A 62-year-old man with chronic atrial fibrillation on telemetry shows an irregularly irregular rhythm. One wide QRS complex with RBBB morphology appears immediately after a long RR interval that itself follows a short RR interval. No compensatory pause follows the wide beat. What explains this wide complex?
- A Ashman phenomenon (aberrant ventricular conduction) ✓
- B Premature ventricular contraction
- C Intermittent pre-excitation via accessory pathway
- D Rate-related left bundle branch block
Correct answer: A. Ashman phenomenon (aberrant ventricular conduction)
Explanation
The long-short cycle sequence is the key: a long preceding cycle lengthens refractoriness of the bundle branches, so the next early supraventricular impulse conducts aberrantly, typically with RBBB morphology since the right bundle recovers more slowly. Absence of a compensatory pause favors aberrancy over a PVC, which usually has a full compensatory pause. Pre-excitation produces delta waves in sinus rhythm, and the RBBB pattern excludes left bundle branch aberrancy.
Reference: Goldberger's Clinical Electrocardiography, 9th ed.
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Written and medically reviewed by the StethoPrep medical team.