Objective The ectopic foci originating from superior vena cava (SVC) may act as an triggers in the occurrence and perpetuation of atrial tachyarrhythmia.The common complications of isolation of SVC were the stenosis of SVC, the phrenic nerve paralysis and the sinus node dysfunction.The current study was to investigate the feasibility of localizing sinus node by activation mapping, the variation of phrenic nerve locations and defining the SVC muscle sleeves.Methods We consecutive collected a group of patients with paroxysmal AF who referred to Beijing Anzhen hospital for atrial fibrillation ablation, all of them also underwent isolation of SVC.Prior to SVC isolation, the sinus node was defined by RA activation mapping during sinus rhythm, the right phrenic nerve was lacalized via pacing form the ablation catheter, the SVC muscle sleeves were defined by electrophysiological methods.Results A total of 80 patients were enrolled into the study.SVC was isolated in all of the patients.Right atrium activation mapping revealed that 11/80 (13.8%) sinus node located in the SVC, 43(53.8%) located at the junction of the SVC-right atrium junctions.48(60%) sinus node located at the anterior lateral segment of SVC, 22(27.4%) located at the posterior lateral, 8(10%) located at the anterior wall, 2(2.6%) located at posterior wall or the anterior septum.A total of 174 SVC muscle sleeves were detected among all 80 patients, 55(31.6%) of them located at the anterior septum, 46(26.4%) located at the posterior septum, 13(7.5%) located at the posterior free wall, 6(3.5%) located at the posterior lateral, 19(10.9%) located at anterior lateral wall and 35(20.1%) located at the anterior free wall.From the pacing maneuver, the right phrenic nerve was predominantly located at the lateral segrnent79/80(98.7%).After 10.1±4.1 months follow-up, on patients developed SVC stenosis, signs of sinus node dysfunction and the phrenic nerve paralysis.Conclusions The sinus node, phrenic nerve and electrical connection sites were distributed along the SVC at expected locations for most patients.SVC could be safely ablated in most patients after defining those structures.