(Circulation. 2000;102:e9023.)
© 2000 American Heart Association, Inc.
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Cardiovascular News
Myocardial Infarction Redefined
If the recommendations of a new consensus document1 are accepted, the world will see an increase in the recorded incidence of myocardial infarction (MI) but a fall in the case fatality rate. Declaring the World Health Organization’s definition of MI outmoded, a joint committee of the European Society of Cardiology and the American College of Cardiology has produced new criteria that depend heavily on biochemical markers, specifically, the cardiac troponins. The most striking proposal is that any myocardial necrosis due to ischemia, however small, will be labeled as MI. Troponins can detect an area of necrosis weighing as little as 1 g. The new definition follows.
Criteria for acute, evolving, or recent MI
- A typical rise and gradual fall (troponin) or more rapid rise and fall
(creatine kinase [CK]-MB) of biochemical markers of myocardial
necrosis with
1 of the following:
- Ischemic symptoms
- Development of pathological Q waves on the ECG
- ECG changes indicative of ischemia (ST segment elevation or
depression)
- Coronary artery intervention (eg, coronary
angioplasty)
- Pathological findings of an acute MI
Criteria for established MI
- The development of new pathological Q waves on serial ECGs.
The patient may or may not remember previous symptoms. Biochemical
markers of myocardial necrosis may have normalized, depending on the
length of time that has passed since the infarct developed.
- Pathological findings of a healed or healing MI.
Announcing the document on August 28, 2000, at the 22nd Congress of the European Society of Cardiology in Amsterdam, Dr J.S. Alpert of Tucson, Ariz, and Dr K. Thygesen of Aarhus, Denmark said that the committee had looked at the implications of a new definition from 7 points of view: pathology, electrocardiography, imaging, clinical trials, biochemistry, epidemiology, and public policy. However, the focus is on biochemistry. An increased cardiac troponin is defined as a value exceeding the 99th percentile of a reference control group, which should be determined by laboratories in their particular settings. If cardiac troponin assays are not available, the best alternative is CK-MB (measured by mass assay), with a raised value again being one that exceeds the 99th percentile. For most patients, blood should be obtained for testing on admission and 6 to 9 hours later. For patients in need of an early diagnosis, the committee recommends a rapidly appearing biomarker, such as CK-MB isoforms or myoglobin, along with one that rises later (such as a troponin).
The revised definition, if accepted, will have at least 2 important consequences. First, because of the high sensitivity of troponins, more people will acquire a label of MI. The committee regards this as a beneficial development, because even a small amount of myocardial necrosis (reflected by a troponin "blip" without elevation of other markers) signifies a worse long-term outcome, and diagnosis allows secondary prevention. The downside is that the MI label can damage a patient’s personal life, for example, by making life insurance or a pilot’s license hard to obtain or by interrupting a career. The new definition will cover a range of events, from minor cell injury caused by the release of emboli during angioplasty ("infarctlet," "necrosette") to the full-blown MI syndrome with shock and heart failure. The committee therefore declares that the term MI must always be qualified by additional descriptors, including size, residual left ventricular function, and whether the infarct developed spontaneously or in relation to a diagnostic or therapeutic procedure.
The second implication is for disease monitoring. Clearly, a new definition will present difficulties for those assessing the impact of public health measures and treatments; the committee therefore proposes that certain epidemiological centers should continue to use the established definitions of MI (such as the World Health Organization criteria or the Minnesota code) and to measure older biomarkers, such as aspartate aminotransferase and total CK, while at the same time applying the new definition based on troponins and CK-MB; the new criteria might then be reconciled with the old.
References
1. Myocardial infarction redefined: a consensus document of the Joint European Society of Cardiology/American College of Cardiology Committee for the Redefinition of Myocardial Infarction. Eur J Cardiol. and J Am Coll Cardiol. In press. Available at: www.acc.org and www.escardio.org
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