Final answer:
The expected reference range for the PR interval on an ECG is 120 to 200 milliseconds (0.12 to 0.20 seconds), and it represents the conduction time from atrial to ventricular depolarization.
Step-by-step explanation:
The PR interval on an electrocardiogram (ECG) is the period that starts at the beginning of the P wave (atrial depolarization) and ends at the beginning of the QRS complex (ventricular depolarization). The expected reference range for the PR interval is typically 120 to 200 milliseconds (0.12 to 0.20 seconds). This measurement is clinically relevant as it reflects the conduction time from the atria to the ventricles, encompassing the atrial depolarization and the delay at the AV node.
Delays or abnormalities in the PR interval can indicate issues with electrical conduction in the heart, such as a blockage in the AV node. If the PR interval is shorter or longer than the reference range, it requires further medical interpretation and possibly diagnostic testing.