In a first-degree atrioventricular block, the P-R interval is greater than how many seconds?

In a first-degree atrioventricular block, the defining characteristic is a prolonged PR interval. The normal PR interval ranges from 0.12 to 0.20 seconds. When the PR interval exceeds 0.20 seconds, it indicates a first-degree AV block. This condition reflects a delay in conduction through the AV node, which results in a longer time for the electrical impulse to travel from the atria to the ventricles. Consequently, the correct answer is 0.20 seconds, as this is the threshold beyond which a first-degree AV block is diagnosed. Understanding this will help in identifying and interpreting electrocardiogram (ECG) readings correctly in clinical practice.