4.3 Limitations
This analysis has several limitations. First, there are currently no randomized controlled trials for LBBAP targeting HFmrEF; therefore, all studies included in this meta-analysis were retrospective and observational. Second, the sample size was small, with 16 centers and 211 patients (207 patients with LVEF followed-up before and after LBBAP, 42 patients with QRS duration followed-up before and after LBBAP) included in the analysis. Third, there was no long-term follow-up data. Fourth, in all studies included in the analysis, the pacing lead used for the procedure was a lumenless lead; therefore, there were no results for stylet-driven leads. Finally, only one study reported clinical outcomes including HF hospitalization and mortality. Thus, large-scale randomized controlled trials with long-term observations are needed.