Br Heart J: first published as 10.1136/hrt.37.8.890 on 1 August 1975. Downloaded from

British HeartJournal, 1975, 37, 890-89I. Escape-capture bigeminy caused by blocked atrial extrasystoles

A. Dubb and L. Schamroth From the Baragwanath Hospital and the University of the Witwatersrand,Johannesburg, S.A.

Afurther mechanism of escape-capture bigeminy is described, viz. blocked atrial extrasystoles.

Escape-capture bigeminy was so called by Bradley . The tracing shows a basic sinus and Marriott (I958), and refers to a bigeminal rhythm of 94 per minute (PP interval=o.64 s). The first rhythm which is caused by an escape beat followed sinus P wave of the tracing precedes but is dissociated by a conducted beat. Three basic mechanisms have from the QRS complex of the atrioventricular nodal been described (Schamroth and Dubb, I965). escape beat. This is followed by a conducted sinus beat (PR interval= 0.17 s). This in turn is followed by a non- i) A basic 3: I ; the blocked conducted atrial extrasystole whose P' wave is superim- impulses allowing an atrioventricular nodal posed upon, and deforms, the ST segment of the con- (or ventricular) escape beat which occurs ducted sinus beat. This leads to a further atrioven- coincidentally with, and is dissociated from, tricular nodal escape dissociated from the ensuing sinus the first sinus beat of the next ensuing 3: I beat. The blocked atrial extrasystole occurs after every sequence. second sinus P wave and this results in an escape- 2) A basic 3:2 ; the blocked capture bigeminy. impulse allowing an atrioventricular nodal Discussion http://heart.bmj.com/ (or ventricular) escape beat which is coinci- The blocked atrial extrasystole discharges the dent with, and dissociated from, the next sinoatrial node and is blocked at the atrioventricular sinus impulse - the first of the ensuing 3:2 node. The next sinus P wave occurs after an interval atrioventricular sequence. which is slightly longer than the sinus PP interval. 3) A potential 3:2 atrioventricular block of the Thus the P'P interval measures 0.75 s. This is caused Wenckebach type ending in a reciprocal return by temporary depression of the sinoatrial node of the atrial impulse to the atria (reversed resulting from its premature discharge (Pick, Lang- reciprocal rhythm) - an atrial echo - which

endorf, and Katz, i951). The effective sinus cycle, on September 24, 2021 by guest. Protected copyright. discharges the sinus pacemaker and thereby i.e. the sinus cycle which is effective or relevant to allows an atrioventricular nodal escape beat, the atrioventricular nodal pacemaker (Schamroth which is coincident with, and dissociated and Dubb, I965) is the PP interval encompassing from, the next potential sinus beat. the blocked atrial extrasystole, i.e. the sum of pre- We present a hitherto unrecognized fourth mech- and post-extrasystolic PP intervals; PP' + P'P which anism caused by blocked atrial extrasystoles. equals I.I2S. This is slightly longer than the atrioventricular nodal escape rhythm and thereby Case report permits the escape ofthe atrioventricular nodal pace- The electrocardiogram (Fig.) was recorded from a 50- maker - the escape interval being i.oo s. year-old woman receiving digitalis for a congestive The escape beat has an obviously inverted T

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...... UIL: .. :.I., ;- ifft 99 FIG. Electrocardiogram (standard lead I), showing escape-capture bigeminy. Br Heart J: first published as 10.1136/hrt.37.8.890 on 1 August 1975. Downloaded from Escape-capture bigeminy caused by blocked atrial extrasystoles 89g wave whereas the of the conducted sinus Mann, R. H., and Burchell, H. B. (I954). Significance of T- wave inversion in sinus beats following ventricular extra- beat is equiphasic. This is an expression of so- systoles. American Heart Journal, 47, 504. called 'post-extrasystolic' T wave change and is Pick, A., Langendorf, R., and Katz, L. N. (I95I). Depression caused by the long pause which the blocked atrial of cardiac pacemakers by premature impulses. American extrasystole occasions. The manifestation usually Heart Journal, 41, 49. connotes organic heart disease (Mann and Burchell, Schamroth, L., and Dubb, A. (I965). Escape-capture bige- miny. Mechanisms in S-A block, A-V block and reversed I954). reciprocal rhythm. British Heart Journal, 27, 667. References Bradley, S. M., and Marriott, H. J. L. (I958). Escape-capture bigeminy. Report of a case of A-V dissociation initiated Requests for reprints to Dr. A. Dubb, Department of by 2: I S-A block with resulting bigeminal rhythm. Medicine, Baragwanath Hospital, P.O. Bertsham, American Journal of Cardiology, I, 64o. Johannesburg, South Africa. http://heart.bmj.com/ on September 24, 2021 by guest. Protected copyright.