Bundle-branch blocks are the most common electrophysiological abnormalities of ventricular conduction. With these abnormalities, the impulse in one branch is impaired while the contralateral branch remains intact. Consequently, one ventricle is activated normally, but the ventricle on the affected side is delayed. 

Right bundle-branch blocks are more common than left bundle-branch blocks. Both types are caused by coronary heart disease, hypertension, heart valve replacement surgeries, and degeneration of the intraventricular conduction system in patients with Lenègre disease.

The ECG records a graphical representation of the impulse vectors in the heart’s electrical conduction system. In the normal ECG, the left ventricular vectors are greater than right ventricular vectors by a ratio of 8:1. When an ECG exhibits significant right ventricular vectors, the patient either has RVH (see section 7) or RBBB.

With complete and incomplete bundle-branch blocks, the electrical conduction is slowed down significantly but not totally occluded. A discernible velocity pattern on the ECG helps to distinguish them as either complete or incomplete. RBBBs resolve after medical or surgical interventions. They generally occur in patients with coronary artery disease, cardiac infection, pulmonary embolism, and trauma. LBBBs also typically resolve after treatment of arterial hypertension.