Patent Publication Number: US-2021178124-A1

Title: Catheter handle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of Provisional Application No. 62/949,339, entitled, “Catheter Handle”, filed Dec. 17, 2019. The contents of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to catheters, and more specifically, to a control handle for a steerable catheter. 
     BACKGROUND 
     A catheter is a well-known medical device consisting of a thin tube of medical grade material that is insertable into the body for introducing drugs or performing other surgical or analytical procedures. Further, a wide variety of known catheter configurations are known and tailored to specific applications, such as cardiovascular, urological, gastrointestinal, etc. 
     Many applications benefit from a steerable catheter, where the catheter tube is connected to a handle having a control mechanism for deflecting the distal end of the catheter tube in order to properly guide and position the catheter for the intended use. However, establishing and then fixing the position can be problematic if the catheter is not effective at maintaining its position due to slippage in the control mechanism. 
     Therefore, it would be desirable to provide a steerable catheter that is simple in construction, easy to use, and reliably accurate in maintaining a fixed catheter position in use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first catheter embodiment with the tip of the catheter in a non-deflected orientation. 
         FIG. 2  is a perspective view of the catheter of  FIG. 1  with the tip of the catheter in a deflected orientation. 
         FIG. 3  is an exploded perspective view of the catheter of  FIG. 2 . 
         FIG. 4  is a top plan view of the catheter handle of the catheter shown in  FIG. 2 . 
         FIG. 5  is side plan view of the racks inside the catheter illustrating movement of the racks. 
         FIG. 6  is a perspective view of a second embodiment of a catheter. 
         FIG. 7  is a perspective schematic view of the second embodiment, including formulas and calculations for specifying gear ratios and track lengths. 
         FIG. 8  is a perspective view of the internal mechanism for a third embodiment of a catheter. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed to a steerable catheter having a catheter tube connected to a catheter handle. A steering wire is affixed at its center point to the distal tip of the catheter tube on the inside of the catheter tube, and each leg of the steering wire extends from the center point to a terminal point fixed on a respective one of a pair of slidable racks. The pair of slidable racks are mounted in opposition to each other within the catheter handle, and each rack has teeth on the commonly facing side thereof. In one embodiment, a rack gear is disposed between the teeth of each rack and directly engages the racks, and a knob is attached to the rack gear. Operating the knob rotates the rack gear and causes the racks to move in opposite directions thereby pulling or feeding one of the wire legs within the catheter tube to provide steering control in the catheter handle. In another embodiment, the rack gear is disposed between the racks, but is driven by one or more other gears in a “gear chain” arrangement intended to provide more pulling force for the steering wire. 
       FIGS. 1-2  illustrate a first embodiment of a steerable catheter  100  configured for electrophysiology (“EP”) study and catheter ablation. This specific embodiment is not intended to be limiting but instead merely illustrative of the principles disclosed herein. The catheter  100  has flexible catheter tube or sleeve  110  coupled at its proximal end  111  to a handle  120 . A number of electrodes  112  including a distal tip electrode  113  are configured on the sleeve  110  at spaced-apart locations of the tubular body. The number of electrodes  112  provided with the catheter  100  depends on the specific application, with some applications requiring up to 20 electrodes, for example. In general, the electrodes  112 ,  113  are used to deliver radio frequency energy in order to map the electrical signals of the heart and/or scar or destroy tissue that may be allowing incorrect electrical signals to cause an abnormal heart rhythm. 
     The sleeve  110  is typically a braided tubular structure formed of a medical grade material, such as polyamides, in a well-known manner. The diameter of the catheter tube also depends on the application and is commonly measured using the French scale (“FR”) or French gauge system, which is three times the diameter measured in millimeters. Thus, a thin catheter tube of 6 FR measures 2 mm in diameter. Typical catheter tube diameters range from 3-7 FR. 
     The handle  120  is a housing with a hollowed out interior portion  130  (see  FIGS. 3-4 ) in which one or more various types of components can be contained within the housing or threaded through the housing. For example, electrical conductors, such as 0.003 inch thin copper wires, can be routed from a connector  115  at the back end of the handle, such as a Redel connector, through the interior portion  130  of the housing, and into the catheter tube  110  for connection to the electrodes  112 ,  113  in well-known manner. Other types of components, such as irrigation or drainage tubes, may also be configured to run through the housing  120  to accomplish other surgical objectives. 
     In particular, however, this disclosure is concerned with the provision and control of a steering wire  125  integrated with the handle  120  for manipulating the catheter sleeve  110 , as further illustrated in  FIGS. 3-4 . For example, in  FIG. 1 , the control knob  140  is in the neutral or rest position and is aligned along the central longitudinal axis of the catheter handle  120 , with the distal tip  113  of the catheter tube  110  not in a deflected position, that is, straight in line with the catheter handle. In  FIG. 2 , however, the control knob  140  has been turned ninety degrees the original rest position, and the distal tip  113  is in a fully deflected position. 
     Referring now to  FIGS. 3-4 , in this embodiment, the handle  120  is a two-part construction having top half portion  120   a  and a bottom half portion  120   b . The two halves  120   a ,  120   b  can be made from a rigid molded plastic material that is food grade at a minimum, and medical grade as required, with the halves attached together using a food grade adhesive at a minimum and medical grade adhesive as required. 
     The top half  120   a  includes a circular hole  121  through the housing portion and a circular recess  122  surrounding the hole on the outside surface of the housing portion. The circular hole  121  accepts and holds in a vertical orientation a pin  151  or axle that extends through the hole as part of a gear assembly  150 . The pin  151  has male threads at its top portion which are securely fastened into corresponding female threads inside a flanged portion  141  (not shown) of the knob  140 . The circular recess  122  is provided to accommodate the flanged portion  141  of knob  140 , which slightly elevates the knob above the surface of the top half portion  120   a  such that the knob can be easily rotated. 
     The top half  120   a  also includes a half cylinder portion  131   a  formed at the front of the housing providing a small opening for accommodating the steering wire  125  and other thin components, such as electrical conductors for the electrodes, into the sleeve  110 . A larger rear circular opening  132   a  is provided for accommodating the connector  115 . The bottom half  120   b  also includes a corresponding half cylinder portion  131   b  and a corresponding rear circular opening  132   b , which are mated with the top half portions when the two halves  120   a ,  120   b  are connected together during assembly. A tip  133  having a thin passageway may be affixed to the front half cylinder portions  131   a ,  131   b  to further secure the interface between the inside of the housing and the catheter sleeve  110 . 
     The bottom half  120   b  includes a circular depression  126  extending below the surface of the bottom half having a diameter that is adequate to accommodate the gear assembly  150 . A flanged portion  127  (not shown) is formed in the center of the circular depression  126  to receive and hold the other end of pin  151  of gear assembly  150 . 
     The top half  120   a  includes the circular hole  121  formed through the housing portion to accommodate pin  151 , as described above. Each of the two halves  120   a ,  120   b  has corresponding sidewalls  134 . The top half  120   a  has a first pair of vertical rails  160   a  each spaced apart from a respective sidewall  134  to thereby define a pair of first channels  161  between respective first rails and sidewalls. The top half  120   a  also has a second pair of vertical rails  162   a  each spaced apart from respective first rails  160   a  to thereby define a pair of second channels  163  between respective first rails and second rails. Similarly, the bottom half  120   b  has a third pair of vertical rails  160   b  each spaced apart from respective sidewall  134  to define the same pair of first channels  161  between respective third rails and sidewalls. The bottom half  120   b  also has a fourth pair of vertical rails  162   b  each spaced apart from respective third rails  160   b  to define the same pair of second channels  163  between respective first rails and second rails. 
     The first channels  161  are provided for accommodating electrical wires or other components through the handle  120 , while the second channels  163  provide a track for a pair of corresponding geared racks  170  to travel back and forth. The first rails  160   a  and third rails  160   b  are taller than the second rails  162   a  and fourth rails  162   b  thereby providing a rigid surface on the outboard side to hold and guide the gear racks. On the inboard side, the gear assembly  150  provides rigid contact against each of the gear racks. 
     The gear tracks  170  are substantially rectangular in shape, and are inserted in a vertical orientation into the second channels  163  between the walls of the first rails  160   a  and the third rail  160   b , respectively, and the gear assembly  150 . Each of the gear racks  170  is smooth on the outboard side with teeth  171  disposed on the inboard side to interact with the gear assembly. 
     Each of the gear racks  170  also has a tab portion  172  at each end provided with female threads so that respective ends of the steering wire  125  can be attached to respective tab portions using a terminal screw  173 . 
     The gear assembly  150  includes the pin  151  which is smooth-bored on the bottom end and threaded at the top end. A toothed gear  152  is fitted onto the pin  151 , with a washer  153  placed on both the top and bottom of the toothed gear. A nut  154  is fastened over the top washer to the threaded portion of the pin  151 . Finally, the threaded portion of the pin  151  extends through the hole  121  in the top half  120   a  of the housing and is secured to corresponding female threads inside the flanged portion  141  of the knob  140 . 
     Operating (turning) the knob  122  directly rotates the toothed gear  152 , which is engaged with the racks  170  and therefore causes one of the racks to move in one direction while the other rack moves in the other direction, as shown in  FIG. 5 . This is a rack and pinion type operation. Because the steering wire is affixed at the tab portions  172  of both racks  170 , the distal tip  113  of the sleeve  110  is deflected when the racks are moved. Thus, the distal tip  113  can be turned so that the catheter  110  can be directed into an appropriate location by the medical professional. The tab portions  172  should preferably be tall enough to avoid or minimize any unnecessary bending of the steering wire  125  as it moves in and out through the tip  133  of the catheter. 
       FIG. 6  illustrates another catheter embodiment  200 . For EP catheters having a large number of ring electrodes embedded in the distal shaft, e.g., 10 or more, the steering wire needs more driving force. However, applying more force can cause problems, such as steering wire elongation. Further, to reach a large steering angle, e.g., 270 degrees, the steering wire must actually be pulled much more, that is, travel over a longer distance. As a result, the direct-driven rack and pinion action of the first catheter embodiment  100  is inadequate to provide sufficient rack travel for the steering wire to be pulled further. 
     In the first catheter embodiment  100 , the handle design provides a one-to-one direct transmission of the lever/knob turning the gear to move the rack and thereby pull the steering wire. In the second embodiment  200 , however, instead of a single gear providing direct transmission, a “gear train” is used to provide some gain in the transmission ratio between the turning of the lever/knob and the lateral movement of the rack, which dictates the pulling length of the steering wire. 
       FIG. 6  shows the handle housing  220  of the catheter  200  with one half removed in order to illustrate the placement and interaction of the various components in the interior region  230  of the housing in this embodiment. The pair of racks  270  are placed in pre-formed channels (not shown) with each end of the steering wire  225  affixed to the terminal ends of respective racks, as in the first embodiment  100 . Similarly, a third gear  250  is fitted between the pair of racks  270  and is affixed to and rotates on a first pin or axle  252  to drive the racks. 
     A second gear  251  is also affixed to and rotates on the first pin  252  together with the third gear  250 , but the second gear is a driven gear that is meshed with a larger first drive gear  255 . The first gear  255  is affixed to and rotates on a second pin or axle  256 . A lever assembly  240  is also affixed to the second pin  256  and is operable to rotate the second pin, which in turn rotates the first gear  255 , thereby driving the second gear  251  and rotating pin  252 . Because the first gear  255  is also affixed with pin  252 , it also rotates thereby driving the tracks  270  in opposite directions. 
     The gear ratio between the first gear  255  and the second gear  251  depends on the size of the catheter.  FIGS. 7A-C  provide an example for specifying the rack lengths and number of teeth for the gears of a catheter handle. In this example, the catheter has a length of 200 mm, a maximum width of 30 mm, and a maximum depth of 22 mm. Based on the sample calculations below, the gear ratio between the second gear  251  and the first gear  255  is Z 2 /Z 1 =0.4, where Z 1 =40 teeth for the first gear  255 ; Z 2 =16 teeth for the second gear  251 ; and Z 3 =24 teeth for the third gear  250 . 
     In general, the length or distance S 3  needed for the gear track to the gear track is determined through the following sets of equations: 
     
       
         
           
             
               
                 
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     where z=number of teeth, ω=rotary speed, {right arrow over (v)}=linear speed vector, R=max radius of teeth, φ=turning angle of lever in radians (not shown); {right arrow over (s)}=distance vector (arc length, distance/length of gear rack); u=gear ratio; and s 3 =distance/length of gear rack. 
       FIG. 8  illustrates the internal mechanism of another catheter embodiment  300 . In this embodiment, the first gear  350  that drives the tracks  370  is a large gear, driven by a smaller second gear  355 , which is directly coupled with gear  354  by a solid axle, and the coupled gears  354 / 55  are driven by a third larger gear  356 . This embodiment is intended to correct for possible steering wire direction errors by reversing the gear drive direction for the tracks. 
     While specific embodiments have been described by way of example, it should be understood that the invention is not limited to the disclosed embodiments. To the contrary, this disclosure is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.