[Marked increase of the number of myocardial infarctions following introduction of the new diagnostic criteria]

Abstract

Background: Hospital admissions for acute myocardial infarction (AMI) declined in Norway during the 1990s. Recently, clinical guidelines for diagnosing AMI have been changed. We wanted to investigate whether this change might have influenced the number of patients hospitalised for AMI.

Material and methods: Data on all AMI admissions from 1991 to 2002 were provided by the Norwegian Patient Register and analysed by gender and by age. Particular emphasis was given to the analysis of change over the last three years.

Results: From 1991 to 2000, the numbers of hospital admissions for AMI (ICD-9 410 and ICD-10 I21/I22) declined by 18%, from 14 457 to 11 892. The reduction was stronger in men (20%) than in women (14%). At the same time striking age differences occurred with a decrease among people below 80 years of age (29%) and an increase among those older than 80 (25%). There was, however, a shift in the downward trend in numbers of AMIs in 2000. From 2000 to 2002, AMI admissions were up from 11 892 to 15 829 (33%).

Interpretation: The striking change in the age distribution among AMI patients could be attributed to a lower incidence in the younger age groups over the last decades, which might have deferred AMIs to older age groups. The increase in AMI numbers from 2000 to 2002 is probably due to the introduction of new diagnostic guidelines and not to a higher real incidence. Application of troponins for the diagnosis of AMI has probably shifted patients previously diagnosed with unstable angina pectoris to the AMI diagnosis.