What defines Mobitz type I (Wenckebach) second-degree AV block?

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Multiple Choice

What defines Mobitz type I (Wenckebach) second-degree AV block?

Mobitz type I (Wenckebach) is a second-degree AV block caused by delaying conduction at the AV node. The defining pattern is a cycle in which the PR interval gradually lengthens with each beat, and then a P wave occurs that is not followed by a QRS complex. After this nonconducted beat, the PR interval resets and the cycle starts over. This progressive slowing and periodic dropped beat is the hallmark of Wenckebach. This pattern fits the option describing progressive PR prolongation with intermittent nonconducted QRS complexes in a repeating pattern. It also makes sense that the block is usually at the AV node, so QRS complexes are typically narrow unless there’s additional downstream conduction disease. Why the other patterns don’t fit: a dropped beat without preceding PR prolongation points to Mobitz II; complete AV dissociation describes third-degree block with no relationship between P waves and QRS; a prolonged PR interval with all beats conducted indicates first-degree AV block.

Mobitz type I (Wenckebach) is a second-degree AV block caused by delaying conduction at the AV node. The defining pattern is a cycle in which the PR interval gradually lengthens with each beat, and then a P wave occurs that is not followed by a QRS complex. After this nonconducted beat, the PR interval resets and the cycle starts over. This progressive slowing and periodic dropped beat is the hallmark of Wenckebach.

This pattern fits the option describing progressive PR prolongation with intermittent nonconducted QRS complexes in a repeating pattern. It also makes sense that the block is usually at the AV node, so QRS complexes are typically narrow unless there’s additional downstream conduction disease.

Why the other patterns don’t fit: a dropped beat without preceding PR prolongation points to Mobitz II; complete AV dissociation describes third-degree block with no relationship between P waves and QRS; a prolonged PR interval with all beats conducted indicates first-degree AV block.

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