What does the ST segment represent in an ECG?

The ST segment in an ECG represents the period of time during which the ventricles are in a state of complete depolarization and are starting to repolarize, making it an important phase of the cardiac cycle. Specifically, the ST segment reflects the timing of ventricular repolarization. During this segment, the heart muscle is not generating any electrical impulses, which is why it is often depicted as an isoelectric line on the ECG tracing.

This segment is critical for identifying potential issues such as ischemia or infarction, where deviations from the normal ST segment can signal significant cardiovascular conditions. While the segment is described as "isoelectric," meaning it appears flat and indicates no net electrical activity, it is crucial to understand that it is not simply a period devoid of activity; it marks a transitional phase of heart function where changes could indicate underlying problems.

Knowledge of the ST segment is central to interpreting an ECG and recognizing various cardiac conditions, as abnormal changes can be indicative of myocardial ischemia or other cardiac events. Understanding its role helps in the comprehensive assessment of the heart's electrical activity and rhythm.