Epicardial connections across the cavotricuspid isthmus

Figure 1. Local activation time mapping demonstrating early activation across the cavotricuspid isthmus (CTI) ablation line in the LAO caudal projection. (A), (B), and (C) correspond to case 1, 4, and 5, respectively, and they indicate epicardial connections lateral to the line as determined by proximal coronary sinus pacing as seen in the accompanying electrograms obtained by the ablation catheter at the site of earliest activation. D: Case 3 represents an epicardial connection seen during typical counterclockwise flutter with earliest activation medical to the CTI line.

Figure 2. A: Local activation time map demonstrating counterclockwise typical flutter in the left anterior oblique (LAO) projection. B: LAO caudal projection showing early activation medial to the cavotricuspid isthmus line, suggestive of epicardial connection with accompanying electrogram seen in (C). D: Final lesion set including lesion and electrogram showing termination of atrial flutter in the area of medial epicardial connection. Extensive regional ablation was required to achieve block, suggestive of broad endocardial connections.