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.