![]() ![]() Premature ventricular depolarization: As exemplified in Figure 1, if the atrial impulse reaches the ventricular His-Purkinje system too early – while conduction fibers are still refractory – the impulse might be blocked. This is a frequent finding among healthy individuals and in those with heart disease.Ashman’s phenomenon.Īberrancy can occur in three different situations, all related to changes in the length of the cardiac cycle. ![]() In clinical practice aberration is commonly seen in patients with atrial fibrillation because these patients have rapid and irregular rhythms with frequently changing RR intervals. The resulting QRS complex has a right bundle branch block morphology (rSR pattern), which is due to aberrant ventricular conduction (aberration, aberrancy). The supraventricular impulse reaches the His-Purkinje system while the right bundle branch is still refractory and therefore blocks the impulse. The figure shows a supraventricular extrasystole (i.e a premature atrial complex/beat) which is conducted with aberration. This is an example of how changes in the length of the cardiac cycle causes aberration.įigure 1. In this case ( Figure 1) it encounters a refractory right bundle branch and therefore the impulse is conducted with right bundle branch block morphology. The impulse from the premature beat reaches the His-Purkinje system early, while some fibers are still refractory. A premature atrial beat is simply an extra (unexpected) beat discharged by an ectopic focus in the atria. Aberrant conduction occurs when the length of the cardiac cycle is changed without a compensatory change in the length of the refractory period. This is explained by the changes of the refractoriness in the His-Purkinje system related to changes in the RR interval.įigure 1 shows a premature atrial beat causing aberrant ventricular conduction. It follows that long cycles (long RR intervals) are associated with long refractory periods and short RR intervals have shorter refractory period. The length of the refractory period is shortened as heart rate increases and vice versa, i.e the length of the refractory period is prolonged as heart rate decreases. The length of the refractory period (discussed in Chapter 1, Basic electrophysiology) varies with heart rate and it changes rapidly with changing heart rate. Should any component of the ventricular conduction system not have repolarized by the time the next impulse reaches the ventricles, the impulse will be blocked there. It is discussed in this chapter because the phenomenon is frequently seen during arrhythmias. As discussed previously all cardiac cells (conduction cells and contractile cells) must repolarize rapidly in order to be excitable by the time the next action potential arrives. Aberrant ventricular conduction (aberrancy, aberration)Īberrant conduction is not a mechanism of arrhythmia it is a ventricular conduction disturbance. ![]()
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