The present study will recruit 40 symptomatic heart failure patients with left ventricular ejection fraction (LVEF) below 35% and complete left bundle branch block(QRSd≥130 ms). Each patient was randomized to either left bundle branch pacing(LBBP) or biventricular pacing(BivP) and was followed up for at least 6 months. The objective is to compare the effects of LBBP and BivP on cardiac resynchronization in the treatment of heart failure by measurable clinical parameters.

The traditional biventricular pacing (BivP) is an established treatment to corrected the cardiac dyssynchrony in heart failure patients with left bundle branch block(LBBB). It has been proved that BivP can improve clinical symptoms and reduce all-cause mortality in heart failure. However, BivP is subject to the variable coronary sinus(CS) anatomy and LV-pacing lead fail to be implanted in 5%-10% of patients due to the lack of appropriate target branch, high threshold or phrenic nerve stimulation. Almost 30%-40% of patients with successful implantation show no response. What's more, BivP just corrects the mechanical dyssynchrony caused by LBBB not corrects the LBBB. Recent studies have demonstrated that His bundle pacing (HBP) can correct LBBB, achieve physiological pacing and realize the cardiac resynchronization. But HBP has high technical requirements, lower sense value and higher threshold of correcting LBBB, which may be further increased in long-term follow-up.

The lastest research shows that pacing left ventricular septum using a transseptal approach can reduce left ventricular(LV) electrical dyssynchrony. Huang et al first confirmed that left bundle branch pacing(LBBP) can correct LBBB and improve cardiac function. LBBP has been reported to offer higher success rate with higher sense value and lower pacing thresholds compared with HBP. In chronic heart failure patients with LBBB that need cardiac resynchronization therapy(CRT), LBBP can achieve the similar electrical and mechanical resynchronization as well as HBP.

There is to date no randomized studies between LBBP and BivP in HFrEF patients with complete LBBB that need CRT. The purpose of this study is to compare the therapeutic effects of LBBP and conventional BivP on LV function and clinical endpoints in such patients. The present study will randomize 40 patients in two centres to LBBP or BivP. Baseline assessments including echocardiography parameters[left ventricular ejection fraction(LVEF ), left ventricular end-systolic volume(LVESV), left ventricular end-diastolic volume(LVEDV)], electrocardiogram(ECG), N-terminal pro B-type natriuretic peptide(NT-proBNP) level, New York Heart Association(NYHA) class, 6-minute walking distance(6MWD) and quality of life score(QOL) will be obtained. At the same time, the LBBP and BivP success rate, intraoperative and postoperative complications are recorded.

Inclusion Criteria:

1. LVEF≤35% as assessed by echocardiography and NYHA class II-IV despite optimal medical therapy for at lest 3 months；
2. Sinus rhythm, complete left bundle branch block (QRS duration ≥130ms)；
3. Between the ages of 18 and 80；
4. With informed consent signed.

Exclusion Criteria:

1. After mechanical tricuspid valve replacement；
2. Unstable angina, acute MI, CABG or PCI within the past 3 months;
3. Persistent atrial fibrillation without atrioventricular block, the expected percentage of ventricular pacing below 95%;
4. Enrollment in any other study；
5. A life expectancy of less than 12 months；
6. Pregnant or with child-bearing potential;
7. History of heart transplantation.