Intervals and Segments Interval refers to the length of a wave plus the isoelectric line that follows it. The length of an interval ends when another wave begins. They are named by using the letters of both waves on either side. Intervals contain waves. Segments refers to the baseline between the end of one wave and the beginning of the next wave.
Segments are the lines between waves.
See diagram below. . I s the length along the baseline from the beginning of the P wave to the beginning of th QRS complex. This Is normally 0.12 to 2.0 seconds in duration. QT Interval Is the beginning of the QRS complex to the end of the T wave. In the presence of a U wave the measure should be from the beginning of the QRS complex to the end of the U wave.