A) Typical atrial basket placement is indicated in the fluoroscopic images. Sequential atrial basket recordings were taken with source elimination prior to PVI. B) Multiple basket positions used per FIRM-mapping epoch to minimize unmapped atrial regions. Positions 1–2 are in the right atrium, positions 3–4 are in the LA. SVC – superior vena cava, RSPV – right superior pulmonary vein, RIPV right inferior pulmonary vein, LSPV – left superior pulmonary vein, LIPV – left inferior pulmonary vein.