The PR interval is a consistently measured metric on electrocardiograms (ECG), used to assess the timing of conduction from sinus node activation to earliest ventricular activation. The PR interval is comprised of trans-myocardial conduction across the right atrium, followed by conduction through the AV node, followed by conduction down the His-Purkinje system. Prolongation of the PR interval is defined as longer than 200 ms, and the delay in conduction can occur at the level of the atrium, the AV node, the His-Purkinje system, or any combination of the above.