As a medical professional with expertise in cardiology, I can explain that ST segment changes on an electrocardiogram (ECG) are critical indicators of the heart's electrical activity. The ST segment represents the period between the end of the depolarization (ventricular contraction) and the beginning of repolarization (ventricular relaxation) of the ventricles. ST depression is typically associated with conditions like myocardial ischemia, where there is an insufficient blood supply to the heart muscle. This can be due to coronary insufficiency or other forms of ischemic heart disease. When we say subendocardial ischemia, we mean that the inner layer of the heart muscle is not receiving enough blood, which can lead to ST depression on an ECG. In contrast, ST elevation is indicative of a more severe form of ischemia that affects the entire thickness of the heart muscle, known as transmural ischemia. This is often a sign of a more serious condition such as an acute myocardial infarction (heart attack). It's important to note that ST segment changes can have various causes, and not all changes are indicative of heart disease. Other factors, including electrolyte imbalances, certain medications, and other medical conditions, can also affect the ST segment. In summary, while ST segment changes can be a sign of heart conditions, particularly ischemia, they must be interpreted in the context of the patient's overall clinical presentation and other diagnostic information. read more >>

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.read more >>