Study selection
Two independent reviewers (Y.L and D.C) screened the citations through the title and abstract, and we make mutual agreement procedural to reach a consensus if divergences exist. Studies met the following explicit selection criteria as follow were evaluated as complete reports: 1) English language publication; 2) randomized controlled trials or observational trials; 3) the subjects of interest was heart failure patients undergoing CRT with or without defibrillator; 4) the outcome was all-cause mortality; 5) a hazard ratio (HR) adjusted by Cox multivariate analysis was available.
The standard of exclusion criteria includes: case reports, case series, editorials, literature review, conference abstract, non-English articles and duplicate reports (we selected the study reporting the largest sample of patients in these cases).