Ashman phenomenon
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Ashman's Phenomenon is an aberrant intra-ventricular conduction abnormality that occurs because of variable cycle length in atrial fibrillation. It presents as isolated wide complex beats manifesting as a right bundle branch block morphology with short RR cycle length immediately following a longer RR cycle. It represents an aberrantly conducted complex that originates above the AV node, rather than a complex that originates in either the right or left ventricle.
In an emergency setting, this phenomenon can be easily confused with non-sustained ventricular tachycardia which also presents with a wide ORS complex. Misinterpretation of this finding can potentially result in unnecessary testing and health care costs.
Historical Perspective
Ashman's phenomenon was first described in a patient with atrial fibrillation in 1947 by Gouaux JL and Ashman R[1].
Pathophysiology
Ashman's phenomenon classically occurs in atrial fibrillation, in which not all impulses originating the atrium are regularly conducted through the AV node. This variability in RR cycle lengths predisposes to the aberrant conduction.
The key to understanding the pathophysiology of Ashman's phenomenon is the fact that refractory period of an impulse that travels in the ventricular muscle varies from beat to beat in patients with an underlying atrial fibrillation. Longer RR cycles(slower hear rate) have longer refractory period whereas shorter RR cycles(faster hear rate) have a shorter refractory period.
When a long RR cycle is followed by a shorter RR cycle, the cardiac muscle cells are still in the refractory period from the preceding longer beat. This gives rise to a bundle branch block like pattern, more commonly a right bundle, leading to aberrant conduction. Also, in atrial fibrillation, there is no P wave to indicate that the tachycardia is supraventricular and not due to aberrant conduction.
Besides atrial fibrillation, Ashman's phenomenon is also seen in multifocal atrial tachycardia and premature atrial tachycardia.
EKG Examples
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Ashman phenomenon
Reference
- ↑ J. L. GOUAUX & R. ASHMAN (1947). "Auricular fibrillation with aberration simulating ventricular paroxysmal tachycardia". American heart journal. 34 (3): 366–373. PMID 20262631. Unknown parameter
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- Ashman R, Byer E. Aberration in the conduction of premature ventricular impulses. J La State Med Soc 8:62, 1946
See also