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?

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.