Laser ablation device

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.

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.sub.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's vasculature or alternatively, directly into the
 patient'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'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'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.

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.sub.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'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 20a and 20b. 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 20a and 20b or can be
 removably fastened to tapered section 24. A ridged surface 28 is formed on
 an outer wall of housing half-sections 20a and 20b to facilitate grasping
 of the device 10.
 FIG. 3 illustrates laser ablation device 10 with housing half-sections 20a
 and 20b and the internal components of the handle portion 11 separated.
 Housing half-sections 20a and 20b 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 20a and 20b. 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 20a and 20b
 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'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.sup.2 to about 60 mJ/mm.sup.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.sup.2 to about 40 mJ/mm.sup.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.sup.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.sup.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'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 120a and 120b. The housing
 half-sections 120a and 120b 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 120a and
 120b. 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 210a and 210b and an
 inner housing 220 formed from molded housing half-sections 220a and 220b.
 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 210a and
 210b 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 220a and 220b 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.