New definition of MI released

A consensus document from several cardiology organizations recently provided new official definitions of myocardial infarction (MI).

The definition, which was the third one released since 2000, was developed by an expert task force from the European Society of Cardiology, American College of Cardiology Foundation, American Heart Association, Inc., and the World Heart Federation. It defined acute MI by the following criteria:

• A change in cardiac biomarkers (preferably cardiac troponin) with at least one value above the 99th percentile upper reference limit, and one of the following:

1. symptoms of ischemia,
2. new significant ST-segment-T wave changes or left bundle-branch block (LBBB),
3. pathological Q waves on an electrocardiogram (ECG),
4. imaging evidence of new loss of viable myocardium or regional wall motion abnormality, and/or
5. intracoronary thrombus identified by angiography or autopsy.

• In cases where cardiac death occurs before biomarkers can be obtained or would have increased, MI is defined by ischemia symptoms and new ECG changes or new LBBB.

The new definition was developed to account for increasingly more sensitive biomarkers and imaging techniques, as well as new management techniques that result in less cardiac damage, the task force said. They noted that it's also important to characterize the type of MI.

Percutaneous coronary intervention-related MI is defined, in patients with normal baseline troponin, as elevation >5 × 99th percentile. If the baseline troponin value was elevated, it is defined as a rise of more than 20%. In addition, in all patients, one of the following should be present: ischemic symptoms, ischemic ECG changes, angiographic findings consistent with a procedural complication, or imaging evidence of new loss of viable myocardium or regional wall motion abnormality.

Coronary artery bypass grafting-related MI is defined, in patients with normal baseline troponin, as elevation >10 × 99th percentile. In addition, one of the following should be present: new pathological Q waves or new LBBB, angiographic evidence of new graft or new native coronary artery occlusion, or imaging evidence of new loss of viable myocardium or regional wall motion abnormality.

Prior myocardial infarction is defined by any one of the following:

• pathological Q waves with or without symptoms, in the absence of non-ischemic causes,
• imaging evidence of a region of lost viable myocardium that is thinned and fails to contract, in the absence of a non-ischemic cause, or
• pathological findings of a prior MI.

The consensus document was published online by the European Heart Journalon Aug. 24.