Abstract Background Pulsed-Field ablation (PFA) is a non-thermal tissue-selective energy source which is increasingly used for pulmonary vein isolation (PVI). A commercially available pentaspline PFA catheter can be transformed between different configurations and is available in two different sizes – 31 and 35 mm of diameter. No clear recommendations for when to choose which catheter size are available to date. Purpose We aimed to assess procedural and outcome differences of the two different catheter sizes. Methods We prospectively included all-comer patients between 07/2022 and 01/2023 who had paroxysmal or persistent atrial fibrillation (AF) and were scheduled for PVI with PFA. There were no exclusion-criteria. 100 patients were randomly assigned to be ablated with either the 31 mm or the 35 mm pentaspline PFA catheter. Patients were routinely scheduled for follow-up visits 6 and 12 months after the ablation. Results Each group consisted of 50 patients and baseline characteristics were comparable. For the 31 mm vs 35 mm group respectively: Mean age 68.5 years vs 68.2 years, mean BMI 28.0 vs 30.3 kg/m², male sex 60% vs 68%, paroxysmal AF 59.6% vs 53.1%, mean LA diameter 40.9 vs 40.3 mm. Acute procedural efficacy defined as accomplishing PVI with the pentaspline PFA catheter was 100% in both groups. The procedural skin-to-skin time was numerically shorter in the 31 mm group (31.4 vs 34.3 minutes, p=0.11), which was attributed to a shorter ablation time (12.5 vs 15.1 minutes, p=0.052). Fluoroscopy time was significantly shorter (5.9 vs 7.1 minutes, p=0.015). The overall freedom of arrhythmia at 180 days was 82,1%. The groups show a numerical difference in freedom of arrhythmia (31 mm: 91,9% vs 35 mm: 73,4%), but no statistically significant difference using the log rank test (p=0.14, Figure 1). A total of 8 repeat procedures were performed in this patient collective for recurrent atrial arrhythmia - 3 in the 31 mm group, 5 in the 35 mm group. While the 3 repeat procedures in the 31 mm group showed no PV reconnections, 4 of the 5 patients in the 35 mm group had reconnected PVs (Fisher exact test p-Value=0.14). Overall, 25% (8/32) of PVs were reconnected, with the RSPV and RIPV being the most commonly reconnected veins (3 times each). Conclusion To the best of our knowledge, we provide the first randomized comparison of the two pentaspline PFA catheter sizes. Our data show longer procedure times and fluoroscopy times using the 35 mm device as well as a higher rate of PV reconnections especially at the septal PVs. Most importantly, we observe a trend towards worse clinical outcomes using the larger catheter. Longer follow-up times will be available at the time of presentation.Freedom from arrhythmia recurrence

31 vs 35 mm: a randomized comparison of the pentaspline pulsed field ablation catheter sizes