CA2197470A1

CA2197470A1 - Mapping r- f ablating liquid injecting screw- in catheter mounted electrode

Info

Publication number: CA2197470A1
Application number: CA002197470A
Authority: CA
Inventors: Peter M. J. Mulier; Michael F. Hoey
Original assignee: Individual
Current assignee: Medtronic Inc
Priority date: 1994-09-08
Filing date: 1995-07-28
Publication date: 1996-03-14
Also published as: EP0779794A1; DE69530493T2; EP0779794B1; WO1996007360A1; JPH10505268A; US5725524A; US5609151A; DE69530493D1; AU692289B2; EP1149564A1; US5906613A; AU3150695A

Abstract

A method and apparatus for ablation of body tissue. A catheter provided with a hollow needle is employed both for mapping the location to be ablated by injection of an excitability reducing agent and for ablating tissue, employing RF energy in conjunction with an injected, conductive fluid. The hollow needle can be shaped in the form of a spring like helix intended to pierce the surface of the organ and then to penetrate into the tissue under the action of a rotation imposed upon the catheter by the operator. The penetration of the electrode into the tissue guarantees efficiency of ablation and prevents dispersion of energy on not targeted locations. A second ablation electrode may be present in a recessed cavity at the catheter distal end. The injection of cool or warm liquids through the helix like needle requires the liquid to be kept at the wished-for temperature along the length of the catheter. To this objective the catheter main lumen is made into three coaxial channels, the innermost of which carries the injection liquid, and the two others create a two way circuit where another heated or cooled liquid is forced to circulate to maintain the temperature of the injection liquid in the innermost tube at the distored level.

Description

~ w o 96/07360 2 1 9 7 4 7 0 .~ 9~78 MAPPING R- F ABLATING LIQUID INJECTING SCREW- IN CATHETER MOUNTED ELECTRODE
ofthelnvention This invention relates geneMlly to the field of devices for cardiac surgery, and more specifically to devices for R-F ablation of cardiac tissue.
~ The present invention is directed toward treatment of la-,h~ ya~ a, which 5 are heart rhythms in which a chamber or chamber of the heart eAhibits an cAu~ ly fast rhythm. In particular, the present invention is directed toward treatment of ~ udi~s, which are due to the presence of ectopic foci within the cardiac tissue or due to the presence of aberrant conduction pathways witbin the cardiac tissue.
Therapies have been developed for treating ~.l.. ~ldi.. ~ by destroying cardiac tissue containing identified ectopic foci or aberrant conduction pathways. A variety of approaches have been taken, including application of electrical energy or other forms of energy to destroy the undesired cardiac tissue. As examples, ablation of cardiac tissue has been ~ .1 by means of radio frequency electrical current, 15 microwave energy, heat, electrical pulses, ..yl .~, and lasers. At present, ablation usrng R-F energy is perhaps the most widely practiced in the context ofablation procedures that can be carried out by means of a catheter, inserted mto the closed heart.
Most R-F ablation catheters employ electrodes which are intended to contact 20 the c..do~dh.l.. of the heart, or, as in U.S. Patent No. 5,083,565, are intended to penetrate the . -~ .l; ., and enter the lllyVl ~ In general, R-F ablation catheters are effective to induce small lesions in heart tissue including the endocardiurn and inner layers of ...~).~.1;~., in the immediate vicinity of the electrode. However, the medical community has expressed a desire for devices 25 which produce larger lesions, to reduce the number of -~ of R-F energy(burns) required to effectively ablate the cardiac tissue associated with the R-F ablation causes tissue in contact with the electrode to heat as a result of resistance of the tissue to the mduced electrical current a~ a..u.,6'l. The actual 30 extent of heating is somewhat ,l.. ~ , However, i l tends to rise as the duration and amplitude of the R-F signal increase. Heatmg of the tissue beyond a certain pornt (i.e. 100 degrees C) can cause dissectiûn or charring of the tissue, W096/07360 2 1 97470 J l/~J.. s 478 resultmg in a high impedance between the R-F electrode and the return electrode,which in turn leads to cessation of the heating~process,~ and, in some cases, causes the electrode to stick to the charred tissue. One response to this p~ has been the mclusion of ll....~n~u I.l within the ablation electrode, in ~..~..j.~-- lil.., with 5 feedback control to modulate the R-F signal to maintain the electrode t~ u~i at a set parameter. One such system is disclosed in U.S. Patent No. 5,122,137.
~mn~q~y of the Lnvention The present invention is directed toward improving the consistency and efficacy of R-F ablation, by more accurately ~l ..";..;ug the ablation site and by 10 increasing the overall size, extent and depth of the lesions induced by R-F ablation.
These goals are pursued by means of an ablation catheter employing a hollow, preferably helical electrode intended to be placed against or preferably inserted into the ....r~,ll,' or other tissue at the site intended for ablation. The electrode is provided with a source of ~hy~;ulO~ic Ringer's solution, saturated Ringer's solution 15 or other conductive f uid for injection into the tissue adjacent the electrode. In its preferred e.lll " t, the conductive sûlution is applied through apertures at the end of or along the length of the electrode. The conductive solution injected prior to application of the R-F signal is believed to displace blood and,'or increase the amount of ;"o... ~ . in the vicinity ûf the electrode. Ringer's solution, for example, has a 20 much higher uùnllu~,livily than blood (a,u~ 'y 3 ~x) or cardiac muscle (O.,U,UI~ / 7x), overall resistance to the induced electrical current is reduced, which is believed to assist in expanding the si~e of the lesion, by spreading the effective area of application of the electrical current over a wider area. Application of the conductive solution during the burn can also increase the thermal l ulldu~,liviLy 25 of the tissue 30 - 50%, and further assists in expandmg the size of the lesion by preventing u~ of the tissue, allowmg for a prolonged application of the R-F
signal, extending beyond the point at whjch burning or charring would otherwise normally occur. Injection of a saturated Ringer's or saline solution has an even more dramatic effect, and produces a 10 - 15 fold increase over the level of ~ ' ,ily30 prDvided by l,L~i,iolo~ Ringer's solution. All of these factors are believed to contribute to an increase in the overall size of the lesion produced by application of R-F energy at a particular location.

.. . . . . .

~ WO 96/07360 2 ~ ~ 7 4 7 0 PCTNS95/09478 In some c ,ho.l;~ , the catheter is also provided with a second electrode, recessed within a lumen open to the distal end of the catheter. The open end of the Iumen is held against heart tissue by the helical electrode, and the lumen is fillcd with a conductive fluid which serves to couple the recesscd electrode to the tissue.
5 The two electrodes may be used alone or in ; with one another to produce lesions of varying shape and location. ~
In some ~lllI,odiull~ , the catheter is adapted to deliver a chillcd or heatcd fluid, such as Ringer's solution, through the elcctrode, onto or into the tissueadjacent the electrode. Chilled fluid may be used to cool the tissue in a fashion similar to cryo-mapping as disclosed in U.S. Patent No. 5,281,213, issued to Milder et al. Typically, the tc~ .ldLulc gradient provided by cryogenic cooling varies as a function of the thermal uullducLivily of the tissue, and the i , c gradient is typically quite steep. In the context of ablation of cardiac tissue, The ability to cool tissue deep in the ventricular wall has thus bcen limited by the ICU,UilCIll.,nt that the tissue adjacent the surface of tbe ventricular wall must not be cooled to the point of causmg cellular damage. Injection of cooled fluid, such as Ringer's solution, serves to l~n~o~ y cool the tissue and increase its thermal curldu_livily, with the netresult that tissue deep in the ventricular wall can be cooled without cellular damage.
In this context, directional injection of the chilled fluid through a laterally facing aperture in a hollow electrode, such as the opening at the distal end of a helical electrode, allows for testing of multiple adjacent tissue locations by simply rotating the electrode in the tissue, without having to reposition the catheter. c ~ , directional delivery of conductive fluid may also be employed in c~ with ablation of the tissue.
Heated Ringer's or other conductive fluid may be delivered through the electrode to further enhance the R-F ablation process. By raising the LIll~ dlulc of the solution to 50 degrces centigrade or less,, ' vily mcreases of up to 200% m the fluid itself and cullc.,~Olr~lul~ "vily increases of up to 307c in the tissue in which the fluid is injccted, can be achievcd. Higher h.,.~,ldlul.,;, bring higher 30 ~ ' iviLi.,, and, for Llu~ ,.c~ above 50 degrees centigrade, can cause ablation due to the hcat of the delivered fluid as an adjunct to or a substitute for R-F ablation.
or more, tissue adjacent the electrode.

w0 96/07360 2 1 9 7 4 7 0 ~ J ,78 ~ ' The catheters and electrodes disclosed are particularly optimized for ablation of heart tissue. However, the benefits provided by the present mvention are believed equally valuable in ~ related to ablation of other tissue types, and m particular are believed valuable m ablation of tumors. It is expccted that electrode 5 sizes and shapes, the cu~duulivili~s~ volumes and flow rates of the injected fluids, and the parameters of the R-F signal applied to the electrodes will vary as a function of the specific type of tissue being ablated.
BriPf DP~rrip~i~n of " ~ Drawir~
Figure 1 is a plan view of a catheter adapted to perform the improved method lO of R-F ablation, accordmg to the present invention.
Figure 2 is a cutaway view through the distal end of the catheter illustrated inFigure l.
Figures 3 illustrates an alternative ....I,o.l;....l to the catheter of Figures 1 and 2, employing a second, recessed electrode.
Figure 4 illustrates a cut-away view of the catheter of Figure 3, with its helical electrode located in heart tissue.
Figure 5 illustrates an ablation catheter adapted to deliver a chilled fluid to its helical electrode, for mapping.
Figure 6 illustrates an ablation catheter adapted to deliver a chilled fluid to a 20 porous, non-helical electrode, for mapping.
Figure 7 illustrates a second ~...1.~1;.. : of an ablation catheter adapted to deliver a chilled fluid to its helical elcctrode, for mappmg, which also employs a recessed, sccond electrode.
Figure 8 illustrates a cut-away view through the distal portion of the catheter illustrated in Figure 5.
Figure 9 illustrates a cut-away view through the distal portion of the catheter illustrated in Figure 6.
Figure lû illustrates a cut-away view through the distal portion of the catheterillustrated in Figure 7.
Figure l l illustrates a the distal portion of the catheter illustrated in Figure 5, with its helical electrode located in heart tissue for directional mapping.
Figure 12 illustrates a pressurized source for Ringer's solution which may be employed m, ; with the catheters m Figures l - 11.

. : .. . . . . . .

2'1 97470 ~ W096/07360 r.,~ rS78 S

Pcrription of the Preferred E ' '' It~C
Figure 1 is a plan view of a cathete} specifically designed for p~,lru~ illg R-F~ ablation according to the present invention. The catheter includes an elongated catheter body 10, comprising an insulative outer sheath 12, which may be made of5 polyurethane, teflon, or other l,;,~c..~ il.lr plastic. A hollow, helical electrode 14 is located at the distal end of the catheter and is coupled to the distal end of an internal tube, running the length of the catheter. At the proximal end of the catheter a fitting 16 is located, to which luer lock 18 is coupled. Luer lock 18 is coupled to the proximal end of the internal tnbe. A swivel mount 20 is mounted to luer lock18, allowing rotation of the catheter relative to luer lock 22. Luer lock 22 is mtended to be coupled to a source of conductive fluid such as Ringer's solution, and allows for application of the Ringer's solution through the catheter and tbroughelectrode 14, while electrode 14 is being screwed into heart tissue. An electrical connector 24 exits fitting 16, and is coupled to electrode 14, allowing for the use of 15 electrode 14 to apply R-F energy to heart tissue. Electrode 14 may also be employed for other related functions such as Ill~,a~Ul~ ,Ut of cle~ u~la~ll, within the heart and pacing of heart tissue by application of low energy pulses a~JIUl for cardiac pacing. In use, the catheter is advanced to the desired site for ablation, which preferably has been previously identified by means of cardiac mapprng in a20 fashion similar to cardiac mapping presently employed with R-F ablation procedures.
The catheter may be guided to the desired location by being passed down a steerable or guidable catheter, for example, as disclosed in U.S. Patent No. S,030,204, issued to Badger et al., or by means of a fixed c~ f~ \ guide catheter, for example in U.S. Patent No. ~,104,393, issued to Isner, both of which patents are illl,Ul~l ' ' 25 herein by reference in their entireties. Alternatively, the catheter may be advanced to the desired site within a heart by means of a deflectable stylet, as disclosed in PCT Patent Application WO 93/04724, published March 18, 1993, or a defiectable guidewire as disclosed in U.S. Patent No. S,060,660, issued to Gambale, et al., both of which patents are ill~Ol~ ' herein by reference in their entireties. When the30 hollow needle 14 is located at the desired location it is screwed into heart tissue by rotatmg the catheter body. A torque cable within the catheter body provides for 1: 1 torque transfer from the proximal end of the catheter to the hollow needle 14.

WO 96/07360 ' 2 1 9 7 ~ 7 0 PCllUS~tY0947X

When advanced to the desired location, luer lock 22 is coupled to a plU;t~UliL~d source of Ringer's or other conductive solution. An ll~)~JIU~)I' ' source is discussed in more detail in ~ with Figure 6 below. However, for purposes of the present invention, a source of Ringer's solution capable of delivermg 5 2 cc per mmute of solution at a~ pressure has been found to be adequate.Delivery of Ringer's solution should begin before or at the time at which the electrode 14 is screwed into the tissue to be ablated. In animal ~.p~, ;", l -: ;. "" the inventors have found that delivery of Ringer's solution for a period of five minutes prior to the delivery of R-F energy assists in producing a larger but still controlled, 10 regular leslon.
After the electrode has been located, and Ringer's or other conductive solution bas been adllli. i~ d for the desired period of time, electrical COMector 24 is coupled to an R-F elc~LIu:,ul~ ,dl power source, of the type ~:ollull~l~;ally available and employed for cutting, electro-t~t~ it~n or ablation. The present inventors 15 have employed an Atakr Ablation System, ~ ulu~duLul~d by Cd~dtiu~hyllnl, San Hose, California, set to 50 watts output. At this setting, a prolonged application of R-F energy, e.g., for periods of two minutes, repeated ' 'y up to six times,may be employed to produce a large, controlled lesiori. Greater or lesser time periods may be employed, however, time periods less than 20 seconds may be 20 counter-indicated, as it appears that the cooling effect of the Ringer's solution, in such shorter R-F application times, may actually decrease the effective size of the lesion.
After R-F ablation, the electrode 14 may be coupled to a cardiac pacemaker, and cardiac pacing energy may be delivered to the lesion site in an attempt to 25 measure the pacimg threshold. Pacing threshold may be measured by delivermg pacing pulses at differing energy levels, e.g. by altering pulse amplitude or width, and t' _ the minimum energy level effective to cause a ~ ii".. of cardiac tissue. The inventors believe that the higher the pacmg threshold, assuming a relatively l..",..,~. .",..~ lesion, the greater lesion size. As such, the electrode 14 30 c~m be used to derive a rough estimate of overall lesion size. The electrode 14 may also be coupled EKG monitoring equipment to assist im ' ' ' ,, whether the Lt~ l.dtd persists and whether the tissue in the vicinity of the electrode is still ~ WO 96/07360 1 ~ ,,478 ..
lLiug in aberrant conduction or ectopic activity, associated with the The helical ~....,li~;l.."l,~" of electrode 14 is believed to be particula}ly beneficial in the context of an ablation electrode. Because the electrode is screwed 5 into and completely located within the heart tissue, out of the bloo.l~ ~u, application of R-F energy is limited to the tissue itself. This differs from traditional R-F ablation electrodes, which simply contact the e~lliOC~UI-' , with the result that a substantial portion of the energy applied is dissipated in the blood within the heart adjacent the electrode site. Moreover, R-F energy applied to the blood~LI~,.u.l may 10 cause clotting of the blood adjacent the electrode, and raise the risk of clots breaking loose of the electrode.
The helical electrode also provides a substantially increased surface area as compared to the needle-like electrodes proposed in the above cited Parins patent, and also serves to anchor the catheter reliably during application of the R-F energy. In 15 addition, the helical shape of the electrode prevents the application of conductive solution ihrough the electrode from causing the electrode to be backed out of its insertion site due to hydraulic pressure, as might occur if a straight, hollow electrode were employed. The elongated path defined by the helical electrode also reduces the possibility of leakage of conductive fluid along the needle and out of the heart tissue.
Figure 2 illustrates a cutaway version through the end of the catheter illustrated in Figure 1. In this view, it can be seen that helical electrode 14 is provided with an internal lumen 26 which is in, with the internal lumen of a tube 30. Tube 30 extends to the proximal end of the catheter and is in 25 full c~,..,... .:. -l;,. with luer lock 18, as discussed above, tube 30 may be fabricated of polyamide tubing or of stainless steel tubing. In the present invention, the stainless steel tubing seNes as an additional conductor, coupling electrode 14 to electrical connector 24 amd enhancing the overall c ~ vily of the catheter. The use of polyamide tubing, while reducing the overall ~:ulllln~,~ivi~y of the catheter 30 enhances the flexibility somewhat, and may be beneficial in some cases. It is~ ' to apply a steady flow of Ringer's solution through the tubing to electrode 14 during passage catheter through the vascular system to the electrode site, if possible. The flow of Ringer's solution in this case assists in ~ the wo 96/07360 -8~ 78 patency of the lumen of tubrng 30, and prevents pluggmg of the exit ports of theelectrode as it is advanced into the cardiac muscle.
Surrounding tube 30 are two coils 32 and 34, which are wound in opposite directions, to provide a torque cable. In the case of the specific devices employed by 5 the inventors, a torque cable as ~ ~d by Lake Region ~i.",. r I l;. ,g Company of Chaska, Minnesota was employed, which torque cable is described in U.S. Patent No. 5,165,421, il~ ' hereinby reference in its entirety. Coils 32 and 34 also serve as c--n~ln-~t~-rC As illustrated, tubing 30 is between metal coils 32 and 34 and helical electrode 14. However, if polyamide tubing is used, the coils 32 and 34 will serve as the only conductor and thus will be electrically coupled to electrode 14 by means of welding, soldering or mechanical i,~
Insulative sleeve 12 serves both to provide a smooth exterior for the catheter and to insulate the metal coils 32 and 34, along the length of the catheter.
Electrode 14 comprises a hollow metal (e.g. stainless steel) tube, which may have only a smgle exit port 36, located as its distal end, or ~ may be provided with a plurality of ports 38, arranged around and along the length of electrode 14. If directional injection of fluid is desired, typically only port 36 will be present. If an even ~lictrih~ltion of fluid is desired, ports 38 will be added to or substituted for port 36.
If desired, an insulative sleeve (not illustrated) which covers the proximal portion of the electrode may be provided, which serves to limit the application of R-F energy to the distal portion of the electrode. Exit ports 38 may be limited to the exposed, l ' ' portion of electrode 14, or may extend along tbe entire length of electrode 14. If desired, a Ih- ~. ~C~J-~ or other t~ c sensing device may be located within or attached to the electrode 14, to allow for: , based feedback control of the R-F power applied to the electrode as described in the above-cited patent issued to Lenmox et al.
Figure 3 illustrates a catheter employmg a second, recessed electrode in addition to a I _, helical electrode 202 c.J"~ ,u"d~" to electrode 14 as illustrated m Figure 1. Electrode 202 protrudes out the distal end of the outer catheter sheath 200, which in turn is coupled to manifold 204, which includes a fluid fitting 206 amd an electrical comnector 208. Extending proximal to manifold 204 is a second manifold 210, preferably mounted rotatably with regard to manifold 204, and ': 2 1 974 73 ~ WO 96/07360 PCT/USS~/09478 _9_ .. .
carrying a second fluid coupling 212 and a sccond electrical connector 214.
Electrical comnector 214 is coupled to electrode 202, and Cullc.~lJullllb to electrical conncctor 24 of the device illustrated in Figure 1. Fluid coupling 212 Cullc:~)U-ld~ to luer lock 22 illustrated in Figure 1, and is employed to deliver Ringer's or other 5 fluid to the interior of electrode 202.
Figure 4 shows a cutaway view of the distal end of the catheter illustrated in Figure 3, with the electro~e 202 screwed intû heart tissue 224. In this view, it can be seen that within the outer catheter tube 200 is a second catheter body 218, which may correspond precisely to the body of the catheter illustrated in Figure 1, and 10 includes an internal lumen couplcd to fluid connector 212 and to the interior of electrode 202, as well as an electrical conductor, for coupling electrode 202 toelectrical connector 214.
Mounted within outer catheter tube 200 is an internal, recessed electrode 216 which is coupled to electrical connector 208 by means of an insulated conductor 220.
1~ In use, electrode 202 is screwed into heart tissue 224, holding the distal end of outer catheter tube 200 tightly adjacent the tissue. Lumen 222 may then be filled withRinger's solution, providing a conductive connection between the ring electrode 216 and the heart tissue 224. Electrodes 216 and 202 may be used individually or in c.. j~ .. with one another, to control the depth and shape of the lesion provided.
A typical lesion outline for the helical elcctrode 202 is illustrated by broken line at A, while a typical lesion outline for the recessed electrode 216 is illustrated at broken out line at B. The lesions produccd by recessed elcctrode 216 tend to be conically shaped, and located more closely adjacent the surface of the tissue. The lesions produced by elcctrode 202 tend to be mûre spherical or ovoid in 2~ ;"" and tend to be located deeper witbin the tissue.
Figure 5 illustrates, ' ~ " of a catheter L)a.li.,.~ adapted for use in delivery of a chilled or a heated fluid through its helical electrode 302, to ~ comrlich .
cardiac mapping, prior to ablation or to enhance, ' viLy during ablation, lc~ ly. The catheter isprovidcd with an elongated outer catheter tube 300, which terminates m a molded plastic member 304, from which the helical electrode302 emerges. At its proximal end, a manifold 306 is couplcd to outer catheter tube 300 and is providcd with fluid couplings 308 and 310, for the ingress and egress, , of a cooling or heating fluid. Manifold 306 is also provided with an W0 96107360 ~ 478 --electrical connector 312 which is coupled electrically to helical electrode 302 and with a fluid coupling 314 which is coupled to the interior of electrode 302, and is used to deliver Ringer solution through electrode 302.
A cutaway view through the distal portion of the catheter illustrated in Figure 5 is shown in Figure 8. In this view, it can be seen that located within outer catheter tube are an inner catheter tube 306 and a metal tube 308, fabricated, for example of stainless l.~od~ .;., tube, which serves to electrically couple electrode 302 toelectrical connector 312 and to provide a fluid pathway from fluid coupling 314 to the interior of electrode 302. Plastic member 304 seals the distal end of the catheter body to the electrode 302. The inventors have determined that it is difficult toinject chilled or heated fluids down the length of the catheter as illustrated in Figure 1 and Figure 2, without the chilled or heated solution d~ ' ,, body h,lll~ d~UlCby the time it reaches the helical electrode. As a result, as illustrated in Figure 8, the inventors have derived a catheter which provides for three fluid flow channels, arranged "y. The inner channel, defined by the hypo tubing 308 serves to deliver the fluid to be heated or cooled(e.g. Ringer's solution) to the tissue, through electrode 302. The second fluid pathway, defned by the space between theinner tubing 306 and the hypo tubing 308, is coupled to fluid coupling 310, which in turn is to be coupled to a pumping means for pumping chilled or heated saline orother fluid down the catheter body, through this ' Iumen, in order to keep the Ringer's solution within hypo tube 308 in a chilled or heated state. At the distal end of the catheter, the cooling fluid leaves the ~ ' Iumen and enters the outer lumen defined by the space between outer catheter tube 300 and inner catheter tube 306, where it travels back up the catheter proximally, to fluid coupling 308, for ~c.,h-.ul~lLiull or disposal. A pressurized source for Ringer's solution to be injected into the tissue is illustrated in Figure 12, and would be coupled to fluid fitting 314, illustrated in Figure 5. Any d~ . ' ' pumping mechanism may be used to deliver heating or coolmg fluid to fluid coupling 310 and to remove it from fluid coupling 308.
For purposes of mappmg, it is preferred that the fluid delivered to the helical electrode 302 and injected mto the tissue be no more than 5~C. In order to ~~~ . ' ~ this, the L.IIIJ~,ldLUI~ of the coolant fluid applied to fluid coupling 310 should be adjusted. If desired, a i , ', as discussed above, might optionally ~ WO 96/07360 1 ~_111).. ~, ~478 be employed in c~ with electrode 302, and employed for ~ .,.I,.,c controlled regulation of the coolant t.ll~ dLulc, as well as for t.l.l,u.,l.,lu c based feedback regulation of our power applied to the electrode ablation.
Tissue mappmg using the catheter of Figure 5 is ~ "".~ h~.l by screwing 5 the electrode 302 mto the tissue to be tested, followed by delivery of chilled Ringer's solution at 5~C or less, in order to slow conduction through the tissue, and monitoring the electrical activity of the heart by means of electrode 302, tbrough electrical connector 312 (Fig. 5), while the patient is ul,d~,.ru .g an episode of s~l or induced Lllcl~ llhylull;d. If cooling of the tissue terminates the10 arrhythmia, the site is identified as an appropriate location for RF ablation.
If the electrode 302 is provided with only a single aperture, or with apertures directed only in a single direction, the catheter may be used to map multiple adjacent tissue sites, as illustrated m Figure 11. Figure 11 shows the distal end of the catheter illustrated in Figure 8, screwed into heart tissue. As illustrated at broken-15 out line C, chilled saline injected tbrough the aperture at the distal end of the helixtends to enter the tissue in a single direction. By rotatmg the helix, while in the tissue, multiple adjacent tissue sites may be sequentially mapped, without the necessity of removing the catheter from the tissue. RF energy may ~ l ly be applied, along with directional injection of Ringers, in order to ablate the identifled 20 dlfllylullc/~ tissue.
Figure 9 illustrates an alternative version of a mappmg/ablation catheter differing from that illustrated in Figure 8 primarily in that rather than a helical electrode 302 (Fig. 8), a porous electrode 402 is provided, mounted to the distal end of the outer catheter tube 400. Porous electrode 402 is preferably fabricated by25 powder metallurgy ' , , similar to those described in ~ with United States Patent No. 4,506,680, issued to Stokes and ill~ul,ul ' ' herein rn its entirety, and is provided with a porosity which provides a high resistance to fluid flow, for example no more than X cc's of fluid per minute at a pressure of Y psi. Electrode 402 is coupled electrically to elect~ical connector 412 and is coupled to a length of 30 hypo tubing within outer catheter body 400, which is in turn coupled to fluidcoupling 414. Fluid couplings 410 and 408, on manifold 406 correspond to fluid couplmgs 308 and 310, moumted on manifold 306, in Figure 5.

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21 q7470 wo 96/07360 . ~ ." J,~478 Figure 9 shows a cutaway version through the distal portion of the catheter illustrated in Figure 6, and in this view it can abe seen that its internal structure is similar to that of the catheter illustrated in Figure 8. A length of hypo tubing 408 is coupled to electrode 402, providing both a fluid pathway to the electrode and an5 electrical connection to the electrode. Coolant enters the catheter through fitting 410, and flows down the catheter between inner catheter tube 306 and hypo tube 408. Coolant exits the catheter flooding proximally between outer catheter tube 400 and inner catheter tube 406. In the context of the present invention, the provision of a porous electrode 402 having a high resistance to fluid flow prevents 10 the delivered chilled fluid from simply leaking out and being washed away in the blood stream. By restricting the flow through the electrode, the electrode can be cooled to a degree which will allow its use for mapping purposes. The catheter may also be employed for ablation, with delivery of Ringer's solution or other fluidthrough hypo tube 408 being employed primarily to prevent U~ h.~iUI~; of electrode 15 402. As in ~..; --.. I;o.: with the e lllb " of the present invention employing helical electrodes, electrode 402 might also optionally be provided with a Il,. .lllf.eu~ , allowing for t '--1" .~ control feedback of electrode i I .
during both mapping and ablation.
Figure 7 illustrates a second bc ' of a catheter, employing features of 20 the catheters illustrated in Figures 3 and 5, in a single device. Outer catheter tube 500 carries a manifold 506 at its proximal end, which includes fluid couplings 508 and 510, for egress and ingress, ~ iiY~Iy, of cooling or heating fluid. Electrical connector 512 is coupled to helical electrode 502. Fluid coupling 514 is coupled to the interior of electrode 502, allowing for delivery of Ringer's solution to the tissue, 25 through electrode 502. Electrical connector 516 ~""~l."-- ~ to electrical connector 208 in Figure 3, and is coupled to a recessed electrode located within outer catheter tube 500. Fluid coupling 518 eu...,~,uu...l~ functionally to fluid coupling 206 illustrated in Figure 3, and serves to allow delivery of Ringer's solution witbin the outer catheter tube 500, in order to couple the recessed electrode tube, in 30 the same fashion as discussed in ~ ; with Figure 4, above.
Figure 10 is a cutaway view through the distal end of the catheter illustrated m Figure 7. In this version of the invention, the catheter defines four concentric fluid paths. The innermost fluid path is defined by hypo tubing 524 which is coupled ~ wo 96/07360 ~ 3178 to helical electrode 502. Ringer's solution is delivered from fluid coupling 514, through tube 524 to electrode 502. Tube 524 also is coupled to electrical connector - 512. Mounted around tube 524 is irmer catheter tube 526, which cvllc,~v~
fimctionally to irmer catheter tubes 306 and 406 as illustrated in Figures 8 and 9, 5 lc~ iv~,ly. Cooling or heating fluid flows distally through the catheter in the fluid space defmed between inner catheter tube 526 and hypo tube 524. T
catheter tube 522 surrounds inner catheoer tube 526, and the space there betweendefines the return fluid flow path for coolant fluid, which is in turn coupled to fluid coupling 508. Plastic number 504 ~:UIIC~L~VIIdtl to plastic number 304 in Figure 8, 10 and serves to seal the distal end of i catheter tube 522. A ring electrode 520 is mounted around plastic number 502 and is coupled to electrical connector 516 by means of insulative conductor 528. The space between outer catheter tube 500 and ' catheter tube 522 defines the fourth, concentric fluid flow path, andis coupled to fluid coupling 518, allowing for injection of Ringer's solution into the interior of outer catheter tube 500, which in turn serves to couple electrode 520 to cardiac tissue, in the same fashion as discussed in c.. ., j, .. ,. ~ ;. ,.. with the catheter illustrated in Figures 3 and 4.
After mapping, and after the tissue has warmed, ablation may be ~ C.. ~ l.. d in the same fashion as discussed above in c.- .. ,; .. l ;- .. with the catheter 20 illustrated in Figures 1 amd 2. ~ ,ly, the catheters of Figures 5 and 7 may be employed to deliver heated Ringer's solution through the helical electrodes to further enhance c ' vily. As noted above, heated Ringer's solution displays an increased cvlld, _livily as compared to body i , I fluid. In addition, with fluid t~ , .,, of 50 degrees C or above the heated fluid itself serves to ablate25 tissue, even m the absence of R-F energy. Any .~ , commercially available heatmg or cooling bath may be employed to regulate the i , c of the applied solution.
Figure 12 illustrates a pressurized source for Ringer's or salme solution which may be employed to deliver solution to the electrodes of the catheters described30 above. A reservoir 100 is provided, which is: 'Iy ~ ' by Block Medical Inc., and sold under the brand name "Home Pump". The reservoir contains Ringer's solution or other conductive fluid and provides the fluid at one ~ v~l/h.,lc pressure to flow control 102, via filter 104. Flow control 102 may, for example, wo 96/07360 -14- PCrNSrs/09478 provide a flow limit of 40 drops or 2 cc per minute. Flow control 102 is coupled to a second flow control element 104, which, in the e~ iu~ ldl apparatus employed by the mventors allows for additional adjual~lJ;lily of flow rates. Flow control 102 or 104 preferably includes a one-way valve, providing a fluid column which prevents 5 tissue from entering and plugging of the holes m the electrode. Flow control 104is coupled to the luer lock 22, illustrated in Figure 1, which in turn is m fluid f.~ 1 with electrode 14 (Figure 1), allowing delivery of Ringer's solution to the electrode. An cL~ uau~ ,dl generator 200 for providing R-F electrical energy is illustrated in functional block form, coupled to electrical commector 24 and 10 to a ground plate electrode 202 (not drawn to scale). All other labeled elements correspand to those illustrated in Figure 1.
While the ~ I ' illustrated above requires a second element (e.g. a guide catheter or guide wire) for advancing and positioning the catheter at its desired location, it is anticipated that the basic apparatus disclosed above may also be15 h~ uld~d into catheters whuch themselves are steerable or rlPnpc~ p~ similar to R-F ablation catheters presently in clinical .~ ..;iu... Similarly, it is anticipated that in f ~ " ', alternative ' - (e.g. precision pumps) for controlling the flow of Ringer's solution may be employed. Srmilarly, while the inventors have employed Ringer's solution, other al~ernative fluids may be workable as well. As such, the .,., I,o~l;.. 1 discussed above should be considered exemplary, rather than limiting, im ; with the following claims.
In ; with the above ~ fi~ -1;ll, we claim:

Claims

1. An ablation catheter system, comprising: an elongated catheter body having a proximal end, a distal end and comprising a first tube having an internal longitudinal lumen;
a hollow conductive electrode mounted to the distal end of said catheter body and having an internal lumen coupled to the internal lumen of said first tube;
fluid delivery means coupled to the internal lumen of said first tube for delivering a conductive fluid to said internal lumen of said first tube;
conductor means for coupling said electrode to a source of R-F
energy;
means other than said electrode and conductor means for altering the temperature of said conductive fluid while in said internal lumen; and

2. An ablation catheter system according to claim 1 wherein said temperature altering means comprises:
a second tube, located exterior to said first tube and having a distal end sealed to said electrode;
a third tube, mounted between said first and second tubes, defining a first flow path between said first and third tubes and a second flow path between said second and third tubes, said first and second flow paths in fluid communications adjacent said distal end of said second tube;
first fluid coupling means for coupling said first fluid path to a source of cooling fluid; and second fluid coupling means for coupling said second fluid path to provide an outlet for said cooling fluid.

3. An ablation catheter system according to claim 1 wherein said temperature altering means comprises:

a second tube, located exterior to said first tube and having a distal end sealed to said electrode;
a third tube, mounted between said first and second tubes, defining a first flow path between said first and third tubes and a second flow path between said second and third tubes, said first and second flow paths in fluid communication adjacent said distal end of said second tube;
first fluid coupling means for coupling said first fluid path to a source of heating fluid; and second fluid coupling means for coupling said second fluid path to provide an outlet for said heating fluid.

4. An ablation catheter system according to claim 1 or claim 2 or claim 3 wherein said electrode is a hollow needle.

5. An ablation catheter according to claim 4 wherein said electrode is a hollow, helical needle.

6. An ablation catheter according to claim 1 or claim 2 or claim 3 wherein said electrode is a porous, conductive electrode.

7. An ablation catheter according to claim 6 wherein said electrode is a porous, metal electrode.

8. An ablation catheter system, comprising:
an elongated catheter body having a proximal end, a distal end and having an internal lumen, open to the distal end of said catheter body;
a conductive electrode within said internal lumen;
a first conductor, coupled to said electrode;
means for coupling said conductor to a source of R-F energy;
fluid delivery means coupled to said internal lumen of said catheter body for delivering a conductive fluid to said internal lumen; and a helical member extending from the distal end of said internal lumen.

9. An ablation catheter system according to claim 8, wherein said helical member is conductive and further comprising a second electrical conductor coupled to said helical member.

10. An ablation catheter system according to claim 9, wherein said helical member is hollow and further comprising means for delivering a conductive fluid to said helical member.

11. An ablation catheter system according to claim 8 or claim 9 or claim 10, further comprising a source of R-F energy, coupled to said first conductor.