7.4.2 Abnormal impulse formation
The most common mechanism of abnormal impulse formation is increased automaticity. This is often responsible for the generation of atrial or ventricular premature beats. Automaticity develops when an abnormal focus within the atria or ventricles becomes a pacemaker site which fires at a higher rate than the usually dominant sinus node. The enhanced impulse initiation results from fast phase 4 depolarisation, The other form of abnormal impulse formation is triggered activity. This form of ectopic focus requires an initiating depolarisation with an afterdepolarisation.
Mechanisms of arrhythmogenesis are important in order to understand the pathophysiology of arrhythmias and the potential effects of disease. More detailed discussions are contained in articles in the reading list. However, as yet, identification of the mechanisms of arrhythmias has had little practical influence on their treatment.