Acute efficacy of pulsed-field ablation of the mitral isthmus using a pentaspline catheter and two different ablation settings

Background There is limited data regarding the use of pulsed-field ablation (PFA) for mitral isthmus (MI) ablation in patients with non-paroxysmal atrial fibrillation (AF). Purpose To assess the acute efficacy of MI ablation using a pentaspline PFA catheter with two different ablation settings. Methods Patients with non-paroxysmal AF undergoing ablation were consecutively enrolled. Exclusion criteria included left ventricular ejection fraction < 30%, a history of prior left atrial catheter ablation, and conditions posing increased risk during analgosedation. All patients underwent pulmonary vein isolation and left atrial posterior wall ablation. In Cohort A, MI ablation was performed in series of 9 PFA applications, each followed by a 20-minute observation period to verify the durability of the MI block. If a durable MI block was not achieved after three such series, one more ablation series could be delivered at the discretion of the operator, this series was not protocol-defined. In Cohort B, ablation series of 20 PFA applications were delivered, each followed by a 20-minute observation period. If a durable MI block was not observed after two such series, one more ablation series not defined by the protocol could be delivered at the discretion of the operator. In both cohorts, the total number of PFA applications to the MI was limited to 50 and the total observational time was limited to 40 minutes. The endpoints were a bidirectional MI conduction block achieved after the first ablation series, verified by a 20-minute observation period ("first pass MI block") and a durable MI conduction block following the full ablation strategy and verified by a 20-minute observation ("final MI block"). Results Between September 2024 and June 2025, 70 patients were enrolled: 30 in Cohort A and 40 in Cohort B. Immediately after the first ablation series, MI block was observed in 86.7% and 95% of patients in Cohort A and B, respectively. However, due to early reconductions, a durable first-pass MI block was achieved in only 10 (33.3%) patients in Cohort A and 28 (70%) patients in Cohort B (p=0.003). A final MI block was present in 27 (90%) and 35 (87.5%) patients in Cohort A and B, respectively (p=1.00). Reconduction rate was highest early after PFA delivery and declined over time with median reconduction time 6 minutes (IQR 2.8–9.4) in Cohort A and 5 minutes (IQR 2.6–8.7) in Cohort B. No major complications occurred; we observed two cases of ST segment changes which resolved spontaneously with no consequences. Conclusion Using series of 20 PFA applications increased the success rate of a first-pass MI block to 70%. The majority of reconductions occurred within the first few minutes following energy delivery. An observation period of 20 minutes to verify the durability of MI block is appropriate.