In third-degree heart block, what is true about PR interval relative to P-P and R-R?

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, what is true about PR interval relative to P-P and R-R?

In third-degree AV block there is complete AV dissociation, meaning the atria and ventricles beat independently. Since the atrial impulses do not conduct to the ventricles, the timing from a P wave to the following QRS (the PR interval) has no fixed relationship to the atrial rhythm (P–P) or the ventricular rhythm (R–R). The P-P interval reflects the sinus node rate, and the R–R interval reflects the ventricular escape rhythm, each marching to its own clock. Because of that dissociation, the PR interval can vary and is not predictably tied to either P–P or R–R, making it effectively not related in this block.

In third-degree AV block there is complete AV dissociation, meaning the atria and ventricles beat independently. Since the atrial impulses do not conduct to the ventricles, the timing from a P wave to the following QRS (the PR interval) has no fixed relationship to the atrial rhythm (P–P) or the ventricular rhythm (R–R). The P-P interval reflects the sinus node rate, and the R–R interval reflects the ventricular escape rhythm, each marching to its own clock. Because of that dissociation, the PR interval can vary and is not predictably tied to either P–P or R–R, making it effectively not related in this block.

More practice questions