In electrocardiography, the PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. It is usually 120 to 200 ms long. On the usual 25 mm/s ECG tracing, this corresponds to 3 to 5 small boxes. The PR interval reflects the time the electrical impulse takes to travel from the sinus node through the AV node where it enters the ventricles. The PR interval is therefore a good estimate of AV node function.
In case a L wave was measured with an ECG, the PR interval is also commonly named "PQ interval" instead.
Variations in the PR interval can be associated with certain medical conditions:
- PR segment depression may indicate atrial injury or pericarditis.
- Variable morphologies of P waves in a single ECG lead is suggestive of an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia