Tehran University of Medical Sciences The Research in Heart Yield and Translational Medicine (RHYTHM) 3115-7270 18 2 2023 04 30 109 114 Sara Zand 1- Tehran Heart Center, Tehran University of Medical Sciences, Tehran, Iran Hakimeh Sadeghian Tehran University of Medical Sciences, Tehran, Iran. Ali Kazemisaid 3- Electrophysiology department, Sina Hospital, Tehran University of Medical Science, Tehran, Iran Masoumeh Lotfi-Tokaldany 4- Tehran Heart Center, Cardiovascular Disease Research Institute, Tehran University of Medical Sciences, Tehran, Iran Arash Jalali 4- Tehran Heart Center, Cardiovascular Disease Research Institute, Tehran University of Medical Sciences, Tehran, Iran Akram Sardari Department of Cardiology, School of Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. 2022 08 22 2023 02 13 Background: The use of cardiac resynchronization therapy (CRT) in heart failure patients with right bundle branch block (RBBB) is under debate. We present early and late echocardiographic characteristics of a series of heart failure patients with RBBB who underwent CRT. Methods: In this retrospective descriptive study, 18 patients with RBBB in the surface electrocardiogram underwent CRT between 2005 and 2015. All the patients had the New York Heart Association functional class III/IV, a left ventricular ejection fraction (LVEF) ≤35%, and a QRS duration ≥120 milliseconds. The median follow-up duration was 19 months. The echocardiographic response was based on a ≥5% increase in LVEF. Results: Within 48 hours after CRT implantation, LVEF increased from 24.58%±7.08% before to 28.46±8.91% after CRT (P=0.005) and to 30.00±9.44% at follow-up (P=0.008). Among the 18 patients, 12 (66.7%) were responders within 48 hours after CRT. The following baseline echocardiographic parameters were higher in the responders than in those without an increased LVEF, although the difference did not reach statistical significance: septal-to-lateral wall delay (48.33±33.53 vs 43.33±38.82 ms), anteroseptal-to-posterior wall delay (41.7±1.75 vs 38.33±18.35 ms), and interventricular mechanical delay (48.50±21.13 vs 31.17±19.93 ms). The mean QRS duration was higher in the responders than in the non-responders (183.58±40.69 vs 169.00±27.36 ms). Death was reported in 3 out of the 18 patients (16.7%) at follow-up. The 3 deceased patients had a higher baseline interventricular mechanical delay than those who survived. Conclusion: Our results indicated that patients with RBBB might benefit from CRT. Further, patients with higher intra and interventricular dyssynchrony and a wider QRS may show better responses. https://rhythm.tums.ac.ir/index.php/jthc/article/view/1707 https://rhythm.tums.ac.ir/index.php/jthc/article/download/1707/1063