transvenous ablation of atrioventricular conduction with ...designed ablater (cardiac recorders...

Br Heart J 1989;62:361-6

Transvenous ablation of atrioventricular conductionwith a low energy power source

EDWARD ROWLAND, DAVID CUNNINGHAM, ARIF AHSAN,ANTHONY RICKARDS

From the National Heart and Lung Institute and National Heart and Chest Hospitals, London

SUMMARY A power source modified to increase voltage delivery and minimise arcing (for a givenenergy) was used for transvenous ablation of atrioventricular conduction to control refractorysupraventricular arrhythmias in 14 patients. Twelve had atrial fibrillation or flutter, one hadatrioventricular nodal reentry tachycardia, and the other had permanent junctional reentrytachycardia. Despite treatment with 5-7 (median 6) antiarrhythmic drugs symptoms had persistedin all the patients. Cathodal discharges of 0-5-39-5 J were delivered to the distal electrode (in onecase in parallel with the middle electrode). In all patients shocks produced complete atrioven-tricular block; this was permanent in eleven (79%). Four patients required a second procedure. Inone patient, only a transient atrioventricular block could be produced and catheter ablation with a

conventional power source also failed. In the other two atrioventricular conduction was modifiedsuch that previously ineffective treatment produced satisfactory control of heart rate. Thecumulative energy delivered to those in whom permanent complete heart block resulted rangedfrom 3 6 to 97 8 (mean 38 3) J with amean ofthree shocks (range 1-7) delivered per patient. Duringfollow up of 1-28 (mean 14) months 11 patients remained in complete heart block and free ofarrhythmia.

Transvenous ablation of atrioventricular conductionconventionally uses high energy discharges gen-erated by a standard defibrillator and has become anaccepted and effective method of creating completeatrioventricular block in patients with refractorysupraventricular arrhythmias.l The precisemechanism by which these high energies. destroy theatrioventricular conduction system is unknown buthigh energy discharges produce an explosive flash(arcing) that is associated with a raised local tem-perature and a high intensity pressure wave.56Examination of the Ablation Registry showed thatthis technique achieved complete heart block in 63%of patients and that the mean cumulative storedenergy required was 611 J.4 The recommended con-ventional technique uses one or more shocks of 150-300 J delivered between one electrode of a standard6F or 7F pacing catheter and a back plate.7 Severaladverse effects have been reported including myocar-

Requests for reprints to Dr Edward Rowland, National HeartHospital, Westmoreland Street, London WIM 8BA.

Accepted for publication 2 May 1989

dial rupture,8 and there is concern about intravas-cular haemolysis9 and right ventricular dysfunction,'0and that gas bubbles may be produced in bothventricles immediately after the shock." Although itis not clear which properties of the high energy causethe desired clinical effect it seems likely that many ofthese adverse effects result from the pressure wave.We have designed a power source that shortens the

energy delivery tune in order to produce shocks thatincrease peak voltage and current for a given ener-gy.2 Our previous work has shown that this energysource has a higher arcing threshold than a standarddefibrillator, with the result that local electricaleffects predominate over those resulting from arcing(barotrauma)."

Patients and methods

Fourteen patients with drug refractory supraven-tricular arrhythmias underwent attempted transven-ous ablation of atrioventricular conduction. Twelvehad paroxysmal or established atrial fibrillation orflutter, one had paroxysmal atrioventricular nodal

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Table Data on patients who had ablation of the atrioventricular pathway by the new ablater

Previous Test shocks Definitive shocks Clinical Follow upCase Age Sex Diagnosis treatment (J) (J) outcome (mnth)

1 54 M PJRT DVQFBADs 2-2 37-5 1 282 69 F PAFI DVBASDsQ 2-0 5-1 2 273 63 M PAFI DVAQP 0-5 31 1 244 61 M PAF DVBASQ 1-4 5-7/21-8/29-3/16 5/16 5/ 3 1*

27-0/27-1/29-4/38-95 52 F PAF DVBASDsF (1) 1-6 (1)6-5 3 18

(2)- (2) 22 16 75 M AF DVASDsFP - 6-9/17-4/38-2 2 177 65 M PAF QDBVSA 1-6 19 9 1 148 69 M PAF DVBDsA 1-6/1-6 26-3/27-7 1 149 63 F EAT DVDsAP 1-4 21-1 1 1410 50 F AF DVADsF (1) 1-5/1-6 (1)22-3/34-0 3 12

(2)1-6 (2) 36-8 111 66 F PAF DVBADsQ (1)- (1) 22-8/21-4 3 10

(2)- (2) 34-0 112 72 F PAF DVBADsF (1) 1-0/1-3/2-0 (1) 4-4 3 9

(2)- (2) 12-0/20-1/20 11 3 69 M PAFI DVBAF 12 8-9 1 714 65 F AVNRT DVBDsQAP 1-3/2-4 - 1 7

Diagnosis: PJRT, permanent junctional reentry tachycardia; PAFI, paroxysmal atrial flutter; PAF, paroxysmal atrial fibrillation; EAT,ectopic atrial tachycardia; AF, established atrial fibrillation; AVNRT, atrioventricular nodal reentry tachycardia.Drugs: D, digoxin; V, verapamil; Q, quinidine; B, c blockers; Ds, disopyramide; F, flecainide; S, sotalol; P, propafenone; A, amiodarone.All energies are the delivered values. Where second procedures were performed the values are indicated for the first (1) and second (2)procedures.Clinical outcome: 1, complete heart block; 2, impaired atrioventricular conduction; 3, no effect.*Surgical ablation of atrioventricular conduction.

reentry tachycardia, and one had the permanent formof junctional reentry tachycardia. All patients hadreceived at least five antiarrhythmic drugs, includingamiodarone, which had either been ineffective or hadbeen stopped because of side effects (table). Nonehad undergone previous transvenous ablation.Antiarrhythmic drugs were stopped before theprocedure in 11 patients-the other three were

continued on atrial stabilising drugs to prevent atrialarrhythmias during ablation.

PROCEDUREAfter informed consent had been obtained andpremedication given a small (4F or 5F) pacingelectrode was introduced percutaneously via theright subclavian vein, positioned at the apex of theright ventricle, and used for temporary ventricularpacing. The His bundle electrogram was recordedwith a 7F USCI tripolar electrode in 13 cases (a 6Ftripolar electrode was used in the other) andpositioned adjacent to the tricuspid valve. Threepatients were in atrial fibrillation at the time of theprocedure and an adequate ( > 200 pV). His bundlecould not be identified; external DC cardioversionwas performed in order to restore sinus rhythm. Inthese a third electrode was used for temporary atrialpacing to maintain atrial stability after DC cardio-version.

Bipolar and unipolar electrograms from thetripolar electrode catheter were recorded and theposition of the electrode catheter adjusted until the

largest His bundle electrogram was recorded on thedistal pair. Unipolar electrograms were also recordedto ensure that the distal electrode had the largest Hisbundle component. If the atrial electrogram on thebipolar signal was lower in amplitude than the Hisbundle potential the catheter was withdrawn towardsthe atrium.When the optimal His bundle electrode catheter

position had been identified the patient was anaes-thetised, a defibrillator plate placed under the leftscapula, and the His bundle electrogram re-checked.A blood sample was then taken for estimation of theserum concentration of creatine kinase (total andMBfraction).The power source used in this study was a specially

designed ablater (Cardiac Recorders CR60), thecharacteristics of which have been described."2 Thisdevice produces a capacitive discharge withoutinductance modification. We used resistive atten-uators and precision differential amplifiers tomeasure the delivered voltage and current: thewaveforms were recorded on a Gould 1425 digitalstorage oscilloscope and data (8 bit) transferred on aserial link to a microcomputer (Hewlett-Packard150) for computation of energy, power, andimpedance. All shocks were delivered synchronouslywith the R wave of a surface electrocardiogram lead.The cathodal output of the ablater was connected

to the distal electrode of the His bundle electrodecatheter and "test" shocks of 0-5, 1, or 2 J wereselected and delivered to test the responsiveness of

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Transvenous ablation of atrioventricular conduction with a low energy power source

atrioventricular conduction. If right bundle branchblock was produced the His bundle electrode cath-eter was withdrawn towards the atrium. In one casethe electrode catheter prolapsed into the atrium whenit was withdrawn; the electrode catheter wastherefore positioned optimally and further shockswere delivered through the distal and middleelectrodes which were connected in common. Theresponse of the atrioventricular conduction systemwas observed for up to 25 minutes.When complete heart block did not persist "defin-

itive" shocks of 5, 10, 20, 30, or 40 J were thenselected and delivered, the energy level chosendepending on the degree and duration of heart blockproduced by the test shock. Shocks were delivered inthe same configuration as that used for the testshocks. The effect of the definitive shock was mon-itored for 25 minutes and if complete heart blockpersisted no further shocks were delivered. Ifatrioventricular conduction returned further shocksof 20, 30, or 40 J were administered.The patients were observed for 24 hours and a

permanent rate responsive ventricular demandpacemaker (VVI) or atrioventricular sequentialpacemaker was implanted when third degreeatrioventricular block persisted or when evidence ofconsiderable impairment of atrioventricular conduc-tion remained. In those in whom atrioventricularconduction returned to normal the ablationprocedure was repeated. On this occasion test shockswere not used; an energy level above that used at thefirst ablation attempt was selected (that is, 20, 30, or40 J).

After each ablation procedure blood was collectedfor estimation of creatine kinase at eight and 24hours.

Results

Permanent complete heart block was achieved in 11patients, there was no change in atrioventricularconduction in one patient, and in the other twopatients atrioventricular conduction was modified.Fifty shocks were delivered in the 14 patients and themean cumulative energy delivered was 50 4 (range3-6-212-2) J. Figure 1 shows the overall persistenceof atrioventricular conduction in response to theshocks. In those in whom permanent complete heartblock was achieved the mean cumulative energydelivered was 38-3 (range 3 6-97 7) J and the meannumber of shocks required was three (range 1-7).

TEST SHOCKSTest shocks were not used in two patients because theelectrode catheter was believed to be in an unstableposition and creation of a heart block was thought to

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Fig 1 Survival of atrioventricular conduction in response toincreasing energy. Each of thefifty shocks used is plotted. Inthree patients (21%) atrioventricular conduction survivedintact. For the purposes of the survival curve the highestenergy shock delivered to a patient who attained permanentheart block was assumed to have been successful.

be more pressing. In one patient the test shock(delivered energy 2-4 J) produced permanentcomplete heart block, associated after 18 hours with anarrow QRS escape rhythm of 55 beats/min. In twopatients the test shock resulted in transient rightbundle branch block and withdrawal of the Hisbundle electrode toward the atrium was associatedwith transient complete heart block when asubsequent test shock was used. Therefore in 11patients delivered energies of 0-5-2-2 J producedtransient interruption of atrioventricular conductionwhich lasted for 30 seconds to 23 minutes.

DEFINITIVE SHOCKSBetween one and nine shocks ranging from 3 1 to38-9 J were delivered in 13 patients. In six permanentcomplete heart block was achieved with a singledefinitive shock (delivered energy 3-1-37-5 J) (fig 2).In one patient only transient interruption ofatrioventricular conduction could be achieved. Inthis patient the His bundle electrogram remainedsmall (100 yV), despite repositioning ofthe electrodecatheter, and repeated shocks of increasing intensityin various positions did not interrupt atrioventricularconduction. Electrode catheter ablation performedsubsequently with a conventional power source(300 J shocks) was equally ineffective. In the remain-ing six patients transient atrioventricular block resul-ted from the first definitive shock and one or twofurther shocks were required to produce completeheart block for the duration of the observationperiod.Four patients had a second ablation procedure

performed because complete heart block did not

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Fig 2 In patient 2 (a woman of 69) a synchronised shock of5 J(*) was delivered during sinus rhythm and resulted incomplete heart block, with simultaneous induction of atrialflutter. Electrocardiographic leads I, II, III, and VI are shown.

persist after the first attempt and atrioventricularconduction returning within 2-6 hours. Completeheart block was achieved in all of them at the secondprocedure.

In three patients atrial fibrillation was induced byone of the ablation shocks but non-sustained orsustained ventricular tachycardia or ventricularfibrillation was not induced in any of them.

In 11 patients serum concentrations of creatinekinase were measured before and after the procedureand in two there was a significant rise, but bothpatients had had multiple transthoracic cardio-versions to establish sinus rhythm during the abla-tion procedure. In none of the patients was there asignificant increase in the creatine kinase MB frac-tion.

FOLLOW UPComplete heart block was maintained in 1 1 patientsduring follow up of 7-28 (mean 14) months. In eachpatient either a rate responsive ventricular demand(10 patients) or atrioventricular sequential pace-maker was implanted. None ofthese patients is beingtreated with antiarrhythmic agents and none hassymptomatic palpitation. One patient had an uncom-plicated anterior myocardial infarction 11 monthsafter the ablation and another experienced an episodeof persistent chest pain five months later but hadno enzyme evidence of infarction. Surgical ablationof the His bundle was successful in the patient inwhom both modified and conventional ablationfailed.

In two patients atrioventricular conductionseemed to return late after the ablation but when itdid there was evidence of impaired conduction. Inpatient 6 atrial fibrillation recurred 24 hours after theprocedure and was conducted at a mean ventricularrate of 68 beats/minute compared with 122 beats/minute before ablation. Although the resting andexercise heart rates during atrial fibrillationsubsequently increased they remained well

controlled on digoxin. Before ablation they hadremained uncontrolled despite combined treatmentwith digoxin and verapamil. This patient was notpaced and repeated ambulatory electrocardiographicrecordings did not show prolonged pauses. The otherpatient who presented with paroxysmal atrial flutter,was in complete heart block after a 5 1 J dischargeand this was thought to be present at the end of theobservation period. Closer analysis showed that therewas high degree (6:1) atrioventricular block at theend of the procedure; subsequently paroxysms ofatrial flutter were conducted slowly. A symptomaticepisode of palpitation recurred, however, six monthsafter the ablation and atrial flutter with 2:1 atrio-ventricular block was documented. Treatment withdigoxin was started and further attacks of atrialflutter were associated with high degree atrio-ventricular block.

Discussion

Electrode catheter ablation of atrioventricularconduction is used to treat patients with supra-ventricular arrhythmias who continue to havesymptoms while taking medical treatment or who areintolerant ofmedical treatment. Data collected by theAblation Registry showed that permanent completeheart block was produced in 63% of360 patients whohad ablation ofthe atrioventricular tract (mean 61 1 J/patient).4 Similar results were reported from theUnited Kingdom and France.'14 Complications may,however, follow the use of these high energy shocks.Ventricular arrhythmias may occur in the short termas may hypotension and cardiac perforation.' Thereis a short lived rise in cardiac enzymes" and evidencethat right ventricular function may be impaired in thelong term.10 Follow up of the registry patients alsoshowed that 2% died suddenly in the mean follow upperiod of nine months.4A defibrillator is conventionally used as the power

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Transvenous ablation of atrioventricular conduction with a low energy power sourcesource for catheter ablation, despite the fact that tominimise injury to the chest wall it has a waveformthat is designed to limit the peak current for a givenenergy. Because the intention of catheter ablation isto cause localised damage this waveform may not beappropriate.

Several physical events result from the dischargeof a high voltage through a small intracardiacelectrode.56 The precise physical features of theenergy that cause damage are unknown. After dis-charge of the defibrillator an intense electric fieldsurrounds the intracardiac electrode and currentflow results in resistive heating. With all but thelowest defibrillator energies arcing will occur acrossthe gas that builds up around the electrode as aconsequence of this local heating. Arcing will resultin a high pressure shock wave that will propagatewithout local attenuation.'5 The series inductance inthe output circuit of a standard defibrillator retardsthe rate ofdischarge ofthe capacitor and increases thetime to peak voltage. This allows a high voltage to bepresent when insulating gas has formed around theelectrode and therefore arc formation is encouraged.The modified ablater was designed to deliver similarvoltage but over a shorter interval, in part to allowdelivery of the maximum amount of energy beforethe build up of gas. This design permits highervoltage and current to be delivered for a given energyand allows the local effects of cellular electric fielddielectric breakdown," ionisation, and heating topredominate over barotrauma.'2 It is likely that therise in temperature is limited to such an extent that itdoes not produce any important tissue damage.Our results indicate that electrode catheter

ablation of atrioventricular conduction is successfulin a high percentage ofpatients at considerably lowerenergies than previously reported. We measured thedelivered voltage and current and were therefore ableto compute delivered energy. Such measurementshave not been systematically reported before andtherefore comparisons with other series cannot easilybe made. In most previous studies only the storedenergies or the energy delivered to a nominal resis-tance were recorded. It is difficult, therefore, toestablish the relation between the voltages andcurrents associated with the energies used in thisstudy and those seen with conventional defibrillatorshocks. Trantham et al, however, did record voltageand current in 12 patients undergoing electrodecatheter ablation by conventional shocks of 200 and300 J-the mean peak voltages were 2 16 and 2-40 kVand the mean peak currents were 42-2 and 58-2 Arespectively.'7 In those patients in our series in whoma single definitive shock caused permanent completeheart block, the mean energy was 16-4 (range2-437T5) J, the mean peak voltage 1-85 (range

0-79-2-78) kV, and the mean peak current 15-5(range 4-6-25) A.We used standard electrodes and techniques for

His bundle recording as well as standard criteria fordetermining the optimal site for energy delivery.Other studies have also attempted to reduce theenergy requirements for electrode catheter ablationof atrioventricular conduction. Holt et al used thespecially shaped design of helical permanent pacingelectrodes to ensure both a closer contact with thetarget and direct the energy." Four shocks of 50 Jeach in 10 patients achieved complete heart block inseven. Polgar et al used a suction electrode to obtainclose contact with the His bundle and achievedcomplete heart block in three of five patients withsingle shocks of 50-150 J.'9 Although the serumconcentration of creatine kinase was raised the con-centration was lower than in a comparative groupundergoing atrioventricular ablation in the conven-tional method. McComb et al attempted electrodecatheter ablation of atrioventricular conduction inseven patients at low levels ofenergy (20-50 J) from adefibrillator in an attempt to impair but not destroyatrioventricular conduction.20 Single initial shocks of50 J, however, produced permanent complete heartblock in three patients.The absence of a rise in cardiac enzymes in our

patients is intriguing. The peak voltages (andassociated peak currents) seen in our patients areequivalent to energies 5-10 times higher when astandard defibrillator is used. Therefore the electricfield intensities are similar to those encounteredwhen the conventional technique is used and cardiacenzymes are increased.'7 If as seems possible myo-cardial damage is produced as a consequence of thediffuse effect of a shock wave, possibly by means ofcavitation, this provides further circumstantialevidence that this modified waveform reduces thearcing tendency and results in a lower pressure shockwave for a given peak voltage.Our protocol for determining the efficacy of

individual shocks differed from reports of othermethods. We used test shocks in an attempt todetermine whether the catheter was positioned at thecorrect level of the conduction system and addition-ally to provide a guide to the responsiveness ofatrioventricular conduction to electrical discharge. Itis clear that the energy-response relation with ourtechnique is wide and presumably influenced by theproximity of the electrode to the conducting system.Whether the amplitude of the His bundle electro-gram is a useful guide to proximity remains con-troversial. In some studies it correlated with clinicalefficacy2 while in others no relation was found.'Clearly no individual value for the amplitude of theHis bundle potential will determine successful

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366 Rowland, Cunningham, Ahsan, Rickardscatheter ablation. We attempted on each occasion toposition the electrode catheter so that it recorded anamplitude > 200 yV, and in two of the three patientsin whom complete heart block was not achieved theHis bundle potential was < 200yV.

Test shocks may dislodge the electrode. If thishappens the catheter will have to be repositionedwhile the His bundle is temporarily disrupted andtherefore not producing as large an electrical signal.In fact movement of the electrode catheter was slightat these low energies, but during the shocks and forthe observation period afterwards the operator heldthe catheter to maintain its position. If dislodgementhad been an important problem we would haveexpected a higher incidence of repeat procedures.But only four (29%) of 14 required second ablationscompared with 37% and 58% in larger series.34This study showed that permanent ablation of

atrioventricular conduction can be achieved with apurpose built ablater. This power source achievedcomplete heart block with cumulative energies thatwere several times lower than those required with aconventional defibrillator. This power source, whichwas designed to optimise the local electrical effectsand reduce the tendency to arcing, gave results thatsuggested that arcing is not essential for the ablationof atrioventricular conduction. We do not knowwhether avoidance of arcing and its attendant effectswill improve the long term outcome of patientsundergoing ablation.

References

1 Scheinman MM, Morady F, Hess S, Gonzalez R.Catheter-induced ablation of the atrioventricularjunction to control refractory supraventriculararrhythmias. JAMA 1982;248:851-5.

2 Gallagher JJ, Svenson RH, Kasell JH, et al. Cathetertechnique for closed-chest ablation of the atrioven-tricular conduction system: a therapeutic altemativefor the treatment of refractory SVT. N Engl J Med1982;306:194-200.

3 Nathan AW, Bennett DH, Ward DE, Camm AJ.Catheter ablation of atrioventricular conduction.Lancet 1984;i: 1280-4.

4 Evans GT, Scheinman MM. Catheter ablation ofventricular tachycardia foci: a report of thepercutaneous cardiac mapping and ablation registry[Abstract]. Circulation 1986;74(suppl II):460.

5 Boyd EGCA, Holt PM. An investigation into theelectrical ablation technique and a method ofelectrode assessment. PACE 1985;8:815-23.

6 Bardy GH, Coltorti F, Ivey TD, et al. Some factors

affecting bubble formation with catheter-mediateddefibrillator impulses. Circulation 1986;73:525-38.

7 Scheinman MM. Catheter ablation for patients withcardiac arrhythmias. PACE 1986;9:551-64.

8 Fisher JD, Kim SG, Matos JA, et al. Complications ofcatheter ablation of tachyarrhythmias: occurrence,protection and prevention. Clin Prog ElectrophysiolPacing 1985;3:292-8.

9 Holt PM, Boyd EGCA. Hematologic effects of thehigh-energy endocardial ablation technique.Circulation 1986;73:1029-36.

10 Schofield PM, Bowes RJ, Brooks N, Bennett DH.Exercise capacity and spontaneous heart rhythm aftertransvenous fulguration of atrioventricular conduc-tion. Br Heart J 1986;56:358-65.

11 Rowland E, Foale R, Nihoyannopoulos P, Perelman M,Krikler DM. Intracardiac contrast echoes duringtransvenous His bundle albation. Br Heart J1985;53:240-2.

12 Cunningham D, Rowland E, Rickards AF. A new lowenergy power source for catheter ablation. PACE1986;9:1384-90.

13 Ahsan AJ, Cunningham D, Rowland E, Rickards AF.Catheter ablation without fulguration: design andperformance of a new system. PACE 1989;12(PartII):131-5.

14 Levy S, Bru P. Interruption electrique par voiepercutanee de la conduction auriculo-ventriculairenormale. Analyse des cas franqais. Arch Mal Coeur1986;79:1145-50.

15 Cunningham D, Rowland E, Rickards AF. Lack ofshock wave absorption after high energy catheterdischarge suggests that barotrauma is a myth[Abstract]. Circulation 1987;76(suppl IV):407.

16 Jones JL, Proskauer CC, Paull WK, Lepeschkin E,Jones RE. Ultrastructural injury to chick myocardialcells in-vitro following "electrical countershock".Circ Res 1980;46:387-49.

17 Trantham JL, Gallagher JJ, German LD, BroughtonA, Guarneri T, Kasell J. Effects ofenergy delivery viaa His bundle catheter during closed chest ablation ofthe atrioventricular conduction system. J Clin Invest1983;72:1563-74.

18 Holt PM, Boyd EGCA, Crick J, Sowton E. Lowenergies and Helifix electrodes in the successfulablation of atrioventricular conduction. PACE1985;8:639-45.

19 Polgar P, Worum F, Kovacs P, Lorincz I, Bekassy Sz,Peterffy A. A new technique for closed-chest humanHis bundle ablation using suction electrode catheterand DC shock. In: Perez-Gomez F, ed. Cardiacpacing, electrophysiology, tachyarrhythmias. NewYork: Futura Media Services, 1985:1582-7.

20 McComb JM, McGovem BA, Garan H, Ruskin JN.Modification of atrioventricular conduction usinglow energy transcatheter shocks [Abstract]. JAm CollCardiol 1985;5:454.



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