ACCS Practice Exam 2026 – Complete Test Preparation Guide

In a third-degree atrioventricular (AV) block, also known as complete heart block, there is a complete dissociation between the atrial and ventricular activity. This means that the electrical impulses from the sinus node do not conduct to the ventricles at all. As a result, there is no consistent relationship between P waves and QRS complexes on the cardiac monitor, leading to the absence of a PR interval. Each component functions independently; the atria contract in response to their own electrical activity (the P waves), and the ventricles contract in response to a separate electrical impulse that may come from a junctional or ventricular pacemaker.

The absence of a PR interval distinguishes third-degree block from other types of AV block, such as first-degree, where the PR interval is prolonged, or second-degree blocks, which may manifest with varying PR intervals. The absence of any discernible PR interval is the hallmark of third-degree AV block, making option C the correct answer.