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

Figure 1. Representative 3-Dimensional Maps From Case 1 (A) Local activation time (LAT) mapping of Case 1 demonstrated endocardial propagation along a macro–re-entrant circuit that intermittently disappeared and subsequently reappeared, indicating a transient shift of conduction into an epicardial pathway (arrows). Activation wavefronts are color-coded from early (red) to late (purple). (B) Peak frequency–enhanced mapping (LAT with omnipolar peak frequency overlay) showed that the entrance site—defined as the point where endocardial activation disappeared into the presumed epicardial pathway—exhibited the highest peak frequency among all mapped regions. Fragmented electrograms at this site indicated electrical instability consistent with functional conduction delay. (C) Peak frequency mapping using a cutoff of >450 Hz further highlighted this entrance region. Sites exceeding 450 Hz corresponded precisely to the endocardial entrance into the epicardial pathway. (D) Bipolar voltage mapping revealed low-voltage signals (<0.5 mV) at the same entrance site, supporting the presence of a diseased substrate contributing to slow or unstable conduction. This case represents an anterior epicardial…

Figure 2. Sparkle Mapping of Case 1 Other mapping modalities are presented in Figure 1. (A) Sparkles were predominantly observed around the entrance site. (B) Sparkles intermittently disappeared and reappeared around the exit site. The yellow dotted arrow indicates the absence of sparkles, suggesting conduction through an epicardial pathway. (C) Sparkles spread from the exit site to the surrounding areas, indicating re-entry into the endocardial surface. Abbreviations as in Figure 1.

Figure 3. Representative 3-Dimensional Maps From Case 2 (A) Local activation time (LAT) mapping, (B) peak frequency–enhanced mapping, (C) peak frequency mapping, and (D) bipolar voltage mapping of case 2. Two oval endocardial circuits with a common entrance and exit, and the epicardial circuit are observed. The common epicardial pathway is located in the left atrial anterior wall. Findings identical to those observed in case 1 (Figure 1) were obtained. This figure demonstrates an anterior wall epicardial re-entry, showing mapping characteristics consistent with those observed in case 1. Abbreviations as in Figure 1.

Visual Summary. Omnipolar Peak Frequency Mapping Identifies the Critical Isthmus in Epicardial-Detour Macro–Re-entrant Atrial Tachycardia: A 5-Case Analysis PF = peak frequency.