Critical Isthmus Identification in Macro–Re-entrant Atrial Tachycardia With Epicardial Conduction by Peak Frequency Mapping

Macro-re-entrant atrial tachycardia (AT) can involve complex conduction pathways, including rare transient epicardial detours that complicate identification of the critical isthmus. We analyzed 5 patients with macro-re-entrant AT in whom activation transiently propagated from the endocardium to the epicardium and then returned to the endocardium. Peak frequency mapping using omnipolar technology was performed in conjunction with local activation and voltage mapping. A transient epicardial pathway was suggested when endocardial activation disappeared and subsequently reappeared along the re-entrant circuit. The entrance site, defined as the point where signals disappeared into the epicardial pathway, consistently demonstrated the highest peak frequency and the lowest voltage among all mapped regions. Radiofrequency ablation targeting this entrance site successfully terminated AT in all patients. These observations suggest that omnipolar peak frequency and voltage mapping may facilitate precise identification of the critical isthmus in macro-re-entrant AT involving transient epicardial conduction.