A Study of the Ventriculophasic Phenomenon in Paroxysmal Atrial Tachycardia with Block

V A R I A T I O N IN THE TIME INTERVALS OF waves of atrial activity (P-P interval) has been observed to occur frequently in both complete and incompkte atrioventricular block and also in interference diisociation.'" The w a l observation is that those P-P intervals containing QRS complexes are shorter in duration than those not containing a ventricular deflection. Rarely the relationship is revelsed so that the P-P intervals without QRS complexes are the shorter ones. This phenomenon has been termed ventriculophasic sinus arrhythmia.'"' The mechanism of such alternating lengths of the sinus cycles is not known, although the rule of arterial vagal presoreceptors, mechanical traction on the atrium, and alternating changes in sinus