A 66-year-old woman with chronic atrial fibrillation has a Holter tracing showing a wide-complex beat with RBBB morphology immediately following the longest RR interval of the strip, which itself follows a short RR interval. All other beats are narrow. What is the mechanism of this wide beat?
- A Ventricular ectopic beat arising from the left ventricle
- B Functional aberrant conduction due to incomplete recovery of the right bundle branch ✓
- C Antegrade conduction over an accessory pathway
- D Rate-related slowing of AV nodal conduction
Correct answer: B. Functional aberrant conduction due to incomplete recovery of the right bundle branch
Explanation
This is the Ashman phenomenon: a long RR interval lengthens the refractory period of the bundle branches, so the next early beat arriving after a short cycle finds the right bundle still refractory and conducts with RBBB aberrancy. The long-short sequence distinguishes it from a ventricular ectopic beat. No treatment is required once it is recognized as supraventricular conduction with aberrancy.
Reference: Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 12th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.