UNRECOGNIZED MYOCARDIAL-INFARCTION - EPIDEMIOLOGY, CLINICAL CHARACTERISTICS, AND THE PROGNOSTIC ROLE OF ANGINA-PECTORIS - THE REYKJAVIK STUDY

Objective: To evaluate the incidence, prevalence, characteristics, and prognosis associated with clinically unrecognized myocardial infarcti on as diagnosed by electrocardiographic changes. Design: Prospective, population-based cohort study with 4- to 20-year follow-up. Setting: I celandic Heart Association Preventive Clinic. Participants: 9141 men r esiding in the Reykjavik area who were born between 1907 and 1934. Mea surements: Patients were assigned to categories of coronary heart dise ase at first visit on the basis of hospital records, Rose chest pain q uestionnaire, standardized 12-lead electrocardiogram, and history and physical examination. Incidence and prevalence of unrecognized myocard ial infarction were determined, survival was measured, and causes of d eath were determined from death certificates and autopsy records. Resu lts: Prevalence was strongly influenced by age. Nearly undetectable in the youngest age group, it increased to more than 5% in the group age d 75 to 79 years. Incidence was almost zero up to age 40, then increas ed steeply to more than 300 cases per year per 100 000 persons at age 60, and decreased with age after age 65. Ten- and 15-year survival pro babilities were 51% and 45%, respectively, and were similar to those f or patients with recognized myocardial infarction. One third of men wi th unrecognized and 58% of men with recognized myocardial infarction h ad a history of angina pectoris (P < 0.001). Angina pectoris had a gre ater effect on coronary heart disease mortality in the former group th an in the latter. The risk ratio for unrecognized myocardial infarctio n was 4.6 without angina (95% CI, 2.4 to 8.6) and 16.9 with angina (CI , 9.4 to 30.3); the risk ratio for recognized myocardial infarction wa s 6.3 without angina (CI, 3.7 to 10.6) and 8.5 with angina (CI, 5.8 to 12.6). Conclusion: At least one third of all myocardial infarctions w ere unrecognized. Prognosis and risk factor profiles for patients with recognized and unrecognized myocardial infarction were similar. Altho ugh those with unrecognized myocardial infarction were less likely tha n those with recognized myocardial infarction to have a history of ang ina pectoris, angina in these cases was usually associated with ischem ic electrocardiographic changes and a poor prognosis, suggesting sever e coronary heart disease.