Incidence and prevalence of recognised and unrecognised myocardial infarction in women. The Reykjavik Study

AIMS: The incidence and prevalence of recognised and unrecognised myocardial infarction were determined in the Icelandic cohort study of 13,000 women (the Reykjavik Study), followed for up to 29 years (mean 15 years). METHODS AND RESULTS: Women attending the Reykjavik Study, born between 1908 and 1935, were examined in five stages from 1968 to 1991. A health survey included history and ECG manifestations of coronary heart disease. Data retrieved from hospitals, autopsy records and death certificates identified 596 fatal and non-fatal myocardial infarctions to the end of 1992 (61 prior to examination, 320 non-fatal and 215 fatal). The incidence of recognised myocardial infarction ranged from 22 cases/100,000/year at 35-39 years to 1800 cases/100,000/year at 75-79 years. The incidence of unrecognised myocardial infarction ranged from 18 cases/100,000/year at 35 years to 219 cases/100,000/year at 75 years. Thirty-three percent of non-fatal myocardial infarctions were unrecognised. More occurred in the younger age groups (40%) than in the older (27%). The prevalence of recognised myocardial infarction was influenced by age and calendar year. In 1990, it was 1.3/1,000 at 35 years and 60/1000 at 75 years. Prevalence showed a time trend, tripling in all age groups from 1968-1992. Fore unrecognised myocardial infarction, prevalence rose from 0.9/1000 at 35 years to 19.2/1000 at 75 years, although there was no evident time trend. CONCLUSION: Myocardial infarction in women is very age-dependent with both incidence and prevalence increasing continuously and steeply with age. There was a significant trend for an increase in prevalence of recognised myocardial infarction from 1968 to 1992. The proportion of unrecognised non-fatal infarctions ranged from 27% in the oldest age group to 40% in the youngest. On average, this form of coronary heart disease is as common as in men.