Adjustable versus fixed cryoballoon size in AF ablation: Usability, Procedural Efficiency, and Short-Term Outcomes

Background: Cryoballoon (CB) pulmonary vein isolation (PVI) is a well-established and highly effective treatment for patients with symptomatic atrial fibrillation (AF). Fixed size 28mm CB may hinder optimal antral positioning and wide antral lesion creation, especially in patients with larger left atria (LA), left common ostia (LCO) or large PV ostia. To address these challenges and enhance adaptability, a dual-size CB has been introduced, which can be enlarged from 28mm to 31mm.

Methods: A prospective, single-center study was performed to evaluate the adjustable dual-sized CB ablation system (Adj-CBA; 28/31mm POLARx FIT ST™) with the conventional fixed-diameter CB system (Conv-CBA; 28mm POLARx ST™, both Boston Scientific) in a blockwise comparison. The study focused on feasibility, efficacy, safety, and short-term outcome in symptomatic AF patients undergoing first AF ablation procedure for PVI.

Results: From February 2021 to May 2024, a total of 246 patients were prospectively enrolled in the study, with a mean age of 65.0±14.0 years. The cohort comprised 102 females (41.5%). The majority of patients suffered from paroxysmal AF (83.7%). Conv-CBA was used in 150 patients (61.0%), while Adj-CBA was utilized in 96 patients (39.0%). There were significantly fewer females (46.7% vs. 33.3%, p<0.05) and more patients with persistent AF (8.8% vs. 26.0%, p < 0.001) in the Adj-CBA group. Regarding procedural parameters, the Adj-CBA procedures had a significantly lower median dose area product compared to the Conv-CBA cohort (647 cGy×cm² vs. 831 cGy×cm², p=0.013).

Overall, acute PVI was achieved in all 940 veins (100%), with a median time-to-isolation (TTI) of 34 [24] seconds and a single-shot success rate (SSSR) of 93.0%. TTI was recorded in 73.7% of cases. A total of 1821 (100%) freeze applications were performed, with a median of 2 [1] applications per PV and a minimum CB temperature of -54 [8] °C. The Adj-CBA group had a significantly higher SSSR (95.3% vs. 91.4%, p = 0.02) but a lower rate of detecting TTI (69.9% vs. 76.1%, p=0.03). There was a total of 1.3% ineffective freezes, with a higher count in the Adj-CBA group (2.0% vs. 0.8%, p=0.03). The expansion feature of the Adj-CB was applied in 18 (18.8%) patients, primarily when targeting the right superior PV (25/176, 14.2%) and the LCO (15/32, 46.9%). In total, 9 PV (0.5%) experienced intraprocedural reconnection. The study population experienced a total of 10 complications (4.1%). No major adverse events were noted; however, two patients (0.8%) experienced persistent phrenic nerve palsy (PNP), and three patients (1.2%) had transient PNP. After a median follow-up of XX months, any atrial arrhythmia recurrence was documented in XX (%) of patients in the Adj-CBA and XX (%) of patients in the Conv-CBA group (p=XX).

Conclusion: Both CBA systems showed high efficacy and safety, with strong performance in achieving TTI, maintaining low minimal balloon temperatures, and high SSSR. The Adj-CB system had a higher single-shot success rate and used less radiation compared to Conv-CB but had a reduced TTI capability. The 31mm expansion feature in the Adj-CBA system was needed in one out of every five patients. The Adj-CBA system may benefit patients with complex LA anatomy or larger PV, while the Conv-CB is adequate for most patients. Longer follow-up studies are necessary to assess the impact of these technical improvements on long-term outcomes.