LASER ABLATION DEVICE AND CONTROL SYSTEM

Abstract: This invention is an apparatus, and method for performing laser ablation, particularly trans-myocardial re-vascularization (TMR). For TMR, the method includes the steps of providing a lasing device (10) having a laser ablation member (11) (e.g., one or more optical fibers), advancing the laser ablation member (11) against the epicardium (52) of a patient, outputting laser energy from the laser ablation member (11) to ablate heart tissue, and create a channel (extending into the patient's ventricule (56), providing at least one control signal from a sensor (18) responsive to the ablation for controlling the laser ablation member (11) and/or the laser energy generated. The apparatus includes a lasing device (10) having a laser ablation member (11) and a detector (18) for detecting sound produced by the laser energy generated. The detector (18) is configured to generate, and transmit at least one signal in response to sound detected to a controller (17) associated with the laser energy generator. The controller (17) can then cause an event to occur with respect to the lasing process or signal the laser operator that an event has occurred.

Description: LASER ABLATION DEVICE AMD CONTROL SYSTEM BACKGROUND 1. Technical Field The present disclosure relates generally to laser ablation devices for surgical use. More specifically, the present disclosure relates to a laser ablation device having a control system for automatically controlling a longitudinally advancing laser energy transmission mechanism and/or a laser generator 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, however, patients may not be suitable candidates for bypass surgery. An alternative or adjunct procedure to bypass surgery is transmyocardial revascularization (TMR) , wherein holes are formed in the heart wall. These holes theoretically provide alternative blood flow channels for ischemic heart tissue and have been attributed to decreased pain (angina) associated with cardiovascular disease. The holes can be created using laser energy. In early laser myocardial revascularization, a CO2 laser was used to produce holes in the heart wall by transmitting laser energy from the laser to the heart wall. Typical CO2 lasers used for transmyocardial revascularization (TMR) are externally located and have an articulated support arm for aiming and directing laser energy through a series of mirrors that reflect the energy onto the heart wall. Thus, some surgical opening of the chest wall is required to access the heart muscle. The entrance wound in the heart can be closed by relatively brief external pressure while the endocardial and myocardial layers remain open to permit blood flow from the ventricle to the heart muscle. Less traumatic approaches to laser myocardial revascularization have been disclosed. These methods include the use of optical fibers introduced either through a patient's vasculature or, alternatively, directly into the patient's chest cavity. The intravascular method involves the direction of laser energy from inside the heart to form a bore in the heart wall while the other method involves introduction of the lasing apparatus through a relatively small incision in the patient's chest to access the outer wall of the heart. In these prior art methods, the optical fiber conveying the laser energy and the laser generating source are typically manually advanced and controlled, respectively, to form a bore. This manual advancement and control presents problems in that depth and rate of penetration are difficult to accurately reproduce for the multiple bores at the different areas of the heart which are necessary in myocardial revascularization procedures. For example, if the advancement rate of the laser is too slow and/or the laser generating source is left on for a long period of time, tissue damage from thermal and acoustic shock can result . U.S. Patent No. 5,607,421 (Jeevanandam, et al . ) discloses the use of a motor to move a laser fiber to a preset stop position, thereby limiting fiber penetration to a preset depth. However, the actual depth needed to form a proper channel can be hard to measure, such as when creating a channel from the epicardium (exterior) of the heart in the left ventricle. 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 and laser source are typically manually advanced and controlled, respectively, the depth of fiber penetration, rate of advancement of the fiber through the obstruction and the duration of the laser firing are generally uncontrolled. Therefore, a need exists for a feedback control system to automatically control the advancement of the fiber and/or the firing of the laser. Specifically, a need exists to automatically terminate the advancement mechanism and/or the laser source when a desired bore has been formed through the target material, such as the heart wall or plaque material. SUMMARY In accordance with the present disclosure, a laser ablation device is provided having a control system for controlling an advancement mechanism provided in engagement with a laser energy transmission mechanism, such as, e.g. an optical fiber device. The control system can further control a laser energy generator optically connected to the laser energy transmission mechanism. 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. The control system preferably includes a detector responsive to sound generated by laser energy as targeted material is ablated. The detector transmits at least one signal to a control module associated with the laser energy generator and/or the advancement mechanism. The control system operates using the principle that there exists an acoustical difference between the sound generated by the lasing process while in a first material being ablated (such as the heart wall or plaque) , and the sound generated in a second material after the laser fiber passes through the first material (such as into a ventricle or artery filled with blood) . The acoustical change, such as, for example, a change in decibel level or pitch, as the end of a laser fiber passes from one medium to another can be detected and allowed to cause an event to occur, such as termination of fiber advancement and/or laser energy transmission and/or activation of a signal, such as an audible sound, to alert the laser operator of the change. BRIEF DESCRIPTION OF THE DRAWINGS Various preferred embodiments are described herein with reference to the drawings : FIG. 1 is a perspective view of one embodiment of the laser ablation device having a control system in accordance with the present disclosure; FIG. 2 is a perspective view of a laser generator and control module; FIG. 3 is a perspective view of a hand piece having an acoustic transducer connected thereto; FIG. 4 is an enlarged side view of the distal end of the hand piece of FIG. 3; FIG. 5 is an exploded view showing the various components of the hand piece; FIG. 6 is a side view illustrating ablation of tissue with the laser ablation device of FIG. 1; FIG. 7 is a side view illustrating the laser fiber entering the heart ventricle; FIG. 8 is a side view showing ablation of tissue with the acoustic transducer mounted on the patient; and FIG. 9 is a side view showing ablation of tissue with the acoustic transducer mounted on the surgeon's finger. FIG. 10 is a side cross sectional view showing a laser fiber ablating plaque in a blood vessel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the laser ablation device having a control system will now be described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements. While the devices and methods described herein are applicable to a wide range of applications, for simplicity they will be primarily described with respect to transmyocardial revascularization (TMR) and the ablation of heart tissue. Referring to FIG. 1, a laser ablation device having an audio feedback control system is designated generally as 10. Lasing device 10 is similar to lasing devices disclosed in copending, commonly assigned U.S. Patent Application Serial No. 08/720,934 to Kolesa et al . , filed October 4, 1996. Device 10 is capable of advancing a laser ablation member 11 through a material, such as tissue, while concomitantly outputting laser energy, where the advancement rate is coordinated with the magnitude of laser energy generated and/or with the pulsing frequency of the laser source. The advancement rate, the magnitude of laser energy generated, and the pulsing frequency of the laser source can be automatically controlled by the control system. This coordination and control enables precise channels to be created. Preferably, the feedback control is achieved by sensing variations of the sound generated by the laser ablation member as it advances through the targeted material, such as heart tissue or plaque. With reference to FIGS. 1 and 2, laser ablation device 10 includes a hand piece 12, an optical fiber advancing mechanism 13, a laser generator 14, a foot operated actuator 16, a control module 17, and at least one transducer 18. The optical fiber advancing mechanism 13 is of the type capable of precisely transmitting longitudinal motion to laser ablation member 11, e.g., an optical fiber, optical fiber bundle or other laser energy transmission mechanism including, but not limited to, wave guides. The controlled longitudinal motion can be provided by one or more motors and preferably by one or more stepper motors . The laser generator 14 may be either a continuous wave laser or a pulsed, high energy laser, such as, for example, an excimer, CO2 , Yag or an alexandrite laser. The optical fiber advancing mechanism 13 and the laser generator 14 are operably connected to foot actuator 16. By depressing foot actuator 16, laser energy is transmitted through the optical fiber 11 by laser generator 14 while fiber advancing mechanism 13 contemporaneously advances optical fiber 11 relative to hand piece 12. An electrical signal from foot actuator 16 actuates control module 17 which communicates with fiber advancing mechanism 13. Control module 17 is programmable via keypad 62 to control the motors or other suitable advancing structure in advancing mechanism 13 upon actuation of foot actuator 16. The control module 17 is further programmable to respond to signals received from a feedback circuit housed within control module 17 and electrically connected to transducer 18 for suspending operation of advancing mechanism 13 and/or laser generator 14 as described below. The control module 17 includes a display 64 for displaying information to the operator. The control module 17 can further include an audible analyzer to determine the depth of the optical fiber 11 within the heart and to map the depth of the various layers throughout the heart using the signals received by the feedback circuit . Mapping information can be displayed on display 64. 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 13 can then be stored in memory within control module 17. A toggle switch 15 can be provided 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 11 is moved sequentially from a retracted position, to a predetermined extended position, and back to the retracted position. Fiber advancing mechanism 13 is preferably equipped with two internal limit switches (not shown) which are manually set to control optical fiber 11. The first limit switch is activated when the optical fiber 11 is at a desired retracted position (i.e., a "home" position), wherein the mechanism that is retracting the fiber is caused to stop. Optical fiber 11 is preferably in the retracted position unless foot actuator 16 is depressed or the test mode is activated. The exact retracted position is selected by means of selector 21, e.g., a rotatable knob. The second limit switch within unit 13 limits/controls the maximum distance that the optical fiber can extend from hand piece 12. External selector 23 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 23 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 maximum position, the fiber's advancement is automatically terminated and laser generation is suspended. By way of example, the operator can select maximum fiber extension positions so that the distal end of the fiber extends from the distal end of hand piece 12 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. The maximum extension position can be chosen to be slightly longer than the heart wall thickness for the particular patient such that fiber 11 will penetrate into the patient's ventricle. This thickness can be estimated by echocardiogram measurements, for example. Once the maximum extended position is reached or the control module 17 receives a signal that the optical fiber 11 has entered the ventricle (see below) , output of laser energy is automatically suspended and the fiber retracted. In accordance with the present disclosure, transduce 18 serves to send accoustical signals to control module 17. Upon detection of an accoustical change, such as when the fiber tip passes from heart tissue to blood, control module can terminate fiber advancement and laser generation. This control is similar to the activation of the second limit switch (described above) but is caused by accoustical change as opposed to a pre-set value. FIG. 3 illustrates a perspective view of the hand piece 12 of laser ablation device 10. Briefly, hand piece 12 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. Optional locator ring 26 is provided at the distal end of conically tapered section 24. The front surface 29 is positioned in abutting relation with the epicardium of a patient directly following the piercing of the epicardium with the tip of fiber 11 during a TMR procedure. Locator ring 26 facilitates proper orientation of the hand piece 12 with respect to the heart tissue. However, 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 27 is formed on an outer wall of housing half-sections 20a and 20b to facilitate grasping of the hand piece 12. The hand piece 12 further includes a mounting assembly 66 for mounting the acoustic transducer 18 in proximity to the tip of fiber 11. FIG. 4 illustrates the transducer 18 mounted to the hand piece 12. The transducer 18 includes a stopper 68 which prevents the transducer 18 from moving while mounted to the hand piece 12. Alternatively, transducer 18 can be mounted within hand piece 12, as discussed in greater detail, below. FIG. 5 illustrates hand piece 12 with housing half- sections 20a and 20b and the internal components 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 50 of housing 20. Locator ring 26 can either swivel, to allow independent rotation of the hand piece 12 relative thereto, or be fixed in place. The optical fiber 11 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. If locator ring 26 is eliminated, front surface 28 of tapered portion 24 can act as the stop which contacts the patient's outer epicardial surface . FIGS. 1, 3 and 4 illustrate perspective views of transducer 18 of laser ablation device 10. Transducer 18 and the control circuit within control module 17 are the main components of the feedback control system of the present disclosure. Transducer 18 includes a housing 70 having a microphone therein for receiving sound waves emanating from the tip of fiber 11 during firing. The microphone transforms the sound waves into electrical signals which are transmitted to control module 17 via cable 72 for controlling ablation of heart tissue. Transducer 18 and cable 72 can also be incorporated into handpiece 12, wherein cable 72 passes through casing 38 to communicate with control module 17. The operation of the feedback control system will become more apparent from a detailed discussion of a TMR procedure using the presently disclosed laser ablation device. Prior to entry into the epicardium 52, the optical fiber 11 is in the retracted position as shown in Fig. 6. The tip of fiber 11 can protrude slightly from the locator ring 26 by distance D-j_ in the range of about 1 to about 5mm (where D-j_ is measured from the distal surface 11a of fiber 11 to the distal surface 29 of locator ring 26) or it can be flush with distal surface of locator ring 26. With fiber 11 initially protruding and without depressing the foot actuator to output laser energy, the fiber tip is brought into contact with epicardium 52 so as to mechanically press on and tents the epicardial outer surface (not shown) . Upon actuation of the laser generator and the fiber advancing mechanism, the pressure initially causes the fiber tip to advance through tissue faster than the rate of fiber advancement. As such, the tissue in the range of D_ will receive less laser energy compared to the remaining tissue to be ablated which can reduce bleeding from the channel. Alternatively, the fiber tip can start flush with the distal end of locator ring 26. With surface 29 in contact with the epicardium as depicted in FIG. 6, the operator/surgeon commences TMR channel formation by depressing foot actuator 16. This initiates operation of laser generator 14 and the advancing mechanism 13 to transmit laser energy from the tip of fiber 11 to ablate heart tissue while correspondingly advancing optical fiber 11. Depression of foot actuator 16 also causes activation of acoustic transducer 18. The fiber tip is advanced through the myocardium 50 and endocardium 54 until: 1) it reaches its maximum extended position (FIG. 7) corresponding to the distance D2 measured from surface 11a of fiber tip and surface 29 of locator ring 26 as preset by selector switch 23 or 2) until its advancement is suspended by the control module 17 in response to signals transmitted by transducer 18. It is preferred for the acoustic transducer 18 to be in an activated state at all times during advancement of the optical fiber 11 for continuous monitoring of sound emanating from the fiber tip as the laser fires. This permits continuous feedback to control the advancement of the optical fiber and the laser energy generator. Preferably, the feedback control system is programmed to advance fiber 11 at a rate that is coordinated with the power level and the frequency of pulsing of the laser generator. For example, optical fiber 11 can be advanced at a rate of between about 0.125 mm/sec (0.005 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 400Hz. Preferably, the optical fiber is advanced at a rate of about 0.75 mm/sec to about 2.0 mm/sec with a laser power level of between about 20 mJ/mm 2 to about 40 mJ/mm 2 and a pulse frequency of about 30 to 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 in addition to laser ablation, 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 35mJ/mm 2 can ablate about 30-35 microns of animal heart tissue per pulse. When fiber 11 penetrates slightly into a cavity, such as ventricle 56, there will be an acoustical change as the laser fires in blood as opposed to heart tissue. Upon detection of the accoustical change, output of laser energy is automatically suspended by the feedback circuit. The motor (s) controlling the fiber advancement can also be programmed to automatically stop and, if desired, reverse the travel of the fiber and return it to the "home" position. The hand piece 12 is drawn away from the heart wall whereby the transmyocardial channel 60 is completed. Once the channel 60 is completed, the fiber 11 can be moved to another location on the epicardium to begin forming another channel. The overall procedure wherein dozens of channels 60 are typically formed can thus be performed much faster as compared to prior art methods. FIGS. 8 and 9 illustrate two alternative methods for utilizing laser ablation device 10. In FIG. 8, acoustic transducer 18 is mounted on the patient and in FIG. 9, acoustic transducer 18 is mounted on the surgeon's hand 74. Of course, transducer 18 can be located almost anywhere as long as it can properly detect the desired acoustics during operation and communicate with the control module. In an alternate embodiment, the controller can provide a signal to the laser operator that the emitted laser energy has moved from one medium to another. This can be in the form of an audible or visual signal such as a beeper, buzzer or light. Upon recognition of this signal, the laser operator can remove pressure from foot pedal 16 to terminate the lasing process . FIG. 10 shows the distal end 11' of laser fiber 11 passing through plaque 100 in blood vessel 200. Similar to that described above, an acoustical change can be detected as the fiber transmits a pulse of energy past the plaque, as compared to that while ablating the plaque. This change can be used to terminate the laser energy and to stop and/or withdraw the fiber. It will be understood that various modifications be made to the embodiments disclosed herein. For example, other types of materials could be ablated and the control system and method of the present disclosure be used to control various processes as an acoustical change is detected. For example, in other surgical applications, acoustical change as the laser energy moves from cartilage to bone or from bone to tissue can be detected. More generally, in both surgical and non-surgical applications, movement of the laser fiber tip from a solid liquid or gas having a first acoustical signature to a solid, liquid or gas having a second, different acoustical signature can be detected. 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 hereto.

Claims: WHAT IS CLAIMED IS: 1. A method of performing transmyocardial revascularization (TMR), comprising the steps of: providing a lasing device having a laser ablation member ; generating laser energy from said laser ablation member to ablate heart tissue and create a channel extending into a patient's ventricle; and providing an audio sensor responsive to said ablation for controlling the laser energy generated. 2. The method according to claim 1, wherein said step of providing a laser ablation member comprises providing an optical fiber. 3. The method according to claim 1, further comprising the step of controlling the laser energy in response to variations in sound emanating from said laser ablation member. 4. The method according to claim 3, wherein the step of controlling the laser energy comprises suspending the energy when said audio sensor detects said laser ablation member within said ventricle. 5. The method according to claim 1, wherein said step of providing the audio sensor includes providing an acoustic transducer and an analyzer for analyzing the output of said acoustic transducer. 6. The method according to claim 1, further comprising the step of advancing the laser ablation member through epicardial tissue to create a channel in the tissue, thereby creating a first acoustical signature and further comprising the step of suspending the step of advancing upon detecting a change in the first acoustical signature. 7. The method according to claim 1, further comprising the step of suspending the generation of laser energy upon detecting said change in the first acoustical signature . 8. The method according to claim 1, further comprising the steps of advancing the laser ablation member and controlling the advancement rate of the laser ablation member. 9. A method for performing transmyocardial revascularization, comprising the steps of: providing a lasing device having a laser fiber for outputting laser energy; outputting laser energy from said fiber to thereby create a channel extending into a patient's ventricle; and providing at least one control signal to said lasing device from at least one sensor responsive to said ablation for controlling a laser energy generated. 10. The method according to claim 9, wherein the step of providing the at least one control signal said at least one control signal provided to said lasing device from at least one sensor responsive to said ablation further provides control over the advancement of said fiber. 11. A lasing device, comprising: laser ablation member having first and second ends ; and a detector for detecting sound produced by laser energy transmitted by said laser ablation member, said detector configured to generate and transmit at least one signal in response to the sound detected to a controller associated with a laser energy generator for controlling the laser energy generator. 12. The lasing device according to claim 11, further comprising: a hand piece having proximal and distal ends and a front surface at said distal end, said first end of said laser ablation member being extendible through said handpiece; a laser energy generator optically connected to the laser ablation member second end; and an advancing mechanism operably connected to the laser ablation member for advancing the laser ablation member through the distal opening of the hand piece. 13. The lasing device according to claim 12, wherein said controller is further associated with said advancing mechanism for controlling said advancing mechanism in response to said at least one signal. 14. The lasing device according to claim 11, wherein said detector is an acoustic transducer. 15. A lasing device, comprising: a hand piece having proximal and distal ends and a front surface at said distal end; a laser ablation member having first and second ends, the first end being extendible through said hand piece; a laser energy generator optically connected to the laser ablation member second end; an advancing mechanism operably connected to the laser ablation member for advancing the laser ablation member through the distal opening of the hand piece; and a feedback controller responsive to operation of said laser energy generator for controlling the advancement of the laser ablation member. 16. The lasing device according to claim 25, wherein said feedback controller comprises : at least one transducer; and a feedback circuit operatively responsive to at least one signal generated by said at least one transducer to control at least one of the laser energy generator or the advancing mechanism. 17. The lasing device according to claim 26, wherein said at least one transducer generates said at least one signal in response to sound emanating from tissue during ablation by said laser ablation member. 18. A method of ablating material with a pulsed laser, comprising the steps of: providing a lasing device having a laser ablation member; providing a first material to be ablated; generating laser energy from said laser ablation member to ablate the material and create a channel extending through the first material; and providing an audio sensor responsive to said ablation for automatically terminating the laser energy generated by the lasing device when the channel extends through the first material. 19. A method of performing transmyocardial revascularization (TMR), comprising the steps of: providing a lasing device having a laser ablation member; generating laser energy from said laser ablation member to ablate heart tissue and create a channel extending into a patient's ventricle; and providing an audio sensor responsive to said ablation for causing an audible or visual signal to be generated.

Inventors: PACALA THOMAS J, PACALA, THOMAS, J.
Applicants: PACALA THOMAS J, UNITED STATES SURGICAL CORP, PACALA, THOMAS, J., UNITED STATES SURGICAL CORPORATION
Application year: 1998
Main classification: A61B17
IPC codes: A61B17, A61B18