How is the PR interval defined?

How is the PR interval defined?

• A. Initiation of atrial depolarization to initiation of ventricular depolarization
• B. Start of P wave to start of QRS
• C. From ventricular depolarization onset to ventricular repolarization onset
• D. From P wave onset to end of QRS

Answer: (A)

The PR interval is the time from when atrial depolarization begins to when ventricular depolarization begins. On the ECG, that means from the start of the P wave (atrial activation) to the start of the QRS complex (ventricular activation). This interval reflects how long impulses take to travel from the atria through the AV node and into the ventricles, i.e., AV nodal conduction time plus conduction through the His-Purkinje system. It does not include the full duration of atrial depolarization nor the ventricular depolarization itself. Normal values are about 120–200 ms in adults.

The PR interval is the time from when atrial depolarization begins to when ventricular depolarization begins. On the ECG, that means from the start of the P wave (atrial activation) to the start of the QRS complex (ventricular activation). This interval reflects how long impulses take to travel from the atria through the AV node and into the ventricles, i.e., AV nodal conduction time plus conduction through the His-Purkinje system. It does not include the full duration of atrial depolarization nor the ventricular depolarization itself. Normal values are about 120–200 ms in adults.