Electrocardiographic evaluation demonstrated modulated parasystole, where a dominant fascicular escape focus was modulated by a closely coupled ventricular ectopic beat.
Case Report (n=1)
This case illustrates the classic behavior of a modulated parasystolic focus, where phase-dependent modulation explains variability in escape cycle length.
A 65-year-old woman with a history of surgical aortic valve replacement presented with shortness of breath. The electrocardiogram demonstrated bradycardia with ventricular rhythm exhibiting 2 distinct QRS morphologies and variable escape intervals. The most likely mechanism was a dominant fascicular escape focus modulated by a second, closely coupled ventricular ectopic beat, which predictably altered subsequent escape timing depending on the coupling interval. This interaction exemplifies the classic behavior of a modulated parasystolic focus. TAKE-HOME MESSAGES: In modulated parasystole, entrance block to the ectopic focus is incomplete, allowing surrounding myocardial activity to electrotonically influence the timing of the parasystolic pacemaker without true resetting. Phase-dependent modulation explains variability in escape cycle length: depolarizing wavefronts arriving early in the pacemaker cycle may delay spontaneous discharge, whereas wavefronts arriving late may trigger premature firing.
Doss et al. (Fri,) conducted a case report in Modulated parasystole (n=1). Electrocardiographic evaluation demonstrated modulated parasystole, where a dominant fascicular escape focus was modulated by a closely coupled ventricular ectopic beat.