What does the electrocardiogram show in unstable angina?

In unstable angina, the electrocardiogram often reveals ST segment depression and T wave inversion. These changes occur due to myocardial ischemia, which indicates that the heart muscle is not receiving enough oxygenated blood, typically caused by transient episodes of incomplete obstruction of the coronary arteries.

During these episodes, patients may experience chest pain or discomfort, and the ECG changes reflect the heart’s response to the stress of ischemia. ST segment depression occurs when the repolarization of the ventricles is altered due to reduced blood flow, while T wave inversion indicates that the heart muscle is under stress.

While some patients with unstable angina might have a normal ECG, the presence of ST segment depression and T wave inversions is characteristic and clinically relevant, as it helps differentiate unstable angina from stable angina and myocardial infarction. In contrast, ST elevation typically indicates myocardial infarction, while normal findings or no changes would not signify the ischemic nature of unstable angina.