Right Bundle Branch Block (RBBB)
- 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.
Typical RSR’ pattern (‘M’-shaped QRS) in V1
Wide slurred S wave in lead I
Typical pattern of T-wave inversion in V1-3 with RBBB
Causes of Right Bundle Branch Block
- 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)
ECG Examples of Right Bundle Branch Block
- 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.
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Dubin D. Rapid Interpretation of EKG’s
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e