Ashman phenomenon
Ashman phenomenon or Ashman beat is a physiological aberrancy of conduction of the ventricle as a result of a change in the QRS cycle length 1. In 1947, Gouaux and Ashman reported that in atrial fibrillation, when a relatively long cycle was followed by a relatively short cycle, the beat with a short cycle often has right bundle-branch block (RBBB) morphology 2. Ashman phenomenon is typically seen in atrial fibrillation when a relatively long cycle is followed by a relatively short cycle. It can also be seen in other supraventricular tachyarrhythmias. The Fisch criteria for the diagnosis of Ashman phenomenon includes—a relatively long cycle immediately preceding the cycle terminated by the aberrant QRS complex, right bundle branch block (RBBB)-form aberrancy with normal orientation of the initial QRS vector, irregular coupling of aberrant QRS complexes and lack of a fully compensatory pause 3. The pathophysiology of Ashman phenomenon depends on the variability of relative refractory period of the conduction tissues depending upon the heart rate. The action potential duration (ie, refractory period) changes with the R–R interval of the preceding cycle. A longer cycle lengthens the ensuing refractory period, and if a shorter cycle follows, the beat terminating the cycle is likely to be conducted with aberrancy. The RBBB pattern is more common because of the longer refractory period of the right bundle branch.
Conditions causing an altered duration of the refractory period of the bundle branch or the ventricular tissue cause Ashman phenomenon 4. These conditions are commonly observed in atrial fibrillation, atrial tachycardia, and atrial ectopy.
Ashman phenomenon is simply an electrocardiographic manifestation of the underlying condition; therefore, the morbidity and mortality is related to the underlying condition.
It is important to understand Ashman phenomenon because it will be useful in differentiating aberrantly conducting beat from wide complex arrhythmia of ventricular origin as their prognosis and treatment are entirely different.
Intermittent ventricular preexcitation, as in Wolf-Parkinson-White syndrome, should also be considered in the differential diagnosis of Ashman phenomenon.
It is important to diagnose and appropriately treat disease entities associated with Ashman phenomenon as well as to diagnose ventricular tachycardia.
The treatment involves the management of the underlying cardiac condition.
Ashman phenomenon key points
- Ashman phenomenon is an aberrantly conducted supraventricular beat due to change in refractory period of conduction system according to the preceding cycle length.
- Ashman phenomenon can be seen in any supraventricular arrhythmia.
- Ashman phenomenon should be differentiated from ventricular premature complexes or rarely ventricular tachycardia, as the prognosis and treatment of both are entirely different.
- Most commonly Ashman phenomenon has right bundle branch block (RBBB) morphology but it can have left bundle branch block (LBBB) morphology also.
Figure 1. Ashman phenomenon ECG
Footnote: ECG showed atrial fibrillation with aberrant conduction suggestive of ‘Ashman’s phenomenon’ in sixth and 14th beat (blue arrows). Note the variation in cycle length (R–R duration) in the preceding beats, that is, short–long–short cycle (black star).
[Source 1 ]Ashman phenomenon causes
Ashman phenomenon is an intraventricular conduction abnormality caused by a change in the heart rate. This is dependent on the effects of rate on the electrophysiological properties of the heart and can be modulated by metabolic and electrolyte abnormalities and the effects of drugs.
The aberrant conduction depends on the relative refractory period of the components of the conduction system distal to the atrioventricular node. The refractory period depends on the heart rate. Action potential duration (ie, refractory period) changes with the R-R interval of the preceding cycle; shorter duration of action potential is associated with a short R-R interval and prolonged duration of action potential is associated with a long R-R interval. A longer cycle lengthens the ensuing refractory period, and, if a shorter cycle follows, the beat ending it is likely to be conducted with aberrancy.
Aberrant conduction results when a supraventricular impulse reaches the His-Purkinje system while one of its branches is still in the relative or absolute refractory period. This results in slow or blocked conduction through this bundle branch and delayed depolarization through the ventricular muscles, causing a bundle-branch block configuration (ie, wide QRS complex) on the surface ECG, in the absence of bundle-branch pathology. A RBBB pattern is more common than a left bundle-branch block (LBBB) pattern because of the longer refractory period of the right bundle branch.
Several studies have questioned the sensitivity and specificity of the long-short cycle sequence. Aberrant conduction with a short-long cycle sequence has also been documented.
A study by Sardar et al 5 indicated that dofetilide, a delayed rectifier potassium current blocker used to treat atrial fibrillation, can promote the development of Ashman phenomenon, possibly through a reverse use-dependence effect associated with prolongation of the ventricular refractory period. The study involved 10 patients with atrial fibrillation who underwent dofetilide loading, receiving 250-500 micrograms of the drug every 12 hours. The investigators found that the total number of Ashman beats rose from 42±24 prior to the administration dofetilide to 93±79 after the first dose of the drug and 133±101 after the second dose.
Ashman phenomenon symptoms
Ashman phenomenon, per se, causes no symptoms. Symptoms, if present, are related to the premature complexes and are not related to whether the complexes are conducted aberrantly.
Ashman phenomenon diagnosis
The diagnosis of Ashman phenomenon is made using ECG evaluation findings. Patients may be asymptomatic or may have symptoms of the underlying cardiac condition.
Ashman phenomenon treatment
No treatment is needed for isolated complexes. Treat the underlying cardiac condition as appropriate.
References- Singla V, Singh B, Singh Y, Manjunath CN. Ashman phenomenon: a physiological aberration. BMJ Case Rep. 2013;2013:bcr2013009660. Published 2013 May 24. doi:10.1136/bcr-2013-009660 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3669876
- Gouaux JL, Ashman R. Auricular fibrillation with aberration stimulating ventricular paroxysmal tachycardia. Am Heart J. 1947. 34:366.
- Lakusic N, Mahovic D, Slivnjak V. Ashman phenomenon: an often unrecognized entity in daily clinical practice. Acta Clin Croat 2010;2013:99–100
- Ashman Phenomenon. https://emedicine.medscape.com/article/161028-overview
- Sardar MR, Khaji A, Robert J, et al. Abstract 10380: The Ashman Phenomenon in Patients With Atrial fibrillation Treated With an IKr Blocker, Dofetilide. Circulation. 2013.
