AIMS: Loss of bipolar electrograms immediately after pulsed field ablation (PFA) makes lesion durability assessment challenging. OBJECTIVE: The aim of this trial (NCT06700226) was to evaluate a novel ablation system that can optically predict lesion durability by detecting structural changes in the tissue during ablation. METHODS AND RESULTS: Patients with paroxysmal atrial fibrillation underwent pulmonary vein isolation (PVI) using PFA (AblaView®, MedLumics). Using polarization-sensitive optical coherence reflectometry (PS-OCR), reflective characteristics of myocardial tissue and visualization of real-time contrast between healthy tissue and ablated tissue using a drop in tissue birefringence (BiR) was assessed. Wide antral PVI was performed using single point irrigated PFA (unipolar, 1800V, 3 trains, 21 s). Remapping was performed at 3 months. Primary efficacy outcome was the ability of PS-OCR to predict lesion durability at 3-month remapping. Serious adverse events were recorded. Ten patients were included. In total, 38/40 PVs could be isolated with the system. The mean drop of BiR was 17.3 ± 11.5%. Dragging across the ablation lines showed a persistent drop in BiR. During the remap procedures (8/10 patients ablated only with PFA), 12 PVs (37.5%) were found to be electrically reconnected. The mean loss of BiR during all PFA for durable lesions was 20.9%, while only 10.1% BiR loss was observed during the index ablation for reconnected areas (P <
0.001). None of the points with ≥17% loss of birefringence was found to be reconnected. CONCLUSION: This first-in-human study supports the use of real-time drop in tissue BiR for lesion assessment and durability during PFA delivery, and its procedural safety.