This study will address whether LBBaP is superior to RVAP in terms of safety and efficacy

• Cardiac pacing is an effective therapy for treating patients with bradycardia due to sinus node dysfunction or atrioventricular block. However, traditional right ventricular apical pacing (RVAP) causes electric and mechanical desynchrony, increasing the risk for atrial arrhythmias and heart failure.
• .Cardiac resynchronization therapy(CRT)is another pacing modality employed for treatment of HF .Clinical studies have demonstrated that CRT promotes left ventricular reverse remodelling and reduces morbidity and mortality in patients with HF . Although CRT's benefits are well demonstrated, the therapy has been associated with significantly high non-response rate(30-40%).Also, the BVP is a non-physiological approach that requires two leads to activate the ventricular myocardium and not the specialized conduction system
• Therefore, there is a need to develop a physiological pacing approach that provides synchronized contraction of the ventricles
• Although His bundle pacing (HBP)has been widely used as a physiological pacing modality, it is limited by challenging implantation technique, unsatisfactory success rate in patients with wide QRS wave, high pacing capture threshold, and early battery depletion.
• Recently, the left bundle branch pacing (LBBP), defined as the capture of the left bundle branch (LBB) via trans ventricular septal approach, has emerged as a new physiological pacing modality.
• this approach has been found to provide physiological pacing that guarantees electrical synchrony of the left ventricle with a low pacing threshold.
• LBBP implantation is done by The Select Secure lead (model 3830) and Select Site C315HisorC304His sheaths are used in operation, while an electrophysiological multichannel recorder is used to simultaneously document intracardiac EGMs and 12-lead ECG .the Pacing System Analyzer (PSA) is used to test the pacing parameters and record intracardiac EGMs. The operation process can be summarized as follows: (1) establishment of the venous access and determination of the initial LBBP site; (2) introducing a pacing lead into the right ventricle and screwing it into the interventricular septum(IVS) until it reached in the LBB areas;(3) assessing the lead depth into ventricular septum and confirming LBB capture; (4)removing the sheath and providing the slack; and(5)programming the pulse generator.
• There is a limited number of clinical studies, featuring small sample sizes, that have shown that, compared with right ventricular apex pacing (RVAP), the QRS duration of postoperative ECG in LBBaP patients is narrower and the cardiac systolic function is improved. Also, there have been limited number of randomized controlled trials (RCTs) evaluating the efficacy and safety of LBBaP in patients with atrioventricular block (AVB) versus those with RVAP.

Inclusion Criteria :

• Patients with AVB who meet indications for pacemaker
• Implantation with an estimated percentage of ventricular pacing ≥50%
• Ability to provide informed consent

Exclusion Criteria:

• Failure to cooperate with follow-up.
• Persistent atrial fibrillation.
• Patients with heart failure (LVEF) ≤35%,
• Estimated glomerular filtration rate less than 30 ml/min.
• Septic shock
• advanced malignant tumor.
• Pregnancy or prepared to get pregnant
• Cardiac tamponade or major hemopericardium

. Patients with AVB who meet indications for pacemaker , with an estimated percentage of ventricular pacing ≥50%