Ashman Phenomenon

Introduction
Background

Ashman phenomenon is an aberrant ventricular conduction due to a change in QRS cycle length. 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.1 This causes diagnostic confusion with premature ventricular complexes (PVCs). If a sudden lengthening of the QRS cycle occurs, the subsequent impulse with a normal or shorter cycle length may be conducted with aberrancy.
Pathophysiology

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.

Frequency
United States

No geographic variations occur. Ashman phenomenon is related to the underlying pathology and is a common ECG finding in clinical practice.
Mortality/Morbidity

Ashman phenomenon is simply an electrocardiographic manifestation of the underlying condition; therefore, the morbidity and mortality is related to the underlying condition.
Clinical
History
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, 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.
Physical
No specific physical examination findings are described for Ashman phenomenon.
Pulse findings may include an irregular pulse, tachycardia, and/or pulse deficit in atrial fibrillation.
Causes

Conditions causing an altered duration of the refractory period of the bundle branch or the ventricular tissue cause Ashman phenomenon. These conditions are commonly observed in atrial fibrillation, atrial tachycardia, and atrial ectopy.

http://emedicine.medscape.com/article/161028-overview