2.2 Study selection and data extraction
Titles and abstracts were retrieved from articles searched using the keywords “left bundle branch pacing” or “left bundle branch area pacing.” Studies were included if the article was in English and met the following criteria: patients aged >18 years; included patients with an LVEF from 35–50%; LVEF or QRS duration follow-up was performed after the procedure; and for LBBAP CRT, both patients with pacing indications (de novo or upgrade), and with HF without pacing indications (de novo CRT), were included. Among studies satisfying the above criteria, a pooled analysis of patients with a baseline LVEF of 35–50% was used. Editorials, review articles, case reports/letters, and abstracts were excluded. The quality of the literature was evaluated by the above two researchers using the Newcastle-Ottawa scale criteria.21