A novel pace-mapping technique for Isthmus Identification in Non-Sustained Uncommon Atrial Flutter Pacing Technique: the INPACT method—a case report

Background: Mapping uncommon atrial flutter (AFL) remains challenging when tachycardia cannot be sustained during the procedure. We developed a novel pace-mapping methodology for identifying critical isthmuses in non-sustained uncommon AFL circuits during sinus rhythm. Case summary: A 70-year-old male presented with persistent AFL (cycle length 370 ms) following mitral valve repair with concomitant surgical pulmonary vein isolation. During electrophysiological study, the tachycardia terminated spontaneously, precluding conventional mapping. We implemented the Isthmus Identification in Non-Sustained Uncommon Atrial Flutter PACing Technique (INPACT), combining Intracardiac Pattern-match ScOring (iPASO) technology with systematic pace-mapping during sinus rhythm. A novel isthmus ratio (IR) metric differentiated potential isthmus sites among those with high morphological correlation (iPASO ≥90%). The critical isthmus was identified within a low-voltage area adjacent to the atrial septotomy line. Radiofrequency ablation targeting the site with the highest IR value eliminated the tachycardia with no recurrence at 6-month follow-up. Discussion: The INPACT enables identification of critical isthmuses without requiring sustained tachycardia, offering a solution for challenging cases where conventional mapping is limited by non-sustained arrhythmia. This approach may improve procedural efficiency and outcomes in complex uncommon AFL.