What is the ST segment on electrocardiography (ECG)?

Updated: Mar 11, 2019
  • Author: Tarek Ajam, MD, MS; Chief Editor: Terrence X O'Brien, MD, MS, FACC  more...
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Answer

Answer

The ST segment is an interval between ventricular depolarization and ventricular repolarization. It is identified as the end of the QRS complex to the beginning of the T wave.

The end of the T wave to the beginning of the P wave is described as the TP segment, which is the zero potential or isoelectric point. The amount of elevation or depression in millimeters is relative to the TP segment.

The J point is located at the junction between the end of the QRS complex and the beginning of the ST segment. J-point elevation is known as an Osborne wave, which represents distortion of the earlierst phase of membrane repolarization, and it is associated with hypothermia.

Myocardial ischemia diagnosed by ECG is an integral part of the acute coronary syndrome (ACS) treatment pathway and allows patient stratification into ST-segment elevation ACS (STE-ACS) and non-ST-segment elevation ACS (NSTE-ACS). [4, 21, 22]  ST-segment wave changes may be in association with disease states such as acute ischemia, myocardial injury, pericarditis, and intraventricular conduction delays.

In the absence of left ventricular hypertrophy (LVH) and left bundle branch block (LBBB), new ST-segment elevation in upward convexity are signs of myocardial infarction (typically 60 msec following the J point in two contiguous leads [with cut-off points in leads V2-V3 of ≥0.2 mV in men ≥40 years, ≥0.25 mV in men ˂40 years, or ≥0.15 mV in women, and/or 0.1 mV in other leads for both men and women]). [23]  New horizontal or down sloping ST depression that is 0.05 mV or more in two contiguous leads and/or T-wave inversion that is 0.1 mV or more in two contiguous leads, with a prominent R wave or an R/S ratio over 1, are also signs of myocardial infarction.  

Coronary spasm may be associated with angina (Prinzmetal) and with transient ST-segment elevation in a coronary artery branch distribution that has the spasm.

Pericarditis is associated with ECG manifestations of diffuse upward concave ST-segment elevation with PR depressions.

See the following images.

ST depression. ST depression.
ST elevation. ST elevation.
ST morphology. ST morphology.

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