ST segment

Normally a flat isoelectric line between the end of the S wave (J point) and the beginning of the T wave

• • May vary from 0.5 mm to 1.0 mm above baseline in limb leads

  • May vary up to 3.0 mm above baseline in precordial leads (benign early repolarization)

  • While some variability may be normal , be cautious when interpreting emergency ECGs where subtle abnormalities can be a sign of early evolving occlusion MI

Non-specific ST segments

• • < 1mm depression or elevation

The ST segment may be elevated or depressed in a variety of pathology, most importantly ACS

• • Elevation may be concave or convex upward

  • Depression may be horizontal, downsloping, or upsloping

Measure (mm) relative to the TP segment (PQ segment in some guidelines)