Extrasystoles in groups

Abstract

Instances of alternation of cycle length during an A-V nodal tachycardia and during a paroxysmal ventricular tachycardia in man are descrbed. In the latter case a similar phenomenon was observed during the change from the tachycardia to sinus rhythm following an intravenous injection of quinine. Application of barium chloride or strophanthin to small areas of the cardiac surface of the dog also causes groups of extrasystoles separated by longer pauses. These arrhythmias were often elicited during vagus and following sympathetic stimulation in these experiments. Finally, the phenomenon was observed during warming of the site of origin of extrasystoles produced by subepicardial injection of strophanthin. Similar observations in the literature are discussed. The different mechanisms which may lead to this disturbance of rhythm are reviewed. Irregular stimulus formation in a center is probable; regular stimulus formation with a disturbance of conduction from the center to the rest of the heart is possible only in some of these tracings.