Bundle branch block


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 health condition, such as heart disease, that caused bundle branch block.

Bundle branch block

Electrical impulses that cause your heart to beat (contract) originate in the upper right chamber (right atrium) of the heart and travel to the lower chambers (ventricles). In bundle branch block, the pathway that these impulses travel on is delayed or blocked. The pathway includes a bundle with two branches — the left and right bundles. If one of these is damaged, it can make it harder for your heart to beat normally, as your ventricles don’t beat in coordination with each other.


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

Signs and symptoms in people who have them might include:

  • Fainting (syncope)
  • 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 if your doctor has already diagnosed you as having bundle branch block, ask your doctor how often you should have follow-up visits. You might want to carry a medical alert card that identifies you as having bundle branch block in case a doctor who isn't familiar with your medical history sees you in an emergency.


Normally, electrical impulses within your heart's muscle signal it to beat (contract). These impulses travel along a pathway, including the right and the left bundles. If one or both of these branch bundles become damaged — due to a heart attack, for example — this can block the electrical impulses and cause your heart to beat abnormally.

The cause for bundle branch blocks can differ depending on whether the left or right bundle branch is affected. It's also possible that this condition can occur without a known cause.

Causes can include:

Left bundle branch block

  • Heart attacks (myocardial infarction)
  • Thickened, stiffened or weakened heart muscle (cardiomyopathy)
  • A viral or bacterial infection of the heart muscle (myocarditis)
  • High blood pressure (hypertension)

Right bundle branch block

  • A heart abnormality that's present at birth (congenital) — such as atrial septal defect, a hole in the wall separating the upper chambers of the heart
  • A heart attack (myocardial infarction)
  • A viral or bacterial infection of the heart muscle (myocarditis)
  • High blood pressure in the pulmonary arteries (pulmonary hypertension)
  • A blood clot in the lungs (pulmonary embolism)

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.


The main complication of bundle branch block, right or left, is to progress to a complete block of the electric conduction from the upper chambers of the heart to the lower. This can slow your heart rate, which can cause fainting and lead to serious complications and abnormal heart rhythms.

People who have a heart attack and develop a left bundle branch block have a higher chance of complications, including sudden cardiac death, than do people who don't develop the condition after a heart attack.

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.


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. This records the electrical impulses in your heart through wires attached to the skin on your chest and other places on your body. Abnormalities might indicate 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 shows the thickness of your heart muscle and whether your heart valves are moving normally. It can pinpoint a condition that caused the bundle branch block.


Most people with bundle branch block are symptom-free and don't need treatment.

However, if you have a heart condition causing bundle branch block, treatment might involve medications to reduce high blood pressure or lessen the effects of heart failure.

Additionally, depending on your symptoms and whether you have other heart problems, your doctor might recommend:

  • A pacemaker. If you have bundle branch block and a history of fainting, your doctor might recommend a pacemaker. This compact device is implanted under the skin of your upper chest (internal pacemaker) with two wires that connect to the right side of your heart. The pacemaker provides electrical impulses when needed to keep your heart beating regularly.
  • Cardiac resynchronization therapy. Also known as biventricular pacing, this procedure is similar to having a pacemaker implanted. However, with this procedure, there's a third wire that's connected to the left side of the heart so the device can keep both sides in proper rhythm.

    This therapy, which is meant to improve the coordination of both lower chambers of the heart so that they contract at the same time, is used in people with low pumping function and a bundle branch block.

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?

Last Updated May 15, 2018

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