Checking Ablation Lines-Is Bidirectional Block Sufficient?

This case report presents a 71-year-old man undergoing repeat ablation for atypical atrial flutter after prior pulmonary vein isolation and subsequent re-ablation involving an anterior mitral line and a posterior box. High-density mapping revealed reconnection at the left superior pulmonary vein, which was successfully re-isolated. Although bidirectional block of the anterior mitral line was confirmed via local activation time (LAT) mapping during differential pacing, burst stimulation induced atrial flutter. Further LAT mapping during flutter identified very slow conduction through a gap in the anterior mitral line. Ablation at this site restored sinus rhythm, and the arrhythmia was no longer inducible. This case highlights that bidirectional block confirmation alone may not suffice to detect gaps with slow conduction. It underscores the necessity of arrhythmia induction and mapping to reliably identify and address such gaps.