A 64-year-old man with recurrent syncope has an ECG showing PR intervals that are constant at 0.24 sec with sudden dropped QRS complexes and a QRS duration of 140 ms with LBBB pattern. Which statement about this conduction disturbance is correct?
- A The block is within the AV node and usually reversible
- B Atropine is the definitive long-term treatment
- C It carries a high risk of progression to complete heart block and warrants pacemaker implantation even if asymptomatic ✓
- D It is almost always caused by increased vagal tone
Correct answer: C. It carries a high risk of progression to complete heart block and warrants pacemaker implantation even if asymptomatic
Explanation
Constant PR intervals with dropped beats define Mobitz type II second-degree AV block. The block is infranodal, typically in the His-Purkinje system, often with bundle branch disease, and it can progress unpredictably to complete heart block with syncope or sudden death. Pacemaker implantation is indicated regardless of symptoms. This distinguishes it from Mobitz I (Wenckebach) block, which is usually nodal, vagally mediated, benign, and responsive to atropine.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.