As a medical professional with expertise in cardiology, I can explain the PR interval in detail. The PR interval on an electrocardiogram (ECG) is a critical measure of the time it takes for electrical impulses to be transmitted from the atria to the ventricles of the heart. Here's what occurs during the PR interval: 1. Atrial Depolarization: This is the initial phase where the atria contract, pushing blood into the ventricles. This is represented by the P wave on the ECG. 2. Conduction Delay: After the atrial contraction, there is a short delay as the electrical impulse travels through the atrioventricular (AV) node and then through the bundle of His, which is the beginning of the ventricles' conduction system. This delay ensures that the atria have enough time to fully contract before the ventricles do. 3. Ventricular Depolarization: Once the impulse passes through the AV node and the bundle of His, it reaches the ventricles, causing them to depolarize. This is represented by the QRS complex on the ECG. The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. A normal PR interval is typically between 0.12 to 0.20 seconds (120 to 200 milliseconds). read more >>

In electrocardiography, the PR interval is the period, measured in milliseconds, that extends from the beginning of the P wave (the onset of atrial depolarization) until the beginning of the QRS complex (the onset of ventricular depolarization); it is normally between 120 and 200ms in duration.read more >>