Redefining myocardial infarction for the 21st century

World Congress of Cardiology Report - Progress in the identification and quantification of biochemical markers of myocardial injury have led to a redefinition of myocardial infarction (MI).

The World Health Organization previously defined acute MI as a combination of at least two of the following three components: symptoms consistent with an acute MI, ECG changes diagnostic of an acute MI, and a temporal pattern of enzyme rise and fall consistent with myocardial cell death. The enzyme that was employed in this traditional definition was creatine kinase (CK) and its MB subfraction.

Unfortunately, CK and CKMB measurements failed to identify a subgroup of patients with an acute coronary syndrome (ACS) who were at increased risk for morbidity and mortality. Troponins are molecules that are integral parts of the myocardial contractile machinery. An elevated blood troponin level has been shown to be a more specific and sensitive marker for myocardial injury than CK or CKMB. Indeed, blood troponin determinations can detect minute quantities of necrotic myocardium. Revision of the current WHO definition for acute myocardial infarction (AMI) occurred in 2001. This redefinition made blood troponin determination a critical component in the identification of myocardial cell death. The new definition of acute MI now includes patients with ACS and elevated blood troponin levels despite normal blood determinations for CK and CKMB. It is important to identify these patients because they experience a reduction in risk of morbidity and mortality with specific therapy. The clear association of troponin elevation with increased mortality along with the availability of therapy that diminishes this risk has led to the current redefinition of acute myocardial infarction. The new definition identifies this previously unidentified and undertreated high risk population.

This original redefinition report, published simultaneously in the European Heart Journal and Journal of the American College of Cardiology in 2000, reviewed the reasoning and the data that led to the redefinition of acute MI. Since previously unidentified, small myocardial infarcts are now being detected, the new definition of MI has many implications including changes in therapy, epidemiology, and public policy. New research, performed over the last 6 years has made it imperative to update the redefinition of MI. An international task force has been working on this "redefinition of the redefinition" for the last three years. The final report from this task force is being assembled at the current ESC meeting in Barcelona in September, 2006. The report will be published during 2007.