ECG Pointers: Ashman’s Phenomenon

Authors: Rachel Bridwell (Attending EM Physician); Brannon Inman, MD (EM Crit Care, Orlando Health); Lloyd Tannenbaum (Staff Physician, Hackensack University Medical Center) // Reviewed by: Jamie Santistevan, MD (@jamie_rae_EMdoc, EM Physician, Presbyterian Hospital, Albuquerque, NM); Manpreet Singh, MD (@MPrizzleER); Brit Long, MD (@long_brit)

Case:

You’re working on shift and the nurses hand you an ECG asking what you want for rate control on this:

Do you think this is atrial fibrillation? Wandering atrial pacemaker? The irregular rate is strange but what do you want to do about it?

Answer:

This EKG shows Ashman’s phenomenon, which was first identified in 1947 by Drs. Gouaux and Ashman. In this phenomenon, there is a prolonged R-R interval, then a short R-R interval, which is then followed by an aberrantly conducted ventricular beat.  This ventricular beat will often show a Right Bundle Branch (RBBB) morphology. It tends to occur most commonly in atrial fibrillation, but it can be seen in other supraventricular dysrhythmias including atrial ectopy and atrial tachycardia. This occurs because the R-R interval of the preceding beat is proportional to the His-Purkinje refractory time (i.e., when there are 2 beats separated by a long R-R, the refractory time will also be long). However, the right bundle has a slightly longer refractory time than the left bundle, rendering a beat aberrantly conducted with an RBBB.

Diagnosis:

To diagnose Ashman’s phenomenon, the Fisch criteria are used, which state the following:

1. A long R-R segment preceding the short R-R segment followed by an aberrantly conducted beat
2. RBBB morphology with normal QRS vector orientation
3. Aberrant QRS complexes that are coupled
4. No compensatory pause seen

While the long-short pattern is common, a series of short-long-short R-R intervals are even more consistent with the Ashman phenomenon. While this phenomenon is typically RBBB in morphology due to its longer refractory period, it is possible to have a LBBB morphology. Ashman’s phenomenon can be conducted consecutively which can mimic wide complex tachycardia, specifically non-sustained ventricular tachycardia. However, Ashman phenomenon does not respond to ventricular tachycardia treatment (e.g., amiodarone or sodium channel blockade). Instead, treatment focuses on rate control with either calcium channel blockade or beta blockade, as underlying rate control will terminate the phenomenon.

Take Home Points:

-Ashman phenomenon typically occurs during atrial fibrillation but can occur in other supraventricular dysrhythmias.

-It is characterized by a prolonged R-R, followed by a short R-R, then an aberrantly conducted beat with RBBB morphology without a compensatory pause.

-It can be mistaken for non-sustained ventricular tachycardia, though the preceding R-R intervals and RBBB pattern should suggest that this could be Ashman phenomenon.

-Rate control is the mainstay of treatment.

References:

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3. Gouaux JL, Ashman R. Auricular fibrillation with aberration simulating ventricular paroxysmal tachycardia. Am Heart J. 1947 Sep;34(3):366-73.
4. Fisch C. Electrocardiography of arrhythmias: from deductive analysis to laboratory confirmation–twenty-five years of progress. J Am Coll Cardiol. 1983 Jan;1(1):306-16.
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