An intraventricular conduction abnormality refers to a conduction disturbance in either the right or left bundle branch or in 1 of the 2 divisions (fascicles) of the left bundle branch. A delay in conduction or block in either the right or left bundle is commonly referred to as a bundle-branch block (BBB; right or left). A delay in conduction through one of the fascicles associated with the left bundle is referred to as a hemiblock or fascicular block. This column will describe the anatomy of the intraventricular conduction system, with a focus on etiologies of bundle-branch blocks and the electrocardiographic criteria associated with each.

The Bundle of His divides into the right and left bundle branches within the ventricular septum (Figure 1). The right bundle branch traverses down the right side of the ventricular septum, branching off into the Purkinje network. The main left bundle almost immediately divides...

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