Abstract: AIM:To evaluate the feasibility and safety of right ventricular outflow tract septum (RVOTS) pacing by comparing the results of RVOTS pacing and right ventricular apex (RVA) pacing. METHODS: Sixty-eight patients with chronic atrial fibrillation and long R-R interval or slow ventricular rate, who were to be implanted with permanent VVI pacemaker, were assigned randomly to two groups: RVOTS pacing group (n=34) and RVA pacing group (n=34). A spiral active fixed lead was implanted in RVOTS whereas a wing-shaped passive fixed lead was implanted in RVA. X-ray exposure time was recorded during the operation and lead parameters and complications were recorded during the operation and 15 min after lead implant and 1, 6 and 12 months after operation. QRS duration was measured in intrinsic rhythm and pacing using electrocardiogram. RESULTS: X-ray exposure time during operation was longer (P=0.01) in RVOTS group (12.8±5.4) than in RVA group (9.5±2.1), but with increased surgical proficiency, X-ray exposure time in RVOTS group was gradually reduced and was close to that in RVA group. The immediate pacing threshold of lead in RVOTS group was higher than in RVA group (0.67±0.40 vs. 0.52±0.18) but no significant difference was observed between groups. Pacing threshold was not statistically significant 15 min after lead or 1, 6 and 12 months after operation between groups. The R wave amplitude and impedance in the two groups were not statistically significant in each period during and after operation. QRS duration of pacing was prolonged significantly (P<0.01) as compared with that of intrinsic rhythm in the two groups, but QRS duration of RVOTS pacing was significantly shorter (P<0.05) than RVA pacing. During intraoperative and follow-up periods, no complications such as electrode dislocation, threshold increase, myocardial perforation, or cardiac tamponade were observed. CONCLUSION: RVOTS pacing with active fixed lead is safe and feasible and the electrical synchronization of ventricular activation is better than that of RVA.