Background: We sought to evaluate the anatomic and functional lesion development over time at different atrial sites immediately following delivery of pulsed field ablation (PFA). Methods: Using a porcine model, PFA ablations were performed in the superior vena cava (SVC), right atrial lateral wall (RA), left atrial appendage (LAA) and right superior pulmonary vein using four different PFA profiles. Mapping was done sequentially in 5–20-minute increments up to 280-minutes post lesion delivery for low voltage area (LVA) assessment and conduction velocity. Lesion characteristics were noted with voltage mapping immediately post ablation and at the serial time points. Results: In 9 animals, 33 sites were ablated. None of the four different profiles across all sites any statistical difference on acute lesion formation or persistence. Higher tissue contact was observed in the SVC and RSPV and lower tissue contact was observed in the LAA and RA locations. Higher contact areas were noted to have higher density electroanatomic low voltage area (LVA) (12/14 vs 5/18, p=0.01) and larger lesions on gross pathology (2 /14 vs 6/16, p =0.01) compared to lower contact areas. Lesion regression occurred in 16/33 sites. Sustained lesions were significantly more prevalent in higher versus lower contact sites (65% vs 38%, p=0.037). Conclusion: The development of significant and durable lesions for PFA appears to be dependent on tissue proximity and contact.

Background: Contact force has been used to titrate lesion formation for radiofrequency ablation. Pulsed Field Ablation (PFA) is a field-based ablation technology for which limited evidence on the impact of contact force on lesion size is available. Methods: Porcine hearts (n=6) were perfused using a modified Langendorff set-up. A prototype focal PFA catheter attached to a force gauge was held perpendicular to the epicardium and lowered until contact was made. Contact force was recorded during each PFA delivery. Matured lesions were cross-sectioned, stained, and the lesion dimensions were measured. Numerical modeling of the catheter-tissue interface under different contact forces was performed to aid in the interpretation of our results and isolate effects of biomechanical tissue displacement. Results: A total of 82 lesions were evaluated with contact forces between 1.3 g and 48.6 g. Mean lesion depth was 4.8 ± 0.9 mm (standard deviation), mean lesion width was 9.1 ± 1.3 mm and mean lesion volume was 217.0. ± 96.6 mm 3. Linear regression curves showed an increase of only 0.01 mm in depth (Depth = 0.01*Contact Force + 4.37, R 2 = 0.06), 0.03 mm in width (Width = 0.03*Contact Force + 8.32, R 2 = 0.12) for each additional gram of contact force, and 2.20 mm 3 in volume (Volume = 2.20*Contact Force + 163, R 2 = 0.11). Numerical modeling found consistent trends with experimental mean values and shows tissue displacement alone is likely not a significant factor to formation of lesion depth. Conclusions: Increasing contact force using a bipolar, biphasic focal PFA system has minor effects on acute lesion dimensions in an isolated porcine heart model.