Patent Publication Number: US-2009221955-A1

Title: Ablative ultrasonic-cryogenic methods

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/845,220 filed Aug. 27, 2007. 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/463,187, filed Aug. 8, 2006, which is now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ablative apparatus and methods that can be used to treat atrial fibrillation and/or other cardiac arrhythmias by ablating cardiac tissue. 
     2. Description of the Related Art 
     Accounting for one-third of the hospitalizations for cardiac arrythmia, atrial fibrillation (AF) is the most common arrhythmia (abnormal beating of the heart) encountered in clinical practice. (ACC/AHA/ESC Guidelines for the Management of Patients With Atrial Fibrillation) AF is a specific type of arrhythmia in which an abnormal beating of the heart originates in one of the heart&#39;s two atrium. Increasing in prevalence, an estimated 2.2 million Americans suffer from AF. (ACC/AHA/ESC Guidelines for the Management of Patients With Atrial Fibrillation) Underlying one out of every six strokes, AF doubles the rate of morbidity compared to patients with normal sinus rhythm. (ACC/AHA/ESC Guidelines for the Management of Patients With Atrial Fibrillation) Further increasing the clinical severity, the presence of AF leads to functional and structural changes in the atrial myocardium (cells responsible for the beating of the heart) that favors its maintenance. As such, AF is a serious disorder requiring medical intervention. 
     Administering drugs that alter the electrical properties of atrial myocardium has been effective in treating less severe cases of AF. (Hurst&#39;s the heart, page 836) However, such drugs often lead to the creation of pro-arrhythmic conditions thereby resulting in the treatment of one type of arrhythmia only to create another. Due to the increased risk of stroke, it is advised that all patients with AF, despite the successfulness of drug therapy, be prescribed warfarin or other anticoagulants to inhibit the formation of blood clots. (Hurst&#39;s the heart, page 833) Besides being difficult to dose, warfarin has several complications associated with its long term use. Altering the metabolism of other drugs, warfarin is known to induce several adverse interactions with other medications commonly prescribed to elderly patients, who are at increased risk of developing AF. 
     AF originates in regions of myocardium contracting, or beating, out of step with the rest of the heart. Heart cells contract in response to electrical stimulation. In a healthy heart, the electrical stimulation signaling contraction originates from the sinus node (the heart&#39;s natural pace maker) and spreads in an organized manner across the heart. In a heart plagued with AF, a region of myocardium elicits a mistimed contraction, or heart beat, on its own or in response to an electrical signal generated from somewhere other than the sinus node. Generating an electrical signal, the mistimed contraction spreads across the heart, inducing contractions in neighboring regions of the heart. Inducing the formation of scar tissue on the heart by ablating, cutting, or otherwise injuring tissue in regions in which AF originates has been shown to be affective in treating AF. The logic behind this treatment is to terminate AF by removing the heart cells responsible for its presence, while preserving healthy cells. Creating scar tissue barriers as to prevent the spread of electrical signals from mistimed contractions has also been shown to be effective in treating AF. (Hurst&#39;s the heart, page 838) 
     Successful surgical intervention eliminates the need for continued warfarin treatment in most patients. (Hurst&#39;s the heart, page 839) Initially surgical treatment was reserved for patients undergoing additional cardiac surgery, such as valve repair or replacement. (Hurst&#39;s the heart, page 838) The high success rate and efficacy of surgical intervention in the treatment of AF has spurred the development of cardiac catheters capable of therapeutically ablating cardiac tissue without the need for open chest or open heart surgery. 
     Heart surgery preformed by means of catheter involves, in it basic conception, the insertion of a catheter either into a patient&#39;s vein or chest cavity. The catheter is then advanced to the heart. When the catheter is inserted into a patient&#39;s vein, the catheter is advanced into one of the heart&#39;s four chambers. When the catheter in inserted into a patient&#39;s chest, the catheter is advanced to the outer walls of the patient&#39;s heart. After the catheter reaches the patient&#39;s heart the surgeon utilizes the catheter to ablate, damage or, kill cardiac tissue. The ideal catheter induced lesion is one that is created from the epicardium (outside) of the beating heart, is able to go through epicardial fat, is performed rapidly over variable lengths, is transmural, causes no collateral injury, and can be applied at any desired anatomic location. (Williams et al., 2004) Ablating cardiac tissue by heating the tissue to 50 degrees Celsius has become the preferred means of inducing lesions (Williams et al., 2004). Cardiac catheters employing a variety of thermal ablative energy sources have been developed, none of which are capable of inducing an ideal lesion. 
     Catheters utilizing radio frequency as an ablative energy source, the current gold standard, are incapable of creating an ideal lesion. (Cummings et al., 2005) In particular, radio frequency catheters have a difficult time creating ablations through the epicardial fat surrounding the heart. Furthermore, inducing deep lesions with radio frequency is not possible without inflicting collateral damage from surface burning and steam popping. (Cummings et al., 2005) Steam popping is the phenomenon in which cells become heated to such a point their internal fluids begin to boil, producing steam that bursts the cell. Simultaneously cooling the site of radio frequency administration reduces the incidence of surface burns but does not reduce the risk of steam popping. (Cummings et al., 2005) In an effort to overcome the shortcomings of radio frequency induced lesions, catheters employing novel energy sources have been developed. 
     In hopes that microwaves would provide sufficiently deep lesions, catheters employing microwaves as an ablative energy source have been developed. Because the penetration of microwaves into tissue has a steep exponential decline, it has been found necessary to bring the catheter into close contact with the tissue in order to induce deep lesions. (Cummings et al., 2005) Furthermore, fat continues to be a significant barrier. (Williams et al., 2004) 
     Lasers have also been applied as an ablative energy source within catheters. Although high powered lasers carry a high risk of crater formation at the site of application, low energy lasers produce lesions with a depth related to the duration of application. (Cummings et al., 2005) 
     Capable of penetrating fat and inducing fasts lesion at specific depths when focused, high intensity ultrasound has been predicted to be an advantageous source of ablative energy in catheters. (Williams et al., 2004) 
     An alternative to ablation by heating is the practice of ablating tissue by freezing. Severe cold, also know cryogenic energy, as an ablative energy source has the advantages of avoiding clot formation. (Williams et al., 2004) Another advantage of catheters employing cryogenic energy is the ability to temporary paralyze regions of myocardium tissue as to test the benefit of a planned lesion. When a region of tissue is paralyzed by freezing it can no longer initiate an arrhythmia. If paralyzing a region of the heart completely or partial restores a normal heart beat, the surgeon knows she has her catheter aimed at the right spot. 
     SUMMARY OF THE INVENTION 
     An ablative apparatus that can be used to ablate cardiac tissue is disclosed. The ablative apparatus comprises an ablation probe, a transducer capable of ultrasonically driving the ablation probe in contact with the proximal end of the ablation probe, a guide wire secured at one end to the transducer and/or ablation probe, electrical leads running along the guide wire and connected to electrodes capable of exposing piezo ceramic discs within the transducer to an alternating voltage, a catheter encasing the ablation probe, transducer, and at least a portion of the guide wire, and a handle secured to the end of the guide wire opposite the transducer. Preferably, the catheter is composed of a biologically compatible polymer. 
     The ablation probe located at the distal end of the catheter system may comprise a proximal surface, a distal surface opposite the proximal surface, at least one radial surface extending between the proximal surface and the distal surface, and at least one abrasive member on at least one surface other than the proximal surface. As the distal end of the ablative apparatus is advanced towards the heart, the ablation probe may be contained within a pocket at the distal end of the catheter. When the distal end of the catheter reaches the tissue to be ablated, the ablation probe may be removed from the pocket, as to expose the abrasive member(s). When the transducer in contact with the proximal surface of the ablation probe is activated by supplying it with an electrical current, the ablation probe becomes driven by ultrasonic energy generated by the transducer and begins to vibrate. As the ablation probe vibrates, the abrasive members on the ablation probe scratch tissues with which the members come in contact, as to create an abrasion in the tissues. Physically inducing an abrasion within a tissue, the vibrating ablation probe is capable of mechanically ablating tissues. When the ablation probe is advanced to the heart, mechanical ablation may be utilized to penetrate epicardial fat, thereby exposing the underlying myocardium. The exposed myocardium may then be subjected to mechanical ablation, cryoablation, ultrasonic ablation, and/or any combination thereof. 
     Flowing a cryogenic material through the catheter, as to deliver cryogenic energy to the ablation probe, to a region of the catheter in close proximity to the ablation probe, and/or to another region of the catheter, may enable cryoablation. Lumens running substantially the length of the catheter and joined by a junction may enable a cryogenic material to flow through the catheter. Such lumens may comprise a cryogenic intake lumen originating at the proximal end of the catheter and running substantially the length of the catheter, through which a cryogenic material flows from the proximal end of the catheter towards its distal end. Likewise, a cryogenic exhaust lumen running substantially the length of the catheter and substantially parallel to the cryogenic intake lumen and terminating at the proximal end of the catheter may permit a cryogenic material to flow towards the proximal end of the catheter. A junction at the distal end of the intake lumen and exhaust lumen connecting the lumens may permit a cryogenic material to be exchanged between the lumens. The cryogenic material may be prevented from exiting the catheter by a partition distal to the junction isolating the intake lumen and exhaust lumen from the remaining distal portions of the catheter. Thus, a cryogenic material may be flowed through the catheter by first flowing through an intake lumen and towards the distal end of the catheter. The cryogenic material then exits the intake lumen and enters the exhaust lumen at a junction connecting the lumens. Completing its flow through the catheter, the cryogenic material then flows through the exhaust lumen and back towards the proximal end of the catheter. 
     Cryogenic ablation may also be enabled by flowing a cryogenic material through the guide wire. As with the catheter, lumens running substantially the length of the guide wire and joined by a junction may enable a cryogenic material to flow through the guide wire. Such lumens may comprise cryogenic intake lumen originating at the proximal end of the guide wire and running substantially the length of the wire, through which a cryogenic material flows from the proximal end of the guide wire towards its distal end. Likewise, a cryogenic exhaust lumen running substantially the length of the wire and substantially parallel to the cryogenic intake lumen and terminating at the proximal end of the wire may permit a cryogenic material to flow towards the proximal end of the wire. A junction at the distal end of the intake lumen and exhaust lumen connecting the lumens may permit a cryogenic material to be exchanged between the lumens. The junction connecting the lumens may comprise a chamber internal to the ablation probe into which the intake lumen and exhaust lumen open. Thus, a cryogenic material may be flowed through the guide wire by first flowing through an intake lumen and towards the distal end of the wire. The cryogenic material then exits the intake lumen and enters the exhaust lumen at a junction connecting the lumens. Completing its flow through the wire, the cryogenic material then flows through the exhaust lumen and back towards the distal end of the catheter. 
     Regardless of whether a cryogenic material is flowed through the catheter or guide wire, the ablative apparatus enables the surgical treatment of cardiac arrhythmias by providing a means to mechanically, ultrasonically, and/or cryogenically ablate myocardial tissue. As such, a surgeon utilizing the disclosed ablative apparatus will be able to select the appropriate ablative means or combination of ablative means best suited for the patient&#39;s particular pathology and the type of lesion the surgeon wishes to induce. Driving the ablation probe with ultrasound energy generated by the transducer enables a surgeon to quickly induce surface abrasions of various depths by adjusting the pulse frequency and duration of the driving ultrasound. This may prove advantageous when the surgeon wishes to induce a lesion at a specific location with minimal collateral injury, such as during AV nodal modification. 
     Combining ultrasonic energy with cryogenic energy, the ablative apparatus may enable the surgeon to cryoablate tissue without the ablation probe adhering to the tissue being ablated. As such, the surgeon may be able to easily move the probe during ablation. The ablation probe may be moved during the induction of a lesion by including control means for steering and/or rotating the ablation probe within the handle. The probe&#39;s mobility during cryoablation could allow the surgeon to create linear lesions in cardiac tissue or isolating lesions in vessel walls. Thus, by combining ultrasonic and cryogenic energy the ablative apparatus may give the surgeon greater control over the lesion induced. Furthermore, it has been hypothesized that the administration of low frequency ultrasound and cryoablation induces the release of several healing factors from the targeted tissue. Therefore, ultrasonically vibrating the ablation probe during cryoablation may improve mobility of the ablation probe and possibly induce healing. 
     Alternatively or in combination, dually administering ultrasonic energy and cryogenic energy may protect surface tissue during the administration of a deep lesion, thereby limiting collateral damage. During the cryogenic induction of a deep lesion, the co-administration of ultrasonic energy will warm the surface tissue preventing it from freezing. Likewise, administering cryogenic energy during the induction of a deep lesion with ultrasonic energy will cool surface tissue thereby protecting it from ablative cavitation, possibly by reducing molecular movement. 
     In the alternative or in combination, the ablative apparatus may also enable the surgeon to deliver various drugs and/or other pharmacological compounds to the location of the lesion and/or other locations. Combining drug delivery with the application of ultrasound energy may assist drug delivery and drug penetration into the targeted tissue. Delivering an antithrombolytic during the induction of a lesion may reduce the likelihood of clot formation, especially during mechanical ablation. The surgeon may also choose to expedite healing by delivering various healing and/or growth factors to the site of the lesion. 
     Drug delivery may be accomplished by coating the ablation probe with a drug or other pharmacological compound. When so coated, driving the ablation probe with ultrasonic energy may liberate the drug coating from the probe and embed it within the targeted tissue. In the alternative or in combination, the catheter may contain a drug lumen and/or reservoir permitting the administration of a drug to internal locations of the patient&#39;s body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The ablative apparatus will be shown and described with reference to the drawings of preferred embodiments and clearly understood in detail. 
         FIG. 1  depicts a possible embodiment of the ablative apparatus. 
         FIG. 2  depicts cross-sectional views of the proximal end of the embodiment of the ablative apparatus depicted in  FIG. 1 . 
         FIG. 3  depicts an alternative embodiment of the ablative apparatus. 
         FIG. 4  depicts cross-sectional views of the proximal end of the embodiment of the ablative apparatus depicted in  FIG. 3 . 
         FIG. 5  depicts various ablation probes each comprising a distal surface, a proximal surface opposite the distal surface, a radial surface extending between the proximal surface and the distal surface, and abrasive members on a surface other than the proximal surface. 
         FIG. 6  depicts different piezo ceramic disc configurations that may be included within the transducer utilized to drive the ablation probe. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Disclosed is an ablative apparatus and methods that may be used to treat atrial fibrillation and other arrhythmias. Preferred embodiments of the ablative apparatus are illustrated in the figures and described in detail below. 
       FIG. 1  depicts a possible embodiment of the ablative apparatus. The ablative apparatus comprises an ablation probe  101 , a transducer  102  capable of capable of ultrasonically driving the ablation probe  101  in contact with the proximal surface  103  of ablation probe  101 , a guide wire  104  secured at one end to transducer  102 , electrical leads  105  running along guide wire  104  and connected to electrodes  113  capable of exposing piezo ceramic disc  112  within transducer  102  to an alternating voltage, a catheter  106  encasing ablation probe  101 , transducer  102 , and at least a portion of guide wire  104 , and a handle  107  secured to the end of guide wire  104  opposite transducer  102 . Preferably, catheter  106  is composed of a biologically compatible polymer. Handle  107  may contain control means  108  for steering and/or rotating ablation probe  101 . Exemplar control means have been described in U.S. Pat. Nos. 4,582,181 and 4,960,134, the teachings of which are incorporated herein by reference. In addition to housing control means, handle  107  may provide a means of rotating ablation probe  101 . When rotated, ablation probe  101  moves in a circular motion similar to the manner in which the hands of clock move about its face. Rotation of ablation probe  101  can be accomplished by the surgeon turning handle  107  with his wrist as if he were using a screw driver. Extending from handle  107 , through catheter  106 , to transducer  102 , guide wire  104  provides rigidity to catheter  106 . Guide wire  104  may also carry electrical leads  105  down catheter  106  to transducer  101 . Transmitting an electrical current generated by generator  127  to transducer  102 , electrical leads  105  energize transducer  102  as to drive ablation probe  101 . 
     In keeping with  FIG. 1 , a portion of the distal end  122  of catheter  106  has been cut away as to expose ablation probe  101  and transducer  102 . Ablation probe  101  comprises a distal surface  109 , a proximal surface  103  opposite the distal surface  109 , at least one radial surface  110  extending between distal surface  109  and proximal surface  103 , and abrasive members  111  on radial surface  110 . Transducer  102 , in contact with the proximal surface  103  of ablation probe  101 , comprises a stack of piezo ceramic discs  112  arranged in a manner similar to that of a roll of coins. Running from generator  127  to electrodes  113 , electrical leads  105  carry a current to electrodes  113  as to expose piezo ceramic discs  112  to an alternating voltage. So energizing transducer  102  induces the expansion and contraction of piezo ceramic discs  112 , as to drive ablation probe  101 . Expanding and contracting, piezo ceramic discs  112  apply ultrasonic energy to ablation probe  101 . Applying ultrasonic energy to probe  101  may induce a vibrating or oscillating movement of probe  101 . As ablation probe  101  moves, abrasive members  111  scratch tissues with which the members  111  come in contact, as to create an abrasion in the tissue. Back drive  114 , located at the proximal end of transducer  102 , stabilizes ablation probe  101  when it is driven by ultrasound energy generated by transducer  102 . 
     Continuing with  FIG. 1 , catheter  106 , encasing ablation probe  101 , transducer  102 , and a portion of guide wire  104 , contains a pocket  115  at its distal end  122  encasing ablation probe  101 . Encasing ablation probe  101  within pocket  115  may enable the distal end of the ablative apparatus to be advanced towards the tissue to be ablated without abrasive members  111  damaging tissue. When the distal end  122  of the catheter  106  reaches the tissue to be ablated, ablation probe  101  may be removed from pocket  115 , as to expose abrasive members  111 , by firmly pulling catheter  106  towards handle  107 . As to facilitate the penetration of the sealed tip  116  at the distal end of pocket  115  by ablation probe  101 , sealed tip  116  may contain single or multiple slits  117 . Slit(s)  117  may completely or partially penetrate sealed tip  116 . Conversely, firmly pulling handle  107  away from the patient while catheter  106  is held stationary returns ablation probe  101  to the inside of pocket  115 . Advancing the ablative apparatus into and through the patient&#39;s body with ablation probe  101  retracted within pocket  115  protects the patient&#39;s internal tissues from damage by abrasive members  111 . When ablation probe  101  has been advanced to the desired location, the surgeon may retract catheter  106 , exposing ablation probe  101 . The surgeon may then mechanically ablate the target tissue by driving ablation probe  101  with ultrasound energy generated by transducer  102 . Alternatively, the surgeon may not expose ablation probe  101 , but rather induce a lesion with low frequency ultrasound energy and/or cryogenic energy. 
     In keeping with  FIG. 1 , flowing a cryogenic material through catheter  106 , as to deliver cryogenic energy to ablation probe  101 , to a region of catheter  106  in close proximity to ablation probe  101 , and/or to another region of catheter  106 , may enable cryoablation. A cryogenic material may be delivered to catheter  106  from a cryogenic storage and retrieval unit  118  in fluid communication with cryogenic intake lumen  119  via cryogenic feed tubing  120 , attached to the proximal end intake lumen  119 . Originating at the proximal end  121  of catheter  106  and running substantially the length of catheter  106 , cryogenic intake lumen  119  permits a cryogenic material entering catheter  106  from storage and retrieval unit  118  to flow towards the distal end  122  of catheter  106 . After reaching the distal end of intake lumen  119 , the cryogenic material flows through a junction connecting intake lumen  119  with exhaust lumen  123  located at the distal end of the intake lumen  119  and exhaust lumen  123 . The specific junction depicted in  FIG. 1  comprises a port  124  between intake lumen  119  and exhaust lumen  123 . Running substantially the length of catheter  106 , substantially parallel to intake lumen  119 , and terminating at the proximal end  121  of catheter  106 , exhaust lumen  123  permits the cryogenic material to flow towards proximal end  121  of catheter  106 . After reaching the proximal end  121  of catheter  106 , the cryogenic material is returned to storage and retrieval unit  118  via cryogenic exhaust tubing  125  attached to the proximal end exhaust lumen  123 , which is in fluid communication with storage and retrieval unit  118  and exhaust lumen  123 . Cryogenic storage and retrieval may alternatively be accomplished by the simultaneous use of separate storage and retrieval units. The storage and retrieval unit may also permit the recycling of the employed cryogenic material as to reduce operation costs. 
     As to prevent the cryogenic material from entering pocket  115  and/or exiting catheter  106 , a partition  126  distal to port  124  isolates intake lumen  119  and exhaust lumen  123  from pocket  115 . 
     In order to prevent catheter  106  from becoming rigid and inflexible as cryogenic material flows through it, catheter  106 , or portion thereof, may be wrapped with a wire conducting an electrical current. The resistance in the wire to the flow of electricity may generate heat that warms catheter  106 , thereby keeping it flexible. Alternatively, the warming wire may be wrapped around guide wire  104 . 
     Disclosed in U.S. patent application Ser. No. 11/454,018, entitled Method and Apparatus for Treating Vascular Obstructions, and filed Jul. 15, 2006, are exemplar configurations of catheter that may be used in the alternative to catheter  106 . The teachings of U.S. patent application Ser. No. 11/454,018 are hereby incorporated by reference. 
       FIG. 2  depicts cross-sectional views of the proximal end of the embodiment of the ablative apparatus depicted in  FIG. 1 .  FIG. 2A  depicts a cross-sectional view of the embodiment of the apparatus depicted in  FIG. 1  with ablation probe  101  extended from pocket  115 .  FIG. 2B  depicts a cross-sectional view of the embodiment of the apparatus depicted in  FIG. 1  with ablation probe  101  retracted into pocket  115 . As previously stated in the discussion of  FIG. 1 , catheter  106  comprises a cryogenic intake lumen  119  and an exhaust lumen  123  (obscured in the present view by intake lumen  119 ) connected by ports  124 . The flow of a cryogenic material from the proximal end  121  of catheter  106  towards the distal end  122  of catheter  106  through intake lumen  119 , across ports  124 , and then back towards the proximal end  121  through exhaust lumen  123  cools pocket  115 . Flowing adjacent to or in close proximity to ablation probe  101  and/or transducer  102 , the cryogenic material flowing through catheter  106  may also cool ablation probe  101  and/or transducer  102 . It should be appreciated that in the alternative to the ports depicted in  FIGS. 1 and 2 , the junction between the intake lumen  119  and exhaust lumen  123  may comprise a chamber. 
       FIG. 3  depicts an alternative embodiment of the ablative apparatus. The depicted embodiment of the ablative apparatus comprises an ablation probe  301 , a transducer  302  capable of ultrasonically driving the ablation probe  301  in contact with the proximal surface  303  of ablation probe  301 , a guide wire  304  secured at one end to ablation probe  301  and/or transducer  302 , electrical leads  305  running along guide wire  304  and connected to electrodes  313  capable exposing piezo ceramic disc  312  within transducer  302  to an alternating voltage, a catheter  306  encasing ablation probe  301 , transducer  302 , and at least a portion of guide wire  304 , and a handle  307  secured to the end of guide wire  304  opposite ablation probe  301 . Handle  307  may contain control means  308  for steering and/or rotating ablation probe  301 . Exemplar control means have been described in U.S. Pat. Nos. 4,582,181 and 4,960,134, the teachings of which were previously incorporated herein by reference. In addition to housing control means, handle  308  may provide a means of rotating ablation probe  301 . As with the embodiment depicted in  FIG. 1 , the rotation of ablation probe  301  can be accomplished by the surgeon turning handle  307  with his wrist as if he were using a screw driver. Extending from handle  307 , through catheter  306 , to ablation probe  301 , guide wire  304  provides rigidity to catheter  306 . Guide wire  304  may also carry electrical leads  305  down catheter  306  to transducer  302 . Transmitting an electrical current generated by generator  327  to transducer  302 , electrical leads  305  energize transducer  302  as to drive ablation probe  301 . 
     In keeping with  FIG. 3 , a portion of the distal end  322  of catheter  306  has been cut away as to expose ablation probe  301  and transducer  302 . Ablation probe  301  comprises a distal surface  309 , a proximal surface  303  opposite the distal surface  309 , at least one radial surface  310  extending between distal surface  309  and proximal surface  303 , and abrasive members  311  on radial surface  310 . Transducer  302 , in contact with the proximal surface  303  of ablation probe  301  and encircling guide wire  304 , comprises a stack of piezo ceramic discs  312  an arranged in a manner similar to that of a roll of coins. Running from generator  327  to electrodes  313 , electrical leads  305  carry a current to electrodes  313  as to expose piezo ceramic discs  312  to an alternating voltage. So energizing transducer  302  induces the expansion and contraction of piezo ceramic discs  312 , as to drive ablation probe  301 . Expanding and contracting, piezo ceramic discs  312  apply ultrasonic energy to ablation probe  301 . Applying ultrasonic energy to probe  301  may induce a vibrating or oscillating movement of probe  301 . As ablation probe  301  moves, abrasive members  311  scratch tissues with which the members  311  come in contact, as to create an abrasion in the tissue. Back drive  314 , located at the proximal end of transducer  302 , stabilizes ablation probe  301  when it is driven by ultrasound energy generated by transducer  302 . 
     Continuing with  FIG. 3 , catheter  306 , encasing ablation probe  301 , transducer  302 , and a portion of guide wire  304 , contains a pocket  315  at its distal end  322  encasing ablation probe  301 . Encasing ablation probe  301  within pocket  315  may enable the distal end of the ablative apparatus to be advanced towards the tissue to be ablated without abrasive members  311  damaging tissue. When the distal end  322  of the catheter  306  reaches the tissue to be ablated, ablation probe  301  may be removed from pocket  315 , as to expose abrasive members  311 , by firmly pulling catheter  306  towards handle  307 . As to facilitate the penetration of the sealed tip  316  at the distal end of pocket  315  by ablation probe  301 , sealed tip  316  may contain single or multiple slits  317 . Slit(s)  317  may completely or partially penetrate sealed tip  316 . Conversely, firmly pulling handle  307  away from the patient while holding catheter  306  stationary returns ablation probe  301  to the inside of pocket  315 . Advancing the ablative apparatus into and through the patient&#39;s body with ablation probe  301  retracted within pocket  315  protects the patient&#39;s internal tissues from damage by abrasive members  311 . When ablation probe  301  has been advanced to the desired location, the surgeon may retract catheter  306 , exposing ablation probe  301 . The surgeon may then mechanically ablate the target tissue by driving ablation probe  301  with ultrasound energy generated by transducer  302 . Alternatively, the surgeon may not expose ablation probe  301 , but rather induce a lesion with low frequency ultrasound energy and/or cryogenic energy. 
     In keeping with  FIG. 3 , flowing a cryogenic material through guide wire  304 , as to deliver cryogenic energy to ablation probe  301 , may enable cryoablation. A cryogenic material may be delivered to guide wire  304  from a cryogenic storage and retrieval unit  318  in fluid communication with cryogenic intake lumen  319  via cryogenic feed tubing  320 , attached to the proximal end intake lumen  319 . Originating at the proximal end  321  of guide wire  304  and running substantially the length of guide wire  304 , cryogenic intake lumen  319  permits a cryogenic material entering guide wire  304  from storage and retrieval unit  318  to flow towards the distal end  326  of guide wire  304 . After reaching the distal end of intake lumen  319 , the cryogenic material flows through a junction connecting intake lumen  319  with exhaust lumen  323  at the distal end of the intake lumen  319  and exhaust lumen  323 . The specific junction depicted in  FIG. 3  comprises an expansion chamber  324  within ablation probe  301  into which intake lumen  319  and exhaust lumen  323  open. Running substantially the length of guide wire  304 , substantially parallel to intake lumen  319 , and terminating at the proximal end  321  of guide wire  304 , exhaust lumen  323  permits the cryogenic material to flow towards proximal end  321  of guide wire  304 . After reaching the proximal end  321  of guide wire  304 , the cryogenic material is returned to storage and retrieval unit  318  via cryogenic exhaust tubing  325  attached to the proximal end exhaust lumen  323 , which is in fluid communication with storage and retrieval unit  318  and exhaust lumen  323 . Cryogenic storage and retrieval may alternatively be accomplished by the simultaneous use of separate storage and retrieval units. The storage and retrieval unit may also permit the recycling of the employed cryogenic material as to reduce operation costs. 
     In order to prevent catheter  306  from becoming rigid and inflexible as cryogenic material flows through guide wire  304 , catheter  306 , or portion thereof, may be wrapped with a wire conducting an electrical current. The resistance in the wire to the flow of electricity may generate heat that warms catheter  306 , thereby keeping it flexible. Alternatively, the warming wire may be wrapped around guide wire  304 . 
       FIG. 4  depicts cross-sectional views of the proximal end of the embodiment of the ablative apparatus depicted in  FIG. 3 .  FIG. 4A  depicts a cross-sectional view of the embodiment of the apparatus depicted in  FIG. 3  with ablation probe  301  extended from pocket  315 .  FIG. 4B  depicts a cross-sectional view of the embodiment of the apparatus depicted in  FIG. 3  with ablation probe  301  retracted into pocket  315 . As previously stated in the discussion of  FIG. 3 , guide wire  304  comprises a cryogenic intake lumen  319  and an exhaust lumen  323  connected by expansion chamber  324 . The flow of a cryogenic material from the proximal end  321  of guide wire  304  towards the distal end  326  of guide wire  304  through intake lumen  319 , across the junction formed by expansion chamber  324 , and then back towards the proximal end  321  through exhaust lumen  323  cools ablation probe  301 . Expansion chamber  324  may be located within ablation probe  301 , as depicted in  FIGS. 3 and 4 . Alternatively, expansion chamber  324  may be located within transducer  302  and could, but need not, extend into ablation probe  301 . It should be appreciated that in the alternative to the expansion chamber depicted in  FIGS. 3 and 4 , the junction between the intake lumen  319  and exhaust lumen  323  may comprise one or a series of ports connecting intake lumen  319  with exhaust lumen  323 . 
     Incorporating threading on a portion of the ablation probe and/or transducer along with corresponding threading on the internal surface of the catheter&#39;s pocket may facilitate a smooth deployment of the ablation probe from the catheter&#39;s pocket. In such an embodiment, the surgeon would advance the ablation probe from the pocket by rotating the guide wire and attached ablation probe. Rotating the guide wire in the opposite direction would retract the ablation probe back into the pocket. 
     The ablation probe of the ablative apparatus may contain one or multiple abrasive members attached to its proximal and/or radial surfaces. Furthermore, the abrasive members may be constructed in various configurations, as depicted in  FIG. 5 . 
       FIG. 5  depicts various ablation probes each comprising a distal surface, a proximal surface opposite the distal surface, and a radial surface extending between the proximal surface and the distal surface, and abrasive members on a surface other than the proximal surface. The ablation probe  501 , depicted in  FIG. 5A , contains an abrasive member comprising a thin band  502  attached to radial surface  503  and spiraling around ablation probe  501  similar to the threads of a screw. Alternatively, the ablation probe  504 , as depicted in  FIG. 5B , may contain abrasive members comprising a thin band  505  attached to radial surface  506  and encircling ablation probe  504 . As indicated by ablation probe  507 , depicted in  FIG. 5C , it also possible for the abrasive member to comprise small particle  508 , conceptually similar to a grain of grit on a piece of sand paper, attached to the proximal surface  509  and/or radial surface  510  of ablation probe  507 . It is also possible, as indicated by ablation probe  511 , depicted in  FIG. 5D , for the abrasive member to comprise a protrusion  512  extending from a surface of the ablation probe  511  other than proximal surface  513 . It should be appreciated that the ablation probes depicted in  FIG. 5  may be constructed by attaching or affixing the depicted abrasive members to their proximal and/or radial surfaces. Alternatively, the ablation probes depicted in  FIG. 5  may be constructed such that the abrasive members are extensions of or integral with the ablation probes. 
       FIG. 6  depicts different piezo ceramic disc configurations that may be included within the transducer utilized to drive the ablation probe. The transducer may be comprised of a single piezo ceramic disc. Alternatively, the transducer may contain a collection of piezo ceramic discs as depicted in  FIG. 6 . For instance, the transducer may contain a collection cylindrical piezo ceramic discs  601  stacked upon one another in a manner resembling a roll of coins, as depicted in  FIG. 6A . Such an arrangement may impart an axial or longitudinal displacement upon the driven ablation probe when the transducer is energized. Alternatively, the transducer may contain a pair of half cylindrical piezo ceramic discs  602  combined to form a cylinder, as depicted in FIG.  6 C. Such an arrangement may impart a circumferential displacement upon the driven ablation probe when the transducer is energized. The transducer may also contain a combination of cylindrical piezo ceramic discs  601  and half cylindrical piezo ceramic discs  602 , as depicted in  FIG. 6B . Such a combination arrangement may impart an axial and circumferential displacement upon the driven ablation probe when the transducer is energized. 
     The ultrasound transducer responsible for driving the ablation probe need not be in direct contact with the ablation probe. Instead, the transducer may be in communication with the guide wire attached to the ablation probe, driving the ablation probe through said communication. In such an embodiment, the transducer may be located anywhere within the ablative apparatus, including, but not limited to, the handle. The transducer may also be located elsewhere within the ablative apparatus, provided the transducer is in direct or indirect communication with the ablation probe. 
     The transducer utilized in the ablative apparatus should be capable of inducing the ablation probe to vibrate at a frequency between approximately 20 kHz and approximately 20 MHz. The recommended frequency of vibration is approximately 30 kHz to approximately 40 kHz. The transducer should also be capable of driving the transducer with ultrasonic energy having an intensity of at least approximately 0.1 Watts per centimeter squared. 
     Pulse duration and treatment time are dependent upon the depth and type of lesion the surgeon wishes to induce. Pulsing the ultrasound energy driving the transducer by repeatedly turning the transducer on and off gives the surgeon control over lesion depth. Incorporating an ultrasound controller may permit the surgeon to control, regulate, or adjust, the pulse duration and pulse frequency of the driving ultrasound. Adjusting the pulse frequency and duration enables the surgeon to control the depth of the lesion inflicted by the ablation probe. 
     When the ablation probe has been advanced to the desired lesion location, the surgeon may retract the catheter as to expose the ablation probe&#39;s abrasive member(s). The surgeon may then mechanical induce an abrasion by driving the ablation probe with ultrasound energy generated by the transducer. Alternatively, the surgeon may not expose the ablation probe&#39;s abrasive members but rather activate the flow of cryogenic material through the ablative apparatus as to induce a lesion by means of cryoablation. If the surgeon wishes to induce a continuous lesion across a segment of cardiac tissue, the surgeon may activate the transducer as to prevent cryoadhesion of the catheter&#39;s distal end to the target tissue. Activating the transducer during cryoablation enables the surgeon to warm surface tissue at the site of ablation, thereby protecting surface tissue from ablation or injury. Likewise, activating the flow of cryogenic material through the apparatus while ultrasonically inducing a lesion enables the surgeon to cool surface tissue at the site of the ablation, thereby protecting it from ablation or injury. 
     Incorporating a mapping electrode placed at or near the distal end of the ablative apparatus may assist the surgeon in locating specific sites of arrhythmia. Alternatively, the mapping electrode may be located at or attached to the ablation probe. A mapping electrode may enable the surgeon to detect the electrical activity of the cells near the electrode. The surgeon could use the detected electrical activity to determine if the cells near the electrode are contributing to the arrhythmia. Furthermore, the surgeon may administer cryogenic energy to a region of myocardium suspected to be contributing to the patient&#39;s arrhythmia as to paralyze the tissue. If paralyzing the tissue completely or partially corrects the arrhythmia, the surgeon may then ablate the tissue with the ablation probe. 
     Incorporating a temperature sensor placed at or near the distal end of the ablative apparatus may enable the surgeon to monitor the temperature at the site of the ablation. Alternatively, the sensor may be located near or attached to the ablation probe. Monitoring the temperature near or at the site of the ablation with the temperature sensor may assist the surgeon in avoiding burning and/or inflicting other undesirable damage or injury. When the temperature of the tissue being ablated reaches or approaches an undesirable level, the surgeon could stop the ablation and allow the tissue to return to a safer temperature. The surgeon may also adjust the ultrasound parameters as to slow the change in temperature. If the ablative procedure being performed involves the administration of cryogenic energy, the surgeon may adjust the flow of the cryogenic material through the catheter system as to slow the change in temperature. 
     The ablative apparatus may also contain a drug lumen through which a drug solution or other fluid or composition may be introduced into the patient&#39;s body. Ultrasonically driving the ablation probe, while simultaneously delivering drug through the apparatus by way of the drug lumen, may be utilized by the surgeon to facilitate the release of the drug from the apparatus, as well as the penetration of the drug into targeted tissue. 
     The ablative apparatus may also contain a drug reservoir at its distal end. The drug reservoir may surround the ablation probe. Alternatively, the drug reservoir may be located distal to the ablation probe. When located distal to the ablation probe, the drug reservoir may contain slits at its base. The slits may completely or partially penetrate the base of the drug reservoir. Retracting the catheter may then cause the ablation probe to penetrate the base of the drug reservoir and eventually the distal end of the reservoir. Traveling through the drug reservoir, the ablation probe may be coated with a drug. Suspending the drug within a viscous or gel solution may offer better coating of the ablation probe as it travels through the drug reservoir. Ultrasonically driving the ablation probe will cause the drug solution clinging to the ablation probe to be liberated from the ablation probe and embedded in the tissue at and surrounding the site of the lesion. Similarly, ultrasonically driving the ablation probe while the probe is retracted may cause the release of drug from the drug reservoir. 
     Alternatively, drug delivery during the induction of lesions may be accomplished by first coating the ablation probe with a pharmacological compound. As in the above mention embodiment, ultrasonically driving the ablation probe will liberate the drug compound coating; dispersing it into the targeted tissue. 
     It should be appreciated that the term “cryoadhesion,” as used herein, refers to the freezing of a cooled and/or cold object to tissues of the body. 
     It should be appreciated that the term “biologically compatible polymer,” as used herein, refers to polymers, or plastics, that will not normally irritate or harm the body. Such polymers are familiar to those skilled in the art. 
     It should be appreciate that term “piezo ceramic disc,” as used herein, refers to an element composed of a ceramic material that expands and contracts when exposed to an alternating voltage. Such ceramics are well known to those skilled in the art. 
     It should be appreciated that “energizing the transducer,” as used herein, refers to inducing the contraction and expansion of piezo ceramic discs within the transducer by exposing the discs to an alternating voltage, as to induce the generation of ultrasonic energy. 
     It should be appreciated that the term “ultrasonically driven,” as used herein, refers to causing the ablation probe to move by applying to the probe ultrasonic energy generated by a transducer in direct or indirect contract with the probe. The induced movement of the probe may include vibrating, oscillating, and/or other manners of motion. 
     It should be appreciated that the term “pulse duration,” as used herein, refers to the length of time the transducer is generating ultrasonic energy. 
     It should be appreciated that the term “pulse frequency,” as used herein, refers to how often the ultrasound transducer generates ultrasound during a period of time. 
     It should be appreciated that the term “mechanical ablation,” as used herein, refers to injuring a tissue by scratching the tissue as to create an abrasion in the tissue. 
     It should be appreciated that the term “surgeon,” as used herein, references all potential users of the disclosed ablative apparatus and does not limit the user of the apparatus to any particular healthcare or medical professional or healthcare or medical professionals in general. 
     It should be appreciated that elements described with singular articles such as “a”, “an”, and/or “the” and/or otherwise described singularly may be used in plurality. It should also be appreciated that elements described in plurality may be used singularly. 
     Although specific embodiments of apparatuses and methods have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, combination, and/or sequence of that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. It is to be understood that the above description is intended to be illustrative and not restrictive. Combinations of the above embodiments and other embodiments as well as combinations and sequences of the above methods and other methods of use will be apparent to individuals possessing skill in the art upon review of the present disclosure. 
     The scope of the claimed apparatus and methods should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.