How are PV entrance and exit blocks assessed during AF ablation?

• A. By pacing from LA and observing PV potentials.
• B. By mapping LA activation times.
• C. Entrance block: no PV potentials entering the LA; Exit block: no LA activation when pacing from the PV; both confirmed with mapping and pacing maneuvers.
• D. By assessing only PV pressures.

Answer: (C)

Bidirectional block testing is what confirms successful PV isolation after AF ablation. Entrance block means the pulmonary veins no longer drive activity into the left atrium. You test this by pacing from the left atrium and seeing whether PV potentials enter the LA; if no PV potentials are observed entering the LA, entrance block is present. Exit block means that pacing from inside the PV does not activate the left atrium, so you pace from the PV and look for LA activation; if the LA does not respond, exit block is present. Demonstrating both with mapping and pacing maneuvers verifies that electrical conduction between the PVs and the LA is completely blocked in both directions. PV pressures don’t inform electrical block, so they aren’t used to confirm isolation.