Electrophysiological properties
A total of 15 perimitral, 7 roof-dependent, and 5 CTI-dependent flutters exhibiting centrifugal propagation were identified by means of high-density mapping associated with conventional entrainment pacing maneuvers. The mean TCL was 303 ± 65 ms, with a mean missing TCL of 67 ± 29 ms (22%) on the activation map. The estimated conduction velocity of the epicardial bypass was 49 [29-63] cm/s, and the mean activated area within 10 ms after the breakthrough was 2.3 ± 1.5 cm². Unipolar electrogram recorded at the breakthrough site exhibited an rS pattern in 17 pseudo-focal ATs (63%). Details for each type of epicardial bypass are provided in Table 2 .