Acute Changes in Cardiac Synchrony and Output According to RV Pacing Sites in Koreans with Normal Cardiac Function

Introduction: The synchrony of the pacing heart can be affected by the right ventricular (RV) pacing site and is crucial to cardiac function in pacemaker recipients. We evaluated the acute changes in cardiac synchrony according to the RV pacing sites in normal systolic functioning subjects with normal QRS. Methods: We conducted this study with 30 patients with the pacing in the RV apex (RVA), RV septum (RVS), and RV outflow tract (RVOT) in a sequential manner . Transthoracic echocardiography was conducted at rest and during pacing in order to measure interventricular and intraventricular dyssynchrony in all patients. Results: QRS duration (148.1 ± 12.8 ms) of RVA pacing was significantly shorter than that of RVS pacing (154.4 ± 14.1 ms, P < 0.01) and RVOT pacing (160.6 ± 15.7 ms, P < 0.001). We noted no statistically significant difference in cardiac output according to the pacing sites. The interventricular dyssynchrony with M‐mode and Doppler echocardiography in RVOT pacing was increased to an insignificant degree as compared with those with RVS pacing or RVA pacing. The intraventricular dyssynchrony with tissue Doppler echocardiography in RVA pacing was reduced significantly as compared with that of RVS pacing or RVOT (RVA = 60.3 ± 32.7 ms, RVS = 82.1 ± 33.8 ms, RVOT = 79.1 ± 33.3 ms; RVA vs RVS = P < 0.05, RVA vs RVOT = P < 0.01, RVS vs RVOT = P = NS). Conclusion: RVA pacing is superior to RVS and RVOT pacing with regard to intraventricular synchrony in normal systolic functioning subjects with normal QRS. Cardiac output at RVA pacing is not inferior to other sites. (ECHOCARDIOGRAPHY, Volume 26, July 2009)