Abstract:
A catheter for the treatment of tissue, particularly for the treatment of cardiac tissue to alleviate cardiac arrhythmias includes a handle housing a combination of steering components, electronic circuitry and/or infusion tubing. An interior notch in the handle around a circumference of the handle perpendicular to the longitudinal axis of the handle provides a means for access to the sealed handle in case a repair to the interior components is necessary during manufacture or reprocessing. The circumferential frangible connection of the two halves of the handle provides access without the use of cutting or drilling devices that could damage the interior components.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a catheter for the treatment of human tissue, particularly cardiac tissue and more particularly cardiac arrhythmias, including atrial fibrillation. Such electrophysiology catheters have control handles which contain important circuitry related to their use and the present invention concerns a handle that readily enables access to such circuitry. The control handles are also often used to deflect the catheter in either a unidirectional or bi-directional mode. 
     BACKGROUND OF INVENTION 
     Cardiac arrhythmias, atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. In patients with normal sinus rhythm, the heart, which is comprised of atrial, ventricular, and excitatory conduction tissue, is electrically excited to beat in a synchronous, patterned fashion. In patients with cardiac arrythmias, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normally conductive tissue as in patients with normal sinus rhythm. Instead, the abnormal regions of cardiac tissue aberrantly conduct to adjacent tissue, thereby disrupting the cardiac cycle into an asynchronous cardiac rhythm. Such abnormal conduction has been previously known to occur at various regions of the heart, such as, for example, in the region of the sinoatrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers. 
     Cardiac arrhythmias, including atrial arrhythmias, may be of a multiwavelet reentrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber and are often self propagating. Alternatively, or in addition to the multiwavelet reentrant type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion. Ventricular tachycardia (V-tach or VT) is a tachycardia, or fast heart rhythm that originates in one of the ventricles of the heart. This is a potentially life-threatening arrhythmia because it may lead to ventricular fibrillation and sudden death. 
     One type of arrhythmia, atrial fibrillation, occurs when the normal electrical impulses generated by the sinoatrial node are overwhelmed by disorganized electrical impulses that originate in the atria and pulmonary veins causing irregular impulses to be conducted to the ventricles. An irregular heartbeat results and may last from minutes to weeks, or even years. Atrial fibrillation (AF) is often a chronic condition that leads to a small increase in the risk of death often due to strokes. Risk increases with age. Approximately 8% of people over 80 having some amount of AF. Atrial fibrillation is often asymptomatic and is not in itself generally life-threatening, but it may result in palpitations, weakness, fainting, chest pain and congestive heart failure. Stroke risk increases during AF because blood may pool and form clots in the poorly contracting atria and the left atrial appendage. The first line of treatment for AF is medication that either slows the heart rate or revert the heart rhythm back to normal. Additionally, persons with AF are often given anticoagulants to protect them from the risk of stroke. The use of such anticoagulants comes with its own risk of internal bleeding. In some patients, medication is not sufficient and their AF is deemed to be drug-refractory, i.e., untreatable with standard pharmacological interventions. Synchronized electrical cardioversion may also be used to convert AF to a normal heart rhythm. Alternatively, AF patients are treated by catheter ablation. Such ablation is not successful in all patients, however. Thus, there is a need to have an alternative treatment for such patients. Surgical ablation is one option but also has additional risks traditionally associated with surgery. 
     Diagnosis and treatment of cardiac arrhythmias include mapping the electrical properties of heart tissue, especially the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy. Such ablation can cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. Various energy delivery modalities have been disclosed for forming lesions, and include use of microwave, laser and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall. In a two-step procedure—mapping followed by ablation—electrical activity at points within the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors (or electrodes) into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the endocardial target areas at which ablation is to be performed. 
     Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart of concern. A typical ablation procedure involves the insertion of a catheter having a tip electrode at its distal end into a heart chamber. A reference electrode is provided, generally taped to the skin of the patient or by means of a second catheter that is positioned in or near the heart. RF (radio frequency) current is applied to the tip electrode of the ablating catheter, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. 
     Electrophysiology catheters also are often connected to electroanatomic mapping systems such as the Carto 3® system from Biosense Webster, Inc. Electroanatomic mapping systems are used in conjunction with mapping catheters to determine the anatomy of the endocardial tissue in the heart and where nerve fibers, nodes and bundles appear on that tissue which may be ablated to treat the aforementioned cardiac arrhythmias. 
     The handles of catheters for the mapping and ablation of cardiac tissue contain electronic circuitry which converts signals from the tip or ring electrodes near the distal end of the catheter into digital signals that can be communicated to the electroanatomic mapping system (such as the Carto 3® system from Biosense Webster) and/or an ablation system. The handles of these catheters must also be made so as to resist contamination from bodily and other fluids present during a procedure. Catheter handles are usually made of two matching halves that are laser welded together to create the final handle surrounding the printed circuit board (PCB) and other internal components. If there is a need to changes the PCB or other components in the handle a dental drill or saw is used to make a cut around the circumference of the handle to allow access to the interior. This can result in damage to the PCB, irrigation tubing or other components if not done with extreme care. 
     U.S. Pat. No. 7,189,228 to Eum discloses a detachable cryosurgical probe includes a disposable probe assembly and a reusable probe assembly. The disposable probe assembly includes a breakaway collar which, when twisted away, activates a finger lock element which provides release of the disposable probe assembly from the reusable probe assembly. 
     U.S. Pat. No. 6,496,228 to Rudie discloses a thermal therapy catheter for treatment of the prostate including a catheter shaft having an outer surface that is insertable into the body lumen The handle of the catheter is a two-piece, molded snap-fit shell according to an exemplary embodiment of the invention 
     U.S. Pat. No. 5,487,757 to Trukai discloses a multi-curve deflectable catheter having a handle with at least two detachable sections. A first detachable section including the structure for moving the stiffener wire and a second detachable section including the structure for applying force to the manipulator wire. A third detachable section could include structure for rotating the core wire. The detachable sections have universal connectors for connecting the detachable sections to each other. The universal connectors preferably comprise a snap fit adapter, wherein a male snap fitting on one detachable section engages a female snap fitting in another detachable section. In this embodiment, the catheter handle is modular, allowing various detachable sections to be selectively added or removed by the manufacturer depending upon the capabilities desired in the catheter, e.g. deflectability, rotatability, or stiffener control. 
     U.S. Pat. No. 5,242,430 to Arenas discloses a rotary handle for attachment to a proximal end of a catheter having components that “snap fit” together for ease of assembly. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a control handle for an electrophysiology ablation and/or mapping catheter having a means for allowing access to the electrical or other components such as the steering components that are sealed within the handle. 
     The present invention is also directed to a method of manufacturing electrophysiology ablation and/or mapping catheters having a means for allowing access to the electrical or other components sealed within the handle during the manufacturing process. 
     The present invention is direct to a catheter for the treatment of cardiac tissue having an elongated tubular member having a proximal end and a distal end where at least one electrode for ablation or mapping is mounted near the distal end of the elongated tubular member. A control handle mounted at the proximal end includes a housing for enclosing an electronic circuit and/or a steering mechanism. The housing of the control handle has a frangible thin-walled portion extending substantially around the circumference of the housing so as to enable the housing to be separated into two sections for access to the steering mechanism and/or electronic circuit. The thin-walled portion of the housing may be circular and substantially perpendicular to the longitudinal axis of the control handle or may be elliptical and angled with respect the longitudinal axis of the control handle. Additionally, the thin-walled portion has a portion parallel to the longitudinal axis of the control handle thereby providing a stepped frangible connection. 
     The frangible connection between portion of the handles provides access for repair during manufacture or reprocessing of the catheter which can include the steps of sterilizing the catheter, placing the catheter in a sterile container, breaking the housing control handle of the catheter at the thin-walled portion to access the interior of the control handle and/or replacing or reprogramming the electronic circuit 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein 
         FIG. 1  is a side view of an embodiment of a bi-directional ablation catheter in accordance with the present invention. 
         FIG. 2  is a side cross-sectional view of the junction of the catheter body and tip section of an embodiment of a catheter according to the invention. 
         FIG. 3  is a transverse cross-sectional view of the catheter body shown in  FIG. 2  taken along line  3 - 3 . 
         FIG. 4  is a side cross-sectional view of the distal end of the tip section shown in  FIG. 2 . 
         FIG. 5  is a transverse cross-sectional view of the tip section along line  5 - 5 . 
         FIG. 6  is a transverse cross-sectional view of a catheter tip section according to the invention where the puller wires are anchored to the side walls of the tip section. 
         FIG. 7  is a longitudinal cross-sectional view of a preferred puller wire T-bar anchor. 
         FIG. 8  is a longitudinal cross-sectional view of the puller wire T-bar anchor of  FIG. 7  rotated 90 degrees to show the cross-piece on end. 
         FIG. 9  is a top exploded view of a control handle of the catheter of  FIG. 1 . 
         FIG. 10  is a view of a control handle of the catheter of  FIG. 9  taken generally along Line V-V with parts broken away for clarity. 
         FIG. 10   a  is a view of the control handle of  FIG. 10  taken generally along Line W-W. 
         FIG. 11  shows components of the steering assembly without deflection in the tip section of the catheter. 
         FIG. 12  shows components of the steering assembly for deflection of the tip section to the right. 
         FIG. 13  shows components of the steering assembly for deflection of the tip section to the left. 
         FIG. 14  shows the proximal end of the control handle of a catheter in accordance with the present invention. 
         FIG. 15  shows a partial perspective close-up view of the notch in the interior of the control handle of a catheter in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In an embodiment of the invention, there is provided a steerable bidirectional electrode catheter. As shown in  FIG. 1 , the catheter  10  comprises an elongated catheter body  12  having proximal and distal ends, a tip section  14  at the distal end of the catheter body  12 , and a control handle  16  at the proximal end of the catheter body  12 . 
     As shown in  FIGS. 2 and 3 , the catheter body  12  comprises an elongated tubular member 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  preferably 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 tip section  14  will rotate in a corresponding manner. 
     The overall length and diameter of the catheter  10  may vary according to the application. A presently preferred catheter  10  has an overall length of about 48 inches. The outer diameter of the catheter body  12  is not critical, but is preferably no more than about 8 french. The inner surface of the outer wall  20  is preferably lined with a stiffening tube  22 , which can be made of any suitable material, preferably nylon or polyimide. The stiffening tube  22 , along with the braided outer wall  20 , provides improved flexural and torsional stability while at the same time minimizing the wall thickness of the catheter body  12 , thus maximizing the diameter of the central lumen  18 . The outer diameter of the stiffening tube  22  is about the same as or slightly smaller than the inner diameter of the outer wall  20 . A particularly preferred catheter  10  has an outer diameter of about 0.092 inch and a lumen  18  diameter of about 0.052 inch. 
     As shown in  FIGS. 4 and 5 , the tip section  14  comprises a short section of flexible tubing  24  having a first off-axis lumen  26  and a second off-axis lumen  28 . The flexible tubing  24  is made of a suitable non-toxic material that is preferably more flexible than the catheter body  20 . A presently preferred material for the tubing  24  is braided polyurethane, i.e., polyurethane with an embedded mesh of braided stainless steel or the like. The outer diameter of the tip section  14 , like that of the catheter body  12 , is preferably no greater than about 7 french, more preferably about 6½ french or less. 
     The off-axis lumens  26 ,  28  extend through diametrically opposed halves of the tip section  14 . The off-axis lumens  26 ,  28  are asymmetrical and therefore non-interchangeable. The first off-axis lumen  26  is smaller than the second off-axis lumen  28 . In an 8 french or 7 french diameter catheter, where the tip section is 6½ french, it is preferred that the first off-axis lumen  26  has a diameter ranging from about 0.018 inch to about 0.025 inch, more preferably from about 0.018 inch to about 0.022 inch. Preferably, the second off-axis lumen  28  has a diameter ranging from about 0.022 inch to about 0.030 inch, more preferably from about 0.026 inch to about 0.028 inch. 
     By using two rather than three lumens along a single diameter, the present design retains the simplified construction of the unidirectional deflectable steerable catheter described in U.S. Pat. No. Re 34,502, which is incorporated herein by reference. However, it is understood that additional lumens may be provided in the tip section. As described in U.S. Pat. No. 6,171,277, the disclosure of which is incorporated herein by reference, the tip section  14  may contain four lumens, two of which have a greater diameter of about 0.029 inch and two of which have a lesser diameter of about 0.018 inch. Lead wires for the electrodes, thermocouple wires and/or electromagnetic sensor cable may extend through different lumen(s) from those through which each of puller wires extends. As such, the present invention may employ two or more lumens in the tip section  14 . 
     A preferred means for attaching the catheter body  12  to the tip section  14  is illustrated in  FIG. 2 . The proximal end of the tip section  14  comprises an outer circumferential notch  34  that receives the inner surface of the outer wall  20  of the catheter body  12 . The tip section  14  and catheter body  12  are attached by glue or the like. Before the tip section  14  and catheter body  12  are attached, however, the stiffening tube  22  is inserted into the catheter body  12 . The distal end of the stiffening tube  22  is fixedly attached near the distal end of the catheter body  12  by forming a glue joint with polyurethane glue or the like. Preferably a small distance, e.g., about 3 mm, is provided between the distal end of the catheter body  12  and the distal end of the stiffening tube  22  to permit room for the catheter body  12  to receive the notch  34  of the tip section  14 . A force is applied to the proximal end of the stiffening tube  22 , and, while the stiffening tube  22  is under compression, a first glue joint (not shown) is made between the stiffening tube  22  and the outer wall  20  by a fast drying glue, e.g. cyanoacrylate. Thereafter a second glue joint is formed between the proximal ends of the stiffening tube  22  and outer wall  20  using a slower drying but stronger glue, e.g., polyurethane. 
     A spacer  36  lies within the catheter body  12  between the distal end of the stiffening tube  22  and the proximal end of the tip section  14 . The spacer  36  is preferably made of a material that is stiffer than the material of the tip section  14 , e.g., polyurethane, but not as stiff as the material of the stiffening tube  22 , e.g. polyimide. A spacer made of polytetrafluoroethylene (PTFE) is preferred. A preferred spacer  36  has a length of from about 0.25 inch to about 0.75 inch, more preferably about 0.50 inch. Preferably the spacer  36  has an outer and inner diameter about the same as the outer and inner diameters of the stiffening tube  22 . The spacer  36  provides a transition in flexibility at the junction of the catheter body  12  and the tip section  14  to bend smoothly without folding or kinking. 
     In the depicted embodiment, the distal end of the tip section  14  carries a tip electrode  38  (see  FIGS. 1 and 4 ). Mounted along the length of the tip section  14  is a ring electrode  40  (see  FIG. 4 ). The length of the ring electrode  40  is not critical, but is preferably about 1 mm to about 3 mm. Additional ring electrodes can be provided if desired. If multiple ring electrodes are used, they are spaced apart in any fashion as desired so long as their edges do not touch. 
     As shown in  FIGS. 2-5 , the tip electrode  38  and ring electrode  40  are each connected to separate lead wires  30 . Each lead wire  30  extends through the second off-axis lumen  28  in the tip section  14  ( FIG. 5 ), through the central lumen  18  in the catheter body  12  ( FIG. 3 ) and into the control handle  16  where it is connected to electronic circuit board  110 . Electronic circuit board  110  ( FIG. 15 ) is connected to an appropriate connector, which can be plugged into or otherwise connected to a suitable monitor, source of energy, etc. Alternatively, lead wires  30  may be connected directly to a connector which is then plugged into or otherwise operably connected to a suitable monitor, source of energy etc. 
     The lead wires  30  are connected to the tip electrode  38  and ring electrode  40  by any conventional technique. Connection of a lead wire  30  to the tip electrode  38  is preferably accomplished by solder or the like. Connection of a lead wire  30  to the ring electrode  40  is preferably accomplished by first making a small hole through the tubing  24 . Such a hole can be created, for example, by inserting a needle through the tubing  24  and heating the needle sufficiently to form a permanent hole. The lead wire  30  is then drawn through the hole by using a microhook or the like. The end of the lead wire  30  is then stripped of any coating and welded to the underside of the ring electrode  40 , which is then slid into position over the hole and fixed in place with polyurethane glue or the like. 
     As also shown in  FIGS. 2-5 , two puller wires  32  extend through the catheter  10 . Each puller wire  32  extends from the control handle  16 , through the central lumen  18  in the catheter body  12  ( FIG. 3 ) and into one of the off-axis lumens  26  and  28  of the tip section  14  ( FIG. 5 ). As described in more detail below, the proximal end of each puller wire  32  is anchored within the control handle  16  and the distal end of each puller wire  32  is anchored within the tip section  14 . 
     Each puller wire  32  is made of any suitable metal, such as stainless steel or Nitinol. Preferably each puller wire  32  has a coating, such as a PTFE or the like. Each puller wire  32  has a diameter preferably ranging from about 0.006 inch to about 0.0010 inch. Preferably both of the puller wires  32  have the same diameter. 
     Each puller wire  32  is anchored near the distal end of the tip section  14 . In the embodiment depicted in  FIG. 4 , the puller wires  32  are both anchored to the tip electrode  38  by a welding or the like. 
     Alternatively, the puller wire  32  in the first off-axis lumen  26  can be anchored to the side wall of the tip section  14 . As shown in  FIGS. 7 to 9 , the puller wire  32  is preferably attached by means of an anchor  44  fixedly attached to the distal end of the puller wire  32 . The anchor  44  is formed by a metal tube  45 , e.g., a short segment of hypodermic stock, that is fixedly attached, e.g. by crimping, to the distal end of the puller wire  32 . The tube has a section that extends a short distance beyond the distal end of the puller wire  32 . A cross-piece  47  made of a small section of stainless steel ribbon or the like is soldered or welded in a transverse arrangement to the distal end of the metal tube which is flattened during the operation. This creates a T-bar anchor  44 . A notch is created in the side of the tip section  14  resulting in an opening in the off-axis lumen  26  carrying the puller wire  32 . The cross piece  47  lies transversely within the notch. Because the length of the ribbon forming the cross-piece  47  is longer than the diameter of the opening into the off-axis lumen  26 , the anchor  44  cannot be pulled completely into the off-axis lumen  26 . The notch is then sealed with polyurethane glue or the like to give a smooth outer surface. The glue flows into the off-axis lumen  26  to fully secure the anchor. A tunnel, in the form of polyimide tubing or the like, can be provided to permit passage of the lead wire  30  through the glue so that this same puller wire anchor construction can be used in the second off-axis lumen  28 . Other means for anchoring the puller wires  32  in the tip section  14  would be recognized by those skilled in the art and are included within the scope of the invention. 
     Referring back to  FIGS. 1 and 2 , the catheter  10  further comprises two compression coils  46 , each in surrounding relation to a corresponding puller wire  32 . Each compression coil  46  is made of any suitable metal, such as stainless steel. Each compression coil  46  is tightly wound on itself to provide flexibility, i.e., bending, but to resist compression. The inner diameter of each compression coil  46  is slightly larger than the diameter of its associated puller wire  32 . For example, when a puller wire  32  has a diameter of about 0.007 inch, the corresponding compression coil  46  preferably has an inner diameter of about 0.008 inch. The coating on the puller wires  32  allows them to slide freely within the compression coil  46 . The outer surface of each compression coil  46  is covered along most of its length by a flexible, non-conductive sheath  48  to prevent contact between the compression coil  46  and the lead wires  30  within the central lumen  18 . The non-conductive sheath  48  made of thin-walled polyimide tubing is presently preferred. 
     As shown in  FIG. 2 , at the distal end of the catheter body, the two compression coils  46  are positioned in diametric opposition within the stiffening tube  22  and spacer  36  so that they can be aligned with the two off-axis lumens  26 ,  28  in the tip section  14 . The compression coils  46  and stiffening tube  22  are sized so that the compression coils  46  fit closely and slidably within the stiffening tube  22 . With this design, the lead wires  30  distribute themselves around the two compression coils  46  without misaligning the coils. 
     The compression coils  46  are secured within the catheter body  12  with polyurethane glue or the like. Each compression coil  46  is anchored at its proximal end to the proximal end of the stiffening tube  22  in the catheter body  12  by a glue joint (not shown). When a stiffening tube  22  is not used, each compression coil is anchored directly to the outer wall  20  of the catheter body  12 . 
     Still referring to  FIG. 2 , the distal end of each compression coil  46  is anchored to the distal end of the stiffening tube  22  in the catheter body  12  by a glue joint  52 , or directly to the distal end of the outer wall  20  of the catheter body  12  when no stiffening tube  22  is used. Alternatively, the distal ends of the compression coils  46  may extend into the off-axis lumens  26 ,  28  of the tip section  14  and are anchored at their distal ends to the proximal end of the tip section  14  by a glue joint. In the depicted embodiment, where the compression coils  46  are each surrounded by the sheath  48 , care should be taken to insure that the sheath is reliably glued to the compression coil. The lead wires  30  can also be anchored in the glue joint. However, if desired, tunnels in the form of plastic tubing or the like can be provided around the lead wires at the glue joint to permit the lead wires to be slidable within the glue joint. 
     Both glue joints preferably comprise polyurethane glue or the like. The glue may be applied by means of a syringe or the like through a hole made between the outer surface of the catheter body  20  and the central lumen  18 . Such a hole may be formed, for example, by a needle or the like that punctures the outer wall  18  and the stiffening tube  22  that is heated sufficiently to form a permanent hole. The glue is then introduced through the hole to the outer surface of the compression coil  46  and wicks around the outer circumference to form a glue joint about the entire circumference of each sheath  48  surrounding each compression coil  46 . Care must be taken to insure that glue does not wick over the end of the coil so that the puller wire cannot slide within the coil. 
     As best shown in  FIGS. 2 and 5 , within the off-axis lumens  26 ,  28 , each puller wire  32  is surrounded by a plastic sheath  42 , preferably made of PTFE. The plastic sheaths  42  prevent the puller wires  32  from cutting into the wall of the tip section  14  when the tip section is deflected. Each sheath  42  ends near the distal end of each puller wire  32 . Alternatively, each puller wire  32  can be surrounded by a compression coil where the turns are expanded longitudinally, relative to the compression coils extending through the catheter body, such that the surrounding compression coil is both bendable and compressible. 
     Longitudinal movement of the puller wires  32  relative to the catheter body  12 , which results in deflection of the tip section  14 , is accomplished by manipulation of the control handle  16 . A suitable bidirectional control handle for use in the present invention is illustrated in  FIGS. 9-15 . 
     As shown in  FIG. 9 , the control handle  16  comprises a generally elongated handle housing  60 , which can be made of any suitable rigid material. The housing  60  can be of a unitary construction or of two opposing halves  64 ,  66  that are joined by glue, sonic welding or other suitable means along a longitudinal peripheral seam  67 . The control handle  16  comprises a steering assembly  68  that controls deflection of the tip section in response to manipulations by the user. In the illustrated embodiment, the steering assembly comprises a lever arm  70  carrying a pair of coordinated pulleys  72  that act on the puller wires  32  to deflect the tip section. The lever arm  70  of the steering assembly  68  is seated for rotation between a top washer  80  and a bottom washer  82 . A friction nut  84  and a pin  86  couple an external deflection knob  88  to the lever arm. The deflection knob seats against an O-ring  90 . Movement of the deflection knob  88  by the user rotates the lever arm  70  about a screw  98  within the housing  60 , as explained below in further detail. Contact between deflection knob  88  and the side of the housing  60  physically limits the range of left and right rotation of the lever arm about a throw axis  75 . 
     The steering assembly  68  also includes an external tension adjustment knob  94  that an adhesive couples to the head of the screw  98 . The tension adjustment knob  94  seats against another O-ring  96 . Movement of the knob  94  rotates the screw  98 . Clockwise rotation of the knob  94  tightens the screw  98  to increase the seating force between the lever arm and the bottom washer  82 . When moved fully clockwise to contact against the housing, the knob  94  imposes a seating force that prevents rotation of the lever arm  70  by the deflection knob  88 . Counterclockwise movement of the tension adjustment knob  94  loosens the screw  98  to decrease the seating force and free the lever arm  70  for rotation. 
     As shown in  FIG. 10 , the lever arm  70  has a rotation angle about a throw axis  75 , which is generally perpendicular to a longitudinal axis  77  of the control handle  16 . A neutral position along axis  102  is defined for the lever arm when its longitudinal axis  104  is generally perpendicular to the longitudinal axis  77  of the control handle  16 . The lever arm is rotatable from its neutral position in the clockwise direction by angle +α and in the counterclockwise direction by angle −α. Because the lever arm is rotationally coupled to the deflection knob  88 , the range of the angle α is also limited by the contact of the deflection knob  88  with the housing  60 . In the disclosed embodiment, the angle α ranges between about 0 and 70 degrees, preferably between about 30 and 60 degrees and more preferably between about 40 to 50 degrees. Accordingly, the disclosed embodiment provides a total range of rotation (from −α to +α) of between about 0 and 140 degrees, preferably between about 60 and 120 degrees and more preferably between about 80 to 100 degrees. The pulleys  72  are located at opposing ends of the lever arm  70 , at a radial distance R from the throw axis  75 . As shown in  FIGS. 11-13 , with rotation of the lever arm  70 , one pulley  72  is translated distally as the other pulley  72  is translated proximally. Moreover, each pulley can rotate counterclockwise or clockwise about its own axis of rotation. 
     In accordance with the present invention, the steering assembly  68  is advantageously configured to provide a relatively shorter angular throw while increasing, if not at least generally doubling, the throw capacity of the catheter. In particular, the steering assembly has a minimized moment of inertia about the throw axis  75 , while generally doubling the travel distance of a puller wire in relation to the travel distance of the respective pulley drawing that puller wire, despite the relatively small interior of the housing. Moreover, the steering assembly provides a minimal angle between the longitudinal axis  77  of the control handle  16  and a segment of the puller wire drawn to accomplish deflection, for more efficient use of the force applied by the user in operating the control handle. To facilitate these movements for deflecting the tip section, the steering assembly  68  also includes a pair of constant force springs  74  that are attached to the proximal ends of the puller wires, and a pair of adjustable stops  76  which prevent the proximal ends of the puller wires from moving proximally past a selected position relative to the longitudinal axis of the control handle. 
     Referring back to  FIG. 10 , the housing  60  is configured at its distal end with a port  90  through which proximal end segments of the puller wires  32  enter the control handle  16 . In the housing half  66 , a divider  92  is configured in the inner surface and distal of the port to extend linearly between the port and the lever arm  70 . At a distal end  94  of the divider, the puller wires (now designated as  32   a ,  32   b ) diverge toward a respective pulley  72  in the lever arm. For ease of discussion, the housing half  66  may be described as divisible along the divider  92  into top and bottom housing quarters  66  am  66   b , (see also  FIG. 15 ), which are more or less mirror counterparts of each other in terms of physical layout and operation. Accordingly, the following description uses similar reference numerals for similar structures except the numerals are followed by the letter a or the letter b. 
     The puller wire  32   a  continues from the port  90  proximally in a minimally diagonal and generally linear direction toward the pulley  72   a  in the lever arm  70 . At the pulley  72   a , the puller wire  32   a  is trained counterclockwise about the pulley before it extends distally toward the spring  74   a  where its proximal end (so designated despite its being physically distal of a preceding segment) is attached to a free end  109   a  of the spring  74   a  by a fastener  111   a , such as a welded joint or a crimp fastener. 
     Correspondingly, the puller wire  32   b  continues from the port proximally in a minimally diagonal and generally linear direction toward the pulley  76   b  in the lever arm  70 . At the pulley, the puller wire  32   b  is trained clockwise about the pulley before it extends distally toward the spring  74   b  where its proximal end, (so designated despite its being physically distal of a preceding segment) is attached to a free end  109   b  of the spring  74   b  by a fastener  111   b , such as a welded joint or a crimp fastener. 
     In the embodiment of  FIG. 10 , each puller wire is trained about its pulley for a predetermined degree ranging between about 185 to 215, preferably 190-210, or more preferably about 195-205. Moreover, in  FIG. 10 , the springs  76   a ,  76   b  are illustrated as flat coil springs. In general, each spring member exerts a force in the distal direction ranging between about 0.25 lbs. and 1.0 lbs, preferably ranging between about 0.4 lbs and 0.8 lbs, and preferably of about 0.6 lbs. 
     In view of the foregoing, the travel path within the housing of each puller wire is as follows: a first generally linear path traversed by puller wire segments  120   a ,  120   b  between the port  90  and the respective pulley  72   a ,  72   b , a non-linear (including, e.g., a U-turn or doubling back) path traversed by puller wire segments  122   a ,  122   b  generally around the respective pulley  72   a ,  72   b , and a second generally linear path traversed by puller wire segments  124   a ,  124   b  between the respective pulley  72   a ,  72   b  and the respective springs  74   a ,  74   b . In that regard, the stops  76   a ,  76   b  guide the direction of travel of the segments  120   a ,  120   b  and  124   a ,  124   b . As best shown in  FIG. 10   a , each stop has a first channel  130  in which one of the segments  120   a ,  120   b  extends and a second channel  132  in which one of the segments  124   a ,  124   b  extends. While the first and second channels are sized to allow the wire segments to move distally or proximally, the distal ends of the second channels are configured to prevent the proximal end of the wires and/or the free ends  109   a ,  109   b  of the springs  74   a ,  74   b  from moving proximally past the distal ends. Third channels  133   a ,  133   b  are provided so that other components of the catheter body (e.g., lead wires, irrigation tubes, etc.) can pass through the control handle without interfering with the steering assembly  68  and movements of the puller wire. 
     Given the foregoing, it can be seen from  FIGS. 11-13  that rotation of the lever member  70  causes deflection in the catheter tip section  14 . That is, when the lever member is rotated in the clockwise rotation (namely, in the +α direction) ( FIG. 12 ), the pulley  72   a  is translated proximally. Because the puller wire  32   a  trained on the pulley  72   a  is stopped at its proximal end by the stop  76   a , the proximal translation of the pulley  72   a  causes it to rotate counterclockwise thereby drawing proximally the wire segment  120   a , which results in deflection of the tip section  14  to the right. Facilitating this deflection is the release of the segment  124   b  as the pulley  72   b  is coincidentally translated distally by the lever arm  70 . The resulting slack in the segment  124   b  is taken up by the spring  74   b  (a tubular coil spring in the illustrated embodiment) as the pulley  72   b  rotates clockwise. 
     Correspondingly, when the lever arm is rotated in the counterclockwise rotation (namely, in the −α direction) ( FIG. 13 ), the pulley  72   b  is translated proximally. Because the puller wire  32   b  trained on the pulley  72   b  is stopped at its proximal end by the stop  76   b , the proximal translation of the pulley  72   b  causes it to rotate clockwise thereby drawing proximally the wire segment  120   b , which results in deflection of the tip section  14  to the left. Facilitating this deflection is the release of the segment  124   a  as the pulley  72   a  is coincidentally translated distally by the lever arm  70 . The resulting slack in the segment  124   a  is taken up by the spring  74   a  (a tubular coil spring in the illustrated embodiment) as the pulley  72   a  rotates counterclockwise. 
     Although each of the actuating pulley has translated proximally only a distance x ( FIGS. 12 and 13 ) along the longitudinal axis  77  as a result of the rotation of the lever arm  70 , the length of the puller wire drawn by that pulley proximally from the port in deflecting the tip section is about 2×. Consequently, the present invention provides a catheter with nearly double the throw in tip deflection, despite the small interior space of the control handle. 
     Moreover, as also shown in  FIGS. 11-13 , an angle of alignment of the segments  120   a ,  120   b  deviates only minimally from the longitudinal axis  77  which provides greater operating efficiency in the force required to deflection the tip section  14 . In the disclosed embodiment, a deviation angle θ may range between about 5 to 12 degrees, preferably between 6 and 10 degrees and more preferably between 7 and 8 degrees, when the lever arm is in the neutral position (namely, when α is at or near 0) ( FIG. 11 ). Because the pulleys  72  each travel a circular path when translated by the lever arm  70 , the angle θ can be further decreased by up to about 2-4 degrees (that is, down to about θ=3 degrees) during this translation ( FIGS. 12 ,  13 ). In any case, given such a minimal range of the angle θ, most of the force that is applied to draw a puller wire proximally along the longitudinal axis  77  for deflecting the tip section in the direction of the off axis lumen in which that puller wire extends is advantageously met by the proximal translation of the pulley drawing that puller wire along the angle θ. 
     In accordance with the present invention, an initial neutral position (with little or no detectable deflection) ( FIG. 11 ) in the tip section  14  can be readily calibrated by selective placement of the stops  76   a ,  76   b  distally or proximally along the divider  92 . With the lever arm  70  resting in the neutral position, the operating position of each puller wire  32  is adjusted so that it is sufficiently taut in drawing the ends  109  of the springs  74  against the stops  76  without causing any detectable deflection in the tip section  14 . In that regard, it is understood that the puller wires can also be adjusted to provide the catheter with a predetermined amount of free play so that the catheter body  12  and/or elements surrounding the puller wires (e.g., outer wall  20  and/or stiffening tube  22 ) can shrink or stretch, such as during sterilization of the catheter, without adversely deforming the puller wires. These adjustments of the stop position of each puller wire can also be made to compensate for certain characteristics in the catheter, including puller wires with unequal actual lengths and/or counterpart components in the steering assembly or the control handle that are not exact duplicates of each other in terms of size or operating characteristics. 
     In accordance with the present invention, each stop  76   a ,  76   b  is configured for coarse and fine adjustments of a stop location for each puller wire past which its proximal end (or its proximal end portion) cannot pass proximally. As described above in relation to  FIGS. 11-13 , the stop location of each stop  76   a ,  76   b  determines how much distance the corresponding pulley needs to be moved (or the corresponding puller wire needs to travel) proximally before the tip section  14  begins to deflect in that direction. 
     In enabling coarse (or incremental) adjustment in the stop position of each puller wire, each stop  76   a ,  76   b  is configured to adjustably engage with the divider  92  at a selected position along the longitudinal axis  77 . In particular, an inner surface of each stop has a plurality of protrusions  136  that can engage with any of a series of recessions  138  formed on either side of the divider  92 . As such, the position of each stop can be adjusted proximally or distally within the control handle along the axis  77 , thereby adjusting proximally or distally the stop location. 
     In enabling fine adjustment, a set screw  140   a ,  140   b  is provided at the distal end of each second channel  132   a ,  132   b , where a distal end of each set screw can be moved proximally or distally by advancing or withdrawing the screws in the channels. A tunnel in the screw allows the puller wires to pass through and move distally or proximally through the screws, but the tunnel is sized to prevent the fasteners  111   a ,  111   b , and/or the free end  109   a ,  109   b  of the springs  74   a ,  74   b  from moving proximally past the distal ends of the set screws. Accordingly, each set screw can be adjusted proximally or distally within the control handle relative to the axis  77 , thereby enabling fine adjustment proximally or distally of the stop location for each puller wire. 
     Stop adjustments should be performed to attain a neutral position with little or no detectable deflection in the catheter tip section  14  before the housing halves  64 ,  66  are joined to each other. Significantly, the control handle  16  is configured such that it need not be fully assembled for the steering assembly  68  and deflection of the tip section  14  to be effectively tested and evaluated. In particular, the steering assembly  68  can be tested and evaluated when assembled within the housing half  66  and operated on by the deflection knob  88  mounted on the lever arm  70  without the housing half  64 . 
     In other embodiments, one or more additional off axis lumens may be provided through which additional components, e.g., infusion tube, optic fiber, etc., may extend. Depending on the intended use of the catheter  10 , it can further comprise additional features such as temperature sensing means, an optic fiber, an infusion tube, and/or an electromagnetic sensor. Additionally, smaller components, such as a temperature sensing means, could also extend through the second lumen in the tip section along with the puller wire and lead wire(s). 
     In the embodiments described above, the central lumen  18  of the catheter body  12  is used for passage of the electrode lead wires  30  as well as the two puller wires  32 , compression coils  46  and, if present, thermocouple wires, electromagnetic sensor cable, optic fiber or infusion tube. It is understood that the catheter body  12  could alternatively comprise a plurality of lumens. However, the single central lumen  18  is preferred because it has been found that a single lumen body permits better control when rotating the catheter  10 . The single central lumen  18  permits the puller wires  32 , compression coils  46  and lead wires  30  to float freely within the catheter body  12 . If such wires are restricted within multiple lumens, they tend to build up energy when the control handle  16  is rotated, resulting in the catheter body  12  having a tendency to rotate back if, for example, the handle  16  is released, or if bent around a curve, to flip over, either of which are undesirable performance characteristics. 
       FIGS. 14 and 15  depict the proximal end of housing half  66  of housing  60  comprising a portion of the control handle  16 . Housing half  66  and mating housing half  64  (not depicted in  FIGS. 14 and 15 ) snap-fit or otherwise temporality mate together and then are ultrasonically welded, laser-welded, glued or otherwise bonded together to form a unitary housing  60  for control handle  16 . The unitary housing  60  for control handle  16  is substantially impervious to contaminants so that the electronic circuit board  110  and/or steering assembly  68  are protected from contamination by fluids present during an electrophysiology procedure. Thin-walled portion  118  is a notch of between 21 mm and 22 mm in width (W), preferably no more than 22 mm that provides for a frangible connection between two quarters  66   a  and  66   b  (which mate with quarters  64   a  and  64   b  not shown) of housing  60  enabling a user to readily break the connection to secure access to the steering assembly  68  and/or the electronic circuit board  110  in the control handle  16 . The depth of the thin-walled portion should be between 0.76 mm and 0.87 mm which would be between approximately 50 percent and 55 percent of the thickness of housing  60 . The thin-walled portion may extend substantially around the entire circumference of the housing  60  and be substantially perpendicular to the longitudinal axis of the control handle  16 . Alternatively, the thin-walled portion  118  could form an elliptical shape angled to the longitudinal axis of the control handle  16  as depicted in  FIGS. 9 and 13  which could provide different portals of access to the internal electronic circuit board or steering assembly. Additionally, thin-walled portion  118  could form a stepped band around the circumference enabling a still different access portal once the frangible connection is severed. 
     In use, the frangible thin-walled portion  118  is snapped by a user thereby opening the interior of the control handle. During manufacture or reprocessing access to this area may be necessary to facilitate the replacement or reprogramming of the electronic circuit board or replacement  110  of parts in the steering assembly  68 . Once the necessary repairs or reprogramming is done the two portions of the handle are put back together using ultrasonic welding, laser welding or other bonding means such as glue or epoxy. The device may then be sterilized using a known sterilization process and placed in a sterile container for delivery to the user. 
     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. 
     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.