The PR segment is the portion of the ECG from the end of the P wave to the beginning of the QRS complex. The PR segment is different from the PR interval, which is measured in units of time.
Remember that segments are different than intervals. The important factor in analyzing segments on the ECG is their change from the isoelectric line — that is, elevation or depression — whereas the important thing in analyzing intervals is their duration.
Although abnormalities of the PR segment are not very common, they can indicate certain cardiac disease states. PR segment depression can be a signal for pericarditis or atrial infarction. PR segment elevation occurs in lead aVR in the setting of pericarditis.