Myocardial infarction

Definition

Death (necrosis) of myocardial cells caused by prolonged ischemia. The Fourth Universal Definition requires a rise and/or fall of cardiac troponin with at least one value above the 99th-percentile upper reference limit plus at least one sign of acute ischemia (symptoms, new ischemic ECG changes, new pathologic Q waves, imaging evidence of new loss of viable myocardium or a new regional wall-motion abnormality, or coronary thrombus on angiography or autopsy). On the ECG, acute infarction shows evolving ST-T changes, and a prior infarction may leave pathologic Q waves (any Q wave of at least 20 ms in V2 or V3, or a QS complex in both V2 and V3; or a Q wave at least 30 ms wide and at least 1 mm deep, or a QS complex, in leads I, II, aVL, aVF or V4 to V6 in two leads of a contiguous group: I and aVL; II, III and aVF; V1 to V6). Q waves are not always permanent: after a more localized infarction they can disappear as the scar contracts. Infarctions are classified into types 1 to 5 (type 4 has subtypes) on pathological, clinical and prognostic grounds.