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Figure 3 Right atrial electroanatomic maps acquired during tachycardia in Patient 1, who had an incision in the interatrial groove, followed by reoperation with the superior trans-septal approach. (A) Bipolar voltage map of the right atrium in a right posterolateral projection. A zone of low voltage is present in the lateral wall of the right atrium, extending to the superior vena cava (SVC) and the inferior vena cava. Tag colors are those used in Figure 2. The green tag (x) is a site of concealed entrainment where ablation terminated atrial tachycardia. At this site, the stimulus to P-wave interval during pacing was identical to the electrogram to P-wave during tachycardia (125 ms). (B) Isochronal activation map. Figure-of-eight re-entry is present, with a common isthmus between two lesions in the lateral wall.