Abstract:
A catheter has an electrode tip assembly that is bendable at the selection of the user in two different directions. The electrode tip assembly assumes different asymmetric predetermined curve configurations when bent in the two directions and is manipulated by means of steering wires adjustably connected tangentially to the lateral edges of a rotatable cam located in the catheter handle.

Description:
RELATED APPLICATION DATA 
     This application is a continuation of application Ser. No. 08/812,195, filed Mar. 6, 1997, now U.S. Pat. No. 5,891,088, which is a continuation of application Ser. No. 08/632,762, filed Apr. 16, 1996, now abandoned, which is a continuation of application Ser. No. 08/324,585, filed Oct. 18, 1994, now abandoned, which is a continuation of application Ser. No. 08/058,319, filed May 6, 1993, now U.S. Pat. No. 5,358,478, which is a continuation-in-part of application Ser. No. 07/790,207, filed Nov. 8, 1991, now U.S. Pat. No. 5,273,535, and a continuation-in-part of application Ser. No. 07/991,474, filed Dec. 16, 1992, now U.S. Pat. No. 5,254,088, which is a continuation of application Ser. No. 07/736,384, filed Jul. 26, 1991, now abandoned, which, is a divisional application of application Ser. No. 07/473,667, filed Feb. 2, 1990, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to steering controls for catheters. In a more specific sense, the invention relates to catheters that can be steered and manipulated within interior regions of the body from a location outside the body. 
     BACKGROUND OF THE INVENTION 
     Physicians make widespread use of catheters today in medical procedures to gain access into interior regions of the body. It is important that the physician can control carefully and precisely the movement of the catheter within the body, especially during procedures that ablate tissue within the heart. These procedures, called electrophysiological therapy, are becoming more widespread for treat cardiac rhythm disturbances. 
     During these procedures, a physician steers a catheter through a main vein or artery (which is typically the femoral artery) into the interior region of the heart that is to be treated. The physician then further manipulates a steering mechanism to place the electrode carried on the tip of the catheter into direct contact with the tissue that is to be ablated. The physician directs radio frequency energy into the electrode tip to ablate the tissue and form a lesion. 
     Cardiac ablation especially requires the ability to precisely bend and shape the tip end of the catheter to position the ablation electrode. 
     SUMMARY OF THE INVENTION 
     The invention provides a catheter having a distal tip section that is bendable at the selection of the user in two different directions. The distal tip section assumes different predetermined curves when bent in each direction. The degree of bending or shape of the predetermined curve can be adjusted in accordance with the invention. 
     The invention provides a catheter having a body that is bendable in different first and second directions in response, to external forces. The catheter includes a steering mechanism that is movable in two paths for applying different external bending forces on the body and wherein the forces can be adjusted by providing for a different length of travel paths for causing bending forces in the first and second directions. 
     The steering mechanism includes a first actuator that operates in response to movement of the steering mechanism in the first path. The first actuator bends the body in the first direction into a first adjustable predetermined nonlinear shape. 
     The steering mechanism also includes a second actuator that operates in response to movement of the steering mechanism in the second path. The second actuator bends the body in the second direction into a second adjustable predetermined nonlinear shape. The second shape is different from the first shape. 
     In one embodiment, the bendable body includes a flexible wire member having left and right faces. In this arrangement, the steering mechanism includes left and right steering wires. The distal ends of the steering wires are attached, respectively, to the left and right faces of the wire member. 
     In this embodiment, the first actuator places the left steering wire into tension to bend the wire member to the left into the first adjustable nonlinear shape. The second actuator places the right steering wire into tension to bend the wire member to the right into the second adjustable nonlinear shape. The steering wires cause asymmetric bending of the wire member by virtue of the fact that the first and second actuators cause the left and right steering wires to travel different distances. 
     In one embodiment, the points of attachment of the distal ends of the left and right steering wires are generally symmetrically spaced on the left and right faces of the wire member. In another arrangement, the points of attachment of the distal ends of the left and right steering wires are generally asymmetrically spaced on the left and right faces of the wire member. 
     In one embodiment, the steering mechanism includes a rotatable cam to the lateral edges of which the proximal ends of the left and right steering wires are adjustably attached. A lever mechanism rotates the rotatable cam to the left and to the right. 
     In this arrangement, the first actuator includes a first cam surface formed on the left side of the rotatable cam. The first cam surface bears against and tensions the left steering wire in response to rotation of the rotatable cam to the left. 
     Also in this arrangement, the second actuator includes a second cam surface formed on the right side of the rotatable cam. The second cam surface is configured differently from the first cam surface and bears against and tensions the right steering wire in response to rotation of the rotatable cam to the right. 
     In one embodiment, the first and second cam faces form curves having different radii. Alternatively, the cam faces may be symmetrical but asymmetric steering is accomplished by adjusting the amount of travel of the steering wires. 
     The steering wires are preferably attached tangentially to the lateral edges of the rotatable cam and can be adjusted so that rotation of the rotatable cam results in a multitude of selectable different left and right curve shapes. In accordance with the preferred embodiment of the invention the control wires extend through adjustable stop members threaded into threaded openings in the lateral edges of the rotatable cam. The proximal ends of the wires are fixed to terminal blocks that are engaged by the stops upon rotation of the rotatable cam to thereby selectively apply tension to the wires. Preferably the steering wires are attached to the terminal blocks by having the ends thereof being bent at an angle exceeding 90°, in fishhook fashion, and being soldered into the blocks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a catheter that embodies the features of the invention; 
     FIG. 2 is a top central sectional view of the handle portion of the catheter of FIG. 1 taken generally along Line  2 — 2  with parts broken away for clarity; 
     FIG. 3 is an exploded view of the electrode tip assembly of the catheter; 
     FIG. 4 is a perspective view of the stiffening assembly for the support wire of the catheter; 
     FIG. 5 is a top view of the catheter in the unbent position with parts broken away to show the steering mechanism; 
     FIG. 6 is top view of the catheter of FIG. 5 steered to the left; 
     FIG. 7 is a top view of the catheter of FIG. 5 with the steering mechanism adjusted to a different setting and steered to the left at a different curvature; 
     FIG. 8 shows the steering mechanism of the catheter with parts disassembled for clarity; 
     FIG. 9 is a top view of a rotatable cam used in the steering mechanism; 
     FIG. 10 is a perspective view of the cam shown in FIG. 9; 
     FIG. 11 is a cross sectional view of the steering wire terminal of the steering mechanism; and, 
     FIG. 12 is a cross sectional view taken along Line  12 — 12  of FIG. 8 showing the adjustable stop used in the steering mechanism. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a steerable catheter  10  that embodies the features of the invention. As there shown, the catheter  10  includes three main parts or assemblies: the handle assembly  12 , the guide tube assembly  14 , and the electrode tip assembly  16 . An electrical cable  48  for providing power to an electrode at the distal tip of the catheter attaches to the back of the housing  20 . 
     The catheter  10  can be used in many different environments. This specification will describe the catheter  10  as used to provide electrophysiologic therapy in the interior regions of the heart. 
     When used for this purpose, a physician grips the handle assembly  12  to steer the guide tube assembly  14  through a main vein or artery (which is typically the femoral arterial) into the interior region of the heart that is to be treated. The physician then further manipulates a steering mechanism  18  on the handle assembly  12  (which will be described later) to place the electrode tip assembly  16  in contact with the tissue that is to be ablated. The physician directs radio frequency energy into the electrode tip assembly  16  to ablate the tissue contacting the electrode tip assembly  16 . 
     As FIG. 2 best shows the handle assembly  12  includes a housing  20  that encloses the steering mechanism  18 . The steering mechanism  18  includes a rotatable cam  23  carried on a screw  24  within the housing  20 . The rotatable cam  23  is seated for rotation between top washer  26  which bears on a shoulder  27  and a bottom washer. Screw  24  is threaded into a central opening in washer  26 . An external steering lever  34  is adhesively bonded or ultrasonically welded to the top of the rotatable cam  23 . A tab  35  on the steering lever  34  is seated in a notch  37  in rotatable cam  23 . The steering lever  34  also seats against an O-ring (not shown). Further details regarded the O-rings and similar assembly details are described in the above-mentioned copending application Ser. No. 790,207, the entire disclosure of which is herein incorporated by reference. 
     Movement of the steering lever  34  by the user rotates the rotatable cam  23  about the screw  24  within the housing  20 . Clockwise movement of the steering level rotates the rotatable cam  23  to the right. Counterclockwise movement of the steering wheel rotates the rotatable cam  23  to the left. Contact between the steering lever  34  and the side of the housing  20  physically limits the range of left and right rotation of the rotatable cam  23  within the housing  20 . 
     The steering mechanism  18  also includes an external locking lever  38  has hexagonal opening into which the hexagonal head of the screw  24  is seated and bonded by an adhesive. The locking lever  38  seats against another O-ring. Movement of the locking lever  38  rotates the screw  24  in the threaded opening in washer  26 . Clockwise rotation of the locking lever  38  tightens the screw  24  to increase the seating force on the rotatable cam  23 . When moved fully clockwise into contact against the housing  20 , the locking lever  38  imposes a seating force that restricts rotation of the rotatable cam  23  by the steering lever  34 . Counterclockwise movement of the locking lever  34  loosens the screw  24  to decrease the seating force and free the rotatable cam  23  for rotation. 
     The rotatable cam  23  includes an asymmetrically shaped forward cam face  41 . The forward cam face  41  is oriented toward the front of the housing  20 , where the guide tube assembly  14  attaches. The forward cam face includes a right side cam surface  44  and a left side cam surface  46 . Surfaces  44  and  46  are located at the bottoms of grooves in the lateral edges of rotatable cam  23 . Surfaces  44  and  46  may either be of the same (symmetric) radii or may be asymmetrically shaped. In the former instance asymmetric steering of the catheter distal tip is accomplished by adjusting the distance traveled by the steering wires and, as a result, the amount of tension applied thereto. 
     The rotatable cam  23  is provided on its lateral edges with threaded holes  51  and  53  into which adjustable stops  55  and  57 , respectively, are threaded. The proximal ends of right and left catheter steering wires  56  and  58 , pass through central openings in stops  55  and  57  and are attached to steering wire terminals  59  and  61 . Steering wires  56  and  58  are bent in fishhook fashion (at an angle greater than 90° at their proximal ends  65  and are soldered ( 67 ) to the interior of the terminal blocks  59  and  61  (as best seen in FIGS. 8 and 11) in order to firmly anchor the wire ends within the terminal blocks. In order to facilitate adjustment of stops  55  and  57 , they are provided with a flattened proximal end  63  which can be engaged by a wrench or similar tool in order to rotate the stops and thus adjust the distance that the stops extend proximally from the edges of rotatable cam  23 . 
     The steering wires  56  and  58  extend from the stops  55  and  57  along the associated left and right side surfaces  44  and  46  of the cam face  41 . The steering wires exit the front of the housing  20  through the interior bore of a tension screw assembly  60 . 
     As will be described in greater detail later, the distal ends of the steering wires  56  and  58  are attached to the electrode tip assembly  16 . They extend from the tension screw assembly  60  through the guide tube assembly  14  to the electrode tip assembly  16 . 
     As also will be described in greater detail, the adjustable wire stops  55 ,  57  in association with the terminal blocks  59 ,  61  and cam faces  44  and  46  translate rotation of the rotatable cam  23  into lateral pulling movement of the steering wires  56  and  58  attached to the electrode tip assembly  16 . 
     By rotating the rotatable cam  23  to the left as shown in FIG. 6 (by moving the steering lever  34  counterclockwise), the left steering wire stop  55  bears against the left terminal block  59  and cam surface  46 . This movement tensions the left steering wire  58  to impose a discrete, constant pulling force that causes the electrode tip assembly  16  to bend to the left in a desired curvature. If a different degree of curvature is desired, for example, as shown in FIG. 7, stop  55  is rotated to extend it distally, thus adjusting the curvature as shown. Also, since cam surface  44  and  46  are asymmetric in shape, the range of possible curvatures is different for the right and left wires. Thus a nearly infinite variety of asymmetric curve shapes is possible by adjustment of the stops. In practice, catheters having a standard number of preset asymmetric curvatures can be factory produced, all using exactly the same component parts. 
     By rotating the rotatable cam  23  to the right (by moving the steering lever  34  clockwise), tension is applied to the right steering wire  56  in exactly the same manner as described in connection with wire  58 , causing the electrode tip assembly  16  to bend to the right. 
     Rotation of the tension screw assembly  60  additionally varies the amount of slack (i.e., tension) in the steering wires  56  and  58 . This controls the responsiveness of the electrode tip assembly  16  to rotation of the rotatable cam  23 . 
     The component parts of the handle assembly  12  can be constructed of various materials, depending upon the durability needed and the sterilization process used. For example, when ETO sterilization is used, the housing  20  and bottom washer  28  can be made of a polycarbonate material. In this arrangement, the rotatable cam  23 , steering lever  34 , and locking lever  38  can be made of a Delrin material. These plastic materials are durable and EtO sterilizable. In this assembly, the nuts, pins, and screw  24  are preferably made of a corrosion resistant metallic material such as brass or stainless steel. 
     As FIG. 3 shows, the guide tube assembly  14  includes a flexible shaft  62  attached to the handle assembly  12 . The flexible shaft  62  encloses an interior bore  64 . The steering wires  56  and  58  pass through the interior bore  64 . 
     The shaft  62  may constructed in various ways. In the embodiment shown in FIG. 3, the shaft  62  comprises a length of stainless steel coiled into a flexible spring enclosing the interior bore  64 . A sheath  66  of extruded plastic material containing wire braids encloses the coil. The sheath  66  is preferably made from a thermoplastic material, such as a polyurethane, a polyolefin or polyetherpolyamide block copolymer. 
     Alternatively the shaft  62  comprises a slotted, stainless steel tube enclosing the interior bore. Further details of such slotted shafts are disclosed in pending Lundquist U.S. patent application Ser. No. 07/657,106 filed Feb. 15, 1991 and entitled “Torquable Catheter  10  and Method.” 
     The handle assembly  12  includes a tubular stem  74  though which the proximal end of the guide tube assembly  14  extends for attachment to the tension screw assembly  60 . Adhesive attaches the proximal end of braided sheath  66  to stem  74 . The guide tube assembly  14  can be made in various lengths. In the case of cardiac ablation catheters, the guide tube assembly  14  is usually about  100  cm in length. 
     As FIGS. 1 and 2 show, a sleeve  76  couples the guide tube assembly  14  to the handle assembly  12 . Adhesive secures one end of the sleeve  76  to the handle stem  74 . The sleeve  76  includes an interior bore that progressively tapers from the handle stem  74  into a tight interference fit about the sheath  66  of the guide tube assembly  14 . The exterior of the sleeve  76  also tapers, extending about 4 to 5 inches beyond the front of the handle housing  20 . 
     The sleeve  76  is made of a material having a high coefficient of friction, like Krayton G2703. The sleeve  76  provides a gripping surface to help the user manipulate the catheter  10 . When used in association with the slotted tube, the sleeve  76  also significant enhances the transmission of torque from the handle assembly  12  to the electrode tip assembly  16  through the guide tube assembly  14 . 
     The electrode tip assembly  16  includes a bendable main support wire or spring  78  having left and right faces  78 L and  78 R. In the illustrated embodiment, the main support wire,  78  is made of stainless steel flat wire stock in an elongated shape about 0.035 inch wide and about 0.005 inch thick. The main support wire  78  is about 3 inches in total length. 
     The opposite ends of the main support wire  78  are cut away to form stepped shoulders  80  and  82 . In the illustrated embodiment, the shoulders  80  and  82  are about 0.024 inch wide and aligned along the centerline of the main support wire  78 . Each shoulder  80  and  82  is about 0.12 inch in length. 
     As FIG. 3 shows, one stepped shoulder  80  fits within the distal end of the flexible guide tube shaft  62  to append the electrode tip assembly  16  to the guide tube assembly  14 . When properly oriented, the left and right faces  78 L and  78 R of the main support wire  78  lie in a plane that is generally parallel to the axis about which the rotatable cam  23  rotates. Stated differently, when the user holds the handle assembly  12  in a horizontal plane, the left and right faces  78 L and  78 R of the main support wire  78  lie in a vertical plane. 
     As FIG. 3 shows, the distal end of the left steering wire  58  is soldered to the left face  78 L of the main support wire  78 . When pulled by left rotation of the rotatable cam  23 , the left steering wire  58  bends the main support wire  78  to the left. 
     Also, the distal end of the right steering wire  56  is soldered to the right face  78 R of the main support wire  78 . When pulled by right rotation of the rotatable cam  23 , the right steering wire  56  bends the main support wire  78  to the right. 
     In the illustrated embodiment, the stiffness of the main support wire  78  is not uniform, but varies along its length. Its stiffest point is near its proximal end region, where it joins the guide tube shaft  62 . Its stiffness is least at the tip end  88  of the shoulder  82 . By varying the stiffness of the main support wire  78  between its proximal end and its distal tip end  88 , the base of the electrode tip assembly  16  (where it joins the guide tube assembly  14 ) resists bending and buckling. The bending forces generated by the steering wires  56  and  58  are directed toward the distal tip end  88  of the main support wire  78 . The variable stiffness of the main support wire  78  concentrates the bending forces at the distal tip end  88  of the electrode tip assembly  16 . 
     There are various ways to varying the stiffness of the main support wire  78  along its length. One way (not shown) is to vary the thickness of the main support wire  78  as it is manufactured, so that it is thickest (i.e., most stiff) near the shoulder  80  that, in use, is fitted within the guide tube shaft  62 . 
     In the illustrated and preferred embodiment (see FIG.  4 ), a stiffening spring assembly  90  stiffens the center support near the distal end of the guide tube shaft  62 . The stiffening spring assembly  90  includes two leaf springs  92  that sandwich the main support wire  78  between them. Each leaf spring  92  is made of stainless steel flat wire stock in an elongated shape that is about 0.035 inch wide and about 0.0025 inch thick. 
     The stiffening spring assembly  90  can be sized and configured to provide the degrees of stiffness and variance wanted. In the illustrated embodiment, the stiffening spring assembly  90  stiffens the main support wire  78  beginning about 0.030 to 0.050 inch from the inner edge of the attachment shoulder  80  and extending from there about 1.5 inches. 
     In the illustrated embodiment, spot welds  94  secure the leaf springs  92  to the main support wire  78 . The three spot welds  94  shown are clustered near the proximal end of the stiffening spring assembly  90 . There, they are evenly spaced, with the most distal spot weld  94  being about 0.10 inch from the proximal end of the stiffening spring assembly  90 . 
     In the illustrated embodiment, the distal end of the electrode tip assembly  16  carries an ablation tip electrode  96  and three ring electrodes  98 . Interior conducting wires  100  are connected to the tip electrode  96  and, the three ring electrodes  98 . The conducting wires  100  extend along the main support wire  78 , through the interior bore of the guide tube shaft  62 , and into the handle housing  20  to join the cable  48  that extends from the rear of the housing  20 . 
     The cable  48  ends with plugs  102 . The plugs  102  connect with appropriate conventional catheter control equipment (not shown). The conducting wires  100  transfer electrical current from the ring electrodes  98  indicative of electrical activity within the heart. The conducting wires  100  also transfer radio frequency energy to the tip electrode  96  to carry out ablation procedures within the heart. 
     There are various ways of securing the attachment between the electrode tip assembly  16  and the guide tube assembly  14 . The illustrated embodiment employs a reinforcing sleeve assembly  104  for this purpose. The reinforcing sleeve assembly  104  holds the steering wires  56  and  58  in close intimate contact against the main support wire  78 . Isolation of the conducting wires  100  from the steering wires  56  and  58  prevents kinking and chafing of the conducting wires  100  during bending operations. 
     The materials used to make the reinforcing sleeve assembly  104  can vary. shrink tubes  114  can be made from medical grade TFE Teflon material having a 2 to 1 shrink ratio. A reinforcing fabric  116  is wrapped in tension over first tube  114  as a single spiral about the tube  114  to obtain a desired, closely spaced pitch. In the illustrated embodiment the fabric  116  is wrapped to a pitch of about 18 to 20 wraps per inch. The preferred material has a wall thickness (after heat shrinkage) of about 0.003 to 0.0045 inch. In the illustrated embodiment, the fabric  116  is a Kevlar 49 Yarn (which is available from DuPont) . This material has a tensile strength of about 410,000 lbs/in 2  and a modulus of about 18,000,000 lbs/in 2 . 
     An outer tube  120  covers the reinforcing sleeve assembly  104 . The tip electrode  96  is soldered to the center support  78  and ring electrodes  98  are attached to the conducting wires  100  and joined to the outer tube  120  by conventional methods to complete the electrode tip assembly  16 . 
     In the illustrated embodiment, the curvature assumed upon bending the electrode tip assembly  16  to the left is different than the curvature assumed upon bending the electrode tip assembly  16  to the right. The electrode tip assembly  16  assumes one curvature when bent to the left and a different curvature when bent to the right. These different left and right curvatures provide the physician with flexibility in steering the tip electrode  96  into position. These differing curvatures as referred to herein as asymmetric curves. 
     In addition to the use of a rotatable cam to cause different amounts of travel of the left and right steering wires, it is contemplated that such different amounts of travel can also be caused by means of other mechanisms, as well. For example, a rotatable gear can be intermeshed with a pair of movable toothed racks to form a rack and pinion arrangement. In such case the two racks can be configured differently, or provided with stops to limit the travel in one direction more than in other. 
     Various features of the invention are set forth in the following claims.