Patent Publication Number: US-2020297417-A1

Title: Catheter having a distal section with spring sections for biased deflection

Description:
CROSS-REFERENCE TO CO-PENDING APPLICATION 
     The present application is a Divisional Application under 35 U.S.C. § 121 of U.S. patent application Ser. No. 13/481,691, filed May 25, 2012. The entire contents of this application is incorporated by reference herein in its entirety. 
    
    
     FIELD OF INVENTION 
     The present invention relates to an electrophysiologic catheter that is particularly useful for ablation and sensing electrical activity of heart tissue. 
     BACKGROUND OF INVENTION 
     Electrode catheters have been in common use in medical practice for many years. Diagnosis and treatment of cardiac arrythmias by means of electrode catheters include mapping the electrical properties of heart tissue and selectively ablating cardiac tissue by application of energy. Such ablation can cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. Various energy delivery modalities have been disclosed for forming lesions, and include use of microwave, laser and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall. 
     In a two-step procedure—mapping followed by ablation—electrical activity at locations within the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors (or electrodes) into the heart, and acquiring data at a multiplicity of locations. These data are then utilized to select the tissue target areas at which ablation is to be performed. 
     In use, the electrode catheter is inserted into a major vein or artery, e.g., the femoral artery, and then guided into a chamber of the heart. A reference electrode is provided, generally taped to the patient&#39;s skin or provided on the ablation catheter or another catheter. Radio frequency (RF) current is applied to the ablation electrode of the catheter, and flows through the surrounding media, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue, as compared to blood which has a higher conductivity than the tissue. 
     Heating of the tissue occurs due to its electrical resistivity. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. During this process, heating of the ablation electrode also occurs as a result of conduction from the heated tissue to the electrode itself. If the electrode temperature becomes sufficiently high, possibly above 60° C., a thin transparent coating of dehydrated blood can form on the surface of the electrode. If the temperature continues to rise, this dehydrated layer of blood can become progressively thicker resulting in blood coagulation on the electrode surface. Because dehydrated biological material has a higher electrical resistance than tissue, impedance to the flow of electrical energy into the tissue also increases. If the impedance increases sufficiently, an impedance rise occurs and the catheter must be removed from the body and the tip electrode cleaned. 
     In a typical application of RF current, circulating blood provides some cooling of the ablation electrode. Another method is to irrigate the ablation electrode, e.g., with physiologic saline at room temperature, to actively cool the ablation electrode instead of relying on the more passive physiological cooling provided by the blood. Because the strength of the RF current is no longer limited by the interface temperature, current can be increased. This results in lesions which tend to be larger and more spherical, usually measuring about 10 to 12 mm. 
     The clinical effectiveness of irrigating the ablation electrode is dependent upon the distribution of flow within the electrode structure and the rate of irrigation flow through the catheter. Effectiveness is achieved by reducing the overall electrode temperature and eliminating hot spots in the ablation electrode which can initiate coagulum formation. More channels and higher flows are more effective in reducing overall temperature and temperature variations, i.e., hot spots. The coolant flow rate must be balanced against the amount of fluid that can be injected into the patient and the increased clinical load required to monitor and possibly refill the injection devices during a procedure. In addition to irrigation flow during ablation, a maintenance flow, typically a lower flow rate, is required throughout the procedure to prevent backflow of blood into the coolant passages. Thus, reducing coolant flow by utilizing it as efficiently as possible is a desirable design objective. 
     Another consideration is the ability to control the exact position and orientation of the catheter tip. This is ability is critical and largely determines the usefulness of the catheter. It is generally known to incorporate into electrophysiology catheters an electromagnetic (EM) tri-axis location/position sensor for determining the location of a catheter&#39;s distal end. An EM sensor in the catheter, typically near the catheter&#39;s distal end within the distal tip, gives rise to signals that are used to determine the position of the device relative to a frame of reference that is fixed either externally to the body or to the heart itself. The EM sensor may be active or passive and may operate by generating or receiving electrical, magnetic or ultrasonic energy fields or other suitable forms of energy known in the art. 
     U.S. Pat. No. 5,391,199, the entire disclosure of which is incorporated herein by reference, describes a position-responsive catheter comprising a miniature sensor coil contained in the catheter&#39;s distal end. The coil generates electrical signals in response to externally-applied magnetic fields, which are produced by field-generator coils placed outside the patient&#39;s body. The electrical signals are analyzed to determine three-dimensional coordinates of the coil. 
     U.S. Pat. No. 6,690,963, the entire disclosure of which is hereby incorporated by reference, is directed to a locating system for determining the location and orientation of an invasive medical instrument, for example a catheter or endoscope, relative to a reference frame, comprising: a plurality of field generators which generate known, distinguishable fields, preferably continuous AC magnetic fields, in response to drive signals; a plurality of sensors situated in the invasive medical instrument proximate the distal end thereof which generate sensor signals in response to said fields; and a signal processor which has an input for a plurality of signals corresponding to said drive signals and said sensor signals and which produces the three location coordinates and three orientation coordinates of a point on the invasive medical instrument. 
     Because of the size of the tip electrode and the limited interior space therein, the EM sensor is often positioned outside of the tip electrode, proximally thereof, and often off-axis from the tip electrode which can reduce the accuracy of the position sensing capabilities of the sensor. Being outside the tip electrode, the position sensor is also exposed to bending stresses and can limit the flexibility and deflection of the distal tip section. Moreover, the sensor can be damaged by RF energy during ablation. 
     Where the distal tip is irrigated, the efficiency of irrigated cooling becomes a significant factor as ablation procedures can last five or six hours resulting in extensive fluid-loading in the patient. Conventional irrigated tip electrodes typically operate with a flow rate of about 17 ml/minute at below about 30 watts of RF ablation energy to about 30-50 ml/minute at about 30 watts or greater. 
     Current catheters include irrigated ring electrodes that are adapted for ablation. Such catheters include coil or single axis sensors (SASs) for visualization of the irrigated ring electrodes. However, the sensors are typically housed in a dedicated lumen of a multi-lumened tubing typically used with deflectable catheters. As lumens are needed for other components, such as puller wires, lead wires, and/or irrigation tubing, it becomes difficult to maintain typical catheter sizes. As catheters become more complex, more components are incorporated and thus the allocation of space for each component becomes more challenging. 
     Deflectable catheters are known. A control handle typically provides an actuator by which a user can deflect the catheter uni-directionally (in one direction) or bi-directionally (in opposite directions within a plane). Linear ablation catheters are utilized to create one or more RF lesions at a given time by means of either uni-polar or bi-polar ablations. The size of the resulting lesion(s) is highly dependent upon good contact of the electrodes with the cardiac tissue. Current linear catheter designs place the ring electrodes on a deflectable or flexible portion. However, if the portion is too stiff, it does not conform to the tissue and the electrodes cannot make solid contact for effective lesions. If the region between the ring electrodes deflects too much during catheter deflection, the ring electrodes may be pulled away from the tissue also preventing the formation of effective lesions. 
     Accordingly, it is desirable that a catheter be adapted for mapping and ablation with improved cooling and position sensing characteristics by providing a tip section that carries irrigated tip and ring electrodes on a structure that is deflectable and contractible in a more controlled and predictable manner. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a catheter having a distal section with a spring member that allows for biased and more predictable deflection to enable better contact between tissue and electrodes carried on the distal section. The spring member has an elongated hollow structure on which ring electrodes are mounted at selected locations along the length of the structure. At least one section of the spring member extending between the ring electrodes has a predetermined cut pattern that includes at least one row of alternating slots and ribs along a first side of the structure and at least one longitudinal spine along a second side of the structure, where the first side is relatively more compressible and the second side is relatively less compressible, in providing the distal section with biased deflection within a plane defined by the two sides. Alternatively, where each section of the spring member has two rows of slots and ribs opposing each other along a first diameter and two longitudinal spines opposing each other along a second diameter, the distal section has a biased deflection in two opposing directions in a first plane defined by the first diameter while having limited, if any, deflection in a second plane defined by the second diameter. Where the first and second diameters are generally perpendicular, the spring member allows the distal section to have bi-directional deflection in the first plane while allowing limited, if any, deflection in the second plane to maintain torquability, axial loading capabilities, and side force performance. 
     Configured for irrigation, each ring electrode carried on the spring member is formed to provide a gap reservoir between the ring electrode and the spring member (and its cover). For each ring electrode, a support member is positioned in the lumen of the spring member under the ring electrode to support it and to enable delivery of irrigation fluid to the ring electrode. The support member is configured with multiple lumens for components extending through the distal section, one lumen of which receives an irrigation tubing that defines an irrigation path for fluid delivery to each ring electrode. A radial irrigation passage is formed in the support member and the spring member to provide fluid communication between the irrigation tubing and the gap reservoir of each ring electrode. 
     Carried on the support member for each ring electrode is a location sensor, e.g., a single axis coil sensor. The sensor is carried on an outer surface of the support member so that lumens within the support member can be used for other components such as lead wires, thermocouple wires, puller wires, irrigation fluid, and/or sensor cable which typically occupy less space than a location sensor. 
     The catheter includes a tip electrode having a shell wall that defines a cavity through which fluid flows and exits via fluid ports formed in the shell wall. The cavity is sealed by an internal member that extends into the cavity to safely house a position sensor for the tip electrode. A proximal portion of the internal member disperses fluid entering the tip electrode for a more uniform flow through the cavity. As such, fluid is fed to the more distal fluid ports in the tip electrode for more uniform cooling at all locations on the tip electrode. 
    
    
     
       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 wherein: 
         FIG. 1  is a perspective of a catheter according to an embodiment of the present invention. 
         FIG. 2A  is a side cross-sectional view of the catheter  FIG. 1 , showing a junction between a catheter body and a deflectable intermediate section, taken along a first diameter. 
         FIG. 2B  is a side cross-sectional view of the catheter of  FIG. 1 , showing a junction between a catheter body and a deflectable intermediate section, taken a long a second diameter generally perpendicular to the first diameter. 
         FIG. 2C  is an end cross-section view of the deflectable intermediate section of  FIG. 2B  taken along line C-C. 
         FIG. 3  is a perspective view of a distal section of the catheter of  FIG. 1 , with components broken away to show the interior. 
         FIG. 3A  is an end cross-sectional view of the distal section of  FIG. 3 , taken along line A-A. 
         FIG. 3B  is a side cross-sectional view of the distal section of  FIG. 3 , taken along line B-B. 
         FIG. 4A  is a perspective view of an embodiment of a spring member. 
         FIG. 4B  is a perspective view of another embodiment of a spring member. 
         FIG. 4C  is an end cross-sectional view of the spring member of  FIG. 4B , taken along line C-C. 
         FIG. 5A  is a side sectional view of an embodiment of a spring member. 
         FIG. 5B  is a side sectional view of another embodiment of a spring member. 
         FIG. 5C  is a detailed side view of an embodiment of a slot of a spring member. 
         FIG. 5D  is a detailed side view of another embodiment of a slot of a spring member. 
         FIG. 5E  is a detailed side view of yet another embodiment of a slot of a spring member. 
         FIG. 6  is a perspective view of an embodiment of a ring electrode. 
         FIG. 7  is a side cross-sectional view of the tip electrode of  FIG. 3 . 
         FIG. 7A  is an end cross-sectional view of the tip electrode of  FIG. 7 , taken along line A-A. 
         FIG. 7B  is an end cross-sectional view of the tip electrode of  FIG. 7 , taken along line B-B. 
         FIG. 7C  is an end cross-sectional view of the tip electrode of  FIG. 7 , taken along line C-C. 
         FIG. 8  is a side cross-sectional view of the catheter of  FIG. 1 , showing a junction between an intermediate section and a distal section, taken along a diameter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an embodiment of a catheter  10  carrying irrigated tip and ring electrodes with improved deflection characteristics. The catheter has an elongated catheter body  12  with proximal and distal ends, an intermediate deflectable section  14  at the distal end of the catheter body  12 , and a distal section  15  which carries an irrigated tip electrode  17  and a plurality of irrigated ring electrodes  21 . The catheter also includes a control handle  16  at the proximal end of the catheter body  12  for controlling deflection of at least the intermediate section  14 . Advantageously, the distal section  15  has a spring member that enables a more controlled and biased deflection, including uni- or bi-directional deflection within a single plane. Along its length, the spring member houses discrete support members, each of which supports a respective ring electrode while allowing the spring member as a whole to deflect more predictably in enabling better contact between the tissue and the electrodes for forming more effective lesions. 
     With reference to  FIGS. 2A and 2B , 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. A presently preferred 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 to increase torsional stiffness of the catheter body  12  so that, when the control handle  16  is rotated, the intermediate section  14  of the catheter  10  will rotate in a corresponding manner. 
     The outer diameter of the catheter body  12  is not critical, but is preferably 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 puller members (e.g., puller wires), lead wires, and any other desired wires, cables or tubings. If desired, the inner surface of the outer wall  20  is lined with a stiffening tube  22  to provide improved torsional stability. A disclosed embodiment, the catheter has an outer wall  20  with an outer diameter of from about 0.090 inch to about 0.94 inch and an inner diameter of from about 0.061 inch to about 0.065 inch. 
     Distal ends of the stiffening tube  22  and the outer wall  20  are fixedly attached near the distal end of the catheter body  12  by forming a glue joint  23  with polyurethane glue or the like. A second glue joint (not shown) is formed between proximal ends of the stiffening tube  20  and outer wall  22  using a slower drying but stronger glue, e.g., polyurethane. 
     Components that extend between the control handle  16  and at least the intermediate deflectable section  14  pass through the central lumen  18  of the catheter body  12 . These components include lead wires  40  for the tip electrode  17  and ring electrodes  21  on the distal section  15 , an irrigation tubing  38  for delivering fluid to the distal section  15 , cables  48  for position/location sensors  36 R and  36 T located in the tip electrode and the ring electrodes, a pair of puller wires  26  for bi-directional deflection of at least the intermediate section  14 , and a pair of thermocouple wires  41 ,  45  to sense temperature at the distal section  15 . 
     Illustrated in  FIGS. 2A, 2B and 2C  is an embodiment of the intermediate section  14  which comprises a short section of tubing  19 . The tubing also has a braided mesh construction with multiple off-axis lumens, for example five lumens  31 ,  32 ,  33 ,  34  and  35 . Each of off-axis, diametrically opposing first and second lumens  31 ,  32  carries a puller wire  26 . A third off-axis lumen  33  carries the lead wires  40  and the thermocouple wires  41  and  45 . A fourth off-axis lumen  34  carries the sensor cables  48 . A fifth on-axis lumen  35  carries the irrigation tubing  38 . 
     The tubing  19  of the intermediate section  14  is made of a suitable non-toxic material that is more flexible than the catheter body  12 . A suitable material for the tubing  19  is braided polyurethane, i.e., polyurethane with an embedded mesh of braided stainless steel or the like. The size of each lumen is not critical, but is sufficient to house the respective components extending therethrough. 
     A means for attaching the catheter body  12  to the intermediate section  14  is illustrated in  FIGS. 2A and 2B . The proximal end of the intermediate section  14  comprises an outer circumferential notch  24  that receives an inner surface of the outer wall  20  of the catheter body  12 . The intermediate section  14  and catheter body  12  are attached by glue or the like. 
     If desired, a spacer (not shown) can be located within the catheter body  12  between the distal end of the stiffening tube  22  (if provided) and the proximal end of the intermediate section  14 . The spacer provides a transition in flexibility at the junction of the catheter body  12  and intermediate section  14 , which allows this junction to bend smoothly without folding or kinking. A catheter having such a spacer is described in U.S. Pat. No. 5,964,757, the disclosure of which is incorporated herein by reference. 
     Each puller wire  26  is preferably coated with Teflon®. The puller wires  26  can be made of any suitable metal, such as stainless steel or Nitinol and the Teflon coating imparts lubricity to the puller wire. The puller wire preferably has a diameter ranging from about 0.006 to about 0.010 inch. 
     As shown in  FIG. 2B , a portion of each puller wire  26  extending through the catheter body  12  passes through a respective compression coil  37  in surrounding relation to its puller wire  26 . The compression coil  37  extends from about the proximal end of the catheter body  12  to about the proximal end of the intermediate section  14 . The compression coil  37  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 puller wire  26 . Within the catheter body  12 , the outer surface of the compression coil  37  is also covered by a flexible, non-conductive sheath  39  ( FIG. 2B ), e.g., made of polyimide tubing. As shown in  FIGS. 2B and 2C , a portion of each puller wire  26  extending through the intermediate section  14  is covered by a nonconductive protective sheath  47 . 
     Proximal ends of the puller wires  26  are anchored in the control handle  16 . Distal ends of the puller wires  26  may be anchored near the distal end of the intermediate deflectable section  14  or in the distal section  15  as desired or appropriate. Separate and independent longitudinal movement of the puller wires  26  relative to the catheter body  12  which results in deflection of the intermediate section  14  and/or tip section  15  is accomplished by suitable manipulation of the control handle  16 . 
     In the illustrated embodiment of  FIG. 1 , the control handle  16  has a deflection actuator  50  that actuates the puller wires for bi-directional deflection. The control handle also includes a deflection tension knob  52  that enables the user to adjust the ease by which the deflection actuator  50  can be rotated. A suitable deflection assembly and control handle are described in co-pending U.S. application Ser. No. 12/346,834, filed Dec. 30, 2008, entitled DEFLECTABLE SHEATH INTRODUCER, the entire disclosure of which is hereby incorporated by reference. Other suitable deflection assemblies are described in co-pending U.S. application Ser. No. 12/211,728, filed Sep. 16, 2008, entitled CATHETER WITH ADJUSTABLE DEFLECTION SENSITIVITY, and U.S. application Ser. No. 12/127,704, filed May 27, 2008, entitled STEERING MECHANISM FOR BI-DIRECTIONAL CATHETER, the entire disclosures of both of which are hereby incorporated by reference. 
     With reference to  FIG. 3 , at the distal end of the intermediate section  14  is the distal section  15  that includes the tip electrode  17  and a plurality of irrigated ring electrodes  21  mounted at selected locations along the length of the distal section  15 . Notwithstanding the ring electrodes  21 , the distal section  15  advantageously has a flexible spring member  60  that allows for controlled or biased deflection in a single plane, in at least one direction, if not in two opposing directions, while allowing only limited deflection outside of the plane or in perpendicular directions to maintain torquability, axial loading capabilities, and side force performance. The spring member is constructed of a suitable material with flexibility and shape memory, such as nitinol or spring steel. 
     As illustrated in  FIG. 4A , the spring member  60  has an elongated tubular form defining a longitudinal axis  61 . The tubular form provides a central lumen  62  extending therethrough. In accordance with a feature of the present invention, the spring member  60  has a controlled or biased deflection that is enabled by at least one section  58  with defined compression characteristics enabled by a predetermined cut pattern, and at least one section  59  that is devoid of any cut pattern for carrying at least one ring electrode. The cut pattern of the section  58  includes a plurality of radial slots  63  with radial ribs  64  that extend from at least one spine  65  spanning the length of the tubular form. The slots  63  are cut or otherwise formed transversely, if not perpendicularly, to the longitudinal axis  61  of the tubular form, with each rib  64  having a generally uniform shape, depth D, width W and spacing S. These parameters may be varied as desired or appropriate for different deflection or bending characteristics. Illustrated herein are a few of the endless possible shapes of the slots, for example, trapezoidal ( FIG. 5C ), triangular ( FIG. 5D ), and circular or keyhole ( FIG. 5E ), and different depths, for example, less than half of the diameter of the tubular structure ( FIG. 5C ), about half of the diameter ( FIG. 5D ), or greater than half of the diameter ( FIG. 5E ). It is understood that tubular form itself may include tubes with circular or noncircular cross-sections. 
     The spring member  60  extends the length of the tip section  15  generally between a distal end of the intermediate deflectable section  14  and a proximal end of the tip electrode. The length may range between about 1.0 cm and 10.0 cm, preferably about 2.0 cm and 5.0 cm, and more preferably about 3.0 cm. In the illustrated embodiment, the spring member  60  has three pre-cut sections  58  and two uncut sections  59 . 
     The distal section  15  as supported by the spring member  60  in its neutral configuration extends linearly (solid line in  FIG. 1 ). The controlled or biased deflection (broken line in  FIG. 1 ) is enabled by the spring member  60  having at least one side  66  along its length that is more elastically compressible as shown in  FIG. 4A . The side  66  patterned by the slots  63  and ribs  64  is relatively more elastically compressible and the side  67  of the spine  65  is relatively less elastically compressible, if not resistant to compression. And, where the sides  66  and  67  are generally opposite to each other, as illustrated in  FIG. 4A , the spring member  60  is biased to deflect within a single plane defined by the two sides  66  and  67  (namely, the YZ plane in  FIG. 4A ), and in one direction in the single plane (namely, toward the +Z axis). 
     In an alternate embodiment, as illustrated in  FIGS. 4B and 4C , the spring member  60  has two rows of radial slots  63   a ,  63   b  and ribs  64   a ,  64   b , with each row extending along a respective side  66   a ,  66   b  that is relatively more elastically compressible, and two spines  65   a ,  65   b  with each spine extending along a respective side  67   a ,  67   b  that is relatively less elastically compressible, if not compression-resistant. And, where the two more compressible sides  66   a ,  66   b  are generally opposite of each other (separated by a radial angle of about 180 degrees) along a first diameter  54 , the two less compressible sides  67   a ,  67   b  are generally opposite of each other (separated by a radial angle of about 180 degrees) along a second diameter  55  and the first and second diameters are generally perpendicular (separated by a radial angle of about 90 degrees), the spring member  60  is biased for deflection in a single plane (namely, the XY plane in  FIG. 4B ), and in opposite directions (or bi-directionally) within the single plane (namely, toward the +X axis and the −X axis).  FIG. 4B  illustrates the embodiment of the spring member  60  employed in the distal section  15  in  FIG. 3 . 
     In  FIGS. 4A and 4B , the slots  63   a  and ribs  64   a  are aligned respectively with the slots  63   b  and ribs  64   b , as better shown in  FIG. 5A . However, it is understood that the slots and ribs of different rows can be offset from each other such that they present an alternating pattern, as shown in  FIG. 5B . 
     It is understood by one of ordinary skill in the art that deflection characteristics of a spring member depends on various factors, including plurality, depth D, separation S, width W of any row of slots/ribs, especially where a spring member has more than one row of slots/ribs with different pluralities, depths and/or widths such that the spines have different widths and/or are not opposite of each other such that their radial separation angle is greater or less than about 180 degrees. 
     The integrity of the spring member  60  is maintained by including a flexible cover  78  over the spring member, as shown in  FIG. 3 . The cover is preferably made of a biocompatible plastic or polymer, such as PELLETHANE or PEBAX, or polyolefin, with a flexibility about equal to that of the spring member. The cover should not hinder the ability of the spring member to bend. The cover protects the spring member against electrical conductivity, particularly where the structure is made of Nitinol or another metal, and also protects against blood and other bodily fluids from entering and clogging the slots. The cover  78  can be longer than the member  60  and has proximal and distal ends extending beyond the member&#39;s proximal and distal ends, respectively. The cover can be secured in place over the member by any suitable methods, such as by gluing, thermal bonding and/or heat shrinking. 
     At least one ring electrode  21  is carried on the spring member  60  over the cover  78 . In the illustrated embodiment, there are three ring electrodes  21   a ,  21   b ,  21   c , although it is understood that the plurality can range between about 2 and 10, and preferably between about 3 and 5. At each ring electrode  21 , a support member  56  is positioned in the central lumen  62  of the spring member  60  to support its respective ring electrode. The support member  56  may be constructed of a sufficiently rigid plastic material suitable for housing position/location sensors, such as SASs, to regulate irrigation flow to irrigated ring electrodes  21  and to act as a substrate on which its respective ring electrode is mounted. With reference to  FIGS. 3, 3A and 3B , each support member  56  has a similar construction with a plurality of lumens, including at least lumens  73 ,  74 ,  75  that preferably are in axial alignment with the lumens  33 ,  34  and  35 , respectively, of the tubing  19  of the deflectable intermediate section  14 , to avoid sharp bends or kinks in the components extending through these lumens. In the illustrated embodiment of  FIG. 3A , each member  56  includes an off-axis lumen  73  for electrode lead wires  40  and thermocouple wires  41 ,  45 , an off-axis lumen  74  for sensor cables  48 , and a center lumen  75  for irrigation fluid. The member may also include off-axis, diametrically opposing lumens  71  and  72  for the puller wires  26  in an embodiment where the puller wires extend into the distal section  15 . 
     The length of each support member  56  can range between about 0.2 cm and 1.0 cm, and preferably about 0.5 cm, which is generally about equal to the length of a ring electrode. The support members  56  may be fabricated using micro machining, micro molding, or machining of extrusions using plastic materials which are sufficiently rigid and sufficiently biocompatible for contact with blood. 
     A circumferential groove  80  is formed in the outer surface of each support member  56 . In the illustrated embodiment of  FIGS. 3 and 3B , the groove  80  is formed near a proximal end of the support member  56 , although it is understood that the groove  80  may be formed near a distal end of the support member  56 . The groove  80  is provided on the support member  56  to carry a wire coil of a sensor  36 R for each irrigated ring electrode  21 . The wire coil (e.g., a single-axis sensor “SAS”) is advantageously wound in the groove  80  on the support member  56  so that it does not occupy any space in the distal section  15  beyond that already occupied by the support member  56 . Moreover, the wire coil does not occupy any lumens of the support member  56 . Rather, the lumens are available to other components, including lead wires, thermocouple wires, irrigation tubing and puller wires, that do not necessarily require dedicated lumens and/or larger lumens as a typical sensor would. 
     A pair of sensor cables  48  are provided for each coil sensor  36 R of a ring electrode  21 , with each end of the coil being connected to one of the pair of cables ( FIG. 3B ). The sensor cables  48  for each coil of the ring electrodes  21  (and for the position sensor  36 T in the tip electrode  17 ) extend through the fourth lumen  74  of the support member  56 . A passage  82  ( FIG. 3B ) through the support member  56  allowing communication between the lumen  74  and the groove  80  is provided at each end of the groove. One sensor cable  48  is fed through a respective passage  82  for connection to each end of the wire coil of the sensor  36 R, so each sensor  36 R has a pair of sensor cables connected to it. 
     Each of the irrigated ring electrodes  21  is adapted for ablation and irrigation and has a similar structure to each other. The ring electrodes may be made of any suitable noble metal, such as platinum or gold, preferably a combination of platinum and iridium or gold and platinum. In the illustrated embodiment of  FIG. 6 , the ring electrode  21  is generally cylindrical with a length greater than its diameter and has a distal end  90 , a mid-section  92  and a proximal end  94 . With a wall  96  of a generally uniform thickness throughout its length, the ring electrode  21  has a larger diameter in the mid-section  92  than in the distal and proximal ends  90 ,  94 . As such, the wall bulges outwardly in the mid-section with curved transitional regions  98  on each side of the mid-section  92  so as to provide the ring electrode with an atraumatic profile without corners or sharp edges. With reference to  FIGS. 3A and 3B , a reservoir in the shape of an annular gap G is formed between an inner surface of the mid-section  92  and an outer surface of the spring member  60  (inclusive of the cover  78 ). A plurality of irrigation apertures  100  are formed in the wall  96  of the mid-section  92  to promote flow in a radial direction, and of the curved transitional regions  98  to promote flow in a more axial direction. In the latter instance, the apertures  100  in the curved transitional regions  98  are particularly effective in minimizing charring and coagulation which are likely to be “hot spots” resulting from higher current densities due to transitions in the electrode profile. In that regard, the curved transitional regions  98  may have a higher aperture density and/or apertures with a greater cross-section so as to minimize the occurrence of hot spots. Suitable ring electrodes are described in US Patent Application Publication No. US2010/0168548 A1, and U.S. patent application Ser. No. 13/174,742, filed Jun. 30, 2011, the entire content of both of which are incorporated herein by reference. 
     The ring electrodes  21  can be made of any suitable solid conductive material, such as platinum or gold, preferably a combination of platinum and iridium. The ring electrodes can be mounted onto the support members  56  with glue or the like. The rings electrodes may be uni-polar or bi-polar. In the illustrated embodiment, there are a distal monopolar ring electrode and a proximal pair of bi-polar ring electrodes. Each ring electrode is connected to a respective lead wire  40 R. 
     Each lead wire  40 R is attached to its corresponding ring electrode  21  by any suitable method. A preferred method for attaching a lead wire to a ring electrode involves first making a small hole through the wall of the non-conductive covering or tubing. Such a hole can be created, for example, by inserting a needle through the support member  56  and its cover  78  and heating the needle sufficiently to form a permanent hole. The lead wire is then drawn through the hole by using a microhook or the like. The end of the lead wire is then stripped of any coating and welded to the underside of the ring electrode, which is then slid into position over the hole and fixed in place with polyurethane glue or the like. 
     As seen in  FIGS. 3 and 3A , at least one opening  77  is formed in each portion of the irrigation tubing  38  extending through each ring electrode  21 . The opening  77  communicates with a radial passage  76  formed in the spring member  60 , its cover  78 , and the support member  56  below each ring electrode  21 . The passage  76  extends radially from the lumen  75  of the support member  56 , through the support member  56 , the spring member  60  and the cover  78  to provide fluid communication between the irrigation tubing  38  and the gap reservoir G of each ring electrode  21 . Each passage  76  is formed at a predetermined radial angle ( FIG. 3A ) so that the passages  76  do not intersect or otherwise interfere with the off-axis lumens in each of the support member  56 . Advantageously, the passages  76  can be precisely dimensioned so as to regulate the volumetric flow rate of the irrigation fluid delivered to the gap reservoirs G. 
     The length of a ring electrode  21  is about equal to the length of a support member  56  so that the support member is covered in its entirety by its respective ring electrode. The groove  80  and the coil sensor  36 R are positioned under a section  59  of the spring member so that the coil sensor  36 R is isolated from and not exposed to irrigation fluid in the gap reservoir G of the ring electrode. The distal and proximal ends  90  and  94  of the ring electrodes are sized relative to the support members  56  so as to form a fluid tight seal enclosing the gap reservoir G. 
     With reference to  FIGS. 3 and 7 , the tip electrode  17  houses an electromagnetic position sensor  36 T in a distal and on-axis location relative to the tip electrode. The tip electrode is configured to promote turbulent flow and dispersion of irrigation fluid for increased thermal transfer from the tip electrode to the fluid and thus with lower flow rates resulting in lower fluid load in the patient. Fluid, e.g., saline or heparinized saline, can be delivered to the ablation site from the tip electrode to cool tissue, reduce coagulation and/or facilitate the formation of deeper lesions. It is understood that other fluids can be delivered as well, including any diagnostic and therapeutic fluids, such as neuroinhibitors and neuroexcitors. 
     The tip electrode  17  has a two-piece configuration that includes an electrically conductive dome shell  110  and an internal member  112 . The shell  110  is generally cylindrical defining a chamber  113  between a closed distal end  114  and an open proximal end (or neck)  116 . The neck  116  connected with a distal end of the nonconductive cover  85  of the connection section  81 . The internal member  112  is configured to fit inside the shell  110  with an elongated distal section  118  that sits inside the chamber  113 , and a proximal core  120  that plugs the neck  116 . The core  120  and the distal section  118  are connected by a stem  119 . The distal end  114  of the shell  110  and the distal section  118  of the internal member  112  are relatively sized so that the chamber  113  functions as a tip reservoir for irrigation fluid entering the tip electrode  17 . Fluid passages  124  are formed in the core  120  to provide fluid communication from the irrigation connector lumen  86  to the chamber  113 . 
     The shell  110  is constructed of a biocompatible metal, including a biocompatible metal alloy. A suitable biocompatible metal alloy includes an alloy selected from stainless steel alloys, noble metal alloys and/or combinations thereof. In one embodiment, the shell is constructed of an alloy comprising about 80% palladium and about 20% platinum by weight. In an alternate embodiment, the shell is constructed of an alloy comprising about 90% platinum and about 10% iridium by weight. The shell can formed by deep-drawing manufacturing process which produces a sufficiently thin but sturdy wall that is suitable for handling, transport through the patient&#39;s body, and tissue contact during mapping and ablation procedures. A deep drawn shell is also suitable for electrical discharge machining (EDM) process to form a large plurality of through-holes or ports  122  in the shell that allow fluid communication between the chamber  113  and outside the shell  110 . 
     The elongated distal section  118  of the internal member  112  is configured to protect and encapsulate the tip electrode sensor  36 T which is positioned centrally within the chamber  113  so that the sensor is distal and centered in the tip electrode for optimum performance. In the disclosed embodiment, the tip electrode sensor  36 T is an electromagnetic (EM) tri-axis location/position sensor using three coils that give rise to signals that are used to determine the position of the device relative to a frame of reference that is fixed either externally to the body or to the heart itself. The EM sensor may be active or passive and may operate by generating or receiving electrical, magnetic or ultrasonic energy fields or other suitable forms of energy known in the art. 
     The core  120  of the internal member  112  sits in the neck  116  of the shell  110 . The core is advantageously configured as a diffuser that provides multiple fluid passages or channels  124  through the neck  116  so as to diffuse the irrigation fluid. As such, the diffusing core  120  provides increased turbulence and a more uniform flow rate in the chamber  113  and thus more increased convective cooling on the shell  110 . Irrigation in the tip electrode  17  is thus more uniform throughout the length of the tip electrode. The internal member  112  effectively counters the tendency for the velocity of the fluid entering the tip electrode  17  to otherwise carry the fluid to the more distal ports and starve the more proximal ports  122 . 
     On a proximal surface of the core  120 , a center opening  130  ( FIG. 7A ) connects a distal end of the irrigation tubing  38  with the channels  124  in the core  120 . Within the core  120 , the channels  124  intersect each other at varying degrees throughout the tip electrode ( FIG. 7B ), and then separate into distinct channels ( FIG. 7C .) In the illustrated embodiment, the channels  124  have a circular cross-section, however, it is understood that the cross-section may be polygonal or any noncircular shape and can have any suitable size, as appropriate. The core  120  is made of electrically conductive material so as to be conductive with the shell  110  when the core  120  is energized by its lead wire  40 T, but the distal section  118  can be made of plastic such as polyimide, or an adhesive or sealant, such as epoxy, to encapsulate the tip electrode sensor  36 T. 
     Also on the proximal surface of the core  120  are blind holes  132 ,  133  ( FIGS. 3 and 7A ) for the tip electrode lead wire  40 T, the thermocouple wires  41 ,  45 . A longitudinal through-hole  134  extending through the core  120 , the stem  119  and into the distal section  118  of the internal member  112  is provided for the cable  48 T for the tip electrode sensor  36 T. The through-hole or passage  134  is routed from a proximal off-axis location in the core  120  to a distal on-axis location in the stem  119  without interfering with the fluid diffusing channels  124 . 
     A distal end of each puller wire  26  has a T-bar  105 . In the illustrated embodiment of  FIG. 8 , the T-bars are anchored in the first and second lumens  31 ,  32  of the tubing  19  at or near the distal end of the intermediate section  14 . However, it is understood that the distal ends of the puller wires  26  may be soldered in diametrically-opposing off axis blind-holes in the proximal surface of the core  120  ( FIG. 3 ) of the tip electrode  17 , as desired or appropriate. 
     In accordance with another feature of the present invention, fluid is delivered through the catheter body  12  ( FIG. 2A ), through the intermediate section  14  ( FIG. 2A ), and through the distal section  15  via the irrigating tubing  38  ( FIG. 3B ) which extends through the lumen  75  of the support members  56 . A portion of the fluid enters the reservoir gap G of each ring electrode via the opening  77  and the passage  76  ( FIG. 3C ), and exits the ring electrodes via the apertures  100 . Another portion of the fluid continues to the tip electrode  17  via the irrigation tubing  38  and the diffusing channels  124  ( FIG. 5 ), where it enters the chamber  113  and exits the tip electrode via irrigation ports  122 . In the tip electrode  17 , the fluid has a flow that is more uniform and equal in the radial direction through the diffusing channels  124  which in turn provides increased turbulence and a more uniform flow rate in the chamber  113  and thus more increased convective cooling on the shell  110 . Irrigation in the tip electrode is thus more uniform throughout the length of the tip electrode. Suitable tip electrodes are described in U.S. patent application Ser. No. 12/767,763, filed Apr. 26, 2010 entitled “IRRIGATED CATHETER WITH INTERNAL POSITION LOCATION SENSOR,” the entire disclosure of which is incorporated herein by reference. 
     The lead wires  40 T and  40 R pass through the lumen  18  of the catheter body  12  ( FIG. 2A ), the lumen  33  of the intermediate section  14  ( FIG. 2A ), and the lumen  73  of the support members  56  ( FIG. 3B ) throughout the distal section  15 . The portion of the lead wires extending through the central lumen  18  of the catheter body  12 , and proximal portion of the lumen  33  can be enclosed within a protective sheath  67  ( FIG. 2A ), which can be made of any suitable material, preferably polyimide. The protective sheath is anchored at its distal end to the proximal end of the intermediate section  14  by gluing it in the lumen  33  with polyurethane glue or the like. Each electrode lead wire has its proximal end terminating in a connector (not shown) at the proximal end of the control handle  16 . The tip electrode  17  and ring electrodes  21  are electrically connected to a source of ablation energy by the lead wires  40 T and  40 R via the connector. The wires may also be electrically connected to an appropriate mapping or monitoring system via the connector. 
     The preceding description has been presented with reference to certain exemplary embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes to the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. It is understood that the drawings are not necessarily to scale. Certain features, including the cut pattern of slots, ribs and spine, may be exaggerated for clarity purposes. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings. Rather, it should be read as consistent with and as support for the following claims which are to have their fullest and fairest scope.