What does ST-segment depression on an electrocardiogram (ECG) indicate?

An electrocardiogram (ECG or EKG) is a commonly used test that records the heart’s electrical activity to assess cardiac function and diagnose heart disease. The ST segment on an ECG refers to the interval between the QRS complex—which represents ventricular myocyte depolarization—and the T wave—which represents ventricular myocyte repolarization. Under normal conditions, the ST segment should be parallel to and relatively flat along the baseline. ST-segment depression refers to a downward deviation of the ST segment below the baseline following the QRS complex, which may indicate inadequate blood supply to certain regions of the heart. ST-segment depression can result from various conditions, including myocardial ischemia (e.g., coronary artery disease), myocardial infarction, pericarditis, subendocardial myocardial injury, electrolyte imbalances (e.g., hypokalemia or hypocalcemia), and drug side effects. The clinical significance of ST-segment depression must be evaluated comprehensively in conjunction with the patient’s specific symptoms and other diagnostic findings; further diagnostic evaluation and treatment may be warranted.