During which EKG phase does myocardial ischemia typically occur?

Myocardial ischemia is a condition where there is a decrease in blood flow to the heart muscle, often resulting from coronary artery disease or other factors. It typically manifests in specific changes on an electrocardiogram (EKG).

The ST segment is particularly significant in the assessment of myocardial ischemia. Under normal circumstances, the ST segment is isoelectric—meaning it is flat and does not deviate from the baseline. However, during episodes of ischemia, the ST segment can become elevated or depressed. Elevated ST segment often indicates a condition known as ST-Elevation Myocardial Infarction (STEMI), while a depressed ST segment can suggest subendocardial ischemia, which is less severe but still indicative of inadequate blood supply to the myocardium.

In contrast, the P wave reflects atrial depolarization, which is not directly involved in ischemia; the QRS complex represents ventricular depolarization and does not primarily show ischemic changes unless there is significant myocardial damage; and the T wave reflects ventricular repolarization. While T wave changes can also indicate ischemia, the ST segment is the most recognized phase for identifying myocardial ischemia on an EKG.

Thus, the ST segment is the critical moment when