Real-Time Prediction of Irreversible Lesion Size During Pulsed Field Ablation: Prospective Validation of a Novel Ablation Index Based on Contact Force and Number of Applications in a Swine Beating Heart Model

BACKGROUND: In a previous study, on pulsed-field ablation (PFA) in the swine ventricle, we found that lesion depth was described (±1 mm accuracy) by a logarithmic function of contact force (CF) and the number of PFA pulses (PF-ablation index). This study was designed to validate prospectively whether the novel PF-ablation index would allow PFA lesions to be created at depths of 3.5, 4.5, 5.5, and 6.5 mm with high prediction accuracy in a swine-beating heart model. METHODS: A 7.5F catheter with a 3.5 mm ablation electrode and CF sensor (ThermoCool SmartTouch SF-Dual Energy) was connected to a PFA system (TRUPULSE 2). In 6 closed-chest swine, a biphasic PFA pulse was delivered between the ablation electrode and a skin patch at 123 separate ventricular sites at 5 different levels of CF (1) low (average CF: 4-15 g; median, 12 g; n=25), (2) moderate (16-30 g; median, 23 g; n=41); 3) high (31-45 g; median, 36 g; n=27), (4) very high (46-68 g; median, 52 g; n=18); or (5) no electrode contact, 1 to 2 mm from the endocardium (n=12). PFA application was terminated when the PF-ablation index reached a predicted lesion depth of 3.5 mm (27 sites), 4.5 mm (25 sites), 5.5 mm (29 sites), and 6.5 mm (30 sites). Swine were euthanized 2 hours after ablation. Lesion size was measured using triphenyl tetrazolium chloride staining. RESULTS: Predicted lesion depth by the PF-ablation index correlated well with actual lesion depthwith ±1.0 mm accuracy in 97/106 (92%) lesions and ±1.5 mm accuracy in all 106 lesions. There were no or poor relationships between intracardiac electrogram attenuation, impedance decrease, electrode temperature, and lesion size. No detectable lesions were created without electrode contact. CONCLUSIONS: A novel PF-ablation index incorporating CF and the number of PFA pulses provides high accuracy in predicting lesion depth in real-time. Intracardiac electrogram attenuation, impedance decrease, and electrode temperature are poor predictors of PFA lesion size.