CA2037242A1 - Rf ablation catheter - Google Patents

Abstract

RF ABLATION CATHETER

ABSTRACT OF THE DISCLOSURE

An intravasaular catheter especially designed to surgically remove atheromas or other forms of stenotic or thrombotic lesions from the interior walls of a blood vessel using an RF discharge between two bipolar electrodes is described. Affixed to the distal end of an elongated, flexible, plastic, tubular member is a bipolar electrode structure comprising a cylindrical insulator having a first conductive metal ring electrode surrounding the periphery of that insulator. Projecting from the distal end of the cylindrical insulator is a second, frusto-conical shaped member whose major base is slightly less in diameter than the diameter of the cylindrical insulator. An insulative material covers all but the distal side edge of the first ring electrode and an annular zone of the second electrode located immediately adjacent to the exposed distal side edge of the first electrode. Wires running through the lumen of the tubular member couple the first and second electrodes to an RF generator coupled to the catheter's proximal end. When appropriately energized, an intense current flow path is created between the exposed electrode surfaces for cutting through the blood vessel obstruction. The cone shaped member is rotatable about an axis which is eccentric to the centerline of the cylindrical insulator and by manually manipulating a torquing wire or tube at its proximal end, the electrode gap can be varied to control the location where cutting occurs. A motor device may also be used to continuously rotate the torquing wire.

Description

Xl.'l~E:S~; M~IL ¦~RB16446G~2 . ~ ~ 20372~2 RF ABLATION CATHETER
CROSS-REFERENCE TO REL~TED APPLICATION
This application is a continuation-in-part in application ~erial no. 07/337,428, ~ilsd April 13, 19~9, and entitled "RF
ABLATION CATHE~ER'I.
BACKGROUND OF THE INVENTION
I. Field of the Invention: This invention relates generally to an electrosurgical device for removing unwanted tissue and more particularly to an intravascular cathetar having blpolar alectrodes at the distal end thereof across which a high intensity RF current can be made to flow for cutting away atheromas or other lesions which may be par~ially occluding a blood ve~sel.
II. Discussion of the Prior Art: The bu~ldup o~ atheromas or the formation of thrombi in a blood vessel can cau~e serious circulatory problems and when complete blockage occurs, distal tissues may be deprived of oxygen and nutrients, leading to damage or destruction of cell tissue distally of the bl~ckage. A~ the bloakage grows, distal tissue may become more ischemic unle~, of course, channelization occurs whereby blood bypasse~ the constrictlon. With a narrowed blood ve~sel, a point may be reached where even a tiny thrombus beaomes lodged creating an infarct.
The treatment of diseased blood vessels depends to a large extent on the location of the blockage~ In the casQ of a blocked or partially blocked coronary artery, it has been the practice to perform coronary bypass surgery. In a like ~ashion, blood vessel shunts have been in~talled in other body areas a~ well. The surgery involved in those proaedures tend~ to be quite traumatic, involving, in the case of coronary-bypa~ ~urgery, the open~ng of the patient's chest and perlcardium. In treating deep vsin : , .

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' thrombosis or other blockage~ in the peripheral va~cula~ure, extensive excision and vessel replacement i~ often requlred.
More recently, following the technique aredited to A. Grunz~q, a balloon catheter has been u~ed to re~tore patency to blood vessels without extensive surgery. In carrying out this technique, a catheter having a small infla-~able balloon on it~ di6tal end is routed through the vascular system ~o the site of the restriction to be treated. The de~lated balloon iB appropriately po~itioned to span the blockage in queetion and then a fluid is lntroduced into the proximal end of the catheter to inflate the balloon to a suf~iciently high pressure whereby the blockage i~ spread open and patency is restored.
As i~ pointed out in the United State~ Patent 4,445,509 to Auth, there are some deficiencies in the Grunziy procedure which renders it ineffective in certain applications. For example, the blockage may be such that it iB not po~sible to sa~ely force the distal tip of the catheter through the blockage prior to the inflation of the balloon. The Auth patent al~o aites a number of other U.S. patents relating to aatheter-mounted cutting device~
intended to "tunnel" through a blockage but without doing damage to the healthy blood vessel tissue. The invention of ths Auth patent is in the desiyn of a rotatably driven cutting tool which will preferentially abrade hard or calcified le~ions while not significantly abrading the endothelial lining of the blood veesel.
Atherectomy cathster~ with rotary cutting head~ are difficult and c06tly to make, especially given the need for providing seal6 on shafts moving at very high ~peeds. The RF ablation catheter of the present invention ie eubetantially eaeier to proau¢e in that no moving part~ are involved. Also, the debri~ releas~d down~tream

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from rotating cuttexs may be ~ub~tantial, whereas debri~ from RF

ablation is very small and more ea~ily tolerated by the body.
SUMMARY OF THE INVENTION
In accordance with the present invention, there i~ provided an RF ablation catheter especially desi~ned for removing ~tenotic lesions from s~riously blocked blood ves6el~. The device comprises an elongated, plastic, flexible, tubular member which i~
dimensioned so a~ to pass through a guide catheter to the site of the lesion to be treated. Di~posed on the distal end of the catheter body i5 a tip member which includes flr~t and ~econd spaced electrodes, with the tip member being configured to produce a general centering thereof within the blood v2~sel being treated.
In this regard, it has been found convenient to provide as the most proximal electrode an electrically conductive annular ring 6urface lying in a transverse plane and as the most di~tal electrode a conic fru3tum which taper~ in the distal dirsction from a larger diameter at its ma;or base to a les~er diameter at ~ts minor base.
The cone portion is dispo~ed eccentrically relative to the center of the annular proximal electrode and i~ rotatable about a longitudinal axis by manipulating a knob at tha proximal ~nd of the catheter body. As such the gap between the elactrode~ can be adjusted. A set of wire~ run the full length of the catheter body BO that an appropriate RF voltage can be impre~sed acro~s the electrodes to generate a high lnten~ity current, e.g. an arc discharge, at a radlal location which can be ehif~ed by rotation of the cone portion. When the ~tenotic tissue i8 expo~ed to the high intensity current path, it electroeurgic~lly cuts away the t~seue comprising th~ blockage. Beaau~e of the design o~ the di~tal tip member, the aro can be preferentially direated, thereby avoiding damage to healthy blood vessel tis~ue.

` 2~372~2 Flgure 1 is a side elevation o~ a electrosurgl~al catheter in accordance wlth the present inventions Figure 2 is a greatly enlarged cro~s-sectional view taken along the lines 2-2 in Figure 1:
Figure 3 i~ a further enlargement of the elsctro~urgical cutting tip showing the location of the arc discharge; and Figure 4 is an anlarged cross-sectional view showing an alternative embodiment of the pre~ent invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referrin~ first to Figure 1 there i~ lndicated generally by numeral 10 an ablatlon catheter constructQd in accordance with the present invention. It is seen to include an elongated tubular body 12, which is preferably formed from a suitable, mediaal-grade plastic and dimensioned such that it may be introduced at a predetermined location in a living body and routed through the vascular system, all in accordance with known catheterization procedures. Affixed to the distal end 14 o~ the tubular body 12 is a tip member 16, the construction details of which are set out hereinafter. Appropriately bonded to the proximal end 18 of the tubular body 12 i8 an electrical connector 20 having a pair of terminals 22 and 24 which can be plugged into a suitable RF voltaye generator and a side entry port 23. The terminal~ 22 and 24 are ~oined by suitabla means to electrical conductor~ 26 and 28 which extend throuyh the lùmen of the tubular body 12 to 6eparate, spaced-apart electrodes on the tip member 16. Conductor 28 is preferably a long, flexible rod, wire or tube which pas~ee into the port 23 and includes a knob 29 to facilitate it~ rotation.
With reference to the cros~-sectional view of Figure 2, the tip member 16 is eeen to comprise a rlght aircular aylinder 30 ` ~37~42 whlch is preferably formed from a ceramic or other non-conductive material capable of withstanding the high operatlng temperat~res encountered. Surrounding the cylindrlcal ceramia core ~0 is a metal annulu~ 3~ to which the conductor 26 iB shown a~ being electrically connected. 'rhe plastic tube 12 extends over a substantial portion of the surface of conductive ring 32 with the remaining distally located portion being covered with a plasma sprayed ceramic 33 capable of withstanding the temperatures proximate the effective electrode surface. ~hus, the effective electrode surface, i.e., the uninsulated surface, of the conductive ring 32 is a circular band 34 whose thickness pre~erably lies in the range of from 0~003 to 0.010 inches.
Mounted for rotation on the transverse distal edge of the ceramic cylinder 30 i5 an eleckrically conductive body 36 of a frusto-conical shape, the major base abuttlng the distal side ~urface of the ceramic cylinder 30~ The wire or rod 28 passes through a centrally located bore 31 in the member 30 and is conductively fastened to the body 36 at a location of~set ~rom it~
central access by a small eccentriaity. As shown in Figures 2 and

3, a ma~ority of the sur~ace of the frusto~conical shaped conductive body 36 is coated with an insulating pla~tic material such as Teflon layer 38 so that only a narrow band 40 comprising a second electrode surface remain~ uncovered. This ~and is immediately adjacent the transverse distal edge o the ceramic core 30 and is displaced from the electrode surfac~ ~band 34) of the metal ring 32 by a variable gap distance. That ie, the diameter of the ma;or base of the body 36 iB less than the diameter of the ceramic member 30 and, accordlngly, ths band 40 comprl~ing the second electrodQ ls off~et from the first electrode (ring 32) by a predetermined gap di~tance. By rotatlng the knob 29 and, hence, . ` 203~2~2 tha body 36, the gap between the two electrods~ may ba made to vary between from about 0.003 inches as a minimum and to 0.020 lnches as a maximum. It is also envisioned ~hat the connecting wire 28 can be continuously torqued by employing a small, D.C. motor 27 either directly coupled or coupled through a gear reduction to drive the wire 28 at a low speed, e.g., 10 - 50 r.p.m. to cause the narrow point of the gap to sweep out a aircular orbit at a fixed rata.
conventional ~lip ring connection (not shown) i8 made between the torque wire 28 and the input kerminal 24, allowing it to rotate while also providing electrical continuity.
A short length of flexible guidewirQ 42 is pre~erably bonded to the minor base of the frusto-conical ~haped electrode 36 and is also covered with a insulativa coating, e.g., Teflon. The guidewire segment 42 facilitates the ~t~erlng o~ the RF catheter into a deslred vascular branch as the knob 29 is manip~lated.
In operatlon, an electrosurgical RF generator, ~uch as of the type disclosed in the U.S. Patent No. 4,903,696, issued February 27, 1990, and entitled ELECTROSURGICAL GENERATOR and a~signed to applicant's assignee, may have its output coupled to the termlnals 22 and 24 of the RF catheter 10. When energized, a RF voltage will be developed between the exposed electrode surfaces 34 and 40. The output of the RF generator may be adjusted so as to create a high intensity current flow path or even an ara discharge as indiaated by the dashed arcuate lines 44 in ~igure 3.
As the catheter of the present invention is advanced against a stenotic lesion which is generally symmetrioally formed on the blood vessel wall, the tapered conical shape o~ th~ member 36 will tend to center itself in whatever lumen may be present in the lesion. Now, when the RF energy i~ applied ~o as to create an arc discharge, the tissue abutting the annular ring will be cut, ' ~ '.'~

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``` 2~372~2 tunneling through the blockage. secau~e the loaation o~ the ~rc i8 precisely focused by includiny the in~ulative coverlngs thereon, only the material comprising the le610n will be e~fected by the RF
cutting, thus leaving the healthy blood vee~el tiseue unaffected.
In the event the leeion to be treated cover~ only a limited portion of a blood vessel, i.e., it is asymmetri~al, the ~urgeon may, by manually rotating the knob ~9, cause the electrode gap to be small in the area of the lesion, but large enough next to the normal vascular tissue to preclude cutting. If a motor iB uaed to torque the wire 2B, the high intensity current/arc u~ed for cuttlng can be made to ~weep in a circular orbit.
Figure 4 i~ another enlarged ViQW 0~ the tip member illustrating the manner in which either flushing or aspiration may be carried out during the procedureO The arrangement shown ln Flgure 4 di~fers from that o~ Figure 2 in that there i5 provided through the ceramic cylinder 30 a central bore 46 which 1B in fluid communication with a hollow 4~ formed in the fru~to-conical member 50. When a fluid i~ injected into ths proximal end of the cathetert it perfusee out thQ interface spaca between ceramic member 30 and the frusto-conical tip portion 50. Alternatively, by coupling a vacuum source to the lumen of the tubular member 12 at its proximal end, the sitQ at which the distal tip member i~
located can be aspiratad. Hence, i~ durlng ths aourse of an electrosurgical ablation o~ a vascular le~ion, carbon particles or ~ulgurated blood and tiseue particle~ can be drawn from the treatment site and through the catheter body.
Thls lnvention has been de~cribQd herein in con~iderable detail in order to comply with the Patent Statutee and to provide those skilled in the art with the information needed to apply the novel principles and to construct and uss ~uch spsaialized ,, , 2~37~
components as are re~uired. ~owever, lt is to be under~tood that the invention can ~e carried ou~ by ~peai~ically dlffexent equipmen~ and devlces, and that various modi~ica~ion~, both as to the equipment details and operating procedures, aan be accomplished without departing from the scope of the invention itself.
What is claimed is:

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Claims (12)

1. An intravascular RF ablation catheter for removing stenotic lesions from a blood vessel, comprising:
(a) an elongated, plastic, flexible tubular member having a proximal end, a distal end and a lumen extending therebetween:
(b) first and second electrical conductors, each having a proximal end and a distal end, said conductors extending through said lumen;
(c) a tip member attached to said distal end of said tubular member, said tip member including (i) a cylindrical insulating member surrounded by an annular first electrode, said insulating member and annular electrode being inset into said distal end of said tubular member with only an edge surface of said first electrode exposed at said distal end of said tubular member, and (ii) a frusto-conical shaped electrically conductive second electrode member. having a major base and a minor base with said major base positioned adjacent said cylindrical insulator and separated from said first electrode by an annular insulating gap;
and (d) means for connecting said first electrode to said first conductor and said second electrode to said second conductor.

2. The RF ablation catheter as in Claim 1 wherein said first electrode is fixed and said second electrode is rotatable relative to said first electrode.

3. The catheter as in Claim 1 and further including an insulating sheath covering predetermined surfaces of said frusto-conical shaped conductive member.

4. The catheter as in Claim 1 and further including a guidewire attached to said minor base of said frusto-conical shaped second electrode member.

5. The catheter as in Claim 1 and further including means for applying an RF electrical voltage between said first and second electrodes to produce a current flow sufficiently intense to cut through body tissue positioned across said annular gap.

6. An intravascular RF ablation catheter comprising:
(a) an elongated, flexible, plastic tubular body having a proximal end and a distal end and a lumen extending therebetween;
(b) an insulating cylindrical plug inset into said distal end of said tubular body;
(c) a first, annular electrode surrounding said plug:
(d) a second, conically-tapered electrode member, said second electrode member being attached to the distal end of said plug such that said second electrode is spaced from said first annular electrode by an annular gap; and (e) conductor means extending the length of said body from said proximal end to said distal end for coupling a RF voltage to said first and second electrodes, said voltage being sufficient to effect cutting of tissue by an intense current flow across said gap.

7. The catheter as in Claim 6 and further including insulating means masking portions of said first and second electrodes for defining the location of said intense current flow.

8. The catheter as in Claim 6 and further including a fixed guidewire attached to the distal end of said conical electrode.

9. The catheter as in Claim 6 wherein said tapered electrode member is rotatably attached to said distal end of said plug.

10. The catheter as in Claim 6 wherein said tapered member is eccentrically and rotatably attached to said distal end of said plug.

11. The catheter as in Claims 9 or 10 and further including means including one of said conductor means coupled to said proximal end of said tubular body for imparting rotation to said tapered member.

12. The catheter as in Claim 11 wherein said means for imparting rotation is a motor operatively coupled to said one of said conductor means.