Table 1 World Health Organization criteria^* for diagnosis of definite acute MI, possible acute MI or old MI

History

The history is typical if severe, prolonged chest pain is present. Sometimes the history is atypical, and the pain may

be mild or even absent, or other symptoms may be predominant

Electrocardiography (ECG)

Unequivocal changes in ECG are the development of abnormal, persistent Q or QS waves, and evolving injury

current lasting longer than 1 day. When the ECG shows these unequivocal changes, the diagnosis may be made

on the basis of ECG alone. In other cases the ECG may show equivocal changes, consisting of a stationary injury

current, a symmetrical inversion of the T-wave, a pathological Q-wave in a single ECG record, or conduction

disturbances

Serum enzymes

Unequivocal changes consist of serial change, or initial rise and subsequent fall of the serum level. The change

must be properly related to the particular enzyme, and to the delay time between onset of symptoms and blood

sampling. Elevation in cardio-specific isoenzymes is also considered unequivocal change. Equivocal change

consists of an enzyme pattern in which an initially elevated level is not accompanied by a subsequent fall - the

curve of enzyme activity is not obtained