The appearance of new Q waves, longer Q waves, or unusual Q waves in some of the leads may be a result of an MI. The clinician must consider the patient’s clinical presentation and history.

Patients in the acute stage of an MI have evolving ST elevation accompanied by chest pain and elevated cardiac markers such as serum troponins and creatine phosphokinase. Pathologic Q waves develop in the subacute stage of an MI. 

During the chronic MI stage, persistent Q waves appear, the ST segment normalizes, and symmetrical negative T waves appear. The Q wave in MI is indicative of myocardial tissue necrosis.

Variants of MI present without Q waves (termed non-Q wave infarctions).