Secular trends and seasonality in first-time hospitalization for acute myocardial infarction—a Danish population-based study

Background: The incidence of acute myocardial infarction has declined in several Western countries during the last decades. The incidence and mortality of acute myocardial infarction follow a seasonal pattern. We examined if changes in the incidence of acute myocardial infarction were associated with any changes in seasonality. Methods: The study was based on 17,989 patients hospitalized with first-time acute myocardial infarction identified in the Hospital Discharge Registry of the County of North Jutland, Denmark, from 1 January 1983 to 31 December 1999. The seasonality of acute myocardial infarction was estimated using a Poisson regression model. Results: The incidence rate decreased by 3.2% (95% confidence interval: 2.7–3.3%) annually. Hospitalizations followed different seasonal patterns depending on age, but not on gender. In the <59-year-old group, the seasonal pattern was dominated by a broad spring peak (April/May) and a minor autumn peak. With increasing age, the spring peak decreased while the autumn peak increased and moved towards December. A seasonal pattern dominated by one peak (December) and one trough (August) was found in the ≥80-year-old category. The shape and extent of these seasonal patterns remained stable throughout the study period despite the decline in hospitalizations for acute myocardial infarction. Conclusion: Hospitalizations for first-time acute myocardial infarction decreased from 1983 to 1999, but the seasonal pattern remained stable over time.