On an ECG, which statement correctly describes the PR interval?

On an ECG, which statement correctly describes the PR interval?

• A. Time from onset of ventricular depolarization to onset of atrial depolarization
• B. Time from the start of the P wave to the end of the T wave
• C. Duration of the QRS complex
• D. Time from onset of atrial depolarization to onset of ventricular depolarization (AV conduction time)

Answer: (D)

The main idea is what the PR interval tells you about electrical conduction between the atria and ventricles. It is the time from the start of atrial depolarization to the start of ventricular depolarization. On the ECG, that means from the beginning of the P wave to the beginning of the QRS complex. This interval includes the atrial depolarization itself plus the delay as the impulse passes through the AV node and into the ventricles (the AV conduction time). A normal PR interval is about 0.12 to 0.20 seconds. This is different from the QRS duration (which only measures how long the ventricles take to depolarize) and from a P-to-T span (which would cover atrial depolarization through ventricular repolarization).

The main idea is what the PR interval tells you about electrical conduction between the atria and ventricles. It is the time from the start of atrial depolarization to the start of ventricular depolarization. On the ECG, that means from the beginning of the P wave to the beginning of the QRS complex. This interval includes the atrial depolarization itself plus the delay as the impulse passes through the AV node and into the ventricles (the AV conduction time). A normal PR interval is about 0.12 to 0.20 seconds. This is different from the QRS duration (which only measures how long the ventricles take to depolarize) and from a P-to-T span (which would cover atrial depolarization through ventricular repolarization).