A 72-year-old man presents with syncope. ECG shows alternating right and left bundle branch block pattern. What does this represent and what is the management?
- A Bifascicular block — monitoring only
- B Wellens' pattern — urgent angiography
- C Bilateral bundle branch block (alternating BBB) — represents advanced infranodal conduction disease requiring permanent pacemaker ✓
- D Rate-dependent BBB — no treatment required
Explanation
Alternating bundle branch block (RBBB on some beats, LBBB on others) represents bilateral conduction system disease with intermittent failure of both bundle branches. This is a high-risk form of trifascicular disease that carries a high risk of complete heart block and sudden death. Class I indication for permanent pacemaker implantation exists per ACC/AHA guidelines even in the absence of documented complete AV block, as syncope in this setting is likely due to intermittent complete block. This is distinct from rate-dependent BBB (aberrant conduction at high rates only) which may not require pacing.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.