A 65-year-old man with recent anterior STEMI develops syncope. ECG shows sinus rhythm at 80 bpm with constant PR interval of 220 ms, but every third P wave is not conducted. QRS duration is 120 ms. Which statement best describes this conduction abnormality?
- A Mobitz type II second-degree AV block, usually infranodal and carries risk of progression to complete heart block ✓
- B Mobitz type I (Wenckebach) second-degree AV block, usually AV nodal and benign
- C First-degree AV block with premature atrial contractions
- D Third-degree AV block with intermittent capture beats
Correct answer: A. Mobitz type II second-degree AV block, usually infranodal and carries risk of progression to complete heart block
Explanation
Mobitz type II is defined by constant PR intervals with intermittent non-conducted P waves (here 3:2 block). Unlike Mobitz type I, there is no progressive PR prolongation before the dropped beat. It indicates infranodal disease (His-Purkinje system), carries a high risk of progression to complete heart block, and often warrants permanent pacemaker implantation regardless of symptoms.
Reference: Braunwald's Heart Disease, 12th ed.
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Written and medically reviewed by the StethoPrep medical team.