25 year trends in first time hospitalisation for acute myocardial infarction, subsequent short and long term mortality, and the prognostic impact of sex and comorbidity: a Danish nationwide cohort study

OBJECTIVES: To examine 25 year trends in first time hospitalisation for acute myocardial infarction in Denmark, subsequent short and long term mortality, and the prognostic impact of sex and comorbidity. DESIGN: Nationwide population based cohort study using medical registries. SETTING: All hospitals in Denmark. SUBJECTS: 234,331 patients with a first time hospitalisation for myocardial infarction from 1984 through 2008. MAIN OUTCOME MEASURES: Standardised incidence rate of myocardial infarction and 30 day and 31-365 day mortality by sex. Comorbidity categories were defined as normal, moderate, severe, and very severe according to the Charlson comorbidity index, and were compared by means of mortality rate ratios based on Cox regression. RESULTS: The standardised incidence rate per 100,000 people decreased in the 25 year period by 37% for women (from 209 to 131) and by 48% for men (from 410 to 213). The 30 day, 31-365 day, and one year mortality declined from 31.4%, 15.6%, and 42.1% in 1984-8 to 14.8%, 11.1%, and 24.2% in 2004-8, respectively. After adjustment for age at time of myocardial infarction, men and women had the same one year risk of dying. The mortality reduction was independent of comorbidity category. Comparing patients with very severe versus normal comorbidity during 2004-8, the mortality rate ratio, adjusted for age and sex, was 1.96 (95% CI 1.83 to 2.11) within 30 days and 3.89 (3.58 to 4.24) within 31-365 days. CONCLUSIONS: The rate of first time hospitalisation for myocardial infarction and subsequent short term mortality both declined by nearly half between 1984 and 2008. The reduction in mortality occurred for all patients, independent of sex and comorbidity. However, comorbidity burden was a strong prognostic factor for short and long term mortality, while sex was not.