Unipolar Electrograms at the Pulmonary Vein Antrum: Spatial and Directional Heterogeneity with Distinct Postablation Morphologies

BACKGROUND: Disappearance of the near-field S-wave in the unipolar electrogram (U-EGM) is commonly used to assess lesion formation during pulmonary vein (PV) isolation; however, interpretation of U-EGMs in anatomically complex atrial regions remains uncertain. OBJECTIVE: We aimed to characterize spatial, directional, and postablation changes in antral PV U-EGMs, and evaluate the limitations of conventional waveform interpretation. METHODS: In 15 patients undergoing radiofrequency ablation for atrial fibrillation, U-EGMs were recorded at 116 antral PV sites during sinus rhythm and distal coronary sinus (CS) pacing before and after ablation. U-EGM morphology and R- and S-wave amplitudes were analyzed. RESULTS: Baseline U-EGMs showed spatial heterogeneity, with a small r and deep S in the right anterior PV antrum transitioning to a positive-dominant morphology (Rs) in the left-lower PV antra. Distal CS pacing altered the activation sequence, causing direction-dependent changes, most prominently in the right PV antrum. After ablation, overall S-wave amplitude decreased from -0.94 ± 0.70 to -0.08 ± 0.55 mV (P<0.001). Residual negative deflections ≥0.5 mV persisted in 18.1% (21/116) of recordings, frequently in association with direction-dependent far-field activity. Newly developed positive deflections ≥1.0 mV were observed in 17/116 sites (14.7%; mean 1.42 ± 0.42 mV), predominantly in the right-sided antra. CONCLUSIONS: Antral PV U-EGMs frequently represent composites of near- and far-field signals with spatial heterogeneity and direction-dependent variation. Postablation responses are diverse, including S-wave disappearance, residual negativity, often reflecting contributions from overlapping far-field components, and newly developed positive deflections. PV-antral U-EGMs should be interpreted in the context of their composite nature.