Background: Pulmonary vein isolation (PVI) using cryoballoon (CB) ablation has comparable efficacy and safety compared to radiofrequency ablation in the treatment of symptomatic atrial fibrillation (AF). Initial randomized controlled trials were performed using Arctic Front Advance Pro™ (AFr) (Medtronic, Dublin, Ireland) CB system.  Novel CB systems have recently become available, including the POLARx™ (Px) (Boston Scientific, Marlborough, Massachusetts, United States) system. There is little data on direct comparison between different CB systems. 
Aims: We aimed to compare PVI using the Px and the AFr CB  systems in terms of procedure characteristics, efficacy, and safety in our patient population. 
Methods:We performed a retrospective analysis of our internal AF ablation registry, containing 264 consecutive patients that underwent first procedure cryo-PVI for symptomatic AF from October 2020 to June 2022. Patients underwent follow-up at 3 and 12 months, either as part of a prescheduled visit or via telephone call to the primary care provider or to the patient.
Results: 55 patients underwent CB ablation with the Px system vs. 209 patients with the AFr system. Relevant baseline characteristics were similar between groups. Minimal freeze temperatures (-49, -48, -52 and -51 °C  vs. -56, -52, -58, and -54 °C for LSPV, LIPV, RSPV and RIPV respectively, p<0.001 for all PVs) and temperatures at time of isolation (-36, -30, -38 and -39 vs.  -48, -46, -42 and -47  for LSPV, LIPV, RSPV and RIPV respectively, p=0.006 for RSPV, p<0.001 for all other PVs) were significantly lower in the Px group. However, the time to isolation (48 (31-64), 36 (25-56), 49 (34–58) and 50 (36-80) vs. 51 (44-92), 62 (51.5-82), 41 (24.5-78.5), 45 (32.5-98.5)s, p=0.551, 0.106, 0.821, and 0.298, for LSPV, LIPV, RSPV and RIPV respectively) and minimal procedural esophageal temperature (24.1 (16.9 – 29.3) vs. 25.0 (15.1 – 33.7), p=0.133) were similar in both groups.
The AFr group showed a significantly shorter procedural duration (60 (55-65) vs. 75 (65-97.5) min, p<0.001), and lower fluoroscopy dose (2025 (1680-7756) vs. 6411 (1568-11231) mGycm2, p=0.046) compared to the Px system. Fluroscopy times remained similar (9.8 (8.3-12.3) vs. 9.7 (9.3-15.6), p=0.077), however.
The primary efficacy endpoints of AF recurrence after 3 (26.6% vs 24.3%, p=0.778) and 12 (29.2% vs. 23.2%, p=0.715) months were similar between the AFr and the Px systems. Complication rates were comparable between both groups (4.8% v. 7.3%, p=0.464). and consisted mostly of groin hematoma. There was one case (1.8%) of suspected right coronary artery air embolism with transient ST-elevation without sequelae in the Px group, as well as one case of transient ischemic attack (0.5%), both occurring post-procedurally, in the AFr group. Phrenic nerve palsy occurred in 5 cases (2.4%) in the AFr group compared to one case (1.8%) in the Px group (p=0.799).
Conclusion: PVIs using the new PolarX™ cryoballoon system showed comparable efficacy and safety to the Arctic Front Advance Pro™ system. Procedure duration and fluoroscopy dose were slightly higher, which might be attributed to the learning curve using the new system. The significantly lower freeze temperatures in the Px group seem to be a measurement effect and do not reflect a lower effective PV temperature.