Registered Cardiovascular Invasive Specialist (RCIS) Practice Test

What is the characteristic PR interval duration in a 1st degree heart block?

1. Less than 0.20 seconds

2. Exactly 0.20 seconds

3. More than 0.20 seconds

4. Varies by patient

The correct answer is: More than 0.20 seconds

In the context of first-degree heart block, the characteristic PR interval duration is indeed more than 0.20 seconds. Typically, a first-degree heart block is identified by a consistently prolonged PR interval that exceeds the normal upper limit of 0.20 seconds. It indicates a delay in the conduction through the atrioventricular (AV) node, which extends the time it takes for electrical impulses to travel from the atria to the ventricles. In healthy individuals, the PR interval usually ranges from 0.12 to 0.20 seconds. When it is prolonged beyond this, it signals that the heart is exhibiting first-degree AV block. This is a benign condition and is often asymptomatic, but it is important to recognize because it may indicate more significant conduction system disease. The other choices do not accurately represent the defining characteristic of this condition. The suggestion of a PR interval less than 0.20 seconds contradicts the very definition of first-degree heart block, while asserting that it is exactly 0.20 seconds overlooks the requirement for it to be prolonged. The idea that the PR interval varies by patient conflicts with the standard diagnostic criteria, which emphasize the consistency of the prolonged interval in patients with this particular heart block.