In a patient with atrial fibrillation, a wide bizarre QRS complex follows a long RR interval immediately succeeded by a short RR interval. The wide complex has a typical right bundle branch block pattern with rsR' morphology in V1 and appears identical across recordings. What explains this phenomenon?
- A Ashman phenomenon: aberrant conduction due to cycle length dependent refractoriness of the right bundle ✓
- B Ventricular ectopy arising from the right ventricular outflow tract
- C Pre-excited conduction over an accessory pathway
- D Rate-related left bundle branch block
Correct answer: A. Ashman phenomenon: aberrant conduction due to cycle length dependent refractoriness of the right bundle
Explanation
Ashman phenomenon is aberrant intraventricular conduction triggered by a long cycle followed by a short cycle: bundle branch refractoriness outlasts the Q-T interval and lengthens after long cycles, so the early beat finds one bundle still refractory. The right bundle, with its longer refractory period, is affected far more often, giving an rsR' pattern in V1. Right ventricular outflow tract ectopy shows a left bundle branch-like pattern, and accessory pathway conduction produces a delta wave, neither of which is present here.
Reference: Braunwald's Heart Disease, 12th ed.
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Written and medically reviewed by the StethoPrep medical team.