PR Interval

The PR interval is the time from the beginning of the P wave until the start of the QRS complex and represents conduction through the AV node. The interval should be between 120-200ms. If it is less than 120ms, then either pre-excitation is usually present (there is an accessory conduction pathway between the atria and ventricles) or there is a junctional (from the AV node) rhythm. If the PR interval is >200ms, then an AV node block is present. Although the PR interval does include the P wave, prolonged P wave duration from atrial enlargement is usually not long enough to cause a prolonged PR interval itself.

Additionally, evaluation of the PR segment includes its evaluation relative to the TP segment. If the PR segment is not isoelectric, it is usually from pericarditis or atrial ischemia. Classically, pericarditis causes PR elevation in aVR+V1 with diffuse PR depression in the other leads.