Left bundle branch block is a heart condition that causes heart fragility. It does not always cause symptoms, but some people may feel lightheaded and develop chest pain.

An electrocardiogram (ECG) can record the heart’s rhythm and indicate the type of heart block a person has.

This article explains a left bundle branch block in more detail and looks at its causes, risk factors, symptoms, and more.

An electrocardiograph.Share on Pinterest
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Bundle branch blocks occur when there is blockage or disruption in the heart’s electrical impulses. They cause those impulses to travel more slowly to the heart’s ventricles.

It can happen on the left and right side pathways of the ventricles, and doctors can see this blockage on an electrocardiogram (ECG) machine.

A left bundle branch block can indicate an underlying heart condition. It causes an abnormal heart rhythm and is common in those who have experienced heart damage.

A right bundle branch block can develop in people without any health conditions.

People with a left bundle branch block have an increased risk of heart disease compared to the general population.

According to the National Library of Medicine (NLM), cardiac resynchronization treatment (CRT), one type of heart block therapy, can reduce death by up to 37%.

In rare cases, people may have congenital heart block, meaning they are born with this condition.

However, in most cases, heart block may develop during adulthood if a person has any of the following:

Dilated cardiomyopathy is one of the primary causes of left bundle branch block. It causes the heart chambers to enlarge so they can no longer contract effectively.

A 2017 review notes that left bundle branch block is more common in older adults. It affects less than 1% of those under 50 and nearly 6% of people who are 80 years and older.

Left bundle branch block does not usually cause symptoms, so people may not know that they have this heart problem unless they get cardiac testing.

It can cause bradycardia, or a slow heart rate, which can lead to any of the below symptoms:

In one 2014 case study, a person with this type of heart block experienced chest pain.

Medical professionals may use the following tools to determine if a person has a left bundle branch block.

Electrocardiogram (ECG)

An ECG measures the heart’s electrical impulses at rest or during exercise and can indicate the type of heart block present.

During the test, the doctors place electrodes on the person’s chest. The ECG produces a visual image of the heart rhythm.

People may also have to wear a portable ECG monitor so doctors can check the heart’s electrical activity over time.

An ECG test is painless, but people may feel some discomfort when the doctor removes the electrodes.

Holter monitor

A Holter monitor is a wearable device that can monitor the heart’s rhythm for up to 48 hours. It can detect changes in the heart’s rhythm, even if a person does not experience them frequently.

Implantable loop recorder

An implantable loop recorder is a heart recorder that medical professionals insert beneath the skin. It can record the heart rhythm for up to 3 years.

There is currently no treatment for a left bundle branch block. Doctors usually treat any accompanying heart condition a person may have.

For example, a pacemaker may be an option for people who develop a heart block while having a heart attack. This can help regulate the heart rhythm, as a bundle branch block can cause bradycardia and the heart to become fragile.

However, if a person has alternating right and left bundle branch blocks, a doctor may also recommend a pacemaker.

The Centers for Disease Control and Prevention (CDC) recommend exercising, eating a balanced diet, and avoiding smoking to help improve heart health.

The American Heart Association also recommends the following for those who have a pacemaker:

  • carrying a pacemaker ID card
  • avoiding strong electrical fields
  • going to regular pacemaker checkups
  • keeping an eye on your heart rate

Research shows that there is no specific treatment for people with left bundle branch block. However, a person may receive treatment if they have another heart condition.

The CDC recommends people seek immediate medical help if they or someone else is experiencing heart attack symptoms. These may include:

A person should also consider seeing a doctor if they have an irregular heartbeat, high blood pressure, or a family history of heart disease.

A left bundle branch block is a heart block condition mostly affecting older adults. It may also develop in people who have had a heart attack or heart surgery.

During an ECG test, a medical professional can examine the heart rhythm and determine if a person has a left bundle branch block.

People should seek medical attention if they experience chest pain, shortness of breath, or lightheadedness.