In third-degree heart block, how are P-P and R-R intervals described?

Prepare for the Cleveland Clinic EKG Test with flashcards and multiple choice questions. Gain insights with hints and explanations. Ace your exam today!

Multiple Choice

In third-degree heart block, how are P-P and R-R intervals described?

In third-degree heart block, the atria and ventricles beat independently because there is complete AV dissociation. The SA node drives the atria, producing a constant, regular P-P interval. The ventricles are paced by an escape rhythm below the block, giving a regular but slower R-R interval. Since there’s no conduction from atria to ventricles, the timing between a P wave and the following QRS complex has no fixed relationship, so the PR interval is not associated. This description—P-P constant, R-R constant, but PR not associated—best fits the pattern of complete AV block.

In third-degree heart block, the atria and ventricles beat independently because there is complete AV dissociation. The SA node drives the atria, producing a constant, regular P-P interval. The ventricles are paced by an escape rhythm below the block, giving a regular but slower R-R interval. Since there’s no conduction from atria to ventricles, the timing between a P wave and the following QRS complex has no fixed relationship, so the PR interval is not associated. This description—P-P constant, R-R constant, but PR not associated—best fits the pattern of complete AV block.

More practice questions