Normal sinus rhythm incomplete right bundle branch block

Right bundle branch block (RBBB) is a slowing of electrical impulses to the heart’s right ventricle. This is the lower-right part of the heart.

In order for your heart to beat properly, electrical impulses are sent through a pathway, including two areas on either ventricle called the right and left bundles.

If either of these bundles becomes damaged due to issues like a heart attack or high blood pressure, the electric impulse can move more slowly. This makes it harder for the heart to pump blood throughout your body and may cause your heart to beat abnormally.

RBBB doesn’t always cause symptoms. In fact, some people have it for years and don’t realize it until it shows up on an electrocardiogram (ECG or EKG).

But in rare cases, a delay in the arrival of electrical impulses to the heart’s right ventricle can cause syncope. Syncope is fainting due to unusual heart rhythms that affect blood pressure.

Some people might also experience something called presyncope. This involves feeling like you’re about to faint but never actually fainting.

RBBB doesn’t always require treatment, especially if you don’t have any underlying heart conditions. If you do have another heart condition, your doctor might suggest treating the underlying cause.

If you have RBBB due to a heart attack with other electrical system conditions, for example, you may need a pacemaker. This is a device that emits electricity to help your heart maintain a consistent rhythm.

If you have high blood pressure, you may need to take medication to help manage it. This will also reduce the strain on your heart.

While treating the underlying condition might not completely get rid of RBBB, it can prevent future damage.

The right side of the heart is responsible for pumping blood to the lungs to be oxygenated. The oxygenated blood returns to the left side of the heart, where it’s pumped to the rest of the body.

This is why RBBB is sometimes related to lung problems, like:

• pulmonary embolism
• cardiomyopathy

Other potential causes of RBBB include:

• heart attack
• heart failure
• infection in the heart tissue or valves
• minor chest trauma

Also, as you age, your heart tissue can gradually change. Sometimes, this results in RBBB.

While anyone can develop RBBB, some people have a higher risk due to other conditions that affect their heart or lungs.

Conditions that can increase your risk of bundle branch block on either the left or right side include:

• atrial or ventricular septal defects
• cardiomyopathy
• high blood pressure

If you have any of these conditions, your doctor might regularly monitor your heart rhythm to detect any signs of a bundle branch block.

Doctors usually diagnose RBBB by using an electrocardiogram. This is a painless test that involves placing stickers called leads around your chest. The leads conduct electricity. They’re connected to wires that sense the electrical impulses of your heart and trace your heart’s rhythm.

Sometimes, a bundle branch block makes it harder for doctors to diagnose other heart conditions, like heart failure or enlargement. If you’ve been diagnosed with RBBB, make sure to tell any other doctors you see that you have one.

When they’re first discovered, right bundle branch blocks can seem alarming, but they’re usually not as serious as they sound. In some cases, you might not even know you have one for many years.

If you have RBBB that needs treatment, your doctor will develop a plan that addresses the underlying cause.

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).

Electrophysiology

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

• 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)
• Myocarditis
• Cardiomyopathy
• 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

Isolated RBBB.

• Typical RSR’ pattern in V1-2
• Widened S waves again demonstrated in lateral leads, especially V4-6
• Appropriate discordance in leads V1-2

Isolated RBBB.

• 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

• 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

Further reading

• Butterly S, Larsen P. Right Bundle Branch Block. HeartHQ
• Butterly S, Larsen P. Left Bundle Branch Block. HeartHQ

Advanced Reading

Online

• 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.

Textbooks

• 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
• Smith SW. The ECG in Acute MI. 2002 [PDF]

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

cite

ECG LIBRARY

Electrocardiogram

Ed Burns

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

Robert Buttner

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner