What Is Left Bundle Branch Block? Everything to Know

Medically Reviewed By Angela Ryan Lee, MD, FACC
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Left bundle branch block (LBBB) is a finding on an electrocardiogram (EKG). It can happen if there is damage to the left bundle branch in the heart or another part of the myocardial region. LBBB can occur in people either with or without a heart condition. Around 0.06–0.1% of the general population has LBBB. In comparison, 33% of people with heart failure have LBBB.

LBBB does not usually cause any symptoms. You may not need any treatment for LBBB unless you have symptoms of a heart condition.

Read on to find out more about what can cause LBBB and what symptoms to look out for. This guide also discusses treatments, when to contact a doctor, and more.

What causes left bundle branch block?

There is a yellow model of a heart.
Yaroslav Danylchenko/Stocksy United

In some cases, left bundle branch block (LBBB) can occur in people who do not have a known heart condition. However, in most cases, it is a sign of a heart abnormality.

Possible causes include:

Learn more about heart conditions.

What are the symptoms of left bundle branch block?

Left bundle branch block (LBBB) is a generally asymptomatic EKG finding. This means that you may not know you have LBBB until your doctor finds it during an EKG they have ordered for another symptom or condition.

However, if LBBB occurs as a result of a heart condition, you may experience symptoms. Symptoms will depend on the condition but can include:

It is important to contact your doctor if you have symptoms that might indicate a heart problem.

Learn about the symptoms of heart disease.

What are the treatments for left bundle branch block?

There is no specific treatment for left bundle branch block (LBBB). If you do not have any symptoms with LBBB, your doctor may not recommend any treatment.

However, if a heart condition is causing LBBB, then you will need treatment for that specific condition. Your doctor will be able to recommend appropriate treatments for your condition.

Your doctor may recommend cardiac resynchronization therapy (CRT) if you have heart failure and have LBBB with a QRS duration of more than 120 milliseconds (ms).

The QRS complex is an EKG reading. A typical QRS duration is less than 100 ms. A 2021 study of 76,220 individuals identified the median QRS duration as 86 ms.

Cardiac resynchronization therapy

CRT involves placing a pacemaker to help synchronize your heart’s beating. In LBBB, there is a delay in the contraction of the left side of the heart. Pacing with CRT can help correct this delay.

In addition to increasing blood flow, CRT may alleviate some symptoms of heart failure, such as shortness of breath.

When should I contact a doctor?

Your doctor will usually detect left bundle branch block (LBBB) during an EKG that you are having for another symptom or condition.

It is important to contact your doctor if you have concerns about your heart health or if you have symptoms that may indicate a heart condition.

Heart failure may not always cause symptoms. Common symptoms of heart failure that may occur include:

Our Heart Failure Appointment Guide can help you prepare for your appointment.

How do doctors diagnose left bundle branch block?

If your doctor detects left bundle branch block (LBBB) when performing an EKG, they may order various tests to check the overall health of your heart.

The tests they order may depend on any other symptoms you have but may include:

They may also order an ambulatory EKG. For this test, you will wear electrodes connected to a small device that you attach to a belt. The device will monitor your heart for 24 hours.

Learn about how doctors diagnose heart failure.

What are the complications of left bundle branch block?

Left bundle branch block (LBBB) may not directly cause any complications. In some people, it can occur without any symptoms or an underlying condition.

However, if LBBB is a result of a heart condition, then you may experience complications related to your specific condition.

It is important to follow your treatment plan and ask your doctor any questions you may have about your condition or the treatments they recommend. This can help reduce your risk of developing complications.

What is the life expectancy for somebody with left bundle branch block?

Left bundle branch block (LBBB) may not directly affect your life expectancy. Some studies suggest that LBBB may increase your risk of sudden death from a heart-related cause. More research into this is necessary.

However, if cardiovascular disease is responsible for LBBB, then this may affect your life expectancy.

Attending your appointments and following your treatment plan can help you stay on top of your heart health.

If you have low blood pressure, it’s important for a medical professional to check your blood pressure at least once per year, according to the American Heart Association. If you have high blood pressure, your doctor will advise you on how often to check your blood pressure.

Q:

Can I have caffeine if I have left bundle branch block?

Anonymous

A:

There is no evidence that those with left bundle branch block need to avoid caffeine. Drinking caffeine in moderation appears to be safe for those with conduction delays like left bundle branch block, as well as other conditions like high blood pressure, arrhythmias like atrial fibrillation, and heart failure.

However, the source of caffeine may be important. Studies have shown that drinking caffeine from energy drinks is associated with higher blood pressure and EKG changes, and that energy drinks have been associated with emergency room visits and even death.

Angela Ryan Lee, MD, FACC Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

Left bundle branch block vs. right bundle branch block

Left bundle branch block (LBBB) happens when there is damage to the left bundle branch in the heart. It typically occurs as a result of an underlying health condition.

Right bundle branch block happens when there is damage to the right bundle branch. Although it can be a sign of an underlying health condition, it is often present in people without a heart condition.

Find out more about right bundle branch block.

Summary

Left bundle branch block (LBBB) is an EKG finding that occurs when there is damage to the left bundle branch in the heart. Although it can be present in people who do not have a heart condition, it may signal an underlying heart condition.

There are no specific treatments for LBBB. Instead, your doctor will recommend treatments for the condition that is causing it.

You may not experience any symptoms with LBBB. This means that you may become aware of it only if you undergo an EKG for another symptom or condition.

However, it is important to contact your doctor if you have concerns about your heart health or if you experience symptoms that might indicate a heart condition. Your doctor will be able to order tests that can help them reach an accurate diagnosis and advise you on the right treatments.

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Medical Reviewer: Angela Ryan Lee, MD, FACC
Last Review Date: 2022 Oct 13
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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