"Sinus node" reentrant tachycardia associated with respiration.

A 77-year-old woman (case 1) and a 57-year-old woman (case 2) with paroxysmal "sinus tachycardia" are reported in whom the tachycardia repeatedly occurred associated with respiration. In both cases, reentrant P' waves are almost the same in configuration as sinus P waves, and P'R intervals are also the same in length as PR intervals. In case 1, the tachycardia was initiated during inspiration, and was terminated during expiration; showing tachycardia-dependent initiation. On the contrary, in case 2, the tachycardia was initiated during expiration, and was terminated during inspiration; showing apparent bradycardia-dependent initiation. Although exact diagnosis was not made by electrophysiologic studies, attempts were made to explain the mechanism of such unique tachyarrhythmias associated with respiration by using the concept of sinus node reentrant tachycardia as a possible mechanism.