ST Segment and T Wave Changes
Changes to the ST segment or T wave are often ominous signs that there's something wrong in the electrical pathways of the heart.
If you suspect any new ST segment or T wave changes, always get a 12-lead ECG.
T Wave
For the most part, the T-wave is upright and rounded, roughly less than 5 mm (or 0.5mV) in height in the limb leads, and 10 mm (or 1.0 mV) in the precordial leads. Changes in the T-wave shape or size are generally noticeable when looking at the cardiac monitor.
ST Segment
The "normal" ST segment lands on the isoelectric line (plus or minus 0.5 mm). Anything higher than that is elevated, while anything lower than that is depressed. Since the ST segment can take on a variety of shapes if it's elevated or depressed, we'll measure if there's elevation or depression at the J-Point, the part where the QRS complex ends and changes shape.
For ST elevation, we sometimes talk about the shape that the ST segment leads into the T wave. A convex shape steeply rises before flattening out, while a concave shape gradually rises.
Convex ST elevations are generally more concerning than concave elevations. However, both could be seen in an MI.
For ST depression, we sometimes talk about the trajectory that the ST segment takes after the J-point, whether it's an upslope, horizontal, or downslope ST depression.