Background: Pulmonary vein isolation (PVI) using cryoballoon (CB) ablation has comparable efficacy and safety to the gold standard of radiofrequency ablation in the treatment of symptomatic atrial fibrillation (AF). Initial trials were performed using the 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 PVIs using the PX and the AFr CB  systems in terms of procedure characteristics, efficacy and safety, using data from our AF registry.  

Methods: The new PX CB system was acquired by our center in October 2020. We performed a retrospective analysis of our AF ablation registry, containing 186 consecutive patients that underwent first procedure cryo-PVI for symptomatic AF from October 2020 to November 2021. Esophageal temperature measurement and phrenic nerve stimulation for prevention of phrenic nerve palsy were performed in all patients. Patients underwent follow-up at 3 months.

Results: 45 patients underwent CB ablation with the PX system vs. 141 patients with the AFr system. Baseline characteristics including sex, mean age, BMI, and percentage of patients with paroxysmal AF (33.3% vs. 34.0%, p=0.162) were similar between groups.  Class Ic or III antiarrhythmic drug use was more frequent (35.5% vs. 26.3%, p=0.037) and mean LA diameter (39.9 ± 6.2 mm vs. 37.6 ± 6.0 mm. p=0.037) was slightly larger in the PX group.

Acute PVI of all veins was achieved in all patients. Minimal freeze temperatures (-56.6±5.5, -53.3±5.5, -55.2±7.7, -54.4±6.9  vs. -50.2±5.5, -46.8±6.4, -50.1±5.7, and -49.0±5.7 °C) and temperatures at time of isolation (-44.2±7.7, -42.4±9.3, -40.8±10.1, -45.3±6.7  vs.  -35.9±8.0, 33.8±8.7 -34.8±8.8, and -35.5±10.4 °C) were significantly lower in the PX group (LSPV, LIPV, RSPV and RIPV respectively, p<0.001 for all PVs). However, time to isolation (52.1±26.2, 63.3±32.5, 48.4±33.0, 76.1±43.2 vs 50.9±24.2, 51.6±34.3,49.0±31.8, and 58.9±36.0 s, p=0.910, 0.867, 0.779, and 0.106, for LSPV, LIPV, RSPV and RIPV) and minimal procedural esophageal temperature (23.3±7.6 vs. 24.9±7.3 °C, p=0.215) were similar, which might indicate that the temperature differences are due to measurement effect.

Procedural duration (83.6±24.0 vs. 71.6±20.7 min, p=0.002) and fluoroscopy time (13.4±5.5 vs. 11.8±4.1, p=0.049) were longer in the PX group, whereas fluoroscopy dose (2823.1±1852.3 vs. 2328.7±1529 mGycm^2, p=0.174) was similar. These differences might be explained by a learning curve with the new PX CB system.

Procedure complications were comparable between groups  (5.6 vs. 4.4 %, p=0.950) and consisted mostly of groin hematoma. Phrenic nerve palsy occurred in 1 case in the PX group, compared to 4 cases in AFr group (p=0.824). There was one incidence of air embolism of the right coronary artery in the PX CB group.

The rates of AF recurrence at 3 month follow-up (17.7 vs. 15.6%, p=0.807) were comparable between groups.

Conclusion: PVIs using the new PX cryoballoon system showed comparable efficacy and safety to the AFr system. Procedure duration and fluoroscopy time were slightly longer, which can 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 lower effective PV temperatures.