A fourth criterion for transient entrainment: the electrogram equivalent of progressive fusion

Area of Science:

• Electrophysiology
• Cardiology
• Cardiac Arrhythmias

Background:

• Transient entrainment phenomena in tachycardias are often explained by pacing capture of reentrant circuits.
• Understanding the precise mechanisms of entrainment is crucial for diagnosing and managing cardiac arrhythmias.

Purpose of the Study:

• To test the hypothesis that rapid pacing at different rates can capture a specific electrogram recording site from different directions.
• To investigate if changes in pacing rate alter conduction time and electrogram morphology, indicating different activation origins.

Main Methods:

• Studied patients with various tachycardias (ventricular tachycardia, AVNRT, atrial tachycardia, atrial flutter).
• Performed single-site rapid pacing at two different constant rates, faster than the spontaneous tachycardia rate.
• Analyzed stimulus-to-electrogram intervals, electrogram morphology, and electrocardiogram for fusion beats.

Main Results:

• A single bipolar electrogram recording site was captured from different directions at two distinct pacing rates without interrupting tachycardia.
• Significant changes in conduction time (mean difference of 238 msec) and electrogram morphology were observed between pacing rates.
• Faster pacing rates resulted in shorter conduction times, with parallel demonstration of progressive fusion beats.

Conclusions:

• The findings support reentry as the underlying mechanism for observed phenomena during pacing.
• Different pacing rates can indeed alter the direction of capture at a specific site, providing insights into tachycardia mechanisms.
• This study offers a novel perspective on understanding transient entrainment and its relationship with reentrant circuits.