Left posterior fascicular block

**Definition:** Disorder of the atrioventricular conduction system characterised by right axis deviation for age (between 90° and 180° in adults), with a qR pattern in inferior leads, rS pattern in leftward leads (I and aVL), and a QRS duration that does not meet age dependent criteria for complete bundle branch block (less than 120 ms in adults, less than 100 ms in children 4 to 16 years of age, and less than 90 ms in children less than 4 years of age)