What does the P-R interval measure in an ECG?

The P-R interval in an ECG measures the time from the beginning of atrial depolarization to the beginning of ventricular depolarization. This interval reflects the time it takes for electrical impulses to travel from the atria through the atrioventricular (AV) node before they trigger ventricular contraction. A normal P-R interval signifies that the electrical activity is proceeding through the heart's conduction system appropriately.

The measurement starts at the onset of the P wave, which indicates atrial depolarization, and ends at the start of the QRS complex, representing the onset of ventricular depolarization. This interval is crucial for evaluating the conduction time between the atria and the ventricles and can provide important information about any delays in conduction that may exist in the heart's electrical system.