Abstract:
A device and method for cryosurgical ablation. A tip has a thermally transmissive region along a length thereof in which the thermally transmissive region is operable at a temperature sufficient to cryosurgically ablate tissue in contact therewith. A plurality of cryosurgical fluid injection lumens each have a first end positioned within the tip at a different point along the length of the thermally transmissive region. Each of the first ends is arranged to cool overlapping respective portions along the length of the thermally transmissive region when cryogenic fluid is ejected from the plurality of cryogenic fluid injection lumens.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     n/a 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     n/a 
     FIELD OF THE INVENTION 
     The present invention relates to cryosurgical tissue ablation, and in particular, to a device and method which increases the effective freezing length in the device tip while simultaneously maintaining a usable device size and safe operating characteristics. 
     BACKGROUND OF THE INVENTION 
     Advances in medical procedures have resulted in the development of procedures which use minimally invasive surgical techniques such that one or more slender implements such as probes or catheters are inserted through one or more small incisions into a patent&#39;s body. These implements include surgical ablation implements having a rigid or flexible structure in which the ablation device is located at or near the implement&#39;s distal end that is placed adjacent to the tissue to be ablated. 
     Radio frequency energy, microwave energy, laser energy, extreme heat and extreme cold can be provided by the ablation device to kill the tissue. Certain procedures, such as cardiac procedures, are performed by selectively ablating the tissue. For example, in the case of a cardiac arrhythmia, the cardiac tissue is selectively ablated to eliminate the source of the arrhythmia. A popular minimally invasive procedure using radio frequency (RF) catheter ablation, has been used as has cryoablation in which the RF and cryogenic devices are arranged to provide very limited spot-sized lesions. As such, these conventional devices are not well suited for tissue ablation along a length, i.e. larger than a spot-sized lesion. 
     In order to achieve freezing ablation along a length using conventional devices, a series of spot ablation lesions are created by moving the device tip located at the distal end of the device along the length to be ablated. The device typically includes a single cryogenic fluid lumen. Use of this arrangement can be time consuming, thereby prolonging procedure duration, and can result in an uneven ablation, reducing the effectiveness of the procedure. It would therefore be desirable to have a cryosurgical device that provides enhanced cooling capability for spot lesions, as well as the capability to create other than spot lesions. 
     SUMMARY OF THE INVENTION 
     The present invention provides a device that provides enhanced cooling capability for spot lesions and the capability to create other than spot lesions, as well as a method for ablating tissue. In an exemplary embodiment the device includes a tip having a thermally transmissive region along a length thereof. The thermally transmissive region is operable at a temperature sufficient to cryosurgically ablate tissue in contact therewith. Fluid injection lumens are positioned within device so that the ends of the lumens are at different points along the length of the thermally transmissive region. Each of the ends are arranged to cool overlapping portions along the length of the thermally transmissive region when cryogenic fluid is ejected from the the fluid injection lumens. 
     In an exemplary method for cryosurgically ablating tissue, a cryosurgical tip is positioned at tissue to be ablated, the tip having a thermally transmissive region along a length thereof. Cryogenic fluid is sequentially injected into the tip through multiple cryogenic fluid injection lumens terminating within the tip at different points along the length of the thermally transmissive region. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a schematic illustration of a cryosurgical system utilizing a cryogenic cooling structure constructed in accordance with the principles of the present invention; 
     FIG. 2 is a diagram of a side view of an exemplar catheter arranged in accordance with the principles of the present invention; 
     FIG. 3 is a block diagram of an arrangement of longitudinally spaced injection lumens and their corresponding cryogenic fluid control valves; 
     FIG. 4 is a block diagram of an integrated fluid provisioning unit; 
     FIG. 5 is a block diagram of a two port cryogenic fluid valve assembly; 
     FIG. 6 is a cut away side view of an integrated fluid provisioning unit positioned within the inner volume of a handle; 
     FIG. 7 is a cut away side view of an alternate arrangement of the present invention of thumbscrews positioned within the inner volume of a handle; and 
     FIGS. 8A-E show diagrammatic views of the thermally transmissive tip region at various times during the sequential operation of the valves. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawing figures in which like reference designators refer to like elements, there is shown in FIG. 1 a schematic illustration of a cryosurgical system utilizing a cryogenic cooling structure constructed in accordance with the principles of the present invention. The system includes a fluid controller  10  coupled to the proximal end  12  of a catheter  14 . The controller  10  allows or causes cryogenic fluid to flow from a cryogenic fluid supply (not shown) through the proximal end  12  of the catheter  14  to a thermally transmissive tip region  16  positioned at the distal end of the catheter  14 . In operation, the fluid controller  10  is responsive to an input from a foot pedal or other human actuable switch to permit the flow of cryogenic fluid into the catheter  14 . One or more temperature sensors (not shown) in electrical communication with the controller  10  can be provided to regulate or terminate the flow of cryogenic fluid into the catheter  14  by a predetermined temperature at a selected point or points on or within the catheter such as in thermally transmissive region  16  is obtained. 
     The cryogenic fluid can be in a liquid or a gas state. An extremely low temperature can be achieved within the thermally transmissive region  16  by cooling the fluid to a predetermined temperature prior to its introduction into the catheter  14 , by allowing a liquid state cryogenic fluid to boil or vaporize, or by allowing a gas state cryogenic fluid to expand. 
     Exemplary liquids include chlorodifluoromethane, polydimethylsiloxane, ethyl alcohol, HFCs such as AZ-20 (a 50-50 mixure of difluoromethane and pentafluoroethane sold by Allied Signal), nitrous oxide, and CFCs such as DuPont&#39;s Freon. Exemplary gases include nitrous oxide and carbon dioxide. 
     FIG. 2 is a diagram of a side view of an exemplar catheter  14  arranged in accordance with the principles of the present invention. As shown in FIG. 2, the catheter  14  preferably includes an electrical connector  18  and a mechnaical connector  20  coupled to the thermally transmissive region  16  via a flexible segment  24 . 
     The electrical connector  18  is coupled to the controller  10  and provides external connection points for electronic signals such as cryogenic fluid valve activation signals, ECG signals, temperature sensing signals and the like. The cryogenic connector  20  preferably has an input opening  26  by which cryogenic fluid is input into the catheter  14  and a cryogenic output opening  28  by which the cryogenic fluid is evacuated from the catheter  14 . 
     The handle  22  is gripped by the user during operation and includes those control elements necessary for the user to “steer” the catheter inside the patient&#39;s body. Further, the handle  22  an be arranged to define an inner volume in which cryogenic fluid valves are located. The arrangement and operation of the cryogenic fluid valves are discussed below in detail. 
     Flexible segment  24  is generally arranged to include an outer fluid and gas impermeable sheath inside of which one or more flexible cryogenic fluid (or vapor) lumen are disposed for carrying the cryogenic fluid from the controller  10  to the thermally transmissive region  16  and returning it. Preferably, the outer flexible sheath includes a return lumen or defines a volume for use as the return path for cryogenic fluid from the thermally transmissive region  16  to the cryogenic output opening  28 . Arrangements for providing a cryogenic fluid return lumen or using all or a portion of an inner volume of the flexible segment  24  as a return path for cryogenic fluid are known. 
     In operation, the cryogenic fluid is provided via the controller  10  to the cryogenic fluid input opening  26 . By applying a negative pressure to the cryogenic output opening  28 , the cryogenic fluid is circulated through the handle  22 , through the flexible segment  24  to the thermally transmissive tip region  16  where the fluid expands, boils, etc., thereby cooling the thermally transmissive region  16 . The spent vapor is returned through the flexible segment  24 , through the handle  22  and out the cryogenic fluid output opening  28 . 
     The catheter  14  is preferably arranged to include a plurality of cryogenic fluid injection lumens having respective openings longitudinally spaced at different points along the length L of the thermally transmissive region  16 . As discussed below in detail, the plurality of injection lumens can be individually arranged to span the entire length of the catheter  14  from the input opening  26  to the thermally transmissive region  16  or can be arranged as a single injection lumen from the input opening  26  to a cryogenic fluid distribution element provided in the handle  22 . 
     FIG. 3 shows a block diagram of an arrangement of the plurality of longitudinally spaced injection lumens and their corresponding cryogenic fluid control valves. Initially, it is noted that although FIG.  3  and the subsequent figures are arranged to show two or four injection lumens, it is contemplated that any quantity of injection lumen can be used subject to the desired length of the thermally transmissive region  16 , the maximum acceptable diameter of the flexible segment  24  for a particular application and the cryogenic fluid input capacity of the system. 
     As shown in FIG. 3, the injection lumens  30   a,    30   b,    30   c  and  30   d  couple the cryogenic fluid valve assembly  32  to the thermally transmissive region  16  at the tip of catheter  14 . Each of the injection lumens  30   a - 30   d  terminate at a different point along length L within the thermally transmissive region  16  or the shaft  24 . For example, as shown in FIG. 3, the injection lumen  30   a  is the longest injection lumen, terminating substantially at the distal end of the catheter  14 . The injection lumen  30   b  is shorter than the injection lumen  30   a,  the injection lumen  30   c  is shorter than the injection lumen  30   b  and the injection lumen  30   d  is shorter than the injection lumen  30   c  such that it is positioned at a point along the length L within the thermally transmissive region  16  closer to the handle  22  than the injection lumens  30   a-c.    
     The cryogenic fluid valve assembly  32  is preferably comprised of an assembly fluid input  34  for each of the injection lumen (shown as assembly fluid inputs  34   a,    34   b,    34   c  and  34   d  in FIG. 3) in fluid communication with a corresponding assembly fluid output  36  (shown as assembly fluid outputs  36   a,    36   b,    36   c  and  36   d  in FIG. 3) via a corresponding valve  38  (shown as valves  38   a,    38   b,    38   c  and  38   d  in FIG.  3 ). Each of the assembly fluid outputs  36   a - 36   d  is coupled to and is in fluid communication with a corresponding injection lumen  30   a - 30   d.  Each of the valves  38   a - 38   d  are individually actuable by mechanical, electrical or electromechanical operation. 
     As shown in FIG. 3, the cryogenic fluid valve assembly  32  includes a valve processor  40  which receives n electronic actuation signals via the corresponding electronic actuation signal lines  42  and where n is the number of signal lines necessary to control actuation of the valves  38 . The valve processor  40  can be any processing unit capable of actuating the valves  38 . For example, the valves  38  can be arranged as piezo-electric valves which are actuable based on well-known piezo-electric principles. In this case, the valve processor  40  operates to control the piezo-electric effect necessary to actuate the valves  38 . The piezo-electric actuation method for the cryogenic fluid valve assembly  32  is preferred because the assembly  32  can be manufactured in a size small enough for placement within the handle  22  of the catheter  14 . Of course, those skilled in the art understand that any suitable method for actuating the valves  38  can be used. 
     Also as shown in FIG. 3, the cryogenic fluid path includes a cryogenic fluid distributor  44  having an input  46  and one or more outputs  48  (shown in FIG. 3 as outputs  48   a,    48   b,    48   c  and  48   d ) corresponding to assembly fluid inputs  34 . The cryogenic fluid distributor  44  is preferably made of any material which can withstand cryogenic fluid temperatures and which can be manufactured in a size small enough to be positioned within the handle  22  of the catheter  14 . In the case where the cryogenic fluid distributor  44  is positioned within the handle  22 , the input  46  is coupled to the cryogenic connector  20  by a tube suitable for carrying cryogenic fluid. 
     Although the cryogenic fluid valve assembly  32  and the cryogenic fluid distributor  44  are shown as separate elements in FIG. 3, it is contemplated that the cryogenic fluid valve assembly  32  and the cryogenic fluid distributor  44  can be provided as a single unit. FIG. 4 is a block diagram showing the integrated fluid provisioning unit  50  which includes the input  46 , the valves  38  and the assembly fluid outputs  36 . The integrated fluid provisioning unit  50  is preferably located within the inner volume of the handle  22  but can also be located in other system components such as the controller  10 . For example, the valves can be in a distal portion of the catheter. 
     Inclusion of the fluid distribution component, whether in the form of cryogenic fluid distributor  44  as shown in FIG. 3 or within the integrated fluid provisioning unit  50  as shown in FIG. 4, advantageously allows a single fluid connection between the catheter  14  and the controller  10 . 
     The present invention may also be arranged without the cryogenic fluid distributor  44  or the integrated fluid provisioning unit  50 . FIG. 5 shows an example of a two port cryogenic fluid valve assembly  32  having two assembly fluid inputs  34   a  and  34   b  and two assembly fluid outputs  36   a  and  36   b  coupled to corresponding injection lumens  30   a  and  30   b.  Valves  38  are not shown in FIG. 5 for the sake of simplicity, it being understood that the valves  38  are included as described above with respect to the cryogenic fluid valve assembly  32 . Using the arrangement shown in FIG. 5, corresponding input lumen  52  (shown in FIG. 5 as input lumens  52   a  and  52   b ) are required to couple the controller  10  to the catheter  14  (via the cryogenic connector  20 ). An arrangement similar to the cryogenic fluid valve assembly  32  shown in FIG. 5 is implemented in the case where the cryogenic fluid distributor  44  is positioned in the controller  10  and the cryogenic fluid valve assembly  32  is located in the handle  22 . 
     FIG. 6 shows a cut away side view of an example of an integrated fluid provisioning unit  50  positioned within the inner volume  54  of a handle  22 . As shown in FIG. 6, the injection lumens  30   a  and  30   b  couple the integrated fluid provisioning unit  50  to the thermally transmissive tip region  16 . A return lumen  56  is provided for evacuating the cryogenic fluid from the thermally transmissive tip region  16  for return to the fluid reservoir  10 . The return lumen  56  is coupled to the cryogenic output opening  28 , the electronic actuation signal lines  42  are coupled to the electrical connector  18  and the cryogenic fluid input  46  is coupled to the input opening  26 . 
     As discussed above with reference to FIGS. 3 and 4, it is contemplated that the cryogenic fluid distributor  44  and/or the cryogenic fluid valve assembly  32  can be located within the inner volume  54  of the handle  22 . 
     FIG. 7 shows a cut away side view of an alternate arrangement of the present invention in which the cryogenic fluid flow is manually actuated by thumbscrew valves  58   a  and  58   b.  As shown in FIG. 7, the human actuable portion of the thumbscrew valves  58   a  and  58   b  protrude through the outer surface of the handle  22   a  as thumbscrews  60   a  and  60   b,  respectively. The thumbscrew valves  58   a  and  58   b  are manually adjustable by the user via a corresponding thumbscrew  60   a  and  60   b  to open or close the cryogenic fluid path between the input lumens  52   a  and  52   b  and the corresponding injection lumen  30   a  and  30   b.  Although the arrangement using manually operated valves can be implemented, the preferable arrangement is using a processor controlled electronic or electro-mechanical switch. The reasoning behind this preference is discussed below in detail with respect to the sequential operation of the lumens  30  in the catheter  14 . 
     The operation of the catheter  14  is described with reference to FIGS. 8A-8E. Each of FIGS. 8A-8E show a diagrammatic view of the thermally transmissive tip region  16  at various times during the sequential operation of the valves  38   a - 38   d.  FIG. 8A shows the thermally transmissive tip region  16  at a state in which none of valves  38   a - 38   d  have been opened, i.e. cryogenic fluid is not flowing in the injection lumens  30   a - 30   d.  The freeze zones  62   a,    62   b,    62   c  and  62   d  show those areas on the surface of the thermally transmissive tip region  16  corresponding to the distal terminus of a corresponding injection lumen  30   a - 30   d.  It is noted that the freeze zones  62   a - 62   d  represent approximate areas along the surface of the thermally transmissive tip region  16  and do not correspond to actual elements. As such, the size and specific location of the freeze zones  62   a - 62   d  can vary and are substantially related to the corresponding distal terminus of the injection lumen  30   a - 30   d.    
     Upon actuation of the device, the valves  38   a - 38   d  are sequentially opened and closed. FIG. 8B shows cryogenic fluid in injection lumen  30   a  causing a freezing condition around the freeze zone  62   a.  As such, the area  64   a  on the exterior of the thermally transmissive tip region  16  is cooled by the ejection of the cryogenic fluid from the distal terminus of the injection lumen  30   a  such that the area  64   a  is cooled to an extent sufficient for the application of cryosurgical ablation. At a point t in time after the valve  38   a  is opened, the valve  38   a  is closed and the valve  38   b  is opened, causing cryogenic fluid to be ejected from the distal end of the injection lumen  30   b  in the thermally transmissive tip region  16 . As a result, the area  64   b  around the freeze zone  62   b  is created which overlaps the area  64   a  and is chilled to a point sufficient for cryosurgical ablation. 
     FIG.  8 D and FIG. 8E are diagrams showing the expansion of the freeze area to include overlapping areas  64   c  and  64   d  as a result of the sequential actuation of the valves  38   c  and  38   d,  respectively. As shown in FIG. 8E, the resultant freeze area occupies a length L along the thermally transmissive tip region  16 . 
     The freeze area along length L is advantageously accomplished by sequentially operating the valves  38   a - 38   d  in a manner which does not require an excessive cryogenic fluid flow rate which would otherwise create a positive pressure inside the catheter  14 . The sequential operation is preferably controlled by a microprocessor or other central processing unit to electronically instruct the valve processor  40  to sequentially actuate the valves  38   a - 38   d.  Electronic control using the valve processor  40  allows precise valve actuation control for sequencing and valve actuation duration. 
     For example, using a 7 French size catheter  14 , it has been found that 1300 cubic centimeters per minute of coolant can create a 28 millimeter long freeze area. By sequentially applying the 1300 cubic centimeter per minute coolant to each of the four injection lumens  30   a - 30   d  in a manner which causes an overlap of the freeze area, a freeze area of approximately 100 millimeters in length can be created. 
     As such, a freeze length L can be achieved using a very small cryogenic fluid flow rate as compared with known devices (3800 cubic feet per minute to achieve a 60 millimeter freeze length using a single injection lumen versus 1300 cubic centimeter per minutes cryogenic fluid flow rate to achieve a 100 millimeter freeze length L). The arrangement of the present invention advantageously conserves cryogenic fluid while providing an extended freeze length L as compared with known similarly sized devices. 
     As eluded to above, in order to preserve the advantage of cryoablation by adhering the thermally transmissive tip region  16  to the patient&#39;s tissue during the ablation procedure, the ejection of cryogenic fluid from one injection lumen should begin after cryogenic fluid ejection is terminated in the previous injection lumen in the sequence, but before the previous areas dislodge, i.e. thaw, from the tissue. Because the sequential application of cryogenic fluid is used, the total procedure time becomes t times m where m is the number of freezing areas (and injection tubes). 
     It is also contemplated that multiple lumens can be logically grouped and activated at substantially the same time, subject to maintaining a cryogenic fluid flow rate which can be evacuated from the catheter  14  while maintaining a negative pressure within the catheter  14 . For example, valves  38   a  and  38   c  can be opened at substantially the same time, then closed and valves  38   b  and  38   d  opened at substantially the same time. This technique shortens the cryoablation procedure time as compared with the discreet sequential operation of the valves  38   a - 38   d  described above while still maintaining a safe operating environment, for example, 2600 cubic centimeters per minute in a 7 French size catheter. 
     Another implementation of the device of the present invention permits use as a mapping and/or selective ablation zone device. Because the freeze area length along the tip of the device is extremely elongated as compared with known devices and because particular areas of the device can be selectively cooled (areas  64   a - 64   d ), the device of the present invention can be used to perform cold mapping to detect tissue regions, such as cardiac tissue regions, which if ablated will eliminate an arrhythmia. Each of areas  64   a - 64   d  can be cooled to determine which areas, if any, will improve or eliminate the arrhythmia. 
     The elongated freeze length L advantageously allows individual areas to be cooled without the need to relocate the thermally transmissive tip region  16  to another tissue point. Once an area is identified as suitable for ablation, the particular valve or valves  38  are opened and the specific section(s) of the thermally transmissive tip region  16  cooled. This arrangement advantageously minimizes tissue destruction such as myocardial tissue destruction and saves time by avoiding the need to repeatedly thaw and relocate the thermally transmissive tip region  16 . 
     Although the present invention is described above with respect to a catheter, it is contemplated that a device constructed in accordance with the principles of the present invention can take other forms, including but not limited to a rigid probe. 
     The present invention advantageously provides a device and method which provides an elongated freeze length within the thermally transmissive tip region in a manner in which specific areas in the thermally transmissive tip region can be cooled or sequentially cooled to provide an elongated freeze length. The arrangement of the present invention is advantageously provided in a manner which maintains a usable device size and which maintains a safe operating mode by maintaining a negative pressure within the device. 
     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.