A national record linkage to study acute myocardial infarction incidence and case fatality in Sweden

BACKGROUND: During the last decades substantial temporal changes, as well as population differences, in coronary heart disease mortality have occurred in Sweden. There is little information to what extent these changes and differences also apply to myocardial infarction incidence. The aim of this paper was to describe the methods used to identify cases in a recently developed National Acute Myocardial Infarction Register in Sweden, and to present estimates of incidence and case fatality in Sweden. MATERIAL AND METHODS: Incident cases of acute myocardial infarction (AMI) were identified by record linkage of routinely collected data on hospital discharges and deaths. Case fatality within 28 days was ascertained by linkage of incident cases to the National Cause of Death Register. RESULTS: About 40 000 new cases of AMI per year were recorded in Sweden during 1987-1995. Well-known differences in incidence with regard to age and gender were observed, as well as a decline in incidence between 1987 and 1995. A similar case fatality was seen in men and women aged 30-89 among hospitalized cases. When fatal cases outside hospital were also considered the case fatality was somewhat higher in men. Examination of medical records for a national sample of ischaemic heart disease patients suggested a high sensitivity (94%) and a high positive predictive value (86%) for ICD-9 code 410 in hospital discharge data with regard to definite AMI. CONCLUSIONS: The National Acute Myocardial Infarction Register offers a new possibility to study the incidence of AMI, as well as case fatality, in Sweden.