Patent Publication Number: US-2005119653-A1

Title: Surgical methods and apparatus for forming lesions in tissue and confirming whether a therapeutic lesion has been formed

Description:
BACKGROUND OF THE INVENTIONS  
      1. Field of Inventions  
      The present inventions relate generally to surgical devices for forming therapeutic lesions.  
      2. Description of the Related Art  
      There are many instances where therapeutic elements must be inserted into the body. One instance involves the formation of therapeutic lesions to the treat cardiac conditions such as atrial fibrillation, atrial flutter and arrhythmia. Therapeutic lesions may also be used to treat conditions in other regions of the body including, but not limited to, the prostate, liver, brain, gall bladder, uterus and other solid organs. Typically, the lesions are formed by ablating tissue with one or more electrodes. Electromagnetic radio frequency (“RF”) energy applied by the electrode heats, and eventually kills (i.e. “ablates”), the tissue to form a lesion. During the ablation of soft tissue (i.e. tissue other than blood, bone and connective tissue), tissue coagulation occurs and it is the coagulation that kills the tissue. Thus, references to the ablation of soft tissue are necessarily references to soft tissue coagulation. “Tissue coagulation” is the process of cross-linking proteins in tissue to cause the tissue to jell. In soft tissue, it is the fluid within the tissue cell membranes that jells to kill the cells, thereby killing the tissue.  
      Depending on the procedure, a variety of different electrophysiology devices may be used to position one or more coagulation electrodes at the target location. Each electrode is connected to a power supply and control apparatus and, in some instances, the power to the electrodes is controlled on an electrode-by-electrode basis. Examples of electrophysiology devices include catheters and surgical devices such as surgical probes and clamps. Catheters are relatively long, flexible devices that are configured to travel through a vein or artery until the coagulation electrodes carried on their distal portions reach the target tissue. The electrodes on the distal portions of surgical devices are, on the other hand, typically placed directly in contact with the targeted tissue area by a physician during a surgical procedure, such as open heart surgery, where access can be obtained by way of a thoracotomy, median stemotomy, or thoracostomy.  
      Catheters used to create lesions typically include a relatively long and relatively flexible body that has one or more coagulation electrodes on its distal portion. The portion of the catheter body that is inserted into the patient is typically from 23 to 55 inches in length and there may be another 8 to 15 inches, including a handle, outside the patient. The proximal end of the catheter body is connected to the handle which includes steering controls. The length and flexibility of the catheter body allow the catheter to be inserted into a main vein or artery (typically the femoral artery), directed into the interior of the heart, and then manipulated such that the electrode contacts the tissue that is to be ablated. Fluoroscopic imaging is used to provide the physician with a visual indication of the location of the catheter. Exemplary catheters are disclosed in U.S. Pat. No. 5,582,609.  
      Surgical probes used to create lesions often include a handle, a relatively short shaft that is from 4 inches to 18 inches in length and either rigid or relatively stiff, and a distal section that is from 1 inch to 10 inches in length and either malleable or somewhat flexible. One or more coagulation electrodes are carried by the distal section. Surgical probes are used in epicardial and endocardial procedures, including open heart procedures and minimally invasive procedures where access to the heart is obtained via a thoracotomy, thoracostomy or median stemotomy. Exemplary surgical probes are disclosed in U.S. Pat. No. 6,142,994.  
      Clamps, which have a pair of opposable clamp members that may be used to hold a bodily structure or a portion thereof, are another example of a surgical device that has been used to create lesions. Examples of clamps which carry coagulation electrodes are disclosed in U.S. Pat. No. 6,142,994. Such clamps are particularly useful when the physician intends to position electrodes on opposite sides of a body structure in a bipolar arrangement.  
      The inventor herein has determined that conventional apparatus and methods for forming therapeutic lesions are susceptible to improvement. For example, inventor herein has determined that conventional methods and apparatus for confirming whether a therapeutic lesion has been properly formed during surgical procedures are susceptible of improvement. The inventor herein has also determined that conventional methods and apparatus for securing stimulation and sensing electrodes to tissue during surgical procedures are susceptible of improvement.  
     SUMMARY OF THE INVENTIONS  
      Surgical devices in accordance with some embodiments of the present inventions include a tissue stimulation element that, in some instances, may also be used for sensing purposes. Some of the surgical devices also include a tissue coagulation element. The present surgical device provide a number of advantages over conventional surgical devices. For example, the some of the surgical devices may be used to form lesions and also used to determine whether or not a therapeutic lesion has been formed. The surgical devices may also be used to bring stimulation and sensing elements into contact with tissue in a manner that is superior to conventional methods.  
      The above described and many other features and attendant advantages of the present inventions will become apparent as the inventions become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Detailed description of preferred embodiments of the inventions will be made with reference to the accompanying drawings.  
       FIG. 1  is a perspective view of a surgical system in accordance with a preferred embodiment of a present invention.  
       FIG. 2  is a plan view of a surgical probe in accordance with a preferred embodiment of a present invention.  
       FIG. 3  is a section view taken along line  3 - 3  in  FIG. 2 .  
       FIG. 4  is a section view taken along line  4 - 4  in  FIG. 2 .  
       FIG. 5  is a section view taken along line  5 - 5  in  FIG. 2 .  
       FIG. 6  is an end view of the surgical probe illustrated in  FIG. 2 .  
       FIG. 6A  is a perspective view of a surgical system in accordance with a preferred embodiment of a present invention.  
       FIG. 6B  is a plan view of a portion of a surgical probe in accordance with a preferred embodiment of a present invention.  
       FIG. 7  is a perspective view of a surgical system in accordance with a preferred embodiment of a present invention.  
       FIG. 8  is a top view of a suction device in accordance with a preferred embodiment of a present invention.  
       FIG. 9  is a side view of the suction device illustrated in  FIG. 8 .  
       FIG. 10  is a bottom view of the suction device illustrated in  FIG. 8 .  
       FIG. 11  is a partial section view taken along line  11 - 11  in  FIG. 9 .  
       FIG. 12  is a section view taken along line  12 - 12  in  FIG. 10 .  
       FIG. 13  is a section view taken along line  13 - 13  in  FIG. 10 .  
       FIG. 14  is a bottom view of showing a portion of the surgical system illustrated in  FIG. 7 .  
       FIG. 15  is a partial section view taken along line  15 - 15  in  FIG. 14 .  
       FIG. 16  is a perspective view of a surgical system in accordance with a preferred embodiment of a present invention.  
       FIG. 17  is a plan view of a tissue coagulation and stimulation assembly in accordance with a preferred embodiment of a present invention.  
       FIG. 18  is a section view taken along line  18 - 18  in  FIG. 17 .  
       FIG. 19  is a section view taken along line  19 - 19  in  FIG. 17 .  
       FIG. 20  is an enlarged view of a portion of the tissue coagulation and stimulation assembly illustrated in  FIG. 17 .  
       FIG. 21  is a section view taken along line  21 - 21  in  FIG. 20 .  
       FIG. 22  is a plan view of a clamp in accordance with a preferred embodiment of a present invention.  
       FIG. 23  is a section view taken along line  23 - 23  in  FIG. 22 .  
       FIG. 24  is a top view of a portion of the clamp illustrated in  FIG. 22 .  
       FIG. 24A  is a side view of a portion of a tissue coagulation and stimulation assembly in accordance with one embodiment of a present invention.  
       FIG. 24B  is a side view of a portion of a tissue coagulation and stimulation assembly in accordance with one embodiment of a present invention.  
       FIG. 24C  is an enlarged view of a portion of a tissue coagulation and stimulation assembly in accordance with one embodiment of a present invention.  
       FIG. 24D  is a section view taken along line  24 D- 24 D in  FIG. 24C .  
       FIG. 24E  is a section view taken along line  24 E- 24 E in  FIG. 24C .  
       FIG. 24F  is an enlarged view of a portion of the tissue coagulation and stimulation assembly illustrated in  FIG. 24C .  
       FIG. 24G  is partial section view taken along line  24 G- 24 G in  FIG. 24F .  
       FIG. 24H  is a section view taken along line  24 H- 24 H in  FIG. 24F .  
       FIG. 25  is a perspective view of a surgical system in accordance with a preferred embodiment of a present invention.  
       FIG. 26  is a section view taken along line  26 - 26  in  FIG. 25 .  
       FIG. 27  is an end view of a probe in accordance with one embodiment of a present invention.  
       FIG. 27A  is an end view of a probe in accordance with one embodiment of a present invention.  
       FIG. 28  is a section view taken along line  28 - 28  in  FIG. 27 .  
       FIG. 29  is a perspective view of a surgical system in accordance with a preferred embodiment of a present invention.  
       FIG. 30  is a section view taken along line  30 - 30  in  FIG. 29 .  
       FIG. 31  is an end view of a probe in accordance with one embodiment of a present invention.  
       FIG. 31A  is an end view of a probe in accordance with one embodiment of a present invention.  
       FIG. 32  is a section view taken along line  32 - 32  in  FIG. 31 .  
       FIG. 33  is a perspective view of a surgical system in accordance with a preferred embodiment of a present invention.  
       FIG. 34  is a top view of a self-anchoring device in accordance with a preferred embodiment of a present invention.  
       FIG. 35  is a section view taken along line  35 - 35  in  FIG. 34 .  
       FIG. 36  is an enlarged section view taken along line  35 - 35  in  FIG. 34 .  
       FIG. 37  is a side view of a self-anchoring device in accordance with a preferred embodiment of a present invention.  
       FIG. 38  is a top view of the device illustrated in  FIG. 37 .  
       FIG. 39  is a side view of a self-anchoring device in accordance with a preferred embodiment of a present invention.  
       FIG. 40  is a top view of the device illustrated in  FIG. 39 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The following is a detailed description of the best presently known modes of carrying out the inventions. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the inventions.  
      The detailed description of the preferred embodiments is organized as follows: 
          I. Introduction     II. Surgical Probes     III. Suction Devices For Use With Surgical Probes     IV. Clamp Based Devices     V. Coagulation Electrodes, Temperature Sensing And Power Control     VI. Stimulation Electrodes And Lesion Confirmation     VII. Tissue Stimulation And Sensing Probes     VIII. Self-Anchoring Tissue Stimulation and Sensing Devices 
 
 The section titles and overall organization of the present detailed description are for the purpose of convenience only and are not intended to limit the present inventions. 
 
 I. Introduction 
       

      Surgical devices in accordance with the present inventions include one or more tissue coagulation elements and/or one or more tissue stimulation elements. The tissue coagulation elements may be used to, for example, form therapeutic lesions and the tissue stimulation elements may be used to, for example, test whether or not the desired therapeutic lesion has been formed. The stimulation elements may also be used to stimulate tissue and sense electrical activity in tissue (such as by pacing and recording) during a surgical procedure. The surgical devices may be used in conjunction with power supply and control apparatus that supply and control power to the tissue coagulation elements in bipolar and/or unipolar modes. The surgical devices may also be used in conjunction with tissue stimulation apparatus, such as pacing and recording apparatus, which supply power that stimulates (but does not coagulate) tissue. Tissue stimulation may be used to confirm whether or not a therapeutic lesion has been formed by, for example, supplying tissue stimulation energy on one side of a lesion and/or monitoring tissue (either electrically or visually) on the other side of the lesion. Tissue stimulation may also be used to determine lesion depth and, correspondingly, whether or not a lesion is transmural.  
      II. Surgical Probes  
      As illustrated for example in  FIG. 1 , an exemplary surgical system  10  in accordance with one embodiment of a present invention includes a surgical probe  100 , a power supply and control apparatus  200 , and a tissue stimulation apparatus  300 . The power supply and control apparatus  200  and tissue stimulation apparatus  300  are discussed in Sections V and VI below. The surgical probe  100  includes a relatively short shaft  102  with a proximal section  104 , which is connected to a handle  106 , and a distal section  108 , on which coagulation electrodes  110  are supported. The coagulation electrodes  110  are discussed in Section V below. The distal section  108  also supports tissue stimulation electrodes  112  and  114 . The tissue stimulation electrodes  112  and  114 , which are discussed in Section VI below, may also be used to sense local tissue activation.  
      Turning to  FIGS. 2-5 , the exemplary shaft proximal section  104  consists of a hypotube  116 , which is either rigid or relatively stiff, and an outer polymer tubing  118  over the hypotube. The handle  106  preferably consists of two molded handle halves and is provided with strain relief element  120 . The shaft proximal section  104  in the illustrated embodiment may be from 4 inches to 18 inches in length and is preferably 6 inches to 8 inches. The shaft distal section  108 , which is preferably either malleable, somewhat flexible or some combination thereof, may be from 1 inch to 10 inches in length and is preferably 3 to 5 inches.  
      As used herein the phrase “relatively stiff” means that the shaft (or distal section or other structural element) is either rigid, malleable, or somewhat flexible. A rigid shaft cannot be bent. A malleable shaft is a shaft that can be readily bent by the physician to a desired shape, without springing back when released, so that it will remain in that shape during the surgical procedure. Thus, the stiffness of a malleable shaft must be low enough to allow the shaft to be bent, but high enough to resist bending when the forces associated with a surgical procedure are applied to the shaft. A somewhat flexible shaft will bend and spring back when released. However, the force required to bend the shaft must be substantial. Rigid and somewhat flexible shafts are preferably formed from stainless steel, while malleable shafts are formed from annealed stainless steel. Additional information concerning “relatively stiff” shafts is provided in U.S. Pat. No. 6,142,994, which is incorporated herein by reference.  
      In those instances where a malleable shaft proximal portion  104  is desired, the hypotube  116  may be a heat treated malleable hypotube. By selectively heat treating certain portions of the hypotube, one section of the hypotube can be made more malleable than the other. The outer tubing  118  may be formed from Pebax® material, polyurethane, or other suitable materials.  
      As noted above, the shaft distal section  108  can be either somewhat flexible, in that it will conform to a surface against which it is pressed and then spring back to its original shape when removed from the surface, malleable, or some combination thereof. In the exemplary implementation illustrated in  FIGS. 1-7 , the distal section  108  includes a malleable proximal portion and a flexible distal portion. Although the relative lengths of the portions may vary to suit particular applications, the malleable proximal portion and a flexible distal portion are equal in length in the illustrated embodiment.  
      Referring more specifically to  FIGS. 4 and 5 , the exemplary shaft distal section  108  includes an outer member  122  that carries the electrodes  110 - 114 . The outer member  122  is a flexible tubular structure which has an outer diameter that is, depending on the diameter of the electrodes  110  and  112 , typically between about 2 mm and about 4 mm. The outer member  122  in the illustrated embodiment, which is intended for use in cardiovascular applications, typically has an outer diameter of about 3 mm. Suitable support structure materials include, for example, flexible biocompatible thermoplastic tubing such as unbraided Pebax® material, polyethylene, or polyurethane tubing.  
      Turning to the interior of the shaft distal section  108 , the exemplary malleable portion includes a mandrel  124  ( FIG. 4 ) made of a suitably malleable material, such as annealed stainless steel or beryllium copper, that may be fixed directly within the distal end of the shaft&#39;s hypotube  116  and secured by, for example, soldering, spot welding or adhesives. Sufficient space should be provided to allow passage of the power lines  126 , which are connected to the coagulation electrodes  110 , the temperature sensor signal lines  128 , which are connected to temperature sensors  130  ( FIG. 5 ) such as thermocouples or thermistors, and signal lines  132 , which are connected to the tissue stimulation electrodes  112  and  114 . As described in greater detail below, the power lines  126  may be used to transmit energy from the power supply and control apparatus  200  to the coagulation electrodes  110 , while signal lines  128  return temperature information from the temperature sensors  130  to the power supply and control apparatus. The signal lines  132  may be used to transmit tissue stimulation energy from the tissue stimulation apparatus  300  to the stimulation electrodes  112  and  114 . The signal lines  132  may also be used to transmit the signals associated with local electrical activity when the tissue stimulation electrode  112  and  114  are used for sensing. An insulating sleeve  134  is placed over the mandrel  124  to protect the power lines  126 , temperature sensor signal lines  128  and signal lines  132 . The insulating sleeve  134  is preferably formed from Pebax® material, polyurethane, or other suitable materials.  
      With respect to the flexible portion, a spring member  136 , which is preferably either a solid flat wire spring ( FIG. 5 ), a round wire, or a three leaf flat wire Nitinol® spring, is connected to the distal end of the mandrel  124  with a crimp tube or other suitable instrumentality. The distal end of the spring member  136  is connected to the electrode  114  by, for example, an adhesive that will also electrically insulate the spring member from the electrode. The electrode  114  is also secured to the distal end of the outer member  122 . Other spring members, formed from materials such as 17-7 or carpenter&#39;s steel, may also be used. The spring member  136  is also enclosed within the insulating sleeve  134 . The spring member  136  may be pre-stressed so that the distal tip is pre-bent into a desired shape. Additional details concerning distal sections that have a malleable proximal portion and a flexible distal portion are provided in U.S. Pat. No. 6,464,700, which is incorporated herein by reference.  
      In an alternative configuration, the distal section  108  may be formed by a hypotube that is simply a continuation of the shaft hypotube  116  covered by a continuation of the outer tubing  118 . However, the distal end hypotube can also be a separate element connected to the shaft hypotube  116 , if it is desired that the distal end hypotube have different stiffness (or bending) properties than the shaft hypotube. It should also be noted that the distal section  108  may be made malleable from end to end by eliminating the spring member  136  and extending the malleable mandrel  124  to the electrode  114 . Conversely, the distal section  108  may be made flexible from end to end by eliminating the malleable mandrel  124  and extending the spring member  136  from the hypotube  116  to the electrode  114 .  
      Turning to  FIGS. 5 and 6 , the power lines  126  and signal lines  128  extend from the coagulation electrodes  110  and temperature sensors  130  to a connector (such as the exemplary PC board  138 ) that is carried by the handle  106 . The handle  106  also includes a port  140  that is configured to receive a connector, such as the connector  206  ( FIG. 1 ) from the power supply and control apparatus  200 , for connection to the PC board  138 . Openings  142  and  144  are provided for the signal lines  132 .  
      The exemplary surgical system  11 , which is illustrated in  FIGS. 6A and 6B , includes a surgical probe  101 , a power supply and control apparatus  200 , a tissue stimulation apparatus  300  and an EP recording apparatus  301 . The power supply and control apparatus  200  is discussed in Section V, while the tissue stimulation apparatus  300  and EP recording apparatus  301  are discussed in Section VI. The exemplary surgical probe  101  is essentially identical to the surgical probe  100  and similar elements are represented by similar reference numerals. Here, however, a plurality of stimulation electrodes  112  are located along the length of the shaft distal portion  108 . In the illustrated embodiment, a stimulation electrode  112  is located between each of the coagulation electrodes  110 . There is also a stimulation electrode  112  proximal of the proximal-most coagulation electrode  110  and a stimulation electrode  112  distal of the distal-most coagulation electrode  110 . A stimulation electrode  114  is also provided on the distal end of the probe. Signal lines  132 , which are connected to the tissue stimulation electrodes  112  and  114 , extend though a cable  115  and are connected to the EP recording apparatus  301  with a connector  117 .  
      In another alternative implementation, pairs of stimulation electrodes  112  may be located between each of the coagulation electrodes  110 , proximal of the proximal-most coagulation electrode, and distal of the distal-most coagulation electrode. A stimulation electrode  114  on the distal end of the probe may also be provided.  
      III. Suction Devices for Use with Surgical Probes  
      As illustrated for example in  FIG. 7 , an exemplary surgical system  20  in accordance with one embodiment of a present invention includes a surgical probe  100 ′, a power supply and control apparatus  200 , a tissue stimulation apparatus  300  and an EP recording apparatus  301 . The power supply and control apparatus  200  is discussed in Section V, while the tissue stimulation apparatus  300  and EP recording apparatus  301  are discussed in Section VI. The exemplary system is also provided with a suction apparatus  400  that includes a suction source  402  and a suction device  404  that may be removably secured to the distal section  108  of the surgical probe  100 ′. The suction device  404  is connected to the suction source  402  by a flexible tube  406 . When the suction source  402  is actuated, the suction device  404  will fix the position of the distal section of the surgical probe  100 ′ relative to the target tissue. Additionally, depending on the rigidity of the suction device  404  and the rigidity of the tissue, the applied vacuum may also cause the tissue and electrodes  110  on the distal section  108  to come into contact with one another because portions of the suction device will deflect, portions of the tissue surface will deflect, or portions of both the suction device and the tissue surface will deflect.  
      The surgical probe  100 ′ is substantially identical to surgical probe  100  and similar elements are represented by similar reference numerals. Surgical probe  100 ′ does not, however, include the tissue stimulation electrodes  112  and  114 . Instead, as illustrated in  FIG. 10 , the suction device  404  is provided with tissue stimulation electrodes  426  and, in some instances, sensing electrodes  428 . The tissue stimulation and sensing electrodes  426  and  428 , which are held firmly against tissue when the suction source  402  is activated, are discussed in Section VI below.  
      The exemplary suction source  402  may be any suitable device that is capable of supplying the desired partial vacuum, which will typically range from about 200 mmHg to about 700 mmHg. Turning to  FIGS. 8-13 , the exemplary suction device  404  includes a main body  407 , a pair of internal suction lines  408  and a plurality of individual suction ports  410 . The suction tube  406  may be connected to the internal suction lines  408  by a connector  412  such as, for example, the illustrated Luer connector. The suction ports  410  are respectively connected to the internal suction lines  408  by a plurality of apertures  414 . The suction ports  410  are also formed in the curved bottom surface  416  (or “bottom wall”) of the main body  407  and define respective suction regions  418  ( FIG. 12 ). During use, the curved bottom surface will form a seal with the tissue surface and air within the suction regions  418  will be drawn through the apertures  414 , thereby causing the suction device  404  to adhere to the tissue surface.  
      The suction device  404  also includes a connector that enables it to be removably secured to the distal portion  108  of the surgical probe  100 ′. Although the present inventions are not limited to any particular connector, the connector in the exemplary embodiment is a slot  420  into which the surgical probe distal portion  108  may be inserted. The slot  420  is generally semi-circular in cross-section and extends between about 180 to 360 degrees, and preferably about 300 degrees. The diameter of the slot  420  will preferably be about the same as the diameter of the surgical probe distal portion  108 . As such, the distal portion  108  may be removably snap fit into the slot  420 . Additionally, once the surgical probe distal portion  108  is within the slot  420 , it may be advanced distally toward the suction device nose  422  and into an aperture  424  for anchoring ( FIGS. 14 and 15 ).  
      The specific size and shape of the suction device  404  will, of course, depend on the intended application, as will the choice of materials. Although the present inventions are not limited to any particular sizes, shapes or materials, one exemplary implementation that is especially well suited for cardiac treatment and use with the above-described surgical probe  100 ′ is described hereafter. The suction device  404  is formed, preferably by molding, from a soft, flexible biocompatible material such as silicone rubber or urethane that is capable of withstanding temperatures up to 120° C. without melting or burning. When molded, the suction device  404  will be an integrally formed (i.e. one piece) structure, although some or all of the connector  412  may be added after molding depending on the type of connector employed. The overall length of the suction device  404 , not including the connector  412 , will be slightly longer than the shaft distal portion  108 , e.g. about 10 cm in an exemplary implementation where the distal portion is about 9 cm.  
      The exemplary suction ports  410  are generally concave and elliptical in shape and have a major diameter of about 5 mm, a minor diameter of about 3 mm, a depth of about 2 mm. In the illustrated embodiment, the spacing corresponds to the spacing of the electrodes on the associated probe. Alternatively, the exemplary elliptical (i.e. 5 mm×3 mm×2 mm) suction ports may be spaced apart by about 6 mm center-to-center. The distance between the bottom of the slot  420  and the bottom of the main body  407  is about 5 mm. This exemplary configuration will result in the surgical probe  100 ′ and suction device  404  mating with one another in the manner illustrated in  FIGS. 14 and 15 .  
      With respect to the electrical connection of the stimulation electrodes  426  to the tissue stimulation apparatus  300  and EP recording apparatus  301 , and referring to  FIGS. 12 and 13 , the stimulation electrodes in the exemplary implementation are connected to signal lines  430  that extend from the stimulation electrodes, around the main body  407 , to a signal line bundle  432  on the top of the main body. Similarly, signal lines  434  extend from the sensing electrodes  428  to a signal line bundle  436 . A silicone rubber overmold  438  may be used to cover the individual signal lines and signal line bundles in those instances where the main body  407  is formed from silicone rubber. Alternatively, in those instances where the main body is formed from polyurethane, the signal lines and signal line bundles may be held in place with an elastic polyurethane adhesive. The signal lines in the bundles  432  and  436  pass through a cable  440  ( FIG. 7 ) and are connected to the EP recording apparatus  301  by a connector  442 . As discussed below, the EP recording apparatus  301  is connected to, and directs the tissue stimulation and recording associated with, the tissue stimulation apparatus  300 .  
      It should also be noted that, instead of the exemplary surgical probe  100 ′, the exemplary suction device  404  may be secured to the distal portion of a conventional electrophysiology catheter. The distal portion of the catheter and suction device  404  could then be used to directly place electrodes against tissue during a surgical procedure. The exemplary suction device  404  may also be permanently secured to a surgical probe or catheter by overmolding the suction device onto the surgical probe or catheter.  
      IV. Clamp Based Devices  
      As illustrated for example in  FIG. 16 , an exemplary surgical system  30  in accordance with one embodiment of a present invention includes an electrophysiology clamp apparatus  500 , a power supply and control apparatus  200 , and a tissue stimulation apparatus  300 . The power supply and control apparatus  200  and tissue stimulation apparatus  300  are discussed in Sections V and VI below. The electrophysiology clamp apparatus  500  includes a clamp and a tissue coagulation and stimulation assembly that may be secured to the clamp. As used herein, the term “clamp” includes, but is not limited to, clamps, clips, forceps, hemostats, and any other surgical device that includes a pair of opposable clamp members that hold tissue, at least one of which is movable relative to the other. In some instances, the clamp members are connected to a scissors-like arrangement including a pair of handle supporting arms that are pivotably connected to one another. The clamp members are secured to one end of the arms and the handles are secured to the other end. Certain clamps that are particularly useful in minimally invasive procedures also include a pair of handles and a pair of clamp members. Here, however, the clamp members and handles are not mounted on the opposite ends of the same arm. Instead, the handles are carried by one end of an elongate housing and the clamp members are carried by the other. A suitable mechanical linkage located within the housing causes the clamp members to move relative to one another in response to movement of the handles. The clamp members may be linear or have a predefined curvature that is optimized for a particular surgical procedure or portion thereof. The clamp members may also be rigid or malleable.  
      One example of a clamp is generally represented by reference numeral  502  in  FIGS. 16 and 22 - 24 . Referring more specifically to  FIGS. 22-24 , the clamp  502  includes a pair of rigid arms  504  and  506  that are pivotably connected to one another by a pin  508 . The proximal ends of the arms  504  and  506  are respectively connected to a pair handle members  510  and  512 , while the distal ends are respectively connected to a pair of clamp members  514  and  516 . The clamp members  514  and  516  may be rigid or malleable and, if rigid, may be linear or have a pre-shaped curvature. A locking device  518  locks the clamp in the closed orientation, and prevents the clamp members  514  and  516  from coming any closer to one another than is illustrated in  FIG. 22 , thereby defining a predetermined spacing between the clamp members. The clamp  502  is also configured for use with a pair of soft, deformable inserts (not shown) that may be removably carried by the clamp members  514  and  516  and allow the clamp to firmly grip a bodily structure without damaging the structure. To that end, the clamp members  514  and  516  each include a slot  520  ( FIGS. 23 and 24 ) that is provided with a sloped inlet area  522  and the inserts include mating structures that are removably friction fit within the slots. The present tissue coagulation and stimulation assemblies may be mounted on the clamp members in place of the inserts.  
      One example of a tissue coagulation and stimulation assembly, which is generally represented by reference numeral  524  in  FIGS. 16-19 , includes first and second tissue coagulation electrodes  526   a  and  526   b,  which are discussed in Section V below, and first and second tissue stimulation electrodes  528   a  and  528   b,  which are discussed in Section VI below. Typically, there will be about 1 to 3 mm between the distal ends of the coagulation electrodes  526   a  and  526   b  and the stimulation electrodes  528   a  and  528   b.  The electrodes are carried on support structures  530   a  and  530   b,  which are connected to a flexible cable  532  by a molded plastic junction  534 . The first and second coagulation electrodes  526   a  and  526   b  are also relatively long electrodes (e.g. about 3 to 8 cm) and, to that end, power lines  536  are connected to each longitudinal end of the first tissue coagulation electrode  526   a  and return lines  538  are connected to each longitudinal end of the second tissue coagulation electrode  526   b.  It should be noted that although the return lines  538  may be used to return power when the surgical system  30  is operating in a bipolar mode, the return lines may also be used to supply power when the system is operating in a unipolar mode.  
      The tissue stimulation electrode  528   a  is connected to a signal line  540 , and the tissue stimulation electrode  528   b  is connected to a signal line  542 . The signal lines  540  and  542  may be used for transmission and return, respectively, when the system is being operated in a bipolar mode, and both may be used for transmission when the system is being operated in unipolar mode. The first and second tissue stimulation electrodes  528   a  and  528   b,  as well as the signal lines  540  and  542 , may also be used to transmit signals when the stimulation electrodes are used for sensing and recording purposes.  
      In the exemplary embodiment, a plurality of temperature sensors  130  ( FIG. 21 ), such as thermocouples or thermistors are carried on the support structures  530   a  and  530   b.  There are four (4) temperature sensors  130  associated with each tissue coagulation electrode  526   a  and  526   b  in the exemplary embodiment. Signal lines  544  are connected to each of the temperature sensors  130 .  
      In an alternative arrangement, one or both of the first and tissue second coagulation electrodes  526   a  and  526   b  may be split into two electrodes that are about 1.5 cm to 4 cm in length and separated by about 1 to 3 mm. Here, each electrode will be connected to a single power or return line and two temperature sensors  130  will be associated with each electrode.  
      As described in greater detail below, the power supply lines  536  may be used to transmit energy from the power supply and control apparatus  200  to the coagulation electrode  526   a  (which is returned by way of coagulation electrode  526   b  and return lines  538 ), while the signal lines  544  return temperature information from the temperature sensors  130  to the power supply and control apparatus. The signal line  540  may be used to transmit tissue stimulation energy from the tissue stimulation apparatus  300  to the stimulation electrode  528   a.  The stimulation energy is returned to the tissue stimulation apparatus  300  by way of the stimulation electrode  528   b  and signal line  542 . The power supply and return lines  536  and  538  and signal lines  540 - 544  extend from the electrodes  526   a - 528   b  and temperature sensors  130 , through the cable  532 , to a handle  545 . The power supply and return lines  536  and  538  and signal lines  544  are connected to a PC board  546  that is carried by the handle  545 . The handle  545  also includes a port (not shown) for a connector  206 ′ from the power supply and control apparatus  200  which connects to the PC board  546 , and openings (not shown) for signal lines  540  and  542 , which are connected to the tissue stimulation apparatus  300 .  
      The exemplary tissue coagulation and stimulation assembly  524  also includes a pair of base members  548   a  and  548   b  which are used to connect the assembly to the clamp  502 . Although the configuration of the energy transmission and stimulation assembly may vary from application to application to suit particular situations, the exemplary energy transmission and stimulation assembly  524  is configured such that the electrodes  526   a  and  526   b  will be parallel to one another as well as relatively close to one another (i.e. a spacing of about 1-10 mm) when the clamp  502  is in the closed orientation. The stimulation electrodes  528   a  and  528   b  will typically be about 5 mm to 50 mm apart when the clamp  502  is opened (in full or in part). Such an arrangement will allow the energy transmission and stimulation assembly to grip a bodily structure without cutting through the structure. Referring more specifically to  FIGS. 20-24 , the base member  548   a  includes a main portion  550 , with a groove  552  that is configured to receive the support structure  530   a  and electrode  526   a,  and a connector  554  that is configured to removably mate with the slot  520  in the clamp  502 . [It should be noted that the configuration of the base member  548   b  is identical to that of the base member  548   a  in the illustrated embodiment.] About 20% of the electrode surface (i.e. about 75° of the 360° circumference) is exposed in the illustrated embodiment. Adhesive may be used to hold the electrode  526   a  and support structure  530   a  in place. The exemplary connector  554  is provided with a relatively thin portion  556  and a relatively wide portion  558 , which may consist of a plurality of spaced members (as shown) or an elongate unitary structure, in order to correspond to the shape of the slot  520 .  
      The base members  548   a  and  548   b  are preferably formed from polyurethane. The length of the base members in the exemplary energy transmission assemblies will vary according to the intended application. In the area of cardiovascular treatments, it is anticipated that suitable lengths will range from, but are not limited to, about 4 cm to about 10 cm. In the exemplary implementation, where the electrodes  526   a  and  526   b  are preferably about 6.4 cm, the base members  548   a  and  548   b  will be about 6.6 cm.  
      The exemplary clamp apparatus  500  is not limited to the exemplary implementation described above and is susceptible to a wide variety of modifications. By way of example, and referring to  FIGS. 24A and 24B , the tissue coagulation and stimulation assembly may be modified such that the position of the first and second tissue stimulation electrodes  528   a  and  528   b  relative to the first and tissue second coagulation electrodes  526   a  and  526   b  and/or the distal ends of the base members may be varied, as they are in base members  548   a ′ and  548   a″.    
      Other exemplary clamp apparatus include a tissue coagulation and stimulation assembly wherein a plurality of stimulation electrodes are associated with one (or both) of coagulation electrodes. The stimulation electrodes may, for example, be located on opposite sides of a coagulation electrode so that the stimulation electrodes will be on opposite side of the lesion for stimulation and sensing purposes. One such tissue coagulation and stimulation assembly is generally represented by reference numeral  524 ′ and is illustrated in FIGS.  24 C-H. The tissue coagulation and stimulation assembly  524 ′ is substantially similar to the tissue coagulation and stimulation assembly  524  illustrated in  FIGS. 17-21  and similar elements are represented by similar reference numerals. Here, however, pairs of stimulation electrodes  529   a   1 / 529   a   2  and  529   b   1 / 529   b   2  are positioned on opposite sides of the coagulation electrode  526   a.  The spacing between the stimulation electrodes  529   a   1 / 529   a   2  and  529   b   1 / 529   b   2 , which are discussed in Section VI below, and the coagulation electrode  526   a  will typically be about 1 mm. The coagulation electrodes  526   a  and  526   b  are carried on support structures  530   a  and  530   b.  The stimulation electrodes  529   a   1 / 529   a   2  and  529   b   1 / 529   b   2  are carried on support structures  531   a  and  531   b.    
      The exemplary tissue coagulation and stimulation assembly  524 ′ also includes a pair of base members  549   a  and  549   b  which are used to connect the assembly to the clamp  502  in the manner described above with reference to base members  548   a  and  548   b.  Referring more specifically to  FIGS. 24F-24G , the base member  549   a  includes a main portion  551 , with a groove  552  that is configured to receive the support structure  530   a  and electrode  526   a,  and a pair of grooves  553  that are configured to receive the stimulation electrodes  529   a   1 / 529   a   2  and  529   b   1 / 529   b   2  and support structures  531   a  and  531   b.  A connector  554  is configured to removably mate with the slot  520  in the clamp  502 . The configuration of the base member  549   b  is identical to that of the base member  548   b  in the illustrated embodiment. Alternatively, the base member  549   b  may be configured to carry stimulation electrodes in the same manner as base member  549   a.  Still another alternative is to configure the assembly such that stimulation electrodes  529   a   1 / 529   a   2  are carried base member  549   a,  stimulation electrodes  529   b   1 / 529   b   2  are carried base member  549   b,  and stimulation electrodes  529   a   1 / 529   a   2  and stimulation electrodes  529   b   1 / 529   b   2  are on opposite side of the coagulation electrodes.  
      The tissue stimulation electrodes  529   a   1 / 529   a   2  are connected to respective signal lines  540  and  542 , as are the tissue stimulation electrodes  529   b   1 / 529   b   2 . The signal lines  540  and  542  may be used for transmission and/or return depending upon the manner in which the electrodes are being used. For example, the stimulation electrodes  529   a   1 / 529   a   2  may be used in bipolar mode to transmit stimulation energy and the stimulation electrodes  529   b   1 / 529   b   2  may be used in bipolar mode to sense local activation.  
      Finally, the clamp and the tissue coagulation and stimulation assemblies described above may be combined into an integral unit that cannot be readily separated. For example, the base members may be molded onto the clamp members. Such base members would, for example, extend completely around the each clamp member and/or include portions that are molded into the slots.  
      V. Coagulation Electrodes, Temperature Sensing and Power Control  
      In each of the surgical systems illustrated in  FIGS. 1-24H , coagulation electrodes adapted to transmit RF energy are employed. However, other types of coagulation elements, such as such as lumens for chemical ablation, laser arrays, ultrasonic transducers, microwave electrodes, ohmically heated hot wires, and the like may be substituted for the coagulation electrodes. Coagulation electrodes may be arranged as a series of spaced electrodes or, alternatively, a single elongate coagulation electrode may be employed.  
      Although the present inventions are not limited to any particular number, the exemplary surgical probes  100 ,  100 ′ and  101  illustrated in  FIGS. 1-15  each include seven spaced coagulation electrodes  110 , while the various clamp apparatus  500  illustrated in  FIGS. 16-24H  includes a single electrode  526   a / 526   b  carried on each of the clamp members  514  and  516 . The coagulation electrodes are preferably in the form of wound, spiral closed coils. The coils are made of electrically conducting material, like copper alloy, platinum, or stainless steel, or compositions such as drawn-filled tubing (e.g. a copper core with a platinum jacket). The electrically conducting material of the coils can be further coated with platinum-iridium or gold to improve its conduction properties and biocompatibility. Preferred coil coagulation electrodes are disclosed in U.S. Pat. Nos. 5,797,905 and 6,245,068.  
      Alternatively, the coagulation electrodes  110  may be in the form of solid rings of conductive material, like platinum, or can comprise a conductive material, like platinum-iridium or gold, coated upon the device using conventional coating techniques or an ion beam assisted deposition (IBAD) process. For better adherence, an undercoating of nickel, silver or titanium can be applied. The coagulation electrodes can also be in the form of helical ribbons. The electrodes can also be formed with a conductive ink compound that is pad printed onto a non-conductive tubular body. A preferred conductive ink compound is a silver-based flexible adhesive conductive ink (polyurethane binder), however other metal-based adhesive conductive inks such as platinum-based, gold-based, copper-based, etc., may also be used to form electrodes. Such inks are more flexible than epoxy-based inks. Open coil electrodes may also be employed for coagulation.  
      The exemplary flexible coagulation electrodes  110  carried by the surgical probes  100 ,  100 ′ and  101  illustrated in  FIGS. 1-15  are preferably about 4 mm to about 20 mm in length. In the preferred embodiments, the electrodes are 12.5 mm in length with 1 mm to 3 mm spacing, which will result the creation of continuous lesion patterns in tissue when coagulation energy is applied simultaneously from adjacent electrodes through tissue to an indifferent electrode. For rigid coagulation electrodes, the length of the each electrode can vary from about 2 mm to about 10 mm. Using multiple rigid electrodes longer than about 10 mm each adversely effects the overall flexibility of the device, while electrodes having lengths of less than about 2 mm do not consistently form the desired continuous lesion patterns. The diameter, whether flexible or rigid, will typically be about 3 mm. Turning to the relatively long coagulation electrodes  526   a  and  526   b  carried by the clamp  502  illustrated in  FIGS. 16-24H , for cardiovascular applications, the length is preferably between about 2 cm and 8 cm in those instances where power is supplied at both longitudinal ends of each electrode, and the end to end resistance is about 5 ohm to about 15 ohm. The diameter of the electrodes described above preferably ranges from about 1.5 mm to about 3 mm for cardiovascular applications and, in one preferred implementation, the outer diameter is about 2 mm.  
      In the exemplary embodiments, the temperature sensors  130  are preferably located within a linear channel, such as the channel  131  in  FIG. 5 , which is formed in the shaft distal portion  108  ( FIGS. 1-15 ) or in the channel  131  in  FIG. 21 , which is formed in the support structures  530   a  and  530   b  ( FIGS. 16-21  and  24 C- 24 H). The linear channel insures that the temperature sensors will all face in the same direction (e.g. facing tissue) and be arranged in linear fashion. This arrangement results in more accurate temperature readings which, in turn, results in better temperature control. As such, the actual tissue temperature will more accurately correspond to the temperature set by the physician on the power supply and control device, thereby providing the physician with better control of the lesion creation process and reducing the likelihood that embolic materials will be formed. A reference thermocouple may also be provided.  
      The power supply and control system  200  includes an electrosurgical unit (“ESU”)  202  that supplies and controls RF power. A suitable ESU is the Model 4810 ESU sold by Boston Scientific Corporation of Natick, Mass., which is capable of supplying and controlling power on an electrode-by-electrode basis. This is sometimes referred to as “multi-channel control.” The ESU  202  transmits energy to the coagulation electrodes and receives signal from the temperature sensors by way of a cable  204  and a connector  206 , which may be connected to the PC board on the surgical probe or clamp in the manner described above. The amount of power required to coagulate tissue ranges from 5 to 150 W. The exemplary ESU  202  is operable in a bipolar mode, where tissue coagulation energy emitted by one of the coagulation electrodes is returned through one of the other coagulation electrodes, and a unipolar mode, where the tissue coagulation energy emitted by the coagulation electrodes is returned through one or more indifferent electrodes  208  that are externally attached to the skin of the patient with a patch, or one or more electrodes (not shown) that are positioned in the blood pool, and a cable  210 . Information concerning suitable temperature sensing and RF power supply and control is disclosed in U.S. Pat. Nos. 5,456,682, 5,582,609 and 5,755,715. Another alternative is to supply power in the combined bipolar/unipolar mode described in U.S. application Ser. No. 10/368,108, which is entitled “Power Supply And Control Apparatus And Electrophysiology Systems For Use With Same” and incorporated herein by reference.  
      With respect to the surgical systems  10 ,  11  and  20  illustrated in  FIGS. 1-15 , a single power line  126  is connected to each coagulation electrode  110 . Typically, there are two temperature sensors  130  for each coagulation electrode  110 . The ESU  202  individually powers and controls each coagulation electrode  110  based on the hottest of the two measured temperatures at that particular electrode.  
      In the surgical system  30  illustrated in  FIGS. 16-24H , first and second power lines  536  are respectively connected to the longitudinal ends of the coagulation electrode  526   a,  first and second return lines  538  are respectively connected to the longitudinal ends of the coagulation electrode  526   b,  and two pairs of temperature sensors  130  (i.e. four temperature sensors) are provided for each of the coagulation electrodes. Each temperature sensor pair includes one temperature sensor  130  at a longitudinal end of the associated coagulation electrode and one temperature sensor located a distance equal to about ⅓ of the total electrode length from the longitudinal end. The ESU  202  will typically be operated in bipolar mode and energy supplied to the coagulation electrode  526   a  will be returned to the ESU by way of the coagulation electrode  526   b.  As such, the ESU connector  206 ′ is connected to the power supply and return lines  536  and  538 .  
      The ESU  202  in the exemplary surgical system  30  may be used to individually power and control two portions of the coagulation electrode  526   a  (one portion on either side of the longitudinal mid-point of the electrode) during a lesion formation procedure. Power to each portion, which has one power line  536  connected thereto and two temperature sensors  130  associated therewith, is controlled based on the highest of the two temperatures sensed by the two temperature sensors associated with that portion. Additional details concerning this power supply and control technique are provided in U.S. application Ser. No. 10/255,025, which is entitled “Electrophysiology Electrode Having Multiple Power Connections And Electrophysiology Devices Including The Same” and incorporated herein by reference.  
      The exemplary ESU  202  is also provided with power output and return connectors  212  and  214  ( FIGS. 1, 6A ,  7  and  16 ), for connection to corresponding connectors on the power output and return cables  204  and  210 , that have different configurations in order to prevent improper connections.  
      VI. Stimulation Electrodes and Lesion Confirmation  
      In addition to forming lesions, the exemplary surgical systems illustrated in  FIGS. 1-24H  may also be used to determine whether or not therapeutic lesions have been properly formed by, for example, supplying tissue stimulation energy on one side of a lesion. The tissue on the other side of the lesion may then be monitored to determine whether an excitation block (typically the result of a continuous transmural lesion) has been formed in the target tissue. Tissue stimulation energy may also be used to determine lesion depth, which in turn, allows the physician to determine whether or not a lesion is transmural. In the exemplary implementations, the tissue stimulation energy is provided by a tissue stimulation apparatus  300  that is capable of providing a pulse of energy that stimulates (but does not coagulate) tissue. One exemplary tissue stimulation apparatus  300  is a conventional pacing apparatus, such as the Medtronic Model Nos. 5330 and 5388 external pulse generators. An ECG machine that is capable of monitoring and recording electrical impulses sensed by electrodes may also be provided.  
      With respect to the stimulation energy, the power delivered to tissue for stimulation purposes will typically be significantly less than that which would form a transmural or otherwise therapeutic lesion in tissue. With respect to the larger stimulation electrodes  112 ,  114 ,  528   a,    528   b,    529   a   1 ,  529   a   2 ,  529   b   1  and  529   a   2  discussed with respect to  FIGS. 1-6B ,  16 - 21  and  24 A- 24 H, which may also be used for sensing, an exemplary stimulation energy delivery would consist of two stimulation pulses per second, each pulse being 1 millisecond. The maximum amplitude would be 20 mA, which would create 1 V, for a total power delivery of 40 μW. Turning to the smaller stimulation and sensing electrodes  426 ,  428  and  604 , an exemplary stimulation energy delivery would consist of two stimulation pulses per second, each pulse being 1 millisecond. The maximum amplitude would be 10 mA, which would create 0.5 V, for a total power delivery of 10 μW. As noted above, the amount of power required to coagulate tissue ranges from 5 to 150 W.  
      In order to facilitate the connection to the tissue stimulation apparatus  300 , the surgical devices discussed above with reference to  FIGS. 1-6  and  16 - 32  are connectors  302  (both transmission and return) that are typically associated with pacing apparatus. Suitable connectors include, for example, 2 mm Hirshman pins. The connectors  302  may be individually connected to the tissue stimulation apparatus  300  (as shown) or combined into a single unit. The configuration of the connectors  302  will also typically be different than the ESU connectors  212  and  214  to prevent improper connections. In the embodiment illustrated in  FIGS. 6A and 6B , on the other hand, there are far more stimulation electrodes and a single connector  117  is used to connect the stimulation electrodes to the EP recording apparatus  301 . Similarly, in  FIGS. 7-15 , where there are many stimulation electrodes, as well as a corresponding number of sensing electrodes, a single connector  442  is used to connect the electrodes to the EP recording apparatus  301 . A suitable EP recording apparatus is the Prucka CardioLab 7000® from GE Medical Systems. Preferably, the configuration of the connectors  117  and  442  will be different than the ESU connectors  212  and  214  to prevent improper connections.  
      It should also be noted that the functionality of the tissue stimulation apparatus  300  may be incorporated into the ESU  202 . Here, however, ESU and associated surgical devices should be configured such that coagulation electrodes will only receive coagulation energy and the stimulation electrodes will only receive stimulation energy. Here too, this may be accomplished with different connector configurations. The functionality of the tissue stimulation-apparatus  300  and the EP recording apparatus  301  may also be combined into a single device.  
      Generally speaking, the present surgical systems may be used to test the effectiveness of a lesion as follows. After the lesion is formed, the physician may use the same surgical device that was used to form the lesion (e.g. the surgical probe, surgical probe and suction device, or clamp based electrophysiology device) to perform a lesion evaluation. As discussed in greater detail below, the stimulation electrodes that are provided on surgical devices may be used to stimulate tissue on one side of a lesion by pacing at a higher rate than normal (e.g. 120 beats/minute). The local activation, if any, on the other side of the lesion will indicate whether or not the excitation block is incomplete. The stimulation electrodes may also be used to sense tissue within an isolated tissue region around which a lesion has been formed. Local activation within the isolated region from the heart&#39;s natural stimulation is indicative of a gap in the lesion. Additionally, the stimulation electrodes may be used to determine lesion depth.  
      There are a number of benefits associated with the present surgical systems. For example, the placement of tissue stimulation electrodes on the same surgical device as the tissue coagulation electrodes allows the physician to quickly and easily evaluate a lesion after it has been formed.  
      Referring to the exemplary surgical system  10  illustrated in  FIGS. 1-6 , the surgical probe  100  is provided with a pair of tissue stimulation electrodes  112  and  114  that may be connected to the tissue stimulation apparatus  300  and used to provide stimulation energy. The tissue stimulation electrodes  112  and  114  may also be used for sensing local tissue activation. Typically, the stimulation electrodes  112  and  114  will operate in a bipolar mode, but may be operated in unipolar mode if desired. The stimulation electrodes  112  and  114  are typically relatively small (i.e. too small to form transmural myocardial lesions). In the exemplary embodiment, stimulation electrode  112  is a ring electrode that is about 0.5 mm to 2 mm in length, the stimulation electrode  114  is a tip electrode that is about 0.5 mm to 2 mm in length, and the spacing therebetween is about 0.5 mm to 2 mm. Alternatively, the stimulation electrode  114  may be in the form of a ring electrode. Stimulation electrode  112  is about 1 mm to 3 mm from the distal-most coagulation electrode  110 . With respect to materials, the stimulation electrodes  112  and  114  may be formed from the same materials as the coagulation electrodes  110 . The diameter of the electrodes  112  and  114  preferably ranges from about 1.5 mm to about 3 mm for cardiovascular applications and, in one preferred implementation, the outer diameter is about 2 mm.  
      The exemplary surgical system  10  may be used to test the quality of lesions formed during a lesion formation procedure in a variety of ways. In the context of pulmonary vein isolation, for example, the coagulation electrodes  110  may be used to form continuous lesions around the pulmonary veins to isolated them from the left atria. Typically, a first lesion will be formed around the right pulmonary vein pair and a second lesion will be formed around the left pulmonary vein pair. The stimulation electrodes  112  and  114  may then be used to provide stimulation energy to the area within the first lesion. The tissue on the other side of the lesion may be monitored (electrically or visually) to determine whether the excitation block formed by the first lesion is complete. A similar procedure may be performed with respect to the second lesion. Alternatively, the stimulation electrodes  112  and  114  may be used to sense tissue within the area defined by the first lesion to determine whether heart&#39;s natural stimulation will produce local activation within the tissue area defined by the lesion. No local activation within the area defined by the lesion is indicative of the formation of a complete excitation block, while local activation is indicative of a gap in the lesion. A similar procedure may be performed with respect to the second lesion. It should also be noted that the surgical system  10  may be used both epicardial and endocardial procedures and that stimulation electrodes  112  and  114  may be used individually in unipolar versions of the aforementioned procedures if desired.  
      The tissue stimulation electrodes  112  and  114  in the exemplary surgical probe  101  illustrated in  FIGS. 6A and 6B  have the same configuration as the tissue stimulation electrodes in the surgical probe  100  and the surgical system  11  may be used to test the quality of lesions in the manner described above. Additionally, the surgical system  11  may be used to determine lesion depth and, correspondingly, whether or not a lesion is transmural at various points along the length of the lesion. Stimulation energy may be used to determine lesion depth because non-viable tissue (e.g. coagulated tissue) cannot be stimulated and will not propagate stimulation energy to nearby tissue. As such, when the application of stimulation energy that should stimulate tissue at a known depth fails to do so, and that depth is greater than or equal to the thickness of the body structure, it may be inferred that a transmural lesion has been formed.  
      In the context of lesions formed within the heart, for example, localized current densities must exceed about 2 mA/cm 2  to stimulate heart tissue. With respect to current transmitted from an electrode to tissue, the current density is about ½ πr 2 , where r is the distance from the electrode. Thus, a 1 mA stimulation pulse will typically stimulate viable tissue that is no more than about 2.8 mm from the electrode, a 2 mA stimulation pulse will typically stimulate viable tissue that is no more than about 4.0 mm from the electrode, a 10 mA stimulation pulse will typically stimulate viable tissue that is no more than about 9.0 mm from the electrode, and a 20 mA stimulation pulse will typically stimulate viable tissue that is no more than about 13.0 mm from the electrode. By varying the amplitude of the stimulation energy pulses over a range of 1 to 20 mA, it is possible to determine how far viable tissue is from the electrode. For example, the left atrium is about 3 mm thick and accordingly, failure to stimulate with a 2 mA stimulation pulse indicates that a transmural lesion has been formed in the vicinity of the stimulation electrode.  
      Referring to the exemplary surgical probe  101 , and as noted above, the tissue stimulation electrodes  112  are located between the coagulation electrodes  110  and proximal of the proximal-most coagulation electrode, while the stimulation electrode  114  is distal of the distal-most coagulation electrode. This arrangement allows the physician to test various points along the length of a lesion when all of the coagulation electrodes  110  are used to form the lesion (without moving the probe). Alternatively, if only the middle three coagulation electrodes  110  are used to form a lesion, for example, then the adjacent four tissue stimulation electrodes  112  could be used to stimulate tissue to determine whether or not the lesion is transmural.  
      The exemplary surgical system  11  may be used to test the quality of lesions formed during a lesion formation procedure in a variety of ways. In the context of lesions within the left atrium, for example, the coagulation electrodes  110  may be used to form a continuous lesion (e.g. around one or more pulmonary veins, or as part of a pattern of therapeutic lesions). After the lesion has been formed, and without moving the surgical probe  101 , one or more of the stimulation electrodes  112  and  114  may be used to provide stimulation energy to the coagulated tissue. For example, the stimulation electrodes  112  and  114 , which are located along the linear or curvilinear region of coagulated tissue may be individually provided with pulses of stimulation energy. The magnitude of the pulses, which should be chosen so as to correspond to the thickness of the tissue structure, will be about 2 mA in the left atrium example. Viable tissue within the left atrium may be monitored (electrically or visually) after each pulse to determine whether the lesion is transmural. More specifically, a lack of local activation within the left atrium from the pulse indicates that the lesion is deep enough (i.e. transmural) in the vicinity of the associated stimulation electrode, while local activation indicates that the lesion is not transmural in the region of the stimulation electrode. In those instances where the lesion (or portion thereof) is not transmural, additional coagulation with the coagulation electrodes  110 , typically at a higher power level than originally employed, may be performed. It should also be noted that the surgical system  11  may be used both epicardial and endocardial procedures.  
      Turning to the exemplary surgical system  20  illustrated in  FIGS. 7-15 , and referring more specifically to  FIG. 14 , the suction device  404  is provided with longitudinally extending bipolar pairs of tissue stimulation electrodes  426  and longitudinally extending bipolar pairs of sensing electrodes  428  near the lateral edges of the suction device. In the illustrated embodiment, a plurality of bipolar pairs of stimulation electrodes  426  extend along essentially the entire length of one side of the suction device  404 , while a plurality of bipolar pairs of sensing electrodes  428  extend along essentially the entire length of the other side of the suction device. Each bipolar pair is adjacent to one of the suction ports  410  and, accordingly, the electrodes will be held firmly against tissue when suction force is applied. The stimulation electrodes  426  are located on one side of the slot  420  and the sensing electrodes  428  are located on the other. As such, the tissue stimulation and sensing electrodes  426  and  428  will be on opposite sides of the surgical probe distal section  108  and the coagulation electrodes  110 , as well as on opposite sides of the lesion formed by the coagulation electrodes.  
      There are, of course, a wide variety of alternative stimulation and sensing electrode schemes. By way of example, but not limitation, the number of bipolar pairs of tissue stimulation and sensing electrodes  426  and  428  may range from a large number of pairs (as shown) to a single pair tissue stimulation electrodes and a single pair sensing electrodes. The single pairs may be located near the middle (measured longitudinally) of the suction device  404 . Another alternative is unipolar stimulation and sensing. Here, single stimulation electrodes (as opposed to a bipolar pair) may be positioned adjacent to each of the suction ports  410  on one side of the suction device  404  and single sensing electrodes may be positioned adjacent to each of the suction ports on the other side of the suction device.  
      With respect to configuration and manufacture, the exemplary tissue stimulation and sensing electrodes  426  and  428  may be relatively small (i.e. too small to form transmural myocardial lesions), low profile devices. Suitable sizes are about 0.5 mm to 1 mm in diameter, and a suitable thickness is about 0.01 mm. Such electrodes may be formed by coating a conductive material onto the suction device  404  using conventional coating techniques or an IBAD process. Suitable conductive materials include platinum-iridium and gold. An undercoating of nickel, silver or titanium may be applied to improve adherence. Conductive ink compounds, such as silver-based flexible adhesive conductive ink (polyurethane binder) or metal-based adhesive conductive inks (e.g. platinum, gold, or copper based) may also be pad printed onto the suction device  404 . The signal lines  430  and  434  are also very thin (e.g. about 40-50 gauge wires).  
      The exemplary surgical system  20  may be used to test the quality of lesions formed during a lesion formation procedure in a variety of ways. For example, the suction source  402  may be used to maintain the position of the suction device  404  after power transmission from the coagulation electrodes  110  on surgical probe  100 ′ has ended. A pulse of stimulation energy (here, about 10 mA) may be applied to viable tissue on one side of the lesion by a pair of stimulation electrodes (such as the pair identified by reference numeral  426   a  in  FIG. 14 ). The viable tissue on the other side of the lesion may be monitored with a pair of sensing electrodes (such as the pair identified by reference numeral  428   a  in  FIG. 14 ) to detect the local excitation from the pulse of stimulation energy. The tissue stimulation apparatus  300  will measure the amount of time between the delivery of the pulse to the tissue by the stimulation electrode pair  426   a  and the detection of the local activation by the sensing electrode pair  428   a  on the other side of the lesion. The amount of time that between pulse delivery on one side of the lesion and local activation on the other (sometimes referred to as a “conduction delay”) is indicative of the quality of the lesion.  
      In the context of the formation of lesions within the heart, the conduction delay from the stimulation electrode pair  426   a  and the sensing electrode pair  428   a  will typically be about 10 ms when the distance between the pairs is about 1 cm, absent a conduction block. Here, the excitation pulse will travel a relatively short distance. Conversely, when a complete conduction block is formed between the stimulation and sensing pairs, the excitation pulse will be forced to travel around the lesion. The longer travel distance results in a longer conduction delay, which is indicative of the formation of a therapeutic lesion. For example, a continuous 50 cm transmural lesion that creates a complete conduction block along its length will typical increase the conduction delay to about 50 ms.  
      The exemplary EP recording apparatus  301  may be configured to simply display measured conduction delays. Alternatively, the EP recording apparatus  301  may be used to store expected propagation delays for various tissue types and suction device configurations (including the positioning of the stimulation and sensing electrodes). The EP recording apparatus  301  will compare the expected propagation delay (e.g. 10 ms) with no block to the measured propagation delay (e.g. 50 ms) and determine whether or not a complete conduction block has been formed. The EP recording apparatus  301  would then provide an audible or visual indication concerning the status of the lesion.  
      It should also be noted that, in a preferred testing method, the lesion will be tested at various points along its length, one point at a time. The lesion may be tested with each of the stimulation and sensing electrode pairs that are adjacent to a coagulation electrode that was used to form a lesion. If for example, the proximal four coagulation electrodes are used to form a lesion, then the proximal four pairs of stimulation and sensing electrodes will be used (one stimulation/sensing at a time) to determine whether or not the lesion creating procedure created a complete conduction block.  
      Referring now to the exemplary surgical system  30  illustrated in  FIGS. 16-24B , and to  FIG. 16  in particular, the energy transmission and stimulation assembly  524  includes first and second tissue stimulation electrodes  528   a  and  528   b.  The stimulation electrodes  528   a  and  528   b  are preferably tip electrodes that are about 1 mm to 2 mm in length, about 2 mm to 4 mm in diameter, and carried on the distal ends of the support structures  530   a  and  530   b.  The stimulation electrodes  528   a  and  528   b  are also about 1 mm to 3 mm from the distal ends of the coagulation electrodes  526   a  and  526   b.  The stimulation electrodes may, alternatively, be ring electrodes that are carried near the distal ends of the support structures  530   a  and  530   b.  Another alternative is to place both stimulation electrodes on one of the support structures in a manner similar to the surgical probe  100  illustrated in  FIG. 1 . The stimulation electrodes  528   a  and  528   b  may also be formed from the materials and methods described above with respect to stimulation electrodes  112  and  114 .  
      Turning to exemplary energy transmission and stimulation assembly  524 ′ illustrated in  FIGS. 24C-24H , the stimulation electrodes  529   a   1 / 529   a   2  and  529   b   1 / 529   b   2  are typically relatively small ring electrodes (i.e. too small to form transmural myocardial lesions) that are about 0.5 mm to 2 mm in length and about 1.5 mm to 3 mm in diameter.  
      The exemplary surgical system  30  may be used to test the quality of lesions formed during a lesion formation procedure in a variety of ways. For example, in the context of the treatment of atrial fibrillation, the surgical system  30  may be used to form lesions around one or more pulmonary veins to isolated the left atria from arrhythmias that originate in the pulmonary veins. In one exemplary procedure, the clamp  502  may be positioned around a pair of pulmonary veins and the coagulation electrodes  526   a  and  526   b  used to form a lesion around the pair. The stimulation electrodes  528   a  and  528   b  may then be used to supply a bipolar pacing pulse (e.g. about 20 mA) on the side of the lesion opposite the left atrium. The physician can determine whether or not a therapeutic lesion (or “complete block”) has been formed by observing the left atrium. If the pacing pulse is able to cross the lesion, the heart will beat faster (e.g. 120 beats/minute). This may be determined by observation or by use of an ECG machine that is monitoring the heart. Here, additional coagulation will be required to complete the lesion. The failure to stimulate the heart from the side of the lesion opposite the left atrium is, on the other hand, indicative of the formation of a therapeutic lesion. Nevertheless, because muscle bundles are not always connected near the pulmonary veins, it is preferable that the stimulation energy be applied to a number of tissue areas on the side of the lesion opposite the left atrium to reduce the possibility of false negatives.  
      Alternatively, the stimulation electrodes  528   a  and  528   b  may then be used to monitor tissue within the region that was intended to be isolated. In the context of pulmonary vein isolation, for example, the stimulation electrodes  528   a  and  528   b  may be placed in contact with viable tissue on the pulmonary vein side of the lesion. Local activation within the isolated region from the heart&#39;s natural stimulation is indicative of a gap in the lesion.  
      The stimulation electrodes  528   a  and  528   b  may also be used in a unipolar operation similar to the bipolar operation discussed above with reference to stimulation and sensing electrodes pairs  426   a  and  428   a.  More specifically, the clamp members  514  and  516  may be positioned such that the electrodes  528   a  and  528   b  are on opposite sides of a continuous linear or curvilinear lesion. For example, electrode  528   a  may be placed within the left atrium and electrode  528   b  may be placed on the pulmonary vein side of a pulmonary vein ostium. A pulse of stimulation energy (about 10 mA) may be applied to viable tissue on one side of the lesion by the electrode  528   a  and the viable tissue on the other side of the lesion may be monitored with the electrode  528   b  to detect whether or not there is local excitation from the pulse of stimulation energy.  
      Additionally, the surgical system  30  may be used to determine whether or not a lesion is transmural. Here, the electrodes  528   a  and  528   b  may be placed on opposite surfaces of the lesion (e.g. the epicardial and endocardial surfaces, or two epicardial surfaces).  
      Turning to  FIGS. 24C-24H , in those instances in which the exemplary surgical system  30  includes the exemplary energy transmission and stimulation assembly  524 ′, the stimulation electrodes  529   a   1 / 529   a   2  and  529   b   1 / 529   b   2  may be used to test a lesion formed with the coagulation electrodes  526   a  and  526   b  without moving the clamp  502 . For example, after the lesion is formed, a pulse of stimulation energy (here, about 10 mA) may be applied to viable tissue on one side of the lesion by stimulation electrodes  529   a   1 / 529   a   2 , while viable tissue on the other side of the lesion may be monitored with stimulation electrodes  529   b   1 / 529   b   2  to detect the local excitation from the pulse of stimulation energy. The tissue stimulation apparatus  300  will measure the conduction delay between the delivery of the pulse to the tissue on one side of the lesion and the detection of the local activation on the other side of the lesion. The conduction delay is, as noted above, indicative of the quality of the lesion.  
      VII. Tissue Stimulation and Sensing Probes  
      As illustrated for example in  FIGS. 25-28 , a surgical tissue stimulation and sensing system  40  in accordance with one embodiment of a present invention includes a tissue stimulation apparatus  300  and a tissue stimulation and sensing probe  600 . The tissue stimulation apparatus  300  is described above. The exemplary tissue stimulation and sensing probe  600  includes a tissue engagement device  602  that carries a pair of stimulation electrodes  604  and is supported on the distal end of a shaft  606 . The electrodes  604  may be used to sense electrical actively in addition to transmitting stimulation energy.  
      The specific size and shape of the tissue engagement device  602  will, of course, depend on the intended application, as will the choice of materials. Although the present inventions are not limited to any particular sizes, shapes or materials, one exemplary implementation that is especially well suited for cardiac treatment is described hereafter. The exemplary tissue engagement device  602  cup-shaped and is formed, preferably by molding, from a soft, flexible biocompatible material such as silicone rubber or urethane. The diameter of the tissue engagement device  602  may range from about 2 mm to about 5 mm and is about 2-3 mm in the exemplary embodiment. With respect to the electrical connection of the stimulation electrodes  604  to the tissue stimulation apparatus  300 , the stimulation electrodes in the exemplary implementation are connected to signal lines  608  that extend from the stimulation electrodes, though a shaft lumen  610 , and an opening (not shown) at the proximal end of the shaft  606 . The signal lines are connected to the connectors  302  on the stimulation apparatus  300  in the manner discussed above.  
      In the exemplary implementations illustrated in  FIGS. 25-32 , the stimulation electrodes  604  are essentially the same as the stimulation and sensing electrodes  426  and  428  described above. For example, the electrodes  604  may be relatively small, low profile devices (e.g. about 0.5 mm to 1 mm in diameter and about 0.01 mm thick) that can be formed by coating one of the suitable conductive materials described above onto the tissue engagement device  602 .  
      Turning to the particulars of the exemplary shaft  606 , the shaft in the illustrated embodiment is relatively short and relatively stiff. More specifically, the exemplary shaft  606  is about 20 cm to 50 cm in length and is formed from a malleable hypotube  612  with an outer tubing  614  formed from Pebax® material, polyurethane, or other suitable materials. A typical hypotube would be about 2 mm and 8 mm in diameter. The stiffness of the shaft  606  allows the physician to firmly place the electrodes  604  against tissue, while the malleability of the shaft allows the physician to vary the shape of the shaft as desired to suit particular needs.  
      The exemplary surgical tissue stimulation and sensing system  40  may be used to, for example, test the quality of lesions formed during a lesion formation procedure in a variety of ways. For example, the physician may first bend the shaft  606  into the appropriate shape to reach to the target tissue. The shaft  606  may, of course, also be used in a linear orientation. The tissue engagement device  602  may be placed against tissue on one side of a lesion and the stimulation electrodes  604  may be used to apply stimulation energy to the tissue. For example, the tissue engagement device  602  may be placed on the pulmonary vein side of a pulmonary vein isolation lesion. The stimulation energy may be in the form of a bipolar pacing pulse (e.g. 10 mA). The physician can determine whether or not a therapeutic lesion (or “complete block”) has been formed by observing the tissue on the other side of the lesion. If the pacing pulse is able to cross the lesion, the heart will beat faster (e.g. 120 beats/minute). This may be determined by observation or by use of an ECG machine that is monitoring the heart.  
      Alternatively, the stimulation electrodes  604  may be used to sense tissue within the area defined by a lesion to determine whether heart&#39;s natural stimulation will produce local activation within the tissue area defined by the lesion. For example, the tissue engagement device  602  may be placed on the pulmonary vein side of a pulmonary vein isolation lesion. No local activation within the area defined by the lesion is indicative of the formation of a complete excitation block, while local activation is indicative of a gap in the lesion.  
      Other methods involve the use of two or more of the tissue stimulation and sensing probes  600 . For example, the tissue engagement devices  602  of two separate probes may be placed against tissue on opposite sides of a lesion. The stimulation electrodes  604  of one probe may be used to apply stimulation energy to the tissue, while the stimulation electrodes on the other may be used to sense local activation. This technique may be used to, amongst other things, test lesions that are formed around one or more of the pulmonary veins. Here, the stimulation electrodes  604  of one probe may be placed against tissue within the left atrium and stimulation electrodes  604  of another probe may be placed on the pulmonary vein side of a pulmonary vein ostium. A pulse of stimulation energy (about 10 mA) may be applied to viable tissue on one side of the lesion and the viable tissue on the other side of the lesion may be monitored to detect the local excitation from the pulse of stimulation energy.  
      Turning to  FIG. 27A , in an alternative implementation, a tissue engagement device  602 ′ that is substantially larger than the tissue engagement device  602  (e.g. about 1 cm in diameter) may be provided on the end of the shaft  606 . The tissue engagement device  602 ′ supports two pairs of stimulation electrodes  604  (i.e. pairs  604   a  and  604   b ). Each pair may be operated in bipolar fashion in a manner similar to that described above with reference to electrode pairs  426   a  and  428   a.  For example, the pairs of stimulation electrodes may be positioned on opposite sides of a continuous linear or curvilinear lesion. A pulse of stimulation energy (about 10 mA) may be applied to viable tissue on one side of the lesion by the electrodes in pair  604   a  and the viable tissue on the other side of the lesion may be monitored with the electrodes in pair  604   b  to detect the local excitation from the pulse of stimulation energy. As noted above, the conduction delay will be indicative of the quality of the lesion.  
      There are a number of advantages associated with the exemplary tissue stimulation and sensing probe  600 . For example, using the tissue stimulation and sensing probe  600  to place stimulation electrodes against tissue is much easier than the conventional method of securing pacing electrodes to tissue, which involves suturing the pacing electrodes to tissue, especially in those instances where the stimulation electrodes will only be in place for a short time. The stimulation and sensing probe  600  also makes it much easier to remove the stimulation electrodes  604  from the patient, or move the electrodes to a new tissue location, as compared to pacing electrodes that are sutured to tissue. It should also be noted the stimulation and sensing probe  600  may be used in a pacing procedure, especially one in which it is desirable to pace at numerous locations within the heart.  
      Another surgical tissue stimulation and sensing system, which is generally represented by reference numeral  50  in  FIG. 29  includes a tissue stimulation apparatus  300 , a suction source  402  and a tissue stimulation and sensing probe  616 . The tissue stimulation apparatus  300  and a suction source  402  are described above. The exemplary tissue stimulation and sensing probe  616  includes a suction device  618  that carries a pair of stimulation electrodes  604  and is supported on the distal end of a flexible tube  620 . The proximal end of the flexible tube  620  is connected to a handle  622 . The suction device  616  is connected to the suction source  402  by way of a lumen  624  that extends through the flexible tube  620  and a flexible tube  406  that is connected to the proximal end of the handle  622  by a connector  626  such as, for example, the illustrated Luer connector. When the suction source  402  is actuated, the suction device  602  will fix the stimulation electrodes  604  against the target tissue.  
      The specific size and shape of the suction device  618  will, of course, depend on the intended application, as will the choice of materials. Although the present inventions are not limited to any particular sizes, shapes or materials, one exemplary implementation that is especially well suited for cardiac treatment is described hereafter. The suction device  618  is formed, preferably by molding, from a soft, flexible biocompatible material such as silicone rubber or urethane. The diameter of the suction device  618  may range from about 2 mm to about 10 mm and is about 2-3 mm in the exemplary embodiment. With respect to the connection of the stimulation electrodes to the  604  to the tissue stimulation apparatus  300 , signal lines  612  extend from the stimulation electrodes though the lumen  624  and though a pair of openings (not shown) in the handle  622 . The flexible tube  620 , which may be formed from polyurethane, Santoprene® or other suitable materials, is preferably about 20 cm to about 100 cm in length.  
      The exemplary surgical tissue stimulation and sensing system  50  may be used to, for example, test the quality of lesions formed during a lesion formation procedure in a variety of ways. For example, the suction device  618  may be secured to tissue on one side of a lesion, either before or after the lesion is formed. This may be accomplished by placing the suction device  618  against tissue (typically with a forceps or other suitable surgical instrument) and then actuating the suction source  402 . The stimulation electrodes  604  may then be used to apply stimulation energy to the tissue. The stimulation energy may be in the form of a bipolar pacing pulse (e.g. 10 mA). The physician can determine whether or not a therapeutic lesion (or “complete block”) has been formed by observing the tissue on the other side of the lesion. If the pacing pulse is able to cross the lesion, the heart will beat faster (e.g. 120 beats/minute). This may be determined by observation or by use of an ECG machine that is monitoring the heart. Alternatively, the stimulation electrodes may be used to sense tissue within an isolated region in the manner described above in order to determine whether a complete line of block has been formed.  
      Other methods involve the use of two or more of the tissue stimulation and sensing probes  616 . For example, the suction device  618  of two separate probes may be placed against tissue on opposite sides of a lesion. The stimulation electrodes  604  of one probe may be used to apply stimulation energy to the tissue, while the stimulation electrodes on the other may be used to sense local activation. This technique may be used to, amongst other things, test lesions that are formed around one or more of the pulmonary veins. Here, the stimulation electrodes  604  of one probe may be placed against tissue within the left atrium and stimulation electrodes  604  of another probe may be placed on the pulmonary vein side of a pulmonary vein ostium. A pulse of stimulation energy (about 10 mA) may be applied to viable tissue on one side of the lesion and the viable tissue on the other side of the lesion may be monitored to detect the local excitation from the pulse of stimulation energy.  
      Turning to  FIG. 31A , in an alternative implementation, a suction device  618 ′ that is substantially larger than the suction device  618  (e.g. about 1 cm in diameter) may be provided on the end of the tube  620 . The suction device  618 ′ supports two pairs of stimulation electrodes  604  (i.e. pairs  604   a  and  604   b ). Each pair may be operated in bipolar fashion in a manner similar to that described above with reference  FIG. 27A .  
      There are a number of advantages associated with the exemplary tissue stimulation probe  616 . For example, using suction force to hold the stimulation electrodes  604  in place on the target tissue is much easier than the conventional method of securing pacing electrodes to tissue, i.e. suturing the pacing electrodes to tissue. The stimulation probe  616  also makes it relatively easy to disconnect the electrodes  604  from the tissue, i.e. by simply ending the suction force, so that the electrodes may be removed from the patient or moved to a new location. The stimulation and sensing probe  616  may also be used in a pacing procedure, especially one in which it is desirable to pace at numerous locations within the heart.  
      Finally, it should be noted that a single stimulation electrode may be provided on the sensing probes  600  and  616 , and a single stimulation electrode may be provided in place of each of the electrode pairs illustrated in  FIGS. 27A and 31A .  
      VIII. Self-Anchoring Tissue Stimulation and Sensing Devices  
      As illustrated for example in  FIGS. 33-36 , a surgical tissue stimulation and sensing system  60  in accordance with one embodiment of a present invention includes a tissue stimulation apparatus  300  and a self-anchoring stimulation and sensing device  700 . The tissue stimulation apparatus  300  is described above. The exemplary self-anchoring stimulation and sensing device  700  includes a pair of stimulation electrodes  702  that are supported on an anchor  704 . The electrodes  702  may be used to sense electrical actively in addition to transmitting stimulation energy.  
      A wide variety of anchors may be employed. The exemplary anchor  704  illustrated in  FIGS. 33-36  includes a flexible, pre-shaped carrier  706  and a pair of tissue piercing members  708 . The exemplary carrier  706  has a pair of end portions  706   a / 706   b  and an interior portion  706   c.  When in an unstressed (or relaxed) state, the interior portion  706   c  will be in spaced relation to a surface, such as a tissue surface, which the end portions  706   a / 706   b  are in contact with. The carrier  706  and tissue piercing members  708  are dimensioned and positioned relative to one another such that the carrier will be deflected (and stressed) when the piercing members are placed into tissue. As a result, the stimulation electrodes  702  will be forced (or “biased”) against the tissue when the piercing members  708  engage the tissue. The exemplary anchor  704  will be bent into a configuration that is flat, such that the interior portion  706   c  engages the tissue, or is close to flat, when the piercing members  708  are completely into the tissue.  
      The exemplary carrier  706  in the illustrated embodiment includes a flexible, pre-shaped spring member  710 , which may be rectangular (as shown), circular or any other suitable shape in cross-section, and a soft plastic coating  712 . Alternatively, a pre-shaped rubber (such as silicone rubber) carrier may be employed. The carrier  706  will typically be about 1 mm to 4 mm wide and about 6 mm to 20 mm long when flattened. The tissue piercing members  708  are malleable structures that are secured to the carrier  706  with a base  709 . With respect to use, the tissue piercing members  708  are held with a clamp during the application and removal process. More specifically, a physician may use a clamp (such as the type of clamp used to attach surgical staples) to spread the piercing members  708  apart slightly,.force the sharpened ends  714  into tissue until the carrier  706  is flat or close to flat, and then urge the piercing member towards one another to secure the self-anchoring stimulation and sensing device  700  to the tissue. The device  700  may be removed by simply spreading the piercing members  708  apart slightly with a clamp (such as the type of clamp used to remove surgical staples) and pulling the device away from the tissue.  
      The exemplary stimulation electrodes  702  may be ring electrodes that are about 0.5 mm to 2 mm in length and are otherwise similar to the ring-shaped stimulation electrodes described above. Alternatively, the stimulation electrodes may be relatively small, low profile devices (e.g. about 0.5 mm to 1 mm in diameter, and about 0.01 mm thick) located on the tissue facing side of the carrier  706 . Such electrodes may be formed by coating a conductive material onto the carrier  706  using conventional coating techniques or an IBAD process.  
      The electrodes are connected by signal lines  716  that extend from the stimulation electrodes  702  and along portions of the carrier  706 . The signal lines  716  are connected to the connectors  302  on the stimulation apparatus  300  in the manner discussed above. An overcoat- 718  may also be provided.  
      Another exemplary self-anchoring stimulation and sensing device is generally represented by reference numeral  720  in  FIGS. 37 and 38 . The device illustrated in  FIGS. 37 and 38  is substantially similar to the device illustrated in  FIGS. 33-36  and similar elements are represented by similar reference numerals. Here, however, the exemplary anchor  722  includes the flexible, pre-shaped carrier  706  and a rotatable tissue piercing device  724  that is associated with the interior portion  706   c.  The rotatable tissue piercing device  724  has a helical member  726  that is connected to a knob  728 . Rotation of the knob  728  in one direction will cause the helical member  726  to screw into the tissue. The rotation may continue until the carrier  706  is flat or close to flat, the interior portion  706   c  is against tissue or close to the tissue, and the stimulation electrodes  702  are forced against the tissue by the carrier. Rotation of the knob  728  in the other direction will unscrew the helical member  726  and facilitate removal of the stimulation and sensing device  720 .  
      Still another exemplary self-anchoring stimulation and sensing device is generally represented by reference numeral  730  in  FIGS. 39 and 40 . The device illustrated in  FIGS. 39 and 40  is substantially similar to the devices illustrated in  FIGS. 33-38  and similar elements are represented by similar reference numerals. Here, however, the exemplary anchor  732  does not pierce the tissue. The anchor  732  is, instead, secured to the tissue with a layer of adhesive  734  on the carrier interior portion  706   c.  Suitable adhesives include cyanoacrylate and thrombin adhesive. A release layer  736  may also be provided. During use, the physician can remove the release layer  736 , place the stimulation and sensing device  730  onto the tissue, and press the interior portion  706   c  down until the adhesive  734  contacts tissue, thereby securing the interior portion to the tissue and forcing the electrodes  702  into close contact with the tissue. The physician will simply peel the stimulation and sensing device  730  off when the procedure is complete.  
      The exemplary surgical tissue stimulation and sensing system  60  may be used to, for example, test the quality of lesions formed during a lesion formation procedure in a variety of ways. For example, one or more of the stimulation and sensing devices  700 ,  720  and  730  may be secured to tissue on one side of a lesion, either before or after the lesion is formed. The stimulation electrodes  702  may then be used to apply stimulation energy to the tissue. The stimulation energy may be in the form of a bipolar pacing pulse (e.g. 10 mA). The physician can determine whether or not a therapeutic lesion (or “complete block”) has been formed by observing the tissue on the other side of the lesion. If the pacing pulse is able to cross the lesion, the heart will beat faster (e.g. 120 beats/minute). This may be determined by observation or by use of an ECG machine that is monitoring the heart. Alternatively, the stimulation electrodes may be used to sense tissue within an isolated region in the manner described above in order to determine whether a complete line of block has been formed.  
      Other methods involve the use of two or more of the stimulation and sensing devices  700 ,  720  and  730 . For example, two separate stimulation and sensing devices  700 ,  720  or  730  may be placed against tissue on opposite sides of a lesion. The stimulation electrodes  702  on one may be used to apply stimulation energy to the tissue, while the stimulation electrodes on the other may be used to sense local activation. As noted above, depending on the type of lesion being tested, the presence or absence of local activation or the conduction delay will be indicative of the quality of the lesion.  
      Although the present inventions have been described in terms of the preferred embodiments above, numerous modifications and/or additions to the above-described preferred embodiments would be readily apparent to one skilled in the art. By way of example, but not limitation, each of the devices described above may be used to pace prior to lesion formation and each of the methods described above may include pacing prior to lesion formation. It is intended that the scope of the present inventions extend to all such modifications and/or additions and that the scope of the present inventions is limited solely by the claims set forth below.