Unipolar electrograms at the pulmonary vein antrum: Spatial and directional heterogeneity with distinct post-ablation morphologies

The disappearance of the near-field S-wave in the unipolar electrogram (U-EGM) is often used to assess lesion formation during pulmonary vein (PV) isolation; however, the interpretation of U-EGMs in anatomically complex atrial regions remains uncertain.

We aimed to characterize spatial, directional, and post-ablation changes in antral PV U-EGMs and evaluate the limitations of conventional waveform interpretation.

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.

Baseline U-EGMs revealed spatial heterogeneity, with a small r and deep S wave 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, the overall S-wave amplitude decreased from -0.94 ± 0.70 to -0.08 ± 0.55 mV (P < .001). Residual negative deflections ≥ 0.5 mV persisted in 18.1% (21/116) of the recordings, frequently in association with direction-dependent far-field activity. Newly developed positive deflections ≥ 1.0 mV were observed in 17 of 116 sites (14.7%; mean 1.42 ± 0.42 mV), predominantly in the right-sided antra.

Antral PV U-EGMs frequently represent composites of near- and far-field signals with spatial heterogeneity and direction-dependent variation. Post-ablation 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.