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Figure 3 Disappearance of pulmonary vein (PV) "spike" potentials after successful radiofrequency ablation. Surface electrocardiographic leads I and II are simultaneously recorded with intracardiac electrograms from the coronary sinus (CS) (CSd and CSp [d = distal and p = proximal]) and the PV (PVd and PVo [o = ostium]). (Left) Before ablation, there are PV spike potentials (PV, upward arrows) on the PVd electrogram, which are unmasked and separated from the preceding low-amplitude, far-field atrial potentials by pacing (S) from the CSd. (Right) After ablation, the PV spikes are no longer seen during sinus rhythm. Note that the amplitude of the "A" potential in the PVo electrogram decreases. A = atrial potential; V = ventricular potential. See text for details.