J. ELECTROCARDIOLOGY, 4 (1) 80-82, 1971

Paroxysmal Atrial Tachysystole With Exit Block BY HENRY MILLER, M.D., F.A.C.C.*

SUMMARY

Two cases Of atrial tachysystole with exit block probably due to digitalis toxicity are presented. The possible mechanism of this unusual and interesting arrhythmia is dis- cussed. In each case, recovery followed dis- continuation of digitalis.

I N T R O D U C T I O N

Exit block has been defined as the failure of impulse propagation from a cardiac pace- maker to the adjacent myocardium 1. The con- cept was introduced by Kaufman and Roth- berger 2 to support their theory of parasystolic origin of extrasystoles. It persists as a plausi- ble explanation of unidirectional conduction of an ectopic pacemaker in parasystole. Most cases of exit block have been reported in ec- topic rhythms of A-V junctional and ventric- ular origin. The occurrence of exit block ip paroxysmal atrial tachyarrhythmias is rare and relatively few cases have been reporteda,*, ~.

Exit block in paroxysmal atrial tachycar- dia may occur in one of two forms. 1) The ectopic impulse fails to reach the atria for one or more cycles. This is manifested by the appearance of long interectopic intervals that are precise multiples of the shorter one. 2) A Wenckebach phenomenon may interpose be- tween the origin of the impulse in the ectopic focus and its emergence into the atria.

The ectopic impulse is only recorded after it has left the ectopic focus and has activated the atrium, thereby resulting in the P wave. The delay or block in conduction is not vis- ible electrocardiographically, but its presence can be inferred by certain rhythmic sequences involving the P-P interyals. These become progressively shorter until one is dropped. The shortening of the P-P interval is similar to the shortening of the R-R interval in Wencke- bach block of the atrioventricular node. The

* From the Division of Cardiology, Rhode Island and Miriam Hospitals, Providence, R. I., and from the Division of Biological and Medical Sciences, Brown University, Providence, R. I. t | Burroughs Wellcome & Co., (U.S.A.) Inc.

passage from ectopic pacemaker to atria takes progressively longer, but the increment by which it increases becomes progressively smaller with each impulse. As a result, the P-P interval becomes shorter until one is blocked. This phenomenon of decreasing in- crement is characteristic of the Wenckebach type of conduction.

CASE REPORTS

Case I. A. B., a seventy-one-year-old white female, was admitted to the Rhode Island Hospital with the clinical diagnosis of arterio- sclerotic heart disease and congestive heart failure. She had been on 0.25 nag digoxin per day and for two to three weeks prior to admission had complained of anorexia, nausea, weakness and visual hallucinations during which she saw bright colors. On ex- amination, the neck veins were flat. The lungs revealed a few rales posteriorly at both lung bases. The cardiac rhythm was regular. The rate was 52/min and the blood pressure was 96/38 mmHg.

On admission, the electrocardiogram showed (Fig. 1) atrial tachysystole with complete atrioventricular block, the atrial rate being 231/rain and ventricular rate 55/rain. The ventricular complexes revealed a typical pat- tern of RBBB. Examination of all tracings showed pauses during which no atrial activity occurred. These intervals averaged 520 msec, twice the basic ectopic cycle length of 260 msec. It was felt that this represented atrial tachycardia with exit block from the ectopic atrial pacemaker.

Case II. J. C., a seventy-six-year-old white male, was admitted to the Miriam Hospital with the clinical diagnosis of arteriosclerotic heart disease and congestive failure, old cerebral thrombosis and pneumonia. He was taking 0.125 mg Lanoxint per day and complained of episodes of dizziness and one episode of syncope. On examination, there were numerous rales posteriorly at the left base. The cardiac rhythm was slow and irregular, with long pauses. The blood pres- sure was 180/100 mmHg. On admission .the electrocardiogram (Fig. 2) showed sinus mechanism, atrial premature beats, nodal escape beats and paroxysmal atrial tachy-

80

PAROXYSMAL ATRICAL TACH YSYSTOL E 8 1

Fig. 1. Atrial tachysystole with complete A-V block. The interatrial cycle measures 260 msec, corresponding to a rate of 231/min. The pauses in atrial activity measure 520 msec.

Fig. 2. Electrocardiogram showing RBBB, left hemiblock and paroxysmal atrial tachycardia, atrial premature beats, shifting pacemaker and nodal ectopic beats.

J. ELECTROCARDIOLOGY, VOL. 4, NO. 1, 1971

82 MILLER

Fig. 3. Electrocardiogram showing paroxysms of atrial tachycardia. The P-P intervals diminish progressively indicating the presence of a Wenckebach conduction sequence at the ectopic focus --- atrial junction. E: ectopic focus. EA: ectopic focus - atrial junction. A: atrial myocardium.

systole. The ventricular complexes revealed RBBB plus block in the superior division of the left bundle branch.

The tracing (Fig. 3) and subsequent elec- trocardiograms revealed numerous sequences during which the P-P intervals became pro- gressively shorter followed by a sudden long pause which suggested the presence of Wenckebach phenomenon. In the strip of lead I I , there are present numerous Wencke- bach sequences with 3:2, 4:3, 5 : 4 and 6 :5 E-A (ectopic atrial pacemaker focus to the surrounding atrial myocardium) block. In the shorter sequences, successive P-P intervals measure 420, 280 msec; in the longer ones, the intervals measure 420, 280, 220, 200 msec. These sequences are followed by a long pause, except when A-V nodal beats occur.

D I S C U S S I O N

The two patients demonstrated recurrent bouts of rapid atrial activity with associated A-V block which appeared to be related to digitalis administration. In the first case, the symptoms of anorexia, nausea, and visual hallucinations, and in both cases, the rapid disappearance of the electrocardiographic abnormalities following discontinuation of the digoxin appeared to confirm the clinical im- pression of digitalis toxicity.

Atrial flutter is a rare manifestation of digitalis toxicity 6. Paroxysmal atrial tachy- cardia is common, with a reported incidence of approximately ten per-cent of all digitalis- induced arrhythmiasL The electrocardio- graphic features consist of an atrial rate of 150-200/min; upright P waves in leads I I and I I I ; isoelectric baseline between atrial complexes; variation in the P-P interval and in the morphology of the P waves; gradual onset and cessation of the arrhythmia and frequent return to sinus mechanism following potassium administration. T he mortality rate associated with this arrhythmia is high. Drei- fus and associates s report an overall mortality of 35% and a 100% mortality when digitalis was continued.

In a critical review of the contrasting fea- tures of P A T with block and atrial flutter,

Rosner 9 indicates that in some cases the elec- t rocardiogram cannot differentiate the two and questions the existence of such a division. Lown 1~ contends that a basic difference exists and that it is possible to differentiate the two. Prinzmetal et al. n consider both rhythms to be produced by an ectopic pacemaker dis- charging at a rate faster than the sinus node, but slower than atrial fibrillation. They classify atrial flutter as a form of atrial tachy- cardia. They feel that the underlying F wave of atrial flutter is specific for this arrhythmia with an atrial rate of 260-320/rain. Others contend that there is no clear cut difference between the two and therefore suggest the term "atrial tachysystole ''g.

REFERENCES 1. Picker, A.: Electrocardiographic features of

exlt-block. In Mechanisms and Therapy of Car- diac Arrhythmias. Ed. Dreifus and Likoff, New York, Grune and Stratton, 1966, p. 469.

2. Kaufmann, R., and Rothberger, C. J.: Beit- rage Zur Entstehungsivelse Extrasystolescher Allorhythmien: Vierte Mitterling. Uber Para- systolie eine besandere Art extrasystolescher Rhythmnsstorungen. (Met 14, text abbildun- gen) Z Ges. Exp. Med. !1:40, 1920.

3. Phibbs, B. : Paroxysmal atrial tachycardla with block around the ectoplc pacemaker. Report of a case. Circulation 28:949, 1963.

4. Dressier, W., Jonas, S., and Javier, R.: Par- oxysmal atrial taehycardia with exit block. Circulation 34:752, 1966.

5. Javier, R. P., Narula, O. S., and Sarnet, P.: Atrial tachysystole (flutter?) with apparent exit block. Circulation 40:179, 1966.

6. Coffman, J. D., and Whipple, G. H.: Atrial,. flutter as a manifestation of digitalis toxicity. Circulation 19:188, 1959.

7. Von Capellar, S., Copeland, G. D., and Stern, T. N. : Digitalis intoxication. A clinical report of 148 cases. Ann. Int. Med. 50:869, 1959.

8. Dreifus, L. S., McKnight, E. H., Katz, M., and Likoff. W.: Digitalis intolerance. Gerl- atrics 18:494, 1963.

9. Rosner, S. W.: Atrial tachysystole with block. Circulation 29:614, 1964.

10. Lown, B., and Levine, H. D.: Atrial Arrhyth- mias, Digitalis and Potassium. Landsberger Medical Books, Inc., New York, 1958.

11. Prinzmetal, M. Corday, E., Oblath, R. W., Kruger, H. E., Brill, I. C., Fields, J., Kenn- amer, R., Osborne, J. A., Smith, L. A., Sellers, A. L., Flieg, W., and Finston, E.: Atrial flut- ter. Am. J. Med. ll:410, 1951.

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