It starts at the J point (junction between the QRS complex and ST segment) and ends at the beginning of the T wave. However, since it is usually difficult to determine exactly where the ST segment ends and the T wave begins, the relationship between the ST segment and T wave should be examined together. The typical ST segment duration is usually around 0.08 sec (80 ms). It should be essentially level with the PR and TP segments.
The ST segment represents the isoelectric period when the ventricles are in between depolarization and repolarization.
Interpretation
Illustration of ST segment elevation and depression The normal ST segment has a slight upward concavity.
Flat, downsloping, or depressed ST segments may indicate coronary ischemia.