Jiang Z, Qiu Y, Qian Z, et al. - Whether S wave in lead V6 can predict cardiac resynchronization therapy (CRT) response in patients with complete left bundle branch block (CLBBB), was investigated in this study including 112 CLBBB patients. These patients were grouped as follows: T-CLBBB group (n = 54)(CLBBB without S wave in V5 or V6), V5S group (n = 32) (CLBBB with S wave in V5 and no S wave in V6) and V5&V6S group (n = 26) (CLBBB with S wave in V5 and V6). Left ventricular end-systolic volume reduction ≥ 15% at 6-month follow-up defined CRT response. Higher incidence of heart failure rehospitalization or all-cause death was observed in patients in V5&V6S group vs the other two groups, as revealed by Kaplan–Meier curves. Findings revealed that low response to CRT and poor long-term outcome was predicted by S wave in lead V6.