Initial 40 msec of the QRS is normal in right bundle branch block (RBBB). The QRS width is more than or equal to 120 msec. Lead V1 shows and 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 repolarisation abnormalities secondary to an abnormal depolarisation sequence due to the conduction abnormality. Lead I and V6 shows 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. 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.
Prof. Dr. Johnson Francis MD, DM, FACC, FRCP Edin, FRCP London
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