β blockers after myocardial infarction with mildly reduced ejection fraction: an individual patient data meta-analysis of randomised controlled trials.

Background: The effects of β-blocker therapy on clinical outcomes in patients with myocardial infarction and mildly reduced (40-49%) left ventricular ejection fraction (LVEF) are largely unknown. Four recently conducted randomised trials tested the efficacy of β blockers after a recent myocardial infarction in patients without reduced LVEF (LVEF ≥40%). However, none were individually powered to assess these effects in the subgroup of patients with mildly reduced LVEF. We aimed to assess the efficacy of β blockers in patients with myocardial infarction and mildly reduced LVEF during the index hospitalisation.

Methods: We conducted an individual patient-level meta-analysis of patients with mildly reduced LVEF and no history or signs of heart failure from four recent clinical trials. These studies were included because they were randomised controlled trials testing long-term effects (median follow-up >1 year) of oral β-blocker therapy in patients who recently had a myocardial infarction (randomisation within 14 days) and had mildly reduced LVEF. No further studies were found in a systematic review (Jan 1, 2020 to June 26, 2025). A one-stage, fixed-effects, Cox proportional hazards regression model was used to assess the treatment effect of β blockers on the predefined primary composite endpoint of all-cause death, new myocardial infarction, or heart failure. All endpoints were independently adjudicated. This meta-analysis was registered with PROSPERO (CRD420251023480).

Findings: 1885 patients with myocardial infarction and mildly reduced LVEF were included in the meta-analysis: 979 from the REBOOT trial, 422 from the BETAMI trial, 430 from the DANBLOCK trial, and 54 from the CAPITAL-RCT trial. Overall, 991 patients were assigned to β blockers and 894 to control (no β blockers). The primary composite endpoint occurred in 106 patients (32·6 events per 1000 patient-years) in the β-blocker group and 129 patients (43·0 per 1000 patient-years) in the no β-blocker group (hazard ratio 0·75 [95% CI 0·58-0·97]; p=0·031). No heterogeneity between the trials (trial-by-treatment p=0·95) or between countries of enrolment was observed (p=0·98).

Interpretation: In patients with acute myocardial infarction with mildly reduced LVEF without history or clinical signs of heart failure, β-blocker therapy was associated with a reduction in the composite of all-cause death, new myocardial infarction, or heart failure. These results extend the known benefits of these agents in patients with myocardial infarction with reduced LVEF to the subgroup with mildly reduced LVEF.

Funding: Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Danish Heart Foundation, Novo Nordisk Foundation, South-Eastern Norway Regional Health Authority, and Research Council of Norway.