Bundle Branch Block

Overview

The heart has a built-in electrical system that tells it when to beat. After the signal starts in the upper chambers, it travels down two pathways, the right and left bundle branches, to make the lower chambers (ventricles) contract together. A bundle branch block is a delay or blockage in one of these pathways, so one ventricle is activated a fraction of a second after the other.

Bundle branch block is usually discovered on an electrocardiogram (ECG) and often causes no symptoms. It can be classified as right bundle branch block (RBBB) or left bundle branch block (LBBB). On its own, the block is not a disease but a sign of how the electrical signal is traveling. Its importance depends largely on whether there is underlying heart disease, which is why doctors look at the bigger picture rather than the ECG finding alone.

Symptoms

Most people with bundle branch block have no symptoms at all, and it is found by chance on an ECG done for another reason. When symptoms occur, they usually come from an underlying heart problem rather than the block itself, and may include:

• Fainting or near-fainting
• Palpitations or awareness of the heartbeat
• Dizziness or lightheadedness
• Shortness of breath, especially with exertion

Fainting in someone with bundle branch block can occasionally signal a more serious conduction problem and should be assessed.

Causes

The cause often differs between the two types. Right bundle branch block can occur in people with completely healthy hearts, while left bundle branch block is more often linked to underlying heart disease. Possible causes include:

• High blood pressure
• Coronary artery disease or a previous heart attack
• Heart muscle disease (cardiomyopathy) or heart failure
• Heart valve disease
• Lung conditions that strain the right side of the heart (for RBBB)
• Aging of the heart's electrical system
• Sometimes no identifiable cause, especially with RBBB in young, healthy people

Risk Factors

• Older age
• High blood pressure
• Coronary artery disease or prior heart attack
• Heart failure or cardiomyopathy
• Chronic lung disease (for right bundle branch block)
• Other heart structural problems

Diagnosis

Bundle branch block is diagnosed on an ECG, and further tests assess whether there is underlying heart disease:

• Electrocardiogram (ECG): Shows the characteristic widened pattern and identifies right versus left block.
• Echocardiogram: An ultrasound of the heart to check the heart muscle, valves, and pumping function.
• Other tests: Such as exercise testing or monitoring, and tests for coronary artery disease when symptoms or risk factors are present.

In a person with no symptoms and no heart disease, especially with RBBB, no further treatment may be needed beyond noting the finding.

Treatment

Bundle branch block itself usually does not require treatment. Care focuses on any underlying condition and on watching for more serious conduction problems:

• Treating the cause: Managing high blood pressure, coronary artery disease, heart failure, or valve disease as appropriate.
• Monitoring: Follow-up ECGs and clinical review, particularly for new left bundle branch block, which may prompt a search for heart disease.
• Pacemaker: Only needed if the block is part of a more advanced conduction problem that causes the heart to beat too slowly or leads to fainting.
• Specialized devices: In selected people with heart failure and left bundle branch block, a particular type of pacemaker may improve heart function.

For many people, especially with isolated RBBB and a healthy heart, no treatment is needed and the outlook is good.

Prevention

• Keep blood pressure well controlled
• Manage cholesterol and avoid smoking to reduce coronary artery disease
• Treat heart conditions such as heart failure or valve disease
• Stay active and maintain a heart-healthy lifestyle
• Attend follow-up so changes in the heart's electrical system can be tracked

When to See a Doctor

If a bundle branch block is found on a routine ECG and you have no symptoms, your doctor will advise whether any further checks are needed. Seek prompt medical care if you experience:

• Fainting or near-fainting
• New or worsening shortness of breath
• Palpitations or a very slow or irregular heartbeat

Seek emergency care for chest pain, severe breathlessness, or collapse, which may signal a heart attack or a serious heart rhythm problem.

Related Topics

Frequently Asked Questions

References

1. Mayo Clinic. Bundle branch block.
2. MedlinePlus, U.S. National Library of Medicine. Bundle branch block.
3. American Heart Association. Conduction disorders.
4. National Heart, Lung, and Blood Institute (NHLBI). Arrhythmia.