Inelectrocardiography, theST segment connects theQRS complex and theT wave and has a duration of 0.005 to 0.150 sec (5 to 150 ms).

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.

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  The normal ST segment has a slight upward concavity.
• Flat, downsloping, or depressed ST segments may indicatecoronary ischemia.
• ST elevation may indicate transmuralmyocardial infarction. An elevation of >1mm and longer than 80 milliseconds following theJ-point. This measure has afalse positive rate of 15-20% (which is slightly higher in women than men) and afalse negative rate of 20–30%.^[1]
• ST depression may be associated with subendocardialmyocardial infarction,hypokalemia, ordigitalis toxicity.^[2]

Infetal electrocardiography, ST waveform analysis (sometimes abbreviated STAN) is used to get an indication of increasing levels of fetalbase deficit.^[3]

• Cardiac electrophysiology
• Diagnostic cardiology

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