Differential Diagnosis

  • Premature ventricular contraction (PVC)
  • Third-degree heart block
  • Ashman phenomenon
  • Atrial fibrillation with rapid ventricular response
  • Nonsustained ventricular tachycardia

Diagnosis

This patient was diagnosed with Ashman phenomenon. This ECG shows an irregularly irregular rhythm with a rate of 83 bpm and a normal axis. There are no p waves present, the QRS complex is generally narrow, and there are no signs of ischemia in the ST segments. There are two aberrantly conducted beats with wide QRS complexes and unifocal morphology. In both instances, a prolonged R-R interval is followed by a relatively short R-R interval, which is then terminated by an aberrant beat. This is consistent with Ashman phenomenon.

Ashman phenomenon was first described by Drs. Gouaux and Ashman in 1947 and is a result of the variability in the refractory periods of the myocardium with varying heart rates.1 The refractory period of the His-Purkinje system is proportional to the length of the preceding R-R interval, so longer R-R intervals result in longer refractory periods and vice versa.

When a long R-R interval precedes a short R-R interval, parts of the His-Purkinje system are still refractory, and the resultant beat appears abnormal (Figure 2). Commonly, this aberrant beat will have a right bundle branch block (RBBB) morphology because the right bundle has a longer refractory period than the left.2

Ashman phenomenon
Figure 2. Prolonged RR interval (*) followed by short RR interval (+) terminating in an aberrantly conducted beat (↓)

This pattern is typically seen in atrial fibrillation, where a short R-R interval can frequently follow a longer one. However, it can also be seen in other supraventricular arrhythmias.

Ashman phenomenon can be diagnosed by the Fisch criteria, first described by Dr. Charles Fisch. The criteria include: a relatively long R-R interval preceding an R-R terminated by the aberrant QRS complex, a RBBB-like aberrancy with normal orientation of the QRS vector, irregular coupling of aberrant QRS complexes, and the lack of a fully compensatory pause following the aberrant beat.3

Ashman phenomenon is often confused for a PVC if a single aberration is present, and less commonly mistaken for nonsustained ventricular tachycardia when a series of aberrant beats are present. It can be differentiated from both by the lack of compensatory pause following the aberrantly conducted complex. PVC action potentials initiate in the ventricles and result in a compensatory pause during which the ventricles repolarize; however, Ashman phenomenon beats are supraventricular in origin and lack a compensatory pause. It is important to differentiate Ashman phenomenon from wide complex tachycardias of ventricular origin and other cardiac dysrhythmias to avoid unnecessary diagnosis and interventions.

Third-degree heart block, a condition in which complete atrioventricular dissociation leads to a slower, escape rhythm, is not present on this ECG, nor is atrial fibrillation with rapid ventricular response.

Learnings/What to Look For

  • Ashman phenomenon is an aberrantly conducted supraventricular beat that results from the variability of refractory periods within the conduction system
  • Identification of this phenomenon will help distinguish it from an ectopic beat or ventricular tachycardia
  • While commonly seen in atrial fibrillation, Ashman phenomenon can be seen in any supraventricular arrhythmia

Pearls for Initial Management

  • No treatment is required for isolated complexes seen in Ashman phenomenon3
  • Identifying Ashman phenomenon and differentiating it from ectopic beats and ventricular tachycardia will prevent unnecessary transfers and consults
  • While there is no treatment necessary for Ashman phenomenon, always consider the underlying cardiac condition and initial presentation when determining the need for transfer or cardiology consult

References

  1. Gouaux, JL, Ashman R. Auricular fibrillation with aberration simulating ventricular paroxysmal tachycardia. Am Heart J. 1947;34(3):366–373.
  2. Singla V, Singh B, Singh Y, Manjunath CN. Ashman phenomenon: a physiological aberration. Case Reports. 2013(May24 1), bcr2013009660–bcr2013009660.
  3. Lakusic N, Mahovic D, Slivnjak V. Ashman phenomenon: an often unrecognized entity in daily clinical practice. Acta Clin Croat;2010;2013:99–100.
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Case courtesy of ECG Stampede www.ECGStampede.com
An 87-Year-Old Male with Chest Pain, SOB, and a History of Valvular AFib, Stroke, and Heart Failure
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