Features of right bundle branch block (RBBB)

Features of right bundle branch block (RBBB)

Initial 40 ms of the QRS is normal in right bundle branch block. The QRS width is 120 ms or more in complete RBBB. Lead V1 shows an rSR’ pattern. The secondary R wave is taller than the initial r wave. The initial r wave may be absent when there is anterior wall myocardial infarction, resulting in QR pattern in V1. There will be associated ST segment depression and T wave inversion, in anterior leads known as secondary ST – T changes. The secondary ST – T changes are repolarization abnormalities secondary to an abnormal depolarization sequence due to the conduction abnormality.

Lead I and V6 show a slurred S wave in RBBB. The QRS axis is normal in isolated right bundle branch block. Left axis deviation indicates associated left anterior hemiblock and right axis deviation indicates associated left posterior hemiblock. Sometimes right upper quadrant axis may be noted when RBBB is associated with other conditions.

Brugada syndrome comes in the differential diagnosis of an RBBB pattern. But the ST segment is elevated in V1 in Brugada syndrome while it is depressed in RBBB. Left ventricular ectopic beats and paced rhythm from the left ventricle also have right bundle branch block pattern.