Intermittent dropped QRS complexes with a constant PR interval indicate which block?

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

Intermittent dropped QRS complexes with a constant PR interval indicate which block?

A non-conducted P wave with a constant PR interval across the beats is the hallmark of a fixed block in the AV conduction system below the AV node. In Mobitz II second-degree AV block, some P waves are not followed by QRS complexes, while the PR interval of the beats that do conduct remains, on average, the same. This distinguishes it from Wenckebach (Mobitz I), where the PR interval progressively lengthens before a dropped beat; from first-degree block, where every P wave is conducted but with a prolonged PR interval; and from complete (third-degree) block, where there is no consistent relationship between P waves and QRS complexes. Thus the described pattern points to Mobitz II second-degree AV block.

A non-conducted P wave with a constant PR interval across the beats is the hallmark of a fixed block in the AV conduction system below the AV node. In Mobitz II second-degree AV block, some P waves are not followed by QRS complexes, while the PR interval of the beats that do conduct remains, on average, the same. This distinguishes it from Wenckebach (Mobitz I), where the PR interval progressively lengthens before a dropped beat; from first-degree block, where every P wave is conducted but with a prolonged PR interval; and from complete (third-degree) block, where there is no consistent relationship between P waves and QRS complexes. Thus the described pattern points to Mobitz II second-degree AV block.

More practice questions