What does a Q wave in the ECG signify?

A Q wave in the electrocardiogram (ECG) is significant because it indicates a previous myocardial infarction. This wave represents depolarization of the ventricles and can be a key marker in diagnosing infarction that has already occurred. When there has been damage to the heart muscle, specifically due to a lack of blood flow, the electrical activity displayed on the ECG may change.

In the case of a myocardial infarction, particularly a significant one where a part of the heart muscle has died, the initial electrical activity changes, leading to the presence of pathological Q waves. These Q waves become associated with this tissue necrosis. They typically appear as deeper and wider than normal, lasting over a prolonged period.

While ongoing myocardial ischemia, normal heart function, and electrical conduction abnormalities can cause changes in the ECG, they do not specifically denote the lasting effects of a heart attack that would produce a Q wave in the same manner as a previous myocardial infarction does. The presence of Q waves points to a past cardiac event rather than current issues or normal function.