Atrioventricular (AV) Blocks Flashcards

In first-degree AV block, which ECG finding is diagnostic?

Answer: PR interval greater than 200 ms with every P wave conducted

First-degree AV block is defined by a PR interval exceeding 200 ms (one large box) with every P wave successfully conducting to the ventricles.

Mobitz type I (Wenckebach) second-degree AV block is best described by which pattern?

Answer: Progressive PR lengthening until a QRS is dropped, then the cycle resets

Wenckebach is characterized by progressive PR interval lengthening with each beat until one P wave is not conducted (dropped QRS), after which the cycle resets.

Mobitz type II second-degree AV block differs from Mobitz type I primarily because it has which characteristic?

Answer: Constant PR interval with sudden unexpected dropped beats

In Mobitz type II, the PR interval remains constant and QRS complexes are dropped suddenly without warning, indicating infranodal disease and higher risk of complete heart block.

In third-degree (complete) heart block, how do atria and ventricles relate to each other?

Answer: They beat completely independently at their own intrinsic rates

In complete heart block, no atrial impulses are conducted to the ventricles, so each chamber maintains its own independent pacemaker and rate.

A patient has second-degree AV block with a 3:2 conduction ratio in Wenckebach pattern. How many P waves appear for every 2 QRS complexes?

Answer: 3 P waves

A 3:2 conduction ratio means 3 P waves for every 2 conducted QRS complexes — one P wave in each cycle is blocked.

Which of the following AV block types is most likely to require immediate pacemaker implantation?

Answer: Mobitz type II second-degree AV block

Mobitz type II carries high risk of sudden progression to complete heart block and usually requires permanent pacemaker implantation.