Abnormal EKG Abnormal PR segment 2017-10-15T13:35:56Z An anomaly of the PR segment, which begins at the endpoint of the P wave and ends at the onset of the QRS complex. The PR segment is normally flat and isoelectric. The PR interval begins at the onset of the P wave and ends at the onset of the QRS complex. This interval reflects the time the impulse takes to reach the ventricles from the sinus node. In contrast, the PR segment begins at the endpoint of the P wave and ends at the onset of the QRS complex. It reflects the conduction from the atrioventricular node, down the bundle of His and through the bundle branches to the muscle.