Pacemaker repetitive nonreentrant ventriculoatrial synchrony. Why did automatic mode switching occur?
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Updated: May 22, 2026

Optimization of Transesophageal Atrial Pacing to Assess Atrial Fibrillation Susceptibility in Mice
Published on: June 29, 2022
S Serge Barold1, Roland X Stroobandt2, Frederic Van Heuverswyn2
1Florida Heart Rhythm Institute, Tampa, FL.
Abstract:
Repetitive nonreentrant ventriculoatrial synchrony during dual-chamber pacing is characterized by long intervals alternating with short intervals. This arrangement activated automatic mode switching in a St Jude dual-chamber pacemaker in which the algorithm requires an atrial sensed event for automatic mode switching initiation. Automatic mode switching activation by an atrial sensed event (retrograde P wave) was puzzling because the programmed postventricular atrial period was longer than the retrograde ventriculoatrial conduction time. The explanation is presented in the form of questions and answers to facilitate the understanding of pacemaker function and complex timing cycles.
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