US20030171743A1

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Publication number: US20030171743A1
Application number: US10/372,591
Authority: US
Inventors: James Tasto; Jean Woloszko; Philip Eggers; Hira Thapliyal
Original assignee: Arthrocare Corp
Current assignee: Arthrocare Corp
Priority date: 1995-11-22
Filing date: 2003-02-21
Publication date: 2003-09-11
Also published as: US6805130B2; US20060189971A1; US20020068930A1

Abstract

Systems, apparatus, and methods are provided for promoting blood flow to a target tissue. In one aspect, the invention involves canalizing or boring channels, divots, trenches or holes through an avascular connective tissue, or through a tissue having sparse vascularity, such as a tendon or a meniscus, in order to increase blood flow within the tissue. In one method, an active electrode is positioned in close proximity to a target site on a tendon, and a high frequency voltage difference is applied between the active electrode and a return electrode to selectively ablate tendon tissue at the target site, thereby forming a channel or void in the tendon. The active electrode(s) may be moved relative to the tendon during, or after, the application of electrical energy to damage or sculpt a void within the tendon, such as a hole, channel, crater, or the like. In another aspect of the invention, an electrosurgical probe is used to elicit a wound healing response in a target tissue, such as an injured tendon, in order to stimulate vascularization of the target tissue. The present invention may also be used for vascularization of a torn or damaged tissue in conjunction with a surgical repair procedure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority from U.S. Provisional Application No. 60/200,712, filed Apr. 27, 2000, and is a continuation-in-part of U.S. patent application Ser. No. 09/089,012, filed Jun. 2, 1998, which is a continuation-in-part of U.S. patent application No. 08/753,227, filed on Nov. 22, 1996, now U.S. Pat. No. 5,873,855, which is a continuation-in-part of U.S. patent application Ser. No. 08/562,331, filed on Nov. 22, 1995, now U.S. Pat. No. 5,683,366, the complete disclosures of which are incorporated herein by reference for all purposes.[0001]

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery and, more particularly, to surgical devices and methods that employ high frequency electrical energy to increase the flow of blood to a target tissue.[0003]

Coronary artery disease, the build up of atherosclerotic plaque on the inner walls of the coronary arteries, causes the narrowing or complete closure of these arteries resulting in insufficient blood flow to the heart. A number of approaches have been developed for treating coronary artery disease. In less severe cases, it is often sufficient to treat the symptoms with pharmaceuticals and lifestyle modification to lessen the underlying causes of the disease. In more severe cases a coronary artery blockage can often be treated using endovascular techniques, such as balloon angioplasty, laser recanalization, placement of stents, and the like.[0004]

In cases where pharmaceutical treatment and endovascular approaches have failed or are likely to fail, it is often necessary to perform a coronary artery bypass graft (CABG) procedure using open or thoracoscopic surgical methods. For example, many patients still require bypass surgery due to such conditions as the presence of extremely diffuse stenotic lesions, the presence of total occlusions and the presence of stenotic lesions in extremely tortuous vessels. However, some patients are too sick to successfully undergo bypass surgery. For other patients, previous endovascular and/or bypass surgery attempts have failed to provide adequate revascularization of the heart muscle.[0005]

Laser myocardial revascularization (LMR) is a recent procedure developed with the recognition that myocardial circulation occurs through arterioluminal channels and myocardial sinusoids in the heart wall, as well as through the coronary arteries. In LMR procedures, artificial channels are formed in the myocardium with laser energy to provide blood flow to ischemic heart muscles by utilizing the heart's ability to perfuse itself from these artificial channels through the arterioluminal channels and myocardial sinusoids. In one such procedure, a CO[0006]₂laser is utilized to vaporize tissue and produce channels in the heart wall from the epicardium through the endocardium to promote direct communication between blood within the ventricular cavity and that of existing myocardial vasculature. The laser energy is typically transmitted from the laser to the epicardium by an articulated arm device. Recently, a percutaneous method of LMR has been developed in which an elongated flexible laser apparatus is attached to a catheter and guided endoluminally into the patient's heart. The inner wall of the heart is irradiated with laser energy to form a channel from the endocardium into the myocardium for a desired distance.

While recent techniques in LMR have been promising, they also suffer from a number of drawbacks inherent with laser technology. One such drawback is that the laser energy must be sufficiently concentrated to form channels through the heart tissue, which reduces the diameter of the channels formed by LMR. In addition, free beam lasers generally must completely form each artificial lumen or revascularizing channel during the still or quiescent period of the heart beat. Otherwise, the laser beam will damage surrounding portions of the heart as the heart beats and thus moves relative to the laser beam. Consequently, the surgeon must typically form the channel in less than about 0.08 seconds, which requires a relatively large amount of energy. This further reduces the size of the channels that may be formed with a given amount of laser energy. Applicant has found that the diameter or minimum lateral dimension of these artificial channels may have an effect on their ability to remain open. Thus, the relatively small diameter channels formed by existing LMR procedures (typically on the order of about 1 mm or less) may begin to close after a brief period of time, which reduces the blood flow to the heart tissue.[0007]

Another drawback with current LMR techniques is that it is difficult to precisely control the location and depth of the channels formed by lasers. For example, the speed in which the revascularizing channels are formed often makes it difficult to determine when a given channel has pierced the opposite side of the heart wall. In addition, the distance to which the laser beam extends into the heart tissue is difficult to control, which can lead to laser irradiation with heating or vaporization of blood or heart tissue within the ventricular cavity. For example, when using the LMR technique in a pericardial approach (i.e., from the outside surface of the heart to the inside surface), the laser beam may not only pierce through the entire wall of the heart but may also irradiate blood within the heart cavity. As a result, one or more blood thromboses or clots may be formed which can lead to vascular blockages elsewhere in the circulatory system. Alternatively, when using the LMR technique in an endocardial approach (i.e., from the inside surface of the heart toward the outside surface), the laser beam may not only pierce the entire wall of the heart but may also irradiate and damage tissue surrounding the outer boundary of the heart.[0008]

The promotion of blood flow to tissue, e.g., via canalization, vascularization or revascularization, is desirable in areas of the body other than the heart. The degenerative changes in the musculoskeletal system can be attributed to aging, trauma, overuse, and diminished focal blood supply. Degenerative changes of the musculoskeletal system are ubiquitous, particularly in the shoulder, knee, elbow, or the like. Conditions such as rotator cuff tendinitis, patellar tendinitis, tennis elbow, and plantar fasciitis are extremely common, and yet have no well-defined minimally invasive treatment protocol. Typically, the treatment consists of physical therapy, non-steroidal anti-inflammatories, and occasionally surgery. Recently in Europe, surgeons have begun using lithotrypsy, receiving only equivocal results.[0009]

One example of an area of the body that would benefit from vascularization is the meniscus tissue. The meniscus tissue, a C-shaped piece of fibrocartilage located at the peripheral aspect of the joint, typically has very little blood supply (particularly the inner portions of the meniscus). For that reason, when damaged, the meniscus is unable to undergo the normal healing process that occurs in most other tissues of the body. In addition, with age, the meniscus begins to deteriorate, often developing degenerative tears. Typically, when the meniscus is damaged, the torn pieces begins to move in an abnormal fashion inside the joint. Because the space between the bones of the joint is very small, as the abnormally mobile piece of meniscal tissue (meniscal fragment) moves, it may become caught between the bones of the joint (femur and tibia). When this happens, the knee becomes painful, swollen and difficult to move.[0010]

Another example of an area of the body that would benefit from vascularization is the tendons. When a tendon is damaged, the tendon usually forms tiny tears which allow collagen to leak from the injured areas. The collagen leakage causes inflammation of the tendon that can cut off the flow of blood and pinch the surrounding nerves. Because tendons are inherently poorly vascularized, and receive less oxygen, nutrients, and blood flow, as compared with other tissues and organs, tendons tend to heal much more slowly than other tissues of the body. Accordingly, there is a need for apparatus and methods to canalize, vascularize, revascularize, and/or increase blood flow to tendons that have been torn or otherwise damaged, so as to stimulate, expedite, or facilitate the healing process.[0011]

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures within or on the surface of a patient's body. The systems, apparatus, and methods of the present invention are particularly useful for treating acute and chronic musculoskeletal or neurological injuries and disorders, such as strains, sprains, tendinitis, fasciitis, arthritis, bursitis and tenosynovitis. In particular, the systems and methods of the present invention are useful for increasing blood flow to a target tissue, by canalization of tissue, stimulating the body's wound healing responses, such as inducing vascularization of tissue, stimulating collagen growth, altering cellular function, or other metabolic or physiologic events that promote healing and regeneration of injured tissue.[0012]

Systems and apparatus according to the present invention generally include an electrosurgical probe or catheter having a shaft with proximal and distal ends, one or more active electrode(s) at the distal end, and one or more connectors for coupling the active electrode(s) to a source of high frequency electrical energy. The distal end portion of the shaft will usually have a diameter of less than 3 mm, preferably less than 1 mm. The active electrode(s) are preferably supported within an electrically insulating support member typically formed of an inorganic material, such as a ceramic, a silicone rubber, or a glass.[0013]

In one method of the present invention, an active electrode is positioned in close proximity to tissue at a target site, and a high frequency voltage difference is applied between an active electrode and a return electrode to volumetrically remove or ablate tissue at the target site. The active electrode(s) may be translated or otherwise moved relative to the body structure during or after the application of electrical energy to form a void within the body structure, such as a hole, channel, stripe, crater, divot, surface damage, or the like. In some embodiments, the active electrode(s) are axially moved toward the body structure to volumetrically remove one or more channel(s), divot(s) or hole(s) through a portion of the structure. In other embodiments, the active electrode(s) are moved across the body structure to remove one or more stripe(s) or channel(s) of tissue. In most embodiments, electrically conductive fluid, such as isotonic saline, is located between the active electrode(s) and the body structure. In the bipolar modality, the conductive fluid generates a current flow path between the active electrode(s) and one or more return electrode(s). High frequency voltage is then applied between the active electrode(s) and the return electrode(s) through the current flow path created by the electrically conductive fluid.[0014]

In one aspect of the invention, a method is provided for vascularization or revascularization of a tendon, ligament, or meniscus. The present invention may be useful for acute muscle or tendon injury, iliotibial band syndrome, tendinitis, fasciitis, bursitis, tenosynovitis, strains, sprains and the like. In one embodiment of the present invention, artificial channels, holes, craters, or lumens are created during this procedure to vascularize the tendon and/or facilitate the healing process. In another embodiment, sufficient RF energy is applied to the tendon to vascularize a region around the target site without creating a hole, channel, crater or the like, in the tendon. According to the present invention, one or more active electrodes can be positioned adjacent to the tendon, and a voltage applied between the active electrode(s) and one or more return electrode(s). In an exemplary configuration, a high frequency voltage heats, damages, and/or ablates, (i.e. volumetrically removes) at least a portion of the tissue to be treated. The active electrode(s) can be advanced axially into the space vacated by the removed tissue to bore a channel through the tissue.[0015]

In one specific configuration, a void, hole, or crater is formed in the tendon by molecular dissociation or disintegration of tissue components. In these embodiments, the high frequency voltage applied to the active electrode(s) is sufficient to vaporize an electrically conductive fluid (e.g., a gel or isotonic saline) between the active electrode(s) and the tissue. Within the vaporized fluid, an ionized plasma is formed and charged particles (e.g., electrons) cause the molecular breakdown or disintegration of the tissue, perhaps to a depth of several cell layers. This molecular dissociation of tissue components is accompanied by the volumetric removal of the tissue. This process can be precisely controlled to effect the volumetric removal of tissue to a depth in the range of from about 10 microns to 150 microns, with minimal heating of, or damage to, surrounding or underlying tissue. A more complete description of this phenomenon is described in commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure of which is incorporated by reference herein.[0016]

One of the advantages of the present invention, particularly over previous methods involving lasers, is that the surgeon can more precisely control the location, depth, and diameter of the vascularizing channels formed in the tissue. The ability to precisely control the volumetric removal of tissue results in a field of tissue ablation or removal that is very defined, consistent, and predictable. This precise control of tissue treatment also helps to minimize, or completely eliminate, damage to healthy tissue structures, such as muscles, cartilage, bone, and/or nerves, which may be adjacent to the target tissue. In addition, any severed blood vessels at the target site may be simultaneously cauterized and sealed as the tissue is removed to continuously maintain hemostasis during the procedure. This increases the surgeon's field of view, and expedites the procedure. In one embodiment, the active electrode can remain in contact with the tendon tissue as the high frequency voltage ablates this tissue (or at least substantially close to the tissue, e.g., usually on the order of about 0.1 mm to 2.0 mm, and preferably about 0.1 mm to 1.0 mm). This preserves tactile sense and allows the surgeon to more accurately determine when to terminate cutting of a given channel so as to minimize damage to surrounding tissues and/or to minimize bleeding.[0017]

In open procedures, or in procedures in “dry” fields, the apparatus may further include a fluid delivery element for delivering electrically conductive fluid to the active electrode(s) and the target site. The fluid delivery element may be located on the probe, e.g., in the form of a fluid lumen or tube, or it may be part of a separate instrument. In arthroscopic procedures, however, the surgical area surrounding the tendon will typically be filled with electrically conductive fluid (e.g., isotonic saline) so that the apparatus need not have a fluid delivery element. In both embodiments, the electrically conductive fluid will preferably generate a current flow path between the active electrode(s) and one or more return electrode(s). In an exemplary embodiment, the return electrode is located on the probe and spaced a sufficient distance from the active electrode(s) to substantially avoid or minimize current shorting therebetween and to shield the return electrode from tissue at the target site.[0018]

According to one aspect of the invention, there is provided an electrosurgical system including a probe having a shaft and an electrode assembly disposed on the shaft; an arthroscope for passing at least a distal end portion of the shaft therethrough; and a sensing unit adapted for determining a boundary of a target tissue. The sensing unit may include an element, such as an ultrasonic transducer, located on the shaft distal end, and an ultrasonic generator. The system may further include an adjustable mechanical stop for limiting the maximum travel of the shaft within a target tissue. The electrode assembly typically includes at least one active electrode and a return electrode. The system further includes a high frequency power supply for applying a high frequency voltage between the active and return electrodes. In one embodiment, the sensing unit may be coupled to the power supply, and the system configured to shut off power from the power supply according to a location of the shaft distal end in relation to a target tissue.[0019]

In one aspect, the invention provides a method for treating a damaged or poorly vascularized tissue, such as a meniscus of a joint, or a tendon. In one embodiment one or more channels or voids are formed in a target tissue via selective electrosurgical ablation of the tissue. One or more implants may be inserted in the one or more channels. In one embodiment, at least one channel bridges a lesion in the target tissue, and an implant inserted in the channel serves as a splint. In another embodiment, an implant is inserted in a channel to maintain patency in the channel, the channel serving as a conduit for blood flow within the target tissue, and the implant serving as a stent. In a further embodiment, an implant is inserted in a channel to promote hemostasis of the channel. In yet another embodiment, a stent is inserted in a distal portion of a channel, and a hemostasis plug is inserted in a proximal portion of the channel.[0020]

In another aspect, the invention provides a method for increasing blood flow to a target tissue by eliciting a wound healing response in the target tissue. In one embodiment, the wound healing response is elicited by the controlled application of heat thereto. Typically, the target tissue is heated using an electrosurgical probe to deliver high frequency, or radio frequency (RF), electrical energy thereto. Usually, the target tissue is heated to a temperature less than about 150° C.[0021]

For a further understanding of the nature and advantages of the invention, reference should be made to the following description taken in conjunction with the accompanying drawings.[0022]

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system, including an electrosurgical probe, a fluid supply unit, and an electrosurgical power supply, constructed in accordance with the principles of the present invention;[0023]

FIG. 2A is an enlarged cross-sectional view of the distal tip of an electrosurgical probe, according to one embodiment of the invention;[0024]

FIG. 2B is an end view of the electrosurgical probe of FIG. 2A;[0025]

FIG. 2C is a cross-sectional view of the proximal end of the electrosurgical probe of FIG. 2A, illustrating an arrangement for coupling the probe to the electrically conductive fluid supply of FIG. 1;[0026]

FIGS. 2D and 2E are cross-sectional views of the distal end of the electrosurgical probe of FIG. 2A, illustrating one method of manufacturing the active electrodes and insulating matrix of the probe;[0027]

FIG. 3 is a perspective view of the distal tip of another electrosurgical probe that does not incorporate a fluid lumen for delivering electrically conductive fluid to the target site;[0028]

FIG. 4A is an enlarged, cross-sectional view of the distal tip of the electrosurgical probe of FIG. 3 illustrating an electrode array;[0029]

FIG. 4B is an end view of the distal tip of the electrosurgical probe of FIG. 3;[0030]

FIG. 5 is a perspective view of a catheter having a shaft with an electrosurgical arrangement at its distal end;[0031]

FIGS.[0032]6-10 illustrate alternative electrode arrangements for the probes of FIGS.1-4 or the catheter of FIG. 5;

FIG. 11 is a sectional view of the human heart, illustrating the electrosurgical catheter of FIG. 5 within the ventricular cavity for performing a transmyocardial revascularization procedure;[0033]

FIG. 12 is a sectional view of the thoracic cavity, illustrating the electrosurgical probe of FIGS. 3, 4A and[0034]4B in a thoracoscopic revascularization procedure;

FIG. 13 is a cross-sectional view of the probe of FIGS. 3, 4A and[0035]4B boring a channel through the myocardium;

FIG. 14 is a cross-sectional view of the probe of FIG. 1 boring a channel through the myocardium;[0036]

FIG. 15 depicts an alternative embodiment of the probe of FIG. 14 having an outer lumen for delivering electrically conductive fluid to the target site, and an inner lumen for aspirating fluid and gases from the transmyocardial channel;[0037]

FIG. 16 is a side view of an electrosurgical probe incorporating a fiberoptic viewing device and a light generator for sighting the probe onto a target site on the heart tissue;[0038]

FIG. 17 schematically illustrates a lumenal prosthesis positioned in a revascularizing channel during a percutaneous procedure to maintain lumen patency;[0039]

FIG. 18 is a cross-sectional view of the probe of FIG. 1 boring a channel into the myocardium with an ultrasound tissue thickness measuring device located on a guide catheter;[0040]

FIG. 19 is a cross-sectional view of the probe of FIG. 1 boring a channel into the myocardium with an ultrasound tissue thickness measuring device located on an electrosurgical catheter;[0041]

FIG. 20 is a cross-sectional view of the probe of FIG. 1 boring a channel into the myocardium with an electrical impedance sensor located on an electrosurgical catheter, to detect crossing through a surface of the heart, at a distance L[0042]₁distal to the electrode array;

FIG. 21 is a schematic cross-sectional view of a hemostasis device for sealing artificial revascularizing channels formed by one of the electrosurgical instruments of the present invention;[0043]

FIG. 22 schematically illustrates a lumenal prosthesis positioned in a revascularizing channel during a thoracoscopic procedure to maintain lumen patency;[0044]

FIG. 23 schematically illustrates a curved revascularizing channel formed by one of the electrosurgical instruments of the present invention;[0045]

FIG. 24A is an anterior view of a right knee;[0046]

FIG. 24B is a superior view of the interior of the knee showing the medial and lateral meniscus;[0047]

FIG. 25 schematically represents treatment of a meniscus with an electrosurgical probe, according to the present invention;[0048]

FIG. 26A schematically represents a procedure for treating a meniscus, according to one embodiment of the invention;[0049]

FIG. 26B schematically represents a procedure for treating a meniscus according to another embodiment of the invention;[0050]

FIG. 27 schematically represents treatment of a tendon using an electrosurgical probe, according to another embodiment of the invention;[0051]

FIG. 28A shows a tendon having a plurality of channels therein;[0052]

FIG. 28B is a side view of a tendon having a hole therethrough;[0053]

FIG. 28C is a side view of a tendon having a crater in the surface thereof;[0054]

FIG. 29 schematically represents electrosurgical treatment of a patellar tendon or patellar ligament, according to another embodiment of the invention; and[0055]

FIG. 30 is a block diagram representing an electrosurgical system for treatment of musculoskeletal disorders, according to a further embodiment of the invention.[0056]

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems, apparatus and methods for selectively applying electrical energy to a target location within or on a patient's body. In particular, the present invention provides systems, devices and methods for vascularizing a target tissue and for increasing blood flow to a region of tissue. In one aspect of the invention, blood flow within the heart is increased by creating lesions, such as artificial channels or lumens, within the myocardium. In another aspect of the invention, musculoskeletal injuries and disorders, such as strains, sprains, tendinitis, fasciitis, arthritis, bursitis and tenosynovitis, are treated by stimulating the body's wound healing response at the area treated. This wound healing response can include the stimulation of greater blood flow, collagen growth, as well as alteration of cellular function or of other metabolic events that promote healing and regeneration of injured tissue through a number of physiologic effects. In one specific embodiment, blood flow is increased to inner aspects of the meniscus by creating damage such as artificial channels or lumens from the outer aspect of the meniscus (which usually has a blood supply). In another specific embodiment, blood flow in a tendon is increased by creating damage to the tendon to invoke a would healing response.[0057]

It should be appreciated that the systems, devices, and methods of the invention can be applied equally well to procedures involving other tissues of the body, as well as to other procedures including open procedures, intravascular procedures, urological, laparoscopic, arthroscopic, thoracoscopic or other cardiac procedures, as well as dermatological, orthopedic, gynecological, otorhinolaryngological, spinal, and neurologic procedures, oncology and the like. For convenience, the remaining disclosure will be directed primarily to the revascularization of the heart, and to vascularization of meniscus tissue, and tendons.[0058]

In the present invention, high frequency (RF) electrical energy is applied to one or more active electrodes in the presence of electrically conductive fluid to remove and/or modify the structure of tissue structures. Depending on the specific procedure, the present invention may be used to: (1) create controlled damage to tissue; (2) volumetrically remove tissue, including bone and cartilage (i.e., ablate or effect molecular dissociation of the tissue structure); (3) form holes, channels, divots, or other spaces within tissue (4) cut or resect tissue; (5) shrink or contract collagen-containing connective tissue; and/or (6) coagulate severed blood vessels.[0059]

In one method, a target tissue is volumetrically removed or ablated. In this procedure, a high frequency voltage difference is applied between one or more active electrode(s) and one or more return electrode(s) to develop high electric field intensities in the vicinity of the target tissue. The high electric field intensities adjacent the active electrode(s) lead to electric field induced molecular breakdown of target tissue by molecular dissociation of tissue components (rather than by thermal evaporation or carbonization). Applicant believes that the tissue structure is volumetrically removed through molecular disintegration of larger organic molecules into smaller molecules and/or atoms, such as hydrogen, oxygen, oxides of carbon, hydrocarbons and nitrogen compounds. This molecular disintegration completely removes the tissue structure, as opposed to dehydrating the tissue material by the removal of water from within the cells of the tissue, as is typically the case with conventional electrosurgical desiccation and vaporization.[0060]

The high electric field intensities may be generated by applying a high frequency voltage that is sufficient to vaporize an electrically conductive fluid over at least a portion of the active electrode(s) in the region between the distal tip of the active electrode(s) and the target tissue. The electrically conductive fluid may be a liquid, such as isotonic saline or blood, delivered to the target site, or a viscous fluid, such as a gel, applied to the target site. Since the vapor layer or vaporized region has a relatively high electrical impedance, it minimizes current flow into the electrically conductive fluid. This ionization, under the conditions described herein, induces the discharge of energetic electrons and photons from the vapor layer and to the surface of the target tissue. A more detailed description of this phenomenon, termed Coblation™, can be found in commonly assigned U.S. Pat. No. 5,683,366 the complete disclosure of which is incorporated herein by reference.[0061]

The present invention applies high frequency, or radio frequency (RF), electrical energy in an electrically conductive fluid environment to remove (i.e., resect, cut, or ablate) a target tissue structure, and to seal transected vessels within the region of the target tissue. The present invention is particularly useful for sealing larger arterial vessels, e.g., on the order of 1 mm or greater. In some embodiments, a high frequency power supply is provided having an ablation mode, wherein a first voltage is applied to an active electrode sufficient to effect molecular dissociation or disintegration of the tissue, and a coagulation mode, wherein a second, lower voltage is applied to an active electrode (either the same or a different electrode) sufficient to achieve hemostasis of severed vessels within the tissue. In other embodiments, an electrosurgical instrument is provided having one or more coagulation electrode(s) configured for sealing a severed vessel, such as an arterial vessel, and one or more active electrodes configured for either contracting collagen fibers within the tissue or removing (ablating) the tissue, e.g., by applying sufficient energy to the tissue to effect molecular dissociation of the tissue components. In the latter embodiments, the electrosurgical system or apparatus may be configured such that a single voltage can be applied to coagulate with the coagulation electrode(s), and to ablate target tissue with the active electrode(s). In other embodiments, the power supply is combined with the electrosurgical instrument such that the coagulation electrode is used when the power supply is in the coagulation mode (low voltage), and the active electrode(s) are used when the power supply is in the ablation mode (higher voltage).[0062]

The present invention is also useful for removing or ablating tissue around nerves, such as spinal, visceral, or cranial nerves, e.g., the olfactory nerve on either side of the nasal cavity, the optic nerve within the optic and cranial canals, the palatine nerve within the nasal cavity, soft palate, uvula and tonsil, etc. One of the significant drawbacks with prior art mechanical cutters and lasers is that these devices do not differentiate between the target tissue and the surrounding nerves or bone. Therefore, the surgeon must be extremely careful during these procedures to avoid damage to the bone or nerves within and around the nasal cavity. In the present invention, the Coblation™ process for removing tissue completely avoids damage to non-target tissue, or results in extremely small depths of collateral tissue damage, as discussed above. This allows the surgeon to remove tissue close to a nerve without causing collateral damage to the nerve fibers. A more complete description of this phenomenon can be found in co-pending U.S. patent application Ser. No. 09/032,375, filed Feb. 27, 1998 (Attorney Docket No. CB-3), the complete disclosure of which is incorporated herein by reference.[0063]

In one method of the present invention, one or more active electrodes are brought into close proximity to tissue at a target site, and the power supply is activated in the ablation mode such that sufficient voltage is applied between the active electrodes and the return electrode to volumetrically remove the tissue via molecular dissociation, as described below. During this process, vessels within the tissue may be severed. Smaller vessels will be automatically sealed with the system and method of the present invention. Larger vessels, and those with a higher flow rate, such as arterial vessels, may not be automatically sealed while the system is operating in the ablation mode. In these cases, the severed vessels may be sealed by activating a control (e.g., a foot pedal) to reduce the voltage of the power supply into the coagulation mode. In this mode, the active electrodes may be pressed against the severed vessel to provide sealing and/or coagulation of the vessel. Alternatively, a coagulation electrode located on the same or a different instrument may be pressed against the severed vessel. Once the vessel is adequately sealed, the surgeon may activate a control (e.g., another foot pedal) to increase the voltage of the power supply back into the ablation mode.[0064]

The electrosurgical instrument will comprise a shaft having a proximal end and a distal end which supports an active electrode. The shaft may assume a wide variety of configurations, with the primary purpose being to mechanically support one or more active electrode and to permit the surgeon to manipulate the electrode(s) from the proximal end of the shaft. Usually, an electrosurgical probe shaft will be a narrow-diameter rod or tube, more usually having dimensions which permit it to be introduced into a body cavity, such as the thoracic cavity, through an associated trocar or cannula in a minimally invasive procedure, such as arthroscopic, laparoscopic, thoracoscopic, and other endoscopic procedures. Thus, the probe shaft will typically have a length of at least 5 cm for open procedures and at least 10 cm, more typically being 20 cm, or longer for endoscopic procedures. The probe shaft will typically have a diameter of at least about 0.5 mm, and will frequently be in the range from about 1 mm to 10 mm.[0065]

The electrosurgical probe may be delivered percutaneously (endoluminally) by insertion through a conventional or specialized guide catheter, or the invention may include a catheter having an active electrode array integral with its distal end. A shaft of the catheter may be rigid or flexible, with flexible shafts optionally being combined with a generally rigid external tube to provide mechanical support. Flexible shafts may be combined with pull wires, shape memory actuators, and other mechanisms for effecting selective deflection of the distal end of the shaft to facilitate positioning of the electrode or electrode array. Such mechanisms are known to the skilled artisan. The shaft of the probe or catheter will usually include a plurality of wires or other conductive elements running axially therethrough to permit connection of the electrode or electrode array and the return electrode to a connector at the proximal end of the shaft. Specific shaft designs will be described in detail in connection with the figures hereinafter.[0066]

The active electrode(s) are preferably supported within or by an electrically insulating support positioned near the distal end of the instrument shaft, e.g., a catheter body. The return electrode may be located on the instrument shaft, on another instrument, or on the external surface of the patient (i.e., a dispersive pad). When the present invention is used in close proximity to the heart, a bipolar design is more preferable because this minimizes the current flow through heart tissue. Accordingly, the return electrode is preferably either integrated with the catheter body, or with another instrument located in close proximity to the distal end of the catheter body. The proximal end of the catheter will include the appropriate electrical connections for coupling the return electrode(s) and the active electrode(s) to a high frequency power supply, such as an electrosurgical generator.[0067]

The current flow path between the active electrodes and the return electrode(s) may be generated by submerging the tissue site in an electrically conductive fluid (e.g., a viscous fluid, such as an electrically conductive gel), or by directing an electrically conductive fluid through a fluid outlet along a fluid path to the target site (i.e., a liquid, such as isotonic saline, or a gas, such as argon). The conductive gel may also be delivered to the target site to achieve a slower more controlled delivery rate of conductive fluid. In addition, the viscous nature of the gel may allow the surgeon to more easily contain the gel around the target site (e.g., as compared with containment of a liquid, such as isotonic saline). A more complete description of an exemplary method of directing electrically conductive fluid between active and return electrodes is described in U.S. Pat. No. 5,697,281, the contents of which are incorporated by reference herein in their entirety. Alternatively, the body's natural conductive fluids, such as blood, may be sufficient to establish a conductive path between the return electrode(s) and the active electrode(s), and to provide the conditions for establishing a vapor layer, as described above. Advantageously, a liquid electrically conductive fluid (e.g., isotonic saline) may be used to concurrently “bathe” the target tissue surface, to provide an additional means for removing any resected tissue fragments, and to cool the tissue at the target site during ablation.[0068]

In some embodiments, the electrode support and the fluid outlet may be recessed from an outer surface of the instrument or handpiece to confine the electrically conductive fluid to the region immediately surrounding the electrode support. In addition, the shaft may be shaped so as to form a cavity around the electrode support and the fluid outlet. This helps to assure that the electrically conductive fluid will remain in contact with the active electrode(s) and the return electrode(s) to maintain the conductive path therebetween. In addition, this will help to maintain a vapor layer and subsequent plasma layer between the active electrode(s) and the tissue at the treatment site throughout the procedure, which reduces the thermal damage that might otherwise occur if the vapor layer were extinguished due to a lack of conductive fluid. Provision of the electrically conductive fluid around the target site also helps to maintain the tissue temperature at desired levels.[0069]

The electrically conductive fluid should possess an electrical conductivity value above a minimum threshold level, in order to provide a suitable conductive path between the return electrode and the active electrode(s). The electrical conductivity of the fluid (in units of milliSiemens per centimeter or mS/cm) will usually be greater than about 0.2 mS/cm, typically will be greater than about 2 mS/cm and more typically greater than about 10 mS/cm. In an exemplary embodiment, the electrically conductive fluid is isotonic saline, which has a conductivity of about 17 mS/cm.[0070]

In some procedures, it may also be necessary to retrieve or remove, e.g., aspirate, any excess electrically conductive fluid and/or ablation by-products from the surgical site. For example, in procedures in and around the heart, or within blood vessels, it may be desirable to aspirate the fluid so that it does not enter the circulatory system. In addition, it may be desirable to aspirate small pieces of tissue fragments that are not completely disintegrated by the high frequency energy, or other fluids at the target site, such as blood, mucus, etc. Accordingly, the system of the present invention may include one or more suction lumen(s) in the instrument, or on another instrument, coupled to a suitable vacuum source for aspirating fluids from the target site. In some embodiments, the instrument also includes one or more aspiration electrode(s) coupled to the aspiration lumen for inhibiting clogging during aspiration of tissue fragments from the surgical site. A more complete description of these embodiments can be found in commonly assigned co-pending application Ser. No. 09/010,382, filed Jan. 21, 1998 (Attorney Docket No. A-6), the complete disclosure of which is incorporated herein by reference for all purposes.[0071]

As an alternative to, or in addition to suction, it may be desirable to contain the excess electrically conductive fluid, tissue fragments and/or gaseous products of ablation at or near the target site with a containment apparatus, such as a basket, retractable sheath or the like. This embodiment has the advantage of ensuring that the conductive fluid, tissue fragments or ablation by-products do not flow into the heart or lungs. In addition, it may be desirable to limit the amount of suction to limit the undesirable effect suction may have on hemostasis of severed blood vessels within heart tissue.[0072]

The present invention may use a single electrode or an electrode array distributed over a distal contact surface of the electrosurgical instrument. In both configurations, the circumscribed area of the electrode or electrode array will generally depend on the desired diameter of the revascularizing channel. For example, applicant has found that smaller diameter channels tend to remain patent for a shorter period of time than larger diameter channels. Thus, a relatively large diameter channel (on the order of about 1.5 mm to 3.0 mm) may be desired to improve lumen patency. The ability to select the diameter of the artificial channels is one of the advantages of the present invention over existing laser procedures, which are typically limited by the concentration of light that is required to generate sufficient energy to ablate the tissue during the still or quiescent period of the heart (i.e., about 0.08 seconds). Usually, the area of the electrode array is in the range of from about 0.25 mm[0073]²to 20 mm², preferably from about 0.5 mm²to 10 mm², and more preferably from about 0.5 mm²to 5.0 mm². In addition, the shape of the array and the distal end of the instrument shaft will also depend on the desired surface area of the channel. For example, the ratio of the perimeter of the electrode array to the surface area of the electrodes may be maximized to increase blood flow from the channel to the surrounding myocardial tissue. Each electrode may take the form of a solid round wire, or a wire having other solid cross-sectional shapes such as squares, rectangles, hexagons, triangles, star-shaped, or the like, to provide a plurality of edges around the distal perimeter of the electrodes. Alternatively, each electrode may be in the form of a hollow metal tube having a cross-sectional shape which is round, square, hexagonal, rectangular or the like. The envelop or effective diameter of the individual electrode(s) ranges from about 0.05 mm to 3 mm, preferably from about 0.1 mm to 2 mm.

The electrode array will usually include at least one isolated active electrode, and in some embodiments may include at least four active electrodes, sometimes at least six active electrodes, and often 50 or more active electrodes, disposed over the distal contact surface(s) on the shaft. By bringing the electrode array(s) on the contact surface(s) in close proximity with the target tissue and applying high frequency voltage between the array(s) and an additional common or return electrode in direct or indirect contact with the patient's body, the target tissue is selectively damaged, ablated or cut, permitting selective removal of portions of the target tissue while desirably minimizing the depth of necrosis to surrounding tissue.[0074]

As described above, the present invention may use a single active electrode or an electrode array distributed over a distal contact surface of an electrosurgical instrument, such as a probe, a catheter or the like. The electrode array usually includes a plurality of independently current-limited and/or power-controlled active electrodes to apply electrical energy selectively to the target tissue while limiting the unwanted application of electrical energy to the surrounding tissue and environment resulting from power dissipation into surrounding electrically conductive fluids, such as blood, normal saline, and the like. The active electrodes may be independently current-limited by isolating the electrodes from each other and connecting each electrode to a separate power source that is isolated from the other active electrodes. Alternatively, the active electrodes may be connected to each other at either the proximal or distal ends of the probe to form a single wire that couples to a power source.[0075]

In one configuration, each individual active electrode in the electrode array is electrically insulated from all other active electrodes in the array within said instrument and is connected to a power source which is isolated from each of the other active electrodes in the array or to circuitry which limits or interrupts current flow to the active electrode when low resistivity material (e.g., blood, electrically conductive saline irrigant or electrically conductive gel) causes a lower impedance path between the return electrode and the individual active electrode. The isolated power sources for each individual active electrode may be separate power supply circuits having internal impedance characteristics which limit power to the associated active electrode when a low impedance return path is encountered. By way of example, the isolated power source may be a user selectable constant current source. In this embodiment, lower impedance paths will automatically result in lower resistive heating levels since the heating is proportional to the square of the operating current times the impedance. Alternatively, a single power source may be connected to each of the active electrodes through independently actuatable switches, or by independent current limiting elements, such as inductors, capacitors, resistors and/or combinations thereof. The current limiting elements may be provided in the instrument, connectors, cable, power supply, or elsewhere along the conductive path from the power supply or controller to the distal tip of the instrument. Alternatively, the resistance and/or capacitance may occur on the surface of the active electrode(s) due to oxide layers which form selected active electrodes (e.g., titanium or a resistive coating on the surface of metal, such as platinum).[0076]

The tip region of the instrument may comprise many independent active electrodes designed to deliver electrical energy in the vicinity of the tip. The selective application of electrical energy to the conductive fluid is achieved by connecting each individual active electrode and the return electrode to a power source having independently controlled or current limited channels. The return electrode(s) may comprise a single tubular member of conductive material proximal to the electrode array at the tip which also serves as a conduit for the supply of the electrically conductive fluid between the active and return electrodes. Alternatively, the instrument may comprise an array of return electrodes at the distal tip of the instrument (together with the active electrodes) to maintain the electric current at the tip. The application of high frequency voltage between the return electrode(s) and the electrode array results in the generation of high electric field intensities at the distal tips of the active electrodes with conduction of high frequency current from each individual active electrode to the return electrode. The current flow from each individual active electrode to the return electrode(s) is controlled by either active or passive means, or a combination thereof, to deliver electrical energy to the surrounding conductive fluid while minimizing energy delivery to surrounding (non-target) tissue.[0077]

The application of a high frequency voltage between the return electrode(s) and the active electrode(s) for appropriate time intervals effects cutting, removing, ablating, shaping, contracting or otherwise modifying the target tissue. The tissue volume over which energy is dissipated (i.e., over which a high current density exists) may be precisely controlled, for example, by the use of a multiplicity of small active electrodes whose effective diameters or principal dimensions range from about 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm, and more preferably from about 1 mm to 0.1 mm. Electrodes (both circular and non-circular electrodes) will typically have a contact area (per active electrode) below about 25 mm[0078]²for electrode arrays, and as large as 75 mm²for single electrode embodiments, preferably being in the range from 0.0001 mm²to 1 mm², and more preferably from 0.005 mm²to 0.5 mm². The circumscribed area of the electrode array is in the range from 0.25 mm²to 75 mm², preferably from 0.5 mm²to 40 mm², and will usually include at least one, often at least two, isolated active electrodes, often at least five active electrodes, often greater than 10 active electrodes, and even 50 or more active electrodes, disposed over the distal contact surfaces on the shaft. The use of small diameter active electrodes increases the electric field intensity and reduces the extent or depth of tissue heating as a consequence of the divergence of current flux lines which emanate from the exposed surface of each active electrode.

The area of the tissue treatment surface can vary widely, and the tissue treatment surface can assume a variety of geometries, with particular areas and geometries being selected for specific applications. The active electrode surface(s) can have area(s) in the range from about 0.25 mm[0079]²to 75 mm², usually being from about 0.5 mm²to 40 mm². The geometries can be planar, concave, convex, hemispherical, conical, linear “in-line” array, or virtually any other regular or irregular shape. Most commonly, the active electrode(s) or active electrode array(s) will be formed at the distal tip of the electrosurgical instrument shaft, frequently being planar, disk-shaped, or hemispherical surfaces for use in reshaping procedures, or being linear arrays for use in cutting. Alternatively or additionally, the active electrode(s) may be formed on lateral surfaces of the electrosurgical instrument shaft (e.g., in the manner of a spatula), facilitating access to certain body structures in endoscopic procedures.

In one embodiment, an electrosurgical catheter or probe comprises a single active electrode that extends from an electrically insulating member, e.g., comprising a silicone rubber, a glass, or a ceramic, at the distal end of the shaft. In one embodiment, the insulating member comprises a tubular structure that separates the active electrode from a tubular or annular return electrode positioned proximal to the insulating member and the active electrode. In another embodiment, the catheter or probe includes a single active electrode that can be rotated relative to the rest of the catheter body, or the entire catheter may be rotated related to the lead. The single active electrode can be positioned adjacent the abnormal tissue (e.g., calcified deposits), energized, and rotated as appropriate to remove this tissue.[0080]

It should be clearly understood that the invention is not limited to electrically isolated active electrodes, or even to a plurality of active electrodes. For example, the array of active electrodes may be connected to a single lead that extends through the instrument shaft to a power source of high frequency current. Alternatively, the instrument may incorporate a single electrode that extends directly through the catheter shaft or is connected to a single lead that extends to the power source. The active electrode(s) may have ball shapes (e.g., for tissue vaporization and desiccation), twizzle shapes (for vaporization and needle-like cutting), spring shapes (for rapid tissue debulking and desiccation), twisted metal shapes, annular or solid tube shapes, or the like. Alternatively, the electrode(s) may comprise a plurality of filaments, rigid or flexible brush electrode(s) (for debulking a tumor, such as a fibroid, bladder tumor or a prostate adenoma), side-effect brush electrode(s) on a lateral surface of the shaft, coiled electrode(s), or the like.[0081]

The power supply may include a fluid interlock for interrupting power to the active electrode(s) when there is insufficient electrically conductive fluid around the active electrode(s). This ensures that the instrument will not be activated when conductive fluid is not present, minimizing the tissue damage that may otherwise occur. A more complete description of such a fluid interlock can be found in commonly assigned, co-pending U.S. application Ser. No. 09/058,336, filed Apr. 10, 1998 (attorney Docket No. CB-4), the complete disclosure of which is incorporated herein by reference.[0082]

The voltage difference applied between the return electrode(s) and the active electrode(s) will be at high or radio frequency, typically between about 5 kHz and 20 MHz, usually being between about 30 kHz and 2.5 MHz, preferably being between about 50 kHz and 500 kHz, more preferably less than 350 kHz, and most preferably between about 100 kHz and 200 kHz. The RMS (root mean square) voltage applied will usually be in the range from about 5 volts to 1000 volts, preferably being in the range from about 10 volts to 500 volts depending on the active electrode size, the operating frequency and the operation mode of the particular procedure or desired effect on the tissue (e.g., contraction, coagulation, cutting or ablation). Typically, the peak-to-peak voltage for ablation or cutting of tissue will be in the range of from about 10 volts to 2000 volts, usually in the range of 200 volts to 1800 volts, and more typically in the range of about 300 volts to 1500 volts, often in the range of about 500 volts to 900 volts peak to peak (again, depending on the electrode size, the operating frequency and the operation mode). Lower peak-to-peak voltages will be used for tissue coagulation or collagen contraction and will typically be in the range from 50 to 1500, preferably from about 100 to 1000, and more preferably from about 120 to 600 volts peak-to-peak.[0083]

As discussed above, the voltage is usually delivered in a series of voltage pulses or alternating current of time varying voltage amplitude with a sufficiently high frequency (e.g., on the order of 5 kHz to 20 MHz) such that the voltage is effectively applied continuously (as compared with e.g., lasers claiming small depths of necrosis, which are generally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle (i.e., cumulative time in any one-second interval that energy is applied) is on the order of about 50% for the present invention, as compared with pulsed lasers which typically have a duty cycle of about 0.0001%. With the above voltage and current ranges, applicant has found that the electrosurgical instrument will usually bore a channel completely through the heart wall in about 0.5 seconds to 20.0 seconds, preferably about 1.0 second to 3.0 seconds in the continuous mode, and preferably about 10 seconds to 15 seconds in the pulsed mode. It has been found that channels that are approximately 0.5 mm to 3.0 mm in diameter and approximately 1 cm to 4 cm deep may be easily and efficiently formed in the heart wall by this method, and that the revascularization procedure dramatically improves the flow of blood to the heart muscle.[0084]

The capability to form the desired channel over a longer period of time significantly reduces the amount of instantaneous power required to complete the channel. By way of example, CO[0085]₂lasers used for LMR typically deliver the power for each channel within an elapsed time of 0.08 seconds. By contrast, the present invention can be used to complete the canalization of the same sized channel within about 1.0 second. As a result, the laser requires about 500 watts to 700 watts to form a 1 mm diameter channel while the present invention requires only {fraction (1/12)} that amount of power, or about 42 watts to 58 watts, to form the same channel. If larger channels are required, the power requirements increase by the square of the ratio of the diameter. Hence, to produce a 2 mm channel in 0.08 seconds using a CO₂laser, the required power will be four-fold higher or 2000 watts to 2800 watts, which requires a very large and very expensive laser. In contrast, the present invention can form a 2 mm diameter channel (of the same length as that cited above) in 1 second with an applied power of about 168 watts to 232 watts.

The preferred power source of the present invention delivers a high frequency current selectable to generate average power levels ranging from several milliwatts to tens of watts per electrode, depending on the volume of target tissue being treated, and/or the maximum allowed temperature selected for the instrument tip. The power source allows the user to select the voltage level according to the specific requirements of a particular cardiac surgery, arthroscopic surgery, dermatological procedure, ophthalmic procedure, open surgery, or other endoscopic surgery procedure. For cardiac procedures, the power source may have an additional filter, for filtering leakage voltages at frequencies below 100 kHz, particularly voltages around 60 kHz. A description of a suitable power source can be found in co-pending patent application Ser. Nos. 09/058,571 and 09/058,336, filed Apr. 10, 1998 (Attorney Docket Nos. CB-2 and CB-4), the complete disclosure of both of which are incorporated herein by reference for all purposes.[0086]

The power source may be current limited or otherwise controlled so that undesired heating of the target tissue or surrounding (non-target) tissue does not occur. In a presently preferred embodiment of the present invention, current limiting inductors are placed in series with each independent active electrode, where the inductance of the inductor is in the range of 10 uH to 50,000 uH, depending on the electrical properties of the target tissue, the desired tissue heating rate and the operating frequency. Alternatively, capacitor-inductor (LC) circuit structures may be employed, as described previously in U.S. Pat. No. 5,697,909, the complete disclosure of which is incorporated herein by reference. Additionally, current limiting resistors may be selected. Preferably, these resistors will have a large positive temperature coefficient of resistance so that, as the current level begins to rise for any individual active electrode in contact with a low resistance medium (e.g., saline irrigant or blood), the resistance of the current limiting resistor increases significantly, thereby minimizing the power delivery from said active electrode into the low resistance medium (e.g., saline irrigant or blood).[0087]

In yet another aspect of the invention, the control system is “tuned” so that it will not apply excessive power to the blood (e.g., in the ventricle), once the electrosurgical instrument crosses the wall of the heart and enters the chamber of the left ventricle. This minimizes the formation of a thrombus in the heart (i.e., the system will not induce thermal coagulation of the blood). The control system may include an active or passive architecture, and will typically include a mechanism for sensing resistance between a pair(s) of active electrodes at the distal tip, or between one or more active electrodes and a return electrode, to sense when the electrode array has entered into the blood-filled chamber of the left ventricle. Alternatively, current limiting means may be provided to prevent sufficient joulean heating in the lower resistivity blood to cause thermal coagulation of the blood. In another alternative embodiment, an ultrasound transducer at the tip of the instrument can be used to detect the boundary between the target tissue and adjacent non-target tissue, e.g., between blood in the ventricle and the heart wall; or between a layer of abnormal tissue and underlying healthy tissue.[0088]

Referring now to the drawings in detail, wherein like numerals indicate like elements, an[0089]

electrosurgical system

11 is shown in FIG. 1 constructed according to the principles of the present invention.Electrosurgical system11 generally comprises an electrosurgical instrument or probe orcatheter10 connected to apower supply28 for providing high frequency voltage to electrosurgicalinstrument10 and afluid source21 for supplying electricallyconductive fluid50 to probe10.

In an exemplary embodiment as shown in FIG. 1,[0090]

electrosurgical probe

10 includes anelongated shaft13 which may be flexible or rigid, with flexible shafts optionally including support cannulas or other structures (not shown). It will be recognized that the probe shown in FIG. 1 will generally be employed in open or thoracoscopic procedures through intercostal penetrations in the patient. For endoluminal procedures into the ventricle, a delivery catheter200 (FIGS. 6 and 11) will typically be employed, as discussed below.Probe10 includes aconnector19 at its proximal end and a single active electrode (not shown) or anarray12 ofactive electrodes58 disposed on the distal tip ofshaft13. A connectingcable34 has ahandle22 with aconnector20 which can be removably connected toconnector19 ofprobe10. The proximal portion ofcable34 has aconnector26 to removablycouple probe10 topower supply28. Theactive electrodes58 are electrically isolated from each other and each of theelectrodes58 is connected to an active or passive control network withinpower supply28 by means of a plurality of individually insulated conductors42 (see FIG. 2A).Power supply28 can have a selection means30 to change the applied voltage level.Power supply28 can also include an element or device for energizing theelectrodes58 ofprobe10 through the depression of a pedal39 in afoot pedal37 positioned close to the user. Thefoot pedal37 may also include a second pedal (not shown) for remotely adjusting the voltage level applied toelectrodes58. The specific design of a power supply which may be used with the electrosurgical probe of the present invention is described in parent application PCT US 94/051,168, the full disclosure of which is incorporated herein by reference.

Referring to FIGS. 2A and 2B, the electrically isolated[0091]

active electrodes

58 are spaced-apart over anelectrode array surface82. Theelectrode array surface82 and individualactive electrodes58 will usually have dimensions within the ranges set forth above. In the preferred embodiment, theelectrode array surface82 has a circular cross-sectional shape with a diameter D (FIG. 2B) in the range of from about 0.3 mm to 4 mm.Electrode array surface82 may also have an oval or rectangular shape, having a length L in the range of 1 mm to 20 mm and a width W in the range from 0.3 mm to 7 mm, as shown in FIG. 8 (discussed below). The individualactive electrodes58 can protrude over theelectrode array surface82 by a distance (H) from 0 mm to 2 mm, preferably from 0 mm to 1 mm (see FIG. 2A).

The[0092]

active electrodes

58 are preferably composed of an electrically conductive metal or alloy, such as platinum, titanium, tantalum, tungsten, niobium, stainless steel, and the like. One preferred material forelectrodes58 is tungsten because of its known biocompatibility and resistance to erosion under the application of high voltages. As shown in FIG. 2B, theactive electrodes58 are anchored in asupport matrix48 of suitable insulating material (e.g., ceramic, glass/ceramic, or glass material, such as alumina, silica glass, and the like) which could be formed at the time of manufacture in a flat, hemispherical or other shape according to the requirements of a particular procedure. In an exemplary embodiment, thesupport matrix48 will comprise an inorganic insulator, such as ceramic, glass, glass/ceramic, or a high resistivity material, such as silicon or the like. An inorganic material is generally preferred for the construction of thesupport matrix48 since organic or silicone based polymers are known to rapidly erode during sustained periods of the application of high voltages betweenactive electrodes58 and thereturn electrode56 during tissue ablation. However, for situations in which the total cumulative time of applied power is less than about one minute, organic or silicone based polymers may be used without significant erosion and loss of material of thesupport matrix48 and, therefore, without significant reduction in ablation performance.

As shown in FIG. 2A, the[0093]

support matrix

48 is adhesively joined to supportmember9, which extends most or all of the distance betweenmatrix48 and the proximal end ofprobe10. In a particularly preferred construction technique,support matrix48 comprises a plurality of glass or ceramic hollow tubes400 (FIG. 2D) extending from the distal end ofshaft13. In this embodiment,active electrodes58 are each inserted into the front end of one of thehollow tubes400 and adhered to thehollow tubes400 so that theelectrodes58 extend distally from eachhollow tube400 by the desired distance, H. Theelectrodes58 are preferably bonded to thehollow tubes400 by a sealing material402 (e.g., epoxy) selected to provide effective electrical insulation, and good adhesion to both thehollow tubes400 and theactive electrodes58. Alternatively,hollow tubes400 may be comprised of a glass having a coefficient of thermal expansion similar to that ofactive electrode58 and may be sealed around theactive electrode58 by raising the temperature of the glass tube to its softening point according to the procedures commonly used to manufacture glass-to-metal seals. Referring to FIG. 2D,lead wires406, such asinsulation408 covered copper wires, are inserted through the back end of thehollow tubes400 and coupled to theelectrodes58 with a suitableconductive adhesive404. The glass tube/active electrode assembly is then placed into the distal end ofsupport member9 to form the electrode array as shown in FIG. 2E. Alternatively, thelead wire406 andactive electrode58 may be constructed of a single wire (e.g., stainless steel or nickel alloy) withinsulation408 removed over the length of the wire inserted into thehollow tube400. As before, sealingmaterial402 is used to seal annular gaps betweenhollow tube400 andactive electrode58 and to adhesively joinactive electrode58 tohollow tube400. Other features of construction are discussed below and shown in FIG. 2E.

In the embodiment shown in FIGS. 1, 2A and[0094]2B,probe10 includes areturn electrode56 for completing the current path betweenactive electrodes58 andpower supply28.Shaft13 preferably comprises an electrically conducting material, usually metal, which is selected from the group consisting of stainless steel alloys, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, and nickel or its alloys. Thereturn electrode56 may be composed of the same metal or alloy which forms theactive electrodes58 to minimize any potential for corrosion or the generation of electrochemical potentials due to the presence of dissimilar metals contained within an electricallyconductive fluid50, such as isotonic saline (discussed in greater detail below).

As shown in FIGS. 2A, 2B, and[0095]2C, returnelectrode56 extends from the proximal end ofprobe10, where it is suitably connected topower supply28 viaconnectors19, to a point slightly proximal ofelectrode array surface82, typically about 0.5 mm to 10 mm, and more preferably about 1 mm to 10 mm, proximal tosurface82.Shaft13 is disposed within an electricallyinsulative jacket18, which is typically formed as one or more electrically insulative sheaths or coatings, such as polyester, polytetrafluoroethylene, polyimide, and the like. The provision of the electrically insulativejacket18 overshaft13 prevents direct electrical contact betweenshaft13 and any adjacent body structure or the surgeon. Such direct electrical contact between a body structure and an exposedreturn electrode56 could result in unwanted heating of the structure at the point of contact causing necrosis.

In the embodiment shown in FIGS.[0096]2A-2C, returnelectrode56 is not directly connected toactive electrodes58. To complete this current path so thatelectrodes58 are electrically connected to returnelectrode56 viatarget tissue52, electrically conductive fluid50 (e.g., isotonic saline) is caused to flow alongfluid paths83. Afluid path83 is formed byannular gap54 betweenouter return electrode56 andtubular support member78. An additionalfluid path83 may be formed between an optionalinner lumen57 within aninner tubular member59. The electricallyconductive fluid50 delivered to the distal end ofinstrument10 provides a pathway for electrical current flow betweentarget tissue52 and returnelectrode56, as illustrated by thecurrent flux lines60 in FIG. 2A. When a voltage difference is applied betweenelectrode array12 and returnelectrode56, high electric field intensities will be generated at the distal tips ofelectrodes58 with current flow fromarray12 through the target tissue to returnelectrode56, the high electric field intensities causing ablation oftissue52 inzone88.

FIG. 2C illustrates the proximal or[0097]

connector end

70 ofprobe10 in the embodiment of FIGS. 2A and 2B.Connector19 comprises a plurality of individual connector pins74 positioned within ahousing72 at theproximal end70 ofprobe10.Active electrodes58 and the attached insulatingconductors42 extend proximally to connector pins74 inconnector housing72.Return electrode56 extends intohousing72, where it can bend radially outward to exitprobe10. As shown in FIG. 1, afluid supply tube15 can be removably coupled tofluid source21, (e.g., a bag of electrically conductive fluid elevated above the surgical site or having a pumping device) and acontrol valve17 located proximal to returnelectrode56. Preferably, an insulatingjacket14 covers at least a portion ofreturn electrode56. One of the connector pins76 is electrically connected to returnelectrode56 to coupleelectrode56 topower supply28 viacable34. Acontrol valve17 allows the surgical team to regulate the flow of electricallyconductive fluid50.

FIGS. 3, 4A, and[0098]4B illustrate another preferred embodiment of the present invention. In this embodiment, aprobe100 does not include a fluid channel for directing electrically conductive fluid to the target site. Applicant has found that the fluids in the patient's heart tissue, such as blood, usually have a sufficient amount of electrical conductivity to complete the electrical path between the active electrode array and the return electrodes. In addition, these fluids will often have the requisite properties discussed above for establishing a vapor layer, creating regions of high electric fields around the edges ofactive electrodes58 and inducing the discharge of energetic electrons and photons from the vapor layer to the surface of the target tissue to effect ablation.

As shown in FIG. 3,[0099]

electrosurgical probe

100 typically has ashaft102 with an exposeddistal end104 and a proximal end (not shown) similar to the proximal end shown in FIG. 2C. Aside from exposeddistal end104, which functions as the return electrode in this embodiment, theentire shaft102 is preferably covered with an electricallyinsulative jacket106, which is typically formed as one or more electrically insulative sheaths or coatings, such as polyester, polytetrafluoroethylene, polyimide, and the like, to prevent direct electrical contact betweenshaft102 and any adjacent body structure or the surgeon. Similar to the embodiments described hereinabove, probe100 typically includes anarray108 ofactive electrodes110 having substantially the same applied potential.Electrodes110 extend from an insulatinginorganic matrix112 attached todistal end104 ofshaft102. As discussed above,matrix112 is only shown schematically in the drawings, and preferably comprises an array of glass or ceramic tubes extending fromdistal end104 or is a ceramic spacer through whichactive electrodes110 extend.

The electrode array may have a variety of different configurations other than the one shown in FIGS. 3, 4A, and[0100]4B. For example, as shown in FIG. 8, the distal end of theshaft102 and/or the insulating matrix may have a substantially rectangular shape with rounded comers so as to maximize the perimeter length to cross-sectional area ratio of the distal tip of the probe. As shown, electrode array surface120 (FIG. 8) has a rectangular shape having a width in the range of from about 2 mm to 5 mm and a length in the range of from about 1 mm to 2 mm. Increasing the perimeter of an artificial channel formed in a tissue may have advantages in that blood flowing through the artificial channel will have a greater area to pass into the tissue for a given cross-sectional area. Thus, this configuration can be a more efficient method of increasing blood flow to a region of tissue.

In another embodiment, the return electrode is positioned on the front or distal face of the probe. This configuration inhibits current flow within the tissue on the sides of the probe as it forms the revascularizing channel. In one configuration, for example (shown in FIG. 9), the[0101]

electrode array surface

122 includes multiple pairs of electrodes, with each pair of electrodes including anactive electrode126 and areturn electrode128. Thus, as shown, the high frequency current passes between the pairs across thedistal surface122 of the probe. In another configuration (shown in FIG. 10), the return orcommon electrode130 is positioned in the center of thedistal probe surface132 and theactive electrodes134 are positioned at its perimeter. In this embodiment, the electrosurgical current will flow betweenactive electrodes134 at the perimeter ofdistal surface132 and return electrode130 at its center to form the revascularizing channel. This allows the surgeon to more precisely control the diameter of the revascularizing channel because the current will generally flow radially from the outeractive electrodes134 to thereturn electrode130. For this reason,electrodes134 will preferably be positioned on the perimeter of distal surface132 (i.e., further radially outward than shown in FIG. 10) to avoid tearing of non-ablated tissue by the perimeter of the probe shaft.

FIG. 6 illustrates yet another embodiment of an[0102]

electrosurgical probe

100′ according to the present invention. In this embodiment, the distal tip of the probe has a conical shape and includes an array of active electrodes along theconical surface140. A conical shape provides less resistance to the advancement of the probe through dense tissue. As shown in FIG. 6, insulatingmatrix142 tapers in the distal direction to form conicaldistal surface140. Theelectrode array144 extends fromdistal surface140, with eachactive electrode146 arranged to protrude axially from the conical surface140 (i.e., rather than protruding perpendicularly from the surface140). With this configuration, theelectrodes146 do not extend radially outward from theconical surface140, which reduces the risk of electric current flowing radially outward to heart tissue surrounding the revascularizing channel. In addition, the high electric field gradients generated by the electric current concentrate near the active electrode surfaces and taper further away from these surfaces. Therefore, this configuration places these high electric field gradients within the diameter of the desired channel to improve ablation of the channel, while minimizing ablation of tissue outside of the desired channel.

FIG. 5 illustrates a[0103]

preferred delivery catheter

200 for introducing anelectrosurgical probe202 through a percutaneous penetration in the patient, and endoluminally deliveringprobe202 to the target site (e.g., a ventricle of the heart as described in detail below).Catheter200 generally includes ashaft206 having aproximal end208 and adistal end210.Catheter200 includes a handle204 secured toproximal end208, and preferably adeflectable tip212 coupled todistal end210 ofshaft206. Probe202 typically has a length in the range of from about 100 cm to 200 cm. Handle204 includes a variety of actuation mechanisms for manipulatingtip212 within the patient's heart, such as atip actuation slide214 and atorque ring216, as well as anelectrical connector218.Catheter shaft206 will generally define one or moreinner lumens220, and one or more manipulator wires and electrical connections (not shown) may extend through lumens (22) to probe202.

In a first aspect, with reference to FIGS.[0104]11-23, the present invention provides methods for increasing the blood flow to the heart through a transmyocardial revascularization procedure to form artificial channels through the heart wall to perfuse the myocardium. These procedures are an alternative to coronary artery bypass surgery for treating coronary artery disease. The channels allow oxygen enriched blood flowing into the ventricular cavity to directly flow into the myocardium, rather than exiting the heart and then flowing back into the myocardium through the coronary arteries.

As shown in FIG. 11,[0105]

electrosurgical probe

202 is positioned into theleft ventricular cavity258 of the heart.Electrosurgical probe202 may be introduced into theleft ventricle258 in a variety of procedures that are well known in the art, such as a percutaneous, minimally invasive procedure. In the representative embodiment,probe202 is introduced into the vasculature of the patient through apercutaneous penetration360 and axially translated viadelivery catheter200 through one of the major vessels, such as thefemoral artery346, through theaorta254 to theleft ventricular cavity258. A viewing scope (not shown) may also be introduced through a percutaneous position to a position suitable for viewing the target location in theleft ventricle258.

Once positioned within the patient's[0106]

ventricle

258,probe202 is aligned with theheart wall260 to form one or moreartificial channels264 for increasing blood flow to the myocardium262 (e.g., FIG. 13). As shown in FIG. 14, thechannels264 will preferably extend from the endocardium266 a desired distance through themyocardium262, without perforating the exterior of theepicardium268. Preferably, the surgeon will employ a detection orinstrument guidance system350, (discussed below in reference to FIGS. 16, 18,19, and20) onprobe202, or another instrument, to determine the location of the probe within the myocardium relative to theepicardium268. The location ofchannels264 may be selected based on familiar endocardial anatomic landmarks. Alternatively,instrument guide system350 may be used to select target sites on the heart wall, as discussed below.

As shown in FIG. 14,[0107]

guide catheter

200 is positioned adjacent the inner endocardial wall and probe202 is axially translated so that theactive electrode270 at its distal end is positioned proximate the heart tissue. In this embodiment, theprobe202 includes a single,annular electrode270 at its distal tip for ablation of the heart tissue. However, it will be readily recognized that the probe may include an array of active electrodes as described in detail above. While viewing the region with an endoscope (not shown), voltage can be applied from power supply28 (see FIG. 1) betweenactive electrode270 andannular return electrode272. The boring ofchannel264 is achieved by engagingactive electrode270 against the heart tissue or positioningactive electrode270 in close proximity to the heart tissue while simultaneously applying voltage frompower supply28 and axially displacingprobe202 throughchannel264. To complete the current path between theactive electrode270 and returnelectrode272, electrically conductive irrigant (e.g., isotonic saline) will preferably be delivered fromfluid supply21 to the target site via annularfluid path274, the latter located external to returnelectrode272 andtubular shaft200. Alternatively, the site may already be submerged in fluid, or the fluid may be delivered through a separate instrument. The electrically conductive fluid provides a pathway for electrical current flow between the heart tissue and returnelectrode272, as illustrated by thecurrent flux lines278 in FIG. 15.

FIG. 15 illustrates an alternative embodiment of a probe for use in conjunction with[0108]

catheter

200. In this embodiment, theprobe280 includes acentral lumen282 having a proximal end attached to a suitable vacuum source (not shown) and an opendistal end286 for aspirating the target site. To complete the current path between theactive electrode270 and returnelectrode272, electrically conductive irrigant (e.g., isotonic saline) will preferably be delivered from fluid supply21 (shown in FIG. 1) through annularfluid path274 betweenreturn electrode272 andtubular shaft200 to the target site. The active electrode is preferably a singleannular electrode270 surrounding the opendistal end286 ofcentral lumen282.Central lumen282 is utilized to aspirate or otherwise remove the ablation by-products (e.g., fluids and gases) generated at the target site and excess electrically conductive irrigant during the procedure.

An alternative embodiment of the percutaneous, endocardial canalization approach is shown in FIG. 23. In this embodiment,[0109]

electrosurgical instrument

100/catheter200 can be guided by the surgeon or surgical assistant during the canalization ofchannel264 using external handpiece340 (FIG. 11). In this embodiment, the distal portion of theelectrosurgical catheter200/probe202 can be caused to follow a curved path to effect a curvedartificial channel264′. By forming a curvedartificial channel264′, the total surface area of the artificial channel can be extended so that the channel is longer than the total thickness L₉of theheart wall260. In addition, by forming a curvedartificial channel264′ of proper curvature as shown in FIG. 23, the penetration of theepicardium268 can be avoided. Still further, the curvedartificial channel264′ can be continued forming a complete “U” shaped channel which reenters theventricular cavity258 providing one continuous channel which penetrates the endocardium at two locations but does not penetrate through theepicardium268.

FIG. 12 illustrates a thoracoscopic procedure for revascularizing the myocardium from the outer wall or[0110]

epicardium

268 inward to theendocardium266. At least one intercostal penetration is made in the patient for introduction of electrosurgical probe100 (FIG. 3) into thethoracic cavity302. The term “intercostal penetration” as used herein refers to any penetration between the ribs of a patient. Typically, such a penetration is in the form of a small cut, incision, hole or cannula, trocar sleeve or the like, through the chest wall between two adjacent ribs. Usually, such a penetration does not require cutting, removing, or significantly displacing or retracting the ribs or sternum. Usually, the intercostal penetration will require a puncture or incision of less than about 5 cm in length. In one embodiment, the intercostal penetration may be via atrocar sleeve300 having a length in the range from about 2 cm to 15 cm, and an internal diameter in the range from 1 mm to 15 mm, commonly known as thoracic trocars. Suitable trocar sleeves are available, for example, from United States Surgical Corp. of Norwalk, Conn., under the brand name “Thoracoport”™. A viewing scope (not shown) may also be introduced through a trocar sleeve to a position suitable for viewing the target location on theheart wall260. A viewing scope (not shown) may also be introduced through the same or another intercostal penetration into thethoracic cavity302 to a position suitable for viewing thetarget location360 on the surface of theepicardium268 of the heart. The viewing scope can be a conventional laparoscope or thoracoscope, which typically comprise a rigid elongated tube containing a lens system and an eyepiece or camera mount at the proximal end of the tube. A small video camera is preferably attached to the camera mount and connected to a video monitor to provide a video image of the procedure. This type of scope is commercially available, for example, from Baxter Healthcare Corporation of Deerfield, Ill., or from United States Surgical Corporation of Norwalk, Conn.

As shown in FIGS. 12 and 13, one or more[0111]

artificial channels

264 are formed by theelectrosurgical probe100 from the outer wall orepicardium268 through themyocardium262 and the inner wall orendocardium266 into theventricular cavity258. Similar to the above described method,electrode array108 is positioned in close proximity to the heart tissue while simultaneously applying voltage frompower supply28 and axially displacingprobe100 throughchannel264. In this embodiment, however, electrically conductive fluid is not supplied to the target site to complete the current path between theactive electrodes110 and returnelectrode102. Applicant has found that the fluids in the patient's heart tissue, such as blood, usually have a sufficient amount of electrical conductivity to complete the electrical path between the active electrode array and the return electrodes. In addition, these fluids will often have the requisite properties discussed above for establishing a vapor layer and inducing the discharge of energetic electrons and photons from the vapor layer to the surface of the target tissue, as well as the creation of high electric fields to effect the ablation of tissue.

To inhibit blood from flowing through[0112]

channels

264 into the thoracic cavity, thechannels264 will preferably be sealed at theepicardium268 as soon as possible after they have been formed. One method for sealing theartificial channel264 at theepicardium268 is to insert a collagen hemostasis device480 (shown in FIG. 21) using atrocar300, acannula484 and a syringe-like delivery system486. The collagen, unaffected by antiplatelet or anticoagulant agents that may be present in the patient's blood stream, attracts and activates platelets from theblood482, rapidly forming a “glue”-like plug near the surface of theepicardium268 of the newly formedchannel264. Suitable collagen hemostasis devices are available from, for example, Datascope Corporation, Montval, N.J. under the brand name “VasoSeal™”. The deployment of thecollagen hemostasis device480 is accomplished with the aid of a viewing scope (not shown) which may also be introduced through a trocar sleeve to a position suitable for viewing the target location on theheart wall260.

To facilitate this sealing procedure, an electrosurgical probe (e.g.,[0113]

probe

354, FIG. 16) will preferably include aguidance system350 for determining when the probe is close to the inner surface of theendocardium266, so that the surgeon can prepare to withdraw the probe and seal thechannel264.

In both of the above embodiments, the present invention provides localized ablation or disintegration of heart tissue to form a[0114]

revascularization channel

264 of controlled diameter and depth. Usually, the diameter will be in the range of from about 0.5 mm to 3 mm, preferably from about 1 mm to 2 mm. Preferably, the radio frequency voltage will be in the range of 300 volts to 2400 volts peak-to-peak to provide controlled rates of tissue ablation and hemostasis while minimizing the depth of necrosis of tissue surrounding the desired channel. This voltage will typically be applied continuously throughout the procedure until the desired length of thechannel264 is completely formed. However, the heartbeat may be monitored and the voltage applied in pulses that are suitably timed with the contractions (systole) of the heart.

Ablation of the tissue may be facilitated by axially reciprocating and/or rotating the electrosurgical probe a distance of between about 1 mm to 5 mm. This axial reciprocation or rotation allows the electrically conductive fluid (FIG. 14) to flow over the tissue surface being canalized, thereby cooling this tissue and preventing significant thermal damage to the surrounding tissue cells.[0115]

FIG. 16 illustrates one[0116]

representative guidance system

350 for guiding anelectrosurgical probe354 to target sites on the heart wall.Guidance system350 is provided for detecting an “end point” for each artificial channel and/or for determining appropriate target sites on the heart wall for forming the artificial channels. Theinstrument guidance system350 will preferably allow a surgeon to determine when the electrosurgical probe354 (or an electrosurgical catheter) is near the other end of the heart wall (i.e., the outer edge of the epicardium or the inner edge of the endocardium). Theguidance system350 indicates to the surgeon to stop axially translating theprobe354 so that the probe does not form a channel completely through a heart wall, which limits bleeding and/or reduces damage to surrounding tissue structures or blood. Alternatively or in addition, theguidance system354 can allow the surgeon to determine anappropriate target site360 on the heart wall at which to form the channel to avoid accidental puncturing of relatively large vessels in the heart wall.

In the embodiment shown in FIG. 16, the[0117]

instrument guidance system

350 includes afiberoptic viewing cable356 withinelectrosurgical probe354, and avisible light generator358, such as a laser beam, integral with the probe, for illuminating atarget site360 on the heart wall. Note that bothlight generator358 andfiberoptic cable356 may be coupled to an instrument other thanprobe354. Thefiberoptic viewing cable356 sites thetarget site360 illuminated by thevisible light generator358 to locate where theprobe354 can bore the hole. This allows the surgeon to avoid puncturinglarger blood vessels362 on the heart wall (e.g., coronary arteries or veins). Visiblelight generator358 may also be used to determine when thedistal end364 ofprobe354 is close to the opposite side of the heart wall, or when theprobe354 has completely penetrated through the heart wall into, or out of, theventricular cavity258.

In a second embodiment, the detection system can be an ultrasound guidance system that transmits sound waves onto the heart wall to facilitate canalization of the heart.[0118]

Referring to FIGS. 18 and 19, an ultrasound tissue thickness measuring system may be incorporated within an electrosurgical instrument of the invention, e.g., probe[0119]100 orcatheter200, to measure the thickness of theheart wall260 adjacent toactive electrode270, and thereby allow the surgeon to pre-set the depth of each channel usingadjustable stop352 on handpiece340 (FIG. 11) before energizingcatheter200/probe100 and ablating the heart tissue. In the embodiment shown in FIG. 18, anultrasonic transducer310, affixed to the distal end of the instrument, and connected to an external ultrasonic generator and sensing system (not shown) vialead312, transmits pulses of ultrasound into the heart tissue in the form of emittedultrasound signal314, and the ultrasound generator and sensing system measures the delay time for reflectedultrasound signal316 to return from the boundary of the heart wall at the surface ofepicardium268 to the sensing system. This delay time can be translated into a thickness of the entire heart wall and allow the surgeon to adjust the maximum travel distance ofcatheter200/probe100 using mechanical stop352 (FIG. 11) to prevent the length ofchannel264 from extending through the outer surface of theepicardium268. The surgeon can choose to stop the canalization of the heart at any selected distance of the epicardium which may typically be in the range from about 1 mm to 10 mm.

A third embodiment is shown in FIG. 19 wherein an[0120]

ultrasonic transducer

310 is affixed to the distal end ofelectrosurgical catheter200/probe100, and connected to an external ultrasonic generator and sensing system (not shown) via leads312, and transmits pulses of ultrasound into the heart tissue in the form of emittedultrasound signal314. The ultrasound generator and sensing system measures the delay time for reflectedultrasound signal316 to return from the boundary of the heart wall at the surface ofepicardium268 to the sensing system. This measured delay time can be translated into the distance betweenactive electrode270 and the surface of theepicardium268. In this arrangement, the surgeon can observe where thechannel264 reaches the preferred distance from theepicardium268, and can interrupt the application of power and advancement ofcatheter200/probe100. In one embodiment, the preferred minimum thickness of the uncanalized heart wall260 (i.e., the minimum distance from the bottom ofchannel264 to the surface of the epicardium268) can be preselected by the surgeon. When this distance is reached based on the thickness of the uncanalized heart wall measured using the ultrasonic generator and sensor system, the ultrasonic generator and sensor system provides an electrical signal to the power source to interrupt the voltage applied tocatheter200/probe100, thereby ending the canalization process and limiting the depth of channel formed. In this manner, the surgeon may hear an audible tone and will “feel” the catheter advancement stop at the moment the applied voltage is interrupted.

A fourth embodiment is shown in FIG. 20, in which an electrosurgical instrument, e.g.,[0121]

probe

100/202 includes a small diameter tissue electricalimpedance measurement sensor319 which extends distally from active electrode(s)270 by a distance L₁.Impedance measurement sensor319 detects the outer surface of theepicardium268 assensor319 enters a region of different electrical impedance (viz, the fluid-filled cavity surrounding the heart). In the present embodiment, asensor tip320 may include a firstimpedance measurement electrode321 and a secondimpedance measurement electrode323. A small, high-frequency potential is applied between first and second

impedance measurement electrodes

321 and323 causing current flow between first and second

impedance measurement electrodes

321 and323 as indicated by current flux lines322. As the first and

second electrodes

321 and323 emerge from theepicardium268 intocavity318 surrounding the heart, the change in electrical impedance is measured, and may be indicated by an audible signal and/or may be used as a direct feedback control signal to interrupt the application of voltage to theelectrosurgical catheter100 by generator or power supply28 (FIG. 1). By this method, the forward advancement of theelectrosurgical catheter100 can be limited to a pre-selected distance L₆between the bottom ofchannel264 and the surface of theepicardium268.

In a fifth embodiment shown in FIG. 13, a guidance system utilizes impedance measurement circuitry integrated with[0122]

active electrodes

110 to detect whenprobe100 is adjacent blood vessels and/or the outer or inner boundaries of the heart wall. Specifically, the current limiting circuitry includes a number of impedance monitors coupled to eachactive electrode110 to determine the impedance between the individualactive electrode110 and thereturn electrode102. Thus, for example, if the measured impedance suddenly decreases atactive electrodes110 at the tip of theprobe100, the applied voltage will be interrupted to avoid power delivery to blood filledventricular cavity258 of the heart, thereby avoiding formation of a thrombus or damage to other tissue structures within theventricular cavity258.

FIG. 17 illustrates a method for implanting a luminal prosthesis, such as a stent or stent-[0123]

graft

370, into theartificial channels264 formed by one of the electrosurgical probes or catheters of the present invention to maintain the patency of thesechannels264. Thestents370 are usually compressed into a narrow-diameter configuration (not shown), and advanced endoluminally to one of theartificial channels264 in the heart wall with a conventional or specialized delivery catheter (not shown). Alternatively, the electrosurgical probe may be designed to deliver and implant thestents370 at the target site. Thestents370 will typically comprise a resilient, radially compressible,tubular frame372 having aproximal end374, adistal end376, and anaxial lumen380 therebetween. Thetubular frame372 includes a plurality of openings or slots (not shown) that allowframe272 to be expanded radially outward into the enlarged configuration shown in FIG. 17 by conventional methods, such as shape memory alloys, expandable balloons, and the like. Thestent370 exerts a radial force against theinner channel walls382 to maintain lumen patency and/or mechanically augment luminal wall strength, thereby maintaining the blood flow from the ventricular cavity to the myocardium. Thestent370 may also include a graft orliner384 for inhibiting cell proliferation and occlusion through the openings and slots offrame372.

In a first embodiment shown in FIG. 17, the[0124]

stent

370 is introduced into theartificial channel264 during a percutaneous procedure as illustrated in FIG. 11. In this embodiment, the length of eachchannel264 and hence the length of eachstent370 extends only partially through the entire thickness ofheart wall260.

In a second embodiment shown in FIG. 22, the stent is introduced into the[0125]

artificial channel

The[0126]

stent frame

372 of the present invention is typically manufactured from a tubular member, such as tubing made out of shape memory alloy having elastic or pseudo-elastic properties, such as Nitinol™, Elgiloy™, or the like. Alternatively,stent frame372 may comprise malleable materials other than shape memory alloys, such as stainless steel. In the latter situation, stent frames372will preferably be expanded at the target site by conventional methods, e.g., an expandable balloon at the distal end of a catheter shaft. The tubular member is usually significantly smaller in diameter as compared to the final diameter of the stent in the expanded configuration withinchannel264. Slots may be cut into the tubular member via laser cutting methods, photo etching, or other conventional methods to form the separate stent frames372. For example, these methods include coating the external surface of a tube with photoresist material, optically exposing the etch pattern using a laser beam while translating and rotating the tubular member, and then chemically etching the desired slot pattern of the stent using conventional techniques. A description of this technique can be found in U.S. Pat. No. 5,421,955 to Lau, the complete disclosure of which is incorporated herein by reference. In other methods, laser cutting technology is used in conjunction with computer controlled stages to directly cut a pattern of slots in the wall of the hypodermic tubing to obtain the desired stent geometry. A description of a typical laser cutting method is disclosed in U.S. Pat. No. 5,345,057 to Muller, the complete disclosure of which is incorporated herein by reference.

In an exemplary configuration, the[0127]

stent frame

372 is formed from a resilient shape memory alloy material that is capable of being deformed by an applied stress, and then recovering to its original unstressed shape. The alloy material will usually exhibit thermoelastic behavior so that the stents will transform to the original unstressed state upon the application of heat (i.e., an A_ftemperature below body temperature). The stents may also exhibit stress-induced martensite, in which the martensite state is unstable and the prosthesis transforms back to the original state when a constraint has been moved (i.e., when the stent is released from an introducing catheter within a body lumen). The material for the shape memory alloy will be selected according to the characteristics desired of a particular prosthesis. Preferably, the shape memory alloy will comprise a nickel titanium based alloy (i.e., Nitinol™), which may include additional elements which affect the characteristics of the prosthesis, such as the temperature at which the shape transformation occurs. For example, the alloy may incorporate additional metallic elements, such as copper, cobalt, vanadium, chromium, iron, or the like.

It should be noted that the[0128]

stents

In another aspect, systems and apparatus of the present invention can be used to promote or increase blood flow to, or within, a connective tissue, such as a meniscus, a tendon, a ligament, and the like. For example, in one aspect the present invention can be used to selectively ablate a target tissue, and to create one or more channels or voids within a meniscus, a tendon, or other target tissue, such that blood can flow through the channel(s) or void(s). In one embodiment, the invention may be used to increase the blood supply within a meniscus of the knee. In another aspect, the invention can be used to promote vascularization, e.g., the formation of new blood vessels, in an avascular or sparsely vascularized tissue, such as a meniscus, a tendon, or other target tissue. In yet another aspect, the invention can be used to promote revascularization, e.g., the reestablishment of a blood supply in a target tissue. In one embodiment, increasing the blood flow to a target tissue may involve angiogenesis. According to one aspect of the invention, increasing the blood supply to a target tissue may involve promoting vascularization of the tissue by eliciting a wound healing response by the controlled application of electrical energy to one or more regions of the target tissue.[0129]

FIG. 24A is an anterior view of a[0130]

right knee

400 in flexion, with the patella omitted to illustrate themedial meniscus402 and thelateral meniscus404.Medial meniscus402 andlateral meniscus404 are located between thefemur406 and thetibia408. With reference to FIG. 24B, each of themedial meniscus402 and thelateral meniscus404 is a crescent-shaped fibrocartilaginous structure. The majority of the meniscus tissue has a very limited blood supply (this is particularly true for the inner portions orinner aspect402a,404aof the meniscus). For that reason, when damaged, the meniscus is unable to undergo the normal healing process that occurs in most other tissues of the body. In addition, with age, the meniscus begins to deteriorate, often developing degenerative tears. Typically, when the meniscus is damaged, the torn pieces begin to move in an abnormal fashion inside the joint. Because the space between the bones of the joint is very small, when the abnormally mobile piece of meniscal tissue (meniscal fragment) moves, it may become caught between the bones of the joint (femur and tibia). When this happens, the knee becomes painful, swollen, and lacks the mobility of a normal knee joint.

FIG. 25 schematically represents treatment of a meniscus with an[0131]

electrosurgical instrument

440, according to one embodiment of the invention. The peripheral portion of the meniscus, termed the menisco-capsular junction410 (FIG. 24B), has a richer blood supply than the inner portion. Accordingly, in one aspect the present invention provides systems and methods for increasing the blood supply to the inner portion of the meniscus by forming artificial channels or lumens, e.g., one or more channels extending from the menisco-capsular junction410 to the inner aspect of the meniscus, as will be described in detail hereinbelow (e.g., FIGS. 26A, 26B). Anelectrosurgical instrument440 may be introduced into the knee cavity either arthroscopically, or in an open procedure. In an arthroscopic procedure, the knee cavity is typically flooded with electricallyconductive fluid445, while in an open procedure, the fluid445 may be delivered to the target site (either viainstrument440, or from a separate fluid supply instrument). As shown,instrument440 is a bipolar probe having ashaft442, one or more active electrode(s)444 at the distal end ofshaft442, and a proximally spacedreturn electrode446. However, alternative configurations forinstrument440 are also possible under the invention.

[0132]

Shaft

442 typically has a maximum lateral dimension in the range of from about 3.0 to 1.0 mm, and often less than about 1.0 mm. A direction of advancement ofinstrument440, during ablation of meniscus tissue, is indicated by the arrow marked A. Active electrode(s)444 are positioned adjacent to a target area on theinner aspect402aofmeniscus402, and a high frequency voltage difference is applied between active electrode(s)444 and return electrode446 such that electric current flows through the electricallyconductive fluid445 therebetween. The high frequency voltage is sufficient to convert the electricallyconductive fluid445 between the target tissue and active electrode(s)444 into an ionized vapor, or plasma (not shown). As a result of the applied voltage difference between active electrode(s)444 and the target tissue (i.e., the voltage gradient across the plasma layer), charged particles (e.g., electrons) in the plasma are accelerated towards the tissue. At sufficiently high voltages, these charged particles gain sufficient energy to cause dissociation of the molecular bonds of target tissue components. This molecular dissociation is accompanied by the volumetric removal (i.e., ablative sublimation) of tissue, and the production of low molecular weight ablation by-products, e.g., gases, such as oxygen, nitrogen, carbon dioxide, hydrogen and methane.

Depending on the procedure, during application of the high frequency voltage between[0133]

active electrode

444 and returnelectrode446, the surgeon may translate the distal end ofshaft442 relative to the target tissue to form holes, channels, stripes, divots, craters or the like within the tissue. In the representative embodiment, the surgeon axially translates theactive electrodes444 into meniscus tissue, as the tissue is volumetrically removed, to form one or more channels (e.g.,channels424a-n, FIG. 26A) in themeniscus402. In one embodiment, channels formed in the meniscus according to the procedure described above are substantially cylindrical. Typically,channels424 have a diameter of less than about 2 mm, and usually less than about 1 mm. As described in detail hereinabove, one advantage of the present invention is the ability to precisely ablate channels or holes within a target tissue without causing necrosis or thermal damage to the underlying or surrounding non-target tissues.

With reference to FIG. 26A, the volumetric removal of meniscus tissue is performed in a controlled manner by careful manipulation of[0134]

instrument

440 to form a channel (e.g., channel424a) of a selected length and width. Thereafter,instrument440 is withdrawn from channel424a, andinstrument440 may be re-positioned with respect tomeniscus402, andinstrument440 again advanced intomeniscus402 for formation of a subsequent channel, e.g., channel424b. According to one embodiment of the invention, the length, or depth, of achannel424a-ncan be controlled with the aid of a sensing unit (e.g., FIG. 19) adapted for determining a boundary of the target tissue (e.g., meniscus inner or outer aspect,402a,402b). In one embodiment, such a sensing unit includes a sensing element, e.g., an ultrasonic transducer located onshaft442, substantially as described hereinabove with reference to FIGS. 18 and 19.

During the ablation process, the ablation by-products may be aspirated from the surgical site via an aspiration device (not shown). The aspiration device may be integral with[0135]

instrument

440, or may be on a separate instrument. The aspiration device may include a suction tube or lumen suitably coupled to a vacuum source. In addition, excess electrically conductive fluid, and other fluids (e.g., blood) may be aspirated from the target site to improve the surgeon's view of the surgical site. During ablation of the tissue, the residual heat generated by the current flux lines, will usually be sufficient to coagulate any severed blood vessels at the site. (Typically, the tissue is exposed to a temperature less than about 150° C.) If not, the surgeon may switch power supply28 (FIG. 1) into the coagulation mode by lowering the voltage to a level below the threshold for fluid vaporization, as discussed above. Thus, the invention can provide simultaneous ablation and hemostasis using a single instrument, resulting in less bleeding and facilitating the procedure.

Procedures which involve forming one or more channels in a meniscus, a tendon, or other poorly vascularized tissue, may be performed alone, or in combination with other arthroscopic procedures, such as a meniscus repair procedure. For example, in prior art meniscus repair procedures, implants are often used for arthroscopic fixation of meniscus lesions. In one conventional procedure, an arrow-like implant is inserted across a lesion to hold the inner and outer portions of the lesion together. The arrow-like implant may comprise a resorbable material that is absorbed into the body after the meniscus has healed. One such implant is called the Meniscus Arrow™ and is commercially available from Bionx Implants, Inc. (Blue Bell, Pa.).[0136]

According to one method of the present invention, treatment of the[0137]

meniscus

402,404 to improve the flow of blood thereto may be performed in conjunction with various procedures for repairing the meniscus. A longitudinal (“bucket-handle”)meniscus lesion420 is shown in FIG. 26A. Specifically, one or more artificial channels orlumens424a-nare created from theinner aspect402ato theouter aspect402bof the meniscus, as described hereinabove, to allow blood to flow fromouter aspect402bthroughchannels424a-ntoinner aspect402a. In an alternative embodiment, one or more artificial channels may be formed fromouter aspect402btoinner aspect402a(e.g.,channel424′, FIG. 26B). Three channels are shown in FIG. 26A, however, in practice a larger number of channels may be formed.

With reference to FIGS. 25 and 26A, distal end of[0138]

instrument

440 is usually advanced distally beyondlesion420 towardsouter aspect402b, which has a blood supply, to create at least one channel, e.g., channel424a, of suitable length and width to allow blood to flow into theinner aspect402a. The resulting increased blood flow within the meniscus, e.g.,402, promotes healing of any tears, ruptures, or other injury, (e.g., tear420, FIG. 26A). Applicant has found that systems, apparatus, and methods of the present invention can quickly and cleanly createsuch channels424 as well as holes, craters, furrows, and the like, in meniscus tissue and other hard connective tissue, using the cold ablation process (known as Coblation™) described herein. A more complete description of methods for forming holes or channels in tissue can be found in U.S. Pat. No. 5,683,366, the complete disclosure of which is incorporated herein by reference for all purposes.

Again with reference to FIG. 26A, after formation of one or more channels, e.g.,[0139]

channels

424a-n, via electrosurgical ablation of the target tissue, anelongate implant422 may be advanced through each of one or more ofchannels424a-n, such thatelongate implant422 extends acrosslesion420 to hold the meniscus in place during healing. In this situation,implant422 serves as a splint, bridginglesion420. In one aspect of the invention, a proportion ofchannels424a-nmay be left as voids, i.e., no implant is inserted into the distal portion ofchannels42a-n, in order to promote greater blood flow through the vacant channels.

According to another embodiment of the invention, an[0140]

elongate implant

422 inserted into achannel424a-n, may comprise a stent to promote patency of such channel(s). Thus, the present invention facilitates the insertion ofimplants422 into damaged tissue, and also increases blood flow to theinner aspect402aof themeniscus402. The use of stents to maintain patency of a channel formed in a target tissue using an electrosurgical device, is described hereinabove, e.g., with reference to FIGS. 17 & 22.

FIG. 26B schematically represents a procedure for forming one or more channels in a[0141]

medial meniscus

402 via localized electrosurgical ablation of meniscus tissue, according to another aspect of the invention. As shown, achannel424 is formed from theinner aspect402atowards theouter aspect402b. Such achannel424 may be formed by axial advancement of the shaft distal end of anelectrosurgical instrument440 towardsmeniscus402. As an example,instrument440 may have a configuration as shown in FIG. 25, includingshaft442, a distal electrode assembly comprising a terminal active electrode, or electrode array,444 and return electrode446 located proximal toactive electrode444. Concurrently with the axial advancement, or other manipulation, ofinstrument440, a high frequency voltage is applied betweenactive electrode444 and returnelectrode446, to effect the volumetric removal of tissue components, with the concomitant formation ofchannel424. Alternatively, or additionally, one or more channels (424′) may be formed fromouter aspect402btowardsinner aspect402a.

Channels

424,424′ may serve as conduits to increase the flow of blood within the meniscus.

Again with reference to FIG. 26B, in one embodiment, a relatively[0142]

short implant

421 may be inserted in a proximal portion of

channel

424,424′ to act as a hemostasis plug, and to prevent any flow of blood fromchannel424/424′ into the joint cavity.Implant421 may comprise a collagenous material, for example, substantially as described for hemostasis device480 (FIG. 21). In one embodiment, patency of one or

more channels

424,424′ may be maintained by insertion of a stent therein. In one aspect of the invention, a stent may be used in channel424 (orchannel424′) to maintain patency in a distal portion ofchannel424, in conjunction with a hemostasis plug (e.g., implant421) located in a proximal portion ofchannel424.

Although the above canalization procedures are described primarily with reference to forming channels within a meniscus of the knee, systems, apparatus, and methods of the invention are also applicable to the treatment of other joints, and other tissue, such as tendons and ligaments. Thus, apparatus and methods of the present invention can also be used to treat a broad range of musculoskeletal injuries and disorders, such as strains, sprains, tendinitis, fasciitis, arthritis, bursitis and tenosynovitis of various joints, including the shoulder, elbow, knee, ankle, and wrist.[0143]

According to one aspect of the invention, a connective tissue having an injury or disorder may be treated using an electrosurgical instrument, e.g.,[0144]

instrument

440, to stimulate or elicit the body's wound healing response in a region of the tissue thus treated. This wound healing response can result in a variety of metabolic, physiological, or anatomical changes, including the stimulation of greater blood flow, collagen growth, alteration of cellular function, or other metabolic events that promote healing and regeneration of injured tissue. In some embodiments, these induced changes may include increased cell metabolism, increased collagen synthesis in fibroblasts, transformation of fibroblasts to myofibroblasts, increased capillary formation with resultant enhanced microcirculation, and/or enhanced clearance of noxious substances associated with the inflammatory response. In other embodiments, the wound healing response can include an increased blood flow to, and vascularization or revascularization of, the treated region, thereby promoting healing and regeneration of injured tissue. In yet other embodiments, the wound healing response can include stimulating the growth of new collagen in the treatment area.

In a specific embodiment, blood flow in a tendon is increased by creating damage to the tendon to invoke a wound healing response. One of the more common afflictions to the tendons is tendinitis, which is an inflammatory condition characterized by pain at tendinous insertions into bone. Common sites of tendonitis include the rotator cuff of the shoulder, insertion of the wrist extensors (tennis elbow), flexors at the elbow, patellar, and popliteal tendons, the iliotibial band at the knee, insertion of the posterior tibial tendon in the leg (shin splints), the wrist (carpal tunnel syndrome), and the Achilles tendon at the heel. Treatment of tendons, according to the invention, increases blood flow therein, e.g., via canalization or by stimulating vascularization thereof, in order to expedite and improve the healing process.[0145]

The methods of the present invention may be performed alone, or in combination with other open or arthroscopic procedures to treat a tendon. For example, FIG. 27 shows a simplified view of an[0146]

elbow joint

500. A common disorder of the elbow is known as tennis elbow, or lateral epicondylitis. When a person has tennis elbow, there is often pain and inflammation in the joint due to tendon damage. The damage to the tendon, e.g.,tendon502, typically consists of tiny tears that allow collagen to leak from the injured area and cause inflammation of the tendon. The inflammation can cut off the flow of blood and pinch the radial nerves. Because tendons have much less blood flow as compared with most tissues, e.g., muscles, tendons generally take much longer to heal as compared with most other tissues of the body. If conventional surgical intervention is required to treat a damaged tendon, a patient typically requires about three months to recover.

The present invention, in one aspect, improves and expedites healing, and increases the blood supply to tendon tissue by heating the tendon so as to cause neovascularization. In one embodiment, such heating causes controlled damage to the tendon tissue. In exemplary embodiments, the heating of the tendon is effected by the bipolar or monopolar delivery of RF energy. It should be appreciated, however, that while the methods of the present invention are described primarily with respect to the use of bipolar or monopolar RF energy, that alternative heating methods can be used to treat the tendon tissue. For example, instead of RF heating, the tendons can be treated with resistive heating, or the like.[0147]

In some embodiments, methods for promoting healing of a tendon include creating artificial channels, lumens, or craters within the tendon to expose internal portions of the tendon. Such openings facilitate the neovascularization of the inner portions of the tendon. Applicants have found that the creation of damage in tissue, including tendon tissue, elicits a wound healing response and causes an inflammatory cell response so that blood clot(s) fill the opening(s) in the tendon. Accordingly, blood products and the inflammatory process can be the major elicitors of angiogenesis within the tendon. In one embodiment, following electrosurgical treatment of tendon tissue, a vascular scar is formed, which in its early stages is hypoxic, and triggers neovascularization in the tendon. In some embodiments, the tendon is heated and damaged only along the surface. Applicants believe that heat alone, applied in a controlled manner, and typically at a temperature below about 150° C., may be sufficient to trigger vascularization of the tendon.[0148]

According to one method of the present invention, treatment of a tendon to stimulate its vascularization may be performed in conjunction with a surgical repair procedure. In one embodiment, one or more artificial voids, channels, lumens, or the like, are created in the tendon to increase blood flow within the tendon. Such channels may be formed either before or after the tendon, e.g.,[0149]

tendon

502, has been otherwise repaired or treated. For the formation of an artificial channel or void in a tendon, according to the instant invention, an electrosurgical instrument, e.g.,instrument440 may be introduced into a patient, e.g., percutaneously, arthroscopically or through an open procedure, such that the distal end ofinstrument440 is in at least close proximity to a target site on the tendon to be treated. For example,instrument440 may be introduced arthroscopically into the joint cavity of the elbow (FIG. 27). Typically,electrosurgical instrument440 comprises a bipolar probe having a distal electrode assembly including one or moreactive electrodes444 and a proximally spaced return electrode446 (FIG. 25). The active electrode(s)444 may be in the form of an electrode array, as described hereinabove (e.g., with reference to FIGS.6-10). In arthroscopic procedures, the joint cavity can be flooded with an electrically conductive fluid, e.g., isotonic saline. In an open procedure, electrically conductive fluid may be delivered to the target site viainstrument440, or from a separate fluid supply device (not shown). In either situation, electrically conductive fluid is provided at the distal end ofinstrument440 so as to provide a current flow path between active electrode(s)444 and returnelectrode446.

During a tendon vascularization procedure according to the invention, active electrode(s)[0150]444 are typically positioned adjacent to a target site on thetendon502, and a high frequency voltage is applied between active electrode(s)444 and return electrode446 such that electric current flows through the electrically conductive fluid. The high frequency voltage is sufficient to convert the electrically conductive fluid between the target tissue and theactive electrode444 into an ionized vapor, or plasma (not shown). As a result of the applied voltage difference between active electrode(s)444 and thetendon502, charged particles in the plasma are accelerated towards the tendon. At sufficiently high voltage differences, the charged particles gain sufficient energy to cause dissociation of the molecular bonds of the tendon tissue components. The molecular dissociation is accompanied by the volumetric removal (i.e., ablative sublimation) of tendon tissue and the production of low molecular weight ablation by-products.

With reference to FIG. 28A, an electrosurgical device, (e.g.,[0151]

instrument

440, FIG. 25), can be axially advanced into a tendon or other tissue to form one ormore channels514 therein. Alternatively, or in addition,instrument440 can be manipulated to form a variety of other openings or voids through a tendon, or on a surface of a tendon. For example, FIG. 28B shows a bore orhole516 throughtendon502, whereas FIG. 28C illustrates a furrow orcrater518 formed in the surface oftendon502. During formation of such channels or voids, e.g.,514,516,518,internal portions512 of the tendon are exposed to heat as a result of radio frequency voltage applied between active and return

electrodes

444,446, respectively. Channels or voids514,516,518 created for the purpose of vascularization oftendon502 will typically have a width or diameter in the range of from about 0.5 mm to about 2.0 mm, usually less than about 1 mm, and most typically about 0.5 mm. Furthermore, opening(s)514,516,518 will typically have a depth in the range of from about 0.5 mm to 4.0 cm, and usually from about 1.0 mm to 2.0 mm. The channels, holes, or craters514,516,518 can be formed randomly along the tendon, at regular intervals along the tendon, or may be strategically located adjacent to a region of the tendon that has undergone repair, for example, repair involving a conventional procedure, such as suturing. It should be appreciated, that the size, depth, number, and spacing of the channel(s), hole(s), and crater(s) may vary depending on the tendon being treated, the condition of the tendon, and the like.

During the volumetric removal of tendon tissue, ablation by-products, together with any excess electrically conductive fluid, and other fluids (e.g., synovial fluid, blood), may be aspirated from the surgical site, substantially as described hereinabove. During ablation of the tissue, the residual heat generated by the current flux lines, will usually be sufficient to coagulate any severed blood vessels at the site. If not, the surgeon may switch the power supply[0152]28 (FIG. 1) into the coagulation mode, as discussed above, to effect hemostasis of the treated tissue.

As a further example, systems, apparatus, and methods of the present invention may be used to improve the blood supply and increase the vascularity of the patellar tendon and/or the patellar ligament. FIG. 29 is an anterior view of the right leg showing the[0153]

patellar tendon

522 and thepatellar ligament524 in relation to thepatella526. As described hereinabove, the instant invention may be used for vascularization of tissue, such as a tendon, or a ligament, in conjunction with other surgical procedures. When the patellar tendon or patellar ligament sustain a tear or rupture due to injury, thepatella526 may lose its anchoring support to thetibia528. Such an injury requires surgical intervention. For example, an open procedure may be performed to reattach the patella to thetibia528, to repair the patellar tendon, or to perform other repairs. After the patella and/or patellar tendon has been repaired, the surgeon can use the systems, apparatus, and methods of the present invention to increase the vascularity of the patellar tendon and/or the patellar ligament. For example, after the patellar tendon has been repaired, anelectrosurgical instrument440 can be positioned adjacent to thepatellar tendon522. An electrically conductive fluid may be delivered to the target site viainstrument440, or from a separate fluid supply device (not shown), to provide a current flow path between active electrode(s)444 and returnelectrode446. A high frequency voltage difference is applied between active electrode(s)444 and return electrode446 such that electric current flows through the electrically conductive fluid. As described above, the high frequency voltage is sufficient to convert the electrically conductive fluid between the target tissue andactive electrode444 into an ionized vapor, or plasma (not shown) so as to cause localized molecular dissociation of the tendon tissue. The molecular dissociation is accompanied by the volumetric removal (i.e., ablative sublimation) of the tendon tissue, and the production of low molecular weight ablation by-products. In one embodiment, the surgeon advances a distal surface of the active electrode(s)444 into the tendon tissue to form openings such as holes, channels, stripes, divots, craters, or the like, to promote blood flow within the tendon. In one embodiment, treatment of a tissue to improve blood flow thereto is performed in conjunction with a surgical repair, of the tissue, and thereafter one or more channels or voids may be placed adjacent to the surgical repair site so as to promote blood flow to the repair site, thereby stimulating the healing process.

It should be appreciated that the size and shape of the electrosurgical systems and devices used to canalize or vascularize the tendon will vary depending on the type of procedure (i.e., creation of holes, channels, or craters) and the position of the tendon to be accessed. If the tendon is treated endoscopically or arthroscopically through a small joint, a smaller wand-type electrosurgical probe will typically be used to perform the vascularization. Alternatively, if the tendon is treated through an open procedure, a larger probe may be used. Although certain of the treatments for increasing blood flow within a tissue are described hereinabove primarily with respect to a tendon of the elbow, apparatus and methods of the invention are also applicable to the treatment of other joints, and to target tissue other than tendons.[0154]

FIG. 30 shows a block diagram representing an[0155]

electrosurgical system

600 for treatment of musculoskeletal disorders, according to another embodiment of the instant invention.System600 generally comprises aprobe610 including ashaft612 having anelectrode assembly614 disposed thereon.Electrode assembly614 typically includes a return electrode mounted onshaft612, and at least one active electrode, or a plurality of active electrodes which may be configured as an electrode array (e.g., FIGS.6-10). Typically, the active electrode or electrode array is disposed on the distal end ofshaft612. An exemplary configuration forelectrode assembly614 is shown in FIG. 25. Typically,shaft612 has a length in the range of from about 5 cm to 20 cm, more typically from about 8 cm to 18 cm.Probe610 may further include aconnector unit616, in communication withelectrode assembly614, for couplingelectrode assembly614 to a highfrequency power supply640.

[0156]

System

600 may include anarthroscope630 adapted for accommodatingshaft612 and for passing at least the distal end ofshaft612 therethrough, whereby a target tissue, e.g., a tendon or a meniscus, within a joint cavity can be accessed byelectrode assembly614.System600 may further include asensing unit620 adapted for determining a boundary of a tissue in relation to the distal end of shaft612 (e.g., FIG. 19). In one embodiment, sensingunit620 may include an ultrasonic transducer disposed on the distal end ofshaft612, generally as described hereinabove with reference to FIGS.18 and/or19. Thus, sensingunit620 may include an external (i.e., non-integral with probe610) ultrasonic generator coupled to the ultrasonic transducer. In one embodiment, sensingunit620 may be used to measure the thickness of a tissue, e.g., a tendon, or a meniscus of the knee, at a target site.

In one embodiment,[0157]

system

600 includes an adjustablemechanical stop618, which can be adjusted, according to the thickness of a target tissue as measured by sensingunit620, to limit the maximum travel distance ofshaft612 in relation to the target tissue. In this manner, the depth of a hole, or the length of a channel (e.g.,channel424, FIG. 26B), can be precisely controlled. In one embodiment,mechanical stop618 is coupled toshaft612. In an alternative embodiment (not shown in FIG. 30),mechanical stop618 may be integral witharthroscope630, for example, in a manner analogous to the arrangement ofmechanical stop352 in relation tohandpiece340 of catheter200 (FIG. 11). In another embodiment, sensingunit620 is coupled topower supply640, andsystem600 is configured to shut off power toelectrode assembly614 at a pre-selected location of the shaft distal end with respect to a boundary of a target tissue.

While the exemplary embodiments of the present invention have been described in detail, by way of example and for clarity of understanding, a variety of changes, adaptations, and modifications will be apparent to those of skill in the art. Therefore, the scope of the present invention is limited solely by the appended claims.[0158]

Claims

What is claimed is:

1. A method of promoting blood flow to a target tissue, the method comprising:

positioning an active electrode in at least close proximity to the target tissue; and

applying a high frequency voltage to the active electrode, the high frequency voltage being sufficient to promote vascularization of the target tissue, wherein the target tissue is selected from the group consisting of a tendon, a ligament, and a meniscus.

2. The method ofclaim 1, wherein the vascularization of the target tissue is at least partly accomplished by volumetric removal of a portion of the target tissue.

3. The method ofclaim 2, further comprising: advancing at least a distal surface of the active electrode into a space vacated by the volumetrically removed target tissue.

4. The method ofclaim 1, wherein said applying step comprises applying the high frequency voltage between the active electrode and a return electrode, the high frequency voltage being sufficient to volumetrically remove at least a portion of the target tissue.

5. The method ofclaim 4, wherein the return electrode is located on an external surface of a patient's body.

6. The method ofclaim 4, wherein the return electrode and the active electrode are both located on an electrosurgical probe.

7. The method ofclaim 4, further comprising: placing an electrically conductive fluid between the active electrode and the return electrode, the electrically conductive fluid providing a current flow path between the active electrode and the return electrode.

8. The method ofclaim 7, wherein the electrically conductive fluid comprises isotonic saline.

9. The method ofclaim 1, wherein the vascularization of the target tissue is at least partly accomplished by forming a void within the target tissue.

10. The method ofclaim 9, wherein the comprises a channel, a hole, or a furrow within the target tissue.

11. The method ofclaim 9, wherein the void has a lateral dimension in the range of from about 0.5 mm to about 2.0 mm.

12. The method ofclaim 9, wherein the void has a depth in the range of from about 0.5 mm to about 4.0 cm.

13. The method ofclaim 1, wherein the active electrode comprises a single electrode adjacent to a distal end of an electrosurgical probe.

14. The method ofclaim 6, wherein the electrosurgical probe includes an electrode array comprising a plurality of electrically isolated active electrodes, and wherein said applying step comprises applying the high frequency voltage to the electrode array.

15. The method ofclaim 1, further comprising:

providing an electrically conductive fluid between the active electrode and the target tissue.

16. The method ofclaim 1, further comprising: introducing at least a distal end of an electrosurgical probe into a patient's knee, shoulder, or elbow; wherein said positioning step comprises positioning the distal end of the probe in at least close proximity to the tendon within the knee, the shoulder, or the elbow.

17. A method of vascularizing a region of a tendon, comprising:

positioning a distal end of an electrosurgical instrument adjacent to the tendon; and

applying energy to the tendon to heat the tendon to promote blood flow to the tendon.

18. The method ofclaim 17, wherein the energy applied is sufficient to damage the tendon.

19. The method ofclaim 17, wherein said applying step is sufficient to remove a portion of the tendon.

20. The method ofclaim 17, wherein said applying step comprises applying a high frequency voltage difference between an active electrode located on the electrosurgical instrument and a return electrode.

21. The method ofclaim 20, further comprising providing an electrically conductive fluid between the active electrode and the return electrode to provide a current flow path therebetween.

22. The method ofclaim 17, further comprising forming a hole in the tendon.

23. The method ofclaim 17, further comprising forming a channel in the tendon.

24. A method of vascularizing a tendon, the method comprising:

positioning an active electrode in at least close proximity to the tendon; and

heating the tendon via a voltage applied to the active electrode so as to damage the tendon, wherein the damage is sufficient to cause a neovascular response and increased blood flow to the tendon.

25. An electrosurgical device for vascularization of a tendon, the device comprising:

an instrument shaft having proximal and distal end portions and an active electrode disposed on the distal end portion; and

a connector disposed on or within the shaft, the connector adapted for coupling the active electrode to a high frequency power supply, the high frequency power supply adapted for applying a high frequency voltage to the active electrode, the high frequency voltage being sufficient to effect the volumetric removal of tendon tissue adjacent to the active electrode and to promote blood flow to the tendon.

26. The device ofclaim 25, further comprising a return electrode adapted for coupling to the high frequency power supply, the high frequency power supply adapted for applying a high frequency voltage difference between the return electrode and the active electrode, the voltage difference being sufficient to effect the volumetric removal of the tendon tissue adjacent to the active electrode.

27. The device ofclaim 26, wherein the return electrode is disposed on the instrument shaft at a location proximal to the active electrode.

28. The device ofclaim 26, wherein the return electrode is a dispersive pad in contact with an external body surface of a patient.

29. The device ofclaim 26, further comprising a fluid delivery element having an opening adjacent to the active electrode, the opening of the fluid delivery element for delivering electrically conductive fluid between the active electrode and the tendon tissue.

30. The device ofclaim 29, wherein the fluid delivery element is configured to provide a current flow path between the active electrode and the return electrode.

31. The device ofclaim 25, wherein the maximum lateral dimension of the distal end portion of the instrument shaft is less than about 1.0 mm.

32. The device ofclaim 25, wherein the active electrode is substantially surrounded by an electrically insulating support.

33. The device ofclaim 25, wherein the instrument shaft is configured for arthroscopic delivery into a joint cavity, the joint selected from the group consisting of a knee, a shoulder, and an elbow.

34. The device ofclaim 25, wherein the distal end portion of the instrument shaft is sized for advancing into a space vacated by the volumetrically removed tissue.

35. The device ofclaim 34, wherein the space is a channel having a maximum lateral dimension of about 2.0 mm.

36. The device ofclaim 25, further comprising an electrode array disposed at or near the distal end of the instrument shaft, the electrode array including a plurality of electrically isolated active electrodes, wherein current flow from at least two of the plurality of electrically isolated active electrodes is independently controlled based on impedance between each of the at least two active electrodes and a return electrode.

37. The device ofclaim 25, further comprising a return electrode coupled to the high frequency power supply, the high frequency power supply adapted for applying a voltage difference between the return electrode and the active electrode, the voltage difference being sufficient to promote vascularization of the tendon tissue.

38. A method of vascularizing a target tissue, the method comprising:

a) positioning an electrosurgical probe in at least close proximity to the target tissue; and

b) applying sufficient radio frequency energy to the target tissue to promote blood flow to the target tissue, wherein the target tissue is selected from the group consisting of a tendon, a ligament, and a meniscus.

39. The method ofclaim 38, wherein said step b) comprises volumetrically removing a portion of the target tissue.

40. The method ofclaim 38, wherein said step b) comprises forming at least one void within the target tissue.

41. The method ofclaim 38, wherein said step b) comprises forming at least one channel in the target tissue.

42. The method ofclaim 38, wherein said step b) comprises inducing a wound healing response in the target tissue.

43. The method ofclaim 38, wherein said step b) comprises heating the target tissue, and the heating promotes vascularization of the target tissue.

44. The method ofclaim 38, wherein said step b) induces angiogenesis in the target tissue.

45. A method of treating a target tissue with an electrosurgical probe, the method comprising:

a) forming one or more channels within the target tissue by the application of electrical energy thereto; and

b) inserting an implant into at least one of the one or more channels.

46. The method ofclaim 45, wherein the target tissue is selected from the group consisting of a tendon, a ligament, and a meniscus.

47. The method ofclaim 45, wherein the electrical energy applied in said step a) comprises a radio frequency voltage in the range of from about 10 volts RMS to about 500 volts RMS, at a frequency in the range of from about 50 kHz to about 500 kHz.

48. The method ofclaim 45, wherein the implant comprises a plug.

49. The method ofclaim 45, wherein the implant promotes hemostasis in the region of the one or more channels.

50. The method ofclaim 45, wherein the implant comprises a stent.

51. The method ofclaim 45, wherein said step a) comprises inserting a stent into a distal portion of the at least one of the one or more channels, and the method further comprises the step of:

c) inserting a hemostasis plug in a proximal portion of the at least one of the one or more channels.

52. The method ofclaim 45, wherein the implant serves as a splint.

53. The method ofclaim 45, wherein the target tissue contains a lesion, and the implant bridges the lesion.

54. The method ofclaim 45, wherein the target tissue contains a lesion, and the one or more channel extends across the lesion.

55. The method ofclaim 54, wherein the target tissue comprises a medial meniscus or a lateral meniscus, and the lesion comprises a tear.

56. The method ofclaim 45, wherein the probe includes a shaft having a distal end, an electrode assembly disposed on the shaft distal end, and a sensing element, the sensing element adapted for determining a location of a boundary of the target tissue with respect to the shaft distal end.

57. A method of vascularizing a target tissue, the method comprising:

a) positioning an active electrode in at least close proximity to the target tissue at a first location;

b) applying a high frequency voltage to the active electrode, the high frequency voltage being sufficient to form a first channel within the target tissue at the first location;

c) re-positioning the active electrode in at least close proximity to the target tissue at a subsequent location;

d) applying the high frequency voltage to the active electrode, the high frequency voltage being sufficient to form a subsequent channel within the target tissue at the subsequent location; and

e) sequentially repeating said steps c) and d) until a suitable number of channels have been formed within the target tissue.

58. The method ofclaim 57, wherein the target tissue is selected from the group consisting of a tendon, a ligament, and a meniscus.

59. The method ofclaim 57, further comprising:

f) inserting an implant in at least one of the number of channels.

60. The method ofclaim 59, wherein the implant comprises a device selected from the group consisting of: a stent, a splint, or a hemostasis plug.

61. The method ofclaim 59, wherein the implant comprises an elongate device adapted for affixing a portion of severed tissue to a second portion of tissue.

62. The method ofclaim 61, wherein the target tissue is the meniscus of the knee.

63. The method ofclaim 57, wherein the first channel and the subsequent channel are formed via molecular dissociation of target tissue components.

64. The method ofclaim 63, wherein the molecular dissociation of target tissue components is plasma-induced.

65. The method ofclaim 64, wherein the plasma is generated by high electric field intensities in the presence of an electrically conductive fluid, the high electric field intensities located at a surface of the active electrode.

66. An electrosurgical system for treating a target tissue of a joint, comprising:

a probe including a shaft having a shaft distal end, and an electrode assembly disposed on the shaft distal end; and

a sensing unit for determining a location of a boundary of the target tissue, wherein the target tissue comprises a tendon, a ligament, or a meniscus.

67. The system ofclaim 66, further comprising:

an arthroscope adapted for accommodating the shaft distal end and for passing the shaft distal end therethrough.

68. The system ofclaim 66, wherein the shaft has a length in the range of from about 5 cm to 20 cm.

69. The system ofclaim 66, wherein the sensing unit includes an ultrasonic transducer disposed on the shaft distal end.

70. The system ofclaim 69, wherein the sensing unit further includes an ultrasonic generator coupled to the ultrasonic transducer.

71. The system ofclaim 66, wherein the sensing unit is adapted for determining a location of a boundary of the target tissue.

72. The system ofclaim 66, further comprising an adjustable mechanical stop adapted for adjusting the maximum travel distance of the electrosurgical probe within the joint.

73. The system ofclaim 66, further comprising a high frequency power supply coupled to the electrode assembly for applying a high frequency voltage between an active electrode and a return electrode, the sensing unit coupled to the high frequency power supply, and the electrosurgical system configured to shut off power from the high frequency power supply to the electrode assembly according to a preselected location of the shaft distal end with respect to the target tissue.

74. An electrosurgical probe, comprising:

a shaft having a shaft proximal end portion and a shaft distal end portion;

an electrode assembly disposed on the shaft distal end portion; and

a sensing element disposed on the shaft.

75. The probe ofclaim 74, wherein the sensing element is disposed on the shaft distal terminus, and the probe is adapted for manipulation within a joint cavity.

76. The probe ofclaim 74, wherein the shaft distal end portion is adapted for arthroscopic insertion into a joint cavity, the joint selected from the group consisting of a knee, an elbow, a wrist, and a shoulder.

77. The probe ofclaim 74, wherein the shaft distal end portion is adapted for passage through an arthroscope.

78. The probe ofclaim 74, wherein the sensing element comprises an ultrasonic transducer adapted for measuring a distance from the shaft distal end portion to a boundary of a target tissue, and the target tissue selected from the group consisting of: tendon tissue, ligament tissue, and meniscus tissue.