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Mayo Clinic Health Library

Bundle branch block

Updated: 10-15-2020

Overview

Bundle branch block is a condition in which there's a delay or blockage along the pathway that electrical impulses travel to make your heart beat. It sometimes makes it harder for your heart to pump blood efficiently through your body.

The delay or blockage can occur on the pathway that sends electrical impulses either to the left or the right side of the bottom chambers (ventricles) of your heart.

Bundle branch block might not need treatment. When it does, treatment involves managing the underlying health condition, such as heart disease, that caused bundle branch block.

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Symptoms

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

Rarely, signs and symptoms may include fainting (syncope) or feeling as if you're going to faint (presyncope).

When to see a doctor

If you've fainted, see your doctor to rule out serious causes.

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

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Causes

Normally, 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, and your heart will beat abnormally.

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:

Left bundle branch block

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

Right bundle branch block

  • Blood clot in the lungs (pulmonary embolism)
  • Heart attack (myocardial infarction)
  • Heart defects that are present at birth (congenital) — 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)
  • Infection of the heart muscle by bacteria or virus (myocarditis)
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Risk factors

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 your risk of having bundle branch block.
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Complications

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 your heart rate, leading to fainting, abnormal heart rhythms and other serious complications.

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

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Diagnosis

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

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

  • Electrocardiogram (ECG or EKG). An ECG records the electrical impulses in your heart using wires attached to the skin on your chest and sometimes your limbs. This test can show signs of a bundle branch block, as well as which side is being affected.
  • Echocardiogram. This test uses sound waves to provide detailed images of the heart's structure and the thickness of your heart muscle. It can show whether your heart valves are moving normally. Your doctor can use this test to pinpoint a condition that caused the bundle branch block.
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Treatment

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 your specific symptoms and other heart conditions.

Medications

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.

Surgeries and other procedures

If you have bundle branch block and a history of fainting, your doctor might recommend a pacemaker. A pacemaker is a compact device implanted under the skin of your upper chest with two wires that connect to the right side of your heart. The pacemaker releases electrical impulses when needed to keep your 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 is meant to improve the coordination of both lower chambers of the heart so that they contract at the same time.

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Preparing for an appointment

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.

What you can do

Be aware of pre-appointment restrictions. When you make the appointment, ask if there's anything you need to do in advance, such as restrict your caffeine intake 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 doctor

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 doctor 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?

What to expect from your doctor

Your doctor is likely to ask you questions, including:

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