A Comparison of Ventricular ArrhythmiasInduced with Programmed Stimulation VersusAlternating Current

MARK CUA and ENRICO P. VELTRI

From the Division of Cardiology, Department of Medicine, Sinai Hospital of Baltimore,Baltimore, Maryland

CUA, M., ET AL.: A Comparison of Ventricular Arrhythmias Induced with Programmed StimulationVersus Alternating Current. In patients undergoing implantation and testing of the implantable cardio-verter defibrillator (ICD), alternating current [AC] may be used to induce ventricular tachyarrhythmiasin a prompt, safe, and efficient manner. These arrhythmias have been previously reported to be similarto those induced during programmed electrical stimulation (PESj. We compared the ventricular tachyar-rhythmias induced by both methods in 14 patients: 8 male, 6 female; mean age 61 years; coronary diseasein 10, cardiomyopathy in 4; mean ejection fraction 31%. The presenting arrhythmia was nonsustainedventricuiar tachycardia (VT] in four, sustained monomorphic ventricular tachycardia (SMVTJ in five,ventricular fibrillation (VF) in four, and unknown in one patient with syncope. PES (single, double, tripleextrastimuli; burst pacing] and AC [1-2 sec application) stimulation via right ventricular endocardialelectrode catheter was performed off antiarrhythmic drugs in the nonsedated state. PES induced SMVTin nine, polymorphic VT in two, and VF in three. AC induced VF in all patients. Although AC canreliably induce ventricular tachyarrhythmias during de/ibrillation threshold and ICD testing, there is poorcorrelation to PES induced tachyarrhythmias. fPACE, Vol. 16, March, Part I 1993)

alternating current, programmed electrical stimulation

Introduction

The deliberate induction of malignant ven-tricular tachyarrhythmias with alternating current(AC) was initially used to achieve cardioplegiaduring open heart surgery. ̂ '̂ Subsequently,Mower et al.^ first reported using AC during diag-nostic electrophysiological studies and duringsurgery to test function of the implantable cardio-verter defibrillator (ICD). In that study, the ACsource was a standard, line-operated batterycharger with a full-wave rectified output of 7 volts.Several observations were made regarding the ar-rhythmias induced with this method: ventricular

Address for reprints: Enrico P. Veltri, M.D., Division of Cardiol-ogy, Sinai Hospital of Baltimore, Belvedere Ave. atGreenspring, Baltimore, MD 21215. Fax: (410) 578-5710.

Received June 5, 1992; revision September 17, 1992; acceptedSeptember 18, 1992.

tachycardia was induced more frequently thanventricular fibrillation (VF), and the tachycardiasinduced were usually similar in rate and morphol-ogy to those induced with programmed electricalstimulation (PES) using direct current (DC). How-ever, these findings have not been substantiated.We report our ongoing clinical experience withthe use of a battery charger to induce ventriculartachyarrhythmias in patients undergoing ICDtesting.

Methods

Thirty-eight consecutive patients who wereundergoing implantation of the ICD using atransvenous approach for sustained ventricular ar-rhythmias refractory to medical therapy were se-lected for this study. Exclusion criteria were thefollowing: (1) presence of noninducible ventricu-lar tachyarrhythmia by PES; and (2) patients whowere on antiarrhythmic drugs (except digoxin.

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beta-adrenergic blockers, and calcium channel an-tagonists) during PES or ICD testing.

Programmed Electrical Stimulation

Prior to being referred for surgery all patientshad undergone full cardiac evaluation of their ar-rhythmias, including PES, and were off all antiar-rhythmic drugs (except digoxin, beta-adrenergicblockers, and calcium channel antagonists), PESwas done using a programmable stimulator(Bloom Associates, Ltd., Reading, PA, USA) thatdelivered a 1,5-msec square wave pulse with a cur-rent of twice diastolic threshold ^ 4 mA, Twostimulation sites were used, the apex and outflowtract of the right ventricle. The programmed stimu-lation protocol has previously been described."Recordings were done on a multichannel recorder(PPG Biomedical Systems, Lenexa, KS, USA)using four surface ECG leads (I, aVF, Vi, Vg), andtwo or three intracardiac recordings (HRA, HIS,RV). Patients were in the postabsorptive nonse-dated state and received only local lidocaine anes-thesia during the procedure.

Battery Charger Stimulation

Prior to hospital discharge (:S l week from thetime of ICD implantation), all patients underwenttesting of ICD function in the absence of all antiar-rhythmic drugs other than digoxin, beta-adrener-gic blockers, and calcium channel antagonists.Ventricular arrhythmias were induced with an ACcharging unit (AICD Check Battery Recharger,Model #BC-2, Cardiac Pacemakers Inc, St, Paul,MN, USA) with an output of 45 mA with a 150ohm resistance; voltage output was 18 volts rootmean square. The waveform was sinusoidal witha 60 Hz cycle. Impulse duration was 1 to 2 sec-onds, and the right ventricular apex was the stimu-lation site. Recordings were made with the samemultichannel recorder used during baseline PESusing the same set of leads. Patients were again inthe postabsorptive nonsedated state and receivedonly local lidocaine anesthesia during the pro-cedure.

Definitions

Sustained monomorphic ventricular tachy-cardia (SMVT) was defined as s: 30 seconds dura-

tion or requiring termination in < 30 seconds dueto hemodynamic collapse. The morphology wasuniform with a cycle length > 200 msec and iden-tifiable isoelectric intervals between surface QRScomplexes. Polymorphic ventricular tachycardia(PVT) was defined as > 30 seconds duration orrequiring termination in < 30 seconds. The mor-phology was nonuniform in that no two sequentialQRS complexes had the same morphology in anysurface lead, VF was differentiated from PVT bynot having any discrete or identifiable QRScomplex.

Results

Patient Population

Of the 38 patients who underwent successfultransvenous implantation of the ICD, 24 were ex-cluded for the following reasons: nine had nonin-ducible ventricular tachyarrhythmia during base-line PES, three were not antiarrhythmic drug-freeduring baseline PES, one did not receive AC stim-ulation during predischarge ICD testing, and 11were not antiarrhythmic drug-free during predis-charge ICD testing. Of the 14 patients included inthis study (Table I), there were eight males andsix females, age 61 ± 8 years (mean ± standarddeviation). Ten patients had coronary artery dis-ease, three had idiopathic dilated cardiomyopa-thy, and one had idiopathic hypertrophic subaor-tic stenosis. Ejection fraction was 31 ± 16%, Clini-cal arrhythmia was identified as VF in fourpatients, SMVT in five, nonsustained ventriculartachycardia (NSVT) in four, and unknown in onewho presented with syncope. Seven patients wereon digoxin alone, two on digoxin and a calciumchannel antagonist, one on digoxin and a beta-ad-renergic blocker, and one on a beta-adrenergicblocker alone.

Baseline PES

Of the four patients who had VF as their clini-cal arrhythmia, two had VF induced with tripleextrastimuli during baseline PES, one had PVT in-duced with double extrastimuli, and one hadSMVT induced with double extrastimuli. Of thefive patients who had SMVT as their clinical ar-rhythmia, SMVT was induced in all five during

PACE, Voi, 16 March, Part I 1993 383

GUA, ET AL.

Pt.

1

23456789

1011121314

Age

7060576959655966626173655438

Clinical Data of

Dx

CADCADIHSSCMPCADCMPCADCADCADCADCADCADCMPCAD

Table 1.

Patients and Arrhythmias

EF

0.200.300.800.200.300.270.350.350.340.200.200.200.400.20

Induced by PES

Clinical

SMVTSMVTSMVTSMVTSMVTVFVFVFVFNSVTNSVTNSVTNSVTsyncope

and AC

Arrhythmia

PES

SMVTSMVTSMVTSMVTSMVTVFVFPVTSMVTSMVTSMVTSMVTPVTVF

AC

VFVFVFVFVFVFVFVFVFVFVFVFVFVF

^S,r alternating current; CAD = coronary artery disease; CMP = cardiomyopathy; Dx = diagnosis; EF = ejection fraction-IHSS = Idiopathic hypertrophic subaortic stenosis; NSVT = nonsustained ventricular tachycardia; PES = programmed electricalstimulation; PVT = polymorphic ventricular tachycardia; SMVT = sustained monomorphic ventricular tachycardia-VF = ventric-ular fibrillation.

baseline studies: one with a single extrastimulus,two with double extrastimuli, and two with tripleextrastimuli. Of the four patients who had NSVTas their clinical arrhythmia, SMVT was inducedin one patient with double extrastimuli and in twopatients with triple extrastimuli. PVT was inducedin one patient with double extrastimuli. The onepatient who had syncope of unknown cause hadVF induced with triple extrastimuli.

AC Stimulation

During predischarge testing of ICD function,VF was induced in all patients with AC stimula-tion. Table I depicts the results of arrhythmias in-duced by PES and AC.

Discussion

The results of this study show that dissimilarventricular tachyarrhythmias were induced byPES and AC. Thus, although AC can reliably in-duce VF for defibrillation threshold testing andICD conversion testing, it has limited diagnostic

utility. Many studies have been performed on theeffects of AC on the heart.^"^° The ability of smallAC discharges to cause malignant ventricular ar-rhythmias in patients with intracardiac lines is aknown hazard.^^'^^ This phenomenon has been ex-ploited to induce cardioplegia during open heartsurgery." Numerous studies have shown that "ag-gressive" programmed stimulation protocols suchas the use of triple or quadruple extrastimuli fre-quently induce PVT or VF.^^-*^ These may be con-sidered to be nonspecific responses because theycould be reproduced even in patients with struc-turally normal hearts.

Although Mower et al.^ used a battery chargerin their study, the waveform of its output was notdescribed. Nevertheless, we believe that it wasprobably similar to that used in the present study.It is unclear why the battery charger used in theformer study induced arrhythmias similar to thatproduced by conventional PES. There are severalconceptual reasons and experimental observa-tions, however, that support the hypothesis thatAC is not comparable to DC in terms of its effectson the heart. The duration of shock used to induce

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VF during ICD testing is at least 1 second and canlast several seconds. PES uses DC in which theduration of shock is usually 1.5 msec, A greateramount of energy is delivered hy the hatterycharger hecause of its longer duration of stimula-tion.^" The energy delivered hy the charger alsospans one to several QRS complexes, while in PESthe extrastimuli are applied to one portion of thediastolic period. One second of AC stimulationwould expose myocardium to a current flux thatchanges 120 times each second, while no morethan two or three extrastimuli are usually deliv-ered during PES. This would make AC more likelyto induce PVT or VF hecause it has a hetter chanceof stimulating the ventricle during its vulnerahleperiod. There is also the possihility that the cur-rent generated hy the hattery charger may have de-leterious effects on the heart. Animal studies haveshown that AC shocks cause more ventricular dys-function than DC shocks.^^

In the study of Mower et al.,^ AC stimulation

was done during ICD implantation under general

anesthesia, and this was comhined with endocar-

dial resection and aneurysmectomy in several pa-

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