Background
Radiofrequency (RF) catheter ablation is a well-developed treatment of atrial fibrillation (AF) (1,2). AF frequently originates from atrial muscular sleeves that extend into the thoracic veins such as the pulmonary veins (PV) and superior vena cava (SVC) (1,3,4) and the electrical isolation between the left atrium and these thoracic veins is the cornerstone strategy of AF ablation (3). An insufficient lesion-creation and conduction recurrence lead to the recurrence of arrhythmias (5~7). Therefore, a durable lesion-formation is a key factor for RF ablation. Lesion-formation depends on several factors such as the catheter contact force (CF), RF delivery time, and power (8). The ablation index (AI), a novel marker for incorporating the CF, RF delivery time, and power in a weighted formula, has been reported to be useful for a durable PVI (9~11). Several studies have reported the optimal value of the AI for PV isolation (PVI) and cavotricuspid isthmus line (CTI) ablation (12~14). However, no study has reported the optimal value of the AI for the SVC isolation (SVCI). In this study, we aimed to investigate the optimal AI for the SVCI.