Abstract:
A bi-directional system for actively deflecting the distal tip of a catheter includes a reconfigurable tube that is positioned proximal to the catheter&#39;s distal tip. The tube is formed with slits that are arranged to allow the tube to be transformed from a relaxed, cylindrical configuration to a plurality of deflected configurations. First and second pull wires are provided, with each wire having a respective distal end that is attached to the distal end of the tube. Each wire extends to a catheter handle where it is attached to a respective reel. The reels can be rotated, back and forth, to selectively deflect or relax the tube. To ensure a smooth recovery after a relatively large deflection, a mechanism is disclosed for delaying an application of tension on one of the pull wires until at least a portion of any tension on the other pull wire is released.

Description:
FIELD OF THE INVENTION 
     The present invention pertains generally to systems and methods for actively deflecting a distal portion of a catheter while the distal portion is positioned within a body conduit. More particularly, the present invention pertains to a bi-directional system for deflecting the distal portion of a catheter. The present invention is particularly, but not exclusively, useful as a system for bi-directionally controlling the cryo-tip of a cryoablation catheter. 
     BACKGROUND OF THE INVENTION 
     Atrial fibrillation is an irregular heart rhythm that adversely affects approximately 2.5 million people in the United States. It is believed that at least one-third of all atrial fibrillation originates near the ostium of the pulmonary veins. Anatomically, two pairs of pulmonary veins are connected to the left atrium of the heart with each pair delivering blood to the heart from one of the patient&#39;s lungs. 
     It is further believed that the optimal technique to treat atrial fibrillation is to create circumferential lesions around the ostia where a pulmonary vein connects with the left atrium. More specifically, the goal is to ablate tissue to form a conduction block to thereby prohibit the transmission of irregular electrical signals that can cause an arrhythmia. To be effective, the conduction block must completely block irregular signals and this often requires the ablation of a relatively deep, uniform lesion. In some cases, more than one pulmonary vein must be treated to cure an arrhythmia. 
     To create circumferential lesions around the ostia using cryoablation, a typical procedure involves contacting tissue around the periphery of an ostium with a cryo-element and then cooling the cryo-element to ablate the contacted tissue. In some cases, the cryo-element can be hoop shaped allowing for a single-contact cryoablation. In other cases, a cryo-element that is arcuate, partially hoop shaped or dome shaped can be used. For such cryo-elements, multiple, successive contacts between the cryo-element and tissue are typically required. More specifically, these procedures require the cryo-element to be successively moved around the ostia to create a continuous ablation band. 
     For all of these types of cryo-elements, it is necessary to articulate the distal end of the catheter with great accuracy to aim and direct the cryo-element into contact with the targeted tissue. Moreover, this manipulation typically must be performed within a relatively limited space (e.g. the left atrium). For this purpose, it is desirable to be able to deflect the distal end of the catheter in more than one direction. With bi-directional capability, the distal end of the catheter can be deflected in a first direction (e.g. upward) to treat a first pulmonary vein, for example, and subsequently deflected in a second direction (e.g. downward) to treat a second vein. Furthermore, the ability to deflect the distal end of the catheter at relatively large deflection angles can potentially simplify and quicken many procedures. 
     In a typical bi-directional deflection system, a first pull wire is used to deflect the distal catheter tip in a first direction and second pull wire is provided to deflect the distal catheter tip in a second direction, opposite the first direction. For these conventional systems, a change in deflection from one direction to another can be problematic. For instance, when the tip is deflected a relatively small amount in the first direction, the second pull wire can typically be retracted to first straighten the catheter tip, and then deflect the tip in the second direction. However, when the deflection of the distal tip in the first direction is relatively large (e.g. ninety to one hundred eighty degrees or more), retraction of the second pull wire does not necessarily operate to smoothly recover the deflection and straighten the tip. Instead, for conventional bi-directional systems, retraction of the second wire can actually cause further deflection in the first direction and may prevent a deflection recover when the tension in the first wire is released. 
     In light of the above, it is an object of the present invention to provide a bi-directional system for actively deflecting a distal portion of a catheter while the distal portion is positioned within a body conduit. It is another object of the present invention to provide a system for bi-directionally controlling the cryo-tip of a cryoablation catheter that transitions from one direction to another with the operation of a single control knob. It is yet another object of the present invention to provide a system for bi-directionally controlling the cryo-tip of a cryoablation catheter that actively controls the amount of tip deflection in both directions and can hold the deflected cryo-tip in place. Yet another object of the present invention is to provide a bi-direction control system which is easy to use, relatively simple to implement, and comparatively cost effective. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a bi-directional system for actively deflecting the distal portion of a catheter. More specifically, the system is typically designed to deflect the catheter&#39;s distal portion in either of two directions. Thus, the distal portion may be deflected in a first direction from a relaxed (i.e. straight) configuration, and thereafter smoothly deflected in a second direction that is coplanar and opposite the first direction. Applications of the bi-directional system can include: 1) steering the distal tip of a catheter through a body conduit during advancement of the distal tip to an internal target location; and 2) placing the distal tip in one or more preselected orientations at the target location. 
     In greater structural detail, the bi-directional system includes an elongated catheter body having a proximal portion, and the distal portion mentioned above. In this combination, the distal portion is formed with a lumen. Also, a tube is disposed in the lumen and located proximal to the catheter&#39;s distal tip. This tube, which is typically made of a metal, has a proximal end and a distal end and it is formed with a plurality of slits that are arranged along the length of the tube. The purpose of these slits is to allow the tube to be transformed from a relaxed configuration, in which the tube is substantially cylindrical and defines a tube axis, into a plurality of deflected configurations. More specifically, in the deflected configurations, the distal end of the tube is displaced from the tube axis in either a first direction or a second direction that is coplanar and opposite the first direction. 
     To deflect the tube in a manner as suggested above, the system includes first and second pull wires. Each of these pull wires has a respective distal end that is attached to the distal end of the tube. From their respective attachment points, each pull wire extends proximally through the tube to a housing on the handle of the catheter. At the handle, a pair of reels (i.e. a clockwise (CW) reel and a counter-clockwise (CCW) reel) are positioned in the handle housing and mounted on the catheter with each reel being rotatable relative to the housing about a common axis of rotation. The proximal end of one pull wire (e.g. the first wire) is attached to the circumference of the CW reel and the proximal end of other pull wire (e.g. the second wire) is attached to the circumference of the CCW reel. With this cooperation of structure, the CW reel can be rotated back and forth to selectively pull and release the first pull wire. Specifically, a pull on the first wire deflects the distal end of the tube in the first direction, while a release of the first wire relaxes the tube into its initial cylindrical configuration. In a similar manner, back and forth rotations of the CCW reel result in the distal end of the tube being deflected in the second direction or relaxed into the initial cylindrical configuration. 
     In addition to the CW and CCW reels, the system further includes a drive cog that is mounted on the handle housing for rotation about the axis of rotation in either a first or second rotation direction. Functionally, when the drive cog is rotated in the first rotation direction, it engages and rotates the CW reel. On the other hand, when the drive cog is rotated in the second rotation direction, it engages and rotates the CCW reel. Each of the reels and the drive cog are stacked along the rotation axis and are positioned inside the handle housing opposite a user operable turn knob. Specifically, the turn knob is positioned outside the handle housing with a friction washer interposed between the housing and the knob. With this combination, a screw can then be used to clamp the knob toward the drive cog at a preselected clamping pressure. As a consequence, the friction washer and the wall of the housing are sandwiched between the turn knob and drive cog. As intended for this structural arrangement, the user can rotate the turn knob to selectively pull on either the first or the second pull wires. Also, the friction washer then “locks” the knob in place after a preselected rotation. This allows the operator to release their hand from the knob while maintaining a preselected tip deflection. 
     In one implementation of the deflection system, a guiding mechanism is provided to maintain both the first and second pull wires adjacent to the inner wall of the tube during a deflection of the tube. For example, this guiding mechanism can include a plurality of indentations that are formed in the tube to hold the pull wires against the inner wall while allowing the pull wires to pass freely through each indentation. Specifically, each indentation can be formed from a portion of the tube wall that is located between a pair of axially adjacent slits in the wall. More specifically, each indentation protrudes radially inward toward the center of the tube to form a passageway that can be used to thread one of the pull wires through the indentation As intended for the present invention, a plurality of such indentations can be formed in an axial direction along the tube to concertedly hold a pull wire. 
     In another aspect of the invention, the system includes a mechanism that is operable on the pull wires for delaying an application of tension on one of the pull wires until at least a portion of any tension on the other pull wire is released. This delay allows for the recovery of large deflections. For the case where CW and CCW reels and a drive cog are used to control the pull wires, the delay mechanism can be implemented by the establishment of a gap between the cog and the reels. Specifically, when the tube is in a relaxed state and there is no tension on either pull wire, the cog is centered between the two reels with a gap between the cog and the CW reel and an equal size gap between the cog and the CCW reel. With properly sized gaps, only one wire at a time can be placed in tension, resulting in the smooth recovery of relatively large deflections. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a perspective view of a cryo-catheter having a bi-directional control system and a system for deflecting a section of the cryo-catheter into a hooped configuration; 
         FIG. 2  is a perspective view of a distal portion of the cryo-catheter, shown with the flexible catheter jacket removed to reveal the internal structure of the catheter; 
         FIG. 3  is an enlarged, perspective view of the distal tip of the cryo-catheter; 
         FIG. 4  is an enlarged, perspective view of the junction between the distal tube and the proximal tube of the catheter; 
         FIG. 5  is a cross-sectional view as seen along line  5 - 5  in  FIG. 1 , showing the distal portion of the cryo-catheter in a relaxed, undeflected state; 
         FIG. 6  is an enlarged, perspective view of a sheath spring; 
         FIG. 7  is an exploded, perspective view of the catheter handle shown in  FIG. 1 ; 
         FIG. 8  is an enlarged, perspective view showing a section through the distal tube to illustrate an indentation for guiding a deflection wire; 
         FIGS. 9A-E  are a series of perspective views showing a distal portion of the cryo-catheter in various states of deflection; 
         FIG. 10  is an enlarged, perspective view of the proximal end of the proximal tube; and 
         FIGS. 11A-E  are a series of top plan views of the catheter handle (with the handle top removed) showing the bi-directional section of the catheter in various states of deflection. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1 , a cryo-catheter for cryoablating a lesion in a body conduit of a patient is shown and generally designated  20 . As indicated in  FIG. 1 , the cryo-catheter  20  can be manipulated into different configurations and orientations. To do this, the cryo-catheter  20  includes a system for deflecting a section  22  of the cryo-catheter  20  into a hoop configuration, as shown. It also includes a bi-directional control system for deflecting a section  24  of the cryo-catheter  20  in both a first direction and a second direction that is substantially coplanar and opposite the first direction.  FIG. 1  further shows that the cryo-catheter  20  includes an elongated catheter body  26  that extends distally from a catheter handle  28 . Although these deflecting systems are shown and disclosed herein as being part of a cryo-catheter  20 , those skilled in the pertinent art will appreciate that these systems can be used as well in other types of catheters where bi-directional control or an actively produced hoop shaped configuration are desirable. 
     Referring now to  FIG. 2 , a distal portion of the cryo-catheter  20 , generally designated  30 , is shown with the outer catheter body  26  removed to reveal internal components. As shown, the cryo-catheter  20  includes a distal tube  34  having a proximal end  36  and a distal end  38 , a proximal tube  40  having a proximal end  42  and a distal end  44 , and a cryo-tip  46  that is mounted on the distal tube  34  at its distal end  38 . For the embodiment shown, the cryo-catheter  20  also includes three EKG band electrodes  48   a - c .  FIG. 2  further shows that the distal tube  34  includes two distinct sections  50 ,  52 , with section  50  extending from the proximal end  36  of the distal tube  34  to a section distal end  54  and section  52  extending from the distal end  54  of section  50  to the distal end  38  of the distal tube  34 . 
     Cross-referencing  FIGS. 2 and 3 , it can be seen that the distal tube  34  has a wall  56  and defines a tube axis  58 . Section  52  of the distal tube  34  further includes a plurality of first slits, of which exemplary first slits  60   a,b  have been labeled, which are cut through the wall  56  and oriented in respective planes that are substantially perpendicular to the tube axis  58 . As further shown, each first slit  60   a,b  extends azimuthally in an arc partway around the axis  58  and each has a center and a substantially same arc length, which is typically slightly greater than one-hundred eighty degrees. Further, it can be seen that the respective centers of these first slits  60  are aligned with each other in a first centerline that is oriented substantially parallel to the tube axis  58 . For the embodiment shown, section  52  of the distal tube  34  is also formed with a plurality of second slits, of which exemplary second slits  62   a,b  have been labeled, and which, like the first slits  60   a,b , establish a second centerline that is substantially parallel to the tube axis  58 . Typically, the second slits  62   a,b  are cut into the tube wall  56  such that the second centerline is diametrically opposed to the first centerline (i.e. located one-hundred eighty degrees around the circumference of the distal tube  34  from the first centerline). With this arrangement of first slits  60  and second slits  62 , the section  52  of the distal tube  34  can be transformed between a first, relaxed configuration wherein section  52  is substantially cylindrical shaped (as shown in  FIGS. 2 and 3 ) and a second, deflected configuration wherein section  52  of the distal tube  34  is substantially hoop shaped (hoop shown in  FIG. 1 ). For the cryo-catheter  20 , the distal tube  34  is typically made of a thin walled stainless steel material (e.g. 304 alloy) that has been cut with a laser to form the slits  60 ,  62  described above. A more detailed description of the tube  34  can be found in co-pending, co-owned U.S. patent application Ser. No. 10/774,665, filed Feb. 9, 2004, which is hereby incorporated by reference in its entirety herein. 
     Continuing with  FIGS. 2 and 3 , the wall  56  of the distal tube  34  within the section  50  is formed with a plurality of first slits  64  and a plurality of second slits  66  which are cut through the wall  56  and oriented in respective planes that are substantially perpendicular to the tube axis  58 . As further shown, each slit  64 ,  66  extends azimuthally in an arc partway around the tube axis  58  and each has a center and a substantially same arc length, which is typically slightly greater than one-hundred eighty degrees. Further, the respective centers of the first slits  64  are aligned with each other in a first centerline, the respective centers of the second slits  66  are aligned with each other in a second centerline and both first and second centerlines are oriented substantially parallel to the tube axis  58 . For the section  50 , the second centerline is diametrically opposed to the first centerline. 
       FIG. 2  further shows that the first slits  64  of section  50  are azimuthally displaced from the first slits  60  of section  52  by approximately ninety degrees. Thus, the first centerline of section  50  is azimuthally displaced from the first centerline of section  52  by approximately ninety degrees. Similarly, the second slits  66  of section  50  are azimuthally displaced from the second slits  62  of section  52  by approximately ninety degrees. With this arrangement of first slits  64  and second slits  66 , the section  50  of the distal tube  34  can be transformed between a first, relaxed configuration wherein section  50  is substantially cylindrical shaped (as shown in  FIGS. 2 and 3 ) and a second, deflected configuration wherein section  50  of the distal tube  34  is curved to establish a transition section between the hoop and the bi-directional section (see  FIG. 1 ). 
       FIG. 2  also shows that the proximal tube  40  has a wall  68  and for the cryo-catheter  20 , the proximal tube  40  is centered along the tube axis  58 . Cross-referencing  FIGS. 2 and 4  it can be seen that the wall  68  of the proximal tube  40  is formed with a plurality of first slits  70  and a plurality of second slits  72  which are cut through the wall  68  and oriented in respective planes that are substantially perpendicular to the tube axis  58 . As further shown, each slit  70 ,  72  extends azimuthally in an arc partway around the tube axis  58  and each has a center and a substantially same arc length, which is typically slightly greater than one-hundred eighty degrees. Further, the respective centers of the first slits  70  are aligned with each other in a first centerline, the respective centers of the second slits  72  are aligned with each other in a second centerline and both first and second centerlines are oriented substantially parallel to the tube axis  58 . For the proximal tube  40 , the second centerline is diametrically opposed to the first centerline. 
     Continuing with cross-reference to  FIGS. 2 and 4 , it can be seen that the distal end  44  of the proximal tube  40  is attached to the proximal end  36  of the distal tube  34 . As shown, the proximal tube  40  has a diameter that is slightly smaller than the diameter of the distal tube  34  allowing the distal end  44  of the proximal tube  40  to be inserted into the proximal end  36  of the distal tube  34  and attached thereto. Typically, the tubes  34 ,  40  are welded or bonded together.  FIGS. 2 and 4  also show that the tube  34  is attached to the tube  40  with the centerline of the first slits  70  aligned with the center line of the first slits  64  of section  50  of the distal tube  34 . Similarly, it can be seen that the tube  34  is attached to the tube  40  with the centerline of the second slits  72  aligned with the center line of the second slits  66  of section  50  of the distal tube  34 . 
     Cross-referencing  FIG. 1  with  FIG. 3 , it can be appreciated that the distal tube  34 , proximal tube  40  and the proximal portion of the cryo-tip  46  are all disposed in the lumen  74  (see  FIG. 5 ) of the distal portion of the catheter body  26 . For the cryo-catheter  20 , the distal portion of the catheter body  26  is made of a flexible, polymeric material which is bonded to the cryo-tip  46 . On the other hand, the proximal portion of the catheter body  26  which extends from the handle  28  to the distal portion of the catheter body  26  is typically made of a polymeric material which is more rigid than the distal portion of the catheter body  26 . For some implementations, the catheter body  26  within the hoop section  22  is made of a polymeric material filled with a conductive material to enhance the conductivity of the catheter body  26  in the hoop section  22 . For example, the composite material typically includes between approximately ten weight percent and thirty weight percent (10 wt. %-30 wt. %) of filler material with the balance being polymeric matrix material. Suitable filler materials can include, but are not limited to, metals, metal alloys, ceramics, carbon and combinations thereof. 
     To deflect the section  22  (see  FIG. 1 ) into a hoop shaped configuration, the cryo-catheter  20  includes a deflection wire  76  (see  FIG. 5 ) having a distal end  78  that is attached to the distal end  38  of the distal tube  34 , as shown in  FIG. 3 . For some embodiments (not shown), the distal end  78  of the deflection wire  76  is attached to the cryo-tip  46  instead of the distal end  38  of the distal tube  34 . As further shown in  FIG. 3 , the attachment can be accomplished by indenting a portion of the distal tube  34  to create a nest between two axially adjacent slits  60  and then bonding or welding the wire  76  to the nest. As best appreciated with cross-reference to  FIGS. 3 and 4 , a central portion of the wire  76  is located within a sheath spring  80  (see also  FIG. 6 ) having a distal end  82  which is attached to the proximal tube  40  near its distal end  44 . As further shown in  FIG. 4 , the attachment is accomplished by indenting a portion of the proximal tube  40  and then bonding or welding the sheath spring  80  to the indented portion of the proximal tube  40 . 
     From their respective distal ends  78 ,  82 , the wire  76  and sheath spring  80  pass through the tubes  34 ,  40  and through the catheter body  26  (see also  FIG. 5 ) to the handle  28  (see  FIGS. 1 and 7 ). As shown in  FIG. 7 , the handle  28  includes a handle housing  84  having a handle top  86  and handle bottom  88 . A generally disk shaped hoop reel  90  is positioned in and attached to the handle housing  84  to allow the hoop reel  90  to rotate about a rotation axis  92  relative to the housing  84 . Although not shown, it is intended that the proximal end of the wire  76  will be partially wound around the hoop reel  90  and attached thereto using the attachment screws  94   a,b . As shown, the screws  94   a,b  are located at a radial distance from the rotation axis  92 . Also, the proximal end of the sheath spring  80  is attached to a ferrule (not shown) which is then fixedly attached to the handle top  86 . With the above-described cooperation of structure, the hoop reel  90  can be rotated relative to the handle housing  84  to axially retract the deflection wire  76  and transform the distal tube  34 . 
     Continuing with  FIG. 7 , it can be seen that the handle  28  includes a user operable knob  96 , a friction washer  98  and a cosmetic cover  100  that are each positioned outside the handle housing  84  and centered on the rotation axis  92 . As shown, the friction washer  98  is interposed between the handle top  86  and the knob  96 . A screw (not shown) is provided to clamp the knob  96  toward the hoop reel  90  at a preselected clamping pressure. As a consequence, the friction washer  98  and the wall of the handle top  86  are sandwiched between the knob  96  and reel  90 . With this structural arrangement, the user operable knob  96  can be rotated to selectively pull or release the deflection wire  76  (see  FIG. 3 ), while the friction washer  98  holds the knob  96  in place after a preselected rotation. This allows the operator to release the knob  96  while maintaining a preselected deflection in the section  22  (see  FIG. 1 ). 
     Referring now to  FIG. 8 , it can be seen that within the distal tube  34 , a guiding mechanism is provided to maintain the deflection wire  76  along the inner wall  102  of the distal tube  34  during axial retraction of the deflection wire  76 . Specifically, as illustrated in  FIG. 8 , a plurality of indentations, such as indentation  104  shown, can be formed in the laser cut distal tube  34  to establish the guiding mechanism. Specifically, as shown, each indentation  104  can be formed in the wall  56  between a pair of axially adjacent slits, such as first slits  60   c  and  60   d . Also shown, each indentation  104  forms a passageway that can be used to thread the deflection wire  76  though the indentation  104  to allow axial movement of the wire  76  relative to the indentation  104 . In a typical embodiment of the cryo-catheter  20 , approximately 5-15 axially spaced indentations  104  are used to maintain the deflection wire  76  along the inner wall  102  of the distal tube  34 . 
     The deflection of section  22  of the cryo-catheter  20  can best be appreciated with initial reference to  FIG. 9A  which shows the hoop section  22 , bi-directional section  24  and transition section  106 , all in a relaxed, undeflected state.  FIG. 9B  shows the cryo-catheter  20  after an initial retraction of the deflection wire  76 . Comparing  FIG. 9B  with  FIG. 9A , it can be seen that the initial retraction of the deflection wire  76  imparts a curvature to the hoop section  22  and the transition section  106 . As shown in  FIG. 9C , further retraction of the deflection wire  76  configures section  22  of the cryo-catheter  20  into a planar, hoop shaped configuration and imparts a curvature to the transition section  106 . As best seen in  FIG. 9C , the transition section  106  and the hoop section  22  deflect in different planes. 
     To deflect the bi-directional section  24  (see  FIG. 1 ), the cryo-catheter  20  includes pull wires  108 ,  110  having respective distal ends  112 ,  114  that are each attached to the proximal tube  40  near the distal end  44  of the proximal tube  40 , as shown in  FIG. 4 . As further shown, the attachment points are located approximately one hundred eighty degrees apart around the circumference of the proximal tube  40 . Also shown in  FIG. 4 , the attachment is accomplished by indenting a portion of the proximal tube  40  to create a nest between two axially adjacent slits and then bonding or welding the pull wires  108 ,  110  to the nest. As best appreciated with cross-reference to  FIGS. 4 and 10 , a central portion of each pull wire  108 ,  110  is located within a respective sheath spring  116 ,  118  (see also  FIG. 6 ) having a respective distal end  120 ,  122  which is attached to the proximal tube  40  near its proximal end  42 . As further shown in  FIG. 10 , the attachment is accomplished by indenting portions of the proximal tube  40  and then bonding or welding the respective sheath springs  116 ,  118  to the indented portion of the proximal tube  40 . Note also from  FIG. 10  that a portion of the proximal tube  40  distal to the nest can be slightly indented to form a distal abutment  124  for the sheath spring  118 . For simplicity, sheath springs  80 ,  116  and  118  have been shown as simple tubes in  FIGS. 4 and 10  and the actual helical structure of an exemplary sheath spring  80  is shown in  FIG. 6 . 
     From their respective distal ends  112 ,  114 ,  120 ,  122 , the pull wires  108 ,  110  and sheath springs  116 ,  118  pass through the proximal tube  40  and through the catheter body  26  (see also  FIG. 5 ) to the handle  28  (see  FIGS. 1 and 7 ). A guiding mechanism can be provided to maintain each pull wire  108 ,  110  along the inner wall of the proximal tube  40  during an axial retraction of one of the pull wires  108 ,  110 . Specifically, the guiding mechanism can be similar to the guiding mechanism described above for guiding the deflection wire  76  within the distal tube  34 , as illustrated in  FIG. 8 . More specifically, a plurality of indentations can be formed in the laser cut proximal tube  40  to establish the guiding mechanism. 
     As shown in  FIG. 7 , the handle  28  includes a clockwise (CW) reel  126  and a counter-clockwise (CCW) reel  128  that are positioned in and attached to the handle housing  84  to allow the reels  126 ,  128  to rotate about the rotation axis  92  relative to the housing  84 . Although it is not shown in  FIG. 7 , it is to be appreciated that in use, the proximal end of the pull wire  108  is partially wound around the CW reel  126  and attached thereto using the attachment screws  130   a,b  (see  FIG. 11A ). Similarly, it is to be appreciated that the proximal end of the pull wire  110  will be partially wound around the CCW reel  128  and attached thereto using the attachment screws  132   a,b  (see  FIG. 11A ). As best seen in  FIG. 11A , the screws  130   a,b  and  132   a,b  are each located at a radial distance from the rotation axis  92 . For the cryo-catheter  20 , the proximal end of sheath spring  116  is attached to a ferrule  134  which is then fixedly attached to the handle bottom  88 . Similarly, the proximal end of sheath spring  118  is attached to a ferrule  136  which is then fixedly attached to the handle bottom  88 . With this arrangement, the CW reel  126  can be rotated clockwise about the rotation axis  92  to selectively pull the pull wire  108  and the CCW reel  128  can be rotated counter-clockwise about the rotation axis  92  to selectively pull the pull wire  110 . 
     As further shown in  FIG. 7 , the handle  28  includes a drive cog  138  having a drive wheel  140  that is formed with a protruding cog  142 . As shown, the drive cog  138  is positioned in and attached to handle housing  84  for rotation about the rotation axis  92 . Cross-referencing  FIGS. 7 and 11A , it can be seen that when the cog  142  is rotated in a clockwise rotation direction it engages and rotates the CW reel  126  and when the cog  142  is rotated in the counter-clockwise rotation direction it engages and rotates the CCW reel  128 .  FIG. 7  further shows that each reel  126 ,  128  and the drive wheel  140  are stacked along the rotation axis  92  and positioned inside the handle housing  84  opposite a user operable turn knob  144  that is positioned outside the handle housing  84 . A friction washer  146  is interposed between the handle bottom  88  and the knob  144 . A screw  147  is then used to clamp the knob  144  toward the drive wheel  140  at a preselected clamping pressure. As a consequence, the friction washer  146  and the wall of the handle bottom  88  are sandwiched between the turn knob  144  and drive wheel  140 . With this structural arrangement, the user operable turn knob  144  can be rotated to selectively retract either pull wire  108 ,  110 , while the friction washer  146  “locks” the knob  144  in place after a preselected rotation. This allows the operator to release their hand from the knob  144  while maintaining a preselected tip deflection. 
     Continuing with  FIG. 7 , it can be seen that the drive cog  138  is formed with a spacer hub  148  to allow the reels  126 ,  128  to rotate after clamping the drive wheel  140  to the knob  144 . In addition, a washer  150  is interposed between the reels  126 ,  128  and the hoop reel  90  to allow the hoop reel  90  to rotate independently of the reels  126 ,  128 . A flat  151  formed on the knob  144  engages a corresponding flat (not shown) on the drive wheel  140  such that the knob  144  and drive wheel  140  rotate together. 
     In the present invention, the drive cog  138 , drive wheel  140 , protruding cog  142 , turn knob  144 , friction washer  146 , and screw  147  cooperate to operate the CW reel  126  and the CCW reel  128 . Specifically, they serve as means operable on the reels  126  and  128  for applying tension to the first pull wire  108  to deflect the catheter structure distal end  44  in the first direction. Thereafter, they delay an application of tension to the second pull wire  110  until at least a portion of the tension on the first pull wire  108  is selectively released. Upon application of tension to the second pull wire  110 , the catheter structure distal end  44  is deflected from the first direction to the second direction. 
     Operation of the bi-directional system for deflecting section  24  of the cryo-catheter  20  can best be appreciated with reference to  FIGS. 11A-E . Beginning with  FIG. 11A , the system is shown with the section  24  in the undeflected or neutral state. In this state, there is no applied tension to either pull wire  108 ,  110 . As further shown in  FIG. 11A , in the neutral state, the cog  142  is positioned between the CW reel  126  and CCW reel  128  with a gap between the cog  142  and reels  126 ,  128 . Thus, as best seen in  FIG. 11B , the user operable knob  144  must be rotated through a small angle, θ 1 , before the cog  142  contacts and engages the CW reel  126 . The functionality of the gap will be described in greater detail below. 
       FIG. 11C  shows the cryo-catheter  20  after a rotation of user operable knob  144  through an angle, θ 2 . It can be seen by comparing  FIG. 11C  with  FIG. 11B  that rotation of the knob  144  through an angle, θ 2 , causes the knob  144  to engage the CW reel  126  and rotate the CW reel  126  in a clockwise direction. This action, in turn, retracts the pull wire  108  and deflects section  24  of the cryo-catheter  20  in a first direction as indicated by arrow  152 , as shown. The deflection of the section  24  pulls the pull wire  110  distally, which in turn rotates the CCW reel  128  clockwise as shown. However, it can be seen from  FIG. 11C  that a gap is still present between the cog  142  and the CCW reel  128 . 
       FIG. 11D  shows the cryo-catheter  20  after a rotation of user operable knob  144  through an angle, θ 3 . This action, in turn, causes a further rotation of the CW reel  126  in a clockwise direction, further retracts the pull wire  108  and deflects section  24  of the cryo-catheter  20  to a greater extent. The increased deflection of the section  24  pulls the pull wire  110  distally, which in turn rotates the CCW reel  128  clockwise as shown. However, the initial gap (see  FIG. 11A ) is sized large enough so that the clockwise rotation of the CCW reel  128 , due to the pull wire  110 , does not cause the CCW reel  128  to engage and rotate the cog  142 . 
       FIG. 11E  shows the cryo-catheter  20  after a rotation of user operable knob  144  through an angle, θ 4 , that is equal to approximately forty-five degrees. This rotation of the knob  144  results in a deflection of the section  24  that is approximately equal to one hundred-eighty degrees, as shown.  FIG. 11E  further shows that a gap is present between the cog  142  and the CCW reel  128 . From the above description, it is apparent that the CCW reel  128  does not engage or apply a force on the cog  142  during a rotation of the knob  144  from the neutral position ( FIG. 11A ) to the position shown in  FIG. 11E . It follows that when the knob  144  is rotated counter-clockwise from the position shown in  FIG. 11E  to the neutral position ( FIG. 11A ) that the cog  142  does not engage the CCW reel  128 . Specifically, due to the gap between the cog  142  and reels  126 ,  128 , the pull wire  110  is not pulled distally by the CCW reel  128  as the tension in the pull wire  108  is released. This allows the section  24  to smoothly recover from large deflections such as the large deflection shown in  FIG. 11E . Moreover,  FIG. 11A  shows that the bi-directional system of the cryo-catheter  20  is functionally symmetric and accordingly it can be expected that a counter-clockwise rotation of the cog  142  will result in a deflection of the section  24  in a direction opposite to arrow  152  shown in  FIG. 11C . 
     The deflection of bi-directional section  22  can also be appreciated with reference to  FIGS. 9C-9E  and  FIG. 1 . Beginning with  FIG. 9C , the cryo-catheter  20  is shown with the hoop section  22  and transition section  106  deflected and the bi-directional section  22  in a relaxed, undeflected state.  FIG. 9D  shows the cryo-catheter  20  after an initial retraction of the pull wire  108  (see also  FIG. 11D ). As shown in  FIG. 9E , further retraction of the pull wire  108  results in a deflection of the section  24  that is approximately equal to one hundred-eighty degrees, in a first direction as indicated by arrow  152 .  FIG. 1  shows the bi-directional section after the pull wire  108  has been released and the pull wire  110  has been pulled distally by the CCW reel  128 . This transition from FIG.  11 E to  FIG. 1  is accomplished by moving the knob  144  counterclockwise approximately ninety degrees. Comparing  FIGS. 11A-E  to  FIG. 1 , it can be seen that the bi-directional section  24  in  FIG. 1  has been deflected in a direction that is opposite and coplanar to the direction of arrow  152 . 
       FIGS. 5 and 8  also show that the cryo-catheter  20  includes a refrigerant supply line having a supply tube  154  and a capillary tube  156 , with the capillary tube  156  attached to the distal end of the supply tube  154 . With this combination, an extracorporeally located refrigerant supply unit (not shown) can be activated to introduce a regulated flow of refrigerant into the supply tube  154  for subsequent flow through the capillary tube  156 . From the capillary tube  156 , the refrigerant expands into the cryo-tip  46  ( FIG. 1 ), or if desired into the hoop section  22 , or both, absorbing heat as it expands. A return line is provided to exhaust expanded refrigerant. For the embodiment shown, the return line is established in the volume between the supply line and catheter body  26 .  FIG. 8  also shows that thermocouple wires  158   a,b  are provided to measure a cryo-tip  46  temperature. A pressure monitoring line  160 , which typically extends from the cryo-tip  46  to an extracorporeally located pressure gauge (not shown) is provided to measure a pressure within the cryo-tip  46 . 
     In one application of the cryo-catheter  20 , the cryo-tip  46 , hoop section  22  and bi-directional section  24  are introduced into the left atrium through an introducer sheath (not shown) using a trans-septum approach. Once in the left atrium, section  22  is deflected into a hoop shape or partial hoop shape. Next, part or all of the deflected section  22  is placed into contact with target tissue which is typically peripheral tissue surrounding an ostium where a pulmonary vein connects with the left atrium. Deflection of the bi-directional section  24  can be used to achieve the desired contact between the hoop section  22  and the target tissue. Once adequate contact is made, refrigerant is expanded in the cryo-tip  46 , hoop section  22  (or both) until an adequate lesion has been created. Sections  22 ,  24  of the cryo-catheter  20  can then be re-configured to contact other targeted tissue or removed from the vasculature to complete the procedure. 
     While the particular System for Bi-Directionally Controlling the Cryo-tip of a Cryoablation Catheter and corresponding methods of preparation and use as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.