Aberrantly-Conducted PAC (Ashman)
normalAberrantly-Conducted PAC (Ashman)
A PAC that conducts but finds a bundle branch — usually the right, which recovers more slowly — still refractory, producing a wide, bundle-branch-block-shaped QRS. It classically follows a long–short cycle sequence (Ashman phenomenon).
- Early beat with a wide QRS
- A preceding P wave IS present (unlike a PVC)
- Long–short RR before the wide beat
- RBBB-type morphology
PAC conducts while a bundle branch is still refractory — wide QRS
Refractoriness is proportional to the preceding R-R interval. After a long cycle, a short-coupled PAC reaches the His-Purkinje system while the right bundle (longer refractory period) has not recovered, so the beat conducts down the left bundle first and inscribes an RBBB-type wide QRS.
- Premature abnormal P followed by a WIDE QRS (~0.12 s, RBBB-type).
- The preceding cycle is long and the coupled cycle short.
- The PRESERVED premature P wave is the key clue that this is aberrancy, not a PVC.
- No compensatory pause.
Benign PVC mimic — do not treat as ventricular
Primary Treatment
No specific treatment.
Additional Options
Identify the preceding P wave and the long–short sequence to distinguish from ventricular ectopy.