.e., that portion that can be inserted into the body excluding the distal assembly  17 , can vary as desired. Preferably the useful length ranges from about 110 cm to about 120 cm. The length of the intermediate section  14  is a relatively small portion of the useful length, and preferably ranges from about 3.5 cm to about 10 cm, more preferably from about 5 cm to about 6.5 cm. 
     Distal the intermediate section  14  is the distal assembly  17 . Extending between the intermediate section  14  and the distal assembly  17  is a generally straight connector section  30 , as shown in  FIG. 2A  and  FIG. 5A , having a tubing of suitable material, e.g., PEEK, with a central lumen  37  that allows the various components extending between the intermediate section  14  and the distal assembly  17  to reorient and reposition as needed for transitioning therebetween, as shown in  FIG. 5B . The components are potted in the lumen  37  of the connector section  30  by a suitable materials, for example, adhesive  112 . Supporting the distal assembly  17  and providing its 3-D shape, the shape-memory support member  50  extends proximally from the distal assembly  17  for a relatively short distance into a distal portion of the connector section  30 . 
     As shown in  FIG. 2A  and  FIG. 6 , the 3-D distal assembly  17  includes a preformed, arcuate distal portion  15 , an elbow portion  21 , and a proximal linear stem  26 . The arcuate distal portion  15  carries a plurality of irrigated ring electrodes  19 . The elbow portion  21  is configured to orient the distal portion  15  obliquely to the longitudinal axis  13  such that the longitudinal axis extends generally through a center of the distal portion  15 , as shown in  FIG. 7 . As such, an oblique angle Θ ( FIG. 2A ) is defined between the longitudinal axis  13  and a plane P generally defined by the distal assembly  17 , wherein the oblique angle Θ ranges between about 45 degrees and 135, preferably about 75 and 100 degrees, and preferably about 90 degrees. 
     With reference to  FIG. 2A ,  FIG. 6  and  FIG. 7 , the elbow portion  21  has a proximal curved section  21 P, an elbow junction or “twist”  42 , and a distal curved section  21 D. The proximal curved section  21 P traces a first arc defined by a first (or proximal) radius R 1  relative to the longitudinal axis  13 . The distal curved section  21 D traces a second arc defined by a second (or mid) radius R 2  relative to an axis  27  oblique to the longitudinal axis  13 . The first radius R 1  is lesser than the second radius R 2 . However, both radii R 1  and R 2  are lesser than a third (or distal) radius R 3  defining a third arc traced by the distal portion  15 . In some embodiments, the radius R 1  ranges between about 0.1″ and 0.25″, the radius R 2  ranges between about 0.15″ and 0.38″, and the radius R 3  ranges between about 0.4″ and 0.6″. As such, the 3-D configuration of the distal assembly  17 , when unconstrained, has a spiral characteristic, with radius R 3  being greater than the radius R 2 . For example, where the oblique angle Θ is about 90 degrees and the longitudinal axis  13  defines a Z axis, the first arc defined by radius R 1  may lie in the Y/Z plane, and the second and third arcs defined respectively by radii R 2  and R 3  may both lie in the X/Y plane, as shown in  FIG. 6 . It is understood that the distal assembly  17  is not limited to the radii R 1 , R 2  and R 3  described above, and may contain more or less radii, as needed or desired. 
     The 3-D configuration of the distal assembly  17 , when unconstrained, also has a helical characteristic in that the distal assembly  17  extends distally as it spirals such that the distal end  25  of the distal assembly  17  is the distal-most portion of the distal assembly  17 , as best shown in  FIG. 2A . 
     Accordingly, the distal assembly  17  has a spiral-helical configuration (or helical-spiral configuration) such that there are a first separation gap between the distal end  25  and the distal curved section  21 D along the longitudinal axis  13 , and a second separation gap between the distal end  25  and the distal curved section  21 D along the oblique axis  27 . The spiral-helical configuration of the distal assembly  17  can be described as tracing from its proximal end to its distal end an enlarging helix that is on-axis with the longitudinal axis, as shown in  FIG. 2A . 
     Depending on the length of the distal portion  15 , the distal assembly  17 , in its neutral, unconstrained 3-D configuration, may subtend a radial angle α of about 360 degrees between the twist  42  and the distal end  25 . In another embodiment, the distal assembly  17  subtends a radial angle α ( FIG. 6 ) greater than 360 degrees, e.g., about 380 degrees. When the distal assembly  17  is contracted, as shown in  FIG. 2B , the spiral-helical form “coils up” and tightens, with the one or more of radii R 1 , R 2 , R 3  traced by the distal assembly  17  decreasing, and the radial angle α subtended by the distal assembly  17  increasing, for example, from about 360 or 380 degrees to about 540 degrees or more between the twist  42  and the distal end  25 . Accordingly, the distal assembly  17  in its neutral, unconstrained configuration may be used for circumferential contact with an ostium having a larger radius, and then be adjusted into its contracted configuration for circumferential contact within the PV of the ostium with a significantly smaller radius. 
     As shown in  FIG. 8 , the distal assembly  17  includes a multi-lumened tubing  56 . In the disclosed embodiment, the tubing  56  has four off-axis lumens, namely, a first lumen  51  for the SAS cable assembly  48  (circumferentially surrounded by a friction-reducing coating  38 , e.g., of TEFLON®), a second lumen  52  for the ring electrode wire pairs  40 ,  41 , a third lumen  53  for irrigation fluid delivered through the irrigation tubing  43 , and a fourth lumen  54  for the support member  50  and the contraction wire  24 , a segment of which is coextensive with the support member  50  in the lumen  54 . Again, position and sizing of the lumens are not critical, except the position of the fourth lumen  54  for the contraction wire  24  is preferably on or near an inner circumference of the spiral-helical form of the distal assembly  17  so that proximal movement of the wire  24  can act more effectively in tightening the spiral-helical form and increasing its coiling. The multi-lumened tubing  56  can be made of any suitable material, and is preferably made of a biocompatible plastic such as polyurethane or PEBAX. 
     In the depicted embodiment, the pre-formed support member  50  of the distal assembly  17  extends through the fourth lumen  54  of the tubing  56  to provide and define the 3-D spiral-helical shape of the distal assembly  17 , which includes the twist  42  and arcs of the proximal section  21 P and the distal section  21 D, and the distal portion  15  defined by radii R 1 , R 2  and R 3 . The support member  50  is made of a material having shape-memory, i.e., that can be straightened or bent out of its original shape upon exertion of a force and is capable of substantially returning to its original shape upon removal of the force. In some embodiments, a suitable material for the support member  50  is a nickel/titanium alloy. Such alloys typically comprise about 55% nickel and 45% titanium, but may comprise from about 54% to about 57% nickel with the balance being titanium. One nickel/titanium alloy is Nitinol, which has excellent shape memory, together with ductility, strength, corrosion resistance, electrical resistivity and temperature stability. 
     In some embodiments, as shown in  FIG. 5A , the support member  50  has a proximal end received and affixed in the connector section  30  In some embodiments, the proximal end of the support member  50  extends at a depth of about 2-3 mm proximal of the distal end of the connector section  30 . Alternatively, the support member  50  can extend further proximally into the lumen  35  of the intermediate section  14 , through the entire length of the intermediate section  14 , and even into the catheter body  12  via the central lumen  18 , as desired or appropriate. 
     Advantageously, the support member  50  has a generally rectangular cross-sectional shape whose height and width dimensions vary in a predetermined manner along the length of the member  50 . As shown in  FIG. 13B  and  FIG. 13C , the generally rectangular cross-sectional area at any location along the length remains constant although its width dimension W and height dimension vary at different locations. There is no reduction or increase in the cross-sectional area at any location along the length in that any loss or gain in one dimension is proportionally gained or lost by the other dimension between a more proximal location and a more distal location along the length of the support member  50 . As a tapered portion or “tail” of the support member  50  narrows in one dimension of the cross-sectional area from the proximal end to the distal end of the member, the other dimension of the cross-sectional area widens from the proximal end to the distal end. The dimension that decreases (for example, the width dimension W along the X axis in  FIG. 13B  and  FIG. 13C ) decreases its resistance to bending in that dimension from the proximal end to the distal end, while the dimension that increases (for example, the height dimension H along the Y axis in  FIG. 13B  and  FIG. 13C ) increases its resistance to bending in that dimension from a proximal end to a distal end of the tapered portion. 
     As shown in  FIG. 6 , the generally rectangular cross-section of the support member  50  at its proximal end has a maximum width W 1  and a minimum height H 1 . For minimizing change or deformation in radii R 1  and R 2  during contraction of the distal assembly  17 , the width and height dimensions of the cross-sectional area of the support member  50  begin to change (or taper) starting at a predetermined location distal of radius R 2  (e.g., at or around location L 2 ) Distal of the predetermined location, in the tapered tail of distal assembly  17 , the width begins to decrease to W 2  (&lt;W 1 ) while the height begins to increase to H 2  (&gt;H 1 ). The width further decreases to W 3  (&lt;W 2 &lt;W 1 ) while the height further increases to H 3  (&gt;H 2 &gt;H 1 ) at distal location L 3 . These decreases and increases are smooth and continuous. This tapered configuration biases the support member  50  to have increasing less resistance to coiling toward the distal end  25  such as when contracted by the contraction wire  24 , while providing increasingly more resistance to oblique forces toward the distal end  25  such as when the distal assembly  17  contacts tissue surface head on. Thus, this varied cross-sectional shape allows the distal assembly  17  to exhibit improved contraction characteristics, including the distal portion  15  being able to contract and coil readily with minimal deformation of the elbow junction  21  and the elbow junction  21  being better able to withstand the load from an axial force that is applied when the distal assembly  17  comes into contact with target tissue. With this varied cross-sectional shape applied to the support member  50 , the distal assembly  17  can be adjusted, upon actuation of the contraction wire  24 , to assume a smaller loop size (see  FIG. 2B ), for example, where the distal portion  15  assumes a curvature that is generally equal to or even be lesser than the curvature of the distal section  21 D. 
     As shown in  FIG. 6 , with a generally rectangular cross-section, the support member  50  resembles a “coiled ribbon” having sides/surfaces  62  and  63  defining a height dimension of the generally rectangular cross-section, and edges  75  defining a width dimension of the generally rectangular cross-section. Advantageously, the inner flat side/surface  62 , along its length, continually faces the inner circumference of the spiral-helical configuration of the distal assembly, and an outer flat side/surface  63  that is opposite of the inner flat surface  62  continually faces outwardly, away from the inner circumference of the spiral-helical configuration. The tapering of the support member  50  results in the “tapered tail” of the distal assembly  17  resembling an increasing wider and thinner ribbon. 
     Moreover, the generally rectangular cross-section at the proximal end of the support member  50  helps anchor the proximal end in the lumen  35  of the tubing  23  of the deflectable section  14  and reduces the risk of the support member rotating about its axis where the proximal end is potted by an adhesive, e.g., epoxy (see  FIG. 4 ). 
     In some embodiments, the support member  50  begins with a round cross-sectional shape, as shown in  FIG. 13A . The support member  50 , for example, a round wire, is progressively flattened to produce the generally rectangular cross-section and tapered tail. Thus, the two opposed ends of the width dimension between the parallel fattened surfaces of the height dimension carry the residual round shape of the original round cross-sectional shape. It is understood that the support member may begin with a square/rectangular cross-sectional shape which would then result in flat opposed ends instead of round opposed ends. In some embodiments, using a round wire may be more economical to manufacture, and rounded opposed ends may ease the assembly of the distal assembly  17 , including insertion of the support member into a radially-constrictive flexible tubing or sleeve  60 , as discussed further below. The rounded opposed ends may reduce the insertion force used to insert the support member  50  into the tubing  60  and also the risk of the support member  50  tearing and damaging the tubing  60 . 
     In some embodiments, the support member  50 , as a round wire, has an initial (pre-flattening) diameter of about 0.019 inches and a length of about 4.25 inches. When flattened, the support member  50  has a generally rectangular cross-sectional dimensions of about 0.021″×0.015″ from its proximal end to the location L 2 . The tapered tail of the support member  50  (distal of location L 2  in  FIG. 6 ) is about 2.9 inches long and has a generally rectangular cross-sectional dimensions of about 0.035″×0.008″ at or near its distal end  25 . In some embodiments, a distal end of the support member  50  has an unflattened section  50 D which retains its round cross-section, as explained below in further detail. 
     The area moment of inertia for the 0.019 inch diameter support member  50  (pre-flattening) is the same regardless of centroidal axis orientation, whereas the area moment of inertia at or near its distal end for the first centroidal axis is 2.5 times less stiff than the moment of inertia at the proximal end. The moment of inertia for the second centroidal axis at the distal end is 4.5 times stiffer than the moment of inertia at the proximal end. Comparing the two centroidal axis area moments of inertia at the distal end with respect to each other, the first centroidal axis is 18.5 times less stiff than the second centroidal axis. Since the contraction wire  24  exerts a constant inwardly line of force (neglecting friction) on the support member  50 , to obtain a small, generally circular contraction, the area moment of inertia of the support member  50  should constantly decrease towards the distal end where it is attached to the contraction wire  24 . 
     The contraction wire  24  has a proximal end anchored in the control handle  16  which provides a rotational control knob  59  (see  FIG. 1 ) for actuating the contraction wire  24  via manipulation by an operator. The contraction wire  24  extends through the central lumen  18  of the catheter body  12  ( FIG. 3 ), the sixth lumen  36  of the intermediate section  14  ( FIG. 4 ), the central lumen  37  of the connector section  30  ( FIG. 5A ) and the fourth lumen  54  of the tubing  56  of the distal assembly  17  ( FIG. 8 ) alongside the support member  50 , to the distal end  25  ( FIG. 9 ). 
     The contraction wire  24  may be covered by a friction-reducing tubing  61  ( FIG. 8 ), e.g., a TEFLON® coated inner diameter of a polyimide or PEEK tubing, so that the contraction wire  24  is physically separated and isolated from the side  62  of the support member  50  and the inside surface of the constrictive tubing  60  that surrounds the contraction wire  24  and the support member  50 , which is described below in further detail. The friction-reducing tubing  61  may have a proximal end in the connector section  30  and a distal end at least distal of the radius R 2 , at or near the location L 2 , if not closer to the distal end of the support member  50 . 
     Advantageously, the support member  50  and the coextensive segment of the contraction wire  24  (and its tubing  61 ) through the lumen  54  of the distal assembly  17  are surrounded and bound together by the tight-fitting flexible tubing  60 . 
     In some embodiments, as shown in  FIG. 6C , the tubing  60  to provide radial constriction includes a woven or braided tubing of a manufactured fiber, spun from a liquid crystal polymer (LCP), for example, manufactured fiber sold under the trademark VECTRAN®. Chemically, it is an aromatic polyester produced by the polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid. These fibers exhibit thermal stability at high temperatures, high strength and modulus, low creep and good chemical stability. 
     The resulting tubing has a high modulus of elasticity which allows for improved contraction of the distal assembly  17 . In some embodiments, the manufactured fiber is braided at high pix per inch (PPI) of about 128 and is free of resin so that there is little restriction on the bending radius of the tubing. A tubing of such manufacture satisfies the strength required to constrain the contraction wire  24  from tearing the sidewall of the tubing  56 . Moreover, the tubing is sufficiently flexible to allow contraction of the distal assembly  17 , and sufficiently strong to withstand frictional fatigue of the contraction wire  24  and other moving components imposed on the tubing fibers. 
     In some embodiments, after the tubing  60  has been slipped onto the support member  50  and the contraction wire  24 , tension force T is applied to its ends to lengthen longitudinally and shorten radially to provide a radially constrictive tight fit around the support member  50  and the contraction wire  24  in ensuring that the contraction wire  24  remains in the proper location relative to the support member  50 , thus ensuring that the pulling force vector is in alignment with the support member  50  for a more efficient loop contraction and improved loop contraction geometry. The tubing  60  may also be fused to the lumen  54 . 
     In other embodiments, as shown in  FIG. 6D , the tubing  60  for radial constriction has an inner diameter  91  composed of a friction-reducing material, such as, TEFLON®, (formed as a first extrusion coat or layer), which is covered by a stainless steel flat braid  92 , which is covered by an outer diameter  93 , such as nylon (formed as a second extrusion coat or layer). The constrictive tubing  60  is slipped over the support member  50  and the contraction wire  24  (with its friction-reducing tubing  61 ) after their distal ends are affixed together, as described further below. 
     In some embodiments, the constrictive tubing  60  has a distal end at or near a junction of the radii R 2  and R 3 , and a proximal end at or near the elbow junction  21 . The constrictive tubing  60  is fitted to provide circumferential/radial constriction around the member  50 , the contraction wire  24  with its friction-reducing tubing  61  (see  FIG. 8 ) so as to secure the tubing  61  against the inner side  62  of the support member  50  in keeping the contraction wire  24  aligned with (or on the side of) the inner side  62  for improving contraction characteristics of the distal assembly  17 , including improved circular shape maintenance and significantly tighter contraction and coiling, as well as improved durability against the contraction wire  24  cutting into the tubing  56  of the distal assembly  17 . 
     Such improved contraction characteristics, particularly of the tapered tail of the distal assembly, is enabled by keeping the contraction  24  against the inner side  62  throughout the length of the support member  50 . For example, where a radius R 3  of the arc of distal portion  15  is about 17 mm when the distal assembly  17  is unconstrained, the distal assembly  17  can be contracted into a tighter coil such that the arcs of the distal curve portion  21 D and the distal portion  15  are both defined by a radius of about 10 mm, for a reduction in the radius R 3  of the arc of the distal portion  15  by about 60% or more. 
     As illustrated in  FIG. 6 , the contraction wire  24  within its tubing  61  runs along the entire length of the inner-facing side  62  of the support member  50  extending between the distal end  25  of the distal assembly  17  and the connector section  30 . This predetermined pattern advantageously minimizes any tendency for the contraction wire  24  to separate and lift from the support member  50  when the contraction wire  24  is drawn proximally. In some embodiments, the contraction wire  24  may also have a rectangular cross-section along its length or along one or more segments thereof. 
     With reference to  FIG. 8  and  FIG. 9 , an assembled structure of the distal ends of the support member  50 , contraction wire  24  and constrictive tubing  60  is oriented within the fourth lumen  54  of the tubing  56  of the distal assembly  17  such that the contraction wire  24  is most adjacent to the inner circumference of the distal assembly  17  to face the center of the distal assembly  17 . With the fourth lumen  54  positioned closer to the inner circumference than the other lumens of the tubing  56 , and the contraction wire  24  within the lumen  54  also positioned closer to the inner circumference than the support member  50 , the contraction wire  24  can effectively contract the distal assembly  17 . 
     Prior to insertion into the lumen  54 , the assembled structure of the distal ends of the support member  50 , the contraction wire  24  and the constrictive tubing  60  is prepared. In some embodiments, a coupling of the distal ends of the contraction wire  24  and support member  50  includes a laser welded coupling having a stainless steel ferrule  65  (e.g.,  304  or  316  series) that is placed over the distal end  25 D of the support member  50  which is not flattened but retains its original round cross-sectional shape. The ferrule  65  is flattened after it is placed over the distal end  25 D. The flattened portion of the support member  50  acts as a stop preventing any proximal migration or dislocation of the ferrule  65  when contraction wire tension is applied to the support member  50 . The ferrule  65  is secured to the round distal end  50 D of the support member  50  by a crimp die which has a flat portion that is clocked parallel to the surface  62  of the support member  50 . The distal end of the contraction wire  24  has a crimped ferrule  80  which has a flat portion that is also fixed to the flat portion of the ferrule  65 . A laser seam weld  101  is made on one common (bottom) side of the ferrules  65  and  80  joining the distal ends of the contraction wire  24  and the support member  50 . 
     In contrast to prior art coupling of the support member and the contraction wire which used lead-free solder to join a nitinol support member to the contraction wire, the laser welded coupling described herein includes the use of strong acid flux to remove oxides from the nitinol and stainless steel before soldering. Moreover, the laser welded coupling provides a much stronger attachment compared to the prior art the lead-free solder with a low shear and tensile strength (about 4000 psi) which can attribute to puller wire detachment failures from the nitinol support member when the lead-free solder contained unexposed voids or was formed as a cold solder joint. 
     The constrictive tubing  60  is then slid over the contraction wire  24  at its proximal end, advanced over the support member  50  at its proximal end, and further advanced until the distal end of the tubing  60  reaches and covers the assembled structure. 
     When the constrictive tubing  60  has been properly positioned over the contraction wire  24  and the support member  50 , the constrictive tubing  60  has a proximal end near a junction of radii R 2  and R 3 , and it distal end is trimmed or otherwise provided with a finished distal end terminating immediately proximal of the stainless steel ferrule  65 . The finished distal end of the constrictive tubing  60  is then affixed to the friction-reducing tubing  61  and the support member  50  by a circumferential application of an adhesive  111 , e.g., LOCTITE®. Notably, the friction-reducing tubing  61  surrounding the contraction wire  24  has a distal end that is well proximal of the soldered stainless steel ferrule  65  so that the adhesive  111  can bond the distal end of the constrictive tubing  60  directly on to the contraction wire  24  and the support member  50 . 
     The assembled structure of the contraction wire  24 , the support member  50  and the constrictive tubing  60  is then inserted into the lumen  54 , where the stainless steel ferrule  65  and its contained components are fixed and anchored at the distal end of the multi-lumened tubing  56  by an adhesive  64 , e.g., polyurethane, which covers the entire distal face of the distal end  25  to form a tip dome, as shown in  FIG. 9 . With this arrangement, the relative positions of the contraction wire  24  and the support member  50  can be controlled so that the contraction wire  24  is positioned on or near the inner circumference of the distal assembly  17 , closer to the center of the spiral-helical form, as described above. The constrictive tubing  60  protects the multi-lumened tubing  56  from the contraction wire  24  cutting into its side wall during contraction of the distal assembly  17 . 
     With reference to  FIG. 3  and  FIG. 4 , a compression coil  68  surrounding the contraction wire  24  extends from the proximal end of the catheter body  12  and through the entire length of the sixth lumen  36  of the intermediate section  14 . Thus, the compression coil has a distal end at or near a mid-location in the connector section  30 . The compression coil  68  is made of any suitable metal, preferably stainless steel, and is tightly wound on itself to provide flexibility, i.e., bending, but to resist compression. The inner diameter of the compression coil is preferably slightly larger than the diameter of the contraction wire  24 . The outer surface of the compression coil is covered by a flexible, non-conductive sheath  67 , e.g., made of polyimide tubing. The compression coil preferably is formed of a wire having a square or rectangular cross-sectional area, which makes it less compressible than a compression coil formed from a wire having a circular cross-sectional area. As a result, the compression coil  68  keeps the catheter body  12 , and particularly the intermediate section  14 , from deflecting when the contraction wire  24  is drawn proximally to contract the distal assembly  17 , as the compression coil  68  absorbs more of the compression. 
     The ring electrodes  19  are mounted on predetermined locations on the distal portion  15 , as shown in  FIG. 2A  and  FIG. 2B . The electrodes can be made of any suitable solid conductive material, such as platinum or gold, preferably a combination of platinum and iridium or gold and platinum, and mounted onto the tubing with glue or the like. A suitable embodiment of an electrode adapted for ablation and irrigation is illustrated in  FIG. 10 . An ablation reservoir (“AR”) electrode is generally cylindrical with a length greater than its diameter. In one embodiment, the length is about 3.0 mm, the outer diameter is about 2.8 mm, and the inner diameter is about 2.33 mm. 
     In some embodiments, the plurality of AR ring electrodes  19  on the distal assembly  17  can ranges from about six to about twenty, more preferably from about eight to about twelve. In some embodiments, the distal assembly  17  carries ten AR electrodes. The electrodes can be approximately evenly spaced along the distal portion  15 . 
     The proximal end of each wire of the wire pairs  40 ,  41  is electrically connected to a suitable connector (not shown) distal of the control handle  16 . In the disclosed embodiment, wire  40  of a wire pair is a copper wire, e.g. a number “40” copper wire, and the other wire  41  of the wire pair is a constantan wire. The wire pairs extend from the control handle  16 , through the central lumen  18  of the catheter body  12  ( FIG. 3 ), the first lumen  31  of the intermediate section  14  ( FIG. 4 ), the central lumen  37  of the connector section  30  ( FIG. 5A ), and the second lumen  52  of the distal assembly  17  ( FIG. 8 ). The distal ends of the wire pairs pass through holes  74  ( FIG. 9 ) formed in the side wall of the tubing  56  to reach the AR electrodes  19 . The wires of each pair are electrically isolated from each other except at their distal ends where they are exposed. Exposed distal ends of a respective wire pair  40 ,  41  are sandblasted, and wrapped in and welded to a folded metal foil  72  (e.g., copper foil) which is then welded to an inner surface  70  near a proximal end  71  of its AR electrode  19 , as shown in  FIG. 10 . 
     Ablation energy, e.g., RF energy, is delivered to the AR electrodes  19  via the wire  40  of the wire pairs. However, the wire pairs inclusive of their respective constantan wire  41  can also function as temperature sensors or thermocouples sensing temperature of each AR electrode  19 . 
     All of the wire pairs pass through one nonconductive protective sheath  39  ( FIG. 3  and  FIG. 4 ), which can be made of any suitable material, e.g., polyimide, in surrounding relationship therewith. The sheath  39  extends with the wire pairs from the control handle  16 , the catheter body  12 , the intermediate section  14 , the connector section  30  and into the second lumen  52  of the distal assembly  17 , terminating just distal of the junction between the connector section  30  and the distal assembly  17 , for example, about 5 mm into the second lumen  52 . The distal end is anchored in the second lumen  52  by glue, for example, polyurethane glue or the like. 
     Irrigation fluid is delivered to the distal assembly by the irrigation tubing  43  whose proximal end is attached to a luer hub  73  ( FIG. 1 ) proximal of the control handle  16  and receives fluid delivered by a pump (not shown). The irrigation tubing  43  extends through the control handle  16 , the central lumen  18  of the catheter body  12  ( FIG. 3 ), the second lumen  32  of the intermediate section  14  ( FIG. 4 ), the central lumen  37  of the connector section  30  ( FIG. 5A ) and a short distance, e.g., about 5 mm, distally into the third lumen  53  of the multi-lumened tubing  56  of the distal assembly  17 . The fluid enters the third lumen  53  where it exits via openings (not shown) formed in the sidewall of the tubing  56  to enter the AR ring electrodes  19  and exits apertures  78  formed in the electrode side wall ( FIG. 10 ). It is understood that the distal portion  15  may carry any form of electrodes, including the aforementioned AR ring electrodes, impedance ring electrodes, and/or combinations thereof, as desired or appropriate. 
     The deflection puller wire  44  is provided for deflection of the intermediate shaft  14 . The deflection wire  44  extends through the central lumen  18  of the catheter body  12  ( FIG. 3 ) and the third lumen  33  of the intermediate section  14  ( FIG. 4 ). It is anchored at its proximal end in the control handle  16 , and at its distal end to a location at or near the distal end of the intermediate section  14  by a T-bar  76  ( FIG. 4 ) that is affixed to the sidewall of the tubing  15  by suitable material, e.g., polyurethane  69 . The puller wire  54  is made of any suitable metal, such as stainless steel or Nitinol, and is preferably coated with TEFLON® or the like. The coating imparts lubricity to the puller wire. The puller wire  44  may have a diameter ranging from about 0.006 to about 0.010 inch. 
     A second compression coil  47  is situated within the central lumen  18  of the catheter body  12  in surrounding relation to the puller wire  44  ( FIG. 3 ). The second compression coil  47  extends from the proximal end of the catheter body  12  to at or near the proximal end of the intermediate section  14 . The second compression coil  47  is made of any suitable metal, preferably stainless steel, and is tightly wound on itself to provide flexibility, i.e., bending, but to resist compression. The inner diameter of the second compression coil  47  is preferably slightly larger than the diameter of the puller wire  44 . A TEFLON® coating (not shown) on the puller wire allows it to slide freely within the second compression coil. Within the catheter body  12 , the outer surface of the second compression coil  47  is covered by a flexible, non-conductive sheath  49 , e.g., made of polyimide tubing. The second compression coil  47  is anchored at its proximal end to the outer wall  20  of the catheter body  12  by a proximal glue joint and to the intermediate section  14  by a distal glue joint. 
     Within the third lumen  33  of the intermediate section  14 , the puller wire  44  extends through a plastic sheath (not shown), preferably of TEFLON®, which prevents the puller wire  44  from cutting into the wall of the tubing  23  of the intermediate section  14  when the intermediate section  14  is deflected. 
     Longitudinal movement of the contraction wire  24  relative to the catheter body  12 , which results in contraction of the spiral-helical form of the distal assembly  17 , is accomplished by suitable manipulation of the control handle  16 . Similarly, longitudinal movement of the deflection wire  44  relative to the catheter body  12 , which results in deflection of the intermediate section  14 , is accomplished by suitable manipulation of the control handle  16 . Suitable control handles for manipulating more than one wire are described, for example, in U.S. Pat. Nos. 6,468,260, 6,500,167, and 6,522,933, the entire disclosures of which are incorporated herein by reference. 
     In one embodiment, the catheter includes a control handle  16  as shown in  FIG. 11  and  FIG. 12 . The control handle  16  includes a deflection control assembly that has a handle body  84  in which a core  86  is fixedly mounted and a piston  87  is slidably mounted over a distal region of the core  86 . The piston  87  has a distal portion that extends outside the handle body. A thumb knob  58  is mounted on the distal portion so that the user can more easily move the piston  87  longitudinally relative to the core  86  and handle body  84 . The proximal end of the catheter body  12  is fixedly mounted to the distal end of the piston  87 . An axial passage  88  is provided at the distal end of the piston  87 , so that various components, including lead wires  40 ,  41 , contraction wire  24 , deflection wire  44 , position sensing cable assembly  48  and irrigation tubing  43  that extend through the catheter body  12  can pass into the control handle. The lead wires  40 ,  41  can extend out the proximal end of the control handle  16  or can be connected to a connector that is incorporated into the control handle, as is generally known in the art. The irrigation tubing  43  can also extend out the proximal end of the control  16  for connection with an irrigation source (not shown) via a luer hub. 
     The proximal end of the deflection wire  44  enters the control handle  16 , and is wrapped around a pulley  83  and anchored to the core  86 . Longitudinal movement of the thumb knob  58  and piston  87  distally relative to the handle body  84  and core  86  draws the proximal end of the deflection wire  44  distally. As a result, the deflection wire  44  pulls on the side of the intermediate section  14  to which it is anchored, thereby deflecting the intermediate section in that direction. To release and straighten the intermediate section  14 , the thumb knob  58  is moved proximally which results in the piston  87  being moved proximally back to its original position relative to the handle body  84  and core  86 . 
     The control handle  16  is also used for longitudinal movement of the contraction wire  24  via a rotational control assembly. In the illustrated embodiment, the rotational control assembly includes a cam handle  81  and a cam receiver  82 . By rotating the cam handle in one direction, the cam receiver is drawn proximally to draw on the contraction wire  24 . By rotating the cam handle in the other direction, the cam receiver is advanced distally to release the contraction wire  24 . The contraction wire  24  extends from the catheter body  12  into the control handle  16 , through the axial passage in the piston  88  and through the core  86  to be anchored in an adjuster  85  by which tension on the contraction wire can be adjusted. 
     In one embodiment, the position sensor cable assembly  48  including a plurality of single axis sensors (“SAS”) extends through the first lumen  51  of the distal assembly  17  ( FIG. 8 ), where each SAS occupies a known or predetermined position on the spiral-helical form of the distal assembly  17 . The cable assembly  48  extends proximally from the distal assembly  17  through the central lumen  37  of the connector section  30 , the fourth lumen  34  of the intermediate section  14  ( FIG. 4 ), the central lumen  18  of the catheter body  12  ( FIG. 3 ), and into the control handle  16 . Each SAS can be positioned with a known and equal spacing separating adjacent SASs. In the disclosed embodiment, the cable carries three SASs that are positioned under the distal-most AR electrode, the proximal-most AR electrode, and a mid AR electrode, for sensing location and/or position of the distal assembly  17 . The SASs enable the spiral-helical form to be viewed under mapping systems manufactured and sold by Biosense Webster, Inc., including the CARTO, CARTO XP and NOGA mapping systems. Suitable SASs are described in U.S. Pat. No. 8,792,962, the entire disclosure of which is incorporated herein by reference. 
     The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. Any feature or structure disclosed in one embodiment may be incorporated in lieu of or in addition to other features of any other embodiments, as needed or appropriate. As understood by one of ordinary skill in the art, the drawings are not necessarily to scale. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.