Patent Publication Number: US-2022218413-A1

Title: Irrigated catheter with improved ablation tip electrode fluid distribution

Description:
FIELD OF INVENTION 
     The present invention relates to electrophysiologic (EP) catheters, in particular, EP catheters for ablating cardiac tissue. 
     BACKGROUND 
     Ablation of cardiac 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 electrodes on the catheter to heat tissue to a destructive temperature in order to create a lesion for the purpose of breaking arrhythmogenic current paths in the tissue. 
     Irrigated catheters are now commonly used in ablation procedures. Irrigation provides many benefits including cooling of the electrode and tissue which prevents overheating of tissue that can otherwise cause adjacent blood to form char and coagulum. Irrigated tip electrodes are known, including tip electrodes with a two-piece construction having an inner support structure and a dome shell mounted thereon. A cavity is formed between the support structure and the dome shell to provide a plenum chamber that enables a flow of fluid exiting the tip electrode via fluid ports formed in the dome shell. However, irrigation fluid may not be uniformly distributed throughout the plenum chamber and thus not all portions of the dome shell may receive uniform cooling. Without uniform cooling, hot spots may result which lead to char formation during ablation. 
     Accordingly, it is desirable that a catheter with a plenum chamber receive more consistent and evenly distributed irrigation cooling to all portions of the dome shell to minimize char formation. It is desirable for the irrigation to reach proximal end portion of the dome shell and other regions with a lesser number of fluid exit ports in the dome shell. 
     SUMMARY OF THE INVENTION 
     A catheter has a tip electrode a shell and a support structure defining a fluid plenum chamber. The catheter advantageously includes a fluid distribution tube that extends longitudinally into the chamber, wherein the fluid distribution tube has fluid apertures along its length for distributing fluid more uniformly throughout the chamber in improved cooling and thus minimizing the risk of char formation on regions of the tip electrode more prone to overheating. 
     In some embodiments of the present invention, an electrophysiologic catheter has an elongated catheter body, a control handle proximal of the catheter body, and a tip electrode distal of the catheter body, the tip electrode configured for irrigation and having a shell and a support member defining an internal chamber. The tip electrode includes a fluid distribution tube that extends longitudinally into the chamber and has a side wall with a plurality of apertures. 
     In some detailed embodiments, the apertures in the side wall of the fluid distribution tube are arranged in a predetermined pattern. 
     In some detailed embodiments, the predetermined pattern includes a distal aperture and a proximal aperture. 
     In some detailed embodiments, the predetermined pattern includes the plurality of apertures are longitudinally aligned. 
     In some detailed embodiments, the predetermined pattern includes a greater spacing between more-proximal adjacent apertures and a lesser spacing between more-distal adjacent apertures in the longitudinal direction. 
     In some detailed embodiments, the apertures have different sizes. 
     In some detailed embodiments, the apertures have different shapes. 
     In some detailed embodiments, the predetermined pattern includes the apertures having different radial positions in the side wall. 
     In some detailed embodiment, the catheter includes an irrigation tubing in fluid communication with the fluid distribution tube. 
     In some detailed embodiments, the internal chamber has a first length and the fluid distribution tube has a second length that ranges between 0.5 and 0.9 of the first length. 
     In some detailed embodiments, at least one aperture is more proximal than one or more most-proximal ports. 
    
    
     
       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 perspective view of catheter in accordance with an embodiment of the present invention. 
         FIG. 2  is an end cross-sectional view of a catheter body of the catheter of  FIG. 1 , taken along line A-A. 
         FIG. 3  is an end cross-sectional view of an intermediate section of the catheter of  FIG. 1 , taken along line B-B. 
         FIG. 4  is side elevational view of a distal tip section of the catheter of  FIG. 1 . 
         FIG. 5  is a perspective illustration representative of various coils in the distal tip section of  FIG. 4 . 
         FIG. 6  is a side-cross-sectional view of the tip electrode of  FIG. 4 . 
         FIG. 7  is an end cross-sectional view of the tip electrode of  FIG. 5 . 
         FIG. 8  is a side-elevational view of a fluid distribution tube, in accordance with an embodiment of the present invention. 
         FIG. 9  is a side cross-sectional view of the fluid distribution tube of  FIG. 8 . 
         FIG. 10  is a side cross-sectional view of a fluid distribution tube, in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an embodiment of a catheter  10  with an improved irrigation-cooled ablation tip electrode. 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  with a tip electrode  17 . The catheter also includes a control handle  16  at the proximal end of the catheter body  12  for controlling deflection (single or bi-directional) of the intermediate section  14  relative to the catheter body  12 . 
     With reference to  FIG. 2 , 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. 
     Components that extend between the control handle  16  and the deflectable section  14  pass through the central lumen  18  of the catheter body  12 . These components include lead wires  30 T and  30 R (for the tip electrode  17  and a plurality of ring electrodes  21  proximal of the tip electrode), an irrigation tubing  38  with lumen  37  for delivering fluid to the tip electrode, a cable  33  for a position sensor  34  carried in or near the distal section  15 , puller wires  32   a ,  32   b  for deflecting the intermediate section  14 , and a pair of thermocouple wires  41 ,  42  to sense temperature at the distal section  15 . It is understood that in some embodiments one of the wires  41  and  42  is configured as a lead wire for delivering electrical energy to the tip electrode  17  in lieu of the lead wire  30 T. 
     Illustrated in  FIG. 3  is an embodiment of the intermediate section  14  which comprises a short section of tubing  19 . The tubing also has a braided mesh construction but with multiple lumens, for example off-axis lumens  23 ,  26   a ,  26   b  and  27  and on-axis lumen  28 . The lumen  27  carries the lead wires  30 T and  30 R, and the thermocouple wires  41  and  42 . The lumen  23  carries the position sensor cable  33 . The lumen  28  carries the irrigation tubing  38 . The lumen  26   a  carries a puller wire  32   a  for deflection of the intermediate section. For bi-directional deflection, the diametrically-opposing lumen  26   b  carries a second puller wire  32   b.    
     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. 
     Each puller wire  32   a  and  32   b  has a lubricious coating, e.g. of Teflon® The puller wires 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. 3 , the portion of each puller wire in the catheter body  12  passes through a compression coil  35  in surrounding relation to its puller wire. Each compression coil  35  extends from the proximal end of the catheter body  12  to at or near the proximal end of the intermediate section  14 . The compression coils are made of any suitable metal, preferably stainless steel, and are tightly wound on themselves 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. Each portion of the puller wires distal of the compression coil  35  may extend through a respective protective sheath  39  to prevent the puller wire from cutting into the tubing  19  of the intermediate section  14  during deflection. 
     Proximal ends of the puller wires  32   a  and  32   b  are anchored in the control handle  16 . Distal ends of the puller wires  32   a  and  32   b  are anchored in the distal section  15 , as described further below. Separate and independent longitudinal movements of the puller wires relative to the catheter body  12 , which results in, respectively, deflection of the intermediate section  14  along a plane, are accomplished by suitable manipulation of a deflection member of the control handle  16 . Suitable deflection members and/or deflection assemblies are described in co-pending U.S. Publication No. US2010/0168827 A1, published Jul. 1, 2010, entitled DEFLECTABLE SHEATH INTRODUCER, and U.S. Publication No. US2008/0255540 A1, published Oct. 16, 2008, entitled STEERING MECHANISM FOR BI-DIRECTIONAL CATHETER, the entire disclosures of both of which are hereby incorporated by reference. 
     With reference to  FIG. 4 , at the distal end of the intermediate section  14  is the distal tip section  15  that includes the tip electrode  17  and a relatively short piece of non-conductive connector tubing or covering  24  between the tip electrode  17  and the intermediate section  14 . In the illustrated embodiment, the connector tubing  24  has a single lumen  44  which receives a distal end of the position sensor cable  33  and allows passage of components including electrode lead wires  30 T and  30 R, thermocouple wires  41  and  42 , and the irrigation tubing  38  into the distal section  15  and tip electrode  17 . The single lumen  44  of the connector tubing  24  allows these components to reorient themselves as needed from their respective lumens in the intermediate section  14  toward their location within the distal section  15  and tip electrode  17 . In the disclosed embodiment, the tubing  24  is a protective tubing, e.g., PEEK tubing, having a length ranging between 6 mm and 12 mm, more preferably about 11 mm. 
     The connector tubing  24  also houses a force sensor  90 . Aspects of a force sensor similar to force sensor are described in U.S. Pat. No. 8,357,152, issued on Jan. 22, 2013 to Govari et al., entitled CATHETER WITH PRESSURE SENSING, and in U.S. Patent Publication No. 2011/0130648, to Beeckler et al., filed Nov. 30, 2009, entitled CATHETER WITH PRESSURE MEASURING TIP, both of whose disclosures are incorporated herein by reference. 
     With reference to  FIG. 4  and  FIG. 5 , the force sensor  90  includes a resilient coupling member  60 , which forms a spring joint. In some embodiments, the coupling member  60  has hollow tubular form with a central lumen  68  therethrough. Coupling member  60  typically has one or more helices cut or otherwise formed in the member, so that the member behaves as a spring. In some embodiments, the coupling member  60  is formed of a superelastic alloy, such as nickel titanium (Nitinol), within force sensor  90 . 
     The force sensor  90  includes a joint sensing assembly comprising coils  76 ,  78 ,  80  and  82  that provides accurate reading of any dimensional change in axial displacement and angular deflection in the spring joint, including when the tip electrode  17  is angularly displaced from a longitudinal axis  84  of the catheter, such as then the tip electrode comes into contact with tissue. These coils are one type of magnetic transducer that may be used with the catheter. A “magnetic transducer,” in the context of the present patent application and in the claims, means a device that generates a magnetic field in response to an applied electrical current and/or outputs an electrical signal in response to an applied magnetic field. Although the embodiments described herein use coils as magnetic transducers, other types of magnetic transducers may be used in alternative embodiments, as will be apparent to those skilled in the art. 
     The coils in the sensing assembly are divided between two subassemblies on opposite sides of the spring joint. One subassembly comprises coil  82  distal of the spring joint, which is driven by a current, via a wire (included in the cable  33 ), to generate a magnetic field. This field is received by a second subassembly, comprising coils  76 ,  78  and  80 , which are located proximal of the spring joint, in a section of the connector tubing  24  that is spaced axially apart from and proximal of the coil  82 . The term “axial,” as used in the context of the present patent application and in the claims, refers to a direction along or parallel to the longitudinal axis  84  of the catheter. The coil  82  typically lies on-axis with the longitudinal axis  84 . 
     Coils  76 ,  78  and  80  are fixed in connector tubing  24  at the same proximal distance from the coil  82  but at different radial locations. (The term “radial” refers to coordinates about the longitudinal axis  84 .) Specifically, in the illustrated embodiment, the coils  76 ,  78  and  80  are all located in the same plane perpendicular to the longitudinal axis  84  but at different equi-azimuthal angles about the longitudinal axis  84 , that is, the three coils are spaced azimuthally 120 degrees apart at the same axial distance from the coil  82  along the longitudinal axis  84 . 
     The coils  76 ,  78  and  80  generate electrical signals in response to the magnetic field transmitted by coil  82 . These signals are conveyed by wires (part of the cable  33 ) extending proximally from the distal section  15 , through the lumen  23  of the intermediate section  14 , through the lumen  18  of the catheter body  12  and into the control handle  16 . The signals are processed by a remote processor in order, for example, to measure the axial displacement of spring joint along the longitudinal axis  84 , as well as to measure the angular deflection of the joint from the longitudinal axis  84 . From the measured displacement and deflection, the processor is able to evaluate, typically using a previously determined calibration table, a magnitude and a direction of the force on the spring joint. 
     The same processor (or another processor) detects and measures the location and orientation of distal section  15 . The method of measurement may be by any convenient process known in the art. In one embodiment, magnetic fields generated external to a patient create electric signals in elements in the distal section  15 , and the processor uses the electric signal levels to determine the distal section location and orientation. Alternatively, the magnetic fields may be generated in the distal section  15 , and the electrical signals created by the fields may be measured external to patient. As shown in  FIG. 4  and  FIG. 5 , the elements in distal section  12  that are used to position and locate the distal section)  12  include orthogonal coil C x  aligned with the X axis, orthogonal coil C y  aligned with the Y axis, and one of the coil  76 ,  78  and  80  (in addition to their use as elements of force sensor), for example, the coil  80  aligned with the Z axis as orthogonal coil C z . The coils C x , C y , C z / 80  are housed in the connector tubing  24 , within the lumen  68  of the coupling member  60 . These coils are the sensing components of the electromagnetic position sensor  34  to which the cable  33  is connected. In some embodiments, the catheter includes a single axial sensor (SAS) cable assembly in lieu of the cable  33  and the electromagnetic position sensor  34  for position and location sensing. A SAS cable assembly suitable for use is described in U.S. Pat. No. 8,792,962, titled CATHETER WITH SINGLE AXIAL SENSORS, the entire disclosure of which is incorporated herein by reference. 
     With reference to  FIG. 6 , the irrigated tip electrode  17  has a two-piece construction that includes an electrically-conductive dome shell  50  and an electrically-conductive internal support member or “plug”  52  which jointly define a cavity of an internal plenum chamber  51  that is surrounded, enclosed and sealed by the shell  50  and the support member  52 . The chamber has a longitudinal length L extending between a distal face  52 D of the plug  52  and a distal inner wall  51 D. The shell  50  has a hollow cylindrical body  50 B with an open proximal portion  50 P and a closed distal portion  50 D adapted for tissue contact. The distal portion  50 D has a dome atraumatic distal end  53 . Formed in shell wall  63  are a plurality of fluid exit ports  56  that allow fluid communication between the chamber  51  and outside the shell  50 . 
     The shell  50  and the plug  52  are 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  50  and the member  52  are constructed of an alloy comprising about 90% platinum and about 10% iridium by weight. In some embodiments, the shell is formed by deep-drawing manufacturing process which produces a sufficiently thin but sturdy shell wall that is suitable for handling, transport through the patient&#39;s body, and tissue contact during mapping and ablation procedures. 
     The lead/thermocouple wires  30 T,  41  and/or  42  and the irrigation tubing  31  pass proximally from the tip electrode  17  through a protective, nonconductive tubing  65  ( FIG. 4 ). The wires and the irrigation tubing pass further through the lumens  27  and  28  of the tubing  19  of the intermediate section  14  and through the lumen  18  of the catheter body  12 . The shell  50  and the plug  52  facilitate the provision of a plenum condition within the chamber  51 ; that is, where fluid is forced or delivered in the chamber  51  and then passes through the exit ports  56  formed in shell wall  63  to exit the tip electrode  17 . 
     As shown in  FIG. 7 , the plug  52  has a plurality of holes. In the illustrated embodiment, the plug  52  has four blind holes, namely,  57   a ,  57   b  and  58 , on its proximal face  52 P and one through-hole  61 . The blind holes  57   a  and  57   b  are off-axis, diametrically opposed and generally in longitudinal alignment with lumens  26   a  and  26   b  of the deflectable section  14  for receiving and anchoring the puller wire  32   a  and  32   b , respectively. One or more blind hole(s)  58  are off-axis and adapted to receive and anchor distal ends of lead wire  30 T and thermocouple wires  41  and  42 . As mentioned, in some embodiments, one of the thermocouple wires  41  and  42  is configured as a lead wire for the tip electrode  17 , obviating the need for the separate lead wire  30 T. The through-hole  61  is on-axis and adapted to receive a distal portion of the irrigation tubing  38 . 
     As shown in  FIG. 6 , extending through the through-hole  61  from a distal face  52 D of the plug  52  is an elongated hollow fluid distribution tube  100  formed with a plurality of graduated fluid distribution apertures  101  arranged in a predetermined pattern. The fluid tube  100  extends linearly and distally into the chamber  51 , on-axis with the longitudinal axis  84  of the catheter. The fluid tube  100  has a closed distal end. Center lumen  102  of the fluid tube  100  is in communication with the lumen  37  of the irrigation tubing  38  and also with the fluid apertures  101  formed in side wall  103  of the fluid tube  100 . Advantageously, the lumen  102  of the fluid tube  101  in the chamber  51  reaches deep into the chamber by extending distally toward the distal end  51 D of the chamber  51  and having a length LF ranging between about 0.5 and 1.0, more preferably about 0.6 and 0.8, of the length L of the chamber  51 , where the side wall  103  of the fluid tube  101  is configured with the fluid apertures  101  in a predetermined pattern. The pattern includes, for example, fluid apertures  101  spanning along the length of the fluid tube  100 , so that there is at least one proximal aperture  101 P and at least one distal aperture  101 D, each occupying a different longitudinal position in the fluid tube  100 , as show in  FIG. 8 . Moreover, the size and/or shape of each aperture  101  may vary. In the embodiment of  FIG. 9 , the fluid tube  100  includes eight apertures: four pairs of diametrically-opposed apertures, with two smaller-sized, most-distal apertures  101 D, two smaller-sized, most-proximal apertures  101 P, and two larger-sized, mid-apertures therebetween  101 M. The spacing S 1  and S 2  and S 3  between adjacent apertures differs, for example, where a more-distal spacing is lesser than a more-proximal spacing, or where S 1 &lt;S 2 &lt;S 3 . In some embodiments, the fluid apertures  101  are longitudinally aligned, occupying similar radial positions in the side wall  103 , as shown in  FIG. 8  and  FIG. 9 . In some embodiments, longitudinally-adjacent apertures  101  occupy different radial positions in the side wall  103 , for example, apertures  101 A are 90 degrees radially offset from apertures  101 B, as shown in  FIG. 10 . 
     In some embodiments, at least some of the apertures  101  are sized smaller than the ports  56  of the shell  50 . In some embodiments, at least some of the apertures  101  are sized about the same as the ports  56 . In some embodiments, at least some of the apertures  101  are sized larger than the ports  56 . In some embodiments, at least one of the apertures  101  is more proximal than the most proximal port(s)  56 . 
     The configurations of the apertures  101  spanning along the length of the fluid tube  100  advantageously provide predetermined distribution patterns of irrigation fluid to both the proximal and distal portions of the chamber  51  which provide better cooling of the tip electrode  17  regardless of the configuration of the exit ports  56  in the wall  63  of the shell  50 . Thus, in the portion(s) of the shell  50  are lacking or devoid of exit ports  56 , e.g., the proximal portion of the shell  50  near the plug  52  (see “x” in  FIG. 6 ), the fluid tube  100  and its apertures  101  enable improved circulation of cooling fluid within the chamber  51 , in contrast to prior plenum chamber where irrigation fluid enters the chamber  51  merely at its proximal end without other mechanisms or forces that delivers fluid more uniformly throughout the entirety of the chamber. The different sizing and/or shape of the apertures  101  enable the fluid to enter the chamber  51  at different velocities for improving circulation within the chamber  51 . Improved circulation improves cooling of all portions of the tip electrode  17  and thus decrease the risk of char formation on all portions of the tip electrode, especially the proximal portion of the tip electrode and portions lacking or devoid of exit ports. By applying computation fluid dynamics (CFD) to variations in tip electrode parameters, including, for example, dome shell/chamber size, the plurality, location, shape and/or size of exit ports  56  in the shell  50 , the relative length of the fluid tube  100  to the chamber length, the plurality location, shape and/or size of apertures  101 , fluid dynamics within the tip electrode  17  are calculated and readily adjusted, as desired or appropriate. 
     It is understood that the fluid tube  100  may be constructed as a portion of the irrigation tubing  38 , for example, of a similar material, as a proximal portion of the irrigation tubing. Alternatively, the fluid tube  100  may be constructed of a different material and/or as a separate or different component from the irrigation tubing, with fluid communication enabled by the through-hole  60  in the plug  52 , or by another fluid tubing. In any case, the fluid tube  100  is constructed for fluid communication between its lumen  102  and the lumen  37  of the irrigation tubing  38 , either directly or indirectly, such that fluid is passed and delivered between the irrigation tubing  38  and the fluid tube  100 . 
     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. Notably, the drawings are not necessarily to scale, and any one or more features of an embodiment may be included in any other embodiment in addition to or in lieu of any feature, as desired or appropriate. 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.