Feasibility and efficacy assessment of a novel size-adjustable cryoballoon for ablation of atrial fibrillation in a multicenter clinical setting

Abstract Background The POLARx-FIT cryoballoon (CB) system introduces a unique feature, allowing the selection of two distinct balloon sizes within a single catheter. This innovation holds promise for treating larger pulmonary veins (PV), providing increased flexibility to achieve optimal occlusions. However, there is a scarcity of clinical data supporting its application in this context. Purpose To compare the benefits and safety of the new POLARx-FIT system to those of the existing POLARx system currently in use for PV isolation (PVI) in patients with atrial fibrillation (AF). Methods The first 140 consecutive patients who underwent CB-based PVI with the POLARx-FIT system were retrospectively compared with 300 consecutive patients treated with the POLARx system. Protocol-directed cryoablation was delivered for 180 sec or 240 sec according to operator’s preference for isolation achieved in ≤60 sec, or 240 sec if isolation occurred >60 sec or when time to isolation was not available. The ablation endpoint was PVI as assessed by entrance and exit block. In the POLARx-FIT group the choice of balloon size (28 or 31 mm) was determined during the procedure while attempting to occlude each vein. Results Two-thousand one-hundred fifty-five cryo-applications (CBA) from 440 patients were analysed (300, 68.2% POLARx; 140, 31.8% POLARx-FIT). PVI was achieved with cryoablation only in all patients. The mean number of freeze applications per patient was similar between groups (5.0±1.4 in the POLARx-FIT vs 5.3±1.8 in the POLARx group, p=0.207) whereas the number of PVs treated in a single-shot fashion was higher in the POLARx-FIT group (444, 80.7% with one shot; 75, 13.7% with 2 shots; 31, 5.6% with more than 2 shots) than in the POLARx one (1168, 70.2% with one shot, p=0.0002; 294, 17.7% with two shots and 143, 8.6% with more than two shots). Among the POLARx-FIT cases, in 54.2% (n=298) of applications, the 31-mm diameter was employed as a first choice, while in the remaining 45.8% (n=252) of applications, the 28-mm diameter was adopted. A switch to a different balloon diameter was applied in 11.6% of cases. The first pass isolation (i.e. a single shot CBA to achieve PVI) was slightly higher when using a 31 mm diameter (n=250, 83.9%) than a 28 mm diameter (n=194, 77.0%, p=0.05). Three (0.7%) transient phrenic nerve palsy were observed (all in the POLARx group, 0.9%, p=0.554), with full recovery in the 48-h post procedure; no major procedure-related adverse events were reported at 30 days post-procedure. Conclusion In this first multicentric experience in a clinical practice setting, this novel cryo-balloon system proved to be safe and effective and resulted in a high proportion of successful single-freeze isolation. The intraprocedural flexibility of balloon size contributed to its versatility, leading to a variation in balloon diameter in about 12% of freeze applications.