- In RBBB, activation of the right ventricle is delayed as depolarisation has to spread across the septum from the left ventricle.
- The left ventricle is activated normally, meaning that the early part of the QRS complex is unchanged.
- The delayed right ventricular activation produces a secondary R wave (R’) in the right precordial leads (V1-3) and a wide, slurred S wave in the lateral leads.
- Delayed activation of the right ventricle also gives rise to secondary repolarization abnormalities, with ST depression and T wave inversion in the right precordial leads.
- In isolated RBBB the cardiac axis is unchanged, as left ventricular activation proceeds normally via the left bundle branch.
ECG changes in RBBB
- Broad QRS > 120 ms
- RSR’ pattern in V1-3 (‘M-shaped’ QRS complex)
- Wide, slurred S wave in the lateral leads (I, aVL, V5-6)
- ST depression and T wave inversion in the right precordial leads (V1-3)
- Sometimes rather than an RSR’ pattern in V1, there may be a broad monophasic R wave or a qR complex.
Causes of RBBB
- Right ventricular hypertrophy / cor pulmonale
- Pulmonary embolus
- Ischaemic heart disease
- Rheumatic heart disease
- Myocarditis or cardiomyopathy
- Degenerative disease of the conduction system
- Congenital heart disease (e.g. atrial septal defect)
More ECG Examples of RBBB
- Incomplete RBBB is defined as an RSR’ pattern in V1-3 with QRS duration < 120ms.
- It is a normal variant, commonly seen in children (of no clinical significance).
Differential Diagnosis of RBBB
- An RSR’ pattern in V1-3 may also be caused by Brugada syndrome – an ECG pattern associated with malignant ventricular arrhythmias.
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- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice (6th edition), Saunders 2008.
- Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.