A 58-year-old man with syncope has an ECG showing dropped QRS complexes without any prior progressive PR prolongation, with constant PR intervals in conducted beats. The escape rhythm, when documented, is broad at 35 bpm. Where is the lesion located and what is the definitive management?

• A AV node; observation with repeat Holter
• B His-Purkinje system; ivabradine therapy
• C AV node; permanent pacemaker implantation
• D His-Purkinje system; permanent pacemaker implantation ✓

Explanation

Mobitz type II second-degree AV block shows abrupt dropped beats with fixed PR intervals, indicating disease distal to the AV node in the His-Purkinje system. It frequently progresses unpredictably to complete heart block and carries a high risk of Stokes-Adams attacks, so a permanent pacemaker is indicated even in asymptomatic patients. Infra-nodal escapes are broad and slow, unlike junctional escapes. Observation is unsafe, and ivabradine slows the sinus node without affecting infranodal conduction.

Reference: Braunwald's Heart Disease, 12th ed.

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Written and medically reviewed by the StethoPrep medical team.