Abstract:
Systems and methods for treating an arrhythmia originating in a pulmonary vein of a patient are described. The system includes a rigid sheath and an elongated catheter that defines an axis and has an ablating distal section. The distal section includes a plurality of conductive bands, with each band establishing an enclosed chamber. The ablating distal section is reconfigurable between a first compact configuration in which each band is positioned relatively near the axis for transit through the sheath and second expanded configuration in which each band is positioned relatively far from the axis. Once in the second configuration, a fluid refrigerant is expanded into each enclosed chamber to cool the bands and cryoablate tissue. The second configuration is particularly useful for ablating a circumferential band of tissue, for example, a band of tissue surrounding the opening (i.e. ostium) where a pulmonary vein connects with the left atrium.

Description:
[0001]     The entire disclosures of each of U.S. Pat. No. 6,035,657, issued Mar. 14, 2000 for a FLEXIBLE CATHETER CRYOSURGICAL SYSTEM (“the &#39;657 patent”), U.S. Pat. No. 5,910,104 issued Jun. 8, 1999 for a CRYOSURGICAL PROBE WITH DISPOSABLE SHEATH (“the &#39;104 patent”), U.S. Pat. No. 5,275,595 issued Jan. 4, 1994 for a CRYOSURGICAL INSTRUMENT (“the &#39;595 patent”), and U.S. patent application Ser. No. 09/872,117 (“the &#39;117 application”), all assigned to CryoGen, Inc. of San Diego, Calif. are hereby expressly incorporated by reference in their entireties.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to devices and methods for the treatment of cardiac arrhythmia, and more specifically relates to devices and methods for the treatment of focal atrial arrhythmia using cryoablation.  
       BACKGROUND OF THE INVENTION  
       [0003]     Normal cardiac rhythm is maintained by precisely timed nerve signals conducted through cardiac tissue to electrically stimulate synchronous contractions of the four heart chambers (2 ventricles and 2 atria). In a normal rhythm, the nerve signals are typically conducted along paths initiating at the sino-atrial (SA) node and passing from there through the atrioventricular (AV) node and the bundle of His to the ventricular myocardial tissue.  
         [0004]     Abnormal cardiac rhythms, or arrhythmias, including atrial fibrillation, are potentially dangerous medical conditions which may result from disturbances in the site of origin and/or the pathways of conduction of the nerve impulses that excite contraction of the four chambers of the heart. The site of origin and pathways of conduction of these signals are currently mapped, for example using an electrocardiograph (ECG) in conjunction with mapping methods such as those described in U.S. Pat. No. 4,641,649 to Walinsky et al.  
         [0005]     One common type of abnormal atrial fibrillation occurs when the contraction initiating signals originate within one or more of the pulmonary veins, rather than at the SA node. These atrial arrhythmias have been treated by a variety of methods including pharmacologic treatments, highly invasive surgical procedures and linear and circumferential radio frequency (RF) ablations of the myocardial wall. However, each of these methods has drawbacks, e.g., the pain and extended recovery time for invasive surgery, relative ineffectiveness of pharmacologic treatments and restenosis at the ablation site due to the application of RF energy or other heat based therapies, and the necessity to repeat the ablation procedure to treat a sufficiently large area of tissue.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to systems and methods for ablating tissue of a patient. For the present invention, the system includes a substantially rigid sheath and an elongated cryoablation catheter that defines an axis. The catheter has an ablating distal section that includes a plurality of conductive bands, with each band establishing an enclosed chamber. For the cryoablation catheter, the ablating distal section is reconfigurable between a first configuration and a second configuration. In the first configuration, each band is positioned relatively near the axis to place the ablating distal section in a relatively compact configuration for transit through the sheath. On the other hand, when the ablating distal section is in the second configuration, each band is positioned relatively far from the axis. The second configuration is useful for ablating a circumferential band of tissue, for example, a band of tissue surrounding the opening (i.e. ostium) where a pulmonary vein connects with the left atrium.  
         [0007]     Once the ablating distal section is in the second configuration, the bands can be placed in contact with selected tissue and cooled to cryoablate the tissue. To cool the bands, a fluid refrigerant is expanded into each enclosed chamber. In greater detail, the fluid refrigerant can be passed through one or more orifices to expand the fluid and cool the bands.  
         [0008]     In a first embodiment of the system, the ablating distal section includes a plurality of cylindrical bands that are each centered on the catheter axis. A capillary tube that is positioned along the axis is formed with one or more orifices and establishes one or more chambers between the inner surface of each band and the outer surface of the capillary tube. Refrigerant is pumped through the capillary tube for outflow into the chamber(s) through the orifice(s). In one implementation, the plurality orifices are arranged along a line that is parallel to the axis, with a proximal orifice having a relatively large diameter and a distal orifice having a relatively small diameter. The remaining orifices (i.e. the orifices between the distal and proximal orifices) have diameters that progressively decrease, from orifice to orifice, in a distal direction. This cooperation of structure is provided to maintain a constant cooling rate along the ablating distal section.  
         [0009]     In the first, compact configuration that is useful for passing the ablative distal section through the sheath, the bands combine to form a cylinder and the capillary tube is substantially straight. On the other hand, in the second configuration, the bands combine to form a coiled structure and the capillary tube typically bends and becomes arcuate. To reconfigure the ablating distal section, a shape memory element which has an arcuate shape when unconstrained can be attached to the bands. With this cooperation of structure, the shape memory element can be deformed (e.g. elastically deformed) until it is straight or only slightly curved, placing the ablating distal section in the first, compact configuration. While the shape memory element is deformed, the ablating distal section can be inserted into and advanced through the sheath, where the sheath acts to constrain the shape memory element. When the ablating distal section exits the distal end of the sheath, the shape memory element becomes unconstrained and assumes its arcuate shape, reconfiguring the ablating distal section into the second, substantially coiled configuration. The coiled ablating distal section can then be used to cryoablate a circumferentially shaped band of tissue in a one-step process. Alternatively, a linear actuator (e.g. pull wire) having a distal end attached to the ablating distal section can be manipulated at an extracorporeal location to reconfigure the ablating distal section into a coiled configuration.  
         [0010]     In another embodiment of the system, the ablating distal section includes a plurality of arms with each arm extending from a proximal end to a distal end and having a hinge joint therebetween. For this embodiment, a band is mounted on each arm between the arm&#39;s hinge joint and arm&#39;s distal end. A linear actuator (e.g. pull rod) is attached to the distal end of each arm to proximally retract the distal end of each arm relative to the arm&#39;s proximal end. In the first configuration, each arm is somewhat straight and the bands are typically positioned very close to the catheter axis. When the rod is pulled, each arm bends at its respective hinge joint causing each band to move radially outward from the axis. This reconfigures the ablating distal section into the second configuration suitable for cryoablating tissue.  
         [0011]     In another embodiment, the ablating distal section includes a plurality of arms, with a band attached to the distal end of each arm. Each arm, when unconstrained, has an arcuate shape. Specifically, when unconstrained, the proximal end of each arm is positioned near the axis and the distal end of each arm deflects from the catheter axis to distance each band from the axis. With this cooperation of structure, the arms can be deformed (e.g. elastically deformed) until they are straight or only slightly curved, placing the ablating distal section in the first compact configuration. With the arms deformed, the ablating distal section can be inserted into and advanced through the sheath, with the sheath constraining the arms. When the ablating distal section is pushed out of the distal end of the sheath, the arms become unconstrained and assume their arcuate shape, reconfiguring the ablating distal section into the second, expanded configuration. With the ablating distal section expanded, the bands can be placed in contact with target tissue and cooled to cryoablate the contacted tissue.  
         [0012]     In one application of the present invention, the distal end of the sheath is inserted into a patient&#39;s vascular system and advanced into the right atrium. The interatrial septum is then pierced and the distal end of the sheath is passed through the septum and into the left atrium. In one implementation, the distal end of the rigid sheath is then maneuvered into a position proximal to a portion of the tissue to be ablated. Next, the distal end of a cryoablation catheter having an ablating distal section, such as one of the ablating distal sections described above, is pushed through the sheath until the ablating distal section is pushed out of the distal end of the sheath. For some embodiments, the ablating distal section reconfigures into an expanded, and in some cases coiled, second configuration as the ablating distal section exits the sheath (see discussion above). For other embodiments, a linear actuator (e.g. a pull wire or pull rod) can be activated once the ablating distal section exits the sheath to reconfigure the ablating distal section into an expanded, and in some cases coiled, second configuration.  
         [0013]     Once the ablating distal section has been placed in the second configuration, the bands are placed in contact with the tissue to be ablated and cooled. Specifically, a refrigerant is passed through the orifices in the ablating distal section to expand the refrigerant into the chamber(s) to cool the bands and contacted tissue. For example, the contacted tissue can be a circumferential band of tissue surrounding the opening (i.e. ostium) where one of the pulmonary veins connects with the left atrium.  
         [0014]     In another implementation, the sheath is formed with a curved distal portion. The curved distal portion is advanced into the left atrium after piercing the interatrial septum. Once in the left atrium, the distal portion of the sheath is maneuvered until the distal end is facing a selected pulmonary vein opening. Next, the ablating distal section of a cryoablation catheter is passed through the sheath and into the selected opening where the pulmonary vein connects with the left atrium. The bands are then placed in contact with the tissue to be ablated and cooled. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     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:  
         [0016]      FIGS. 1 and 1   a  are side elevation views showing an embodiment of a cryoablation catheter according to the present invention;  
         [0017]      FIGS. 2 and 2   a  are cross sectional views showing details of the embodiment shown in  FIG. 1 ;  
         [0018]      FIG. 3  is a cross sectional view on line III-III of the embodiment shown in  FIG. 1 ;  
         [0019]      FIG. 4  is a side view showing a second embodiment of the cryoablation catheter according to the present invention;  
         [0020]      FIG. 5  is a side view showing a third embodiment of the cryoablation catheter according to the present invention;  
         [0021]      FIG. 6  is a side view showing a fourth embodiment of the cryoablation catheter according to the present invention;  
         [0022]      FIG. 7  is a side view showing an embodiment of the device according to the present invention in position for penetrating the foramen ovale of a patient;  
         [0023]      FIG. 8  is a side view showing the device of  FIG. 7  in position with a dilator penetrating the opening in the foramen ovale;  
         [0024]      FIG. 9  is a side view showing the device of  FIG. 7  in position within a pulmonary vein; and  
         [0025]      FIG. 10  is a side view showing the device of  FIG. 7  in position within the pulmonary vein, with the catheter deployed.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals.  
         [0027]     In many cases, arrhythmia results from contraction initiating signals that originate within one or more of the pulmonary veins rather than from the SA node. Known techniques may be used to locate the point of origin of the aberrant signals, and their paths of conduction. Once these locations have been determined, the device and method according to the present invention may be employed to ablate a portion of tissue within the identified pulmonary vein between the source of the signals and the left atrium, e.g., near the opening or collar of the pulmonary vein, to create a circumferential conduction block within the pulmonary vein. This conduction block prevents the abnormal contraction originating signals from propagating into the left atrium to restore a normal contraction sequence.  
         [0028]     The present method and apparatus allows for ablation of an elongated strip of tissue (e.g. a linear ablation) and can reduce the number of applications required to create the circumferential conduction block, thereby reducing the time required to complete the procedure as well as the trauma to the patient.  
         [0029]      FIG. 1  shows a portion of the catheter according to the present invention that is placed in contact with a portion of tissue to be treated. The cryoablation device  100  in this exemplary embodiment is designed to extend from a sheath, not shown in  FIG. 1 , after the sheath has pierced the septum of the heart, and has been positioned near the tissue to be treated. Cryoablation device  100  includes a catheter  102  that may be extended and manipulated as more fully described in the &#39;657 patent.  
         [0030]     Catheter  102  may include a spiral portion  104  which may be shaped to match a surface of the portion of tissue to be ablated. In one exemplary embodiment, the spiral portion  104  is maintained in a straight configuration while received within the sheath, and deploys to the spiral configuration only after being pushed outside the sheath. A shape memory element  106  may urge the spiral portion  104  to assume the desired configuration once the spiral portion  104  has left the sheath and is no longer restrained thereby. Shape memory element  106  may, for example, be a stylet made of Nitinol, which can be both external or internal to the catheter  102 . In an exemplary use, the catheter  102  may be straightened by a user outside of the patient, before being introduced into the sheath, and remains straight while therewithin. Once the catheter  102  has been pushed out of the distal end of the sheath, the shape memory element  106  returns to its unconstrained shape, and causes the spiral portion  104  to assume the desired shape.  
         [0031]     The exemplary embodiment of the catheter  102  according to the present invention shown in  FIGS. 1 and 2  may also include a pull wire coupled to a distal end thereof and extending through the catheter  102  to a proximal end thereof so that, when a user pulls the pull wire proximally, the distal tip of the catheter  102  is pulled toward the shaft, to control the shape or size of the spiral portion  104 . As shown in  FIG. 1   a , pull wire  200  extends from a proximal end of the catheter  102  to the distal tip  126  of the spiral portion  104 . In one exemplary embodiment, pull wire  200  is attached to spiral portion  104  at a point  202  by welding or by another secure method. Pull wire  200  may be pulled proximally or released by an operator to control the size or diameter of spiral section  104 , to fit the orifice of a particular pulmonary vein. A tip union  204  may be included to provide a support for pull wire  200 , so that all the tension is applied to the spiral section  104 . Pull wire  200  may be contained within a tubular sheath  206 , which can resist compression along the length of pull wire  200 , but which allows bending of catheter  102 . The purpose of sheath  206  is to prevent bowing or snaking of catheter  102  when tension is applied to pull wire  200 . In one exemplary embodiment, sheath  206  may be formed by a coil spring.  
         [0032]     Cross referencing  FIGS. 1 and 2  shows that one or more thermally conductive bands  108  may also be included on the surface of catheter  102 . According to the exemplary embodiment of the invention, the bands  108  may preferably be made of a material that efficiently conducts heat, for example gold plated copper. As shown more clearly in  FIG. 2 , the catheter  102  may include a capillary tube or lumen  110  that extends from near the distal portion  112  of catheter  102  to a portion of the catheter  102  which remains outside the patient&#39;s body during use. The capillary tube  110  may be connected to a source of refrigerant fluid  114  that provides a flow of refrigerant fluid to the catheter  102 . The refrigerant fluid may be a hydrocarbon refrigerant, nitrous oxide, or a mixed gas refrigerant.  
         [0033]     The capillary tube  110 , in the exemplary embodiment shown in  FIG. 2 , includes a plurality of orifices  116 , each opening into a corresponding expansion chamber  118 . Expansion chambers  118  may be defined by an outer surface  120  of the capillary tube  110  and an inner surface  122  of the bands  108 . Those skilled in the art will understand that all of the orifices  116  may open into a single large expansion chamber  118  extending along the length of the spiral portion  104 . As will be understood by those of skill in the art, refrigerant fluid provided at high pressure within the capillary tube  110  expands through the orifices  116  creating a Joule Thompson cooling effect and lowering the temperature within the chamber  118 . Since the bands  108  are made of thermally conductive material while the rest of the surface of the catheter  102  is formed of thermally insulating material, the cooling from the Joule Thompson effect is substantially directed to the portion of the surface of the catheter  102  (i.e., the bands  108 ) that is in contact with the portion of tissue to be ablated.  
         [0034]      FIG. 3  shows a cross sectional view of catheter  102 , taken along line III-III of  FIG. 1 . An exemplary embodiment of an expansion chamber  118  is depicted, with orifices  116  opening through the capillary tube  110  to allow expansion of the refrigerant fluid therefrom. As the refrigerant fluid expands out of the orifices  116  into the chamber  118 , it cools down and in turn cools down bands  108 . Bands  108  are disposed along catheter  102  so that the tissue ablated by adjacent bands  108  overlaps to form a continuous strip of ablated tissue along the length of the spiral portion  104 . As shown in  FIG. 2 , in order to maintain a degree of cooling substantially equal along the length of the spiral portion  104 , the opening area of the orifices  116  decreases from a maximum size for the proximal-most orifice  116  to a minimum size of the distal-most orifice  116 . Thus, as would be understood by those of skill in the art, although the pressure in the capillary tube  110  decreases from the proximal-most orifice  116  to the distal-most orifice  116 , as the size of the openings is correspondingly decreased, the velocity of the refrigerant gas exiting the orifices  116  remains substantially the same, and thus, the cooling effect remains substantially constant along the length of the spiral portion  104 .  
         [0035]     In a different exemplary embodiment according to the present invention, the cooling along the length of the ablating distal section may be balanced by providing orifices  116  having the same dimensions, each having an independent supply of refrigerant fluid. For example, as shown in  FIG. 2   a , capillary tubes  110 ,  110 ′ and  110 ″ extend from a refrigerant source (not shown) to a single corresponding orifice  116 ,  116 ′ and  116 ″. Since each capillary tube  110 ,  110 ′ and  110 ″ only supplies refrigerant to one orifice  116 ,  116 ′ and  116 ″, the pressure of the refrigerant reaching each of the orifices,  116   116 ′ and  116 ″ is substantially the same, and the respective bands  108  undergo substantially the same amount of cooling.  
         [0036]     A conductive distal tip  126  may also be included in the catheter  102 , located at the most distal portion of the ablating section, according to an embodiment of the invention. Tip  126  may be used to ablate pinpoint portions of tissue, or may combine with the bands  108  to cryoablate an extended band of tissue around the circumference of the pulmonary vein in a single application. As described above, the tip  126  is cooled by refrigerant fluid from the capillary tube  110  expanded through a distal-most orifice  116 .  
         [0037]      FIG. 4  shows another exemplary embodiment of a cryoablation catheter according to the present invention. Catheter  402  is shown in a deployed configuration extending from a sheath  400 , in position adjacent to an opening  410  of a pulmonary vein  411 . The catheter  402  includes extensible arms  406  that deploy in an operative, basket-like, configuration as shown in  FIG. 4  when pushed out of sheath  400 . Arms  406  include conductive bands  412  that are cooled by expansion of a refrigerant fluid, as described above in regard to  FIGS. 1 and 2 . In the exemplary embodiment of  FIG. 4 , the distal ends of arms  406  are coupled to one another at a common joint  409 . A distal end of rod  407  is also connected to arms  406  at joint  409 , such that rod  407  can slide longitudinally with respect to sheath  400 . Thus, after the arms  406  have been moved distally out of the sheath  400 , an operator may deploy the arms  406  to the operative position by pulling the rod  407  proximally, to draw proximally the joint  409  where arms  406  are coupled to one another. This causes the arms  406  to bow outward radially from the axis of the catheter  402  so that the conductive bands  412  are spaced circumferentially and face distally toward the tissue to be ablated. In the operative position of arms  406 , conductive bands  412  are deployed in a two-dimensional or a three-dimensional array. For example, there can be four arms  406  in an orthogonal configuration, each with a conductive band  412 . A fifth conductive band  412  may be located centrally, at joint  409 .  
         [0038]     Once the arms  406  are deployed, the user advances the catheter  402  distally until the conductive bands  412  are in contact with the portion of tissue to be ablated. Cooling is initiated and maintained until the tissue adjacent to each of the conductive bands  412  is ablated. The user then allows the conductive bands  412  to return to body temperature so that they may be removed from contact with the tissue without harm thereto. If further ablation is required to complete a circumferential conduction block, the user rotates the catheter  402  around the axis thereof so that the conductive bands  412  are offset from their former positions, and the process is repeated until the circumferential conduction block is complete. Then, when the operation has been completed, the arms  406  may be returned to the collapsed configuration by simply withdrawing the catheter  402  into the sheath  400  or by extending rod  407  distally.  
         [0039]     As would be understood by those of skill in the art, the arms  406  may alternatively be deployed to the operative position by a stylet as described above, or by a different mechanism that may include shape memory and/or resilient elements as would be understood by those of skill in the art. As shown in  FIG. 4 , the device may, for example, include four arms  406  disposed equiangularly around the axis of the catheter  402 . However, those skilled in the art will understand that different configurations with more or fewer arms may be used.  
         [0040]     The exemplary embodiment shown in  FIG. 4  includes an occluding structure  408  that may be used to occlude the flow of blood through pulmonary vein  411 . In one embodiment, the occluding structure  408  may be a balloon inflated by providing an inflation fluid through an inflation lumen  401  of the catheter  402 . Once the catheter  402  has been properly positioned adjacent to the tissue to be treated, the occluding structure  408  is inflated to reduce or stop the flow of blood near the conductive bands  412 . This reduces the heat transfer between the blood, the inner surfaces of the pulmonary vein  411  and the conductive bands  412 . The expanding refrigerant fluid flowing in the capillary tube  110  is thus required to remove less heat to cool the tissue to a desired temperature, making the ablation process more efficient.  
         [0041]      FIG. 5  shows another embodiment of the cryoablation catheter according to the present invention. The catheter  502  is shown in the deployed configuration, after exiting sheath  500 . Deployable arms  504  are shown in the operative configuration, such that conductive bands  506  are spaced from the axis of the catheter  502 , azimuthally spaced from one another and facing a circumferential region of tissue to be ablated within the pulmonary vein  411 . As in the embodiments described above, in an initial configuration, the arms  504  are constrained within the sheath  500 , which is positioned near the tissue to be ablated. Once the desired position has been reached, the catheter  502  is pushed distally out of the sheath  500  and the arms  504  deploy under the force of, for example, memory shape elements such as those described above. Refrigerant fluid is then used to cool conductive bands  506 , as described above, to create a circumferential conduction block.  
         [0042]     An ablation element  600  according to a further embodiment of the invention shown in  FIG. 6  may be used as a stand alone medical device, for example, during open heart surgery to ablate selected portions of tissue to treat cardiac arrhythmias. Ablation element  600  may preferably be plastically deformable in this embodiment so that a user may bend the ablation element  600  into a desired shape which desired shape would be retained during use of the ablation element  600 . For example, the ablation element  600  may be formed of copper tubing so that it may be bent into a desired shape which shape will be retained during use. The ablation element  600  includes a capillary tube  602  that provides refrigerant fluid to the distal end of the ablation element  600  as described above in regard to the catheter embodiments. The capillary tube  602  includes a plurality of orifices  604  that permit the refrigerant fluid to expand out of the capillary tube  602  to cool the ablation element  600  to a desired temperature. The orifices  604  are disposed along the length of a portion of the capillary tube  602  facing a side of the ablation element  600  to be placed in contact with the tissue to be treated. As described above, the orifices  604  may be of different dimensions, for example, decreasing in size from a proximate portion of the ablation element  600  to a distal portion thereof, to compensate for decreasing pressure of the refrigerant fluid along the capillary tube  602 . As shown in  FIG. 6 , the orifice  604 ′ is the furthest from tip  608 , and has a larger diameter than orifice  604 ″, that is nearest to tip  608 .  
         [0043]     As described above, an outer surface  606  of the ablation element  600  may be formed of, for example, copper or another thermally conductive material. The outer surface  606  is cooled by the refrigerant fluid expanding within the chamber  616  to provide a substantially uniformly cooled cryoablation surface for ablating tissue. In one exemplary embodiment, an additional orifice  618  may be provided at a distal end of the capillary tube  602  to cool a distal tip  608  of the ablation element  600 . This allows a user to ablate specific points of tissue by applying the distal tip  608  thereto. Furthermore, the outer surface  606  may have a thermally insulating coating applied to predetermined portions thereof so that the cooling effect is substantially directed toward that portion of the outer surface  606  which is to contact the tissue to be ablated. For example, a coating of Pebax™ may be applied by RF fusion techniques to surfaces facing away from the orifices  604 . Alternatively, an insulating cover may be provided to surround selected portions of the ablation element  600  while leaving the tissue contacting portions of the outer surface  606  exposed. That is, as with the insulative coating described above, the insulating cover may cover parts of the ablation element  600  that are not intended to contact the tissue to be ablated. Thus, the insulating cover  610  concentrates the cooling effect of the expanding refrigerant fluid at the tissue contacting portions of the ablation element  600  thereby reducing the amount of cooling required. Furthermore, those of skill in the art will understand that an insulative coating or cover as described herein may also be employed in any of the previously described catheter-based embodiments.  
         [0044]      FIGS. 7-10  show a sequence of steps that may be used to introduce any of the cryoablation catheters described in regard to  FIGS. 1-5 , into the heart of a patient. Those skilled in the art will understand that, although the catheter illustrated more closely resembles the catheter  100  of  FIG. 1 , the same steps may be applied to use of any of the catheters of  FIGS. 1-5 . As shown in  FIG. 7 , a dilator  728  at the end of sheath  722  may include a Brockenbrough needle  730 . The assembly is inserted through a central lumen  723  of the rigid sheath  722  until a distal end of the dilator  728  extends beyond a distal end of the rigid sheath  722 . The user may then probe the interatrial septum noting the relative strength of various locations on the interatrial septum, until the precise location of the foramen ovale (FO) is determined (i.e., the FO forms a soft apical spot on the septum). Those skilled in the art will understand that intracardiac ultrasound may also be used to assist in locating the FO. Then the Brockenbrough needle  730  is extended from the distal end of the dilator  728  to pierce the FO forming a transeptal puncture (TP) extending into the left atrium (LA) as shown in  FIG. 7 . The dilator  728  is then advanced through the TP in the interatrial septum to expand a diameter of the TP as shown in  FIG. 8 .  
         [0045]     Thereafter, the Brockenbrough needle  730  is retracted into the dilator  728  and removed from the body. The rigid sheath  722  is then advanced along the dilator  728  to pass through the TP into the LA. A flexible section  712 , which may for example be constructed in accord with the teaching of the &#39;117 application, is then pushed along the rigid sheath  722  (utilizing the longitudinal rigidity of the flexible section  712 ) until a distal end of the flexible section  712  extends through the opening in the interatrial septum and into the LA, as shown in  FIG. 9 . The dilator  728  may then be removed from the patient.  
         [0046]     The ablation catheter  724  is then advanced distally through the rigid sheath  722  until the cryogenic tip  726  extends distally beyond the distal end of the rigid sheath  722  and the distal end of the flexible section  712 . Several known techniques may be used for maneuvering catheter  724  to a desired position within the opening of the one of the PV&#39;s from which the contraction origination signals are improperly originating. In certain embodiments, the catheter  724  is deflectable via a deflection mechanism associated with the catheter handle, which may ease the positioning of the catheter. Furthermore, by advancing the rigid sheath  722  further into the LA, a pre-formed bend in the tip of the rigid sheath  722  may be employed to assist in aiming the cryogenic tip  726  toward the desired PV opening. After the cryogenic tip  726  has been properly positioned well within the PV, the flexible section  712  is advanced distally along the ablation catheter  724  until the distal end of the flexible section  712  is near the orifice at which the PV opens into the LA. To aid in ensuring proper positioning of the cryogenic tip  726  and the flexible section  712  in the orifice of the PV, the flexible section  712  and the rigid sheath  722  may include radiopaque markers at the respective distal ends thereof, or at other desired locations.  
         [0047]     Once the flexible section  712  has been positioned near the opening of the PV, the user may inject contrast media into the PV via the flexible section  712 . The contrast media may exit the flexible section  712  via openings  736  of the flexible section  712 . This may be done to aid in locating, under fluoroscopic imaging, the orifice of the PV. The user may then inflate the balloon  718  to occlude the PV. In one embodiment, the inflation fluid may be a diluted contrast media solution such that the balloon  718  may more easily be seen under imaging. The flexible section  712  is then advanced until the balloon  718  is seated on the orifice of the PV, thereby occluding the flow of blood from the PV into the LA as shown in  FIG. 10 . The description herein of a balloon  718  does not imply that blood flow must be occluded by an inflatable cuff. Rather, any structure which is radially extendible to occlude blood flow will serve the purposes of this invention. There are many alternative constructions for this structure, which will be known to those skilled in the art.  
         [0048]     In the preceding specification, the present invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broadest spirit and scope of the present invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense. For example, while the invention has been described for use with PV ablation, the device may be used in other parts of the vascular system.  
         [0049]     While the particular cryoablation systems and methods 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.