What does a depressed ST segment mean?

As a medical professional with expertise in cardiology, I can explain the significance of a depressed ST segment in an electrocardiogram (ECG) reading. An ST segment is the flat part of the ECG that represents the period between the end of the atrial depolarization (ventricular contraction) and the beginning of the ventricular repolarization (ventricular relaxation). Normally, the ST segment is at the same level as the baseline of the ECG, which is considered an isoelectric line. When the ST segment is depressed, it means it is below the isoelectric line. This can be a sign of ischemia, which is a condition where the heart muscle is not receiving enough oxygen-rich blood. Ischemia is often caused by coronary artery disease (CAD), where the arteries that supply blood to the heart become narrowed or blocked, usually due to a buildup of plaque. A depressed ST segment can also be seen in other conditions such as pericarditis (inflammation of the tissue surrounding the heart), hyperkalemia (high levels of potassium in the blood), or as a normal variant in some individuals. It's important to note that the interpretation of an ECG requires a comprehensive evaluation that includes the patient's medical history, symptoms, and other diagnostic tests. A single finding, such as a depressed ST segment, should not be used in isolation to diagnose a condition.

It is often a sign of myocardial ischemia, of which coronary insufficiency is a major cause. Other ischemic heart diseases causing ST depression include: Subendocardial ischemia or even infarction. Subendocardial means non full thickness ischemia. In contrast, ST elevation is transmural (or full thickness) ischemia.