Abstract: Abstract: Objective To compare the efficacy of cardiac resynchronization therapy (CRT) on chronic heart failure (CHF) patients with different left bundle branch block (LBBB) morphologies. Methods Patients（n=45）who were treated with CRT were enrolled. According to the intrinsic ECG morphologies, patients were divided into 1) "genuine" LBBB group (n=32) who present negative dominant V1 and V2 lead wave (QS or rS); mid-QRS notching or slurring in at least 2 leads of Vl, V2, V5, V6, I and aVL as well as QRS duration≥140 ms in male or ≥130 ms in female and 2) "false" LBBB group (n=10) who meet traditional standards but fail to meet“genuine”LBBB diagnostic standard. The QRS duration, echocardiographic indi⁃ ces and New York Heart Association (NYHA) Functional Classification were evaluated at the 12 months follow-up. CRT re⁃ sponder was defined as patient with≥1 decrease in NYHA class and/or with≥15%reduction in left ventricular end-systolic volume (LVESV). CRT super-responder was defined as patient with≥30% reduction in LVESV. Results There was no dif⁃ ference in basic characteristics of patients between groups. At the 12 months follow-up, 20 patients in "genuine" LBBB group and 6 patients in "false" LBBB group were identified as responders (P > 0.05). Compared with those in "false" LBBB group, the responders in "genuine" LBBB group showed better improvement in left ventricular ejection fraction and left ven⁃ tricular end diastolic diameter (LVEDD) (both P < 0.05). Conclusion Left bundle branch block morphology is less predic⁃ tive for the efficacy of CRT. However, patients who show response to CRT with "genuine" LBBB profile may get more bene⁃ fits from CRT treatment than the patients with "false" LBBB profile.

Key words: heart failure, bundle- branch block, ventricular function, left, cardiac resynchronization therapy, left bundle branch block