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Electrocardiographic Manifestation of Modulated Parasystole With Variable Escape Timing
Journal article   Open access   Peer reviewed

Electrocardiographic Manifestation of Modulated Parasystole With Variable Escape Timing

Ramy Doss, Karim Nathan, Jay Jaiswal, Steven P. Kutalek and Ashwani Gupta
JACC. Case reports, v 31(20), 108236
20 May 2026
DOI: https://doi.org/10.1016/j.jaccas.2026.108236
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https://doi.org/10.1016/j.jaccas.2026.108236View
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Abstract

bradycardia electrocardiogram Electrophysiology
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.

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