Patent Publication Number: US-8535301-B2

Title: Surgical system and procedure for treatment of medically refractory atrial fibrillation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 12/403,123 (“the &#39;123 application”), filed 12 Mar. 2009, now U.S. Pat. No. 8,177,780, which is a continuation of U.S. application Ser. No. 11/935,582 (“the &#39;582 application), filed 6 Nov. 2007, now U.S. Pat. No. 7,517,345 (“the &#39;345 patent”), which is a continuation of U.S. application Ser. No. 10/171,411 (“the &#39;411 application”), filed 12 Jun. 2002, now U.S. Pat. No. 7,387,126 (“the &#39;126 patent”), which is a continuation of U.S. application Ser. No. 09/606,742 (“the &#39;742 application”), filed 29 Jun. 2000, now abandoned, which is a continuation of U.S. application Ser. No. 08/943,683 (“the &#39;683 application”), filed 15 Oct. 1997, now U.S. Pat. No. 6,161,543 (“the &#39;543 patent”), which is a continuation-in-part of U.S. application Ser. No. 08/735,036 (“the &#39;036 application”), filed 22 Oct. 1996, now abandoned. This application is also related to U.S. Pat. No. 5,797,960 (“the &#39;960 patent”), issued 25 Aug. 1998, which is a continuation in part of U.S. Pat. No. 5,571,215 (“the &#39;215 patent”), issued 5 Nov. 1996, which is a continuation-in-part of U.S. Pat. No. 5,452,733 (“the &#39;733 patent”), issued 26 Sep. 1995. The complete disclosures of the &#39;123, &#39;582, &#39;411, &#39;742, &#39;683, and &#39;036 applications and the &#39;345, &#39;126, &#39;543, &#39;960, &#39;215, and &#39;733 patents are hereby incorporated by reference as though fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     It is well documented that atrial fibrillation, either alone or as a consequence of other cardiac disease, continues to persist as the most common cardiac arrhythmia. According to recent estimates, more than one million people in the U.S. suffer from this common arrhythmia, roughly 0.15% to 1.0% of the population. Moreover, the prevalence of this cardiac disease increases with age, affecting nearly 8% to 17% of those over 60 years of age. 
     Although atrial fibrillation may occur alone, this arrhythmia often associates with numerous cardiovascular conditions, including congestive heart failure, hypertensive cardiovascular disease, myocardial infarction, rheumatic heart disease and stroke. Regardless, three separate detrimental sequelae result: (1) a change in the ventricular response, including the onset of an irregular ventricular rhythm and an increase in ventricular rate; (2) detrimental hemodynamic consequences resulting from loss of atrioventricular synchrony, decreased ventricular filling time, and possible atrioventricular valve regurgitation; and (3) an increased likelihood of sustaining a thromboembolic event because of loss of effective contraction and atrial stasis of blood in the left atrium. 
     Atrial arrhythmia may be treated using several methods. Pharmacological treatment of atrial fibrillation, for example, is initially the preferred approach, first to maintain normal sinus rhythm, or secondly to decrease the ventricular response rate. While these medications may reduce the risk of thrombus collecting in the atrial appendages if the atrial fibrillation can be converted to sinus rhythm, this form of treatment is not always effective. Patients with continued atrial fibrillation and only ventricular rate control continue to suffer from irregular heartbeats and from the effects of impaired hemodynamics due to the lack of normal sequential atrioventricular contractions, as well as continue to face a significant risk of thromboembolism. 
     Other forms of treatment include chemical cardioversion to normal sinus rhythm, electrical cardioversion, and RF catheter ablation of selected areas determined by mapping. In the more recent past, other surgical procedures have been developed for atrial fibrillation, including left atrial isolation, transvenous catheter or cryosurgical ablation of His bundle, and the Corridor procedure, which have effectively eliminated irregular ventricular rhythm. However, these procedures have for the most part failed to restore normal cardiac hemodynamics, or alleviate the patient&#39;s vulnerability to thromboembolism because the atria are allowed to continue to fibrillate. Accordingly, a more effective surgical treatment was required to cure medically refractory atrial fibrillation of the heart. 
     On the basis of electrophysiologic mapping of the atria and identification of macroreentrant circuits, a surgical approach was developed which effectively creates an electrical maze in the atrium (i.e., the MAZE procedure) and precludes the ability of the atria to fibrillate. Briefly, in the procedure commonly referred to as the MAZE m procedure, strategic atrial incisions are performed to prevent atrial reentry and allow sinus impulses to activate the entire atrial myocardium, thereby preserving atrial transport function postoperatively. Since atrial fibrillation is characterized by the presence of multiple macroreentrant circuits that are fleeting in nature and can occur anywhere in the atria, it is prudent to interrupt all of the potential pathways for atrial macroreentrant circuits. These circuits, incidentally, have been identified by intraoperative mapping both experimentally and clinically in patients. 
     Generally, this procedure includes the excision of both atrial appendages, and the electrical isolation of the pulmonary veins. Further, strategically placed atrial incisions not only interrupt the conduction routes of the most common reentrant circuits, but they also direct the sinus impulse from the sinoatrial node to the atrioventricular node along a specified route. In essence, the entire atrial myocardium, with the exception of the atrial appendages and the pulmonary veins, is electrically activated by providing for multiple blind alleys off the main conduction route between the sinoatrial node to the atrioventricular node. Atrial transport function is thus preserved postoperatively, as generally set forth in the series of articles: Cox, Schuessler, Boineau, Canavan, Cain, Lindsay, Stone, Smith, Corr, Chang, and D&#39;Agostino, Jr., The Surgical Treatment of Atrial Fibrillation (pts. 1-4), 101 THORAC CARDIOVASC SURG., 402-426, 569-592 (1991). 
     While this MAZE III procedure has proven effective in ablating medically refractory atrial fibrillation and associated detrimental sequelae, this operational procedure is traumatic to the patient since substantial incisions are introduced into the interior chambers of the heart. Moreover, using current techniques, many of these procedures require a gross thoracotomy, usually in the form of a median sternotomy, to gain access into the patient&#39;s thoracic cavity. A saw or other cutting instrument is used to cut the sternum longitudinally, allowing two opposing halves of the anterior or ventral portion of the rib cage to be spread apart. A large opening into the thoracic cavity is thus created, through which the surgical team may directly visualize and operate upon the heart for the MAZE III procedure. Such a large opening further enables manipulation of surgical instruments and/or removal of excised heart tissue since the surgeon can position his or her hands within the thoracic cavity in close proximity to the exterior of the heart. The patient is then placed on cardiopulmonary bypass to maintain peripheral circulation of oxygenated blood. 
     Not only is the MAZE III procedure itself traumatic to the patient, but the postoperative pain and extensive recovery time due to the conventional thoracotomy substantially increase trauma and further extend hospital stays. Moreover, such invasive, open-chest procedures significantly increase the risk of complications and the pain associated with sternal incisions. While heart surgery produces beneficial results for many patients, numerous others who might benefit from such surgery are unable or unwilling to undergo the trauma and risks of current techniques. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a surgical procedure and system for closed-chest, closed heart ablation of heart tissue. 
     It is another object of the present invention to provide a surgical procedure and system for ablating medically refractory atrial fibrillation. 
     Yet another object of the present invention is to provide a surgical procedure and surgical devices which are capable of strategically ablating heart tissue from the interior chambers or external cardiac surfaces thereof without substantially disturbing the structural integrity of the atria. 
     Still another object of the present invention is to enable surgeons to ablate medically refractory atrial fibrillation while the heart is still beating. 
     In accordance with the foregoing objects of the invention, the present invention provides surgical systems and methods for ablating heart tissue within the interior and/or exterior of the heart. This procedure is particularly suitable for surgeries such as the MAZE III procedure developed to treat medically refractory atrial fibrillation since the need for substantial, elongated, transmural incisions of the heart walls are eliminated. Moreover, this technique is preferably performed without having to open the chest cavity via a median sternotomy or major thoracotomy. The system is configured for being introduced through a small intercostal, percutaneous penetration into a body cavity and engaging the heart wall through purse-string incisions. As a result, the procedure of the present invention reduces potential postoperative complications, recovery time and hospital stays. 
     A system for transmurally ablating heart tissue is provided including an ablating probe having an elongated shaft positionable through the chest wall and into a transmural penetration extending through a muscular wall of the heart and into a chamber thereof. The shaft includes an elongated ablating surface for ablating heart tissue. The system of the present invention further includes a sealing device fixable to the heart tissue around the transmural penetration for forming a hemostatic seal around the probe to inhibit blood loss therethrough. 
     A preferred method and device for ablating the heart tissue is with a cryosurgical ablation device. Although cryosurgical ablation is a preferred method, a number of other ablation methods could be used instead of cryoablation. Among these tissue ablation means are Radio Frequency (RF), ultrasound, microwave, laser, heat, localized delivery of chemical or biological agents and light-activated agents to name a few. 
     More specifically, the system of the present invention enables the formation of a series of strategically positioned and shaped elongated, transmural lesions which cooperate with one another to reconstruct a main electrical conduction route between the sinoatrial node to the atrioventricular node. Atrial transport function is thus preserved postoperatively for the treatment of atrial fibrillation. 
     The system includes a plurality of surgical probes each having an elongated shaft. Each shaft includes an elongated ablating surface of a predetermined shape for contact with at least one specific surface of the heart and specifically the interior walls of atria chamber. Such contact with the ablating surface for a sufficient period of time causes transmural ablation of the wall. Collectively, a series of strategically positioned and shaped elongated, transmural lesions are formed which cooperate with one another to treat atrial fibrillation. Each transmural penetration includes a purse-string suture formed in the heart tissue around the respective transmural penetration in a manner forming a hemostatic seal between the respective probe and the respective transmural penetration to inhibit blood loss therethrough. 
     When using a cryosurgical probe, the probe includes a shaft having a delivery passageway for delivery of pressurized cryogen therethrough and an exhaust passageway for exhaust of expended cryogen. The pressurized cryogen is expanded in a boiler chamber thereby cooling the elongated ablating surface for cryogenic cooling of the elongated ablating surface. The elongated shaft is configured to pass through the chest wall and through a penetration in the patient&#39;s heart for ablative contact with a selected portion of the heart. 
     In another aspect of the present invention, a surgical method for ablating heart tissue from the interior and/or exterior walls of the heart is provided including the steps of forming a penetration through a muscular wall of the heart into an interior chamber thereof and positioning an elongated ablating device having an elongated ablating surface through the penetration. The method further includes the steps of forming a hemostatic seal between the device and the heart wall penetration to inhibit blood loss through the penetration and contacting the elongated ablating surface of the ablating device with a first selected portion of an interior and/or exterior surface of the muscular wall for ablation thereof. 
     More preferably, a method for ablating medically refractory atrial fibrillation of the heart is provided comprising the steps of forming a penetration through the heart and into a chamber thereof positioning an elongated ablating devices having an elongated ablating surface through the penetration and forming a hemostatic seal between the ablating device and the penetration to inhibit blood loss therethrough. The present invention method further includes the steps of strategically contacting the elongated ablating surface of the ablating device with a portion of the muscular wall for transmural ablation thereof to form at least one elongated transmural lesion and repeating these steps for each remaining lesion. Each transmural lesion is formed through contact with the ablating surface of one of the plurality of ablating device and the strategically positioned elongated transmural lesions cooperate to guide the electrical pulse pathway along a predetermined path for the surgical treatment of atrial fibrillation. 
     The entire procedure is preferably performed through a series of only five purse-strings sutures strategically located in the right and left atria, and pulmonary vein portions. Generally, multiple lesions can be formed through a single purse-string either through the use of assorted uniquely shaped ablating devices or through the manipulation of a single ablating device. 
     It should be understood that while the invention is described in the context of thoracoscopic surgery on the heart, the systems and methods disclosed herein are equally useful to ablate other types of tissue structures and in other types of surgery such as laparoscopy and pelviscopy. 
     The procedure and system of the present invention have other objects of advantages which will be readily apparent from the following description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an upper left, posterior perspective view of a human heart incorporating the system and procedure for treatment of medically refractory atrial fibrillation constructed in accordance with the principles of the present invention. 
         FIG. 2  is a right, antero-lateral perspective view of the human heart incorporating the present invention system and procedure thereof. 
         FIGS. 3A and 3B  are schematic diagrams of the atria portion of the heart illustrating the pattern of transmural cryolesions to create a predetermined conduction path in the atrium using the system and procedure of the present invention. 
         FIG. 4  is a top plan view of a set of cryoprobe devices constructed in accordance with the present invention, and utilized in the system and procedure of the present invention. 
         FIG. 5  is a top perspective view of a patient showing use of the system and procedure on the patient. 
         FIG. 6  is an enlarged, fragmentary, top plan view, in cross-section, of one of the cryoprobes in the set of cryoprobes of  FIG. 4 , illustrating the expansion chamber thereof. 
         FIGS. 6A-6D  illustrate use of a slidable insulative tube for insulating portions of the probe. 
         FIG. 7  is a front elevation view, in cross-section, of the ablating end of a cryoprobe, taken substantially along the plane of the line  7 - 7  in  FIG. 6 . 
         FIG. 8  is a front elevation view, in cross-section, of an alternative embodiment of the ablating end of  FIG. 7 . 
         FIG. 9  is a transverse cross-sectional view of the system and patient, taken through the patient&#39;s thorax generally along the plane of the line  9 - 9  in  FIG. 11A , showing the relative positioning of the right and left intercostal percutaneous penetrations. 
         FIG. 10  is a front schematic view of a patient&#39;s cardiovascular system illustrating the positioning of a cardiopulmonary bypass system for arresting the heart and establishing cardiopulmonary bypass in accordance with the principles of the present invention. 
         FIGS. 11A-11D  is a series of top plan views of the patient undergoing a pericardiotomy as well as the installation of a purse-string suture and a stay suture to assist in suspending the pericardium. 
         FIGS. 12A-12C  is a series of enlarged, fragmentary side elevation views looking into the patient&#39;s thoracic cavity at the right atrium through a soft tissue retractor (not shown) in the system of  FIG. 5 , and illustrating the introduction of cryoprobes constructed in accordance with the present invention through purse-strings for the formation of a posterior longitudinal right atrial cryolesion and a tricuspid valve annulus cryolesion. 
         FIG. 13  is an enlarged, fragmentary, transverse cross-sectional view, partially broken away, of the system and patient&#39;s heart of  FIG. 5 , and illustrating the introduction of a tricuspid valve cryoprobe through a purse-string suture in the right atrial freewall to form the elongated, transmural, tricuspid valve annulus cryolesion. 
         FIG. 14  is a side elevation view peering at the right atrial appendage through the soft tissue retractor passageway (not shown) in the system of  FIG. 5 , showing the formation of a perpendicular right atrial cryolesion. 
         FIG. 15  is a fragmentary, transverse cross-sectional view of the system and patient&#39;s heart, illustrating the formation of a right atrial anteromedial counter cryolesion. 
         FIG. 16  is an upper left, posterior perspective view the human heart of  FIG. 1 , illustrating the location of the purse-string sutures in the right and left atrial walls, to access opposite sides of the atrial septum wall for the introduction of an atrial septum clamping cryoprobe. 
         FIG. 17  is a fragmentary, transverse cross-sectional view, partially broken away, of the system and patient&#39;s heart, showing the atrial septum clamping cryoprobe engaged with the atrial septum wall for the formation of an anterior limbus of the fossa ovalis cryolesion. 
         FIGS. 18A and 18B  is a sequence of enlarged, fragmentary, transverse cross-sectional views, partially broken away, of the system and patient&#39;s heart, illustrating the technique employed to enable insertion of the distal ends of the atrial septum clamping cryoprobe through the adjacent purse-string sutures. 
         FIGS. 19A-19D  is a series of fragmentary, transverse cross-sectional views, partially broken away, of the system and patient&#39;s heart, showing the formation of an endocardial pulmonary vein isolation cryolesion using a four-step process. 
         FIGS. 20A and 20B  is a sequence of fragmentary, transverse cross-sectional views, partially broken away, of the system and patient&#39;s heart, showing the formation of the pulmonary vein isolation cryolesion through an alternative two-step process. 
         FIG. 21  is an upper left, posterior perspective view of the human heart illustrating the formation of an additional epicardial pulmonary vein isolation cryolesion. 
         FIG. 22  is a fragmentary, transverse cross-sectional view of the system and patient&#39;s heart, showing the formation of a left atrial anteromedial cryolesion. 
         FIG. 23  is a fragmentary, transverse cross-sectional view of the system and patient&#39;s heart, illustrating the formation of a posterior vertical left atrial cryolesion. 
         FIG. 24  is a top plan view of the right angle cryoprobe of  FIGS. 12A and 12B . 
         FIG. 25  is a top plan view of the tricuspid valve annulus cryoprobe of  FIG. 13 . 
         FIG. 26  is a top plan view of an alternative embodiment of the tricuspid valve annulus cryoprobe of  FIG. 25 . 
         FIG. 27  is a top plan view of the right atrium counter lesion cryoprobe of  FIG. 15 . 
         FIG. 28  is a top plan view of the atrial septum clamping cryoprobe of  FIGS. 17 and 18 . 
         FIG. 29  is an enlarged front elevation view, in cross-section, of a coupling device of the septum clamping cryoprobe, taken substantially along the plane of the line  29 - 29  in  FIG. 28 . 
         FIG. 30  is an enlarged rear elevation view, in cross-section, of an aligning device of the septum clamping cryoprobe, taken substantially along the plane of the line  30 - 30  in  FIG. 28 . 
         FIG. 31  is an enlarged, fragmentary, top plan view of an alternative embodiment to the atrial septum clamping cryoprobe of  FIG. 28 . 
         FIG. 32  is a top plan view of an all-purpose cryoprobe of  FIGS. 19A and 19B . 
         FIG. 33  is a top plan view of the pulmonary vein loop cryoprobe of  FIGS. 20 and 21 . 
         FIG. 34  is a top plan view of the left atrial anteromedical cryoprobe of  FIG. 22 . 
         FIG. 35  is a top plan view of an alternative embodiment of the all-purpose cryoprobe of  FIG. 23 . 
         FIG. 36  is an enlarged, fragmentary, top plan view of an alternative embodiment to the cryoprobes formed for contact of the ablation surface with the epicardial surface of the heart. 
         FIG. 37  is an exploded view of a cryogen delivery tube. 
         FIG. 38  is a partial cross-sectional view of the probe having the delivery tube of  FIG. 37 . 
         FIG. 39  is an exploded view of the outer tube of the probe of  FIG. 38 . 
         FIG. 40  is an end view of the ablating surface of the probe of  FIG. 39 . 
         FIG. 41  shows a probe having a delivery tube with adjustable holes wherein an outer tube is slidably movable relative to an inner tube. 
         FIG. 42  shows the probe of  FIG. 41  with the outer tube moved distally relative to the inner tube. 
         FIG. 43  shows a probe having vacuum ports for adhering the probe to the tissue to be ablated. 
         FIG. 44  is a cross-sectional view of the probe of  FIG. 43  along line I-I. 
         FIG. 45  shows a probe having a malleable shaft. 
         FIG. 46  shows the tip of the probe of  FIG. 45 . 
         FIG. 47  is a cross-sectional view of the probe of  FIG. 45  along line II-II. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Attention is now directed to  FIGS. 1-3  where a human heart H is illustrated incorporating a series of strategically positioned transmural lesions throughout the right atrium RA and the left atrium LA formed with the heart treatment procedure and system of the present invention.  FIG. 1  represents the desired pattern of lesions created on the right atrium RA, including the posterior longitudinal right atrial lesion  50 , the tricuspid valve annulus lesion valve annulus lesion  51 , the pulmonary vein isolation lesion vein isolation lesion  52  and the perpendicular lesion  53 ; while  FIG. 2  represents a right, anterior perspective view of the heart H illustrating right atrium RA including a right atrial anteromedial counter lesion  55 . The cumulative pattern of lesions reconstruct a main electrical conduction route between the sinoatrial node to the atrioventricular node to postoperatively preserve atrial transport function. Unlike prior surgical treatments, the system and procedure of the present invention, generally designated  56  in  FIGS. 4 and 5 , employ a closed-heart technique which eliminates the need for gross multiple elongated incisions of the atria to ablate heart tissue in the manner sufficient to preclude electrical conduction of reentrant pathways in the atria. 
     In accordance with the heart treatment procedure and system of the present invention, a set of uniquely-shaped, elongated tip ablation probes  57  ( FIG. 4 , to be discussed in detail below) are employed which are formed and dimensioned for insertion through at least one of a plurality of heart wall penetrations, preferably sealed by means of purse-string sutures  58 ,  60 ,  61 ,  62  and  63 , strategically positioned about the atria of the heart H. Once the distal end of the probe is inserted through the desired purse-string suture, an elongated ablating surface  65  thereof is maneuvered into contact with the selected endocardial surface of an interior wall of the atria to create an elongated, transmural lesion. As shown in  FIGS. 3A and 3B , these individual lesions collectively form a pattern of transmurally ablated heart tissue to surgically treat medically refractory atrial fibrillation. 
     Briefly,  FIG. 4  represents a collection or set of probes  57  constructed in accordance with the present invention which are employed to preclude electrical conduction of reentrant pathways in the atria using closed-heart surgical techniques. Collectively, as will be apparent, the probes enable the surgical formation of a series of lesions which are illustrated in  FIGS. 3A and 3B . Each probe ( FIGS. 24-28  and  32 - 35 ) includes an elongated shaft  66  formed to extend through an access port or passageway  67  in a retractor  68  ( FIG. 5 ) which is mounted in a percutaneous intercostal penetration. The terms “percutaneous intercostal penetration” and “intercostal penetration” as used herein refer to a penetration, in the form or a cut, incision, hole, retractor, cannula, trocar sleeve, or the like, through the chest wall between two adjacent ribs wherein the patient&#39;s rib cage and sternum remain generally intact. These terms are intended to distinguish a gross thoracotomy, such as a median sternotomy, wherein the sternum and/or one or more ribs are cut or removed from the rib cage. It should be understood that one or more ribs may be retracted to widen the intercostal space between adjacent ribs without departing from the scope of the invention. 
     Proximate the distal end of each probe is an elongated ablating end  70  having an ablating surface  65  formed to transmurally ablate heart tissue. Access to the selected portions of the atria of the heart H are provided by the specially shaped shafts  66  and ablating ends  70  which are configured to position the elongated ablating surface  65  through the chest wall of patient P and through a strategically positioned penetration in the muscular wall of the patient&#39;s heart H for ablative contact with a selected portion of an interior surface of the muscular wall. Subsequent contact of the ablating surface  65  with specific selected wall portions of the atria enable selected, localized transmural ablation thereof. 
     In a preferred embodiment the probes  57  form the lesions by freezing the heart tissue. Although freezing is a preferred method of ablating tissue, the probe  57  may use any other method such as RF ablation, ultrasound, microwave, laser, localized delivery of chemical or biological agents, light-activated agents, laser ablation or resistance heating ablation. Regarding the localized delivery of chemical or biological agents, the device may include an injection device capable of injecting the chemical or biological agent onto or into the desired tissue for localized ablation thereof. The source of the chemical or biological agent may be stored in a reservoir contained in the probe or be stored in an external reservoir coupled to the injecting end of the probe. 
     When the probe freezes tissue during ablation, an opposite end of the probe has a fitting  71  formed for releasable coupling to an end of a delivery hose which in turn is coupled to a source (both of which are not shown) of cryogenic media. A threaded portion  72  of the fitting is formed for removable mounting to the delivery hose and further provides communication with the cryogenic media for both delivery to and exhaust from the probe. 
     As shown in  FIG. 6 , each probe includes an elongated shaft  66  sufficiently dimensioned and shaped to enable manual manipulation of the ablating end  70  into contact with the desired heart tissue from outside the thoracic cavity. The shaft  66  is preferably tubular-shaped and defines a communication passageway  73  extending therethrough which provides both delivery and exhaust of the cryogen to and from the ablating end  70 . Communication passageway  73  extends fully from the fitting  71  ( FIG. 4 ) to a closed-end boiler chamber  75  where the cryogen exits the ablating end  70 . Preferably, the tubular shaft  66  includes an outer diameter in the range of about 2.0 mm to about 5.0 mm, and most preferably about 4.0 mm; while the inner diameter is in the range of about 1.5 mm to about 4.5 mm, and most preferably about 3.0 mm. 
     Concentrically positioned in the communication passageway  73  of each probe is a delivery tube  76  ( FIG. 6 ) which extends from the fitting  71  to proximate the boiler chamber  75  for communication therebetween enabling delivery and dispersion of the cryogen to the boiler chamber. The proximal end of delivery tube  76  is coupled to the cryogen liquid source through a conventional fitting for delivery of the cryogen through a delivery passageway  77 . The outer diameter of delivery tube  76  is dimensioned such that an annular exhaust passageway  78  is formed between the outer diameter of the delivery tube  76  and the inner diameter of the tubular shaft  66 . This exhaust passageway  78  provides a port through which the expended cryogen exiting the boiler chamber can be exhausted. Preferably, the delivery tube  76  includes an outer diameter in the range of about 1.4 mm to about 3.0 mm, and most preferably about 2.0 mm; while the inner diameter is in the range of about 1.15 mm to about 2.75 mm, and most preferably about 1.50 mm. 
     The shaft of each probe  56  is specifically formed and shaped to facilitate performance of one or more of the particular procedures to be described in greater detail below. However, due to the nature of the procedure and the slight anatomical differences between patients, each probe may not always accommodate a particular patient for the designated procedure. Accordingly, it is highly advantageous and desirable to provide an exhaust shaft  66  and delivery tube  76  combination which is malleable. This material property permits reshaping and bending of the exhaust shaft and delivery tube as a unit to reposition the ablating surface for greater ablation precision. Moreover, the shaft must be capable of bending and reshaping without kinking or collapsing. Such properties are especially imperative for the devices employed in the pulmonary vein isolation lesion formation which are particularly difficult to access. 
     This malleable material, for example, may be provided by certain stainless steels, NiTi or a shape memory alloy in its superelastic state such as a superelastic alloy. Moreover, the shaft portion, with the exception of the ablating surface, may be composed of a polymer material such as plastic which of course exhibits favorable thermoplastic deformation characteristics. Preferably, however, the exhaust and delivery shafts  66  and  76  are composed of bright annealed 304 stainless steel. The delivery tube  76  may also be composed of NiTi or other superelastic alloy. 
     To prevent or substantially reduce contact between the concentric tubes during operation, due to resonance or the like, the delivery tube  76  may be isolated and separated from contact with the inner walls of the exhaust shaft  66  by placing spacers around the delivery tube. These spacers may be provided by plastic or other polymer material. Alternatively, the delivery tube may be brazed or welded to one side of the inner wall of the exhaust shaft  66  along the longitudinal length thereof to resist vibrational contact, as illustrated in  FIG. 8 . 
     In accordance with the present invention, the lesions formed by this system and procedure are generally elongated in nature. The ablating end  70  is thus provided by an elongated ablating surface  65  which extends rearwardly from the distal end a distance of at least about seven (7) times to about thirty (30) times the outer diameter of the ablating end, which incidentally is about the same as the outer diameter of the shaft  66 . Hence, the length of the ablating surface is at least three (3) cm long, more preferably at least four (4) cm long, and most preferably at least five (5) cm long. Alternatively, the ablating surface  65  has a length of between about three (3) cm to about eight (8) cm. 
     In most applications, uniform cryothermic cooling along the full length of the ablating surface is imperative for effective operation. This task, alone, may be difficult to accomplish due primarily to the relatively small internal dimensions of the probe, as well as the generally curved nature of the boiler chambers in most of the cryoprobes ( FIG. 4 ).  FIG. 6  represents a typical cross-sectional view of an ablating end  70  of one of the probe devices of the present invention in which the ablating surface  65  is formed to contact the heart tissue for localized, transmural ablation thereof. Ablating end  70  therefore is preferably provided by a material exhibiting high thermal conductivity properties suitable for efficient heat transfer during cryogenic cooling of the tip. Such materials preferably include silver, gold and oxygen free copper or the like. 
     The ablating end  70  is preferably provided by a closed-end, elongated tube having an interior wall  80  which defines the boiler chamber  75 , and is about 1.0 mm to about 1.5 mm thick, and most preferably about 1.25 mm thick. This portion is specifically shaped for use in one or more ablation procedures and is formed for penetration through the muscular walls of the heart. The distal end of exhaust shaft  66  is preferably inserted through an opening  81  into the boiler chamber  75  such that the exterior surface  82  at the tip of the exhaust shaft  66  seatably abuts against the interior wall  80  of the ablating end  70  for mounting engagement therebetween. Preferably, silver solder or the like may be applied to fixably mount the ablating end to the end of the exhaust shaft. Alternatively, the proximal end of ablating end  70  can be mounted directly to the distal end of exhaust shaft  66  (i.e., in an end-to-end manner) using electron-beam welding techniques. In either mounting technique, a hermetic seal must be formed to eliminate cryogen leakage. 
     Proximate the distal end of delivery tube  76  is a delivery portion  83  which extends through the opening  81  and into boiler chamber  75  of the ablating end  70 . This closed-end delivery portion includes a plurality of relatively small diameter apertures  85  which extend through the delivery portion  83  into delivery passageway  77  to communicate the pressurized cryogen between the delivery passageway and the boiler chamber  75 . Using the Joule-Thompson effect, the cryogen flows through the delivery passageway in the direction of arrow  86  and into the delivery portion  83  where the cryogen expands through the apertures from about 600-900 psi to about 50-200 psi in the boiler chamber. As the cryogen expands, it impinges upon the interior wall  80  of the ablating end cooling the ablating surface  65 . Subsequently, the expended cryogen flows in the direction of arrow  87  passing through the exhaust passageway  78  and out through the delivery hose. 
     The number of apertures required to uniformly cool the ablating end is primarily dependent upon the length of the boiler chamber  75 , the diameter of the apertures, the type of cryogen employed and the pressure of the cryogen. Generally, for the preferred cryogen of nitrous oxide (N 2 O), these delivery apertures  85  are equally spaced-apart at about 5 mm to about 12 mm intervals, and extend from the proximal end of the boiler chamber to the distal end thereof. The preferred diameters of the apertures  85  range from about 0.004 inch to about 0.010 inch. These diameters may vary of course. 
     For most probes, three to four apertures or sets of apertures spaced-apart longitudinally along delivery end portion are sufficient. Only one aperture  85  may be required at each longitudinal spaced location along the delivery portion  83  ( FIG. 8 ). This one aperture may be strategically positioned radially about the delivery portion to direct the stream of cryogen onto the portion of the interior wall  80  directly beneath or near the predetermined portion of the ablating surface  65  which is to contact the heart wall tissue for a particular procedure. Hence, the spaced-apart apertures may be strategically positioned to collectively direct the cryogen onto particular surfaces of the ablating end to assure maximum cooling of those portions. In some instances, however (as shown in  FIG. 7 ), more than one aperture  85  may be radially positioned about the delivery portion  83  at any one longitudinal spaced location, proximate a plane extending transversely therethrough, for additional cryogenic cooling of the ablating surface. This may be especially important where the probe is to be employed in more than one procedure. 
     Due to the elongated and curved nature of the ablating surface  65 , it is difficult to maintain a generally uniform temperature gradient along the desired portions of the ablating surface during cryogenic cooling. This may be due in part to the pressure decrease in the delivery passageway  77  of the delivery portion  83  as the cryogen passes therethrough. To compensate for this pressure loss as the cryogen passes through the delivery portion, the diameters of the apertures  85 ,  85 ′,  85 ″ etc., may be slightly increased from the proximal end of the delivery portion  83  to the distal end thereof. Thus, as the cryogen travels through the delivery portion  83  of the delivery tube, a more uniform volume of cryogen may be distributed throughout the boiler chamber  75  even though the cryogenic pressure incrementally decreases from the proximal end of the delivery portion  83 . 
     Moreover, the delivery volume of the cryogenic cooling also may be controlled by varying the number of apertures at particular portions of the ablating end i.e., increasing or decreasing the number of apertures at a particular location. This directed cooling will have a localized cooling effect, and is exemplified in the ablating end  70  of  FIG. 4 . In this embodiment, the increased number of apertures along the inner bight portion  88  of delivery portion  83  delivers a more direct and greater volume of cryogen against the inner bight portion  88 , as compared to the outer bight portion  90 . 
     An insulative coating or tubing  89  is preferably included extending circumferentially around portions of the cryoprobe shaft  66  near the ablation end  70 . This insulative tubing provides an insulatory barrier around shaft  66  to prevent inadvertent direct contact between the shaft, which will be cooled by the expended cryogen flowing through the exhaust passageway  75 , and any organs or tissue of the percutaneous penetration. The insulative tubing is preferably spaced from the shaft  66  to define an air gap between the inner surface of the tubing and the outer surface of the shaft. 
     The insulative tubing  89  preferably extends around the elongated shaft  66  from the base of the ablation end  70  to the fitting  71 . In some instances, however, the tubing may only need to extend from the base of the ablation end to a midportion of the elongated shaft. The insulative tubing  89  is preferably provided by heat shrink polyolefin tubing, silicone, TEFLON®, or the like. 
     In the preferred form, as shown in  FIG. 7 , the transverse, cross-sectional dimension of the ablating end  70  is circular-shaped having a substantially uniform thickness. However, it will be understood that the ablating surface  65  may include a generally flat contact surface  91  formed for increased area contact with the heart tissue without requiring a substantial increase in the diameter of the ablating surface. As best viewed in  FIGS. 8A-8C , contact surface  91  may be generally flat or have a much larger radius than that of the ablating end. Moreover, the spaced-apart apertures  85  are preferably oriented and formed to deliver the cryogen into direct impingement with the underside of the contact surface  91  of ablating end  70 . In this arrangement, the delivery portion  83  of the delivery tube  76  may be mounted to one side of the interior wall  80 , as set forth above. 
     Alternatively, the contact surface can be provided by a blunted edge or the like to create a relatively narrow lesion. Although not illustrated, the transverse cross-sectional dimension of this embodiment would appear teardrop-shaped. 
       FIGS. 6A-6D  illustrate an embodiment of the probe  57  in which an insulative jacket or sleeve  304  is disposed on the probe so as to be movable relative thereto. The sleeve  304  has a window or cut-out portion  305  which exposes a selected area of the probe  57 .  FIG. 6A  shows the sleeve  304  located around the probe shaft, while  FIG. 6B  shows the sleeve after it has been slid over part of the probe ablating surface  65 .  FIG. 6C  shows the sleeve  304  after it has been slid completely over the ablating surface  65  to a position where the window  305  exposes one area of the surface  65  for ablating tissue.  FIG. 6D  shows the sleeve  304  rotated to a different position where the window  305  exposes a different area of the surface  65  for ablating tissue. The sleeve  304  may be slidable and rotatable relative to the probe as show in  FIGS. 6A-6D . Alternatively, the sleeve  304  may be fixed axially with respect to the probe  57  but rotatable relative thereto so that the window is able to expose different areas of the ablating surface. Further still, the sleeve  304  may be fixed on the probe  57  such that only a selected area of ablation surface  65  is exposed through window  305 . The sleeve  304  may be formed of any suitable material, for example, a flexible polymer having low thermal conductivity. 
     The preferred cryogen employed in the devices of the present invention is nitrous oxide (N 2 O) which is normally stored in a compressed gas cylinder (not shown). Other cryogenic fluids may be employed which include liquid nitrogen or liquified air stored in a Dewar vessel (not shown), freon 13, freon 14, freon 22, and normally gaseous hydrocarbons. 
     To cool the ablating end of the cryoprobe, cryogen is selectively delivered through the delivery passageway  77  of delivery tube  76  into the delivery conduit thereof. As the cryogen flows through delivery apertures  85 , the gas expands into the boiler chamber  75 , cooling the ablating surface using the well known Joule-Thompson effect. The elongated ablating surface  65  is then immediately cooled to a temperature of preferably between about −50 degrees C. to about −80 degrees C., when nitrous oxide is employed. Direct conductive contact of the cooled, elongated ablating surface  65  with the selected heart tissue causes cryogenic ablation thereof. Subsequently, a localized, elongated, transmural lesion is formed at a controlled location which sufficiently prevents or is resistant to electrical conduction therethrough. 
     To assure preclusion of electrical conduction of reentrant pathways in the atria, the lesions must be transmural in nature. Hence, the minimum length of time for conductive contact of the ablating surface with the selected heart tissue necessary to cause localized, transmural ablation thereof is to a large degree a function of the thickness of the heart wall tissue, the heat transfer loss due do the convective and conductive properties of the blood in fluid contact with the ablating surface, as well as the type of cryogen employed and the rate of flow thereof. In most instances, when employing nitrous oxide as the cryogen, tissue contact is preferably in the range of about 2-4 minutes. 
     As mentioned, while the closed-heart surgical system and procedure of the present invention may be performed through open-chest surgery, the preferred technique is conducted through closed-chest methods.  FIGS. 5 and 9  illustrate system  56  for closed-chest, closed-heart surgery positioned in a patient P on an operating table T. The patient is prepared for cardiac surgery in the conventional manner, and general anesthesia is induced. To surgically access the right atrium, the patient is positioned on the patient&#39;s left side so that the right lateral side of the chest is disposed upward. Preferably, a wedge or block W having a top surface angled at approximately 20 degrees to 45 degrees is positioned under the right side of the patient&#39;s body so that the right side of the patient&#39;s body is somewhat higher than the left side. It will be understood, however, that a similar wedge or block W is positioned under the left side of patient P (not shown) when performing the surgical procedure on the left atrium In either position, the patient&#39;s right arm A or left arm (not shown) is allowed to rotate downward to rest on table T, exposing either the right lateral side or the left lateral side of the patient&#39;s chest. 
     Initially one small incision 2-3 cm in length is made between the ribs on the right side of the patient P, usually in the third, fourth, or fifth intercostal spaces, and most preferably the fourth as shown in  FIG. 11A . When additional maneuvering space is necessary, the intercostal space between the ribs may be widened by spreading of the adjacent ribs. A thoracoscopic access device  68  (e.g. a retractor, trocar sleeve or cannulae), providing an access port  67 , is then positioned in the incision to retract away adjacent tissue and protect it from trauma as instruments are introduced into the chest cavity. This access device  68  has an outer diameter preferably less than 14 mm and an axial passage of a length less than about 12 mm. It will be understood to those of ordinary skill in the art that additional thoracoscopic trocars or the like may be positioned within intercostal spaces in the right lateral chest inferior and superior to the refractor  68 , as well as in the right anterior (or ventral) portion of the chest if necessary. In other instances, instruments may be introduced directly through small, percutaneous intercostal incisions in the chest. 
     Referring again to  FIGS. 5 and 9 , the retractor  68 , such as that described in detail in commonly assigned U.S. patent application Ser. No. 08/610,619 filed Mar. 4, 1996, surgical access to the body cavity of patient P through the first intercostal percutaneous penetration  92  in the tissue  93 . Briefly, refractor  68  includes an anchoring frame  95  having a passageway  67  therethrough which defines a longitudinal refractor axis. The anchoring frame  95  is positionable through the intercostal percutaneous penetration  92  into the body cavity. A flexible tensioning member  96  is attached to anchoring frame  95  and extendible from the anchoring frame out of the body through intercostal penetration  92  to deform into a non-circular shape when introduced between two ribs. The tensioning member  96  is selectively tensionable to spread the tissue radially outward from the longitudinal axis. Hence, it is the tension imposed on the flexible tensioning member  96  which effects refraction of the tissue, rather than relying on the structural integrity of a tubular structure such as a trocar sheath. 
     Once the retractor  68  has been positioned and anchored in the patient&#39;s chest, visualization within the thoracic cavity may be accomplished in any of several ways. An endoscope  97  ( FIG. 5 ) of conventional construction is positioned through a percutaneous intercostal penetration into the patient&#39;s chest, usually through the port of the soft tissue retractor  68 . A video camera  98  is mounted to the proximal end of endoscope  97 , and is connected to a video monitor  100  for viewing the interior of the thoracic cavity. Endoscope  97  is manipulated so as to provide a view of the right side of the heart, and particularly, a right side view of the right atrium. Usually, an endoscope of the type having an articulated distal end such as the Distalcam 360, available from Welch-Allyn of Skameateles Falls, N.Y., or a endoscope having a distal end disposed at an angle between 30 i  and 90 i  will be used, which is commercially available from, for example, Olympus Corp., Medical Instruments Division, Lake Success, N.Y. A light source (not shown) is also provided on endoscope  97  to illuminate the thoracic cavity. 
     Further, the surgeon may simply view the chest cavity directly through the access port  67  of the retractor  68 . Moreover, during the closed heart procedure of the present invention, it may be desirable to visualize the interior of the heart chambers. In these instances a transesophageal echocardiography may be used, wherein an ultrasonic probe is placed in the patient&#39;s esophagus or stomach to ultrasonically image the interior of the heart. A thoracoscopic ultrasonic probe may also be placed through access device  68  into the chest cavity and adjacent the exterior of the heart for ultrasonically imaging the interior of the heart. 
     An endoscope may also be employed having an optically transparent bulb such as an inflatable balloon or transparent plastic lens over its distal end which is then introduced into the heart. As disclosed in commonly assigned, co-pending U.S. patent application Ser. No. 08/425,179, filed Apr. 20, 1995, the balloon may be inflated with a transparent inflation fluid such as saline to displace blood away from distal end and may be positioned against a site such a lesion, allowing the location, shape, and size of cryolesion to be visualized. 
     As a further visualization alternative, an endoscope may be utilized which employs a specialized light filter, so that only those wavelengths of light not absorbed by blood are transmitted into the heart. The endoscope utilizes a CCD chip designed to receive and react to such light wavelengths and transmit the image received to a video monitor. In this way, the endoscope can be positioned in the heart through access port  67  and used to see through blood to observe a region of the heart. A visualization system based on such principles is described in U.S. Pat. No. 4,786,155, which is incorporated herein by reference. 
     Finally, the heart treatment procedure and system of the present invention may be performed while the heart remains beating. Hence, the trauma and risks associated with cardiopulmonary bypass (CPB) and cardioplegic arrest can be avoided. In other instances, however, arresting the heart may be advantageous. Should it be desirable to place the patient on cardiopulmonary bypass, the patient&#39;s right lung is collapsed and the patient&#39;s heart is arrested. Suitable techniques for arresting cardiac function and establishing CPB without a thoracotomy are described in commonly-assigned, co-pending U.S. patent application Ser. No. 08/282,192, filed Jul. 28, 1994 and U.S. patent application Ser. No. 08/372,741, filed Jan. 17, 1995, all of which are incorporated herein by reference. Although it is preferred to use the endovascular systems described above, any system for arresting a patient&#39;s heart and placing the patient on CPB may be employed. 
     As illustrated in  FIG. 10 , CPB is established by introducing a venous cannula  101  into a femoral vein  102  in patient P to withdraw deoxygenated blood therefrom. Venous cannula  101  is connected to a cardiopulmonary bypass system  104  which receives the withdrawn blood, oxygenates the blood, and returns the oxygenated blood to an arterial return cannula  105  positioned in a femoral artery  106 . 
     A pulmonary venting catheter  107  may also be utilized to withdraw blood from the pulmonary trunk  108 . Pulmonary venting catheter  107  may be introduced from the neck through the interior jugular vein  110  and superior vena cava  111 , or from the groin through femoral vein  102  and inferior vena cava  103 . An alternative method of venting blood from pulmonary trunk  108  is described in U.S. Pat. No. 4,889,137, which is incorporated herein by reference. In the technique described therein, an endovascular device is positioned from the interior jugular vein in the neck through the right atrium, right ventricle, and pulmonary valve into the pulmonary artery so as to hold open the tricuspid and pulmonary valves. 
     For purposes of arresting cardiac function, an aortic occlusion catheter  113  is positioned in a femoral artery  106  by a percutaneous technique such as the Seldinger technique, or through a surgical cut-down. The aortic occlusion catheter  113  is advanced, usually over a guidewire (not shown), until an occlusion balloon  115  at its distal end is disposed in the ascending aorta  116  between the coronary ostia and the brachiocephalic artery. Blood may be vented from ascending aorta  116  through a port  120  at the distal end of the aortic occlusion catheter  113  in communication with an inner lumen in aortic occlusion catheter  113 , through which blood may flow to the proximal end of the catheter. The blood may then be directed to a blood filter/recovery system  121  to remove emboli, and then returned to the patient&#39;s arterial system via CPB system  104 . 
     When it is desired to arrest cardiac function, occlusion balloon  115  is inflated until it completely occludes ascending aorta  116 , blocking blood flow therethrough. A cardioplegic fluid such as potassium chloride (KCl) is preferably mixed with oxygenated blood from the CPB system and then delivered to the myocardium in one or both of two ways. Cardioplegic fluid may be delivered in an anterograde manner, retrograde manner, or a combination thereof. In the anterograde delivery, the cardioplegic fluid is delivered from a cardioplegia pump  122  through an inner lumen in aortic occlusion catheter  113  and the port  120  distal to occlusion balloon  115  into the ascending aorta upstream of occlusion balloon  115 . In the retrograde delivery, the cardioplegic fluid may be delivered through a retroperfusion catheter  123  positioned in the coronary sinus from a peripheral vein such as an internal jugular vein in the neck. 
     With cardiopulmonary bypass established, cardiac function arrested, and the right lung collapsed, the patient is prepared for surgical intervention within the heart H. At this point in the procedure, whether cardiac function is arrested and the patient is placed on CPB, or the patient&#39;s heart remains beating, the heart treatment procedure and system of the present invention remain substantially similar. The primary difference is that when the procedure of the present invention is performed on an arrested heart, the blood pressure in the internal chambers of the heart is significantly less. Hence, it is not necessary to form a hemostatic seal between the device and the heart wall penetration to inhibit blood loss through the penetration thereby reducing or eliminating the need for purse-string sutures around such penetrations, as will be described below. 
     In the preferred embodiment, however, the procedure is conducted while the heart is still beating. Accordingly, it is necessary to form a hemostatic seal between the ablation device and the penetration. Preferably, purse-string sutures  58 ,  60 ,  61 ,  62  and  63  ( FIGS. 3A and 3B ) are placed in the heart walls at strategic or predetermined locations to enable introduction of the ablating probes into the heart while maintaining a hemostatic seal between the probe and the penetration. 
     As best viewed shown in  FIG. 11A , in order to gain access to the right atrium of the heart, a pericardiotomy is performed using thoracoscopic instruments introduced through retractor access port  67 . Instruments suitable for use in this procedure, including thoracoscopic angled scissors  130  and thoracoscopic grasping forceps  131 , are described in commonly assigned U.S. Pat. No. 5,501,698, issued Mar. 26, 1996, which is incorporated herein by reference. 
     After incising a T-shaped opening in the pericardium  132  (about 5.0 cm in length across and about 4.0 cm in length down,  FIG. 11A ), the exterior of the heart H is sufficiently exposed to allow the closed-chest, closed-heart procedure to be performed. To further aid in visualization and access to the heart H, the cut pericardial tissue  133  is refracted away from the pericardial opening  135  with stay sutures  136  ( FIG. 11C ) extending out of the chest cavity. This technique allows the surgeon to raise and lower the cut pericardial wall in a manner which reshapes the pericardial opening  135  and refracting the heart H slightly, if necessary, to provide maximum access for a specific procedure. 
     To install stay suture  136 , a curved suture needle  137  attached to one end of a suture thread  138  is introduced into the chest cavity through passageway  67  with of a thoracoscopic needle driver  140  ( FIG. 11B ). Once the suture needle  137  and thread  138  have been driven through the cut pericardial tissue, the suture thread  138  is snared by a suture snare device  141 . This is accomplished by positioning a hooked end  142  of suture snare device  141  through at least one additional percutaneous intercostal penetration  143  positioned about the chest to enable penetration into the thoracic cavity. In the preferred arrangement, a trocar needle (not shown) is employed which not only forms the penetration, but also provides access into the thoracic cavity without snaring tissue during removal of the snare device. 
     Accordingly, both sides of the suture thread  138  are snared and pulled through the chest wall for manipulation of the stay suture from outside of the body cavity. The ends of the stay suture  136  are coupled to a surgical clamp (not shown) for angled manipulation and tension adjusting. While only two stay sutures are illustrated, it will be appreciated that more stay sutures may be employed as needed to further manipulate the pericardial opening. 
     Turning now to  FIG. 11C , a first 4-0 purse-string suture  58 , for example, is placed in the heart wall proximate the site at which it is desired to initiate the first heart wall penetration  146  ( FIG. 11D ). Again, this is accomplished by using a thoracoscopic needle driver to drive the suture needle through the heart wall to form a running stitch in a circular pattern approximately 1.0-3.0 mm in diameter. A double-armed suture may also be used, wherein the suture thread  145  (about 3 mm to about 10 mm in diameter) has needles (not shown) at both ends, allowing each needle to be used to form one semi-circular portion of the purse-string. Suture thread  138  is long enough to allow both ends of the suture to be drawn outside of the chest cavity once purse-string suture  58  has been placed. The suture needle is then cut from thread  145  using thoracoscopic scissors. 
     To tension the purse-string suture  58 , the suture threads  145  are pulled upon gathering the stitched circular pattern of tissue together before commencement of the formation of a penetration through the heart wall within the purse-string suture. One or a pair of thoracoscopic cinching instruments  147 , such as a Rumel tourniquet, may be employed to grasp a loop of purse-string suture  58 . As best viewed in  FIG. 11D , cinching instrument  147  comprises a shaft  148  with a slidable hook  150  at its distal end thereof for this purpose. Hook  150  may be retracted proximally to frictionally retain suture thread  145  against the distal end of shaft  148 . By retracting or withdrawing the cinching instrument  147 , the purse-string suture  58  is cinched tightly, thereby gathering heart wall tissue together to form a hemostatic seal. 
     The cinching instrument may be clamped in position to maintain tension on suture thread  145 . Preferably, however, a slidable tensioning sleeve  151  ( FIG. 11D ), commonly referred to as a snugger, may be provided in which the suture threads are positioned through a bore extending therethrough. The snugger is then slid along the suture thread until it abuts against the epicardial surface  152  of the heart wall. The cinching instrument is then pulled proximally relative to tensioning sleeve  151  to obtain the desired degree of tension on suture thread  145 . Tensioning sleeve  151  is configured to frictionally couple to suture thread  145  to maintain tension on the suture. 
     An incision device  153  is introduced through access device  68  into the chest cavity for piercing the heart H. A blade  155  positioned on the distal end of a manipulating shaft  156  is advanced to pierce the heart wall within the bounds of purse-string suture  58 . The blade  155  is preferably about 5.0 mm in length and about 3.0 mm wide terminating at the tip thereof.  FIG. 11  D illustrates that as the incision device  153  is manually moved further into contact with the epicardial surface  152  of the heart wall, blade  155  will be caused to pierce therethrough to form a penetration of about 1.0-2.0 mm across. 
     In the preferred form, the blade  155  is rigidly mounted to shaft  156  for direct one-to-one manipulation of the blade. Alternatively, however, the incision device may employ a spring loaded mechanism or the like which advances the blade forwardly from a retracted position, retracted in a protective sleeve of the shaft, to an extended position, extending the blade outside of the sleeve and into piercing contact with the tissue. In this embodiment, a button or the like may be provided near the proximal end of the shaft for operation of the blade between the retracted and extended positions. 
     To facilitate formation of the penetration by the incision device, a thoracoscopic grasping instrument (not shown) may be employed to grasp the heart wall near purse-string suture  58  to counter the insertion force of blade  155  and incision device  153 . As blade  155  penetrates the heart wall, incision device  153  is advanced to extend transmurally into the heart through the penetration  146  formed in heart wall. 
     As above-indicated in  FIGS. 3A and 3B , the entire procedure is preferably performed through a series of only five purse-strings sutures  58 ,  60 ,  61 ,  62  and  63 , and the corresponding cardiac penetrations  146 ,  157 ,  158 ,  160  and  161  of which two penetrations  158 ,  160  are strategically positioned in the right atrium RA; one penetration  161  is positioned in the left atrium LA; and two penetrations  158 ,  160  are positioned near the pulmonary vein trunk  108 . Such small incisions are significantly less traumatic on the heart tissue muscle than the elongated transmural incisions of the prior MAZE techniques. 
     Referring now to  FIGS. 3A ,  12 A- 12 C and  13 , the system and procedure of the present invention will be described in detail. Preferably, the first series of lesions is formed on the right atrium RA to form a posterior longitudinal right atrial lesion  50  and a tricuspid valve annulus lesion  51 . It will be appreciated, however, that the transmural lesions can be formed in any order without departing from the true spirit and nature of the present invention. 
     By strategically placing the first heart wall penetration  146  of first purse-string suture  58  at the base of the right atrial appendage RAA where the anticipated intersection between the longitudinal right atrial lesion  50  and the tricuspid valve annulus lesion  51  are to occur ( FIG. 12C ), these two lesions can be formed through a series of three independent ablations. As best viewed in  FIG. 12A , the upper section segment  162  (half of the longitudinal right atrial lesion  50 ) is formed using a right angle probe  163  ( FIG. 24 ) having a first elbow portion  166  positioned between the generally straight elongated shaft  66  and the generally straight ablating end. The first elbow portion has an arc length of about 85 degrees to about 95 degrees and a radius of curvature of about 3.2 mm to about 6.4 mm. The ablating end  70  is preferably about 2.0 mm to about 4.0 mm in diameter, and about 2.0 cm to about 6.0 cm in length. In this configuration, the ablating surface  65  extends, circumferentially, from a distal end  165  thereof to just past an elbow portion  166  of the right angle probe  163 . 
     Initially, the probe ablating end  70  and the shaft  66  of probe  163  is introduced into the thoracic cavity through the retractor  68  by manipulating a handle (not shown) releasably coupled to fitting  71 . To facilitate location of the first penetration with the probe, the distal end  165  is guided along the shaft  156  of incision device  153  ( FIG. 11D ) until positioned proximate the first penetration  146 . Subsequently, the blade  155  of incision device is withdrawn from the first penetration whereby the distal end of the probe is immediately inserted through the first penetration. Not only does this technique facilitate insertion of the probe but also minimizes loss of blood through the penetration. 
     Once the distal end  165  of the right angle probe  163  has been inserted and negotiated through the first penetration, the first purse-string suture may require adjustment to ensure the formation of a proper hemostatic seal between the penetration and the shaft of the probe. If the loss of blood should occur, the purse-string suture can be easily tightened through either a Rumel tourniquet or tensioning sleeve  151 . 
       FIG. 12A  best illustrates that the right angle probe  163  is preferably inserted through the penetration  146  until an elbow portion  166  thereof just passes through the penetration. Although the angular manipulation of the end of the right angle probe is limited due to the access provided by the refractor, the insertion should be easily accommodated since the heart wall tissue of the right atrium is substantially resilient and flexible. Again, a thoracoscopic grasping instrument (not shown) may be employed to grasp the heart wall near the first purse-string suture  58  to counter the insertion force of right angle probe  163  through the first penetration  146 . Once the ablating end is inserted to the desired depth and through the assistance of either direct viewing or laparoscopic viewing, the elongated ablating end  70  is oriented to position a longitudinal axis thereof generally parallel to the right atrioventricular groove. This upper section segment  162  of the longitudinal right atrial lesion  50  extends generally from the first penetration  146  to the orifice of the superior vena cava  111 . By retracting the probe rearwardly out of the passageway of the retractor  68  generally in the direction of arrow  167 , the ablating surface will be caused to sufficiently contact the right atrial endocardium. 
     As mentioned above, the probe may use any method to ablate the heart tissue. When using a cryogenic ablating system, the cryogen stored in a Dewar vessel or pressurized cylinder is selectively released where it passes into the boiler chamber  75  of the device  163 , thereby cooling the probe ablating surface for localized ablation of heart tissue. As previously stated, to warrant proper transmural ablation of the interior wall of the right atrium, continuous contact of the ablating surface therewith should occur for about 2-4 minutes. Visually, however, transmural cryosurgical ablation of the tissue is generally represented by a localized lightening or discoloration of the epicardial surface  168  of the ablated heart tissue which can be directly viewed through the access port  67  of access device  68 . This method of determining cryoablation of the tissue can be used in combination with the timed probe contact therewith. As a result, the upper section segment  162  of the longitudinal right atrial lesion  50  will be formed. 
     Once the desired elongated portion of heart tissue has been ablated, caution must be observed before the ablating surface  65  probe can be separated from the contacted endocardial surface of the heart tissue. Due to the extremely low temperatures of the ablating surface (i.e., about −50 degrees C. to about −80 degrees C.) and the moistness of the heart tissue, cryoadhesion can occur. Accordingly, the probe tip must be properly thawed or defrosted to enable safe separation after the tissue has been properly ablated. 
     For example, after sufficient transmural cryoablation of the heart tissue, thawing is commenced by halting the flow of cryogen through the probe and maintaining continuous contact between the probe ablating surface and the cryoablated tissue. After about 10-20 seconds, and preferably about 15 seconds, the conductive and convective heat transfer or heat sink effect from the surrounding tissue and blood is sufficient to reverse the cryoadhesion. Of course, it will be appreciated that such heat transfer is more efficient when the procedure is performed on a beating heart as opposed to an arrested heart. Alternatively, the system may also be provided with a defrost mode which serves to warm the tissue to room temperature. This may be accomplished by raising the pressure of the cryogen adjacent the ablating surface such that its temperature increases, for example, by restricting the exhaust gas flow. 
     Furthermore, to facilitate thawing of the exterior surface of the ablated tissue, a room temperature or slightly heated liquid may be wetted or impinged upon the exterior surface of the ablated area. In the preferred embodiment, such liquid may include saline or other non-toxic liquid introduced into the thoracic cavity through the retractor passageway  67 . 
     Generally, multiple lesions can be formed through a single purse-string suture either through the use of assorted uniquely shaped ablating devices or through the manipulation of a single ablating device. Accordingly, while maintaining the hemostatic seal between the probe shaft and the penetration, the respective ablating device can be manipulated through the respective penetration to strategically contact the corresponding elongated ablating surface with another selected portion of the interior surface of the muscular wall for transmural ablation thereof. For instance, without removing the right angle cryoprobe from the first penetration, the ablating surface  65  is rotated approximately 180 degrees about the longitudinal axis to re-position the distal end generally in a direction toward the orifice of the inferior vena cava  103 . As shown in  FIG. 12B , such positioning enables the formation of the remaining lower section segment  170  of the longitudinal right atrial lesion  50 . However, since the lower section segment  170  of the lesion is shorter in length than that of the upper section segment, the length of the elongated ablating surface contacting the interior wall of right atrium must be adjusted accordingly. This length adjustment is accomplished by partially withdrawing the probe ablating surface  65  from the first penetration  146  by the appropriate length to ablate the lower section segment  170 . Due to the substantial flexibility and resiliency of the heart tissue, such maneuverability of the probe and manipulation of the tissue is permissible. 
     Similar to the formation of the upper section segment  162  of the longitudinal right atrial lesion  50 , the right angle probe  163  is retracted rearwardly, generally in the direction of arrow  167 , causing the ablating surface  65  of the probe to sufficiently contact the endocardium of the right atrium. After the cryogen has continuously cooled the elongated ablating surface  65  of the probe for about 2-4 minutes, the remaining lower section segment of the longitudinal right atrial lesion  50  will be formed. Thereafter, the probe is defrosted to reverse the effects of cryoadhesion. It will be understood that while it is beneficial to employ the same right angle probe to perform both the upper and lower section segments of the longitudinal right atrial lesion, a second right angle probe having an ablating surface shorter in length than that of the first right angle probe could easily be employed. 
     Utilizing the same first penetration, the tricuspid valve annulus lesion  51  can be formed employing one of at least two probes. Preferably, the right angle probe  163  may again be used by rotating the elongated ablating surface  65  about the probe shaft longitudinal axis to reposition the distal end trans-pericardially, generally in a direction across the lower atrial free wall and toward the tricuspid valve  171  ( FIGS. 12C and 13 ). The distal end of the probe ablating surface  65 , however, must extend all the way to the tricuspid valve annulus  172 . Hence, in some instances, due to the limited maneuvering space provided through the retractor passageway, the formation of the tricuspid valve annulus lesion  51  with the right angle probe may be difficult to perform. 
     In these instances, a special shaped tricuspid valve annulus probe  173  ( FIGS. 13 and 25 ) is employed which is formed and dimensioned to enable contact of the probe ablating surface  65  with appropriate portion of the right atrium interior wall all the way from the first penetration  146  to the tricuspid valve annulus  172  to form the tricuspid valve annulus lesion  51 . The ablating end  70  and the shaft  66  of this probe cooperate to form one of the straighter probes  57  of the set shown in  FIG. 4 . 
       FIG. 25  best illustrates the tricuspid valve annulus probe  173  which includes an elongated shaft  66  having a first elbow portion  166  positioned between a generally straight first portion  175  and a generally straight second portion  176  having a length of about 2.0 cm to about 6.0 cm. The first elbow portion has an arc length of about 20 degrees to about 40 degrees and a radius of curvature of about 13.0 cm to about 18.0 cm. Further, a second elbow portion  177  is positioned between the second portion  176  and a third portion  178  of the shaft, angling the third portion back toward the longitudinal axis of the first portion  175  of the elongated shaft  66 . The third portion  178  includes a length of about 2.0 cm to about 6.0 cm, while the second elbow portion has an arc length of about 5 degrees to about 20 degrees and a radius of curvature of about 15.0 cm to about 20.0 cm. The ablating end  70  is relatively straight and is coupled to the distal end of the third portion  178  of the elongated shaft  66  in a manner angling the ablating end back away from the longitudinal axis and having an arc length of about 5 degrees to about 20 degrees and a radius of curvature of about 13.0 cm to about 18.0 cm. The ablating end  70  is formed to extend from the first penetration and to the rim  172  of the tricuspid valve  171  from outside of the body cavity. For this probe, the ablating surface  65  is preferably about 2.0 cm to about 6.0 cm in length. It will be understood that while the illustrations and descriptions of the probes are generally two dimensional, the configurations of the shaft and ablating end combinations could be three dimensional in nature. 
     Using the insertion technique employed by the right angle probe  163  during the formation of the longitudinal right atrial lesion  50 , upon withdrawal of the right angle probe from the first penetration  146 , the distal end of the tricuspid valve annulus probe  173  is immediately inserted therethrough to facilitate alignment and minimize the loss of blood. 
     Regardless of what instrument is employed, once the probe ablating surface  65  is strategically oriented and retracted to contact the endocardial surface, the cryogen is selectively released into the boiler chamber to subject the desired tissue to localized cryothermia. Due to the nature of the transmural ablation near the tricuspid valve annulus, the need for dividing all atrial myocardial fibers traversing the ablated portion is effectively eliminated. Thus, the application of the nerve hook utilized in the prior MAZE procedures is no longer necessary. 
     As illustrated in  FIG. 13 , the distal end of the probe must extend to the base of the tricuspid valve annulus  172 . This lesion is difficult to create since the right atrial free-wall in this region lies beneath the atrioventricular groove fat pad (not shown). To facilitate orientation of the ablating end of the probe relative the valve annulus and to better assure the formation of a lesion which is transmural in nature, an alternative tricuspid valve clamping probe  180  ( FIG. 26 ) may be employed rather than or in addition to the tricuspid valve annulus probe  173 . 
     This probe includes a primary shaft  66  and ablating end  70  which are cooperatively shaped and dimensioned substantially similar to the tricuspid valve annulus probe  173 . A clamping device  181  of clamping probe  180  includes a mounting member  179  providing an engagement slot  182  formed for sliding receipt of a pin member  184  coupled to primary shaft  66 . This arrangement pivotally couples the clamping device  181  to the primary shaft  66  for selective cooperating movement of a clamping jaw portion  183  of the clamping device  181  and the ablating end  70  between a released position, separating the clamping jaw portion from the ablating end  70  (phantom lines of  FIG. 26 ), and a clamped position, urging the clamping jaw portion against the ablating end  70  (solid lines of  FIG. 26 ). 
     The clamping jaw portion  183  is shaped and dimensioned substantially similar to the corresponding ablating end  70  to enable clamping of the heart tissue therebetween when the tricuspid valve clamping probe  180  is moved to the clamped position. At the opposite end of the clamping jaw portion  183  is a handle portion  185  for manipulation of the jaw portion between the released and clamped positions in a pliers-type motion. 
     To perform this portion of the procedure using the tricuspid valve clamping probe  180 , the clamping jaw is moved toward the released position to enable the distal end of the ablating end to be negotiated through the first penetration  146 . Using direct viewing through the retractor or visually aided with an endoscope, the ablating end is moved into contact with the predetermined portion of the right atrium interior wall all the way from the first penetration  146  to the tricuspid valve annulus  172 . Subsequently, the clamping jaw portion is moved to the clamped position, via handle portion  185 , to contact the epicardial surface  168  of the heart wall opposite the tissue ablated by the probe. This arrangement increases the force against the ablating surface  65  to facilitate contact and heat transfer. Cryogen is then provided to the boiler chamber to cool the ablating surface  65  thereby forming the tricuspid valve annulus lesion  51 . Once the probe is removed from the first penetration  146 , the first purse-string suture  58  is further tightened to prevent blood loss. 
     The engagement slot  182  of mounting member  179  is formed to permit release of the pin member  184  therefrom. Hence, the clamping device  181  can be released from primary shaft  66  of the clamping probe  180 . This arrangement is beneficial during operative use providing the surgeon the option to introduce the clamping probe  180  into the thoracic cavity as an assembled unit, or to first introduce the ablation end  70  and primary shaft  66 , and then introduce of the clamping device  181  for assembly within the thoracic cavity. 
     Turning now to  FIG. 14 , a second 4-0 purse-string suture  59  is placed in the right atrial appendage RAA proximate a lateral midpoint thereof in the same manner as above-discussed. This portion of the heart is again accessible from the right side of the thoracic cavity through the first access device  68 . A second penetration  157  is formed central to the second purse-string suture wherein blood loss from the second penetration is prevented through a second tensioning sleeve  186 . Subsequently, the distal end of a right angle probe or a right atrium counter lesion probe  187  ( FIGS. 15 and 27 ), is inserted through second penetration  157  and extended into the right atrial appendage chamber. Second purse-string suture  59  may then be adjusted through second tensioning sleeve  186 , as necessary to maintain a hemostatic seal between the penetration and the probe. 
     The right atrium counter lesion probe  187  includes an elongated shaft  66  having a first elbow portion  166  positioned between a relatively straight first portion  175  and a generally straight second portion  176 , whereby the first elbow portion has an arc length of about 85 degrees to about 95 degrees and a radius of curvature of about 1.9 cm to about 3.2 cm. The second portion is preferably about 2.0 cm to about 6.0 cm in length. Further, a second elbow portion  177  is positioned between the second portion  176  and a generally straight third portion  178  of the shaft which is about 2.0 cm to about 6.0 cm in length. The second elbow portion has an arc length of about 40 degrees to about 70 degrees and a radius of curvature of about 3.2 cm to about 5.7 cm, angling the third portion  178  back toward the longitudinal axis of the first portion  175  of the elongated shaft  66 . The ablating end  70  is coupled to the distal end of the third portion  178  of the elongated shaft  66 , and includes an arc length of about 85 degrees to about 95 degrees and a radius of curvature of about 6.0 mm to about 19.0 mm to curve the distal end thereof back toward the longitudinal axis of the first portion  175  of the shaft  66 . Thus, this equates to an ablating surface length of preferably about 4.0 cm to about 8.0 cm in length. 
     This configuration enables the ablating end  70  of probe  187  to access the right lateral midpoint of the atrial appendage RAA where the second penetration  157  is to placed.  FIGS. 14 and 15  best illustrate that the position of this second penetration  157  is higher up than the first penetration, relative the heart, when accessed from the predetermined intercostal penetration  92 . Upon insertion of the distal end of the probe through the second penetration  157 , the ablating end  70  is inserted into the right atrium chamber to the proper depth. The handle (not shown) of the probe  187  is manipulated and oriented from outside the thoracic cavity to position the distal end of the ablating surface  65  in a direction generally toward the first purse-string suture  58 . The probe is retracted rearwardly out of the refractor passageway, generally in the direction of arrow  167  in  FIG. 14 , to urge the ablating surface  65  of the probe into contact with the endocardial surface of the interior wall of the right atrial appendage RAA. As a result, the perpendicular lesion  53  of the right atrial appendage is transmurally formed. 
     The next lesion to be created is the anteromedial counter lesion  55  which is to be formed through the second penetration  157 . This lesion is positioned just anterior to the apex of the triangle of Koch and the membranous portion of the interatrial septum. Without removing the right atrium counter lesion probe  187  from the second penetration  157 , the elongated ablating surface  65  is urged further inwardly through the second penetration  157  toward the rear atrial endocardium of the right atrial appendage RAA ( FIG. 15 ). Upon contact of the ablating surface  65  with the rear atrial wall, the probe  187  is slightly rotated upwardly in the direction of arrows  191  in  FIG. 15  to exert a slight force against the rear endocardial surface. Again, this ensures ablative contact therebetween to enable formation of the anteromedial counter surgical lesion  55 . Subsequently, the probe is properly defrosted and withdrawn from the second penetration  157  whereby the second purse-string suture  59  is cinched tighter to prevent blood loss therefrom. It will be understood that since these two lesions are formed through cryothermic techniques, the need for atrial retraction and endocardial suturing employed in connection with the formation of the transmural incision of the MAZE III procedure can be eliminated. 
     The next step in the procedure is an atrial septotomy to from an anterior limbus of the fossa ovalis lesion  192 . The formation of this lesion will likely be performed without direct or laparoscopic visual assistance since the ablation occurs along internal regions of the interatrial septum wall  193 . Initially, as best illustrated in  FIGS. 16-18 , two side-by-side purse-string sutures  61  and  62  are surgically affixed to an epicardial surface  168  proximate the pulmonary trunk  108  using the same techniques utilized for the first and second purse-string sutures. The third purse-string suture  61  is positioned on one side of the septum wall  193  for access to the right atrium chamber, while the fourth purse-string suture  62  is positioned on the opposite side of the septum wall for access to the left atrium chamber. 
       FIG. 17  further illustrates that the introduction of thoracoscopic instruments and access to the third and fourth purse-strings are preferably provided through the retractor  68 . After the third and fourth tensioning sleeves  195 ,  196  have been mounted to the respective suture threads, an incision device (not shown) is introduced into the thoracic cavity to incise the penetrations central to the respective purse-string sutures. Due to the angle of the upper heart tissue surface relative the retractor  68 , the incision device may incorporate an angled end or blade for oblique entry through the heart wall tissue in the direction of arrow  197  to form the third and fourth penetrations  158 ,  160  ( FIG. 18 ). Alternatively, the incision device may include a blade end which is capable of selective articulation for pivotal movement of the blade end relative the elongated shaft. Use of a thoracoscopic grasping instrument facilitates grasping of the epicardium near the pulmonary trunk  108  to counter the insertion force of the angled blade during formation of the respective penetrations  158 ,  160 . 
     To create the lesion across the anterior limbus of the fossa ovalis lesion  192 , a special atrial septum clamping probe  198  ( FIGS. 17 and 28 ) is provided having opposed right angled jaw portions  200 ,  201  formed and dimensioned for insertion through the corresponding third and fourth penetrations  158 ,  160  for clamping engagement of the anterior limbus of the fossa ovalis therebetween. As illustrated in  FIG. 28 , the atrial septum clamping probe  198  includes a primary clamping member  202  having a generally straight, elongated clamping shaft  66  with a first elbow portion  166  positioned between the clamping shaft  66  and a generally straight outer jaw portion  200  (ablating end  70 ), whereby the first elbow portion has an arc length of about 85 degrees to about 95 degrees and a radius of curvature of about 3.2 mm to about 6.4 mm. The ablating surface extends just beyond elbow portion  166  and is of a length of preferably about 2.0 cm to about 6.0 cm. 
     In accordance with the special atrial septum clamping probe  198  of the present invention, an attachment device  203  is coupled to the clamping shaft  205  which includes an inner jaw portion  201  formed and dimensioned to cooperate with the outer jaw portion  200  (i.e., the elongated ablating surface  65 ) of clamping member  202  for clamping engagement of the interatrial septum wall  193  therebetween ( FIG. 17 ). Hence, the inner jaw portion and the outer jaw portion move relative to one another between a clamped condition ( FIG. 17  and in phantom lines in  FIG. 28 ) and an unclamped condition ( FIG. 14A  and in solid lines in  FIG. 28 ). In the unclamped condition, the inner jaw portion  201  of the attachment device  203  is positioned away from the outer jaw portion  200  to permit initial insertion of the distal end  165  of the outer jaw portion  200  of the clamping probe  198  into the fourth penetration  160 , as will be discussed. 
     The attachment device  203  is preferably provided by a generally straight, elongated attachment shaft  206  having a first elbow portion  207  positioned between the attachment shaft  206  and a generally straight inner jaw portion  201 .  FIG. 28  best illustrates that the first elbow portion of inner jaw portion  201  has an arc length and radius of curvature substantially similar to that of the outer jaw portion  200 . Further, the length of the inner jaw portion is preferably about 2.0 mm to about 6.0 mm. 
     In the preferred form, the attachment shaft  206  is slidably coupled to the clamping shaft  66  through a slidable coupling device  208  enabling sliding movement of the inner jaw portion  201  between the clamped and unclamped conditions. Preferably, a plurality of coupling devices  208  are provided spaced-apart along the attachment shaft  206 . Each coupling device includes a groove  210  ( FIG. 29 ) formed for a sliding, snap-fit receipt of the clamping shaft  66  therein for sliding movement of the attachment device in a direction along the longitudinal axis thereof. 
     The coupling devices are preferably composed of TEFLON®, plastic, polyurethane or the like, which is sufficiently resilient and bendable to enable the snap-fit engagement. Further, such materials include sufficient lubricating properties to provide slidable bearing support as the clamping shaft  66  is slidably received in groove  210  to move inner jaw portion  201  between the clamped and unclamped conditions. Moreover, the coupling device configuration may permit rotational motion of the inner jaw portion  201  about the attachment shaft longitudinal axis, when moved in the unclamped condition. This ability further aids manipulation of the clamping probe  198  when introduced through the access device  68  and insertion through the corresponding fourth penetration  160 . 
     In the clamped condition, the inner jaw portion  201  is moved into alignment with the outer jaw portion  200  of the clamping member  202  for cooperative clamping of the septum wall  193  therebetween. An alignment device  211  is preferably provided which is coupled between the clamping member  202  and the slidable attachment device  203  to ensure proper alignment relative one another while in the clamped condition. This is particularly necessary since the inner jaw portion  201  is capable of rotational movement about the clamping shaft longitudinal axis, when moved in the unclamped condition. In the preferred embodiment,  FIG. 30  best illustrates that alignment device  211  is provided by a set of spaced-apart rail members  212 ,  212 ′ each extending from the outer jaw portion  200  to the clamping shaft  66  of the clamping member  202 . The rail members  212 ,  212 ′ cooperate to define a slot  213  therebetween which is dimensioned for sliding receipt of an elbow portion  207  of the inner jaw portion  201 . 
     To further facilitate alignment between the inner jaw portion and the outer jaw portion, the elbow portion  207  of the inner jaw portion  201  may include a rectangular cross-section dimensioned for squared receipt in the slot  213  formed between the rail members  212 ,  212 ′. Alternatively, alignment may be provided by the inclusion of a locking device positioned at the handle of the probe, or by indexing detents included on the clamping shaft. 
     Due to the relatively close spacing and placement of the third and fourth purse-string sutures  61 ,  62  in relation to the heart and the retractor  68 , substantial precision is required for simultaneous insertion of the jaw portion distal ends  165 ,  215 . This problem is further magnified by the limited scope of visualization provided by either direct viewing through the retractor and/or with the endoscope. Accordingly, the septum clamping probe  198  includes staggered length jaw portions which position the distal end  165  of the outer jaw portion  200  slightly beyond the distal end  215  of the inner jaw portion  201  to facilitate alignment and insertion through the penetrations  158 ,  160 . In the preferred form, the right angled clamping member  202  is initially introduced through access device  68  for positioning of the distal end proximate the fourth purse-string suture  62 . Upon alignment of the outer jaw distal end  165  with the fourth penetration  160 , the clamping member  202  is manipulated in the direction of arrow  197  for insertion of the outer jaw portion partially into the left atrium chamber. The initial insertion depth of the tip is to be by an amount sufficient to retain the outer jaw portion  200  in the fourth penetration, while permitting the shorter length inner jaw portion  201  of the attachment device to move from the unclamped condition toward the clamped condition ( FIGS. 18A and 18B ). 
     It will be understood that the slidable attachment device  203 , at this moment, will either be unattached to the right angle probe or will be prepositioned in the unclamped condition. In the former event, the slidable attachment device  203  will be introduced through the access device  68  and slidably coupled or snap fit to the clamping shaft  66  of the clamping member  202  via coupling devices  208 . As the inner jaw portion  201  is advanced in the direction of arrow  216  toward the clamped condition, the attachment shaft  206  is rotated about its longitudinal axis, if necessary, until the elbow portion  207  is aligned for receipt in the slot  213  formed between the spaced-apart rails members  212 ,  212 ′. In this arrangement, the inner jaw portion  201  will be aligned co-planar with the outer jaw portion  200  of the clamping member  202 . 
     The length of the inner jaw portion  201  is preferably shorter than the length of the outer jaw portion  200  of clamping member  202  (preferably by about 5 mm). With the distal end  165  of the outer jaw portion  200  partially penetrating the fourth penetration  160  and the distal end  215  of the inner jaw portion  201  aligned with the third penetration  158  ( FIG. 18B ), the jaw portions are moved in the direction of arrow  197  to position the jaws through the penetrations, on opposite sides of the septum wall  193 , and into the atrial chambers. 
     As shown in  FIG. 17 , the jaw portions  200 ,  201  are inserted to a desired depth whereby the clamping probe can be aligned to pass through the anterior limbus of the fossa ovalis. When properly oriented, the jaw portions can be moved fully to the clamped position exerting an inwardly directed force (arrows  216 ,  216 ′) toward opposed sides of the interatrial septum wall  193 . Subsequently, the cryogen is released into the boiler chamber of the outer jaw portion of the clamping member thereby cooling the ablating surface  65  and subjecting the septal wall to cryothermia. 
     Due in part to the substantial thickness of this heart tissue, to secure proper transmural ablation of the interior septal wall of the right atrium, continuous contact of the ablating surface  65  therewith should transpire for at least 3-4 minutes to create the anterior limbus of the fossa ovalis ablation. The clamping probe  198  and the septum wall are to be properly defrosted and subsequently withdrawn from the third and fourth penetrations  158 ,  160 , whereby the third and fourth purse-string sutures  61 ,  62  are cinched tighter to prevent blood loss therefrom. 
     The length of the outer jaw portion is preferably between about 3 cm to about 5 cm, while the length of the inner jaw portion is generally about 5 mm less than the length of the outer jaw portion. Further, the diameter of the inner and outer jaw portions is preferably between about 2-4 mm. The determination of the diameter and/or length of the particular jaw portions and combinations thereof to be utilized will depend upon the particular applications and heart dimensions. 
     The clamping arrangement of this probe enables a substantial clamping force urged between the two opposed jaw portions for more efficient heat conduction. This configuration more effectively ablates the relatively thicker septum wall since greater leverage can be attained. Accordingly, in the preferred embodiment, only the outer jaw portion  200  (i.e., the ablating surface  65 ) of the clamping member  202  needs to be cooled to be effective. It will be appreciated, however, that the attachment device  203  may include the boiler chamber to cool the inner jaw portion as well for ablation of both sides of the septum wall  193 . 
     In an alternative embodiment of the clamping probe  198 , as shown in  FIG. 31 , the outer and inner jaw portions  200 ,  201  may cooperate to provide a gap  217  at and between the outer elbow portion  166  and the inner elbow portion  207 . This gap  217  is formed to accommodate the typically thicker tissue juncture  218  where the septum wall  193  intersects the outer atrial wall  220 . Hence, when the clamping probe  198  is moved to the clamped condition, the gap  217  is formed to receive this tissue juncture  218  so that a more constant compression force may be applied across the septum wall between the opposing jaws. This may be especially problematic when the tissue juncture is significantly thicker than the septum wall which, due to the disparity in thickness, may not enable the distal ends of the respective jaw portions to effectively contact the septum wall for transmural ablation thereof. 
     While  FIG. 31  illustrates that the gap  217  is primarily formed through the offset curvature at the elbow portion  207  of inner jaw portion  201 , it will be understood that the outer jaw portion  200  alone or a combination thereof may be employed to form the gap  217 . Further, in some instances, the clamping probe  198  may be derived from the right angle probe set forth above. 
     After completion of the above-mentioned series of elongated lesions formed through the retractor, the right atrial appendage RAA may be excised along the direction of solid line  221  in  FIG. 3  and broken line  222  in  FIG. 19 , to be described below. This excision is optional depending upon the particular circumstance since the risk of a fatal clot or thromboembolism is not as great as compared to left atrial appendage LAA. Should this excision be performed, the right atrial appendage RAA will, preferably, first be sutured closed along broken line  222  using conventional thoracoscopic instruments. This closure must be hemostatic to prevent blood loss when the right atrial appendage is excised. Once a hemostatic seal is attained, the appendage is excised using thoracoscopic scissors or an incision device. 
     While suturing is the preferred technique for hemostatically sealing the right atrial chamber, the right atrial appendage may first be surgically closed along broken line  222  using staples. In this procedure, a thoracoscopic stapling device would be inserted into the thoracic cavity through the retractor passageway  67  for access to the appendage. Moreover, the right atrial appendage may be conductively isolated by applying a specially designed cryoprobe clamping device (not shown) formed to be placed across the base of the appendage to engage the exterior surface thereof. This lesion will extend completely around the base along the line  221 ,  222  in  FIGS. 3 and 19  which corresponds to the right atrial appendage excision in the prior surgical procedures. 
     The next series of lesions are accessed through the left atrium LA. Accordingly, a second access device  223 , preferably the retractor  68 , placed between the ribs on the left side of the patient P, usually in the third or fourth intercostal space, and most preferably the third intercostal space as shown in  FIG. 11A . Again, this percutaneous penetration is positioned so that thoracoscopic instruments introduced through it may be directed toward the left atrium LA of the heart H. When additional maneuvering space is necessary, the intercostal space between the ribs may be through spreading of the adjacent ribs, or portions of the ribs can be easily removed to widen the percutaneous penetration. Further, the right lung will be re-inflated for use, while the left lung will be deflated to promote access while surgery is being performed. Other lung ventilation techniques may be employed such as high frequency ventilation without departing from the true spirit and nature of the present invention. 
     Subsequently, a pericardiotomy is performed to gain access to the left side of the heart H utilizing thoracoscopic instruments introduced through the refractor  68 . Using the same technique mentioned above, a fifth 4-0 purse-string suture  63  is then formed in the atrial epicardium of left atrial appendage LAA proximate a lateral midpoint thereof. Through a fifth penetration  161  formed central to the fifth purse-string suture  63 , the orifices of the pulmonary veins can be accessed to procure conductive isolation from the remainder of the left atrium LA. 
     In the preferred embodiment, the pulmonary vein isolation lesion  52  is formed using a two or more step process to completely encircle and electrically isolate the four pulmonary veins. In the preferred form, a four-step technique is employed initially commencing with the use of a C-shaped, probe  225 . As best viewed in  FIGS. 19A and 32 , the probe includes an elongated shaft  66  and a C-shaped ablating end  70  mounted to the distal end of the shaft  66 . The C-shaped ablating end  70  is shaped and dimensioned such that a distal end of the ablating end curves around and terminates in a region proximate the longitudinal axis extending through the shaft. The ablating end preferably includes an arc length of about 120 degrees to about 180 degrees, and a radius of the arc between about 6.0 mm to about 25.0 mm. This equates to an ablating surface length of preferably about 3.0 cm to about 6.0 cm. 
     With the aid of a thoracoscopic grasping instrument (not shown in  FIG. 19A ), the distal end of probe  225  is inserted through fifth penetration  161  to a position past the semi-circular ablating surface  65 . A fifth tensioning sleeve  226  may be cinched tighter in the event to prevent blood loss therefrom. 
     To create the first segment  227  of the pulmonary vein isolation lesion  52 , the distal end of the all-purpose probe is preferably positioned to contact the pulmonary endocardial surface  228  of the left atrium LA about 3-10 mm superior to the right superior pulmonary vein orifice  230 . Through the manipulation of the probe handle from outside the body, a bight portion  232  of the ablating surface  65  is positioned about 3-10 mm outside of and partially encircling the right superior and left superior pulmonary vein orifices  230 ,  231 . Once aligned, the ablating surface  65  of the probe is urged into ablative contact with the desired pulmonary endocardial surface  228  to form about ⅓ of the pulmonary vein isolation lesion  52  (i.e., the first segment  227 ). 
     Without removing the probe  225  from the fifth penetration  161 , the probe  225  is rotated approximately 180 degrees about the longitudinal axis of the probe shaft  66  to reorient the ablating surface  65  to form the second segment  233  of the pulmonary vein isolation lesion  52 .  FIG. 19B  best illustrates that the bight portion  232  of the probe is positioned on the other side of pulmonary trunk to contact the pulmonary endocardium about 3-10 mm just outside of and partially encircling the right inferior and left inferior pulmonary vein orifices  235 ,  236 . To ensure segment continuity, the distal end of the probe is positioned to overlap the distal of the first segment  227  by at least about 5 mm. Once the probe bight portion  232  is aligned to extend around the pulmonary vein orifices, the ablating surface  65  thereof is urged into ablative contact with the desired pulmonary endocardium to form the second segment  233  of the pulmonary vein isolation lesion  52 . After ablative contact and subsequent probe defrosting, the probe is refracted rearwardly from the fifth penetration  161  and removed from the second retractor  68 . An articulating probe (not shown) may also be employed for this procedure which includes an ablating end capable of selected articulation of the ablating surface to vary the curvature thereof. In this probe, the articulation of the end may be manually or automatically controlled through control devices located at the handle portion of the probe. This probe may be particularly suitable for use in the formation of the pulmonary vein isolation lesion due to the anatomical access difficulties. 
     Immediately following removal of the probe  225 , a right angle probe is to be inserted through the fifth penetration  161  of the left atrial appendage LAA, in the manner above discussed, to create a third segment  237  of the pulmonary vein isolation lesion  52 . The formation of this segment may require a different right angle probe, having a shorter length ablating surface  65  (about 2.0 cm to about 6.0 cm) than that of the first right angle probe  163  utilized in the previous ablative procedures. As shown in  FIG. 19C , the ablating surface  65  is oriented just outside the left superior pulmonary vein orifice  231  by at least about 5 mm. Again, to ensure proper segment continuity, it is important to overlap the distal end of the ablating surface  65  with the corresponding end of the lesion during the formation of the third segment  237  of the pulmonary vein isolation lesion  52 . After the probe is manually urged into contact with the desired pulmonary endocardial surface  228 , cryothermia is induced for the designated period to transmurally ablate the third segment  237  of the pulmonary vein isolation lesion  52 . Subsequently, the right angle probe ablating surface  65  is properly defrosted to reverse cryoadhesion and enable separation from the tissue. 
     Similar to the use of the probe  225 , without removing the right angle probe from the fifth penetration  161 , the probe is rotated approximately 180 degrees about the longitudinal axis of the probe shaft to position the ablating surface  65  just outside the left inferior pulmonary vein orifice  236  by at least about 5 mm ( FIG. 19D ). Again, to ensure proper segment continuity, it is important to overlap both the distal end and the elbow portion of the ablating surface  65  with the corresponding ends of the second and third segments  233 ,  237  during the formation of the fourth segment  238  of the pulmonary vein isolation lesion  52 . Fiberoptic visualization or the like is employed to facilitate proper continuity between the segments and placement of the probe. Once the probe is urged into contact with the desired left atrium interior surface, cryothermia is induced for the designated period to ablate the fourth segment of the pulmonary vein isolation lesion  52 . After the right angle probe ablating surface  65  is properly defrosted, the probe is retracted rearwardly from the fifth penetration  161  and removed from the second retractor  68 . 
     Formation of this last segment (i.e., fourth segment  238 ) completes the reentrant path isolation encircling the pulmonary veins (i.e., the pulmonary vein isolation cryolesion  52 ). It will be appreciated, of course, that the order of the segment formation which collectively defines the pulmonary vein isolation lesion  52  may vary. It is imperative, however, that there be continuity between the four segments. If the four-step procedure is performed properly, the opposed ends of the four segments should all overlap and interconnect to form one unitary ablation transmurally encircling the pulmonary trunk  108 . 
     In accordance with the system and procedure of the present invention, an alternative two-step endocardial procedure may be performed to isolate the pulmonary veins. As shown in  FIGS. 20A and 33 , an S-shaped end probe  240  is provided having a uniquely shaped, opened-looped ablating surface  65  formed to substantially extend around or encircle the pulmonary vein orifices. The S-shaped probe  240  includes an elongated shaft  66  having a substantially straight first portion  175  and a C-shaped second portion  176  mounted to the distal end of the first portion and terminating at a position proximate the longitudinal axis of the first portion  175  of shaft  66 . Mounted to the distal end of the C-shaped second portion  176  is a C-shaped ablating end  70  which curves back in the opposite direction such that the two C-shaped sections cooperate to form an S-shaped end. This unique shape enables the ablating surface  65  of ablating end  70  to have an arc length of between about 290 degrees to about 310 degrees, with a radius of curvature of about 1.2 cm to about 3.0 cm. 
       FIG. 33  illustrates that the C-shaped ablating end  70  is shaped and dimensioned such that a distal end of the ablating end curves around and terminates in a region proximate the longitudinal axis extending through the shaft. Consequently, the ablating end  70 , having a radius of about 12.0 mm to about 25.0 mm, can then extend substantially around the endocardial surface of the pulmonary vein trunk. This is accomplished by providing the C-shaped second portion  176  having a radius of curvature of at least bout 5 mm to about 7 mm which enables the unimpeded flow of cryogen through the delivery tube of the shaft  66 . The elimination or substantial reduction of this C-shaped second portion  176  positioned just before the C-shaped ablating end  70  would create such an acute angle that the flow of cryogen about that angle may be impeded. 
     Using thoracoscopic grasping instruments, the distal end of this probe is carefully inserted through the fifth purse-string suture penetration  161 . Due in part to the unique near-circular shape of the ablating surface  65 , initial insertion through the fifth penetration may be one of the most difficult and problematic portions of this procedure. 
     As shown in  FIG. 20A , after the ablating surface  65  of the probe  240  is successfully inserted through the fifth penetration  161 , the looped ablating surface  65  is aligned and positioned to substantially encircle the pulmonary vein orifices. Through manipulation of the probe handle from outside the thoracic cavity, the probe ablating surface  65  is urged into contact with the pulmonary endocardial surface  228  about 3-10 mm just outside of the pulmonary vein orifices. Upon proper alignment and ablative contact with the epicardial tissue, a first segment  241  of this technique is formed ( FIG. 20B ) which preferably constitutes at least about ¾ of the pulmonary vein isolation lesion. After proper defrosting, the loop probe is removed from the fifth penetration and withdrawn through the retractor. 
     To complete this alternative two-step procedure, an alternative right angle probe, above-mentioned, is inserted through the fifth penetration  161  upon removal of the S-shaped probe  240 .  FIG. 20B  illustrates that both the distal end and the elbow portion of the probe ablating surface  65  are aligned to overlap the corresponding ends of the first segment  241  during the formation of a second segment  242  of the pulmonary vein isolation lesion  52 . This ensures continuity between the two connecting segments. 
     It will be understood that other shape probes may be employed to isolate the pulmonary trunk. The particular customized shape may depend upon the individual anatomical differences of the patient, especially since atrial fibrillation patients often have enlarged or distorted atria. 
     It may be beneficial to access and perform portions of either the four-step procedure or the two-step procedure through the right side of the thoracic cavity. In these instances, access may be achieved through the first access device  68  and the fourth penetration  160  of the fourth purse-string suture  62 . Moreover, due to the arduous nature of the formation, placement and alignment between these segments composing the endocardial pulmonary vein isolation lesion in either the two or four segment procedure, it may be necessary to ablate an epicardial lesion  243  in the epicardial surface  168  encircling the pulmonary trunk  108  to ensure effective transmural tissue ablation for pulmonary vein isolation. Referring to  FIGS. 21 and 33 , an epicardial pulmonary vein loop probe  240 , substantially similar to the probe employed in the procedure of  FIG. 20A , is provided for introduction through the passageway of the retractor. This probe instrument includes an open-looped ablating surface  65  defining an opening  245  ( FIG. 33 ) formed for passage of the pulmonary trunk  108  therethrough. Using thoracoscopic grasping instruments, the probe  240  is situated under the pulmonary veins wherein the pulmonary trunk  108  is urged through the opening  245  in the looped ablating surface. Once the ablating surface  65  is aligned to contact a pulmonary epicardial surface  168  of the pulmonary trunk  108  at a position opposite the epicardial pulmonary vein isolation lesion  52 , cryogenic liquid is introduced into the boiler chamber of the loop probe  240  for cryogenic cooling of the ablating surface  65 . After contact for the designated period (2-4 minutes) and proper probe defrosting, the loop probe is separated from the pulmonary trunk and retracted rearwardly out of the retractor  68 . 
     Alternatively, this pulmonary epicardial surface isolation may be performed from the right side of the thoracic cavity through the first access device  68  (not shown). In this alternative method, the open-looped ablating surface  65  of the loop probe  240  is positioned behind the superior vena cava  111 , across the anterior surface of the right pulmonary veins, and underneath the inferior vena cava  103 . Once properly positioned, the epicardial surface  168  of the pulmonary trunk  108  can be ablated. 
     Turning now to  FIG. 22 , formation of the left atrial anteromedial lesion  246  will be described in detail. This lesion  246  is relatively short extending only about 5-7 mm from the anteromedial portion of the left atrial appendage LAA to the pulmonary vein isolation lesion  52  proximate a central portion between the left superior and inferior pulmonary vein orifices  231 ,  236 . Due to the position of this lesion and the flexible nature of the appendage tissue, any one of a number of probes already mentioned, such as the probes illustrated in  FIG. 32 , the right angle probe ( FIG. 24 ) or the pulmonary vein to mitral valve probe ( FIG. 34 ), can be employed for this task. Typically, the probe device  247  of  FIG. 34  is employed which includes an elongated shaft  66  having a first elbow portion  166  positioned between a relatively straight first portion  175  and a generally straight second portion  176 . The first elbow portion has an arc length of about 45 degrees to about 65 degrees and a radius of curvature of about 3.2 cm to about 5.7 cm. Further, a second elbow portion  177  is positioned between the second portion  176  and the ablating end  70 , angling the ablating end back toward the longitudinal axis of the first portion  175  of the elongated shaft  66 . The ablating end  70  preferably includes the second elbow portion  177 , having an arc length of about 80 degrees to about 100 degrees, and a radius of curvature of about 6.0 mm to about 1.9 mm. This translates to an ablating surface of about 2.0 cm to about 6.0 cm in length. 
     One of the above-mentioned probes will be introduced through the second retractor  68  where the distal end of the probe will be inserted through the same fifth penetration  161  central to the fifth purse-string suture  63 . Once the selected probe  247 , as shown in  FIG. 22 , is properly aligned, the ablating surface  65  is urged into contact with the atrial endocardial surface of the left atrial appendage LAA for localized ablation. Subsequently, the left atrial anteromedial lesion  246  will be formed. 
     Since the left atrial wall at the anteromedial portion thereof is exceedingly thin, this transmural ablation could be performed from outside the heart H. Hence, upon contact of the ablating surface of a selected probe (not shown) with the atrial epicardial surface of the left atrial appendage LAA, localized, transmural cryothermia may be applied externally/epicardially to form this left atrial anteromedial lesion  246 . 
     The last lesion to be performed through the fifth penetration  161  is the posterior vertical left atrial lesion  248 , also known as the coronary sinus lesion ( FIG. 23 ), extending from the pulmonary vein isolation lesion  52  to the annulus  250  of the mitral valve MV. This lesion may be critical since improper ablation may enable atrial conduction to continue in either direction beneath the pulmonary veins. This may result in a long macro-reentrant circuit that propagates around the posterior-inferior left atrium, the atrial septum, the anterior-superior left atrium, the lateral wall of the left atrium beneath the excised left atrial appendage, and back to the posterior inferior left atrium. 
     Therefore, it is imperative that the coronary sinus be ablated circumferentially and transmurally in the exact plane of the atriotomy or lesion. Proper transmural and circumferential ablation near the coronary sinus effectively eliminates the need for dividing all atrial myocardial fibers traversing the fat pad of the underlying atrioventricular groove. 
     In the preferred embodiment, a modified probe  251  ( FIG. 35 ) is employed to ablate this critical coronary sinus lesion  248 . This probe  251  includes an elongated shaft  66  having a first elbow portion  166  positioned between a generally straight first portion  175  and a generally straight second portion  176 . The first elbow portion has an arc length of about 30 degrees to about 50 degrees and a radius of curvature of about 1.2 cm to about 3.0 cm. Mounted at the distal end of the second portion  176  is the ablating end which is substantially similar in shape to the ablating end of the probe of  FIG. 32 . The ablating end  70  curves back toward the longitudinal axis of the first portion  175  of the elongated shaft  66 . 
     Again, this interior region of the heart H is accessed through the fifth penetration  161 , via the second access device  223 . The distal end of the probe  251 , is positioned through the penetration in the same manner as previous ablations. The unique curvature of this probe  251  enables manipulation of the ablating surface  65  from outside the thoracic cavity into proper alignment.  FIG. 23  best illustrates that ablating surface  65  is moved into contact with the endocardial surface of the left atrial wall atrium for localized ablation extending from the pulmonary vein isolation lesion  52  to the mitral valve annulus  250 . Particular care, as mentioned above, is taken to assure that this lesion extends through the coronary sinus for circumferential electrical isolation thereof. After contact for the designated period of 2-4 minutes, the ablating surface  65  of the probe is properly defrosting and the probe  251  is retracted rearwardly from the fifth penetration  161  for removal from the retractor. Subsequently, the fifth penetration  161  is further cinched to prevent blood lose through the fifth purse-string suture  63 . 
     Due to the criticality of the circumferential ablation of the coronary sinus during formation of the pulmonary vein to mitral valve annulus lesion  248 , an epicardial ablation may be performed on a portion of the outside heart wall opposite the endocardial ablation of the coronary sinus. Thus, the placement of this additional lesion (not shown) must be in the same plane as the coronary sinus lesion  248  (i.e., to the mitral valve annulus lesion) to assure circumferential ablation of the coronary sinus. This is performed by introducing a standard probe through the refractor  68 , and strategically contacting the epicardial surface at the desired location opposite the coronary sinus lesion. 
     Upon completion of the above-mentioned series of elongated lesions, the left atrial appendage LAA is excised along the direction of broken line  252  in  FIG. 23 , similar to that of the prior procedures. This excision is considered more imperative than the excision of the right atrial appendage RAA since the threat of thromboembolism or clotting would more likely be fatal, induce strokes or cause other permanent damage. In the preferred form, this excision is performed in the same manner as the excision of the right atrial appendage (i.e., through suturing or stapling. After hemostatic closure is attained, the left atrial appendage LAA is excised using thoracoscopic scissors or an incision device. This left appendagectomy will extend completely around the base of the left atrial appendage along the solid line  252  in  FIG. 3  or the broken line  253  in  FIG. 23 , which corresponds to the left atrial appendage excision in prior procedures. 
     Alternatively, the probes may be formed and dimensioned for contact with the epicardial surface  168  of the heart H. In these instances, no purse-string suture may be necessary for elongated transmural ablation. As an example, as best viewed in  FIG. 36 , a right-angle clamp type probe  255  is provided having an outer clamping portion  256  coupled to and formed to cooperate with a right angle probe or inner clamping portion  257  for transmural ablation of the heart wall through contact with epicardial surface  168  of the heart H. In this embodiment, an outer jaw portion  258  of outer clamping portion  256  is relatively thin (about 0.5 mm to about 2.0 mm in diameter) and preferably needle shaped to facilitate piercing of the heart wall at puncture  260 . At the end of the needle-shaped outer clamping portion  256  is a pointed end  261  which enables piercing of the heart wall without requiring an initial incision and subsequent purse-string suture to prevent blood loss through the puncture  260 . 
     Similar to clamping probe  198 , when properly positioned, the outer and inner jaw portions  258 ,  262  of inner clamping portion  257  are moved inwardly in the direction of arrows  216 ,  216 ′ (the outer jaw portion  258  contacting endocardial surface  228 , and the inner jaw portion  262  contacting epicardial surface  168 ) to clamp the heart wall therebetween.  FIG. 36  illustrates that inner jaw portion  262  includes ablation end  70  having ablation surface  65  which contacts epicardial surface  168  for ablation. Upon withdrawal of the needle-shaped outer jaw portion  258  from the heart wall, the puncture  260  may be closed through a single suture (not shown). 
     In these embodiments, an alignment device  263  is provided which cooperates between the outer and inner clamping portions  256 ,  257  for operating alignment between the outer jaw portion  258  and the inner jaw portion  262 . This alignment device may be provided by any conventional alignment mechanism such as those alignment devices employed in the clamping probe  198 . 
     To ensure transmural ablation, the needle-shaped outer jaw portion  258  may incorporate a temperature sensor  265  ( FIG. 36 ) embedded in or positioned on the outer jaw portion to measure the temperature of the endocardial surface. Measurement of the proper surface temperature will better ensure transmural ablation. These temperature sensors may be provided by a variety of conventional temperature sensors. 
     Referring to  FIGS. 37-40 , another probe  280  is shown. A cryogen delivery tube  282  is positioned within an outer tube  284 . A tip  286  seals an end of the outer tube  284 . The delivery tube  282  is coupled to the source of cryogen (not shown) for delivering the cryogen to a boiler chamber  288 . The cryogen is exhausted from the boiler chamber  288  through the annular area between the delivery tube  282  and outer tube  284 . The delivery tube  282  has an end cap  290  which receives first and second tubes  292 ,  294  for delivery of cryogen to the boiler chamber  288  from the delivery tube  282 . The first tube  292  has an exhaust port  296  which extends further into the boiler chamber  288  than an exhaust port  298  of the second tube  294  so that the cryogen is distributed throughout the boiler chamber  288 . Although  FIG. 38  depicts only the first and second outlet tubes  292 ,  294 , any number of tubes may be provided. 
     Ablating surface  300  of the outer tube  284  is preferably made of a highly thermally conductive material such as copper. Referring to the end view of  FIG. 40 , the ablating surface  300  preferably has a ribbed inner surface  302  for enhanced thermal conduction between the boiler chamber  288  and the ablating surface  300 . The probe  280  may take any of the configurations described herein. 
     Referring to  FIGS. 41 and 42 , another probe  306  is shown which has a device for adjusting the delivery rate of cryogen. The delivery tube  308  includes an inner tube  310  and an outer tube  312 . The inner and outer tubes  310 ,  312  have holes  314 ,  316  therein through which the cryogen is delivered to boiler chamber  318 . The outer tube  312  is slidable relative to the inner tube  310  and can be locked relative to the inner tube  310  at a number of discrete positions where the holes  314  in the inner tube  310  are aligned with the holes  316  in the outer tube  312 . The holes  314  in the inner tube  310  are larger than holes  316  in the outer tube  312  so that when the outer tube  312  is in the position of  FIG. 41  a larger amount of cryogen is delivered than when the outer tube  312  is in the position of  FIG. 42 . Thus, the amount of cryogen delivered, and therefore the rate of ablation and temperature of the probe  306 , can be changed by moving the outer tube  312  relative to the inner tube  310 . The delivery tube  308  may be used in the manner described above with any of the probe configurations described herein. 
     Referring to  FIGS. 43 and 44 , still another probe  318  is shown which includes suction ports  320  for ensuring intimate contact between the ablating surface  322  and the tissue. The suction ports  320  are coupled to a longitudinal channel  324  which is coupled to a vacuum source for applying suction. A cryogen delivery tube  326  delivers cryogen to boiler chamber  328  in the manner described herein. 
     Referring to  FIGS. 45-47 , a probe  330  having a malleable shaft  332  is shown. A malleable metal rod  334  is coextruded with a polymer  336  to form the shaft  332 . A tip  338  having a boiler chamber  340  is attached to the shaft  332 . The rod  334  permits the user to shape the shaft  332  as necessary so that the tip  338  can reach the tissue to be ablated. The tip  338  has fittings  342  which are received in a cryogen exhaust path  344  and a cryogen delivery path  346  in the shaft  332 . The rod  334  is preferably made of stainless steel and the polymer  336  is preferably polyurethane. The tip  338  may be made of a suitable thermally conductive material such as copper. Cryogen is delivered through ports  348  in a delivery tube  350  and is expanded in the boiler chamber  340 . The cryogen is then withdrawn through the exhaust path  344 . 
     Finally, as set forth in the parent application incorporated herein by reference, access devices may be placed in the heart walls to enable the passage of the probes through the wells of the access devices. 
     While the present invention has been primarily directed toward ablation from the endocardial surfaces of the atria, it will be understood that many lesions or portions of the lesions may be created through ablation of the endocardial surfaces of the atria employing the present probes. While the specific embodiments of the invention described herein will refer to a closed-chest surgical procedure and system for the treatment of medically refractory atrial fibrillation, it is understood that the invention will be useful in ablation of other tissue structures, including surgical treatment of Wolfe-Parkinson-White (WPW) Syndrome, ventricular fibrillation, congestive heart failure and other procedures in which interventional devices are introduced into the interior of the heart, coronary arteries, or great vessels. The present invention facilitates the performance of such procedures through percutaneous penetrations within intercostal spaces, eliminating the need for a median sternotomy or other form of gross thoracotomy. However, as will be apparent although not preferred, the system and procedure of the present invention could be performed in an open-chest surgical procedure as well.