International Cardiology Societies Collaborate on New MI Definition

A new universal definition of myocardial infarction (MI) was unveiled at the European Society of Cardiology meeting in Munich. The document was developed jointly by the European Society of Cardiology (ESC), the American College of Cardiology Foundation (ACCF), the American Heart Association (AHA), and the World Heart Federation (WHF).

The definition establishes the troponin levels required to make a diagnosis of MI in various situations. Here is a summary from a fact sheet published by the AHA:

The preferred biomarker overall and for each specific category of MI is cardiac troponin (cTn) (I or T), which has high myocardial tissue specificity as well as high clinical sensitivity. An increased cTn concentration is defined as a value exceeding the 99th percentile of a normal reference population (upper reference limit, URL).

Myocardial infarction is determined by the specified cTn value, and at least one of the five following diagnostic criteria:

1. Symptoms of ischemia

2. New (or presumably new) significant ST-T wave changes or left bundle branch block

3. Development of pathological Q waves on electrocardiogram (ECG)

4. Imaging evidence of new loss of viable myocardium or regional wall-motion abnormality

5. Identification of intracoronary thrombus by angiography or autopsy

Comment: The diagnosis of myocardial infarction should be made when the clinical setting suggests ischemia and testing reveals a rising and/or falling pattern of biomarkers with at least one value above the 99th percentile of the upper reference limit. This value is different for each assay, so clinicians need to know which assays are in use at the sites in which they are practicing. Defining a changing pattern is also assay-dependent and can be challenging; it can easily be accomplished, however, with the help of laboratory professionals who can calculate the difference necessary to establish that a change is not a variation in the measure itself. In some populations — such as the elderly, individuals with diabetes, and those who have just undergone surgery — presentation of MI can be atypical, so clinical judgment is necessary.

Several types of MI are defined:

• In type 1, or spontaneous MI, plaque rupture is the presumed etiology of the MI.

• Type 2 MI events are caused by supply–demand imbalance, which can be associated with all of the above clinical findings and can be present with or without coronary artery disease.

• Type 3 MI is when death occurs before biomarker values can be obtained or before a rising pattern can be established.

• Type 4a MI occurs after percutaneous coronary intervention (PCI) and requires a normal baseline biomarker value (<99th percentile URL) or a documented stable or declining set of values prior to the PCI. If the baseline value is normal, the diagnosis requires a 5-fold elevation in biomarkers, along with either symptoms or angiographic complications. If baseline values are stable or declining, a >20% increase (as with reinfarction) is required, again with the requisite signs and/or symptoms.

• Type 4b MI refers to infarction with stent restenosis and uses the criteria for types 1 and 2.

• Type 5 MI occurs after coronary artery bypass grafting and requires a 10-fold increase in biomarkers and ECG or imaging evidence of an event.

We acknowledge that heart failure and a variety of other situations may lead to increases in cardiac troponin levels. Some of these may be type 2 or even type 1 MIs, but all such elevations need not lead to an MI diagnosis. In the absence of supporting criteria for MI, a designation of cardiac injury is reasonable.