ECG Diagnostic criteria
- QRS duration > 120ms
- RSR’ pattern in V1-3 (“M-shaped” QRS complex)
- Wide, slurred S wave in lateral leads (I, aVL, V5-6)
Associated features incude:
- Appropriate discordance with ST depression and/or T-wave inversion in right precordial leads (V1-3).
In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads
- In RBBB, the left ventricle is activated normally, thus the early part of the QRS complex correlating to septal depolarisation is unchanged
- There is delayed activation of the right ventricle as depolarisation originates from the left ventricle across the septum. This produces a secondary R wave (R’) in the precordial leads, and a wide, slurred S wave in lateral leads
- Normal activation of the left ventricle means that cardiac axis remains normal in isolated RBBB
ECG QRS Morphology
QRS Morphology in V1
Sometimes rather than an RSR’ pattern in V1, there may be a broad monophasic R wave or a qR complex.
QRS Morphology in Lateral Leads
- Appropriate discordance refers to the fact that abnormal depolarisation should be followed by abnormal repolarisation, which appears discordant to the preceding QRS complex
- In RBBB, this manifests as ST depression and/or T-wave inversion in leads V1-3
Causes of Right Bundle Branch Block
- Right ventricular hypertrophy / cor pulmonale
- Pulmonary embolus
- Ischaemic heart disease
- Rheumatic heart disease
- Congenital heart disease (e.g. atrial septal defect)
- Lenègre-Lev disease: primary degenerative disease (fibrosis) of the conducting system
There is increasing literature suggesting that in the context of chest pain, a new RBBB is highly concerning for OMI and a potential indication for immediate reperfusion therapy. The right bundle branch is supplied by LAD perforators in most patient populations and thus occlusion of this branch may manifest as a new RBBB +/- LAFB.
ECG Examples of Right Bundle Branch Block
RBBB with LAFB.
- Broad QRS > 120ms
- Note the prominent delayed RV conduction, manifested as a tall, broad R wave (R’) best seen in lead V1
- Widened S wave is best appreciated in lead I
- There is appropriate discordance in the right precordial leads with T-wave inversion
- Typical RSR’ pattern in V1-2
- Widened S waves again demonstrated in lateral leads, especially V4-6
- Appropriate discordance in leads V1-2
- RSR’ pattern in V1-3
- Lateral S wave changed are not evident here
- Note note normal axis in isolated RBBB
RBBB with LAFB in the context of chest pain.
- RBBB is seen with RSR’ pattern in V1-3 and slurred S waves in lateral leads
- There is concordant ST segment changes best seen in V2, and hyper-acute T waves inferiorly. This patient was found to have a 99% proximal LAD occlusion. See OMI: Replacing the STEMI misnomer for further case details
- 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.
- Left bundle branch block LBBB
- Right Bundle Branch Block RBBB
- Left anterior fascicular block LAFB
- Left posterior fascicular block LPFB
- Interventricular Conduction Delay IVCD
- Bifascicular block
- Trifascicular block
- Complete Heart block CHB
- OMI: Replacing the STEMI misnomer
- Wiesbauer F, Kühn P. ECG Yellow Belt online course: Become an ECG expert. Medmastery
- Wiesbauer F, Kühn P. ECG Blue Belt online course: Learn to diagnose any rhythm problem. Medmastery
- Rawshani A. Clinical ECG Interpretation ECG Waves
- Smith SW. Dr Smith’s ECG blog.
- Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
- Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
- Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
- Hampton J. The ECG Made Practical 7e, 2019
- Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography 1e, 2009
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
- Mattu A, Brady W. ECG’s for the Emergency Physician Part I 1e, 2003 and Part II
- Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004
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