Prolonged PR interval (>200 ms) with all QRS complexes conducted defines 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

Prolonged PR interval (>200 ms) with all QRS complexes conducted defines which block?

The main idea here is recognizing a one-to-one conduction with a delayed AV nodal transmission. When the PR interval is prolonged beyond 200 ms but every P wave is followed by a QRS complex, the impulse is being conducted but through a slowed pathway at the AV node. This is first-degree AV block. The hallmark is a consistently long PR interval with all beats conducted, and the QRS usually remains narrow if there’s no bundle branch disease. It’s often benign and can be seen with increased vagal tone or drugs that slow AV nodal conduction (like certain beta-blockers, calcium channel blockers, or digoxin). Other patterns would behave differently: Mobitz I shows progressively lengthening PR intervals until a P wave is not followed by a QRS (a dropped beat). Mobitz II has fixed PR intervals with sudden non-conducted P waves (dropped QRS) without the progressive lengthening. Third-degree block has complete AV dissociation, with P waves and QRS complexes marching independently and no consistent relationship between them.

The main idea here is recognizing a one-to-one conduction with a delayed AV nodal transmission. When the PR interval is prolonged beyond 200 ms but every P wave is followed by a QRS complex, the impulse is being conducted but through a slowed pathway at the AV node. This is first-degree AV block. The hallmark is a consistently long PR interval with all beats conducted, and the QRS usually remains narrow if there’s no bundle branch disease. It’s often benign and can be seen with increased vagal tone or drugs that slow AV nodal conduction (like certain beta-blockers, calcium channel blockers, or digoxin).

Other patterns would behave differently: Mobitz I shows progressively lengthening PR intervals until a P wave is not followed by a QRS (a dropped beat). Mobitz II has fixed PR intervals with sudden non-conducted P waves (dropped QRS) without the progressive lengthening. Third-degree block has complete AV dissociation, with P waves and QRS complexes marching independently and no consistent relationship between them.

More practice questions