What is a sign of subendocardial ischemia on an ECG?

Subendocardial ischemia on an ECG is typically characterized by ST segment depression. This reflects a reduction in blood flow and oxygen supply to the inner layer of the heart wall, which is particularly sensitive to ischemic conditions. When myocardial cells experience this lack of oxygen, they struggle to repolarize properly, leading to a downward shift in the ST segment.

In contrast, ST segment elevation is more commonly associated with transmural ischemia, where the ischemic damage extends through the entire heart wall. QT interval prolongation and QRS complex widening are indicators of different cardiac issues, such as electrolyte imbalances or conduction abnormalities, rather than directly representing ischemic changes. Thus, recognizing ST segment depression is crucial for identifying subendocardial ischemia in clinical practice.