What does the PR interval measure?

The PR interval measures the time from the onset of atrial depolarization to the onset of ventricular depolarization. This interval reflects the conduction time through the atrioventricular (AV) node and the bundle of His, which is essential for coordinating the timing between the contraction of the atria and the ventricles. A normal PR interval indicates that the electrical impulse travels efficiently through the heart’s conduction system, allowing the atria to contract and fill the ventricles with blood before the ventricles contract.

While the other options reference important aspects of cardiac physiology and the EKG, they do not accurately define what the PR interval represents. Understanding the significance of the PR interval is crucial for diagnosing and managing various cardiac conditions, such as AV block, which may affect the conduction time between the atria and ventricles.