Sex differences in mortality after myocardial infarction - Evidence for a sex-age interaction

Background: Studies of sex differences in mortality after myocardial infarction (MI) have shown conflicting results. Objectives: To test the hypothesis that sex differences in mortality after MI vary according to patients' age, with younger women, but not older women, having a higher mortality compared with men. Methods: We performed a retrospective cohort study of 1025 consecutive patients who met accepted criteria for MT in 1992 and 1993 in 15 Connecticut hospitals. Data for the study were abstracted from medical records. Results: Women had a 40% higher hospital mortality rate than men. Simple age adjustment eliminated the sex difference in mortality rate (odds ratio, 0.99; 95% confidence interval, 0.66-1.48). However, when the sample was subdivided into 2 age groups, women younger than 75 years showed twice as high a mortality rate as men in the same age group, while among older patients no difference in mortality was found. In multivariate analyses the interaction of sex with age was highly significant, even after adjusting for comorbid conditions, clinical severity, process of care, and hospital characteristics. In the fully adjusted model, this interaction indicated that among patients younger than 75 years women had 49% higher odds of hospital death than men, while in the age group 75 years or older women had 46% lower odds of death compared with men. Conclusions: A higher mortality of women compared with men after MI is confined to the younger age groups. The sex-age interaction should be considered when examining sex differences in mortality after MI.