4 DISCUSSION
The value of this meta-analysis on LBBAP is that it included almost all types of patients with pacing indications, and self control study showed that LBBAP had a good therapeutic effect. Our meta-analysis demonstrated that: (1) LBBAP produces a favorable QRS duration, not only stabilizing patients with a normal QRS duration, but also significantly shortening the prolonged QRS duration; (2)In patients receiving LBBAP, there are the following changes in pacemaker parameters after a period of follow-up: a. the stable capture threshold for a long time; b.a positive trend in R-wave amplitude; c. a negative trend in pacing impedance; (3) In the included studies, the average success rate of LBBAP was high, the overall safety of the procedure was reliable, and there were no specific complications of pacemaker surgery.
It has been confirmed that RV apical pacing was associated with high incidence of heart failure, AF, and mortality due to its abnormal activation propagation and obvious LV contraction delay23-24.Other pacing sites just like the septum or outflow tract did not show obvious results in improving clinical outcomes25-26.Up to now, His-bundle pacing was considered as the physiological pacing method. However, challenges with His bundle pacing including difficulty in identifying the location of the His bundle, a relative high capture threshold with potential long-term instability, especially in patients who already have cardiac conduction disease such as LBBB, which withheld the widespread application of this pacing6,27.
. Pacing the LBB that directly capture the left bundle branch by deep septal pacing was first introduced by Huang in 20178, which is likely to fill many of the deficits of HBP.The left bundle branch is flat banded and fan-shaped in the subendocardium, with a wider distribution than His bundle and fewer fiber wrapping28,29. For the LBBAP procedure, the anatomic characteristics of the LBB provide a relatively large area for the selection of a pacing site. Lead fixation could be more easily achieved by screwing the lead into the ventricular septum. Baseline bundle branch block might be more likely corrected by LBBAP beyond the site of block8,17.
The sequence of ventricular excitation and ventricular systolic synchrony are two important factors affecting postoperative cardiac function. The coherence and similarity of the QRS morphology between intrinsic QRS and paced QRS can indirectly reflect the difference of the sequence of downward transmission and ventricular excitation. So the QRS duration is an important indicator of the synchronization of the contractions of both ventricles, which affects the risk of death and heart failure in patients after pacing surgery30-32. LBBAP proved its effectiveness both in maintaining a normal QRS duration and in generating narrower QRS duration in our study. The rich myocardial tissue surrounding the electrodes guarantee the characteristic of higher R-wave amplitude with a lower threshold for LBBAP, which was also confirmed in our study. These stable pacing parameters indicated that some sensing or threshold issues that are common in HBP or RVP might be avoided in LBBAP.
In our included study, LBBAP was shown to be effective in the treatment of slow arrhythmias such as AVB and SND. In particular, in patients with HBP failure or CRT indications, LBBAP can maintain better electrical and mechanical synchronization, and its efficacy and safety have been further validated as an excellent alternative to HBP.So it could become a mainstream pacing technology in the future.