Coexistence and spontaneous transition between orthodromic atrioventricular reentrant tachycardia and atrial tachycardia: The mechanism of atrial activation sequence.

UNLABELLED: The coexistence of multiple supraventricular tachycardias during electrophysiological study (EPS) is rare and can complicate diagnosis and treatment. We present a case of coexisting orthodromic atrioventricular reentrant tachycardia (AVRT) and atrial tachycardia (AT) with spontaneous transitions. A 15-year-old girl with palpitations underwent EPS revealing orthodromic AVRT via a left-sided accessory pathway (AP) and AT originating from the right atrium. The tachycardias had similar cycle lengths and exhibited spontaneous transitions. During AT, a unique cyclic atrial activation sequence was observed, hypothesized to result from fusion of antegrade AT conduction and retrograde conduction via a left-sided AP. Radiofrequency catheter ablation targeting the AP successfully terminated the arrhythmias, with no recurrence observed during follow-up. This case highlights the complex electrophysiological interplay between coexisting AVRT and AT, the mechanism of spontaneous tachycardia transitions, and the unique cyclic fusion atrial activation pattern resulting from combined antegrade AT conduction and retrograde conduction via a left-sided AP.

LEARNING

OBJECTIVE

This case highlights the complex electrophysiological interplay between coexisting atrioventricular reentrant tachycardia and atrial tachycardia (AT), the mechanism of spontaneous tachycardia transitions, and the unique cyclic fusion atrial activation pattern resulting from combined antegrade AT conduction and retrograde conduction via a left-sided accessory pathway.