Background: The purpose of this study is to investigate the impact of oxygen therapy on cardiovascular outcomes in relation to sex in patients with confirmed myocardial infarction (MI).

Methods: The DETermination of the role of Oxygen in suspected Acute Myocardial Infarction trial randomized 6,629 patients to oxygen at 6 L/min for 6-12 hours or ambient air. In the present subgroup analysis including 5,010 patients (1,388 women and 3,622 men) with confirmed MI, we report the effect of supplemental oxygen on the composite of all-cause death, rehospitalization with MI, or heart failure at long-term follow-up, stratified according to sex.

Results: Event rate for the composite endpoint was 18.1% in women allocated to oxygen, compared to 21.4% in women allocated to ambient air (hazard ratio [HR] 0.83, 95% confidence interval [CI] 0.65-1.05). In men, the incidence was 13.6% in patients allocated to oxygen compared to 13.3% in patients allocated to ambient air (HR 1.03, 95% CI 0.86-1.23). No significant interaction in relation to sex was found (P=.16). Irrespective of allocated treatment, the composite endpoint occurred more often in women compared to men (19.7 vs 13.4%, HR 1.51; 95% CI, 1.30-1.75). After adjustment for age alone, there was no difference between the sexes (HR 1.06, 95% CI 0.91-1.24), which remained consistent after multivariate adjustment.

Conclusion: Oxygen therapy in normoxemic MI patients did not significantly affect all-cause mortality or rehospitalization for MI or heart failure in women or men. The observed worse outcome in women was explained by differences in baseline characteristics, especially age