Parasystolic ventricular tachycardia with variable exit block

J. ELECTROCARDIOLOGY 15 (4), 1982,411-416

Parasystolic Ventricular Tachycardia with Variable Exit Block BY GIUSEPPE GRETO, M.D., FRANQESCO ARRIGO, M.D., SEBASTIANO COGLITORE, M.D., MICHELE GIANNETTO, M.D. AND FAUSTO CONSOLO, M.D.

SUMMARY This case is an example of ventricular parasystolic tachycardia associated with variable expressions of ectopic-ventricular (E-V) exit block. The exit block manifestated with 2:1, 3:2, 4:3 and higher ratios of E-Y conductions, interspaced with periods of 1:1 conduction. Concealed E-V conduction of the ectopic impulse could also be deduced.

frontal plane QRS axis of -90 degrees; b) a qR complex in lead V I; and c) rS complex in lead Y 6' These features suggest an ectopic ventricular origin." Some of these QRS complexes are followed by retrograde P' waves (Fig. 1). The beats appear in groups of two, three, four and larger numbers. Each group shows a progressive shortening of the R-R intervals, followed by a long pause. The long pause is nearly always less than twice the shortest R-R interval (Fig. 2). This pattern reflects the presence of a regularly discharging ventricular focus with the type 1 (Wenckebach) form of ectopic-ventricular (E-V) block. There is also a retrograde Wenckebach form of A-V conduction. This is marked by a progressive prolongation of the R-P' intervals, representing progressive prolongation of retrograde A-V conduction, ending in a block of retrograde conduction (Fig. 2). This was interspaced with periods of 1:1 retrograde A-V conduction (Fig. 3). At times the intervals between two consecutive ectopic beats are longer, corresponding roughly to twice the ectopic cycle length calculated from the Wenckebach periods. This pattern is consistent with a 2:1 E-V block (Fig. 2). In other recordings (Fig. 3) a 1:1 E-V conduction is present for 10 to 30 beats, resulting in a ventricular tachycardia with a rate of 150 beats per minute, associated with a slightly irregular R-R cycle. Occasionally pure sinus rhythm reappeared, lasting for one to five beats, with rates varying between 60 and 90 beats per minute. Occasional fusion beats (beats labelled F in Fig. 5) appeared during these periods. The sinus rhythm did not affect, i.e., reset, the ectopic cycle. Tachycardia thus reappeared at the calculated time, the interectopic interval always being a multiple of the calculated ectopic cycle length (Fig. 5).

In some cases of parasystole, the ectopic focus appears to discharge at a rate slower than the extrinsic rate, as a result of exit block.tf In such circumstances the duration of the true ectopic cycle may be calculated from: a) analysis of the interectopic intervals; or b) directly, if exit block momentarily disappears, resulting in conduction of two or more consecutive ectopic impulses. 2-5 ,7 A parasystolic tachycardia occurs when consecutive impulses generated by a rapid parasystolic center are able to depolarize the surrounding myocardium due to temporary absence of exit block l ' 5,8 The ventricular parasystolic tachycardia, however, is usually associated with intermittent exit block, during which the sinus rhythm, or the basic supraventricular rhythm, emerges. Such exit block is often a second degree 2:1 or a Mobitz type 2 block The occurrence of type 1 (Wenckebach type) of exit block is much less frequent.f This report describes a rare case of parasystolic ventricular tachycardia with variable 2:1 and Wenckebach form of exit block

CASE REPORT A 65 year old man with angina was admitted to the hospital for evaluation of the arrhythmia discussed below. The patient was completely symptom-free and, except for the irregular pulse, did not show any abnormal physical signs. The ECG is illustrated in Fig. 1 and shows irregularly spaced wide QRS complexes with: a) a superior The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. § 1734 solely to indicate this fact. Reprint requests to: Giuseppe Oreto, M.D., Clinica Medica 1a, Policlinico Universitario, University of Messina, Messina, Italy.

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Fig. 2. Standard lead II (a continuous recording) reflecting Wenckebach ectopic-ventricular sequences, characterized by the typical progressive shortening of the R-R intervals. The top strip shows consecutive periods of 3:2, 4:3, 2:1, 3:2 and 3:2 E-V block. The bottom strip shows a 3:2 sequence and two 6:5 sequence. Retrograde A-V Wenckebach conduction is evident, particularly in the bottom strip. Time intervals are expressed in hundredths of a second.

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tachycardia reappeared after some 20 minutes. Oral administration of the drug was ineffective. Amiodarone (600 mg/day p.o for 7 days) was also unsuccessful in the treatment of this arrhythmia. As the patient was symptomless, he refused further medication. An ECG recorded two weeks after the interruption of treatment revealed normal sinus rhythm, and six month follow-up was also normal.

DISCUSSION The parasystolic character of the ectopic arrhythmia is evident from the fact that both sinus rhythm, and atrial or ventricular pacing were unable to affect the regular discharge of the ectopic focus, reflecting the presence of entrance block. The entrance block in this case could, according to Scherf's theory--", be due to the high rate of ectopic discharge (about 150 per minute),

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ORETO ET AL

Fig. 5. A continuous recording of standard lead II. Numbers above the tracing express the intervals between consecutive ectopic beats; numbers below the tracing refer to the calculation of the ectopic cycle length.

which caused the E-V junction to be permanently refractory. Several cases of parasystolic ventricular tachycardia with intermittent exit block have been reported,1-5,8,lO,1l but the occurrence of associated Wenckebach exit block is exceptionally rare.f The minimal variation in the duration of the ectopic cycle length does not negate the diagnosis of parasystole. Cases of parasystole showing variations up to 27 hundredths of a second, based on the shortest interectopic interval, have been reported.l-P Moreover, day-to-day variations of the ectopic cycle length have also been described.f It is well established that the ectopic cycle length appears shorter when it is calculated from a long interectopic interval, as compared with direct measurements of the ectopic cycle length. 1,4,5 These variations are believed to be due to variable delay in conduction through the ectopic-ventricular junction, i.e., the E-V conduction time is longer when two or more consecutive impulses have to traverse the junction. This case is also instructive because it illustrates concealed E-V conduction. Fig. 5 shows several 3:2 Wenckebach sequences and one 2:1 sequence in the top strip. In the middle and bottom strips, fusion beats (labelled F) and sinus beats are manifest. It is evident that the sinus rhythm does not reset the ectopic rhythm: the long interectopic intervals are still multiples of the calculated ectopic cycle length. When the ectopic rhythm reappears after the sinus beats, the first ectopic cycle length (labelled *) is 73 or 75 hundredths of a second. In other words, it has a duration equal to the second interval of a Wenckebach sequence. It can therefore be deduced that concealed E-V conduction of an ectopic impulse occurs concomitantly with the last sinus beat. Thus, the first ectopic beat following sinus

rhythm is actually the second complex of a 3:2 Wenckebach E-V sequence. The first manifest ectopic cycle following a period of sinus rhythm may be therefore longer than normal because it, in fact, represents the long manifest ectopic cycle containing the blocked impulse of a 3:2 Wenckebach sequence (Fig. 5). This case thus illustrates the multiplicity of electrocardiographic manifestations which can result from the interplay of a protected ectopic pacemaker, a sinus pacemaker, and variability of concealed E-V conduction. Acknowledgment: The authors are grateful to Leo Schamroth, M.D.. for his helpful criticism of the manuscript.

REFERENCES 1. CHUNG, E K: Principles of Cardiac Arrhythmias. William & Wilkins, Baltimore, 1971

2. KATZ, L N AND PICK, A: Clinical Electrocardiography. Part 1. "The Arrhythmias". Lea & Febiger, Philadelphia, 1958 3. PICK, A: The electrophysiologic basis of parasystole and its variants. In: The Conduction System of the Heart, H J J WELLENS, K I LIE AND M J JANSE, eds. Stanfert Kroese, Leiden, 1976, p 143 4. SCHAMROTH, L: The Disorders of Cardiac Rhythm. 2nd Edition. Blackwell, Oxford, 1980 5. SCHERF, D AND BORNEMANN. C: Parasystole with a rapid ventricular center. Am Heart J 62:320, 1961 6. WATANABE, Y: Reassessment of parasystole. Am Heart J 81:451, 1971 7. FRIEDBERG, H D AND SCHAMROTH, L: Atrial parasystole, Br Heart ,J 32:172, 1970 8. TOUBOUL. P, DELAYE. J, CLEMENT, C. DELAHAYE. J P AND GONIN, A: Tachycardie ventriculaire parasystolique. Arch Mal Coeur 63:1414, 1970 J. ELECTROCARDIOLOGY 15 (4), 1982

PARASYSTOLIC VENTRICULAR TACHYCARDIA

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D, BLUMENFEI,D, SAND YILDIZ, M: Extrasystoles and parasystole. Am Heart J 64:357, 1962 10. CHUNG, E K, WALSH, T J AND MASSIE, E: Ventricular parasystolic tachycardia. Br Heart J 27:392, 1965 SCHERF,

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ROELANDT, J AND SCHAMROTH, L: Ventricular parasystolic tachycardia. With observations on differential stimulus-threshold as possible mechanism for exit block. Br Heart J 4:505, 1971 12. CHUNG, E K: Parasystole. Prog Cardiovas Dis 11:64, 1968

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ACKNOWLEDGMENT The Editorial staff wishes to express its gratitude to the individuals who served as guest reviewers during the last year. We greatly appreciate their assistance. Donald K. Chung, M.D. Memorial Hospital Medical Center Long Beach, CA

G. Pitts, M.D. University of Virginia Charlottesville, VA

Guy P. Curtis, M.D., Ph.D. University of California, San Diego San Diego, CA

S.W. Rabkin, M.D. The University of British Columbia Vancouver, B.C., Canada

Kenneth B. Desser, M.D. Good Samaritan Hospital Phoenix, AZ

Stanley Rush, Ph.D. University of Vermont Burlington, VT

Peter Friedman, M.D. Harvard Medical School Boston, MA

Madison S. Spach, M.D. Duke University Medical Center Durham, NC

Larry S. Green, M.D. The University of Utah Salt Lake City, UT

Jerome Stolzenberg, M.D. Miami Heart Institute Miami Beach, FL

Iraj A. Kashani, M.D. University of California, San Diego San Diego, CA

Boris Strasberg, M.D. The Abraham Lincoln School of Medicine Chicago,IL

Paul D. Kligfield, M.D. New York Hospital-Cornell Medical Center New York, NY

Paul Swaye, M.D. Miami Heart Institute Miami Beach, FL

Jerome Liebman, M.D. Rainbow Babies and Childrens Hospital Cleveland,OH

Robert L. Vick, Ph.D. Baylor College of Medicine Houston, TX

Jay W. Mason, M.D. Stanford University Medical Center Stanford, CA

Mary Anne Warnowicz, D.O. University of California, San Francisco San Francisco, CA

P. Molyvdas, Ph.D. University of Virginia Charlottesville, VA

Eliot Young, M.D. Harvard Medical School Boston, MA

Jeffrey W. Moses, M.D. The New York Hospital-Cornell Medical Center New York, NY

J. ELECTROCARDIOLOGY 15 (4), 1982