Patent Publication Number: US-2019175875-A1

Title: Cardiovascular Catheter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119(e) from U.S. Provisional Patent Application No. 62/596,641, filed on Dec. 8, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The disclosed embodiments are directed to a cardiovascular catheter and, in particular, a cardiovascular catheter having improved anchoring of control lines. 
     BACKGROUND 
     Ultrasound devices are an essential tool for evaluation and treatment of various diseases, especially in the field of interventional cardiology. The use of intracardiac echocardiography (ICE), with its power to visualize cardiac structures and blood flow from the inside, provides very useful support in many procedures. ICE uses a catheter-based steerable ultrasound probe that is introduced into the right heart chambers to display cardiac structures from the inside. These devices include features such as maneuverability, with the possibility of anterior/posterior and left/right deflection of the catheter. 
     In conventional approaches, a steerable catheter may have lumens within its walls and an anchor at the distal end thereof having corresponding lumens. Each of the lumens may carry a control line secured by a retention knot or crimping a ball at the end face of the anchor to create the resistance needed for articulation of the catheter without allowing the ends of the control lines to slip or pull out of the anchor. In such a case, the catheter wall must adequately support the anchoring knot, i.e., must be thick enough so that the knots at the ends of the control lines do not extend beyond the inner or outer wall surfaces of the catheter in a transverse direction. The outer diameter is dictated by use considerations and, in general, cannot be increased. Therefore, the use of retention knots results in a catheter having a smaller inside diameter, i.e., having a smaller central lumen. This is undesirable because the space in the central lumen is highly valuable space, as it sets the limit for available space necessary for other components/elements which may be inserted through the catheter at one time. 
     SUMMARY 
     In one aspect, the disclosed embodiments are directed to a steerable catheter. The catheter includes a flexible elongate tube having an inner wall surface defining a central lumen and an outer wall surface defining an outer diameter of the tube, and a first pair and a second pair of control line lumens disposed between the inner wall surface and the outer wall surface and extending along a length of the elongate tube. The catheter further includes an anchor disposed at a distal end of the elongate tube, the anchor being cylindrical in shape and having an inner wall surface defining a central lumen and an outer wall surface defining an outer diameter. The catheter further includes a first and a second continuous control line, extending through the first and second pair of control line lumens, respectively. A portion of each of the first and the second continuous control lines is secured at the anchor so that retraction toward a proximal end of the elongate tube of ends of the first continuous control line causes movement of the distal end of the elongate tube in two directions in a first plane of movement, and retraction toward the proximal end of the elongate tube of ends of the second continuous control line causes movement of the distal end of the elongate tube in two directions in a second plane of movement orthogonal to the first plane of movement. 
     In another aspect, the disclosed embodiments are directed to a method of manufacturing a steerable catheter. The method includes providing a flexible elongate tube having an inner wall surface defining a central lumen and an outer wall surface defining an outer diameter of the tube, and further having a first pair and a second pair of control line lumens disposed between the inner wall surface and the outer wall surface and extending along a length of the elongate tube. The method further includes providing an anchor at a distal end of the elongate tube, the anchor being cylindrical in shape and having an inner wall surface defining a central lumen of the anchor and an outer wall surface defining an outer diameter of the anchor. The method further includes threading a first and a second continuous control line through the first and second pair of control line lumens, respectively. The method further includes securing a portion of each of the first and the second continuous control lines at the anchor so that retraction toward a proximal end of the elongate tube of ends of the first continuous control line causes movement of the distal end of the elongate tube in two directions in a first plane of movement, and retraction toward the proximal end of the elongate tube of ends of the second continuous control line causes movement of the distal end of the elongate tube in two directions in a second plane of movement orthogonal to the first plane of movement. 
     The disclosed embodiments may include one or more of the following features. 
     Both ends of each of the first and the second continuous control lines may extend from the first and the second pair of control line lumens at a proximal end of the elongate tube, and an approximate midpoint of each of the first and the second continuous control lines may be secured in place at the anchor. The anchor may include a first pair and a second pair of anchor control line lumens disposed between the inner wall surface of the anchor and the outer wall surface of the anchor and extending along a length of the anchor, the first pair and the second pair of anchor control line lumens being aligned with the control line lumens of the elongate tube. A first pair and a second pair of anchor threading lumens may be disposed between the inner wall surface of the anchor and the outer wall surface of the anchor and extending along a length of the anchor. The first pair of anchor threading lumens may be positioned between the first pair of anchor control line lumens in a radial direction of the anchor, and the second pair of anchor threading lumens may be positioned between the second pair of anchor control line lumens in the radial direction of the anchor. 
     The first and the second continuous control lines may be disposed in: the first and the second pair of control line lumens, respectively; the first and the second pair of anchor control line lumens, respectively; and the first and the second pair of anchor threading lumens, respectively. The first and the second continuous control lines may extend from the first and the second pair of control lines lumens of the anchor, may extend across a distal face of the anchor, and may extend into the first and the second pair of anchor threading lumens, respectively. The first continuous control line extends from one anchor threading lumen of the first pair of anchor threading lumens, extends across a proximal face of the anchor, and extends into another anchor threading lumen of the first pair of anchor threading lumens, the second continuous control line extends from one anchor threading lumen of the second pair of anchor threading lumens, extends across a proximal face of the anchor, and extends into another anchor threading lumen of the second pair of anchor threading lumens. A portion of the first continuous control line extending across the proximal face of the anchor may include a midpoint of the first continuous control line, and a portion of the second continuous control line extending across the proximal face of the anchor may include a midpoint of the second continuous control line. The anchor may be formed of a polymer having a higher hardness than the material of the elongate tube of the catheter. The first and the second continuous control lines may be formed of manufactured crystalline flexible fiber. 
     The catheter may include a control housing, wherein the elongate tube is mounted in the control housing, the control housing including a first actuator connected to both ends of the first continuous control line and a second actuator connected to both ends of the second continuous control line. The catheter may further include an anchor cap attached on at least a distal portion of the anchor, thereby securing the first and the second continuous control lines at the anchor. The anchor cap may be attached by thermoplastic melting of the anchor cap and the anchor. The first pair of control line lumens may be separated by a radial angle of about 90 degrees, and the second pair of control line lumens may be separated by a radial angle of about 90 degrees. The central lumen of the anchor may have a diameter approximately equal to a diameter of the central lumen of the elongate tube, and the outer diameter of the anchor may be approximately equal to the outer diameter of the elongate tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an ultrasound cardiovascular catheter assembly mounted in a control housing; 
         FIG. 2  is a partial cutaway view of the catheter assembly, including control lines, an anchor, and an anchor cap at the distal end thereof; 
         FIG. 3  is a perspective view of the distal end of the anchor threaded with the control lines; 
         FIG. 4  is a perspective view of the proximal end of the anchor threaded with the control lines; 
         FIG. 5  is a partial cutaway view of the catheter assembly, including control lines, an anchor, a cladding section, and an anchor cap at the distal end thereof; 
         FIG. 6  is cross-sectional view of the anchor showing control line lumens and anchor lumens disposed between the inner and outer walls of the catheter; and 
         FIG. 7  depicts a process for manufacturing the catheter assembly. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts an ultrasound cardiovascular catheter assembly  100 , which includes a catheter tube  120  mounted in a control housing  110 . The control housing  110  is connected at the proximal end  115  to equipment, such as, for example, ultrasound imaging equipment (not shown). The catheter tube  120  extends from the distal end of the control housing  110 . The control housing  110  includes one or more actuators  125  for applying and releasing tension to control lines (not shown) within the walls of the catheter tube  120 . In disclosed embodiments, the actuators  125  may be in the form of a pair of rotating rings disposed at the distal end of the control housing  110 . The rings may be configured so that rotation thereof applies tension to ends of a number of control lines. In disclosed embodiments, each actuator  125  applies tension and/or retracts the two opposite ends of a single continuous control line. For example, a first actuator  125  of the pair of actuators may be connected to the opposite ends of a first continuous control line which runs from a first point of attachment with the actuator  125 , to the distal end of the catheter tube  120 , and back to a second point of attachment with the actuator  125 . The second actuator  125  may be similarly connected to the opposite ends of a second continuous control line. Rotating a control ring actuator  125  in one direction applies tension and/or retracts one end of its associated control line. Rotating the control ring actuator  125  in the opposite direction applies tension and/or retracts the opposite end of the associated control line. 
       FIG. 2  is a partial cutaway view of the catheter tube  120 , which has a hollow, tubular structure having an outer wall surface  205 , an inner wall surface  210  and a central lumen  220  disposed within the inner wall surface  210 . The catheter tube  120  may have various outer diameters depending upon the specific applications in which it is to be used. The inner diameter may be set to particular values to establish a desired wall thickness, given a determined outer diameter. In various embodiments, the catheter tube  120  may have an outer diameter of about: 8 French (inner diameter of, e.g., 52 mils), 9 Fr (inner diameter of, e.g., 73 mils), 10 Fr (inner diameter of, e.g., 55 mil), 12.5 Fr (inner diameter of, e.g., 93 mils). In disclosed embodiments, the catheter tube  120  is formed of a flexible material, such as thermoplastic material, e.g., polyether block amide (PBAX), nylon, silicone, polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK), etc. The catheter tube  120  is thin and flexible enough to be inserted into the right heart chambers (e.g., the inferior vena cava) of a patient during a procedure to provide sonographic images of cardiac structures from the inside. 
     Control lines  230   a ,  230   b ,  240   a ,  240   b  are disposed in control line lumens  250  (for clarity, only one of the four control line lumens is labeled) running within the wall between the inner  210  and outer wall surfaces  205  of the catheter tube  120 . As discussed in further detail below, the control lines  230   a ,  230   b ,  240   a ,  240   b  may be formed of a non-metallic material, such as, for example, flexible fiber. Alternatively, the control lines may be formed of a metal, such as, for example, multiple-strand stainless steel wire. In disclosed embodiments, the control lines  230   a ,  230   b ,  240   a ,  240   b  may be formed of a fiber with sufficient tensile strength to articulate the distal end of the catheter tube  120  without breaking, such as, for example, a manufactured multifilament yarn spun from liquid crystal polymer. An anchor  260  disposed at the distal end of the catheter tube  120  acts as an attachment point for the mid-points of the control lines  230   a ,  230   b ,  240   a ,  240   b , as discussed in further detail below. An anchor cap  270  may be provided which acts as a cover for the anchor  260  after the control lines  230   a ,  230   b ,  240   a ,  240   b  have been attached to the anchor  260  (the anchor cap  270  is shown unattached to the anchor  260  in  FIG. 2  for clarity). 
       FIGS. 3 and 4  are perspective views of the distal  305  and proximal ends  310 , respectively, of the anchor  260 . In disclosed embodiments, there may be two continuous control lines  230 ,  240  which each extend from the control housing  110  to the anchor  260  and back to the control housing  110 . Each of the two continuous control lines  230 ,  240  may be considered to have two “halves” (or “ends”)  230   a ,  230   b ,  240   a ,  240   b  which run along the length of the catheter tube  120  (the control lines may not be divided exactly in half). Consequently, there are four control line lumens  250  (see  FIG. 2 ) which along the length of the catheter—two for each of the two continuous control lines. These four control line lumens  250  in the catheter tube  120  have corresponding control line lumens  350  in the anchor  260 . 
     The anchor  260  may be formed (e.g., in an injection molding or continuous extrusion process) of a thermoplastic material which is harder that the material of the catheter tube  120 , such as, for example, a higher hardness polymer. The control lines  230   a ,  230   b ,  240   a ,  240   b  are attached to the anchor  260  so that tension applied to the control lines  230   a ,  230   b ,  240   a ,  240   b  cause the anchor  260  to retract toward the proximal end of the catheter tube  120 , thereby causing the catheter tube  120  itself to bend in a specific direction, i.e., allowing the catheter tube  120  to be “steered.” 
     As shown in  FIG. 5 , in disclosed embodiments, a material may be used for the anchor  262  which does not result in melting of the anchor  262  during the manufacturing process. For example, a high temperature engineering material, such as a high-temperature resin or high-temperature thermoplastic may be used to form the anchor  262 . Other materials, such as metal, may also be used. The melting range for the catheter tube  120  and anchor cap  270  thermoplastic materials is typically about 180-230° C. Therefore, a material may be selected for the anchor  262  which has a melting point which is significantly higher than this range. For example, high temperature thermoset engineering materials, e.g., polyetherimide, polyether ether ketone, polyphenylsulfone, etc., have melting temperatures higher than about 600° C. In such a case, the anchor  262  remains solid in the thermoplastic reflow (i.e., melting) process which is used to attach the anchor cap  272  and secure the control lines  230   a ,  230   b ,  240   a ,  240   b  in place. In contrast to the material used in the embodiments discussed above, which is a pliable thermoplastic material, an anchor formed of high-temperature engineering material would maintain its shape during the manufacturing process and during use. Therefore, the geometry of the anchor and anchor lumens, and the resulting sharp bends in the control lines, would remain stable while the device is in use, which would help to hold the lines within the anchor. 
       FIG. 5  is a partial cutaway view of the catheter tube  120 . The anchor  262  is disposed at the distal end of the catheter tube  120  and acts as an attachment point for the mid-points of the control lines  230   a ,  230   b ,  240   a ,  240   b , as in the embodiments discussed above. The anchor cap  272  acts as a cover for the anchor  262  after the control lines  230   a ,  230   b ,  240   a ,  240   b  have been attached to the anchor  262  (the anchor cap  272  is shown unattached to the anchor  262  in  FIG. 2  for clarity). In disclosed embodiments, the anchor  262  is formed of high-temperature engineering material and is covered with a section of cladding  280  on the outside to prevent contact between the material and the internal tissues of the patient. The cladding section  280  may be formed, e.g., of a layer of polyether block amide (PBAX) of about 2-10 mils thickness. The outer diameter of the cladding section  280  is the same as the outer diameter of the catheter tube  120  to avoid discontinuities in the outer surface of the catheter assembly  100 . Accordingly, in this embodiment, the outer diameter of the anchor is reduced by the thickness of the cladding section  280 . In disclosed embodiments, the cladding section  280  may have an axial length which is the same length as the anchor  262 . 
       FIG. 6  is cross-sectional view of the anchor  260  showing, in accordance with disclosed embodiments, four anchor control line lumens  350  which are separated by 90 degrees and two pairs of anchor threading lumens  360  disposed between pairs of the anchor control line lumens  350 . The anchor control line lumens  350  correspond in position to the control line lumens  250  in the catheter tube  120  (see  FIG. 2 ). At the distal end of the catheter tube  120 , the two ends  230   a ,  230   b ,  240   a ,  240   b  of each control line  230 ,  240  enter the proximal end  310  of the anchor  260  and extend completely through a pair of anchor control line lumens  350  (see  FIG. 4 ). At the distal end  305  of the anchor  260 , the ends of the control lines  230   a ,  230   b ,  240   a ,  240   b  extend from the pairs of anchor control line lumens  350 , extend along the distal face  305  of the anchor  260 , and extend into a pair of anchor threading lumens  360  therebetween (see  FIG. 3 ). The control lines  230 ,  240  exit at the proximal face  310  of the anchor  260  such that the approximate midpoint  232 ,  242  of each control line  230 ,  240  extends between the anchor threading lumens  360  along the proximal face  310  of the anchor  260  (see  FIG. 4 ). This configuration results in each continuous control line experiencing six 90-degree bends as it is threaded back and forth through the anchor, as well as increased surface contact between the control line and the anchor, which enhances slippage prevention. 
     In disclosed embodiments, the control line lumens  250  in the catheter tube  120 , and the corresponding lumens  350  in the anchor  260 , are positioned 90 degrees apart around the circumference of the catheter tube  120 , i.e., these four lumens are “on axis.” In disclosed embodiments, the adjacent pair of anchor threading lumens  360  may be positioned so as to have a separation distance which is less than that of the corresponding anchor control line lumens  350 . 
       FIG. 7  depicts an embodiment of a process for manufacturing the catheter assembly  100 . A thermoplastic catheter tube  120  having five lumens (including the central lumen thereof), as described above, is provided, e.g., from an extrusion process ( 710 ). A nine-lumen anchor  260  is provided, e.g., produced by an extrusion process and cut to a determined length ( 720 ) or molded. The anchor control line lumens  350  and anchor threading lumens  360  are formed within the walls of the anchor  260 , resulting in the anchor  260  having nine lumens (including the central lumen of the anchor). The threading of the control lines  230 ,  240  is performed beginning with the anchor threading lumens  360  ( 730 ), followed by the anchor control line lumens  350  ( 740 ). The control lines  230 ,  240  are then threaded through the control line lumens  250  of the catheter tube  120  ( 750 ). The control lines  230 ,  240  are pulled until the anchor  260  abuts the distal end of the catheter tube  120  ( 760 ). Weights (e.g., 10-30 g) may be applied to the proximal ends of the control lines  230 ,  240  to keep them taut during the manufacturing process. The weights help to keep the control lines  230 ,  240  in the same relative location during attachment of the anchor cap  270 , e.g., in a thermoplastic melting process. A metallic mandrel is inserted into the central lumen to maintain the shape of the central lumen during the melting process ( 770 ). A single-lumen anchor cap  270  is inserted distally against the anchor  260 , thereby covering at least a distal portion of the anchor  260  ( 775 ). The catheter assembly  100  is inserted into a glass tube to maintain the shape of the outer wall of the catheter tube  120 , the anchor  260 , and the anchor cap  270  ( 780 ). Heat is applied at a determined temperature (based on the specific materials being used), e.g., using a hot air, infrared, conductive heating, or laser device, to melt and fuse (i.e., “reflow”) the thermoplastic material of the anchor cap  270  and the anchor  260  ( 790 ). 
     In alternative embodiments, one end of each of the control lines  230 ,  240  is threaded sequentially through the control line lumens  250  in the catheter tube  120 , through the anchor control line lumens  350  and anchor threading lumens  360 , and back though the control line lumens  250  of the catheter tube  120  to achieve the threading arrangement described above. The anchor cap  270  is attached as a cover for the anchor  260  and fixed in place by an attachment process, such as, for example, bonding with adhesive, fixing by tension fit between the anchor cap  270  and the anchor  260 , or by a thermoplastic melting process in which the anchor cap  270  is fused with the anchor  260 . 
     The anchor cap  270  serves as a connection element for a sensor tip (not shown), e.g., an ultrasonic transducer. In disclosed embodiments, the anchor cap  270  may be an integral part of the sensor tip. Alternatively, an anchor cap  270  having a flat distal face  275 , as shown herein, may be bonded to a sensor tip. Other types of mechanical connections between the anchor cap  270  and a sensor tip are also possible As noted above, the attachment of the anchor cap  270 , e.g., by thermoplastic melting, prevents the control lines  230 ,  240  from shifting within the lumens of the anchor  350 ,  360  so that tension can be independently applied to the two ends  230   a ,  230   b ,  240   a ,  240   b  of a single continuous control line  230 ,  240 . Therefore, in disclosed embodiments, the control lines  230 ,  240  are thermally encapsulated within the lumens  350 ,  360  of the anchor  270  to prevent slippage. Thus, the two halves  230   a ,  230   b ,  240   a ,  240   b  of each control line  230 ,  240  may be considered to be, in effect, a separate control line. Therefore, the independent application of tension to the ends  230   a ,  230   b ,  240   a ,  240   b  of each single continuous control line  230 ,  240  can provide movement of the distal end of the catheter tube  120  in two directions in a single plane of motion. Because there are two such control lines, this configuration provides for the catheter to be steerable in four directions in two orthogonal planes. 
     Embodiments described herein are solely for the purpose of illustration. Those in the art will recognize other embodiments may be practiced with modifications and alterations to that described above.