Patent Publication Number: US-6656173-B1

Title: Method and device for enhancing vessel occlusion

Description:
This application is a continuation of U.S. patent application Ser. No. 08/605,765, filed Feb. 22, 1996, now issued as U.S. Pat. No. 6,270,495, the entire disclosure of which is expressly incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to methods and devices for the selective occlusion of body lumens. More particularly, the present invention relates to methods and devices for applying high frequency electrical energy to vaso-occlusion elements within the body lumen to enhance fibrogenic occlusion of the body lumen. 
     The selective occlusion of blood vessels in a patient is a part of many modem therapeutic treatments, including the control of internal bleeding, the occlusion of blood supply to tumors, the isolation of diseased body organs prior to removal, the relief of blood pressure in a region of aneurism, and the like. While such procedures rely generally on the blockage of arteries, the selective occlusion of veins is also useful in procedures such as veiniotomy. 
     The selective occlusion of blood vessels can be achieved by a variety of specific techniques. One such technique involves mechanically clamping or occluding the target site within the blood vessel. For example, in open surgical and endoscopic procedures, the body vessel can be externally clamped and radiofrequency energy applied. While the external procedures can be very effective, it requires external access to the lumen and is unsuitable for endoluminal techniques. 
     Mechanical endoluminal techniques for selective vessel occlusion are also in use. Such techniques include the use of detachable balloons, embolic and vaso-occlusion coils, and the like to physically block the vessel lumen. Detachable balloons are typically advanced to the vessel site at the end of a catheter and inflated with a suitable fluid, such as saline, x-ray contrast or a polymerizable resin, and released from the end of the catheter. These detachable balloons, however, are difficult to deliver and may not be suitable for permanent implantation unless they are used with the polymerizable resin. In addition, the catheter or the balloon can rupture or release prematurely during filling, leaking monomer resin into the vasculature. 
     Embolic or vaso-occlusion coils are typically introduced through a catheter in a stretched linear form, and assume a relaxed, helical shape when released into a vessel. One of the limitations of these coils is that recanalization of the occlusion site can occur when the initial blood clot is broken down by the body&#39;s natural anticoagulant mechanism (i.e., resorption of the clot). In addition, once the embolic coils are released by the introducer catheter, they are no longer under control and they frequently migrate from the point of initial implantation. 
     To completely arrest the flow of blood in a vessel and to inhibit recanalization, current methods of coil embolization typically require the use of several embolic coils at the target site in the blood vessel. In this “nesting technique”, the embolic coils are deposited within a vessel to create a mechanical “plug”. It has been found, however, that the use of several coils does not always prevent recanalization of the blood vessel, particularly in larger, high flow vessels. Moreover, it often takes a relatively long time for the blood vessel to completely occlude. Therefore, the embolic coils may often migrate into a non-target site prior to vessel occlusion, particularly in larger or high flow vessels. Multiple coils are also more expensive than a single coil and they require more time to position within the vessel, thereby further increasing the cost of the procedure and prolonging the patient&#39;s exposure to the fluoroscope. 
     Of particular interest to the present invention, the use of monopolar and bipolar radiofrequency devices has been proposed for the occlusion of body vessels from a surrounding lumen or body cavity. For example, U.S. Pat. No. 5,403,311 describes control of vessels bleeding into a body lumen using electrosurgical electrodes which puncture the vessel from within a larger lumen enclosing that vessel. Catheters for radiofrequency injury and occlusion of the cystic duct are described in Becker et al. (1989)  Radiology  170:561-562 and (1988)  Radiology  167:63-68 and Tanigawa et al. (1994)  Acta Radiologica  35:626-628. Methods and catheters for electrosurgical endovascular occlusion are described in Brunelle et al. (1980) Radiology 137:239-240; Cragg et al. (1982)  Radiology  144:303-308; and Brunelle et al. (1983) Radiology 148:413-415. Such techniques, however, have not generally been useful in large or high flow blood vessels. 
     For these reasons, it would be desirable to provide improved methods and devices for endoluminal occlusion of body lumens, and particularly of blood vessels, for use in the procedures described above. Such methods and devices should provide effective occlusion of large or relatively high flow body lumens as well as small body lumens. Preferably, the methods and devices will permit the physician to re-access the occlusion site, to correct recanalization and/or to enhance the occlusion of this site to prevent subsequent recanalization of the body lumen. 
     2. Description of the Background Art 
     Methods and devices for implanting vaso-occlusive elements, such as coils, in blood vessels and other lumen are described in U.S. Pat. Nos.  5,354,295; 5,350,397; 5,312,415; 5,261,916; 5,250,071; 5,234,437; 5,226,911; 5,217,484; 5,122,136; 5,108,407; `4,994,069 ; and 3,868,956; and published PCT applications WO 94/11051; WO 94/10936; WO 94/09705; WO 94/06503; and WO 93/06884. Some of the devices described in the above listed patents and published applications suggest passing direct current through the element to enhance blood clotting. 
     Electrosurgical probes for electrosurgical, electrocautery, and other procedures are described in U.S. Pat. Nos. 5,405,322; 5,385,544; 5,366,490; 5,364,393; 5,281,216; 5,236,410; 4,685,459; 4,655,216; 4,582,057; 4,492,231; 4,209,018; 4,041,952; 4,011,872; 4,005,714; 3,100,489; 2,022,065; 1,995,526; 1,943,543; 1,908,583; and 1,814,791; and published Japanese application 2-121675; published German applications DE 4139029; DT 2646228; and DT 2540968; and published PCT applications WO 95/02366 and WO 93/01758. 
     A method and system employing RF energy for the direct occlusion of blood vessels and other body lumens are described in co-pending application Ser. No. 08/488,444 filed on Jun. 7, 1995 (attorney docket No. 16807-3), the full disclosure of which is incorporated herein by reference. See also the patent and publications described in the Field of the Invention above. 
     SUMMARY OF THE INVENTION 
     Methods and apparatus are provided for deploying vaso-occlusive elements into body lumens, such as blood vessels, to occlude a target site within the lumen and for enhancing the occlusion of body lumens that already have vaso-occlusive elements deployed therein. The technique involves applying high frequency electrical energy to an electrically conductive, vaso-occlusive element and generating a thermal reaction at the target site to damage the luminal wall and induce fibrogenic occlusion of the blood vessel around the vaso-occlusive element. The vaso-occlusive element, which is typically an electrically conductive wire coil, helps reduce blood flow within the vessel and provides a larger surface for energy transfer between the electrical energy source and the tissue wall and surrounding blood. The high frequency electrical energy, typically radiofrequency current, is usually sufficient to induce local heating of the luminal wall and also to enhance coagulation of the surrounding blood, thereby initiating clotting. The thermally injured wall then contributes to subsequent fibrosis, thus permanently occluding the lumen. 
     The vaso-occlusive coil typically has a relatively low electrical resistance so that the high frequency electrical energy flows directly through the vaso-occlusive coil to the luminal wall (i.e., without substantially heating the coil). The electrical energy heats the luminal wall, thereby causing damage and subsequent fibrogenic occlusion of the target site. Alternatively, the vaso-occlusive coil may comprise sufficient electrical resistance such that a portion of the high frequency electrical energy is transferred directly to the coil (rather than the luminal wall) to heat the coil and enhance occlusion around the coil. In this case, the vaso-occlusive coil will preferably have an electrical resistance slightly less than the tissue wall to ensure that the electrical energy flows through at least a substantial portion of the coil. 
     In one aspect, the method comprises contacting a vaso-occlusive coil that is already deployed at a target site within a body lumen with at least one electrode and applying the high frequency electrical energy to the coil in a monopolar or bipolar fashion. Preferably, the energy is applied in a monopolar mode by contacting the patient&#39;s body with a second, dispersive or return, electrode and then delivering a high frequency current to the first or active electrode, through at least a portion of the vaso-occlusive coil, the surrounding tissue, and finally to the second electrode. For bipolar operation, a separate second electrode may be provided on the catheter, typically spaced proximally from the first electrode so that it will be located within the body lumen. The second electrode will usually be spaced a distance of about 2 mm to 10 cm from the active electrode. 
     The first electrode will usually be disposed on the distal end of an intravascular catheter. The catheter can be percutaneously introduced via well-known procedures and advanced to the target site in a body lumen in a known manner, typically over a guide wire. The first electrode can be engaged against the vaso-occlusive coil in a variety of ways. For example, the electrode (and optionally a pair of electrodes for bipolar operation) can simply be disposed at a distal location on the catheter which will contact the vaso-occlusive coil when the catheter is advanced through the body lumen to the target site. 
     Alternatively, the electrode may be provided by a separate member, such as an insulated conventional or specialized guide wire, or a positioner device, which may be insulated by the catheter body. In use, the guideline positioner is extended distal to the catheter body, placed against the vaso-occlusive coil, and the radiofrequency current is applied thereto. In the latter case, a distal portion of the positioner may comprise the active electrode, while the return electrode is located on the catheter or placed externally on the patient. 
     In other aspects, the method may comprise deploying the vaso-occlusive coil at the target site within the body lumen, adjusting the position of an already deployed vaso-occlusive coil within the target site, or repositioning the coil to another location in the vasculature. For initial deployment, the vaso-occlusive coil will be releasably engaged by the positioner and optionally advanced through the axial lumen of the catheter for deployment. For repositioning, the coil may be captured by the positioner and partially or fully retracted into the axial lumen for adjusting coil placement or repositioning the coil to another location. Typically, the coil will be repositioned when previous attempts to occlude a target site have not completely succeeded and the coil is not fixed at the site. A particular advantage of the present invention is that the coil can be held in place within the body lumen by the positioner until the high frequency voltage or current has been applied thereto. Once the voltage has generated a sufficient thermal reaction to induce spasm and localized edema/narrowing of the vessel (and subsequent fibrogenic occlusion of the lumen) around the coil, the coil will be released from the positioner and the positioner removed from the vasculature. In this manner, the fibrogenic occlusion of the blood vessel will slowly and permanently lock the coil in position at the occlusion site, while the coil is temporarily held in place by the spasm or narrowing of the vessel. This prevents or at least inhibits migration of the coil downstream through the body lumen after it has been released by the positioner. 
     Devices according to the present invention will generally comprise a shaft having proximal and distal ends and an axial lumen therebetween. For vascular applications, the shaft will typically be a non-conductive, tubular catheter body capable of being introduced to the vascular system over a guide wire in a conventional manner. A positioner is slidably disposed within an axial lumen of the shaft and includes a first electrode at the distal end for contacting the vaso-occlusive coil. The positioner may be a guide wire that is also used for advancing the shaft through the body lumen or a separate device inserted into the catheter body after it has been advanced to the target site. The first electrode is coupled to a source of high or radiofrequency electrical energy by the positioner itself, an electrical conductor extending through the positioner, or through the catheter body. 
     The positioner preferably comprises a conductive shaft having an outer insulating sheath extending to a distal portion of the shaft. The distal portion includes an engaging element for releasably engaging the vaso-occlusive coil to either deploy the coil at the target site or to reposition a deployed coil to another location in the patient&#39;s vasculature. In one embodiment, the engaging element comprises a pair of opposed elements which can be selectively opened and closed to engage and release a proximal portion of the coil. Usually, the opposed elements will be openable jaws that are actuated manually with an actuator located on a handle at the proximal end of the positioner. In another embodiment, the distal engaging element comprises a plurality of resilient hooks that are biased away from each other and held together by the catheter body. In yet another embodiment, the distal engaging element comprises a distal pusher element adapted to contact the coil and push it through the catheter body to the target site. 
     The system of the present invention will also include a second electrode operatively coupled to the high frequency energy source. The second electrode can be either a second bipolar electrode disposed on the positioner (usually spaced proximally from the first electrode), the catheter. or introducing sheath, or a dispersive or return electrode attachable directly to the patient&#39;s skin (where the first or active electrode will function in a monopolar manner). The electrodes are thus utilized to apply monopolar or bipolar high frequency energy to the vaso-occlusive coil within the vessel lumen. For example, a separate guide wire could be provided as either a monopolar or one bipolar electrode. 
     Frequently, the first electrode(s) will be associated with the distal engaging elements. For example, the opposing jaws or the resilient hooks can also define the treatment electrodes on the positioner. In the bipolar mode, most likely, a separate, second radiofrequency electrode can be provided on the catheter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a lumen occlusion system constructed in accordance with the principles of the present invention; 
     FIG. 2 is an enlarged perspective view of a distal end of a positioner device of the lumen occlusion system of FIG. 1, illustrating a pair of opposed elements shown in their open configuration; 
     FIGS. 3A-3D illustrate the use of the system of FIG. 1 and a method for enhancing occlusion of a blood vessel according to the principles of the present invention; 
     FIG. 4 is a sectional view of the distal portion of a second embodiment of a lumen occlusion device, illustrating a method of deploying or repositioning a vaso-occlusive coil in a body lumen; 
     FIG. 5 is a detailed, cross-sectional view of the lumen occlusion device of FIG. 4, illustrating a plurality of coil-engaging elements releasably holding the vaso-occlusive coil; 
     FIG. 6 is a partial sectional view of a third embodiment of a lumen occlusion device constructed in accordance with the principles of the present invention; and 
     FIG. 7 is a partial sectional view of a portion of a lumen occlusion device according to another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     The methods and devices of the present invention will be useful for selectively occluding virtually any body lumen that can be occluded with a vaso-occlusive element(s) followed by the application of energy. While the present invention will find its greatest use in the selective occlusive of blood vessels, including both arteries, veins, fistulas and aneurysms, it will also find use with other body lumens, such as the fallopian tubes, bile ducts, and the like. The present invention will be particularly useful for occluding relative large, high flow arteries, veins and vascular malformations, because the present invention presents a method of releasably holding a vaso-occlusive element(s) until the target site of the fluid vessel is partially or completely occluded. In high flow vessels, this effectively prevents the vaso-occlusive element(s) from becoming dislodged and migrating downstream of the target site. 
     In the case of blood vessel occlusion, the high frequency electrical energy will coagulate surrounding fluids, such as blood, and thermally injure the intima of the body luminal wall in the occlusion region, thus initiating a process of thrombosis and fibrosis which will result in relatively complete vessel occlusion. The high frequency electrical energy passes through the vaso-occlusive element, which usually takes the form of an electrically conductive coil, into the body luminal wall. The electrical energy heats the luminal wall, thereby enhancing the thrombogenic and fibrogenic occlusion of the coil at the target site. The vaso-occlusive coil typically has a relatively low electrical resistance so that the high frequency electrical energy flows directly through the coil to the luminal wall and surrounding fluid (in fluid carrying vessels) without substantially heating the coil. The electrical energy heats the body luminal wall, creating a thermal effect and thereby causing damage and subsequent fibrogenic occlusion of the target site. The temperature of the luminal wall will be typically be raised to about 45° C. to 95° C., preferably about 55° C. to 85° C. 
     Alternatively, the vaso-occlusive coil may comprise a material having some electrical resistance so that a portion of the high frequency electrical energy heats the vaso-occlusive coil. In this case, the coil will preferably have an electrical resistance less than the tissue wall to ensure that the electrical energy flows through at least a substantial portion of the coil. 
     Preferably, the energy source will provide radiofrequency electrical energy, such as that supplied by conventional electrosurgical power supplies, such as those available from commercial vendors, including Valleylab®, Aspen®, Bovie®, and Birtcher®. The power supply will usually provide energy at frequencies from 200 kHz to 12 MHz, preferably from 250 kHz to 500 kHz and may employ a conventional sinusoidal or non-sinusoidal wave form. The current provided will usually be in the range from about 25 mA to 1 A, preferably from about 50 mA to 250 mA from about 5 seconds to 4 minutes, usually from 10 seconds to 1 minute. The actual amplitude and duration of the current will depend primarily on vessel size, i.e. larger vessels will usually require higher currents and longer durations. 
     As discussed in more detail in connection with the specific embodiments below, the RF current may be applied in a monopolar or a bipolar fashion in or near the occlusion region. By “monopolar” it is meant that current flow will pass between (1) one or more “active” electrodes on the introducing catheter or the positioner which have surface areas and configurations which transfer the energy to the vaso-occlusive coil in order generate a thermal reaction in the region of the target site; and (2) a “dispersive” or return electrode which is located remotely from the active electrode(s) and which has a sufficiently larger area so that the current density is low and non-injurious to surrounding tissue. In some cases, the dispersive electrode may be on the same probe as the active electrode, and in other cases, the dispersive electrode may be attached externally to the patient, e.g., using a contact pad placed on the patient&#39;s flank. 
     Bipolar devices according to the present invention will generally employ a pair of electrodes in relatively close proximity each having an area and geometry selected to have a desired physiologic effect on adjacent tissue. In the case of bipolar devices, one or more electrodes will be connected to one pole of the radiofrequency power supply and will be placed in contact with the vaso-occlusive coil. The other electrode will be directly or indirectly in contact with the body luminal wall. Thus, the current flow in the occlusion region will be concentrated through the vaso-occlusive coil, then through the luminal wall or through the fluid located between electrode pair(s), rather than from one or more electrodes to a remote, dispersive electrode (which is the case in monopolar operation). 
     Devices according to the present invention will comprise an introducing catheter, typically including a shaft having proximal and distal ends and an axial lumen therebetween. For vascular applications, the shaft may be in the form of a conventional catheter body, typically having a length in the range from 40 cm to 200 cm, usually from 75 cm to 120 cm. The catheter body will usually include means for introducing the body over a movable guide wire, typically having a guide wire lumen running through at least a distal portion of the catheter body. Thus, the catheter body can have either conventional “over-the-wire” design where a movable guide wire is received through the entire length of the catheter body or may have a “rapid exchange” or “monorail” design where the guide wire is received through a lumen which extends only over a distal length of the body, typically from 5 cm to 25 cm. The catheter body will have an outside diameter consistent with its intended use, typically being from 1 mm to 5 mm, usually from 2 mm to 4 mm. 
     The catheter body may be formed from a variety of conventional catheter materials, including natural and synthetic polymers, such as polyvinyl chloride, polyurethanes, polyesters, polyethylenes, polytetrafluoroethylenes (PTFE&#39;s), nylons, and the like. The catheter bodies may optionally be reinforced to enhance their strength, torqueability, and the like. Exemplary reinforcement layers include metal fiber braids, polymeric fiber braids, metal or fiber helical windings, and the like. Optionally, a portion of the catheter body could be formed from a metal rod or hypo tube, particularly when the catheter body is a rapid exchange or monorail design. 
     The catheter will also include at least one electrode for initiating radiofrequency current flow, as described above. The electrode may be disposed on the catheter shaft, may be part of a separate positioner (described below), and/or may be associated with the guide wire used to introduce the shaft to the body lumen, usually a blood vessel. Configuration of the electrode element will vary depending on whether it is intended to actively contact the vaso-occlusive coil or to function as a return or dispersive electrode. 
     The dispersive electrode will typically have a substantially larger surface area, on the order of at least 2 to 3 times larger, than the active electrode. Active electrodes (the electrode and the occlusive coil) will typically have relatively small total surface areas, typically being below about 20 mm 2 , usually being below about 10 mm 2 . Dispersive electrodes will typically have a somewhat larger area, typically being greater than 50 mm 2  for probe-mounted dispersive electrodes and greater than 120 cm 2  for external dispersive pads. 
     The positioner will generally comprise a shaft that extends through the catheter body and includes a distal engaging element for releasably engaging a vaso-occlusive coil. The distal engaging element will also comprise the active electrode(s) (or one of a pair of electrodes in the bipolar mode). The engaging element will preferably comprise a holding or grasping mechanism that holds a proximal portion of the coil for deploying and/or repositioning the coil within a blood vessel. In this embodiment, the engaging element will be capable of holding onto the coil beyond the distal end of the catheter body and/or grasping an already deployed coil for establishing positive electrical contact between the engaging element and the coil, repositioning the coil or withdrawing the coil from the body lumen. Alternatively, the engaging element may comprise a mechanism for contacting the coil and pushing the coil through the catheter body. In this embodiment, the coil will generally disengage from the engaging element when its proximal end moves past the distal end of the catheter body. Electrical current may be re-established by subsequently advancing the positioner to contact the coil. Specific examples of each of these approaches are described in more detail in connection with the figures below. 
     The present invention will generally be useful with virtually any type of vasoocclusive device or coil that may be endoluminally advanced to a target site of a body lumen to block fluid passage therethrough. The vaso-occlusive device will typically be formed from an elongate element, such as a wire, which is extendable from a relaxed, convoluted condition, to an extended, linear condition in which the wire can be advanced through the catheter. The vaso-occlusive coil(s) will have a relatively large surface area compared to the electrode to facilitate transfer of the electrical energy to the tissue wall and surrounding blood. This surface area will usually depend on the size of the coil, which is typically chosen based on the size of the blood vessel. Larger vessels will typically require a higher rate of energy transfer due to a larger surface area. 
     The vaso-occlusive wire generally takes the form of a coil, and may be formed by wrappings or windings of a fine wire comprised of platinum, stainless steel, tungsten, gold or the like. The wire may be covered with a fibrous material, such as polyester, to induce thrombus in blood. The wire may be pre-formed so that it adopts a convoluted configuration in a relaxed condition. Alternatively, the vaso-occlusive device may be formed from a flexible pre-shaped polymer tube or rod that is doped with electrically conducting material so that the rod is more electrically conductive than the tissue of the body lumen. The convoluted shape of the tube or rod may be achieved by a combination of a helical winding and/or irregularities which are imparted during heat treatment, or by shaping the device as it is extruded, before cooling, or by injection molding. 
     Referring now to FIGS. 1-3, a lumen occlusion system  2  according to the present invention comprises a shaft in the form of a flexible catheter body  4  having a proximal end  6  and a distal end  8 . A positioner  10  includes a flexible shaft  12  sized to extend through catheter body  4  and having a proximal end  13  attached to a handle  14 . A pair of opposing elements or jaws  16 ,  17  are attached to a distal end  15  of flexible shaft  12  for movement between open and closed positions. Once catheter body  4  has been positioned within a blood vessel of the patient (discussed below), jaws  16 ,  17  may be introduced through proximal end  6  of catheter body  4  and advanced through distal end  8 , as shown in FIG.  1 . 
     Handle  14  includes an actuator mechanism for opening and closing jaws  16 ,  17 . Preferably, the actuator mechanism comprises an inner rod  20  slidably disposed within shaft  12  and extending through an inner lumen  22  within handle  14 . Rod  20  is coupled to a trigger  24  having a lever arm  26  extending through a slot  28  in handle  14 . Distal movement of lever arm  26  through slot  28  moves rod  20  in the distal direction, causing jaws  16 ,  17  to open (see FIG.  2 ). A spring  30 , positioned between a bushing  32  within lumen  22  and trigger  24 , biases lever arm  26  proximally so that jaws  16 ,  17  are biased into the closed position (FIG.  1 ). 
     FIG. 2 illustrates a preferred embodiment of the distal end  15  of positioner  10 . 
     As shown, jaws  16 ,  17  are pivotally coupled to each other by a pivot pin  60  extending through jaw  17 . Jaw  17  has a proximal end portion  62  pivotally coupled to a linkage  64  which is, in turn, pivotally coupled to the distal end  66  of rod  20 . Proximal movement of rod  20  withdraws linkage  64  into shaft  12 , thereby pivoting proximal end portion  62  of jaw  17  toward shaft  12 . In this manner, distal end portion  70  of jaw  17  is pivoted downward towards jaw  16  into the closed position (FIG.  1 ). Jaw  16  preferably has a recess  72  sized to receive jaw  17  to minimize the profile of positioner  10  in the closed position. Similarly, distal movement of rod  20  causes jaws  16 ,  17  to open (FIG.  2 ). 
     In this embodiment, jaws  16 ,  17  also serve as a common active electrode for providing radiofrequency current flow in a monopolar procedure. Referring again to FIG. 1, occlusion system  2  further comprises a suitable RF power supply  40  connected to handle  14  via a connection plug  42 . Jaws  16 ,  17  are preferably coupled to connection plug  42  through inner rod  20  and a lead wire  44  within handle  14 . Inner rod  20  may comprise an electrically conducting material or a lead wire (not shown) may extend through an inner lumen within rod  20 . Positioner shaft  12  will be fabricated from an insulating material to insulate rod  20  from the patient. The occlusion system  20  further includes a dispersive or return electrode, which is an external dispersive plate  50  coupled to RF power supply  40  and adapted for mounting on the patient&#39;s skin. Of course, the dispersive electrode  50  could be located elsewhere in different form (e.g., a sleeve) on the catheter body  4 . 
     FIGS. 3A-3C illustrate use of the lumen occlusion system  2  to enhance occlusion of a target site TS within a blood vessel BV having one or more vaso-occlusive coils  100  already deployed at the target site TS. The physician will typically monitor the blood vessel with a fluoroscope to determine whether the vessel is completely occluded after coil  100  has been deployed (or to determine if recanalization has subsequently taken place). If the target site is not completely occluded, lumen occlusion system  2  will be used to apply radiofrequency energy to the coils at the target site to cause thermal damage to the luminal wall (this will induce a fibrogenic reaction). Of course, system  2  can also be utilized to deploy the initial coil  100  (or additions to the coil) at target site TS, as described in more detail in later embodiments. 
     Referring to FIG. 3A, the distal end  8  of catheter body  4  is introduced transluminally to a target site TS within a blood vessel BV or other body lumen. Typically, a guide wire (not shown) will first be introduced to the target site TS in a conventional manner. Note that positioner  10  may also be used as the guide wire, if desired, or positioner  10  may be used without the catheter if no additional coils are necessary. Once the guide wire is in position, the catheter body  4  will be introduced over the guide wire in a conventional “over-the-wire” manner until the distal end  8  of the body  14  is positioned slightly proximal of the vaso-occlusive coil  100 , as shown in FIG.  3 A. 
     After reaching the target site TS, positioner shaft  12  is advanced through catheter body  4  until jaws  16 ,  17  extend beyond distal end  8 . Positioner shaft  12  will include an outer insulating sheath  102  proximal to the grasping end to protect the blood vessel wall from electrical energy delivered therethrough (discussed below). Jaws  16 ,  17  are opened by moving lever arm  26  (FIG. 1) in the distal direction, as described above. As shown in FIG. 3B, positioner shaft  12  will then be advanced distally until jaws  16 ,  17  contact a proximal portion of coil  100 . As shown in FIG. 3C, jaws  16 ,  17  are preferably closed over a portion of coil  100  to establish electrical contact between the active electrodes (jaws  16 ,  17 ) and the coil and to ensure that this electrical contact remains intact during application of energy to the coil. A radiofrequency power supply  40  (FIG. 1) applies a radiofrequency voltage to jaws  16 ,  17  to initiate a radiofrequency current flow between the contiguous coil  100  and the return electrode  50 . The radiofrequency power supply  40  may be optionally modified to provide an optimum impedance match. The radiofrequency current flows through coil  100 , and the surrounding blood and the wall of blood vessel BV. The current thermally damages the blood vessel wall, causing localized swelling around the coil, as shown in FIG.  3 C. 
     After maintaining the radiofrequency current flow for a desired time and at a desired current level, jaws  16 ,  17  will be opened to release coil  100 . The positioner  12  is then withdrawn through catheter body  14 . At the time of device removal, the blood vessel will be thrombosed and totally or mostly occluded. Subsequent fibrosis of the thrombus will make the occlusion substantially permanent. 
     A second embodiment  110  of the lumen occlusion system of the present invention is illustrated in FIGS. 4 and 5. System  110  is similar to system  2  in that it includes a proximal handle and an external, dispersive electrode coupled to an RF power supply (see FIG.  1 ). The system  110  differs from system  2 , however, in that it includes a plurality of resilient hooks  112 - 114  for grasping vaso-occlusive coil  100  and delivering a radiofrequency current thereto. As shown in FIG. 4, a positioner shaft  116  has a proximal end (not shown) connected to the proximal handle, a distal end  118  and an axial lumen  119 . An inner rod  120  is slidably positioned within axial lumen  119  and connected to an actuator mechanism (not shown) on the proximal handle. 
     Resilient hooks  112 - 114  are connected to the distal end of rod  118  and biased outward into a spaced apart configuration (not shown). When hooks  112 - 114  are completely or partially (FIGS. 4 and 5) withdrawn into shaft  116 , the inner wall  122  of shaft  116  urges the hooks  112 - 114  towards each other. One or more of the hooks  112 - 114  is also an active electrode for delivering RF energy to coil  100 . To that end, positioner shaft  116  includes an electrical conductor, such as a wire (not shown) extending through rod  118  to couple active electrode  112  with the RF power supply. 
     Occlusion system  110  can be used for deploying vaso-occlusive coil  100  at a target site TS in a blood vessel BV and for delivering radiofrequency energy to coil  100  to enhance fibrogenic occlusion of the target site TS. In use, hooks  112 - 114  are moved proximally outward beyond the distal end of positioner shaft  116  so that they are spaced apart from each other. The coil  100  is then positioned between hooks  112 - 114  and the hooks are partially withdrawn into shaft  116  so that the inner wall (not shown) of shaft  116  urges the hooks  112 - 114  together to grasp coil  100  (this partially withdrawn position is depicted in FIGS.  4  and  5 ). Positioner shaft  116  and coil  100  are then advanced through catheter body  4  to the target site (the distal end  8  of catheter body  4  is positioned at the target site as described previously). The inner wall  122  of cathetor body  4  facilitates the interlock between hooks  112 - 114  and coil  100  during movement through the catheter body. 
     Once coil  100  is advanced beyond the distal end  8  of catheter body  4 , it will begin to relax into a convoluted configuration for occlusion of blood vessel BV, as shown in FIG.  4 . Positioner shaft  116  is advanced until at least a portion of coil  100  or the entire coil and the hooks  112 - 114  extend beyond the distal end  8  of catheter body  4  (FIG.  5 ). An RF voltage is then delivered through active electrode or hooks  112 - 114  to the coil to generate thermal damage within blood vessel BV and induce subsequent fibrogenic occlusion of the blood vessel (as discussed previously). Since coil  100  is held in position by hooks  112 - 114 , it will not migrate from TS during the occlusion process. Once the target site is damaged, localized swelling and thrombosis fixes coil  100  in place. Rod  120  is then moved distally to expand hooks  112 - 114  and release the coil  100 . Rod  120  is typically biased proximally to a closed hook position. The positioner  116  and catheter  4  can then be removed from the patient&#39;s vasculature. 
     After the occlusion system has been removed from the blood vessel BV, a secondary RF treatment may become necessary if, for example, the target site is not sufficiently occluded. In this case, the occlusion system will be re-inserted as described above to re-access the occlusion coil  100 , to recouple the coil to the RF electrode and to deliver additional RF energy to the target site. 
     FIGS. 6 and 7 illustrate bipolar embodiments of the present invention. Referring to FIG. 6, a positioner  150  comprises a flexible shaft  152  extending through catheter body  4  as in the previous embodiments. Positioner  150  includes one bipolar electrode in the form of a disc  154  disposed at the distal end of shaft  152 . Disc  154  is electrically coupled to the RF power source by an inner conductive wire  156  extending through shaft  152 . Shaft  152  is contained within an electrically conductive sheath proximal to its distal end to form a second electrode  158 . Second electrode  158  is coupled to RF power source  40  by a second inner conductive wire  160  that extends through shaft  152  and is electrically insulated from wire  156 . Note that second electrode  158  is schematically illustrated in FIG.  6  and may be larger than that shown. Second electrode  158  will preferably have a larger surface area than disc  154  and coil  100  to minimize tissue damage at the second electrode. 
     In use, positioner shaft  152  is advanced beyond the distal end of catheter body  4  so that active electrode disc  154  contacts the vaso-occlusive coil  100  deployed at the target site TS within blood vessel BV, as shown in FIG.  6 . Electrode disc  154  may also be used as a pusher to deploy coil  100  by pushing the coil through catheter body  4 . RF voltage is applied between electrode  158  and electrode  154  so that an RF current is initiated therebetween. Since the coil is more conductive than tissue, the RF current flows through at least a portion of coil  100 . The surrounding blood and other fluids provide a path for the RF current from coil  100  and electrode  154  to electrode  158 . The RF current will be sufficient to coagulate blood and to generate thermal damage to the intima of the tissue wall to enhance the occlusion of target site TS. 
     Referring to FIG. 7, another embodiment of positioner  170  comprises a shaft  172  and a pair of jaws  174 ,  176  extending from a distal end of shaft  170 . Similar to previous embodiments, positioner  170  includes an inner rod  178  slidably disposed within shaft  172  and coupled to a proximal actuator (not shown) for opening and closing jaws  174 ,  176 . In this embodiment, first jaw  174  and a distal portion  180  of second jaw  176  are the first electrodes. The second electrode  158  is disposed proximal to the first electrodes  174 ,  176 , similar to FIG.  6 . The jaws  174 ,  176  and second electrode  158  are each coupled to an RF power source by inner conducting elements  184 ,  186 , respectively, which can comprise wires, rods or the like. RF voltage is applied between jaws  174 ,  176  and second electrode  158  to initiate RF current therebetween (via the coil). 
     Although the foregoing invention has been described in some detail by way of illustration and example, for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.