A 64-year-old man presents with an episode of syncope. His ECG shows a constant PR interval of 200 ms with sudden dropped QRS complexes occurring without any preceding PR prolongation. The QRS complexes are wide at 130 ms. What is the most appropriate next step?

• A Permanent pacemaker implantation ✓
• B Observation with annual ECG follow-up
• C Atropine infusion and discharge
• D Electrophysiology study to assess sinus node function

Explanation

Mobitz II second-degree AV block shows constant PR intervals with intermittently non-conducted P waves. It localizes to the His-Purkinje system, is usually associated with a wide QRS, carries a high risk of progression to complete heart block and sudden death, and is an accepted class I indication for permanent pacing even when asymptomatic. Atropine is unreliable here because it shortens the sinus rate and may worsen infranodal block by increasing the number of impulses reaching diseased Purkinje tissue.

Reference: Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 12th ed.

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Written and medically reviewed by the StethoPrep medical team.