Second Degree Heart Block Type II is best described as an AV block with fixed PR intervals and intermittent nonconducted QRS complexes. Which option matches this description?

• A. Progressive PR prolongation with dropped beats
• B. Fixed PR interval with intermittent nonconducted QRS
• C. Complete AV dissociation
• D. Irregular rhythm with no dropped beats

Answer: (B)

The main idea is recognizing Mobitz type II second-degree AV block, which shows a fixed PR interval on beats that are conducted and occasional nonconducted P waves that fail to produce a QRS complex. That combination—constant PR for the beats that do go through, with intermittent dropped QRS after a P wave—is classic for this block.

Progressive PR prolongation with dropped beats describes Mobitz type I (Wenckebach), where the PR interval lengthens before a nonconducted beat. Complete AV dissociation is third-degree block, where P waves and QRS occur independently with no fixed relationship. An irregular rhythm with no dropped beats doesn’t match Mobitz II, which by definition includes dropped QRS after some P waves.

So the description of a fixed PR interval with intermittent nonconducted QRS precisely matches Mobitz type II second-degree AV block.