Trends in the incidence of acute myocardial infarction between 1984 and 1993 - The Halifax County MONICA Project

BACKGROUND: According to vital statistics data for Halifax County, between 1984 and 1993 the annual mortality rate decreased for ischemic heart diseas e and myocardial infarction (MI). OBJECTIVES: To estimate the change in MI mortality, applying standardized d iagnostic criteria; to determine whether decreased case fatality or decreas ed MI event rate, or both, caused decreased mortality; and to determine the contribution of MI incidence rate to altered event rate. PATIENTS AND METHODS: All persons in the study area aged 25 to 74 years and admitted to hospital or dying outside hospital with suspected acute corona ry syndromes were registered prospectively. Demographic, health history and clinical data were extracted from medical records or collected from medica l examiner reports, next-of-kin interviews or family physicians. Definite o r possible MI was diagnosed according to World Health Organization MONItori ng of trends and determinants in CArdiovascular disease (MONICA) criteria. Trends in age- and sex-standardized rates were estimated by using log-linea r regression analysis. RESULTS: Of 4283 patients admitted to hospital for MI, 23.9% died within 28 days; 1401 patients who had suffered an MI died before admission to hospit al. MI mortality decreased annually by 3.9% (95% CI 1.9 to 5.8); two-thirds of the decline was due to MI event rates (2.6%; CI 1.3 to 3.8) and one-thi rd to a decrease in 28-day case fatality (1.3%; CI 0.2 to 2.3). A decrease in MI incidence rate (3.2%; CI 1.7 to 4.8), rather than a decline in MI rec urrence rate (1.4%; CI 0.7 to -3.5), was the major reason for the declining event rate. CONCLUSIONS: A decrease in the Incidence of MI, possibly due to primary pre vention, had a major impact on the declining MI mortality. Decreased in-hos pital MI fatality, possibly due to improved treatment, was responsible for the decline in case fatality.