Electrophysiological Significance of QRSAlternans in Narrow QRS Tachycardia

GIOVANNI PULIGNANO, NICOUNO PATRUNO, PAOLA URBANI,CESARE GRECO, and GIUSEPPE GRITELLI

From the Deparfment of Cardiology, University of Rome "La Sapienza", Rome, Italy

PULIGNANO, G., ET AL.: Electrophysiological Significance of QRS Alternans in Narrow QRS Tachycar-dia. To investigate the electrophysiological significance of QRS alternans during narrow QRS tachycardia,fransesophageal atrial pacing and recording was performed in 24 patients wiih a history of paroxysmalsupravenlricular tachycardia. Standard eJectrocardiograms showed ventricular preexcitation in 15 pa-tients and normal QRS paKern in nine patients. The ventriculoatrial interval during tachycardia, asdefined by means 0/ transesophageal eiectrogram, allowed tentative diagnosis 0/ the tachycardia mecha-nism. A 12-lead ECG was recorded either during spontaneous or induced tachycardia, as well as duringtransesophageai atriai pacing at increasing rates. Electrical alternans occurred spontaneously in eightpatients (33%, group A): jive with accessory pathway reentry (mean VA; 136 ±43 msec], and three with AVnodal reentry (mean VA: 48.3 ± 12 msec). Tachycardia rate ranged between 170 and 230 beats/min (mean200.7 ± 16}. In (wopafients, aJternalion of the QRS occurred only in the presence of a hearf rate exceeding180 and 190 beats/min, respectively. The amplitude 0/QRS remained stable during tachycardia in 16patients (67%, group B): 14 had accessory pathway reentry (mean VA: 137.5 ± 32 msec), and two had AVnodal reentry (mean VA: 45 ± 7 msec). In this group, the tachycardia rate ranged from 150 to 210beats/min (mean 175 ± 12}. Incremental transesophageal atria/ pacing up to rates equal to that of tachy-cardia was performed in five patients from group A and in five patients from group B. Electrical alternanscould not be induced in both groups with pacing at progressively increasing rates. In contrast, the phenom-enon could be elicited in two patients from group A when an abrupt pacing at the same rate thai hadshowed the spontaneous occurrence of QRS alternans was instituted. This article suggests that alternationof QRS is relatively common during narrow QRS tachycardia. The phenomenon is a rate-dependent event,unrelated to the substrate of the tachycardia. (PACE, Vol. 13, February 1990}

QRS alternans, supraventricular tachycardia, Wol^-Parkinson-White syndrome, AV nodal reentry

Introduction

The occurrence of alternation of QRS ampli-tude (EA) during supraventricular tachycardiahas been considered indicative of reentry by anatrioventricular accessory pathway (AP), andtherefore diagnostic for the Wolff-Parkinson-White syndrome.^ This hypothesis, however, has

Supported by Grant 8700735-57 Consiglio Nazionale delle Ri-cerche. Rome. Italy.

Address for reprints: Giuseppe Gritelli M.D., Istituto di Car-diochirurgia, Policlinico Umberto I, Viale del Policlinico 1,00161 Rome, Italy.

Received April 4, 1989; revision October 3, 1989; acceptedOctober 3, 1989.

not been confirmed, since recent studies haveshown that EA is a rate-related event, indepen-dent on the tachycardia mechanism.^

In an attempt to clarify the electrophysiologi-cal significance of EA during supraventriculartachycardia, we investigated the relationship ofthis phenomenon to heart rate and mechanism ofarrhythmia, in patients with narrow QRS tachy-cardia.

Patients and Methods

Twenty-four patients (14 males, 10 females),aged 9-67 years (mean age 32 ± 15 yrs) with ahistory of paroxysmal supraventricular tachycar-

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dia were evaluated. Standard electrocardiogramsshowed ventricular preexcitation in 15 patients,normal QRS pattern in 9 patients. In all patients,no organic heart disease was found with physicalexamination and routine diagnostic techniques.

After informed consent was obtained, car-dioactive drugs were discontinued for at least 5half-lives and a transesophageal eiectrophysioiog-icai study was performed.^'' During postabsorh-tive state, a bipolar flexible electrode catheter (CBBioelettronica, Florence, Italy) 30-mm interelec-trode spacing, was introduced through the nostriland positioned in the distal esophagus. Trans-esophageal atrial pacing (TAP) was performed bymeans of a multiprogrammable electrical stimula-tor (Sep 3, CB Bioelettronica). The proper pacingsite was defined as the electrode position where alarge and stable transesophageal atrial electro-gram was recorded. A pulse duration of 10 msecand a current output ranging from 15 to 25 mAwere used for pacing. Extrastimulus pacing tech-nique and pacing at increasing rates were used fortachycardia induction. During the study, stan-dard electrocardiograms and transesophagealatrial electrogram (TAE) were simultaneously re-corded. The ventriculoatrial interval duringtachycardia (VA)—as defined by the time intervalbetween the surface QRS and TAE—was used foridentification of the probable tachycardia mecha-nism. Thus, a VA interval longer than 70 msecwas considered diagnostic for reentry by an AP,

while a VA interval < 70 msec suggested reentrywithin tbe AV node.^

The amplitude of QRS complexes was evalu-ated initially during induced reciprocating tachy-cardia. EA was defined as change in the ampli-tude of QRS > 0.1 mV and was considered to bepresent if it lasted for at least 10 seconds and oc-curred at least 10 seconds after the onset of thetachycardia.

After restoration of sinus rhythm by stimula-tion techniques, two different pacing modalitieswere performed in order to investigate the rela-tion of EA with the heart rate: (1) Progressivesbortening of pacing cycle length in a "ramped"manner; (2) Burst pacing at progressively shortercycle lengths, where cycle length was held con-stant for 10 seconds, each burst being institutedfollowing a pause of 30 seconds. In both pacingmodalities the initial cycle length was 600 msec,and the end point was the occurrence of tachycar-dia or second-degree AV block.

Statistical analysis was accomplished usingan unpaired (-test for continuous variables and aFisher's exact test for discrete variables, A proba-bility (P) value of <0,05 was considered signifi-cant.

Results

Results of tbe study are summarized in TableI. EA occurred spontaneously in eight patients

Number of patientsSubstrate of Tachycardia

AP reentryAV node reentry

Tachycardia Ratemean (bpm)range (bpm)

Transesophageal Atrial PacingWean induced rate (bpm)

EA occurrence:Incremental TAPAbrupt TAP

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Table 1.

Eiectrophysioiogicai Findings

Group A(with EA)

8 (33%)

53

200.7 ± 16170-230

5

206.8 ± 17

02

February 1990

Group B(without EA)

16 (67%)

142

175 ± 14150-210

8

188.7 ± 18

00

p

NSNS

<0.001

145

PULIGNANO, ET AL.

(33%, group A), while the ampHtude of the QRScomplexes remained stahle during tachycardia in16 (67%. group B).

QRS Alternans and the Substrate of Tachycardia

Among patients of group A. reentry by an APwas identified as the underlying mechanism ofthe tachycardia in five patients (mean VA inter-val: 136 ± 43 msec), while AV nodal reentry wasdocumented in three patients (mean VA interval:48.3 ±12 msec). Among patients of group B, an APreentry was found in 14 [mean VA interval: 137.5± 32), while a reentry confined within the AVnode was responsible for tachycardia in two pa-tients (VA intervals 40 and 50 msec, respectively).

The differences in the distribution of tachycardiamechanism between group A and group B werenot statistically significant. Figure 1 shows EA in apatient with supraventricular tachycardia due toreentry by an AP. In Figure 2, the occurrence ofthe phenomenon in a patient with AV nodal reen-try tachycardia is shown.

QRS Alternans and the Tachycardia Rate

The mean rate of tachycardia in groups A andB was, respectively, 200.7 ± 16 and 175.7 ± 12beats/min (P < 0.001). In two patients from groupA, one with AV nodal reentry and one with reen-try by an AP, EA occurred only in the presence of

isec

aVL

aVF

V4

B

ESO

0.5 SEC

Figure 1. Orthodromic reciprocating tachycardia of 220 bpm. A: EA is evident in all electrocar-diographic leads. B: the VA Interval (190 ms} suggests reentry by an AP. ESO = transesophagealelectrogram; A = utrial electrogram; V = ventricular eleclrogram.

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'JJJJMiW

B

ESO

0.5 SEC

Figure 2. AV nodal reciprocaling tachycardia of 2^0 bpm. A; EA {with alternation of QRSmorphology in leads 1 and HI) is present in leads I, aVL, V,, V2, and V5. B: The VA interval (45 ms)suggests reentry ivithin the AV node. Abbreviations as in Figure 1.

a heart rate exceeding 180 and 190 beats/min,respectively (Figs. 3 and 4A and B).

Findings During Incremental TransesophagealPacing

Incremental TAP up to rates equal to orhigher than that of the tachycardia was per-formed in five patients of group A (mean inducedrate; 206.8 ± 17 bpm) and in eight from group B(mean induced rate: 188.7 ± 18 bpm). In the re-maining 11 patients, the test was hampered by theeasy occurrence of tachycardia and/or the pres-ence of anterograde AP conduction during TAP.EA could not be elicited in both groups with TAPat progressively increasing rates, but the phenom-

enon could be induced in two patients from groupA when an abrupt pacing at the same rate thathad showed the spontaneous occurrence of EAwas instituted (Fig. 4C).

DiscussionThe electrophysiological significance of EA

during narrow QRS tachycardia is still controver-sial. Green et al.̂ retrospectively studied 161 pa-tients with supraventricular tachycardia. As a re-entry involving an AP had been documented in92% of tachycardia episodes showing EA, the au-thors concluded that the phenomenon is diagnos-tic for Wolff-Parkinson-White syndrome. Furtherstudies, however, did not confirm this hypothesis.Morady et al.^ found that EA is a rate-related

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PULICNANO, ET AL.

Isec

190bpm 230bpm

B

ESO

V A 105ms0.5SEC

Figure 3. The occurrence of EA ot fast rates in a patient with orthodromic reciprocating tachy-cardia is shown. A: EA is not observed at a rate of 190 bpm, while the phenomenon appears at 230bpm. B: The VA interval (105 ms} indicates reentry by an AP. Abbreviations as in Figure J.

event. Furthermore, reports on the occurrence ofEA during either atrial flutter with 1:1 AV con-duction or supraventricular tachycardia withaberrancy, as well as during ventricular tachycar-dia,^"'' argue against the specific significance ofthe phenomenon.

Our data indicate that EA is a rate-dependentevent, unrelated to the underlying substrate ofthe tachycardia. This is suggested by the follow-ing findings: (1) The rate of the tachycardia wassignificantly faster in patients with EA than inpatients without EA, regardless of the site of thereentry circuit: (2) EA was observed either in pa-tients with reentry confined within the AV nodeor in patients with AP reentry. (3) In two patientswith variability of the tachycardia rate, EA oc-curred only at rates exceeding 180 and 190beats/min, respectively.

According to Morady's data,^ TAP at progres-

sively increasing rates did not elicitate EA, inspite of an induced heart rate equal to or higherthan the rate at which the phenomenon occurredspontaneously. In contrast, EA could be repro-duced in two patients from group A by means ofan abrupt atrial pacing at the same rates that hadshowed the spontaneous occurrence of the phe-nomenon. Such findings are consistent with re-sults of in vitro studies,^ which documented thatalternation of action potential duration of papil-lary muscle occurred only when pacing at fastrates was instituted suddenly. Indeed, even if EAcould not be induced with incremental TAP, inany of our patients, the phenomenon was gener-ally observed during spontaneous tachycardia,where the increase in rate occurred suddenly.

As far as the eiectrophysioiogicai substrate ofQRS alternans is concerned, the phenomenonmight result from oscillations of action potential

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180 bpm 200 bpmisec

B0.5 SEC

V

Figure 4. AV nodal reentry tachycardia with variability of the heart rate. A: EA is not seen al arale of 180 bpm, but it occurs at 200 bpm. B: The VA interval (50 ms) is suggestive of reentrycon^ned wifhin (he AV node. C: Abrupf TAP nt a rate of 210 bpm elicita(e.s EA. See tex( fordiscussion. Abbreviations as in Figure J.

duration and changes in the refractoriness of theHis-Purkinje system or ventricular myocardium,as a consequence of sudden increase of the heartrate.^

The occurrence of EA in patients with AVnodal reentry has been ascribed by Green et al.̂ toalternating superimposition of the P wave to theQRS complexes, rather than changes in the QRS

amplitude itself. Our data do not suggest sucb apossibility, since alternation of AA intervals wasnot seen in our patients with AV nodal reentry.

In conclusion, this article indicates that EArepresents a relatively common event duringnarrow QRS tachycardia. Its occurrence is a rate-dependent phenomenon, unrelated to tbe sub-strate of tbe arrhythmia.

References1. Green M, Heddle B, Dassen W. et al. Value of QRS

alternation in determining the site of origin of nar-row QRS supraventricular tachycardia. Circulation1983; 68:368-373.

2, Morady F, Di Carlo LA, Baerman |M, et al. Determi-nants of QRS aiternans during narrow QRS tachy-cardia. I Am Coll Cardiol 1987; 9:489-499.

3. Gallagher JI. Smith VVM, Kerr CR, et al. Esophageal

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6.

pacing: A diagnostic and therapeutic tool. Circula-tion 1982; 65:336^341.Benson DW, Sanford M. Dunnigan A, et al. Trans-esophageal atrial pacing threshold: Role of inter-electrode spacing, pulse width and catheter inser-tion depth. Am f Cardiol 1984; 53:63-66.Kremers MS. Miller fM, Josephson ME. Electricalalternans in wide complex tachycardias. Am I Car-diol 1985; 56:305-308.Ellenbogen KA. Rogers RR. Szentpetery S. Electro-physiological observations during QRS alternationin a patient with incessant tachycardia. PACE 1988;11:413-418.

Morady F. The spectrum of tachyarrhythmias inpreexcitation syndromes. In DG Benditt. DW Ben-son (Eds.): Cardiac Preexcitation Syndromes. Ori-gins. Evaluation and Treatment. Boston. MartinusNijhoff, 1986; p. 129.Hoffman BE. Suckling EE. Eifect of heart rate oncardiac membrane potentials and the unipolarelectrogram. Am I Physiol 1954; 179:123-130.Tchou PJ, Leheman MH, Dongas J, et al Effect ofsudden rate acceleration on the human His-Pur-kinje system: Adaptation of refractoriness in adampened oscillatory pattern. Circulation 1986;73:920-929.

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