ABSTRACT
Q waves are usually absent from most of the leads of a normal electrocardiogram (ECG). Q waves start to appear within a few hours of the onset of ST segment elevation myocardial infarction and in 90 per cent of cases become permanent. The presence of Q waves alone therefore gives no clue about the timing of the infarction. The diagnosis of acute myocardial infarction is usually apparent from the presenting symptoms and ECG changes that are present, and can be confirmed by serial cardiac marker measurements. Q waves can be a normal finding and result from depolarization of the interventricular septum. If the septum hypertrophies, its muscle mass increases, and the Q waves become deeper. Left ventricular hypertrophy often involves the septum, and so deep Q waves are often seen in leads looking at the left and inferior surfaces of the heart.
