A Novel Pace-Mapping Technique for Isthmus Identification in Non-Sustained Uncommon Atrial Flutter Pacing Technique: The INPACT Method - A Case Report

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  Overview of the Isthmus Identification in Non-Sustained Uncommon Atrial Flutter PACing Technique workflow and clinical outcome in non-sustained uncommon atrial flutter. During sinus rhythm, (1) high-density voltage mapping defines the substrate (low-voltage zones and post-surgical scar/incision lines), (2) systematic pace mapping with Intracardiac Pattern-match ScOring (iPASO) identifies candidate sites with a morphology match score ≥90%, and (3) the isthmus ratio (IR), calculated from the stimulus-to-distal coronary sinus time (t) among high-iPASO sites, differentiates exit sites (low IR) from the central critical isthmus (high IR). Isthmus Identification in Non-Sustained Uncommon Atrial Flutter PACing Technique-guided focal radiofrequency (RF) ablation at the high-IR target terminated the tachycardia, requiring two RF applications and showing no recurrence at 6-month follow-up (low-IR site: failed; high-IR site: successful).

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  Figure 1. Twelve-lead ECG during the clinical tachycardia (uncommon atrial flutter; TCL = 370 ms).

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  Figure 2. (A) Local activation time map during brief tachycardia. The histogram shows incomplete circuit mapping (Tachycardia Cycle Length = 370 ms). (B) Voltage map demonstrating low-voltage areas with fragmented electrograms near the atrial septotomy.

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  Figure 3. (A) Intracardiac Pattern-match ScOring score distribution: yellow (≥90%), blue (≥85%), and light blue (≥75%). High scores concentrate along the septal isthmus. (B) Alternative visualization with Intracardiac Pattern-match ScOring scores as negative values. (C) Decision algorithm integrating electrophysiological parameters for isthmus targeting.

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  Figure 4. (A–C) Activation map colour-coded by isthmus ratio for high-Intracardiac Pattern-match ScOring sites. (D) Twelve-lead electrocardiogram during pacing from central isthmus showing morphology match with clinical tachycardia. (E) Intracardiac electrograms during isthmus pacing. (F) Isthmus Identification in Non-Sustained Uncommon Atrial Flutter PACing Technique-guided focal ablation sites. Red area: initial ablation at low isthmus ratio site (unsuccessful). Green area: successful ablation at high IR site (central isthmus).