What is the main purpose of the ST segment in an ECG?

The main purpose of the ST segment in an ECG is to indicate the end of ventricular depolarization and the beginning of repolarization. During this segment, the ventricles are in a state of electrical inactivity after their contraction has completed. This is crucial because it corresponds to the point when the myocardium is recovering from the depolarization that initiated contraction and is preparing for the next cycle of depolarization.

The ST segment is significant in diagnosing certain cardiac conditions, such as ischemia and infarction. Any deviations from the normal ST segment can indicate various issues such as myocardial ischemia, where the heart muscle is not receiving enough oxygen, or other pathological states like pericarditis or early repolarization abnormality.

In contrast to the purpose of the ST segment, atrial contraction is represented by the P wave, while heart rate is measured using the intervals between R waves on the ECG. Pacemaker activity is reflected primarily by the P wave and the intrinsic pacing of the heart, rather than by the ST segment. Thus, recognizing the role of the ST segment is essential for interpreting the overall health and function of the heart.