Abstract Body (Do not enter title and authors here): Background
Guidelines recommend the use of beta-blockers (BB) in patients with acute myocardial infarction (MI) and reduced left ventricular ejection fraction (LVEF). However, recent randomized trials have reported no benefit from BB use in acute MI patients with preserved LVEF. Yet, studies on the use of BB in acute MI patients with an LVEF of 40% to 50% are limited.

Methods
A total of 3,966 acute MI patients were enrolled from the Korean Acute Myocardial Infarction Registry-V (KAMIR-V) between January 2016 and June 2020, whose LVEF ranged between 40% and 50%. Patients were divided into two groups based on BB use, and propensity score matching (PSM) was applied. The primary endpoint was all-cause death, while secondary endpoints included cardiac death, non-cardiac death, recurrent MI, and hospitalization for heart failure.

Results
Among the 3,966 patients with acute MI and mildly reduced LVEF, 819 were not using BB, and 3,147 were using BB. After 1:2 PSM, 819 patients not using BB and 1,638 patients using BB were analyzed. Baseline characteristics were well balanced between the two groups after PSM. For the primary endpoint, the BB group showed a significantly lower occurrence compared to the non-BB group after PSM (2.7% vs. 3.5%, Hazard Ratio [HR] 0.55, 95% Confidence Interval [CI], 0.33 to 0.90; P=0.02). Regarding secondary endpoints, the BB group exhibited a significantly lower rate of cardiac death (1.5% vs. 2.2%, HR 0.38, 95% CI, 0.19 to 0.76; P=0.01). However, no difference was observed between the two groups in terms of recurrent MI and hospitalization for heart failure.

Conclusion
The use of BB in patients with acute MI and mildly reduced LVEF demonstrated a reduction in mortality. Further randomized controlled trials are needed.