What condition is indicated by a deep, wide Q wave?

A deep, wide Q wave is characteristic of myocardial infarction (MI) because it indicates prior damage to the myocardial tissue. During an MI, the area of the heart muscle that is deprived of adequate blood supply begins to necrose, leading to changes in the electrical activity of the heart. The deep Q wave appears when there is a significant loss of viable myocardial tissue, affecting the depolarization in the region of the heart that corresponds to the damaged area.

In the context of an ECG, these deep Q waves reflect the electrical differences between healthy tissue and the scarred tissue from the infarction. Over time, these Q waves become more prominent, distinguishing the event as a past myocardial infarction rather than a current issue.

Other conditions listed do not primarily lead to the presence of deep, wide Q waves: bundle branch blocks typically produce widened QRS complexes but not specific deep Q waves; atrial enlargement is identified by changes in the P wave rather than Q waves; and normal variants do not generally show such pronounced Q waves that signify myocardial damage. Therefore, the presence of a deep, wide Q wave is a definitive marker of a previous myocardial infarction.