Abstract:
A controlled advancement laser ablation device is provided for precise ablation of body matter. The laser ablation device includes a laser energy transmission mechanism such as, e.g. a fiber optic fiber mounted for controlled translational longitudinal movement relative to a housing structure. A laser energy generator is optically connected to the laser energy transmission mechanism. A controlled advancement mechanism is provided in engagement with the laser energy transmission mechanism for advancing the mechanism through the housing structure at a controlled rated coordinated with the laser energy generator output to ablate body tissue. Controlled advancement mechanisms include constant and/or variable rate springs, motors, and other mechanisms which can be coordinated with the laser energy generator to advance the laser energy transmission mechanism as the targeted substance is ablated. The device is particularly suitable for use in transmyocardial revascularization (TMR) and angioplasty procedures.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to laser ablation devices for surgical use. More specifically, the present disclosure relates to laser ablation devices having a longitudinally advancing laser energy transmission mechanism to facilitate ablation of body tissue. The laser ablation device is particularly suited for use in performing transmyocardial revascularization (TMR) and angioplasty. 
     2. Background of the Related Art 
     A variety of procedures and apparatus have been developed to treat cardiovascular disease. For example, minimally invasive surgical procedures such as balloon angioplasty and atherectomy have received extensive investigation and are in wide use. In some patients, however, circumstances still require conventional open heart bypass surgery to correct or treat advanced cardiovascular disease. In some circumstances patients may be too weak to undergo the extensive trauma of bypass surgery or repetitive bypasses may already have proved unsuccessful. 
     An alternative procedure to bypass surgery is transmyocardial revascularization (TMR), wherein holes are formed in the heart wall to provide alternative blood flow channels for ischemic heart tissue. This procedure can be done by laser. In early laser myocardial revascularization, a CO 2  laser was used to produce holes in the heart wall. In this procedure, laser energy is transmitted from the laser to the heart wall by an externally located articulated support. Thus, some surgical opening of the chest wall is required to access the heart muscle. The entrance wound in the heart is closed by external pressure with the objective that the endocardial and myocardial layers remain open to permit blood flow from the ventricle to the heart muscle. 
     A less traumatic approach to laser myocardial revascularization is disclosed in U.S. Pat. Nos. 5,380,316 and 5,389,096 to Aita et al. These references disclose methods of myocardial revascularization using a deflectable elongated flexible lasing apparatus which is either introduced through a patient&#39;s vasculature or alternatively, directly into the patient&#39;s chest cavity. The intravascular method requires the direction of laser energy from inside the heart to form a bore in the heart wall while the other method requires introduction of the lasing apparatus through the patient&#39;s chest and into contact with the outer wall of the heart. 
     In both of these methods, the optical fiber conveying the laser energy is advanced and controlled by hand to form the bore. This manual advancement and control presents problems in that depth and rate of penetration are difficult to accurately reproduce for the multiple bores necessary in a myocardial revascularization procedure. 
     In addition, if the advancement rate of the laser fiber is too slow, tissue damage from thermal and acoustic shock can result. On the other hand, if the advancement rate of the fiber is too fast (i.e., faster than the laser ablation rate), the fiber itself, not the laser energy, can mechanically form at least a portion of the hole, which may be undesirable. 
     Similar problems are present in other cardiovascular procedures such as, e.g. laser angioplasty wherein an optical fiber is inserted and manually advanced into a patient&#39;s vasculature to apply laser energy to obstructions and/or restrictions typically caused by plaque build-up. Both continuous wave and pulsed high energy lasers have been used to provide the vaporizing laser energy. Insuring the plaque is actually ablated and not just pushed aside is important to prevent or delay restenosis. Once again, because the fiber is manually advanced, the rate of advancement of the fiber through the obstruction is generally uncontrolled. 
     SUMMARY 
     In accordance with the present disclosure, a controlled advancement laser ablation device is provided for precise ablation of body matter. The laser ablation device includes a laser energy transmission mechanism such as, e.g. an optical fiber device mounted for controlled longitudinal movement relative to a housing structure. A laser energy generator is optically connected to the laser energy transmission mechanism for initiating laser energy. A controlled advancement mechanism is provided in engagement with the laser energy transmission mechanism for advancing the mechanism through the housing structure at a controlled rate coordinated with the laser energy generator output to ablate body tissue. Controlled advancement mechanisms include constant and/or variable rate springs, motors, and other mechanisms which can be coordinated with the laser energy generator to advance the laser energy transmission mechanism during ablation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various preferred embodiments are described herein with references to the drawings: 
     FIG. 1 is a perspective view of one embodiment of the laser ablation device in association with a control assembly; 
     FIG. 2 is a perspective view of the handle and fiber optic portion of the laser ablation device shown in FIG. 1; 
     FIG. 3 is a perspective view with parts separated of the handle and fiber optic portion shown in FIG. 2; 
     FIG. 4 is a side cross-sectional view of the handle portion shown in FIG. 2 engaging body tissue with the optical fiber retracted within the housing of the device; 
     FIG. 5 is a side cross-sectional view of the handle portion shown in FIG. 2 engaging body tissue with the optical fiber extended into body tissue; 
     FIG. 5A is a side cross-sectional view of the handle portion shown in FIG. 2 engaging body tissue with the optical fiber extended through the body tissue; 
     FIG. 6 is a side cross-sectional view of the distal end of the optical fiber of the laser ablation device shown in FIG. 1 extending within vascular tissue; 
     FIG. 7 is a side cross-sectional view of the distal end of the optical fiber of the laser ablation device shown in FIG. 1 extending into plaque within vascular tissue; 
     FIG. 8 is a side cross-sectional view of vascular tissue having a channel formed in plaque by the laser ablation device shown in FIG. 1; 
     FIG. 9 is a perspective view of an alternate embodiment of a handle portion of the laser ablation device; 
     FIG. 10 is a perspective view of the handle portion shown in FIG. 9 with a half-housing section removed; 
     FIG. 10A is a side cross-sectional view of the internal components of the handle portion shown in FIG. 10; 
     FIG. 11 is a side cross-sectional view of the handle portion shown in FIG. 9 positioned adjacent to body tissue with the optical fiber extended; 
     FIG. 11A is a side cross-sectional view of the handle portion shown in FIG. 9 engaged with body tissue with the optical fiber retracted; 
     FIG. 12 is a side cross-sectional view of the handle portion shown in FIG. 9 with the optical fiber extending through the body tissue; 
     FIG. 13 is a perspective view of another alternate embodiment of the handle portion with the inner assembly in a fully extended position; 
     FIG. 14 is a perspective view of the handle portion shown in FIG. 13 with the inner assembly in a partially retracted position; 
     FIG. 15 is a perspective view with partial separation of parts of the handle portion shown in FIG. 13; 
     FIG. 16 is a partial cross-sectional view in perspective of the housing and spring biasing member of the handle portion shown in FIG. 15; 
     FIG. 17 is a perspective view with parts separated of the internal assembly of the handle portion shown in FIG. 13; 
     FIG. 18 is a partial side view in perspective of the housing and spring biasing member of the handle portion shown in FIG. 17; 
     FIG. 19 is a partial perspective view of the handle portion shown in FIG. 13 with a half-housing section removed; 
     FIG. 20 is a partial side cross-sectional view of the handle portion shown in FIG. 13; 
     FIG. 21 is a sectional view of the handle portion shown in FIG. 13 adjacent body tissue; 
     FIG. 22 is a sectional view of the handle portion shown in FIG. 13 adjacent body tissue with the inner assembly and optical fiber retracted; 
     FIG. 23 is a sectional view of the handle portion device shown in FIG. 13 adjacent body tissue with the inner assembly partially advanced and the optical fiber extending through body tissue; 
     FIG. 24 is a sectional view of the handle portion shown in FIG. 13 adjacent body tissue with the outer housing partially extended, the inner assembly partially advanced, and the optical fiber extending through body tissue; and 
     FIG. 25 is a side partial cross-sectional view of the handle portion shown in FIG. 13 and a heart during a TMR procedure with the optical fiber extending through the myocardium. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the laser ablation device will now be described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. 
     One embodiment of the presently disclosed laser ablation device will now be described with reference to FIGS. 1-8. FIG. 1 illustrates a laser ablation device shown generally at  10 . Device  10  preferably includes handle portion  11 , an optical fiber advancing mechanism  12 , a laser generator  14 , a foot operated actuator  16 , and a control module  17 . The optical fiber advancing mechanism  12  is of the type capable of precisely transmitting longitudinal motion and, optionally, rotational motion, to an optical fiber, optical fiber bundle or other laser energy transmission mechanism. The controlled longitudinal and/or rotational motion can be provided by one or more motors and preferably by one or more stepper motors. The stepper motors can be of the type commercially available from Haydon Switch and Instrument, Inc. of Waterbury, Conn. or Eastern Air Devices, Inc. of Dover, N.H. The laser generator  14  may be either a continuous wave laser or a pulsed, high energy laser; such as, for example, an excimer, CO 2 , Yag, or an alexandrite laser. Preferably, a pulsed high energy xenon chloride excimer laser, such as those available from Spectranetics of Colorado Springs, Colo., is used. 
     The optical fiber advancing mechanism  12  and the laser generator  14  are operably connected to foot switch  16 . By depressing foot switch  16 , laser energy is transmitted through the optical fiber by laser generator  14  while fiber advancing mechanism  12  advances the laser fiber relative to handle portion  11 . As shown, the signal from foot switch  16  actuates control module  17  which communicates with fiber advancing mechanism  12 . Control module  17  is programmable and controls the motors or similar advancing structure in advancing mechanism  12  upon actuation of foot switch  16 . Control module  17  is shown with a receptacle  19  adapted to engage a terminal of a programmable computer to interface control module  17  with the computer. As such, instructions required to operate advancing mechanism  12  can then be stored in control module  17 . Such instructions are commercially available, for example, through Intelligent Motions Systems, Inc. of Taftville, Conn. A toggle switch  15  may be provided on the control module  17  to switch from an operation mode to a test mode. In a particular test mode, when the foot actuator  16  is acted upon, the flexible optical fiber is moved sequentially from a retracted position, to a predetermined extended position, and back to the retracted position. 
     Fiber advancing mechanism  12  is preferably equipped with two internal limit switches (not shown). The first limit switch is preferably positioned to be activated when the optical fiber is at a desired retracted position (i.e., a “home” position), wherein the mechanism that is retracting the fiber is caused to stop. The second limit switch limits/controls the maximum distance that the optical fiber can extend from handle portion  11 . Most preferably, an external selector  21  is provided so that the operator can select the desired maximum extension of the distal end of the optical fiber from the handpiece. For example, selector  21  can be in the form of a rotatable knob that can be set at selectable positions, wherein each position corresponds to a predetermined maximum longitudinal position of the optical fiber. When the fiber reaches the selected position, a limit switch can automatically terminate the fiber&#39;s advancement. In a most preferred embodiment, the operator can select fiber extension positions so that the distal end of the fiber extends from the distal end of the hand piece from between about 0.5 cm and about 5.0 cm, with the ability to select in increments of about 0.25 cm to about 0.5 cm. 
     FIG. 2 illustrates a perspective view of the handle portion  11  of laser ablation device  10 . Briefly stated, handle portion  11  includes housing  20  formed from molded housing half-sections  20   a  and  20   b.  Housing  20  has an elongated body  22  with a conically tapered section  24 . An optional locator ring  26  is provided at the distal end of conically tapered section  24  that can be positioned in engagement with body tissue, i.e., the wall of the heart during a TMR procedure, to facilitate proper orientation of the handle portion with respect to the body tissue. Locator ring  26  can be formed integrally with housing half-sections  20   a  and  20   b  or can be removably fastened to tapered section  24 . A ridged surface  28  is formed on an outer wall of housing half-sections  20   a  and  20   b  to facilitate grasping of the device  10 . 
     FIG. 3 illustrates laser ablation device  10  with housing half-sections  20   a  and  20   b  and the internal components of the handle portion  11  separated. Housing half-sections  20   a  and  20   b  define a central bore  30 , a proximal recess  32 , and a distal recess  34 . The proximal recess  32  is configured to receive a swivel connector  36  which is fastened to the optical fiber casing  38 . The swivel connector  36  has an annular flange  40  dimensioned to be received within an increased diameter section  42  of proximal recess  32  to permit rotation of housing  20  with respect to optical fiber casing  38 . 
     As shown, the locator ring  26  has a cylindrical body portion  44  having an annular flange  46  formed at its proximal end. The cylindrical body portion  44  includes a central bore  50  and is configured to be received within the distal recess  34  defined by housing half-sections  20   a  and  20   b.  Central bore  50  of cylindrical body portion  44  is aligned with a central opening  48  formed in the distal end of the housing  20  and the central bore  30  of housing  20 . Locator ring  26  can either swivel, to allow independent rotation of the handle portion relative thereto, or be fixed in place. The optical fiber  18  is slidably positioned within central bores  30  and  50  such that it can be advanced through opening  48  in housing  20 . Pins or screws  49  can be used to fasten the housing half-sections  20   a  and  20   b  together to secure the locator ring  26  and the swivel connector  36  to the housing  20 . 
     FIGS. 4-5A illustrate laser ablation device  10  during use in a TMR procedure. Locator ring  26  has been positioned against the epicardium  54  of the heart  56 . Because the heart may be beating during a TMR procedure, the locator ring  26  greatly enhances the surgeon&#39;s ability to position and stabilize the laser ablation device  10  with respect to the heart  56 . In FIG. 4, the foot operated actuator  16  (FIG. 1) has not been actuated and the optical fiber  18  is in a retracted position with its distal end  60  positioned in central bore  50  of locator ring  26 . 
     Referring now to FIGS. 5 and 5A, foot operated actuator  16  (FIG. 1) has been actuated to initiate operation of laser generator  14  and the advancing mechanism  12  to ablate tissue and advance optical fiber  18 . The distal end  60  of optical fiber  18  has been advanced in the direction indicated by arrow “A” to produce a channel  57  from the epicardium through to the myocardium  58  in the ventricle of the heart  56 . During the TMR procedure, 1 or more channels can be ablated into the heart to facilitate blood delivery to ischemic areas of the heart. The distal end  60  of the optical fiber  18  which can be a single fiber or a bundle or fibers, is preferably advanced at a rate that is coordinated with the power level and the frequency of pulsing of the laser generator to form channels in the heart. For example, optical fiber  18  can be advanced at a rate of between about 0.5 mm/sec (0.02 in/sec) to about 12.7 mm/sec (0.5 in/sec) with a laser power level of about 10 mJ/mm 2  to about 60 mJ/mm 2  and a pulsing frequency of about 5 Hz to about 100 Hz. Preferably, the optical fiber is advanced at a rate of about 1.0 mm/sec to about 2.0 mm/sec with a laser power level of between about 30 mJ/mm 2  to about 40 mJ/mm 2  and a pulse frequency of about 50 Hz. In a most preferred embodiment, the rate of advancement of the optical fiber is no greater than the rate of ablation of tissue in order to minimize mechanical tearing by the fiber. Alternatively, if some degree of mechanical tearing is desired, the advancing mechanism can be set to advance the fiber at a rate greater than the ablation rate. Studies have shown that a xenon chloride excimer laser operating at a power level of about 35 mJ/mm 2  can ablate about 30-35 microns of animal heart tissue per pulse. 
     In one study, channels were successfully created in canine heart tissue using a xenon chloride excimer laser (308 nm) optically connected to a 1.8 mm solid fiber bundle. The laser was set to provide about 30 mJ/mm 2  at a rate of about 50 Hz, while the advancing mechanism was set to advance the laser fiber bundle at various constant speeds between about 1.3 mm/sec (0.05 in/sec) and about 13 mm/sec (0.5 in/sec). 
     Typically, a healthy heart has a wall thickness of 10-15 mm. A diseased heart may be as thick as 40 mm (measured from the outer surface of the epicardium to the inner wall of the myocardium). At a minimum, the laser ablation device  10  and control assembly should be capable of advancing the optical fiber  18  through a stroke having a length at least as great as the thickness of the heart being treated. Alternately, it is possible to create channels in the myocardium from within the heart by introducing the laser fiber into the patient&#39;s vasculature or through an opposing heart wall and directing the fiber tip to the desired location. See, for example, U.S. Pat. No. 5,389,096 to Aita et al. In this approach, once the fiber is properly placed, controlled advancement of the fiber can be achieved as described above. However, with this approach the fiber preferably will not penetrate the epicardium. 
     Referring now to FIGS. 6-8, laser fiber  18  and fiber advancing mechanism  12  (FIG. 1) can also be used to perform laser angioplasty. During the laser angioplasty procedure, the optical fiber  18  is inserted into a blood vessel  62  such that the distal end  60  of the optical fiber  18  is positioned adjacent a plaque obstruction  64  (FIG.  6 ), as is known in the art. The foot operated actuator  16  (FIG. 1) is actuated to initiate operation of the advancing mechanism  12  and the laser generator  14  to simultaneously advance, in the direction indicated by arrow “B”, and ablate plaque  64  to produce a channel  66  through the obstruction. As discussed above, the rate of advancement of the optical fiber  18  and the power level and frequency of pulsing of laser energy are coordinated, via control module  17 , to form the channel  66  through the plaque. By precisely controlling the rate of advancement of the laser fiber, the user can ensure that the plaque is truly ablated by the laser energy and not just pushed aside. Ablation/removal of plaque reduces the likelihood of or delays restenosis as compared to mere mechanical manipulation of the plaque. 
     An alternate, preferred embodiment of the presently disclosed laser ablation device will now be described with reference to FIGS. 9 to  12 . The handle portion of the laser ablation device shown in this embodiment has a self-biasing advancing mechanism incorporated therein. FIGS. 9 and 10 illustrate the handle portion of the laser ablation device shown generally as  100 . Briefly described, handle portion  100  includes a housing  120  formed from molded housing half-sections  120   a  and  120   b.  The housing half-sections  120   a  and  120   b  are formed with mating recesses  114  configured to slidably receive the internal components. A proximal opening  115  and a distal opening  116  are formed in housing  120  to permit an optical fiber  118  to extend through the housing  120 . A swivel connector (such as  36  in FIGS. 3-5A) and fiber casing (such as  38  in FIG. 3) can also be included. 
     An engagement assembly  113  is slidably positioned within a channel  122  defined by mating recesses  114  formed in housing half-sections  120   a  and  120   b.  The engagement assembly  113  includes a cylindrical cap  124 , a flexible engagement washer  128 , and a compression screw  130 . The cylindrical cap  132  has a threaded blind bore  126  dimensioned to receive the flexible engagement washer  128 . The compression screw  130  has a threaded end  134  dimensioned to be threaded into the blind bore  126 . The cylindrical cap  124 , the engagement washer  128  and the compression screw  130  all have a central throughbore to permit the optical fiber  118  to extend through the housing  120 . 
     Referring to FIG. 10A, the engagement washer  128  is positioned in the blind bore  126  of cylindrical cap  124  and compression screw  130  is threaded into the blind bore  126 . As the engagement washer  128  is compressed between the compression screw  130  and the base of blind bore  126 , the washer  126  deforms inwardly into frictional engagement with the optical fiber  118  to fasten the optical fiber  118  to the engagement assembly  113 . 
     The advancing assembly  112  includes a guide member  136  and a biasing member  138 . The guide member  136  is positioned in abutting relation with the proximal end of the cap  124  of engagement assembly  113 . An elongated rib  140  extends along the longitudinal periphery of guide member  136  and is configured to be received within a longitudinal slot  142  formed on an internal wall of the housing  120 . The rib and slot engagement limits rotation of the guide member  136  with respect to the housing  120  to avoid inadvertent disengagement of the guide member  136  and biasing member  138 . 
     The biasing member  138  is positioned to engage the proximal end of the guide member  136  as to bias the guide member  136  distally into the engagement assembly  113  to move the engagement assembly  113  distally in channel  122 . The biasing member  138  preferably includes a constant force spring having a first end  144  connected through an opening  146  to the housing  120  and a body portion  148  positioned in a recess  150  formed in the proximal end of the guide member  136 . The constant force spring allows for controlled advancement of the laser fiber, which has advantages in TMR and angioplasty procedures, similar to those previously described. 
     FIGS. 11-12 illustrate the handle portion  100  of laser ablation device during use in a TMR procedure. FIG. 11 illustrates the handle portion  100  prior to engagement with heart  152 . The biasing member  138  has moved the guide member  136  into abutment with the engagement assembly  113  to advance the engagement assembly distally in channel  122 . Because of the frictional connection between washer  128  and optical fiber  118 , optical fiber  118  has been advanced distally with the engagement assembly  113  and extends through opening  116  in housing  120 . 
     Referring now to FIG. 11A, the handle portion  100  of laser ablation device has been pushed against the epicardium  154  of the heart  152 . The force on the distal end of the optical fiber  118  is sufficient to overcome the force of the biasing member  138  to retract the optical fiber  118 , in the direction indicated by arrow “C”, to a position within housing  120 . It is noted that the strength of the biasing member should be less than that capable of puncturing the heart  152 , e.g., the optical fiber  118  should not pierce the heart when the distal end of the optical fiber is pushed against the epicardium. 
     In FIG. 12, laser energy has been conducted to the optical fiber  118  to ablate heart tissue adjacent the distal end  160  of the optical fiber  118 . As the heart tissue adjacent the distal end  160  of the optical fiber is ablated, biasing member  138  continually advances the optical fiber  118  through the heart tissue until a channel  162  is formed in the ventricle of the heart from the epicardium through the myocardium  156 . The laser energy level and pulse frequency are coordinated with the rate of advancement provided by the biasing member  138 . A similar biasing mechanism can be used to controllably advance the laser fiber during laser angioplasty. 
     A further alternate, preferred embodiment of the presently disclosed laser ablation device is shown in FIGS. 13-25. The handle portion  200  of the laser ablation device in this embodiment includes a self-biasing advancing mechanism substantially identical to that incorporated in the handle portion  100  described above. The device further includes a compensating mechanism suitable for use in performing a TMR procedure on a beating heart. 
     FIGS. 13 and 14 illustrate the handle portion of laser ablation device shown generally as  200 . Briefly, handle portion  200  includes an outer housing  210  formed from molded housing half-sections  210   a  and  210   b  and an inner housing  220  formed from molded housing half-sections  220   a  and  220   b.  The inner housing  220  is slidably positioned within outer housing  210 , as indicated by arrow “E”, and includes a distal conical portion  222  having an opening  224  dimensioned to permit passage of an optical fiber  218 . 
     Referring now to FIGS. 15 and 16, the outer housing half-sections  210   a  and  210   b  have recesses which together form a channel  226  in which the inner housing  220  is slidably positioned. Proximal and distal openings  228  and  230  are also formed in the outer housing  210  and are dimensioned to permit passage of the optical fiber  218  and the inner housing  220 , respectively. As with the previous embodiment, a swivel connector (such as  36  in FIGS. 3-5A) and fiber casing (such as  38  in FIG. 3) can also be included but are not shown. A biasing member  232  is positioned within the outer housing  210  to engage and urge the inner housing  220  towards the distal end of channel  226 . The biasing member  232  can be a spring having a first portion retained in a slot  234  formed in the outer housing  220  and a second portion engaging a retainer  236  secured to the inner housing  220 . The outer housing half-sections  220   a  and  220   b  can be fastened together with pins or screws  238  to secure inner housing  220  within channel  226 . 
     FIGS. 17-20 illustrate the inner housing  220  with parts separated. The internal components of the inner housing  220  include an engagement assembly and an advancing mechanism, which are similar to those disclosed with respect to the housing portion  100  and will only be briefly discussed herein. The engagement assembly includes a cylindrical cap  240 , a flexible engagement washer  242 , and a compression screw  244 . The cylindrical cap  240  has a threaded blind bore  245  which is adapted to receive a threaded end  246  of compression screw  244 . The compression screw  244  is threaded into blind bore  245  to compress and deform the engagement washer  242  into frictional engagement with optical fiber  218 , which extends through a central bore formed in the engagement assembly. 
     The advancing mechanism includes a guide member  248  and a biasing member  250 . The guide member  248  is positioned in abutting relation to the proximal end of cap  240 . The biasing member  250  is positioned to engage and bias the guide member  248  distally within a channel  252  formed in the inner housing  220  to move the engagement assembly towards the distal end of the channel  252 . An elongated rib  254  is formed on the outer periphery of the guide member  248  and is received in a slot  256  formed along channel  252  to prevent the guide member  248  from rotating and becoming disengaged from the biasing member  250 . The inner housing half-sections can be fastened together with pins  258  to secure the engagement assembly and the advancing mechanism within channel  252 . 
     FIGS. 21-25 illustrate a handle portion  200  of a laser ablation device during use in a TMR procedure. FIG. 21 illustrates the handle portion  200  after the optical fiber  218  has been pressed against the epicardium  262  of the heart  260  but before laser energy has been conducted to the optical fiber  218 . Engagement between the distal end  264  of optical fiber  218  creates a compressive force in the optical fiber  218  that overcomes the force of biasing member  250  to cause retraction of the optical fiber  218  in the direction indicated by arrow “E”. 
     Referring to FIG. 22, the distal end  266  of the inner housing  220  is positioned in abutting relation with the heart  260 . If the heart  260  and the handle portion  200  move towards each other with the handle portion  200  in this position, such as when the heart beats or the patient breathes, the force on the distal end  264  of inner housing  220  overcomes the force of biasing member  232  (FIG.  19 ), to permit the inner housing  220  to move proximally within channel  252 , in the direction indicated by arrow “F”. Outer housing  210  and biasing member  232  form a compensation assembly in this respect. 
     Referring now to FIGS. 23-25, laser energy has been conducted to the optical fiber  218  to ablate heart tissue adjacent to the distal end  264  of the optical fiber  218 . As the heart tissue is ablated, biasing member  250  controllably advances distal end  264  of optical fiber  218 , in the direction indicated by arrow “G”, through the heart tissue until a channel  268  is formed from the epicardium  262  through the myocardium  270 . Once again, the power output of the laser generator conducting energy to optical fiber  218  is coordinated with the advancement mechanism to provide channels  268  in the heart. 
     It will be understood that various modifications can be made to the embodiments disclosed herein. For example, in the first embodiment, any type of motor, such as air, hydraulic, pneumatic or other electrical motor can be used in place of a stepper motor. In addition, alternate devices can be used to actuate the laser advancing device and the laser energy source, such as a trigger mechanism associated with the handle portion. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended thereto.