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.

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 ...

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 ...