Definition of EC
We assessed ECs only between the RPV carina and the RA. If the
breakthrough site at the RPV carina was present as early as the
Bachmann’s bundle area (anteroseptal LA), the patients were classified
into the EC group during RA pacing. If an EC was observed, it was
confirmed that the breakthrough was not anatomically in the closest
proximity to the RA and that the local potential of the breakthrough was
not dull. If there was no EC, the patients were classified into the
non-EC group.