Catheter ablation is an established treatment method for atrial fibrillation. In most cases, the arrhythmia substrate is located within the pulmonary veins and their isolation has become the cornerstone of catheter ablation therapy. However, it is estimated that in 10–20% of patients, the trigger and/or sustaining factors for the arrhythmia are located outside the pulmonary veins. This is particularly relevant in patients with significant disease progression and persistent forms of AF, where these sites are likely responsible for treatment failure and arrhythmia recurrence. Identifying non-pulmonary vein triggers of AF and understanding their impact on disease progression is crucial but remains insufficiently explored. Gaining such insights offers hope for optimizing treatment strategies and improving outcomes for patients. The most commonly mentioned ectopic arrhythmogenic focus include the superior vena cava (SVC). Despite its clinical significance in arrhythmogenesis, the detailed electrophysiological properties of the SVC have received relatively limited research attention compared to other cardiac structures. Moreover, scientific papers that present extensive knowledge on SVC- from its embryology to the electrophysiology scarce. Therefore we would like to offer a comprehensive analysis of existing literature concerning SVC as an arrhythmogenic substrate for AF.

Background: An adequate interlesion distance (ILD) applied during point-by-point pulmonary vein (PV) isolation for atrial fibrillation (AF) has never been established. We hypothesized that maximum tolerated ILD may differ between PV regions and may influence long-term ablation outcomes. Methods: A total of 260 AF patients underwent PV isolation with 3D electroanatomical platform. Postablation, ILD values were classified into 5 groups (6–5.5 mm, 5.5–5.0 mm, 5.0–4.5 mm, 4.5–4.0 mm and <4.0 mm); the number of tags in each group was calculated and correlated with postablation AF recurrence (AFR). All measurements were performed globally for the entire encirclement around each individual PV and regionally for designated PV anatomic segments. Results: Single-procedure freedom from AF was 81% for paroxysmal and 66% for persistent AF at 12 months. Global analysis showed that AFR was not related to median ILD nor the number of lesions within each ILD tag group for any PV. Segmental analysis showed that AFR was not related to median ILD. However, the presence of tags from the 5.5–6.0 mm ILD group located on the posterior aspect of right upper PV (RUPV) correlated with AFR. This was confirmed in a multivariable logistic regression model. Conclusions: Maximum tolerated ILD of 6.0 mm translated into well-accepted ablation results. However, the study suggests that it may be inadequate at the posterior aspect of RUPV.