CA2109793A1

CA2109793A1 - Combination monophasic action potential/ablation catheter and high-performance filter system

Info

Publication number: CA2109793A1
Application number: CA002109793A
Authority: CA
Inventors: Stuart D. Edwards; Michael R. Franz; Russell B. Thompson; Roger A. Stern
Original assignee: Individual
Current assignee: EP Technologies Inc
Priority date: 1991-05-24
Filing date: 1992-04-16
Publication date: 1992-12-10
Also published as: WO1992021285A1; AU1899292A; JPH06507797A; AU1998892A; US5398683A; WO1992021278A1; EP0588864A4; EP0588864A1

Abstract

A combination catheter for both detecting monophasic action potentials and ablating surface tissue in an in vivo heart of a patient is provided. The apparatus includes a catheter probe having a terminal tip portion (10) and an electrode (20) carried on the tip such that a portion of the tip electrode (20) is exposed to ambient. A reference electrode (50) is spaced along the tip from the first electrode for supplying a reference potential signal. An ablating electrode (30) is located adjacent to but electrically insulated from both the tip (20) and reference (50) electrodes for providing electromagnetic energy to the tip. The electrodes are electrically connected to the proximal end of the catheter through individual conductors or wires (22, 32, and 50) that run through an insulated cable. An electronic filter is provided to permit the recording of MAPs during ablation without radiofrequency interference. The catheter may also include standard mapping and/or pacing electrodes (80 and 75) respectively. The catheter may further include a steering mechanism for positioning the catheter at various treatment sites in the heart, and a structure for holding the tip electrode in substantially perpendicular contact with heart tissue with a positive pressure, and for spacing the reference electrode from the heart tissue.

Description

WO 92/2i285 PCT/US92/03142 21097~

COMBI~ION MONOPH~SIC ACTION POTENTIAL/ABLATION CATUETER
AND HIGH-P~RFORMANCE_FILTER SYSTEM

Back~round of t~e Invention-This invention relates to a ca~heter fsr t~e I0 - simultaneous or near-si~ultaneous recordi~g of monophasic action potentials (MAPs) and ablating. arrhythmia-causing tissue by coupling radiofrequency energy to tissue surrounding the catheter tip, and more particularly to a method a~d apparatus for simultaneous~y recording MAPs 15 and ablating by contacting heart tissue with a small dual MAPIablating electrode under positi~e pressure.
The electri~al charge of the outer membrane of an individual heart muscle cell is known as the "membrane potential". During each heart beat, the membrane potential discharges (depolarizes) and then slowly recharges (repolarizes). The wavef~rm of this ~eriodic depolarization and repolarization is called the "transmembrane action potential." Mechanistically, ~he action potential is produced by a well-organized array of ionic currents across the cell membrane.
A~ the turn of the century, it had already been recognized that a potential similar in shape to the later-discovered transmembrane potentia} could be recorded if one brouqht into contact a first electrode ~ith an ~njured spot of the heart and a second reference e1ec~rode with an intact spot. Those signals became known as "injury potentials" or "monophasic action potentials" (MAPs) because o4 the waveform shape.
The ur~her develoDment o the science ~ u~p5 _ ~ay be ~ound in United States Paten~ No. ~,955,182, ~he , SllBSTITUTE SHEFI-2~5 21~9793 disclosure of which is hereby incorporated by reference.
It has been recognized that local heart muscle injury is not a prerequisite for the generation of MAPs, and that application of slight pressure with the tip against the S inner wall of the heart will result in the generation of monophasic action potential signals. These signals can be rerorded reliably (i.e., withou~~dis~ortion) by using ~dire t current (DC) coupled amplification.
One-pro~le~ to overcome in ~AP recordation is the slow DC drift cau~ed by electrode polarization in conventional electrical material used in the recording of int~acardiac electrical signals, such as silver or platinu~. These materials are polarizable and cause offset and drift--which is not a problem in conventional intracardiac recordings, because those signals are AC
coupled, which eliminates offset and drift. The MAPs, however, are ts be recorded in DC fashion, and therefore are susceptible to electrode polarization. The use of a sil~er-silver chloride electrode material yields surprisingly good results in terms of both long-term s~ability of the signal and extremely low noise levels.
Another important discovery has ~een that the tip electrode of the catheter should be held against the inner sur~ace of the heart with slight and relati~ely Z5 constant pressure. In order to accomplîsh this in a vigorously beating heart, a spring-steel stylet is inserted into a lumen of the catheter to act as an elastic spring, ~eeping the tip electrode in stable contact pressure with the endocardium throughout the cardiac cycle. This leads to major improvements in signal stability.
Another design objective for a gosd MAP
catheter is to ensure a relatively perpendicular position of the electrode tip with the endocardial wall. .~aain, ^5 _he spring electrode is useful in this respect.

8UBSTITUTE SHEE~

PCT/US92/031~2 W092/2~285 Conven~ional catheters are usually brought into contact with the heart wall in a substantially tangential manner.
Such convantional catheters are designed simply to record intercardiac electro~ramc, not MAPs. For the monoph~sic action potential catheter, direct contact between the tip electrode and~the endocardium is made. This also ~eeps the reference electrode, which~is`locàted along the .
`~ catheter shaft, away from the heart muscle.
To facilita~e the maneu~er bility of the catheter during a procedure in tha human heart, the distal end of the catheter should be relatively flexible during the tim~ of insertion, and the spring-loading feature preferab~y comes into action only after a stable position of the catheter tip has been obtained. Thus, in a preferred embodi~ent the catheter is constructed in such a way that the spring wire situated in the lumen of the catheter is retractable. During catheter insertion, t~e spring wire or stylet is withdrawn from its distal position by approximately 5 cm, ma~ing the ~ip relatively soft. Once the catheter is positioned, the spring wire is again advanced all the way into the catheter in order to stiffen it and to ~ive it the elastic properties that are important for the described properties. Improved stylets and wires that position the tip electrode perpendicularly to the heart surface with ~he proper amount of constant pressure are described in U.S. Patent No. 4,955,382.
~ ~ Thus, a main feature of a good cathetPr is the ability to bring into close and steady contact wi~h the inner surface of the myocardial wall a nonpolarizable electrode which both produces and records MAPs. To achieve this property, the electrodes are formed from nonpolarizable material such as silver-silver chloride, and the tip electrode should be maintained at a ~5 8UBSTITUTE SHEFr .

WO 92/21285 ~

2~09~

relatively constant pressure against the myocardial wall, - preferably with some type of spring loading.
The catheter of the present invention preferably contains a spring-steel guide wire which provides a high degree of elasticity or resilience, allowing the cathe~er tip to follow the ~yocardial wall t~rou~out the hear~beat without losing`its contacting . . ~. J
force and without being dislodged. The inner surface o~
the heart is lined wit~ crevices and ridges (called t~e lo trabeculae carneae) that are helpful in keeping the spring-loaded catheter tip in its desired location. The ~ontact pressure exerted by the tip electrode against the endocardial wall is strong enough to produce the amount of local myocardial depolarization required to produce the MAP. The contact pressure is, on the other hand, soft and gentle enough to avoid damaging the endocardium or the myocardium or cause other complications. In particular, no cardiac arrhythmias are obser~ed during the application of the catheter. Usually a single extra Deat is observed during the initial contact of the catheter tip against the wall.
The tip electrode is responsible for the generation and the recording of the MAP itself. A
re~erence electrode, or "indifferent" electrode, required to close the electrical circuit, is located approximately 3 to 5 mm from the tip electrode in the catheter sha~t and is embedded in the wall so that it is flush with or slight,ry recessed in the catheter shaft. In this position, the electrode makes contact only with the surrounding blood and not with the heart wall itself.
This reference electrode is brought into close proximity with the tip electrcde, since the heart as a whole is a ~orceful electrical potential generator and _hese potentials are eve~where in the cardiac cavities.

BUBSTITUTE SHEEr PCr/USg2103142 W~92~212~5 210~7')~

If the reference electrode were in a remote location, then the amplifier circuit would pick up the QRS complex.
Another feature of this invention relates to th~rmal destruction, or ablation. Ablation of abnormal 5 myocardial tissue (such as arrhythmia-causing tissue) is a therapeutic procedure used with increasing frequency for t~eatment of cardiac arrhythmia~ such as, for examp~e, ventricular tachycardia. The medical techni~ue of ablation is- discussed in G. Fo~taine et al., Ablat~2n in Card ac Arrhvthmi~s (New York: Futura Publishing Co., 1987), and D. Newman et al., "Catheter Ablation of Cardiac Arrhythmias", in Current Problems in Cardioloqv, Year Book Medical Publishers, 1989.
Catheter ablation of ventricular ~achycardia was ~irst d~scribed in 19~3 as a method for destroying arrhythmia-causing tissue. Typically, a pacing catheter is introduced into the left ventricle of the heart, and manipulated until the site of earliest activation during . ventricular tachycardia is found, indicating the location 20 o~ the problem tissue. Electrical energy, often high voltage DC pulses are then applied between a catheter-mounted electrode and an external chest wall electrode.
In this way, arrhythmia-causing cardiac tissue is destroyed.
2~ More recently, less drastic methods than high voltage pulses have been developed, which are painful (requiring general anaesthesia), and dangerous due to arcin~ and explosive gas formation at the catheter tip.
Thé use of electromagnetic energy, more particularly radiofrequency (RF3 or ~icrowave energy, is currentlv in popular use. RF and microwave energy, unless otherwise noted, re~ers to energy in the electromagnetic spectr~m from about 10 kHZ to 100 ~Hz. RF ablation, usually in the range of 300-1200 k~z, is a safer alternative to high 7 5 voltage DC pulsing in which RF enersy is applied to the ~3UBS rmJTE SHEEr PCT~US~2/~3142 W~ 9~/21285 endocardium via an catheter elPctrode. Tissue destruction, or ablative injury, is effected by heating generated by the RF electric field. RF ablation results in a more controllable lesion size, with no gas or shock wave formation. A~lation may also be effected with energy ha~ing microwave frequencies, from about 700 MHz to lQ0 G~z. .A~
. Currently, no relia~le on-linè method exists to quickly and accurately de~ermine whether radiofrequency (RF) energy application has resulted in lesions of a size suf~icient to destroy the injured myocardial tissue.
That is primarily because previously, no pro~ision has - been made for accurately measuring the electrophysio-logical activity of the heart in th~ im~ediate vicinity lS of heart tissue which is being abla~ed by an ablating catheter. Moreover, if it is desired to pace the heart at the same time as measuring MAPs in the heart, two entrance sites to the patien~ must ~e created and two catheters must be utilized, which is highly undesirable.
Because of the complexity of electrical cardiac activity, when a pacing or ablating electrode is inserted into the heart, and it is desired to measure the resulting monophasic action potentials of the heart, it would be of extreme usefulness to be able to measure such potentials in the vicinity of the ablation, rather than at a more remote location.
Important applications of the present invention are ~ ,the areas of studying and treating myocardial ischemia and cardiac arrhythmias. In particular, the present invention per~its (l) precisely loca~ing areas of myocardial ischemia by studying localized MAPs and directly treating them; and (2) diagnosing the nature and locality of arrhythmias originating fro~ after-depolarizations and t-eating those arrhythmias. These afte~-~epolarizations have heretofore been detected only SUE~STITUTE SHEFr WO ~/21~85 2 1~ 3 in isolated animal tissue preparations where microelectrodes can be applied. The MAP/ablation catheter is a tool that can allow the clinical investi~ator to detect and remedy such abnormal potentials in the human heart and thereby significantly broaden the ability to diagnose this gro~p o~
arrhythmias.- - ~

Summary of the Invention The present invention overcqmes ~he drawbacks in the prior art by permitting abla~ion both in the same region where MAPs are being recorded, and at the same or nearly the same time as they are being record~d. The system uses an electronic filter system to eliminate radiofrequency interference that would otherwis~ preven~
simultaneous ablation and recordation. Although simultaneous ablation and EKG reading has previously been possible, simultaneous ablation and MAP recordation offers more information to the user, as the MA~ signal is a more sensitive indicator of tissue viability.
Previously, simultaneous ablation and MAP
recording was possible using two catheters. However, this method was more invasive and more uncertain, as situating the two catheters at precisely the same location was difficult or impossible. Therefore, the present invention pro~ides a heretofore unavailable single ablating catheter capable of being a precise ins~taneous indicator of thrombus conditions or tissue death.
By permitting ablation and MAP recordation at approximately the same time and same location in the heart, the presen~ invention also potentially minimizes the necessary lesion size, as ablation may be stopped immediately upon recognition of t-ssue death.

SVBSTITUl'E SHEEr PCTIU~92/0314 ~:~097~3 Therefore, it is an object of the present invention to providP an apparatus for measuring monophasic action po~entials and, at a~out the same time, ablating surface myocardial tissue with electromagnetic energy.
It is another object of the present invention .
to provide an apparatus ~or measuring monop~asic action potentials and, at about the same time, ablating surface myocardial tissue with radiofrequency energy~
A further object of the present invention is to provide a MAP measuring apparatus which can accurately record action potentials and ablate surface myocardial tissue over sustained periods of time.
Another object of the present invention is to provide a MAP measuring appara~us which can a~late surface myocardial tissue and measure action potentials in a vigorously beating in-situ heart.
Another object of the present invent~on is to provide a method of using the apparatus for recording MAPs while simultaneously ablating surface myocardial tissue, or immediately before or after ablating surface myocardial tissue.
A further object of the present invention is to provide a method of detecting and correcting ischemia by 2S sensing MAPs and, at approximately the same time and location in the heart, ablating surface myocardial tissue.
~ ~ In accsrdance with the above objects, the present in~ention includes an apparatus ~or both detecting monophasic action potentials and ablating surface tissue in an in vivo heart of a patient. Th~
apparatus co~prises a catheter probe having a ter~inal tip portion and a first electrode carried on the tip such that a portion of the firs~ electrode is exposed ~o ~, ambient. .~ second electrode is spaced along the tip from SUBSTI~E SHEEl-2 ~ 3 the first electrode for supplying a rPferenre potential signal. A third electrode is loca~ed adjacent to the first electrode but electrically insulated from both the first and second electrodes for providing electromagnetic energy, preferably radiofrequency or microwa~e en~rgy.
The electrodes are electrically connected to the p~oximal~end of th~ catheter through`individual conductors or wires tha~ run through an insulated cable.
In one emb~diment of the inventio~, coaxial cable may be used as the conductors and cable toge~her. ~he connection of one conductor to the third electrode (the ablation electrode) will include an antenna for r~ceiving electromagnatic energy. The antenna may be formed by th~
conductor itself, or may be a separate component, such as a conductor wound in the form o~ a helix. Helical antennas, and their connection in an ablating catheter system, are described in U.S. Pa~ent No. 4,94~,912, the disclosure of which is hereby incorporated by reference.
The system of this invention may also include a steering mechanism for positioning the catheter in various locations in the heart. The mechanism permits the distal end of the catheter to be bent into varying shapes, and will include proximally located controls, a flexible steering shaft, and a distal apparatus for bending the distal end. Suitable steering mechanisms are disclosed in commonly-owned, copending United States Application Serial No. 07/~73,667, the disclosure of which~is hereby incorporated by reference.
In accordance with further aspects of the invention, an electronic filter is provided to permit the recording of MAPs during ablation without radio~requency interference. The probe may also be provided with a structure for holdin~ the first electrode in contact with hear~ ~issue with a ~ositi~e pressure without causing ?~ signi~-cant macroscopic damage to the heart tissue and SlJBSTrTUTE SHE~

P( 'l / U~Y~/ UJ~
WO92/21~85 210~3 ,.

for orienting the probe such that the second electrode is spaced from t~e heart tissue and the third electrode remains near the heart tissue.
The f irst and second electrodes of this invention are non-polarizable, preferably formed of silver-silver chloride, to-avoid direct c~rrent drift during the course of in~estigatio~. ~
~ ,:
Brief ~esç~i~ion of the D~awinqs Figure 1 is a schematic view of the tip portion o~ the apparatus nf the invention.
Figure 2 is a sectional view of the tip portion shown in Figure 1.
Figure 3 is ano~her sectional Yiew of an alternate e~bodiment of the tip portion of the apparatus o~ the invention.
Figure 4 is a schematic view of the tip portion of an alternate embodiment of the invention.
Figure 5 is a sectional view of a variable tip assembly, an alternate embodiment of the invention.
Figure 6 is another sectional view of an alternate embodiment of the tip portion of the apparatus of the invention.
Figure 7 is an electrical schematic of the electronic filter system of the invention.
Figure 8 is a schematic view of a combination MAP/ablation/pacing catheter tip of the invention.
~ ~ Figure 9 is an overall schematic view of the catheter system of the invention.
Detailed Descri~tion of the Invention FIGS. 1 and 2 show the tip portion 10 of a probe according to the present in~ention. Tip 10 comprises an exposed tip electrode 20 for detecting onophasic action potentials. ~lectrode 20 is a sintered SUBSTrrUTE 3SHEFr . - i -~V92~21~5 2~û97 fi3a depolari~ing electrode, preferably formed of silver- -silver chloride. Adjacent to, but electrically insulated from the tip electrode i~ the ablating electrode 30.
Electrode 30 is preferably formed of stainless steel or platinum, and is insulated from electrode 20 by skirt ~0.
Skirt ~0 may be made of Teflsn tubing, for example, or a~y o~her insulating material.- Skirt 40 has à thickness of .OOl - .200 i~ches, most preferably .002 - .020 inches.
In ~his manner, the ablating electrode 30 is located in close proximity to the MAP recording tip electrode 20, and the catheter tip will effectively be recording MAP signals at the ~ame location where ablation is taking place. The ~wo electrodes may be as close as possible, limited only by the finite thickness of insul ating skirt 40. If the two electrodes are separated by much more than .200 inches, however, the ablating electrode may no longer be effectively ablating the area where the MA~ signals are recorded, or it may be ablating a different area.
Located proximally from electrode 30 is a side electrode 50, which serves as the ~'indifferent~ electrade for tip electrode 20. Side electrode 50 is electrically insulated from the tip and ablation electrodes by an insulating insert 60. Insert 60 is preferably formed from ~n insulating material such as plastics or rubbers, more preferably Delrin.
~ ~ The tip and side electrodes 20 and ~0 are preferably formed ~rom a sintered silver-silver chloride material. An alternative structure for the electrodes 20 and 50 is provided by utilizing silver-silver chloride flakes bound together by cyanoacrylate adhesive. It has been found that it is desirable to place side electrode 50 proximally fro~ the tip electrode 20 by a suitable distance as, for exa~ple, 3-lO mm, preferably 3-5 mm.

SOBSTm~l'E SHFFr PCT/US~2/03142 21~793 As seen in FIG. 2, electrodes 20, 30 and 50 are electrically connected to the proximal end of the catheter via electrical conductors 22, 32 and 52, respectively. The electrical cond~ctors are formed of a suitable material such as insulated copper and serve as signal wires. Tip electrode 20 is soldered to ce~ter - condu~tor 22, which is cov2red with a teflon sleeve for electrical insulation. Electrical conductor 22 may also act as an antenna for receiving transmitted electromagnetic energy.
FIGS. 1 and 2 also show an ablating skirt 73, which is in fact an optional component of the present invention. Skirt 70 forms a ring on the probe surface at the proximal end of electrode 30. The thickness of skirt 70 varies based on its axial distance from the junction of electrode 30 and insert 60. The ~hickness of skirt 70 tapers to zero at the distal rim and monotonically increases to about ~010-.040 inches at the proximal rim.
The skirt is formed frsm a partially conductive material, preferably a partially conductive epoxy such as a silver epoxy. Proximally located to skirt 70 on the probe surface is insert 60, although electrode 30 may have a tapered base, thereby extending proximally beyond skirt 70 in the probe interior as seen in FIG. 2.
S~irt 70 is for~ed so that the electrical properties at the electrode-insert junction are tempered.
Without the skirt, the junction forms a hot spot and an undes~rable charring focus. The presence of a partially conduc~ive skirt with resistive or capacitive properties 39 changes the surface impedance, equalizes the external electric fields and improves radial penetration of ~he field. By vastly reducing or eliminating the aberrational electrical fields, the skirt eliminates the charring p-oblem.
., S

SUBSTmJTE SHEE~

PCT/U~92/~3142 WO 92~21285 21~g7~3 ' :::

-13- ~.

FIG. 3 shows an alternate embodiment of the - housing for the tip and ablating-electrodes. Soc~et 3s is designed to receivP electrode 30 (as shown in FIG. 6), which tapers at its base to about .058 inches in diameter. When inserted, electrode 30 i5 thereby fitted in teflon s~irt ~5 with an inner diameter of about .058 inc~e~ and an outer diameter of .080 inc~es. Electrode 30 extends a~out .046 inches down the probe and sits on the thin botto~ of the teflon skirt.
FIG. 4 shows an alternate embodiment of the catheter of the invention which, in addition to performing simultaneous MAP recordation and radiofrequency ablation, is able ~o simultaneously perform standard mapping through a number of standard mapping electrodes. The process of mapping t~rough mapping electrodes is well known as described in Zipes et al., Cardiac Electro~h~sio~oqv (Saunders Pub. Co.). The probe shown in FIG. 4 consists of a distal end identical to that shown in FIG. l, but utilizes a series of proximally located standard mapping electrodes 80 separated by a series of insulating inserts 90. Although the drawing depicts three mapping electrodes, as few as 1 and as many as 16 or more could actually be used.
FIG. 5 shows an alternate embodiment of the tip of the current invention. In this embodiment, a variable tip assembly is utilized so that alternate tip shape or configuration may be easily substituted. Tip shapes inc~u~ing "peanut", "hourglass~' or bulbous geometries are contemplated. The tip electrode and ablating electrode ~0 are contained on remoYabl~ head loO, which varies in size from 3-10 mm and attaches to probe 110 through threaded plug 120. Plug 120 is a watchmaker's thread screw and screws into threaded hole 130 to sit on teflon s~ir~ 1~0.
Electrical conductors to the electrodes extend throuah ~_ plug 120 and att ch to conductors located centrall~ in SUBSTITIJTE 5HEFr W~ 92/2~5 ~CT/US92/03142 7 ~

probe 110 through hole 130. Loc~ite is used to fix head 100 in proper position.
The variable tip assembly configuration of FIG.
5 can be used to provide nonsterilized tips, which can be S easily sterilized by conventional methods prior to use, permitting ease o~ manufacture and use.
FIG. 6 shows-yet another alternative embodiment . of the cath~ter of the~current inv ntion in -which t~e tip and ablatin~ electrodes have been inserted into socket 9 of the device of FIG. 3. In particular, this figure shows a central bore $~0 running from the proximal end of the probe to the tip electrodP at the distal tip. Bore 1~0 contains the electrical conductors that electrically connect the distal ~lectrodes to the proximal end, and may also contain steering wires for controlling catheter steering.
FIG. 7 is a schematic diagram of the electronic filter system of the invention. The filter is a DC-accurate 5 kHz low pass filter that receives the MAP
signal from electrode 20 via conductor 22 as shown in FIG. 1. The filter permits passage of frequencles only below 5 XHz. Accordin~ly, all ablating frequencies (RF
and microwave) do not pass, and only MAP signals will pass. The outputs 202 and 203 pass the filtered signal to a display device such as an oscilloscope or strip chart recorder.
The filter in FIG. 7 uses two inputs 209 and 201.~~~hese two inputs ~ay be connected to either the distal tip electrode 20, proximal side electrode 50, 25 shown in FIG. 1, or directly to the s~in o~ thè patient.
When the inputs are the connected to th~ two electrodes, the system is called a '!distal bipolar" system. ~ distal or proximal l'unipolar" syste~ occurs when input 200 is csnnected to one electrode and input 201 is connectec _o ~5 ~he patient's skin.

8UBSTITI.JTE SHEFr WO 92/212$5 2~J7~ -FIG. ~ shows an alternative embodiment of the - in~ention, depicting a catheter 10 which is a combination pacing, ablation and MAP catheter. FIG. B is similar to FI~. 1, the difference ~ying in the presence of a pair of pacing electrodes 7~. The function and method of use of pacing electrodes such as electrodes 75 for activating is w~ll.known in the àrt in standard configurations o~
:~ pacing eleetrode catheters; that is, the sa~e types of i electrical signals which are provided to pacing }0 elec~rodes in standard pacing catheters may also be provided to the electrodes 75 in the present invention.
The two pacing electrodes 75 are .Q35" platinu~
dot electrodes, and are positioned substantially diametrically opposite each other on the exterior surface of the cathe~er. Side electrode 50 is radially positioned halfway between said two pacing electrode--, but may be loca~ed axially toward or away from ~he catheter tip.
FIG. 9 is a schematic o~erview of a combination MAP, ablation, and pacing catheter 200, in which pacing electrodes 210 and 220 are mounted at the distal end 230 of the cathe~er 200. In addition, a tip electrode 240 a side electrode 250, and an ablation electrode Z~5 are provided, as in the configuration of FIG. 1, and are electrically connected to connections such as plugs 260 and 270.
The pacing electrodes 210 and 220 are similarly conne~ted to plugs 280 and 290, respectively. Plugs 280 and 290 are standard plugs. It will be unders~ood that contained within FI5. 8 are the necessary elect~ical leads to the elec~rodes 210, 220, 240, 250 and 255, and in addition stylets and other features as described herein with respect to sther embodiments may be included.
The electrical lead to electrode 255 may be connected to ~5 an elec~romagnetic ener~y source, such as a SVBSTITUTE 5HEE~

WO 92/21285 PCT/U~92/03142 2.109~3 radiofrequency source or microwave source, for providing abla~ing energy to the catheter tip. The electrical leads to electrodes 240 and 2S0 may provide input to the RF filter of FIG. 7, as described above.
A coupling 30U for ~he plugs 260-290 is provided, insuring a reliable connec~ion between the plugs-to the electrical leads contained within the catheter 200. This coupling 300 is pre~erably of a hard material such as polycarbonate, and has an enlarged diameter relatiYe to the catheter 200. This pro~ides greater torque control for the user of the cat~eter when manipulating the catheter into the heart and positioning the tip electrode 24C against the endocardium.
In addition to the coupling 300, a knurled knob 310 may be attached at the proximal end 329 of the catheter 200. The knob 310 is preferably connected to the catheter 200 in a nonrotatable fashion, such that axial rotation of the ~nob 3~0 causes similar axial rotation of the catheter 200. As shown in FIG. B, the ~nob 310 may be generally cylindrical in configuration, or may be of some other convenient shape for twisting by hand.

Methods of ~se The general principle of identifyiny ischemic, infarction, and arrhythmia-causing sites using MAPs is described fully in U.S. Patent No. 4,9S5,382. That procedure is basically followed in the current inven_ion with the following additions.
To localize and treat myocardial ischemia o~
ventricular tachycardia, the catheter of ~he present inven~ion is inserted endocardially, and as the catheter is consecutively placed at multiple endocardial locations, I~AP signals are detected until an abnormal ~5 condition is disco~vered. This abnormal condition may be ~3UBSTITUTE 5HEEr PCT/US9~/03142 2 1 ~

the lat arrival of the action potential, or the wrong potential. When the abnormal MAP is detected, RF energy is passed to the ablation electrode to ablate the abnormal tissue. While the ablating RF energy is being dissipated to the tissue, ~he MAP signal is simultaneously being read and recorded. When the MAP
signal has disappeared-for a'`certain period of time, the tissue is presumed dead and ablation may-cease.
After the procedure has ~een performed, the success of the procedure may be determined by oonventional methods. For example, the heart may be paced to induce ~he arrhythmia or tachycardia using pacing electrodes both before and a~ter the procedure.
The ability to simultaneously re ord MAPs and ablate cardiac tissue with a combination M~P/ablation catheter has been examined in do~s. In one study o~ 22 left ventricular sites in six closed-chest dogs, RF
ablation at 25 watts was applied for 60 seconds or until a rise in impedance occurred. Simultaneous MAP recording throughout each RF application took place using the low-pass filter system described above. Before RF ablation, stable MAP signals of 2Z + 7 mV amplitudP were obtained at each site. In 13 RF applications, MAP signal amplitude decreased to less than 20% of baseline within only 3-5 sec of RF ablation. In these cases, power was shut o~f at 6-8 sPc (group A). In 5 RF applications, MAP
amplitude decreased more slowly, falling below 20% within 40-60-,~econds. In these cases, power was shut off at 60 sec (group B). In the 4 remaining applications, MAP
amplitude decreased by only 35-65%, and upon cessation of RF ablation (at 60 sec) recovered to 50-85% of baseline (group C). Post-m~rtem analysis showed similar lesion volumes in group A and B (135 ~ 24 mm3 vs. 88 + 36 mm3, ~JS) ~ut smaller lesion ~olumes in group C (52 ~ ~2 ~m~;
5 p~O . 05 vs . group A).

8VE~5TITUTE S~EEr WO92/2128~ PCT~U~92/03142 2109~7~3 In another set of experiments, application of RF en~rqy of low power and short duration were delivered ~o t~e canine hear~ through the combination MAP/ab~ation catheter of the current invention to observe the relationship hetween RF power and duration on one hand and lesions size and change in MAP signal morphology on the o~er hand. MAP signals were recorded using the low-pass filter and distal bipolar signals, proximal unipolar signal~, and ~istal unipolar sign~ls were all recorded before, during and af~er RF ablations.
In total four lesions were made in the left ventricle and two in ~he right ventricle. RF power varied ~rom 5-10 watts and duration varied from 10-60 seconds or until an impedance rise occurred. Changes in MAP signal morphology during and after ~F ablation were recorded. These morphology changes can l~tar be correlated to lesion depth, volume and location. The animal is then sacrificed to determine lesion depth, volume and location.
These experiments demonstrate that simultaneous MAP monitoring during RF ablation provides instantaneous feedback about the magnitude and permanence of myocardial tissue destruction, even during very brief ~F pulses.

8VBSTlTU'rE SHEE~

Claims

Claims We claim:

1. An apparatus for both detecting monophasic action potentials and ablating surface tissue in an in vivo heart of a patient, comprising:
a catheter having a proximal end and a distal end, said distal end having a terminal tip and an exterior surface, and said catheter being adapted for insertion into a patient for detecting said potentials;
a first electrode carried at said distal tip for contacting surface tissue of the heart of the patient for measuring potentials at said surface tissue;
a second electrode carried on said catheter and spaced from said first electrode for supplying a reference potential signal;
a third electrode carried on said catheter adjacent to said first electrode and electrically insulated from said first electrode for providing electromagnetic energy to said surface tissue;
first electrical means coupled to said first and second electrodes for generating signals representing said action potentials; and second electrical means coupled to said third electrode for providing said electromagnetic energy to said third electrode.

2. The apparatus of claim 1, further comprising an electronic filter system electrically connected to said first electrical means and said second electrical means to eliminate radiofrequency interference.

3. The apparatus of claim 1, wherein at least one of said first and second electrodes is formed from sintered silver-silver chloride.

4. The apparatus of claim 1, wherein said third electrode comprises a ring made of a partially conductive material of variable thickness and positioned at the proximal end of said third electrode, said ring having a proximal end and a distal end, and said thickness of said ring monotonically increasing from the distal end to the proximal end of said ring.

5. The apparatus of claim 4, wherein said partially conductive material is an epoxy.

6. The apparatus of claim 1, further comprising:
a plurality of pacing electrodes carried on said catheter at varying distances from said first electrode; and a third electrical means for providing a cardiac pacing signal to said pacing electrodes;
wherein said plurality of pacing electrodes are for pacing the heart tissue.

7. The apparatus of claim 6 wherein said plurality of pacing electrodes includes two electrodes positioned substantially diametrically opposite each other on said exterior surface, and wherein said second electrode is radially positioned between said two pacing electrodes.

8. The apparatus of claim 1 further comprising means carried by said catheter for maintaining said distal end in a substantially perpendicular configuration with respect to said surface tissue and with a substantially constant force against said surface tissue, for depolarizing heart cells in a vicinity of s id first electrode while avoiding injury to said cells.

9. The apparatus of claim 1, further comprising:
a plurality of mapping electrodes carried on said catheter at varying distances from said first electrode; and a third electrical means for providing cardiac mapping signals from said mapping electrodes to the proximal end of the catheter;
wherein said plurality of mapping electrodes are for mapping heart tissue.

10. A method for detecting monophasic action potentials and ablating surface tissue in an in vivo heart of a patient using a catheter having a proximal end and a distal end, with a first electrode carried at the distal end, a second electrode carried on a surface of the catheter and spaced from the first electrode, and a third electrode adjacent to but electrically insulated from the first electrode, including the steps of:
inserting the distal end into the heart;
positioning the distal end in a substantially perpendicular configuration against endocardium of the heart such that the first electrode contacts said endocardium with a force sufficient to depolarize myocardial cells in the vicinity of the first electrode and such that the second electrode does not contact said endocardium;
detecting first signals by means of said first and second electrodes, said first signals relating to the monophasic action potentials of the heart;

delivering radiofrequency energy to the heart by means of said third electrode, said energy sufficient to ablate the heart tissue; and repeating said detecting and delivering steps until no monophasic action potential signals are detected.