Abstract:
An electrosurgical instrument and method for treating varicose veins. In one embodiment, an elongate catheter has a distal working end that carries an electrosurgical energy delivery surface comprising at least one electrode with a positive temperature coefficient of resistance (PTCR) surface and/or an electrode with a pressure sensitive variable resistance to provide a smart surface for controlling Rf current flow at the interface of electrosurgical surface and the tissue. The electrode surface then can limit or modulate Rf energy delivery through the surface in response to the temperature of the surface or the engagement pressure of the surface against the engaged tissue. In operation, the smart electrosurgical surface prevents arcing at the electrode-tissue interface, and thus controls ohmic heating to prevent tissue desiccation, charring and emboli formation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 11/199,555, filed Aug. 8, 2005, which claims the benefit under 35 U.S.C. § 119 of Provisional U.S. Patent Application Ser. No. 60/600,419, filed Aug. 10, 2004; U.S. patent application Ser. No. 11/199,555 is also a continuation-in-part of each of the following: U.S. patent application Ser. No. 10/032,867, filed Oct. 22, 2001; U.S. patent application Ser. No. 10/351,449, filed Jan. 22, 2003; U.S. patent application Ser. No. 10/441,519, filed May 20, 2003; and U.S. patent application Ser. No. 10/643,787, filed Aug. 19, 2003. All of the above applications are incorporated herein by reference and made a part of this specification. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention pertains to methods and devices for endovascular surgery, and more particularly to devices and methods for treating varicose veins. 
         [0004]    2. Description of the Related Art 
         [0005]    Varicose veins are distended, visible superficial veins on the legs, and are almost always the result of problems with valves within the venous system of the leg. All leg veins contain one-way flap valves which are designed to help the flow of blood in the veins in an upward direction on its return to the heart. When one or more of these valves fails to function correctly and leaks, some blood is able to flow back down into the leg in the wrong direction and tends to distend branches of superficial veins under the skin. Over a period of time, this additional pressure of blood causes the veins to stretch, bulge and become visible. At the same time, tiny capillary branches of the veins are also overfilled with blood, producing multiple spider veins and often a purple discoloration. Leaky venous valves can occur at any site in the leg but the great majority of varicose veins are caused by faulty valves in the groin or behind the knee. At both these sites there is a major junction at which superficial veins (those subject to varicose veins) flow into the important deep veins of the leg, with a one-way valve to control flow at the junction. Numerous surgical treatments of varicose veins have been developed such surgical stripping and surgical vein removal. Also, radiofrequency (Rf) ablation catheters and laser catheters are used to shrink and ablate varicose veins. 
       SUMMARY OF THE INVENTION 
       [0006]    In general, the apparatus of the invention comprises a catheter member with a working end having an electrosurgical energy delivery surface for translating along a vessel lumen to shrink and occlude the lumen. The working end comprises a resilient polymer sleeve that is moveable from a first reduced cross-section for introduction to a second expanded cross-section for engaging the vessel wall. In one embodiment, the working end is a resilient sleeve of a polymer having a memory expanded shape that is dimensioned to slide over a guidewire wherein the guidewire is capable of acting as a substantially rigid member to maintain the sleeve in a linear pre-deployed configuration. 
         [0007]    Of particular interest, the working end of the sleeve has exposed electrodes that have a PTCR (positive temperature coefficient of resistance) coating that can modulate Rf current flow to the vessel lumen without thermocouples and controller feedback circuitry. The PTCR material consists of a conductively doped polymer such as silicone. The electrodes are embedded in the catheter sleeve and can operate in bi-polar or mono-polar mode. The PTCR material maintains a low base resistance over a selected temperature range with a dramatically increasing resistance above a selected narrow temperature range as Rf energy is delivered to tissue through the PTCR material. In operation, it can be understood that current flow through the PTCR material will apply active Rf energy (ohmic heating) to the engaged tissue until the point in time that any portion of the material is heated to a range that substantially reduces its conductance. This effect will occur across the PTCR surface thus allowing portions thereof to deliver an independent level of power therethrough. This localized limiting of Rf current can be relied on to prevent any arcing in or about the electrosurgical surface. The system thus eliminates the possibility of tissue char and the potential of emboli. Further, when the PTCR material is elevated in temperature to the selected thermal treatment range, the retained heat of the material volume can also apply thermal energy to the engaged vessel lumen. In one embodiment, the working end will modulate the application of energy to the vessel wall between active Rf ohmic heating and passive conductive heating to maintain a selected temperature level to shrink and occlude the vessel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0008]      FIG. 1  is a side view of the distal end of a Type “A” catheter-like sleeve and guidewire of the invention in a first linear shape for endoluminal navigation. 
           [0009]      FIG. 2  is a side view of the Type “A” catheter sleeve of  FIG. 1  with the guidewire withdrawn and the sleeve in a second expanded shape for treating a varicose vein. 
           [0010]      FIG. 3  is a cut-away view of a small portion of the Type “A” sleeve of  FIG. 1  taken along line  3 - 3  of  FIG. 2 . 
           [0011]      FIG. 4  is a sectional view of the Type “A” sleeve of  FIGS. 1-2  engaging tissue. 
           [0012]      FIG. 5  is a sectional view of the Type “B” sleeve similar to that of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    1. Catheter Sleeve Including PTCR Electrosurgical Surface for Treating Varicose Veins. 
         [0014]      FIGS. 1 and 2  illustrate the distal working end  102  of a Type “A” elongated catheter that includes a distal region that includes a distal sleeve end  110  that comprises an electrosurgical surface  112  corresponding to the invention that is adapted for controllably applying energy to the lumen of a blood vessel or other tubular body structure. The sleeve  110  can be any suitable length along axis  115  for endoluminal navigation to a targeted site. The cross-section of the sleeve can be a suitable dimension, for example, 4 French with a 2 French lumen indicated at  116 . The lumen  116  is dimensioned to slide over a guidewire  120  with the guidewire capable of acting as a substantially rigid member to straighten the sleeve  110  to allow endoluminal navigation. 
         [0015]    In the exemplary embodiment of  FIGS. 1 and 2 , it can be seen that sleeve  110  has a first untensioned condition in  FIG. 2  that has an expanded cross-sectional shape for engaging the walls of a vessel lumen. In  FIG. 1 , the sleeve  110  is in a second tensioned linear condition with a lesser cross-section when the guidewire  120  extends therethrough as in  FIG. 1 . The untensioned, expanded cross-sectional shape of the sleeve  110  in  FIG. 2  is provided by the memory shape of the polymer of the sleeve, and/or by at least one resilient spring element (not shown) molded into the wall  122  of sleeve  110 . Preferably, as can be seen in  FIG. 3 , electrode elements  125 A and  125 B in sleeve wall  122  can also provide resilient spring properties to maintain a thin sleeve  110  in an open condition. In use, the working end  102  of sleeve  110  is navigated to the targeted site in the tensioned, linear configuration of  FIG. 1 . Thereafter, the guidewire is withdrawn partly (see  FIG. 2 ) to allow the sleeve  110  to expand to its untensioned position as in  FIG. 2 . 
         [0016]    The sleeve  110  is fabricated of a suitable polymer such as a silicone that is easily deformable between its linear and expanded cross-sectional shapes ( FIGS. 1 and 2 ) after release from its constraint by the guidewire  120 . It should be appreciated that the sleeve member  110  also can be a rod-like member and constrained by, and released from, a bore in a more rigid catheter (not shown). The expanded cross-section of sleeve  110  in  FIG. 2  can define an outer diameter of any dimension, for example 2 mm. to 2 cm. and will thus gently push outward to engage the vessel wall as the working end is pulled along the vessel lumen. 
         [0017]    In one embodiment, the sleeve  110  provides a distal working end including an electrosurgical energy delivery surface  112  that comprises helical windings or conductors  125 A and  125 B that function as mono-polar or bi-polar electrodes wherein the conductors  125 A and  125 B have a surface coating of a positive temperature coefficient of resistance (PTCR) polymeric material  126  that functions to control and limit Rf current flows and ohmic heating in the engaged tissue. In the exemplary embodiment of  FIG. 1 , shown in cut-away views in  FIGS. 3 and 4 , it can be seen that the conductors or electrodes  125 A and  125 B are coupled to, but exposed, in a surface of sleeve wall  122  which is fabricated of a non-conductive polymer. The polymeric PTCR material  126  thus is exposed to provide the electrosurgical energy delivery surface  112  that is adapted to interface with the vessel lumen. More in particular, the PTCR material comprises a non-conductive polymer that is doped with conductive particles. Suitable PTCR materials corresponding to the invention are described in co-pending U.S. Patent Applications listed in the Section above titled CROSS-REFERENCE TO RELATED APPLICATIONS. The polymer portion of the PTCR material can have any thermal conductivity property, but preferably has a low thermal conductivity. The conductive particles can be carbon, gold, platinum, silver, or a stainless steel coated with gold, platinum, silver or the like. In one embodiment, the ration by weight of the polymer-to-conductive particles can range from about 10/90 to about 70/30 (polymer/carbon particles) to provide the selected range at which the sleeve wall will function to substantially limit electrical conductance therethrough at a selected switching range between about 80° C. and 120° C. The non-conductive base polymer  160   a  can comprise silicone, high density polyethylene or polypropylene. 
         [0018]    As can be seen in  FIGS. 3 and 4 , the polymer of sleeve wall  122  can be formed partly around the conductive elements or electrodes  125 A and  125 B and maintain a selected spacing therebetween. The conductive elements  125 A and  125 B are coupled to a voltage (Rf) source  180  and controller  182  by a connector cable that is detachable from a proximal handle end of sleeve  110 . Thus, the Rf source  180  can apply electrical potential of a first and second polarities (+) and (−) to the conductors  125 A and  125 B and PTCR surfaces  126  and thereafter to the engaged vessel lumen L. 
         [0019]    In the embodiment of  FIG. 3 , the conductive elements  125 A and  125 B comprise spaced apart helical coils that are indicated as having opposing polarities, or the conductors  125 A and/or  125 B can have a common polarity to allow operation in a mono-polar manner in cooperation with a ground pad  185 . In one embodiment, the voltage source  180  and controller  182  are configured to switch energy delivery by means of a multiplexer between bi-polar and mono-polar modes. As also can be seen in  FIG. 3 , the inner wall surface  184  of wall  122  comprises a portion of the insulative material of sleeve wall  122  that prevents any contact of the electrical components of the sleeve (i.e., PTCR material and electrodes  125 A and  125 B) with the guidewire  120  or blood in the sleeve&#39;s lumen during operation (see  FIGS. 1-2 ). 
         [0020]    In one method of the invention, the sleeve  110  and electrosurgical surface  112  can limit current flows in tissue and modulate the delivery of energy through electrosurgical surface  112  to the vessel lumen L (see  FIGS. 4 and 5 ). The distal end of the sleeve  110  is advanced distally through a targeted varicose vein. The working end is then expanded (see  FIG. 2 ) and energized as it is pulled retrograde through the vein. Rf energy application to the vessel lumen will shrink and damage the vessel wall to thereby occlude the vein. When operating in a mono-polar mode as described above, the PTCR material  126  illustrated in  FIGS. 3 and 4  will cause current flow in the engaged tissue until the vessel wall reaches a selected switching temperature and thereafter heat is conducted back from the tissue to the PTCR material  126 . Local regions of the PTCR material will then switch off Rf current delivery therethrough which will prevent arcing, charring and tissue desiccation at the interface of the electrosurgical surface  112  and the tissue. This effect will about the surface of each electrode to provide spatially localized modulation of ohmic heating in the engaged tissue. The PTCR material  126  thus senses the tissue temperature that results from ohmic heating and limits current flows to maintain the temperature of the engaged tissue at or about the targeted treatment range. 
         [0021]    Referring again to  FIG. 4 , the conductive elements  125 A and  125 B are shown operating in a bi-polar mode and wherein the current flows in tissue a selected distance C (not-to-scale; electrode center-to-center dimension) which in turn controls the depth of ohmic heating in tissue. The electrosurgical surface delivers Rf current flows to the endoluminal tissue wherein the Rf current flows are limited by changes in temperature in at least portions of the PTCR material  126  resulting in the denaturing of proteins within the engaged tissue while substantially preventing desiccation and charring of the tissue. The protein denaturation causes tissue effects that include shrinkage, ablation, occlusion and vessel closure. The sleeve  110  assembly can be manufactured in a number of manners such as extruding an inner portion of the insulative sleeve  110  then using precision windings systems to wind at least one coil of fine wire (with PTCR coating) about the inner sleeve portion. Thereafter, and additional polymeric material can be deposited to partly embed the PTCR coated coils in the sleeve surface. The spacing of the electrodes  125 A and  125 B and temperature resistance profile of the PTCR material  126  are selected to cause the desired Rf current depth and switching temperature. 
         [0022]    In another mode of operation, still referring to  FIG. 4 , electrical potential of opposing polarities is applied between conductors  125 A and  125 B which results in current flow through the PTCR material  126  and the engaged tissue T—depending on center-to-center spacing and the conductivity of the PTCR material  126  which is in constant flux as its temperature changes from its conductive heating from engaged ohmically heated tissue. By this means, as described above, the surface  112  acts as a continuously localized temperature control mechanism without the thermocouples and feedback circuitry that are common in many prior art electrosurgical devices. The entire working end assembly can be pulled proximally within the lumen of the blood vessel to cause ohmic heating of a selected length of the blood vessel. The PTCR material  126  will prevent any blood from coagulating about the surface  112  due to its ability to prevent hot-spots or charring as described in previous disclosures referenced above. The method as described above will shrink and occlude the blood vessel to thereby treat varicose veins. 
         [0023]      FIG. 5  illustrates the distal working end of another embodiment of sleeve and electrosurgical surface  112  that is substantially the same as the previously described embodiment. This system is provided with a controller  182  that allows selection of the center-to-center distance between groups of two or more helical conductors operating in a bi-polar mode, in addition to singly paired electrodes as shown in  FIG. 4 . The system also can be provided with a multiplexer to automatically switch between different single and multiple arrangements of electrode windings. In this embodiment, at least 4 separate helical coils, or as many as about  24  coils, are independently connected to the electrical source and controller. In operation, the progressively more widely spaced apart bi-polar electrode groups can cause ohmic heating to a greater selected depth in the engaged tissue. Thus, a single diameter sleeve  110  can be adapted for optimal ohmic heating depth no matter the diameter and wall thickness of the blood vessel, whether the blood vessel in 2 mm. or 10 mm. 
         [0024]    In another embodiment, the sleeve can be similar in all respects to the embodiments of  FIGS. 1-5  except that the coating on the electrodes can be a pressure sensitive resistive material as disclosed in Ser. No. 10/032,867 filed Oct. 22, 2001; and U.S. patent application Ser. No. 10/351,449 filed Jan. 22, 2003; and U.S. patent application Ser. No. 10/441,519 filed May 20, 2002. 
         [0025]    It should be appreciated that the scope of the invention includes any catheter sleeve  110  that is adapted to provide a first contracted shape for endoluminal navigation and a second expanded shape for engaging the vessel walls, wherein the electrosurgical surface  112  of the sleeve includes at least one electrode and a PTCR polymer  126  having a positive temperature coefficient of resistance. For example, the member be articulatable with pull-wires or the like, or the member may have a core of a shape memory material such as a Nitinol wire or tube. 
         [0026]    Although particular embodiments of the present invention have been described above in detail, it will be understood that this description is merely for purposes of illustration. Specific features of the invention are shown in some drawings and not in others, and this is for convenience only and any feature may be combined with another in accordance with the invention. Further variations will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.