Abstract:
A method for purging a cryotreatment system, in particular, for clearing moisture and thus preventing ice blockages within a fluid flow path that may be formed when moisture pockets within the fluid flow path of the system are encountered by a first injection of refrigerant at the beginning of a cryotreatment procedure. The method may include injecting refrigerant from a refrigerant source into a fluid delivery conduit at a preselected pressure for a first period of time, the refrigerant flowing from the fluid delivery conduit through a fluid injection element and into a fluid recovery conduit, and evacuating refrigerant from the fluid recovery conduit by vacuum pressure generated by the vacuum pump for a second period of time. This method may be repeated for a plurality of cycles.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    n/a 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    n/a 
       FIELD OF THE INVENTION 
       [0003]    The present invention relates to a method and system for purging refrigerant pathways of moisture immediately prior to cardiac procedures. 
       BACKGROUND OF THE INVENTION 
       [0004]    Cryoablation systems are frequently used for treating tissue in a cardiac setting, either to cool the tissue sufficiently to stun it and allow cold mapping of the heart and/or confirmation of catheter position with respect to localized tissue lesions. Additionally, such systems may be used to apply a more intense cold to ablate an area of target tissue, for example, tissue that has been identified as propagating an aberrant electric current in cases of cardiac arrhythmia. 
         [0005]    In general, when used for endovascular access to treat the cardiac wall, cryoablation catheters must meet fairly demanding limitations regarding their size, flexibility, and the factors of strength, electrical conductivity and the like. These constraints generally require that the catheter be no larger than several millimeters in diameter so as to pass through the vascular system of the patient to the heart. Thus, any electrodes and refrigerant passages must fit within a catheter body of small size. 
         [0006]    A number of different fluids have been used for the refrigerant component of prior art cryotreatment catheters, such as a concentrated saline solution or other liquid of suitably low freezing point and viscosity, and of suitably high thermal conductivity and heat capacity, or a liquified gas such as liquid nitrogen. In all such constructions, the refrigerant must circulate through the catheter, thus necessitating multiple passages leading to the cooling area of the tip from the catheter handle. In some systems, a phase change refrigerant is used that travels through the body of the catheter at a relatively normal or ambient temperature and attains cooling only upon expansion within a chamber at the tip region. In some systems, pressurized gas travels through the body of the catheter and into a spray nozzle in a cooling chamber at the tip region, where cooling is achieved by the Joule-Thomson effect when the gas expands. Due to the size limitations on the device as a whole, however, the outlet holes of the spray nozzle or other fluid injection outlets are necessarily very small. Consequently, the outlet holes easily become clogged or blocked, which may lead to failure at the beginning of a cardiac procedure. 
         [0007]    One cause of blockage in the cryoablation system may be ice formation that occurs at the first fluid injection at the beginning of a cardiac procedure. Ambient humidity may creep into the system, for example, the refrigerant injection lumen, refrigerant recovery lumen, and/or injection apertures. This ambient humidity may create pockets of moisture within the system that rapidly become frozen when the refrigerant is first injected into the system at the beginning of a new cardiac procedure, creating ice blockages within the system. When this occurs, the system must be thawed and purged before the procedure may take place, and this delay may have disastrous effects. The small holes of an injection nozzle are particularly susceptible to retaining moisture and becoming blocked with ice. 
         [0008]    Moisture pockets generated by ambient humidity within the system must be addressed immediately before a cardiac procedure. New moisture pockets may develop in a short period of time, and therefore may be present at the beginning of a procedure even if the system was purged within a few hours of the procedure. However, presently known purging processes are inefficient or take too long, thus also contributing to a delay in urgent cardiac procedures. 
         [0009]    Accordingly, a cryoablation system purging process is desired that is efficient and effective, and can be performed quickly immediately prior to the beginning of a cardiac procedure. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention advantageously provides a method and system for purging a cryotreatment flow path. In particular the method is for purging moisture and thus preventing ice blockages that may occur within a fluid flow path when moisture pockets within the fluid flow path of the system are encountered by a first injection of refrigerant at the beginning of a cryotreatment procedure. The method may generally include (a) providing a cryotreatment system including a refrigerant source, a fluid delivery conduit in fluid communication with the refrigerant source, a fluid injection element in fluid communication with the fluid delivery conduit, a fluid recovery conduit in fluid communication with the fluid injection element, and a vacuum pump in fluid communication with and providing a low pressure environment within the fluid recovery conduit, (b) injecting refrigerant from the refrigerant source into the fluid delivery conduit at a preselected pressure for a first period of time, the refrigerant flowing from the fluid delivery conduit through the fluid injection element and into the fluid recovery conduit, and (c) evacuating refrigerant from the fluid recovery conduit by vacuum pressure generated by the vacuum pump for a second period of time. Steps (b) and (c) may be performed a plurality of times (for example, each of Steps (b) and (c) may be performed four times. The first period of time is approximately 2 seconds and the second period of time is approximately 1 second. the predetermined pressure is between approximately 250 psi and approximately 350 psi, in particular, approximately 300 psi. 
         [0011]    In one embodiment, the method may include (a) providing a cryotreatment system defining a fluid flow path including a fluid delivery conduit in fluid communication with a refrigerant source, a cryotreatment device having a balloon defining a lumen, a fluid injection element in fluid communication with the fluid delivery conduit and being disposed within the balloon lumen, a fluid recovery conduit in fluid communication with the balloon lumen, a vacuum pump in fluid communication with and providing a low pressure environment within the fluid flow path, and a compressor in fluid communication with the fluid recovery conduit and the fluid delivery conduit. The method may further include (b) injecting compressed refrigerant from the refrigerant source into the fluid delivery conduit at a pressure of between approximately 250 psi and approximately 350 psi for approximately two seconds, the compressed refrigerant flowing from the fluid delivery conduit through the fluid injection element and into the balloon lumen where the compressed refrigerant expands, the expanded refrigerant then flowing into the fluid recovery conduit, (c) evacuating the expanded refrigerant from the fluid recovery conduit into the fluid recovery conduit by low pressure generated by the vacuum pump for approximately one second, (d) directing the expanded refrigerant into the compressor and recompressing the expanded refrigerant, the compressor becoming the refrigerant source, and (d) repeating (b) and (c) for a plurality of additional cycles. 
         [0012]    In another embodiment, the method may include (a) providing a cryotreatment system defining a fluid flow path including a refrigerant source, a fluid delivery conduit in fluid communication with the refrigerant source, a cryotreatment device having an elongate body, a balloon defining a lumen and a shaft having at least a portion disposed within the elongate body and at least a portion disposed within the balloon lumen, a fluid injection element in fluid communication with the fluid delivery conduit and being disposed about at least a portion of the shaft within the balloon lumen, a fluid recovery conduit in fluid communication with the balloon lumen, a fluid recovery reservoir in fluid communication with the fluid recovery conduit, and a vacuum pump in fluid communication with and providing a low pressure environment within the fluid recovery reservoir. The method may further include (b) injecting refrigerant from the refrigerant source into the fluid delivery conduit at a pressure of between approximately 250 psi and approximately 350 psi for approximately two seconds, the refrigerant flowing from the fluid delivery conduit through the fluid injection element, into the balloon lumen, and then into the fluid recovery conduit, evacuating refrigerant from the fluid recovery conduit into the fluid recovery reservoir by vacuum pressure generated by the vacuum pump for approximately one second, and repeating (b) and (c) for three additional cycles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
           [0014]      FIG. 1A  shows a cryoablation system that may be purged using a method described herein; 
           [0015]      FIG. 1B  shows a close-up view of a fluid injection nozzle having a plurality of openings or apertures; 
           [0016]      FIG. 2  shows a first embodiment of a fluid flow path of a cryoablation system; 
           [0017]      FIG. 3  shows a second embodiment of a fluid flow path of a cryoablation system; and 
           [0018]      FIG. 4  shows a flow chart of a method for purging a cryoablation system of moisture. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring now to  FIGS. 1-3 , a cryoablation system  10  that may be purged using a method described herein is shown. The cryoablation system  10  may be used with any type of cryosurgical device  12  having a fluid injection means; however, a typical cryoballoon catheter having a fluid injection nozzle  14  in an expansion chamber is shown. The expansion chamber may be within an expandable element, such as a cryoballoon  16  and cryoballoon lumen  18 , as shown in  FIG. 1A . Alternatively, if a focal catheter is used that does not include an expandable element, the expansion chamber may be within a lumen within the catheter that is in thermal communication to a treatment element at, for example, the distal portion of the catheter. The system  10  generally includes a medical device  12  that may be coupled to a control unit or operating console  20 . The medical device  12  may generally include one or more treatment regions, for example, one or more cryoballoons  16 , for energetic or other therapeutic interaction between the medical device  12  and a treatment site. Although the system  10  described herein is used at least for cryogenic treatments, the system  10  may also be configured to deliver, for example, radiofrequency energy, microwave energy, ultrasound energy, or provide other energetic transfer with a tissue area in proximity to the treatment regions, including cardiac tissue. 
         [0020]    The medical device  12  may include an elongate body  22  passable through a patient&#39;s vasculature and/or proximate to a tissue region for diagnosis or treatment, such as a catheter, sheath, or intravascular introducer. The elongate body  22  may define a proximal portion  24  and a distal portion  26 , and may further include one or more conduits  28 ,  30  disposed within the elongate body  22  thereby providing fluid, mechanical, and/or electrical communication between the proximal portion  24  of the elongate body  22  and the distal portion  26  of the elongate body  22 . 
         [0021]    The medical device  12  may include a shaft  32  at least partially disposed within a portion of the elongate body  22 . The shaft  32  may extend or otherwise protrude from a distal portion  26  of the elongate body  22  and into the lumen  18  of the cryoballoon  16 , and may be movable with respect to the elongate body  22  in longitudinal and rotational directions. That is, the shaft  32  may be slidably and/or rotatably moveable with respect to the elongate body  22  (as depicted by the double-headed arrow in  FIG. 1A ). However, the movement of the shaft  32  may not have any impact on the purging process shown and described in  FIG. 2 . 
         [0022]    The medical device  12  may further include a fluid delivery conduit  28  traversing at least a portion of the elongate body  22 , from the proximal portion  24  to the distal portion  26 . The fluid delivery conduit  28  may be coupled to or otherwise extend from the distal portion  26  of the elongate body  22 , and may further be coupled to the shaft  32  of the medical device  12 . For example, the fluid delivery conduit  28  may have a distal portion  34  and a proximal portion  36 , and the distal portion  34  may be coiled or wound about a portion of the shaft  32  within the cryoballoon lumen  18 , as shown in  FIG. 1A  and in greater detail in  FIG. 1B . Alternatively, if a focal catheter is used, the fluid delivery conduit may be disposed within a lumen of the catheter. The fluid delivery conduit  28  may define a lumen therein for the passage or delivery of a fluid from the proximal portion  24  of the elongate body  22  and/or the console  20  to the distal portion and/or treatment region of the medical device  12 . For example, the proximal portion  36  of the fluid delivery conduit  28  may be in fluid communication with a fluid reservoir or refrigerant source  38  and the distal portion  34  of the fluid delivery conduit  28  may be within the cryoballoon lumen  18  and include one or more apertures or openings  40  to provide for the dispersion or directed ejection of fluid from the fluid delivery conduit  28  to the cryoballoon lumen  18 . These apertures or openings  40  may be particularly susceptible to ice blockages. 
         [0023]    The medical device  12  may further include a fluid recovery conduit  30  traversing at least a portion of the elongate body  22 , from the distal portion  26  to the proximal portion  24 . The fluid recovery conduit  30  may define a distal portion  44 , a proximal portion  46 , and a lumen for the passage or delivery of a fluid from the distal portion  26  of the elongate body  22  to the proximal portion  24  of the elongate body  22 . For example, the distal portion  44  of the fluid recovery conduit  30  may be in fluid communication with the cryoballoon lumen  18 , from where expanded refrigerant may enter the fluid recovery conduit  30  through an opening or aperture  48  within the fluid recovery conduit  30 . The proximal portion  46  of the fluid recovery conduit  30  may be in fluid communication with a fluid recovery reservoir  50  and vacuum pump  52 . 
         [0024]    The medical device  12  may include a handle  54  coupled to the proximal portion  24  of the elongate body  22 . The handle  54  can include circuitry for identification and/or use in controlling of the medical device  12  or another component of the system  10 . For example, the handle  54  may include one or more pressure sensors to monitor the fluid pressure within the medical device  12 . The handle  54  may also include connectors  56  that are matable directly to the fluid reservoir  38 , fluid recovery reservoir  50 , and console  20  or indirectly by way of one or more umbilicals  58  (which may be part of the fluid delivery and recovery conduits). The handle  54  may further include blood detection circuitry in fluid and/or optical communication with the fluid delivery conduit  28  and fluid recovery conduit  30 . The handle  54  may also include a pressure relief valve in fluid communication with the fluid delivery conduit  28  and/or fluid recovery conduit  30  to automatically open under a predetermined threshold value in the event that value is exceeded. 
         [0025]    The system  10  may further include one or more sensors to monitor the operating parameters throughout the system  10 , including for example, pressure, temperature, flow rates, volume, or the like in the console  20  and/or the medical device  12 , in addition to monitoring, recording or otherwise conveying measurements or conditions within the medical device  12  or the ambient environment at the distal portion of the medical device  12 . The one or more sensors may be in communication with the console  20  for initiating or triggering one or more alerts or therapeutic delivery modifications during operation of the medical device  12 . One or more valves, controllers, or the like may be in communication with the one or more sensors to provide for the controlled dispersion or circulation of fluid through the fluid flow path (also referred to as a “fluid pathway”) of the medical device  12 . Such valves, controllers, or the like may be located in a portion of the medical device  12  and/or in the console  20 . 
         [0026]    The system  10  may further include one or more compressors and/or condensers, generally indicated as  60 , to compress recovered expanded refrigerant for reuse during the purge process and/or cryosurgical procedure. In such an embodiment, such as is shown in  FIG. 2 , the fluid pathway  62  of the system  10  may be referred to as a closed loop configuration. Fluid may flow from the refrigerant source  38 , into the fluid delivery conduit  28 , into the fluid injection nozzle  14  (or other fluid injection element) into the expansion chamber (for example, a cryoballoon lumen  18 , as shown in  FIG. 1A ), into the fluid recovery conduit  30 , and through the one or more compressors and/or condensers  60 , at which point the recovered refrigerant may be compressed and/or conditioned for reuse. Finally, the compressed and/or conditioned refrigerant may then flow back into the fluid delivery conduit  28 . In an embodiment in which the recovered refrigerant is not reused, such as is shown in  FIG. 3 , the fluid pathway  62  of the system  10  may be referred to as an open-loop configuration. In this embodiment, fluid may flow from the refrigerant source  38 , into the fluid delivery conduit  28 , into the fluid injection nozzle  14  (or other fluid injection element) into the expansion chamber (for example, a cryoballoon lumen  18  as shown in  FIG. 1A ), into the fluid recovery conduit  30 , and into the fluid recovery reservoir  50 . The recovered refrigerant may then be discarded. 
         [0027]    In an exemplary system, a fluid supply  60  including a coolant, cryogenic refrigerant, or the like, an exhaust or scavenging system for recovering or venting expended fluid for re-use or disposal, as well as various control mechanisms for the medical system  10  may be housed in the console  20 . In addition to providing an exhaust function for the catheter fluid supply, the console  20  may also include pumps, valves, controllers or the like to recover and/or re-circulate fluid, the elongate body  22 , and/or the fluid pathways of the medical device  12 . A vacuum pump  62  in the console  20  may create a low-pressure environment in at least the fluid recovery conduit  30  so that fluid is drawn into the fluid recovery conduit  30 , away from the distal portion  26  and towards the proximal portion  24  of the elongate body  22 . The fluid delivery conduit  28  and fluid recovery conduit  30  may be releasably coupled to the fluid reservoir  38  (such as a refrigerant source) and fluid recovery reservoir  50 , respectfully, so that the reservoirs  38 ,  50  may be changed or replaced. The console  20  may include one or more controllers, processors, and/or software modules containing instructions or algorithms to provide for the automated operation and performance of sequences or procedures. 
         [0028]    While the medical device  12  may be in fluid communication with a refrigerant source  38  to cryogenically treat selected tissue, it is also contemplated that the medical device  12  may alternatively or additionally include one or more electrically conductive portions or electrodes thereon coupled to a radiofrequency generator or power source as a treatment or diagnostic mechanism. 
         [0029]    Referring now to  FIG. 4 , a flow chart of a method for purging a cryoablation system  10  of moisture is shown. The purge process may flush moisture from the fluid flow path and thus prevent any blockage due to ice formation within the system  10  that occurs at the initial refrigerant injection at the beginning of a procedure, for example, a cardiac procedure such as cryablation. In one study, for example, the failure rate associated with obstructed flow at first refrigerant injection was approximately 0.46%. The blockage may occur at any point within a fluid pathway of the system  10 , including umbilicals, fluid injection conduit, fluid injection nozzle  14  apertures, and fluid recovery conduit  30 . 
         [0030]    Although  FIG. 4  includes four cycles, the purge process may comprise more than four cycles. In each cycle, nitrous oxide or other refrigerant may be injected from the fluid reservoir  38  (such as a refrigerant source) into the fluid delivery conduit  28  at a high pressure that evacuates or flushes any humidity or moisture within the fluid pathway. For example, the nitrous oxide or other refrigerant may be injected at a pressure of between approximately 250 psi to approximately 350 psi, which is lower than the minimum injection pressure used during a cryoablation procedure. 
         [0031]    In the first step of the purge process, the proximal portion  36  of the fluid delivery conduit  28  may be connected to a refrigerant source  38  via one or more umbilicals  58  (which may be part of the fluid delivery and recovery conduits) and/or connecting means  56 . Likewise, the proximal portion of the fluid recovery conduit  30  may be connected to a fluid recovery reservoir  50  under vacuum pressure via one or more umbilicals  58  (which may be part of the fluid recovery and delivery conduits) and/or connecting means  56 . This may establish a fluid pathway  62  from, generally, the refrigerant source  38 , into the fluid delivery conduit  28 , through the fluid injection nozzle  14  (or other fluid injection element), into the fluid recovery conduit  30 , and into the fluid recovery reservoir  50 . 
         [0032]    In the second step of the purge process, nitrous oxide or other refrigerant from the fluid reservoir  38  (such as a refrigerant source) may be injected into the fluid delivery conduit  28 . The refrigerant may be injected at a pressure of 300 psi for a period of approximately 2 seconds. The refrigerant is injected into the fluid pathway  62  at a lower pressure than the injection pressure used in a cryoablation procedure. As such, the refrigerant flushes moisture or humidity from the fluid pathway  62  and thus prevents ice blockages from forming when refrigerant is later injected at a normal procedure pressure (as a non-limiting example, normal procedure pressure may be between approximately 400 psi and 800 psi). Refrigerant injected into the fluid delivery conduit  28  flows into the fluid injection nozzle  14  (or other fluid injection element) and into the cryoballoon lumen  18 . 
         [0033]    In the third step of the purge process, the nitrous oxide or other refrigerant may be evacuated from the fluid recovery conduit  30  under vacuum pressure for approximately 1 second. In this step, refrigerant from the cryoballoon lumen  18  may be drawn in to the fluid recovery conduit  30  under vacuum pressure, from where it is collected in a fluid recovery reservoir  50 . The recovered fluid may be discarded or it may be compressed and/or conditioned by one or more compressors and/or condensers  60  for reuse in a subsequent cycle. 
         [0034]    In the fourth step of the purge process, Steps 2 and 3 are repeated for a plurality of cycles. For example, Steps 2 and 3 may each be performed four times each. At the end of the purging process, the fluid pathway of the system  10  may be clear of moisture, and the system  10  may be ready for performing a medical procedure without the risk of ice blockages occurring at the initial injection of refrigerant. The entire purge process may take far less than one minute. Therefore, the purge process described herein may reduce the delay required by presently known purging processes and may eliminate the delay caused by injection failure due to ice blockages in the flow path of the system  10 . Thus, medical procedures such as cryosurgical procedures may be performed quickly and efficiently. 
         [0035]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.