New definition of MI lacks evidence base

The European Society of Cardiology (ESC) and American College of Cardiology (ACC) have proposed a new definition of MI, which differs substantially from the widely used WHO definition and hinges on increased troponin concentration as a marker for MI.

Now an editorial cautions against relying too much on this marker without knowing the value of troponins across the entire range of acute coronary disease. “There is little justification for adopting at face value the holistic approach suggested by the joint ESC/ACC document, at least not immediately.” MI should continue to be diagnosed as before, until enough evidence becomes available from clinical trials, the editorial recommends.

Under the new definition, unstable angina as previously defined would become MI, with important consequences for epidemiology, patients, and resources. At a practical level troponin assays have not been tested for their robustness, their reproducibility over time is uncertain, and they need to be standardised. Also their cost effectiveness should be compared with that for standard assays for other biochemical markers such as creatine kinase.

Troponins have come to the fore in diagnosing MI because of new terminology for acute coronary syndromes, in which acute Q wave MI is added alongside non-Q wave MI and unstable angina, and management is based on ECG and biochemical markers—especially troponins—at presentation. Troponin concentration is currently used to identify non-ST segment MI from an atypical clinical picture with no acute ECG changes or unstable angina if acute ischaemia is present.

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