A new definition for myocardial infarction: what difference does it make?

As a response to changing diagnostic tools of myocardial infarction (MI), new case definitions for acute coronary events were published in 2003 as the American Heart Association Scientific Statement. We assessed the new definition in hospitalized patients in a large population-based MI register study.We identified all suspected acute coronary syndromes with data either on troponin T or on troponin I and at least one of the enzymatic markers of myocardial injury (n=6104). The 2003 definition with the use of troponins identified 83% more definite MIs than the WHO MONICA definition using cardiac enzymes. The additional patients were older, had more often diabetes, and received less often thrombolysis and revascularization than those having MI by both definitions. Adjusting for age, sex, study area, and study year, the additional patients with their first MI aged 25-74 had a higher risk of cardiovascular death within 1 year than patients having definite MI by both definitions (hazard ratio 1.6, 95% CI 1.1-2.2).The changing diagnostic criteria present a considerable challenge for the assessment of long-term trends in MI events in the community as well as for longitudinal studies of the natural history of MI. The 2003 definition, when applied using troponins, identified a sizable new group of MI patients, among persons with suspected acute coronary syndrome, at high risk of a recurrent event.