Cardiac aberrancy is a type of disruption in the shape of the electrocardiogram signal, representing abnormal activation of the ventricular heart muscle via the electrical conduction system of the heart. Normal activation utilizes the bundle of His and Purkinje fibers to produce a narrow (QRS) electrical signal. Aberration occurs when the electrical activation of the heart, which is caused by a series of action potentials, is conducting improperly which can result in temporary changes in the morphology that looks like:
This is in contrast to a permanent dysfunction of the electrical pathways that produces wide QRS complexes in one of the above patterns or combinations of patterns (ie, bifascicular block).
In the context of atrial fibrillation, the Ashman phenomenon is a form of aberrancy.
Aberrancy is due to prematurity in which part of the conduction system is still refractory and cannot conduct the premature depolarization. This effect can sometimes be seen in the setting of a faster heart rate (tachycardia) and so is termed "rate-related aberrancy." After the first aberrant complex, subsequent complexes may be wide due to concealed conduction rather than aberrancy.