Background/Objectives: Pulmonary vein isolation (PVI) is the standard treatment for atrial fibrillation (AF), but medium-term success rates remain suboptimal. Non-pulmonary vein triggers, particularly from the superior vena cava (SVC), contribute to AF recurrence. Empirical SVC isolation (SVCi) in addition to standard PVI may improve outcomes. This study evaluated the acute procedural efficacy and safety of PVI with adjunctive SVCi versus PVI alone in patients with paroxysmal AF (PAF). Methods: In this randomized, controlled, single-center study, 149 patients with PAF were assigned to either standard PVI (n = 74) or PVI with adjunctive empirical SVCi (n = 75) using a fourth-generation CB. Primary endpoints were acute procedural success and the incidence of procedure-related complications, particularly phrenic nerve injury (PNI) and sinus node dysfunction. Results: Acute PVI was achieved in all patients; SVCi was successful in 84.9% of the PVI + SVCi group. Major complication rates were low and comparable between groups (0% vs. 2.6%, p = 0.157). However, the overall complication rate was significantly higher in the PVI + SVCi group (50.6% vs. 6.8%, p < 0.001), driven primarily by transient or impending right PNI (38.6% vs. 6.8%, p < 0.001) and sinus node dysfunction. All PNI events resolved before the end of the procedure. Conclusions: Empirical SVCi using a fourth-generation CB is feasible and generally safe, but carries a higher risk of transient PNI and reversible sinus node dysfunction. Therefore, CB SVCi should be approached with caution. Further studies are needed to evaluate long-term outcomes and assess whether the potential benefits outweigh these procedural risks.

Background: Pulmonary vein isolation (PVI) is the standard of care for patients with atrial fibrillation (AF), but medium-term success rates are far from ideal. Therefore, new methods are being developed, with emphasis on ectopic foci outside the pulmonary veins. Superior vena cava (SVC) is one of the most important non-pulmonary origins of AF and some studies suggested that empiric SVC isolation could improve outcomes in ablation of paroxysmal atrial fibrillation (PAF). Although complications have been reported in SVC ablation, most studies found complication rates of SVC ablation similar to conventional cryoballoon PVI. Aim: This prospective, single-center study aimed to assess the complication rate and success rate of PVI followed by SVC isolation by cryoballoon application in comparison with conventional cryoballoon PVI. Methods: We designed an unblinded, randomized clinical trial and recruited consecutive patients with PAF who were randomized to a conventional cryoballoon PVI or PVI and additional SVC cryoballoon isolation using single 180 s freeze. Results: A total of 140 patients (61.4% male, mean age 62.1 years) with PAF were included and 67 (47.9%) were randomized to SVC isolation in addition to conventional ablation. Planned 180-s freeze in the SVC could be completed in 15 (22.4%) patients, while 27 (40.3%) patients received at least 120-s freeze. The mean time to SVC isolation was 40.2 ± 37.9 s. Real-time recording of SVC isolation was observed in 39 (58.2%) patients. Right phrenic nerve palsy (PNP), impending or transient, occurred in 6 (8.2%) patients in the PVI-only group and in 25 (37.3%) patients in the SVC-group (Chi-square test p < 0.001). There were no persistent PNP cases. Bradycardia or junctional rhythm was observed during a procedure in 15 (22.4%) patients who received SVC isolation. One patient eventually received a permanent AAI pacemaker due to a sinus node injury. Conclusion: Our data suggest that SVC isolation can be successfully achieved in the majority of PAF patients using conventional cryoballoon. However, this significantly increases the rate of transient or impending PNP and sinus node injury in comparison to conventional cryoballoon PVI. Therefore, careful phrenic nerve function monitoring and attention to sinus bradycardia or junctional rhythm are important to mitigate this risk. Follow-up data are being collected to determine whether this risk could be outweighed by a lower rate of PAF recurrence.