Which block represents complete failure of atrial impulses to reach the ventricles?

Which block represents complete failure of atrial impulses to reach the ventricles?

• A. Third-degree AV block
• B. First-degree AV block
• C. Second-degree AV block
• D. Tachyarrhythmia

Answer: (A)

Complete failure of atrial impulses to reach the ventricles is third-degree AV block, which shows AV dissociation. The atria fire regularly, but none of those impulses get through to the ventricles, so the ventricles pace themselves with a slower escape rhythm. On ECG, P waves occur at one rate and QRS complexes at another, with no fixed relationship between them—the PR interval is effectively meaningless. This differs from a first-degree block, where all atrial impulses still reach the ventricles but with a uniformly prolonged PR interval, and from a second-degree block, where some atrial impulses are conducted and others are dropped. Tachyarrhythmia is a fast heart rhythm, not a conduction block.

Complete failure of atrial impulses to reach the ventricles is third-degree AV block, which shows AV dissociation. The atria fire regularly, but none of those impulses get through to the ventricles, so the ventricles pace themselves with a slower escape rhythm. On ECG, P waves occur at one rate and QRS complexes at another, with no fixed relationship between them—the PR interval is effectively meaningless. This differs from a first-degree block, where all atrial impulses still reach the ventricles but with a uniformly prolonged PR interval, and from a second-degree block, where some atrial impulses are conducted and others are dropped. Tachyarrhythmia is a fast heart rhythm, not a conduction block.