Right Bundle Branch Block

Before we discuss bundle branch blocks, a review of normal cardiac conduction is warranted. In a normal heart, cardiac conduction begins with stimulus from the sinoatrial (SA) node. This firing of the SA node causes the atria to depolarize and contract simultaneously. During atrial depolarization, the stimulus continues downward to the atrioventricular (AV) node, where it is slowed, allowing for complete contraction of the atria. From the AV node, the stimulus travels through the His bundle and then on to the left and right bundle branches. In normal conduction, the bundle branches carry the stimulus downward at exactly the same speed to the Purkinje fibers of their respective ventricles such that the ventricles depolarize and contract at exactly the same time (Figure 1). This pathway is the most efficient way to provide maximal cardiac output: simultaneous contraction of the atria followed by simultaneous contraction of the ventricles