What is the contemporary definition of myocardial infarction?
For many years, the diagnosis of acute MI relied on the revised criteria established by the World Health Organization (WHO) in 1979. Two of these criteria were required for diagnosis of an acute STEMI:
- Chest discomfort characteristic of ischemia
- Typical ECG pattern including the development of Q waves
- Typical elevations in serum markers of myocardial injury, usually creatine kinase (CK)-MB
Patients with typical chest pain, no evidence of ST elevation or Q waves, and elevated CK-MB would have an NSTEMI. In comparison, patients with an unstable pattern of chest pain, possible ECG changes of ischemia but no ST elevation or Q waves, and normal CK-MB would have UA.
However, this definition of MI is too restrictive. Many patients with an acute MI have no recognizable symptoms, a substantial number have an ECG that reveals only nonspecific changes or may even be normal, and some patients have normal serum CK-MB but elevated troponins. According to the WHO criteria above, a patient with ischemic symptoms, no ST elevation, and a normal serum CK-MB but elevated serum troponins would be considered to have UA.
As a result of these limitations, a joint European Society of Cardiology (ESC) and American College of Cardiology (ACC) committee proposed the following definition of an acute, evolving, or recent MI in 2000: Typical rise and gradual fall (troponin) or more rapid rise and fall (CK-MB) of biochemical markers of myocardial necrosis with at least one of the following:
- Ischemic symptoms
- Development of pathologic Q waves on the ECG
- ECG changes indicative of ischemia (ST segment elevation or depression)
- Coronary artery intervention (eg, angioplasty)