Objective:To investigate the influence of different right ventricular (RV) pacing sites on QRS width, and to provide a potential reference site for permanent right ventricular pacing in patients implanted with permanent pacemakers. Pacing at the site with the shortest QRS duration may reduce the deleterious effects of RV pacing on LV function, and thus having beneficial effects on patient's outcome. Methods: All consecutive patients who were planned to have permanent pacemaker implantation for a Class I or IIa indication at our department from October 2010 to July 2012 were screened for the participation in this prospective, single center, non-randomized study. The baseline surface ECG was analyzed for QRS width and morphology, respectively. During the implantation procedure patients were transiently paced at different RV locations (right ventricular apex, right ventricular inflow tract [RVIT], mid septum, high septum and right ventricular outflow tract [RVOT]) before the lead was placed at its final position. During pacing at the different positions the surface 12-leads ECG was recorded. Based on the surface of ECG QRS duration and morphology of the different right ventricular pacing sites were analyzed and compared with baseline and to each other. Results: A total of 216 patients (39% female, mean age 69 ± 13 years, higher degree AV block 30.5%) was enrolled in the study. Paced QRS duration was significantly different between all right ventricular pacing sites compared with the baseline ECG (baseline:106 ms±21 ms;mean paced:158 ms±16 ms;p<0.001). RVA pacing showed the widest QRS (168 ms±16 ms). QRS duration with RVIT pacing was 166 ms±15 ms, and that with RVOT pacing was 165 ms ± 15 ms, respectively. QRS duration was not significantly different between these three positions. Mid-septal pacing showed the narrowest QRS (139 ms±19 ms) compared to all other pacing sites (p<0.001). Pacing at the high-septum showed a broader QRS (153 ms ± 14 ms) than that pacing at the mid-
septum. Compared to other right ventricular pacing sites, QRS morphology at the mid-septum was close to normal, and electrical axis was unchanged as compared to baseline. Conclusion: Pacing at different right ventricular sites showed the significant widening of QRS compared to baseline. The shortest QRS duration was seen with mid-septal pacing. Therefore, mid-septal pacing may have less deleterious effect on LV function compared to other RV pacing locations, which may be the optimal right ventricular pacing site in permanent pacemaker recipients.