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.

P-wave duration was measured from the conclusion of the TP segment (P-wave onset) to return to baseline (PR interval). For biphasic P waves, both positive and negative deflections from baseline ...

PR segment depression can be from acute pericarditis ... Clockwise atrial flutter causes positively deflected P waves in the inferior leads while counterclockwise atrial flutter causes negative ...