What is measured by the P-R interval?

The P-R interval is a critical component of an electrocardiogram (ECG or EKG) that measures the time from the onset of atrial depolarization (the P wave) to the beginning of ventricular depolarization (the QRS complex). This interval reflects the time it takes for electrical impulses to travel from the atria through the atrioventricular (AV) node and into the ventricles.

An appropriate P-R interval indicates that the electrical signal is efficiently conducting through the heart's conduction pathways. A prolonged or shortened P-R interval can suggest various types of heart block or pre-excitation syndromes. Thus, the correct answer highlights the direct relationship between atrial and ventricular activity during the heart's electrical cycle and serves as a key measurement in assessing cardiac health.