Electrosurgical catheter apparatus and method

A catheter adapted to increase the patency of a body conduit includes an elongate tube having an axis extending between a proximal end and a distal end, and a balloon disposed at the distal end of the tube and having properties for being expanded to a high-profile state and for being contracted to a low-profile state. A sleeve disposed over the balloon has a pair of ends disposed on opposing sides of a central section, the ends having a floating relationship relative to the tube with the central section disposed circumferentially of the balloon. An electrode disposed outwardly of the sleeve has properties for being electrosurgically energized to incise materials defining the body conduit when the balloon is in the high-profile state. The electrode can be formed of a plurality of elements stranded to increase the surface area of the electrode. The catheter can be inserted relative to a guide member having a conductor which carries the electrosurgical energy from the proximal end of the tube to the electrode at the distal end of the tube. An associated method includes the step of introducing electrosurgical energy into the conductor of the guide member to energize the electrode of the catheter.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates generally to surgical devices and more specifically
 to electrosurgical catheters adapted to incise body material defining a
 body conduit.
 2. Discussion of the Prior Art
 Various surgical devices have been used to electrosurgically ablate or
 otherwise cut body materials. In this type of surgery, electrosurgical
 energy is passed between two electrodes creating a high current density
 which ablates the body materials. In a typical monopolar system, the
 patient is coupled to a large grounding pad which forms one of the
 electrodes. The electrosurgical device forms the other electrode. In this
 system, the electrosurgical device provides a very low surface area and
 consequently a very high current density for ablation or cutting in
 proximity to the device. In a bipolar system, the two electrodes are
 included in the device and high current density is achieved in the small
 area between the electrodes.
 These electrosurgical devices include a catheter having a balloon and an
 electrode extending over the surface of the balloon as disclosed in
 applicant's co-pending applications, Ser. No. 08/241,007, filed on May 11,
 1994, and entitled "Angioplasty Catheter and Method for Making Same", and
 Ser. No. 08/216,512, filed on Mar. 22, 1994, and entitled "Improved
 Catheter with Electrosurgical Cutter". The entirety of this disclosure is
 incorporated herein by reference. This catheter is used in a monopolar
 system where an electrode, in the form of a wire, is disposed over a
 radially expandable balloon of the catheter. As the balloon is inflated,
 the electrode is carried radially outwardly into proximity with the body
 material to be ablated or cut. Although it has always been of interest to
 increase the current density associated with the wire electrode, this has
 been difficult to achieve as smaller wire sizes necessarily result in
 reduced electrode strength and integrity. The balloon material has also
 been restricted to insure against over-expansion and electrode proximity.
 Materials forming non-distensible balloons have been preferred, but have
 made it difficult to achieve a low-profile state for insertion.
 SUMMARY OF THE INVENTION
 In accordance with the present invention, an electrosurgical catheter is
 provided with a balloon and an electrode extending axially along the outer
 surface of the balloon. A sleeve is disposed over the balloon and provided
 with ends which float along the catheter body between a low-profile state
 and a high-profile state for the sleeve. In the high-profile state, the
 sleeve has a predetermined maximum diameter which limits the radial
 dimension of the balloon. Portions of the electrode extend through the
 sleeve to facilitate the electrosurgical function. The sleeve can also be
 provided with characteristics whereby the sleeve is biased to its
 low-profile state further facilitating a minimal profile for the catheter.
 The sleeve will typically be manufactured of a thermoplastic or thermoset
 material.
 The sleeve can be formed from a plurality of elements which are woven,
 braided, or otherwise stranded to form an expandable structure. The
 electrode may form one of these elements in the sleeve. The electrode may
 also be formed from elements which are stranded to increase the surface
 area of the electrode without increasing its diameter. The electrode, the
 balloon, or the sleeve can be coated with an insulation to control the
 electrical relationships between these elements.
 For example, the electrode can be formed of stranded elements which provide
 the electrode with an outer surface having peaks and valleys. Portions of
 this insulation can be removed to expose the elements in a straight or
 curved pattern. The electrode can be connected at each of its ends through
 conductors to the proximal end of the catheter thereby facilitating
 increased current flow to the electrode.
 In another embodiment, the guidewire can be provided with an electrically
 conductive core which is exposed through insulation to energize the
 electrode at the distal end of the catheter. Using the guidewire as a
 conductor eliminates the need for an additional conductor in the catheter
 to energize the electrode. The conductive guidewire also facilitates
 operative disposition of the catheter at the surgical site.
 In a semi-bipolar system, either the balloon or the sleeve can be used as a
 second electrode replacing the grounding pad in a typical monopolar
 system. With the wire forming one of the electrodes, the metalized balloon
 or sleeve forms the other electrode in a semi-bipolar system. This system
 provides the advantage of current density at the wire, but does not
 require electrical current to be conducted throughout the body of the
 patient. The electrosurgical current need only flow from the active
 electrode with a minimal surface area to the balloon or sleeve which
 provide a high-surface area.
 In one aspect of the invention, a catheter is adapted to increase the
 patency of a body conduit and comprises an elongate tube having an axis
 extending between a proximal end and a distal end. A balloon is disposed
 at the distal end of the tube and provided with properties for being
 expanded to a high-profile state and for being contracted to a low-profile
 state. A sleeve is disposed over the balloon and provided with a pair of
 ends which define a central section of the sleeve. The ends of the sleeve
 are disposed to floatingly engage the tube with the central section
 disposed circumferentially of the balloon. An electrode includes portions
 disposed outwardly of the sleeve and having properties for being
 electrosurgically energized to incise the body materials and increase the
 patency of the body conduit.
 In another aspect of the invention, the electrode is formed of a plurality
 of elements stranded between a proximal end and a distal end to provide
 the electrode with an elongate configuration.
 In a further aspect of the invention, the electrode has a radial
 cross-section which is non-circular in configuration.
 In a further aspect of the invention, a guide member is adapted to
 facilitate insertion of a catheter into a body conduit. The guide member
 includes a core extending along an axis between a proximal end and a
 distal end, the core having properties for conducting energy. Insulation
 is disposed over the core with a portion of the insulation defining an
 exposed portion of the core at the proximal end of the guidewire and at
 the distal end of the guidewire.
 In a further aspect of the invention, a combination includes the guide
 member and a catheter with an elongate shaft adapted to be moved along the
 guide member. An electrode disposed along the catheter is coupled to an
 exposed conductive core of the guide member to permit passage of energy
 from the proximal end of the guidewire along the core to the electrode at
 the distal end of the catheter.

DESCRIPTION OF PREFERRED EMBODIMENTS AND BEST MODE OF THE INVENTION
 A catheter is illustrated in FIG. 1 and designated generally by the
 reference numeral 10. The catheter 10 is illustrated to be operatively
 disposed in a patient 12 having a ureter 14 extending between a kidney 16
 and a bladder 18. The catheter 10 is adapted to increase the patency of
 the ureter 14, particularly at the upper pelvic junction 21 which is
 commonly occluded by strictures 23.
 The catheter 10 typically includes an elongate tube 25 having a lumen 27
 extending through a hub 30 at a proximal end 32, and an electrode assembly
 34 at a distal end 36. The electrode assembly 34 is electrically energized
 through a conductor 38 at the proximal end 32. Operative placement of the
 catheter 10 can be facilitated by a guide catheter or a guidewire 41.
 FIG. 2 shows an enlarged view of the upper pelvic junction 21 with the
 electrode assembly 34 including a balloon 45, a sheath 47 extending over
 the balloon 45, and an electrode 50. These elements are perhaps more
 easily identified in the radial cross-section view of FIG. 3.
 The side elevation views of FIGS. 4 and 5 illustrate the electrode assembly
 34 in a low-profile state and a high-profile state, respectively. In the
 low-profile state of FIG. 4, the catheter 10 is adapted for insertion
 through the bladder 18 and into the ureter 14. Once the catheter 10 is
 operatively disposed, the balloon 45 is expanded, for example by
 inflation, to a high-profile state, as illustrated in FIG. 5. In the
 high-profile state, as illustrated in FIG. 2, the balloon 45 functions to
 carry the electrode 50 radially outwardly into proximity with the
 strictures 23 to facilitate the electrosurgical effect. The balloon 45 in
 the high-profile state also functions to tension the walls of the ureter
 14 so that the ureter 14 expands as the strictures 23 are cut by the
 electrode 50. Any potential for bleeding is inhibited by the tamponade
 effect of the inflated balloon 45.
 The cross-section views of FIGS. 6 and 7 illustrate a preferred embodiment
 wherein the electrode 50 exits the tube 25 exteriorally of the balloon 45,
 but interiorly of the sheath 47. Portions of the electrode 50, designated
 generally by the reference numeral 52, extend through the sheath where
 they are exposed axially along the outer surface of the sheath 47.
 The side elevation views of FIGS. 4 and 5 are perhaps best suited to
 disclose another feature of the present invention. In these figures, the
 balloon has ends which are fixed to the tube 25 by windings 54, 56. With
 the windings 54, 56 fixed to the tube, axial movement of the balloon 45 is
 inhibited, so that expansion of the balloon 45 is limited generally to the
 radial direction. By comparison, the ends of the sheath 47 are fixed to
 bushings 58, 61 which are separated by a central section 63 are free to
 float axially along the tube 25. Thus, the bushings 58 and 61 have inside
 diameters which are greater than the outside diameter of the tube 25. In
 the low-profile state illustrated in FIG. 4, the bushings 58 and 61 have a
 maximum distance of separation as the length of the sheath 47 increases in
 response to radial compression of the balloon 45 and the sheath 47.
 As the balloon 45 expands radially outwardly, it carries with it the
 central section 63 of the sheath 47. This radial expansion of the sheath
 47 draws the floating bushings 58, 61 together reducing their distance of
 separation. In the high-profile state illustrated in FIG. 5, the floating
 bushings 58, 61 of the sheath 47 abut the fixed windings 54, 56 of the
 balloon 45. At this point, the distance separating the bushings 58, 61 can
 no longer be reduced. With the ends of the sheath 47 limited against
 further proximal movement, the maximum diameter of the sheath 47 is fixed
 to a diameter which dictates the predetermined high-profile state of the
 electrode assembly 34. Note that this also fixes the maximum radial
 separation of the catheter tube 25 and the exposed portions 52 of the
 electrode 50.
 Theoretically, the electrode 50 and the conductor 38 should be sized and
 configured to conduct the maximum amount of current through the conductor
 38 to the electrode 50, and then to provide an electrode 50 of minimum
 surface area in order to increase the current density at the electrode 50.
 Of course, there are maximum size and flexibility constraints on the
 conductor 38, as well as strength and integrity constraints on the
 electrode 50 which place practical demands on these theoretical
 considerations. In the past, both the conductor 38 and the electrode 50
 have been formed of wires having a circular cross-section as illustrated
 in FIG. 8. Within the practical constraints noted, the round conductor 38
 has been chosen with a maximum diameter and the round electrode 50 has
 been chosen with a minimum diameter. In U.S. Pat. No. 5,628,746, Applicant
 discloses and claims a concept for providing a relatively large electrode
 wire with surface insulation that is removed to expose only a very small
 area of the electrode. This has had the same effect of providing a
 high-current density, but has enabled use of a relatively large electrode
 to do so. As a result, electrodes as large as the associated conductors
 have been used in the past. When the practical constraints on the
 conductor have been maximized, embodiments providing for a relatively
 large electrode tapering to a relatively small conductor have been used.
 Against this background of evolution, it has now been found that electrical
 energy passing through a conductor at radio frequencies tends to flow
 along the outer surface of the conductor. This is referred to as the "skin
 effect." Taking this phenomena into account, the conductor 38 and
 electrode 50 of the present invention can be provided with a generally
 non-circular shape in axial cross-section. This shape can take the form
 illustrated in FIG. 9, for example, or can naturally result from a
 stranded conductor 38, as illustrated in FIG. 10. In this embodiment, the
 conductor 38 electrode 50 include at least two elongate elements 70, 72
 which are stranded, such as woven, braided, or twisted, along an axis 75
 from the proximal end of the conductor 38 through to the distal end of the
 electrode 50. These elements 70, 72 may have a circular cross-section, as
 illustrated in FIG. 10, or may also be provided with a non-circular
 cross-section maximizing their individual surface areas.
 Another embodiment illustrated in FIG. 11 provides an even further increase
 in the surface area of the conductor 38 and electrode 50. In this
 embodiment, each of the elements 70, 72 is formed of a plurality of fibers
 74. These fibers 74 are twisted together to form the individual elements
 70, 72, which are further twisted together to form the conductor 38 and
 electrode 50. In the FIG. 11 embodiment, the resulting conductor 38 and
 electrode 50 have a generally hollow configuration so that none of the
 elements, such as the elements 70 and 72, extend along the axis of the
 conductor 38. By comparison, the conductor 38 and electrode 50 illustrated
 in FIG. 12 include a further element 76 which extends along the axis 75,
 with the remaining elements 70, 72 twisted around the core element 76.
 From these embodiments illustrated in FIGS. 9-12, it will be apparent that
 an increased surface area can be achieved generally with any non-circular
 cross-section. In FIG. 9, the conductor 38 is solid and the outer surface
 is sculptured to provide the increased surface area. In the embodiment of
 FIG. 10, multiple elements are stranded to provide the increased surface
 area. The cross-section of these individual elements can also be
 non-circular. Importantly, there can be two or more elements, such as the
 elements 70, 72, in this embodiment. The more elements, the greater the
 surface area. This is more apparent from the FIG. 11 embodiment which
 includes six elements, such as the elements 70, 72. To further increase
 the surface area, each of these elements is formed from individual fibers
 which can also be provided with other than round cross-sections. Whether
 the cross-section of the connector 38 is hollow, as illustrated in FIG.
 11, or generally solid, as illustrated in FIG. 12, it is apparent that the
 surface area of the conductor 38 is greatly increased over the generally
 cylindrical circular cross-section associated with the conductors and
 electrodes of the prior art.
 Turning now to the electrode 50 illustrated in FIG. 13, it will be apparent
 that the conductor 38 with a spiraled configuration can offer significant
 advantages when covered with an insulation 81. When this insulation is
 removed, individual windows 83 are formed and exposed portions 86 of the
 convolutions 85 are individually exposed. This is perhaps best illustrated
 in the axial cross-section view of FIG. 14 where the insulation 81 is
 removed in an area designated generally by the reference numeral 87. From
 this view it can be seen that the outer surface of the convolutions 85
 forms peaks 89 alternating with valleys 91. When the insulation is removed
 from the area 87, it tends to remain in the valleys 91 so that only the
 peaks 89 and the convolutions 85 are exposed. This produces the individual
 windows 83 and the discreet, exposed convolutions 85 of the conductor 38,
 as illustrated in FIG. 13.
 It should be noted that with this window configuration, the exposed area of
 the conductor 38 can be even further reduced, greatly increasing the
 current density of the electrode 50. In the past, the entire conductor was
 exposed within the area of the removed insulation 87. In the window
 embodiment, as illustrated in FIG. 13, the much smaller area of exposure
 can provide a substantial increase in current density.
 From these views, it can be appreciated that the particular surface
 configuration associated with the conductor 83, and the pattern for
 removing the insulation 81, can provide the windows 83 and the exposed
 portions 86 of the conductor 38 with different spatial relationships. For
 example, in FIG. 15, the windows 83 and exposed portions 86 have a curved,
 radial relationship. In FIG. 16, the windows 83 and exposed portions 86
 have a generally straight, axial relationship. Finally, in FIG. 17, the
 windows 83 and exposed portions 86 are curved with a spiral relationship.
 A further embodiment of the invention is illustrated in FIG. 18 wherein the
 conductor 38 is formed of multiple elements as taught generally with
 reference to FIGS. 10, 11. These elements 70, 72 are individually provided
 with an insulation coating 101FIG. 18, which enables them to be
 individually and separately energized or controlled. While this control
 may provide for variations in the magnitude of energy, it will typically
 be a matter of timing that energy at each window 83. Thus, the individual
 and discrete windows 83 and the insulation 81 can be separately, and
 perhaps progressively, energized to further maximize the current density
 as the elements 70, 72 are selectively energized at the associated windows
 83.
 A further embodiment of the invention is illustrated in FIGS. 19a-23a and
 their associated cross-sectional views in FIGS. 19b-23b. In this
 embodiment, the balloon 45 is provided with a metal coating 105, but only
 along a portion of its radial surface. For example, in the views
 illustrated, the metal coating 105 extends only 180.degree. around the
 circumference of the balloon 45. This greatly aids in the radial
 orientation of the balloon 45 and, of course, facilitates operative
 disposition of the electrode 50. Radiopague markers 107 can also be
 provided to further enhance axial location of the catheter 10.
 Viewing the catheter 10 fluoroscopically will present a side-elevation view
 such as those associated with FIGS. 19a-23a. From these fluoroscopic
 observations, the surgeon will attempt to rotate the catheter 10 along its
 axis in order to accurately place the electrode 50 in the desired radial
 disposition. By providing the balloon 45 with the metalized coating 105, a
 sharp line of demarcation 109 is now apparent along the entire length of
 the balloon 45. If the surgeon requires an upper placement of the
 electrode 50, the catheter 10 can merely be turned on its axis until the
 fluoroscopic view of FIG. 19a is achieved. Different fluoroscopic views
 can be sought to achieve other preferred positions for the electrode 50.
 For example, progressive 45.degree. turns in a clockwise direction are
 illustrated in the side-elevation views of FIGS. 19a-23a.
 It should be apparent from these views that the metalized coating 105
 greatly facilitates operative disposition of the electrode 50. Although a
 semi-cylindrical placement of the coating 105 is illustrated in this
 embodiment, many other shapes of the coating 105 can also be relied on to
 facilitate radial placement of the electrode 50. Fluoroscopically, the
 embodiment illustrated in FIGS. 19a-23a provides the longest line of
 demarcation 109 and perhaps the greatest visual indication of electrode
 orientation. It should also be noted that the metalized coating, such as
 the coating 105 on the balloon 45, can also be applied to the sheath 47
 individually or in combination with the balloon 45.
 As previously discussed, it is desirable to maximize the magnitude of radio
 frequency current which can be delivered to the electrode 50. In the past,
 the electrode 50 has been provided with a proximal end 110 and a distal
 end 112. The proximal end 112 has been coupled to the connector 38 in
 order to energize the electrode 50. More typically, the metal core of the
 electrode 50 has been formed integral with the conductor 38 as a mere
 extension of the conductor 38. The distal end 112 of the electrode 50 has
 been terminated in the tube 25 of the catheter 10.
 In accordance with the embodiment FIG. 24, a second conductor 114 is
 provided which extends through the hub 30 at the proximal end 32, and is
 coupled to the distal end 112 of the electrode 50. The second conductor
 114 provides a further path for the transmission of electrical current to
 the electrode 50. The resulting increase in current which can be
 transmitted provides a commensurate increase in current density at the
 electrode 50.
 A semi-bipolar embodiment of the catheter 10 is illustrated in FIG. 25. In
 this embodiment, either or both the balloon 45 and the sheath 47 have a
 metallic outer surface 118 which provides a large area of contact with the
 body material, such as the strictures 23 (FIG. 1), which define the body
 conduit. In this embodiment, the conductor 38 is connected to the
 electrode 50 in the manner previously discussed. A second conductor 121,
 also emanating from the hub 30, is connected to the metallic surface 118.
 With the electrosurgical signal introduced across the conductors 38 and
 121, the catheter 10 tends to function in a bipolar mode with current
 passing from the relatively small surface area of the electrode 50 to the
 relatively high surface area of the metallic surface 118. This
 configuration is bipolar in that both of the poles of the electrosurgical
 circuit are carried by the catheter 10. The configuration is monopolar to
 the extent that one of the poles presents a surface area so large that the
 current density at this pole has no effect upon the tissue of the patient.
 This embodiment is referred to herein as semi-bipolar.
 In order to facilitate insertion of the catheter 10, it is always of
 interest to minimize the cross-sectional area of the tube 25. This is
 accomplished in a preferred embodiment illustrated in FIGS. 27-29, where
 the tube 25 has but a single lumen 27 (FIG. 3). This lumen 27, which can
 be used to inflate the balloon 45, is primarily sized and configured to
 receive the guidewire 41.
 The guidewire 41 in this case is especially constructed with a
 non-conductive distal portion 125 coupled at a junction 127 to a
 conductive proximal portion 130. The conductive proximal portion 130 is
 covered generally centrally with insulation 132 leaving exposed a distal
 patch 134 near the junction 127, and a proximal patch 136 at the proximal
 end of the guidewire 41.
 At the proximal end of the catheter 10, the hub 30 can be provided with a
 threaded male fitting 138 which is adapted to receive the guidewire 41. A
 complementary cap 141 includes a female fitting 143, adapted to receive
 the fitting 138, and a tube 145 which extends proximally axially from the
 fitting 143. A conductor 147 is molded into a closed end 149 of the tube
 145.
 In operation, the guidewire 41 is inserted into the body conduit, such as
 the ureter 14, in a manner well-known in the art. The catheter 10 is then
 threaded over the proximal end of the guidewire 41 and pushed distally
 toward its operative position until the proximal end of the guidewire 41
 is exposed at the hub 30. At this point, the cap assembly 141 is moved
 over the proximal end of the guidewire 41 until the proximal patch 136
 achieves electrical conductivity with the conductor 147. Holding the hub
 30 in one hand, and moving the cap assembly 141 forces the guidewire 41
 distally relative to the catheter, but also brings the female fitting 143
 into an abutting relationship with the male fitting 138. At this point,
 the cap assembly 141 can be tightened to the male fitting 138 to hold the
 catheter 10 and guidewire 41 in a fixed axial relationship. This
 relationship is facilitated by a radial seal 152 in the embodiment of FIG.
 29.
 At the distal end of the catheter 10, the electrode 50 is provided with a
 proximal end 110 that is foreshortened, but exposed within the lumen 27 in
 proximity to the sheath 47. The exact location of the proximal end 110 of
 the electrode 50 is predetermined relative to the hub 30. This known
 distance can be used to locate the distal patch 134 of the conductor 130
 on the guidewire 41 so that complete assembly of the guidewire 41 and
 catheter 10, as illustrated in FIG. 29, brings the proximal end 110 of the
 electrode 50 into electrical contact with the distal conductive patch 134.
 With these structural relationships, electrosurgical energy applied to the
 conductor 147 at the proximal end of the cap assembly 141 will pass
 through the conductor proximal portion 130 to the conductive patch 134.
 This energy will then be transferred to the distal end 110 and into the
 electrode 50.
 In this manner, the guidewire 41 can be used to energize the electrode 50,
 thereby eliminating the need for any energizing conductor such as the
 conductor 38 (FIG. 5). It will be noted that, with the guidewire 41 thus
 configured, there are no conductive elements of the guidewire 41 which
 extend beyond the distal end of the catheter 10. Also, although the
 insulation 132 over the conductor portion 130 is provided in a preferred
 embodiment, this may be eliminated in another embodiment since the
 conductor 130 is effectively insulated by the tube 25 of the catheter 10.
 A further advantage associated with this system relates to the axial
 placement of the catheter 10. Once the guidewire 41 is axially oriented
 with the junction 127 disposed at a predetermined position, location of
 the catheter 10 and associated electrode 50 is fixed along the length of
 the guidewire 41. Not only is the catheter 10 fixed to the guidewire 41 at
 this preferred location, but the electrode 50 is only energized at this
 predetermined location along the guidewire 41.
 It will be understood that many other modifications can be made to the
 various disclosed embodiments without departing from the spirit and scope
 of the concept. For example, various sizes of the surgical device are
 contemplated as well as various types of constructions and materials. It
 will also be apparent that many modifications can be made to the
 configuration of parts as well as their interaction. For these reasons,
 the above description should not be construed as limiting the invention,
 but should be interpreted as merely exemplary of preferred embodiments.
 Those skilled in the art will envision other modifications within the
 scope and spirit of the present invention as defined by the following
 claims.