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A New Definition of Myocardial Infarction

The revised criteria for diagnosing myocardial infarction, based on elevated troponin levels, increased the number of diagnoses among patients with suspected acute coronary syndromes without missing any cases diagnosed by the old criteria.

The gold standard for diagnosing myocardial infarction has been the World Health Organization definition, which requires any 2 of 3 criteria: ischemic symptoms, electrocardiographic changes, and elevated creatine kinase-MB levels. Recently, the American College of Cardiology and the European Society of Cardiology published a new definition that for the first time includes elevated troponin levels. (See Eur Heart J 2000; 21:1502.) The new criteria are elevated troponin or CK-MB levels and either ischemic symptoms or electrocardiographic changes. These authors evaluated the clinical implications of the new definition.

In a study of 493 patients with suspected acute coronary syndromes, patients with ischemic symptoms and elevated cardiac enzymes (none had electrocardiographic changes) were classified into 2 groups: those with elevated CK-MB levels, with or without elevated troponin levels (the WHO-criteria group), and those with elevated troponin levels but normal CK-MB levels (the troponins-only group). Using the new criteria, 51 additional cases of acute MI were diagnosed, and none of the 224 cases detected by the WHO criteria were missed. Mortality at 6 months was higher in the troponins-only group (consistent with findings in the GUSTO IIa trial), but this difference was due to higher rates of comorbidities in that group. Patients in the troponins-only group were older and more often female. The authors posit that more aggressive treatment of patients who would have been diagnosed with unstable angina by the WHO criteria but meet the new definition for acute MI may improve outcomes.

Comment: This new definition of MI based on elevated troponin levels threatens to retire CK-MB levels, the longtime standard, to the historical junkyard along with serum glutamate oxaloacetate transaminase and lactate dehydrogenase. Stay tuned.

— J. Stephen Bohan, MS, MD, FACP, FACEP

Published in Journal Watch Emergency Medicine September 25, 2002

Citation(s):

Meier MA et al. The new definition of myocardial infarction: Diagnostic and prognostic implications in patients with acute coronary syndromes. Arch Intern Med 2002 Jul 22; 162:1585-9.

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