By Mayo Clinic Staff

In most people, bundle branch block doesn't cause symptoms. Some people with the condition don't know they have bundle branch block.

Rarely, symptoms of bundle branch block may include fainting (syncope) or feeling as if you're going to faint (presyncope).

If you've fainted, see a health care provider to rule out serious causes.

If you have heart disease or have been diagnosed with bundle branch block, ask your provider how often you should have follow-up visits.

Electrical impulses within the heart muscle cause it to beat (contract). These impulses travel along a pathway, including two branches called the right and the left bundles. If one or both of these branch bundles are damaged — due to a heart attack, for example — the electrical impulses can become blocked. As a result, the heart beats irregularly.

The cause for bundle branch blocks can differ depending on whether the left or the right bundle branch is affected. Sometimes, there is no known cause.

Causes can include:

• Heart attack (myocardial infarction)
• High blood pressure (hypertension)
• Inflammation of the heart muscle (myocarditis)
• Thickened, stiffened or weakened heart muscle (cardiomyopathy)

• Blood clot in the lungs (pulmonary embolism)
• Heart attack (myocardial infarction)
• Heart structure problems that are present at birth (congenital heart defects) — such as a hole in the wall separating the upper chambers of the heart (atrial septal defect)
• High blood pressure in the pulmonary arteries (pulmonary hypertension)
• Inflammation of the heart muscle (myocarditis)

Risk factors for bundle branch block include:

• Increasing age. Bundle branch block is more common in older adults than in younger people.
• Underlying health problems. Having high blood pressure or heart disease increases the risk of having bundle branch block.

If both the right and the left bundles are blocked, the main complication is a complete blockage of the electric signaling from the upper to the lower chambers of the heart. The lack of signaling can slow the heart rate. A slowed heart rate may lead to fainting, irregular heart rhythms and other serious complications.

Because bundle branch block affects the electrical activity of the heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks. It may lead to delays in proper management of those heart conditions.

If you have a right bundle branch block and you're otherwise healthy, you might not need a full medical checkup. If you have a left bundle branch block, you will need a thorough medical exam.

Tests that can be used to diagnose a bundle branch block or its causes include:

• Electrocardiogram (ECG or EKG). This quick and painless test measures the electrical activity of the heart. During an ECG, sensors (electrodes) are attached to the chest and sometimes to the arms or legs. An ECG can show how well the heart is beating. It can show signs of a bundle branch block, as well as which side of the heart is being affected.
• Echocardiogram. This test uses sound waves to provide detailed images of the heart and heart valves. It can show the structure and the thickness of the heart muscle. Your provider can use this test to pinpoint a condition that caused the bundle branch block.

Most people with bundle branch block don't have symptoms and don't need treatment. For example, left bundle branch block is not treated with medications. However, treatment depends on the specific symptoms and other heart conditions.

If you have a heart condition causing bundle branch block, treatment might involve medications to reduce high blood pressure or reduce symptoms of heart failure.

If you have bundle branch block and a history of fainting, your health care provider might recommend a pacemaker. A pacemaker is a small device implanted under the skin of the upper chest. Two wires connect it to the right side of the heart. The pacemaker releases electrical impulses when needed to keep the heart beating regularly.

If you have bundle branch block with low heart-pumping function, you may need cardiac resynchronization therapy (biventricular pacing). This treatment is similar to having a pacemaker implanted. But you'll have a third wire connected to the left side of your heart so the device can keep both sides in proper rhythm. Cardiac resynchronization therapy helps the heart's chambers squeeze (contract) in a more organized and efficient way.

Be aware of pre-appointment restrictions. When you make the appointment, ask if there's anything you need to do in advance. For example, you may need to limit or avoid caffeine before having heart function tests.

Make a list of:

• Your symptoms, including any that seem unrelated to the reason for which you scheduled the appointment, when they began and how often they occur
• Key personal information, including major stresses or recent life changes
• All medications, vitamins and supplements you take, including the doses
• Questions to ask your health care provider

Ask a family member or friend to come with you, if possible, to help you remember the information you receive.

For bundle branch block, questions to ask your provider include:

• What are the most likely causes of my symptoms?
• What tests do I need?
• What treatments are available, and which do you recommend?
• Will the bundle branch block return after treatment?
• What side effects might I expect from treatment?
• I have other health conditions. How can I best manage them together?
• Do you have brochures or other printed material I can have? What websites do you recommend?

You're likely to start by seeing your primary care doctor. You might be referred to a doctor trained in heart disorders (cardiologist).

Here's some information to help you get ready for your appointment.

Your health care provider is likely to ask you questions, including:

• Does anything seem to improve your symptoms?
• What, if anything, appears to worsen your symptoms?
• Has a health care provider ever told you that you have a bundle branch block?