Anatomical substrate
The mean distance between the collision site and the breakthrough site was 24 [19-40] mm. In all 27 ATs, the collision site co-localized with a low-voltage area, while the breakthrough site co-localized with an epicardial musculature. The presence of a low-voltage area at the collision site was: (1) spontaneous in 2 patients (8%) and (2) iatrogenic in 24 patients (92%). The missing portion of the circuit was bypassed by: (1) the CS-GCV bundle (Figure 1 ) in 6 ATs (22%); (2) the VOM bundle (Figure 2 ) in 4 ATs (15%); (3) the Bachmann bundle (Figure 3 ) in 6 ATs (22%); (4) the septopulmonary bundle (Figure 4 ) in 4 ATs (15%); (5) the fossa ovalis (Figure 5 ) in 2 ATs (7%); and (6) a low RA bridge (Figure 6 ) in 5 ATs (19%). Details for each type of epicardial bypass are provided in Table 2 .