Key Takeaways
- Left bundle branch block (LBBB) occurs when cardiac electrical impulses cannot follow a typical pathway to regulate heart rhythm. It can be a sign of underlying heart disease. Most people with LBBB don’t experience symptoms, but some feel breathless or fatigued.
- If your healthcare provider diagnoses LBBB, treatment such as a pacemaker may be necessary. Lifestyle changes, like eating heart-healthy foods and quitting smoking, can lower your risk of LBBB. Talk with your healthcare provider if you have concerns or symptoms that may be LBBB.
Left bundle branch block (LBBB) is a problem where the electrical impulse that controls your heartbeat is not working in the usual way. It is considered an abnormal finding on an electrocardiogram (ECG).
LBBB doesn’t always indicate a problem with your heart, especially if you have no underlying health conditions. However, it can sometimes be an indication of a cardiac problem, so anyone diagnosed with left bundle branch block on their ECG should have a cardiac evaluation.
This article explains the symptoms, causes, diagnosis, and treatment of LBBB.
Verywell / Laura Porter
Bundle Branch Function
The bundle branches are part of the heart’s electrical “wiring.” They carry electrical impulses evenly through the ventricles, ensuring these chambers contract in sync.
In LBBB, the branch carrying impulses to the left ventricle is fully or partially blocked, delaying its contraction. This causes the right ventricle to contract before the left.
For the heart to beat efficiently, both ventricles should contract simultaneously. As such, left bundle branch block can reduce the efficiency of the heartbeat.
In someone whose heart is otherwise healthy, this reduced function may be trivial. However, in someone with heart failure, left bundle branch block can produce a significant decrease in the heart’s efficiency.
This reduced efficiency can accelerate the deterioration of heart failure and make symptoms significantly worse.
Symptoms
Most people with LBBB do not experience symptoms directly linked to LBBB. However, if you have additional heart conditions along with LBBB, you’re more likely to experience symptoms. These may include:
- Shortness of breath
- Fatigue
- Fainting (syncope)
Causes
LBBB may develop without a specific cause but is often linked to various heart issues.
One of the primary causes of LBBB is dilated cardiomyopathy. This is a heart disease where a weakened heart can’t contract normally. The heart muscle enlarges and stretches as it tries to compensate. LBBB can be a cause or a result of this condition.
Often, the cause of dilated cardiomyopathy remains unknown, but risk factors include:
- Genetics
- Heart valve abnormalities
- Infections that can lead to heart damage (Lyme disease and Chagas disease)
- Ischemia (lack of oxygen to living tissue)
- Hypertension (high blood pressure)
- Some medications (anthracyclines)
- Alcohol, cocaine
- HIV, diabetes, thyroid problems
- Pregnancy-related heart failure (peripartum cardiomyopathy)
- Heart diseases involving abnormal substances in the heart (infiltrative cardiomyopathies)
LBBB mainly affects older adults. It occurs in less than 1% of people under 50; in contrast, nearly 6% of 80 year olds have left bundle branch block.
Significance of LBBB
Left bundle branch block most often occurs as a result of some underlying heart problem.
The LBBB itself causes the heart to work a bit less efficiently, which makes a big difference in people with certain heart disease types.
Diagnosis
Left bundle branch block produces characteristic changes on an ECG. Healthcare providers are typically able to diagnose this condition by examining these test results.
The standard ECG recording shows 12 different views of the heart’s electrical activity. Ten electrodes (or “leads”) that are attached to the body transmit these images.
QRS Complex
The portion of the ECG called the QRS complex represents the electrical impulse distributed across the ventricles.
Typically, because both ventricles are stimulated simultaneously, the QRS complex is between 0.08 and 0.1 seconds in duration. However, the QRS complex is much wider with left bundle branch block, often greater than 0.12 seconds.
Differential Diagnoses
Most people with left bundle branch block have some form of underlying heart disease. This means anyone of any age who has LBBB should have a cardiac evaluation to look for underlying heart disease.
Frequent underlying conditions include:
In one study, 47.7% of people with left bundle branch block also had high blood pressure.
During an early landmark study in cardiology, 89% of the people who developed left bundle branch block were subsequently diagnosed with some form of significant cardiovascular disease.
If you have CAD risk factors, your healthcare provider may order additional tests, including:
If, after a thorough cardiac evaluation, no evidence of heart disease is found, especially if you are under 50, your prognosis is quite good. In these cases, the left bundle branch block is considered a benign (harmless), incidental ECG finding.
About one-third of people with heart failure also have LBBB.
Treatment
For people without underlying heart disease, treatment may not be necessary. However, cardiac resynchronization therapy (CRT) or a pacemaker may be options for those with an underlying condition.
CRT
CRT is a type of pacemaker that re-coordinates the contraction of the ventricles. It can improve the heart’s efficiency in people with LBBB and heart failure.
Unless there is a reason to insert a CRT pacemaker to re-coordinate the function of the ventricles, most people with LBBB never require a pacemaker.
Chronic Pacemaker Therapy
The typical permanent pacemaker paces the heart from a pacing lead located in the right ventricle. Since the electrical impulse from the pacemaker stimulates the right ventricle before the left ventricle, people with permanent pacemakers, in effect, have a pacemaker-induced left bundle branch block.
In recent years, some evidence has suggested that people with permanent pacemakers who have reduced left ventricular ejection fraction—when the heart is less efficient at pumping blood—may have an increased risk of developing heart failure due to the pacemaker-induced left bundle branch block.
For this reason, some experts now routinely use CRT pacemakers (which avoid pacemaker-induced left bundle branch block) in people with reduced ejection fractions who are entirely dependent on permanent pacemakers.
If you have an underlying heart condition, the heart’s electrical signal can become disrupted in several ways. When that happens, significant bradycardia (slow heart rate) may develop. If it does, you might require a permanent pacemaker. For this reason alone, people with LBBB should make sure they have regular medical checkups.
Managing LBBB
If you have LBBB, make sure you see your healthcare provider regularly, even if you don’t have any symptoms. Your healthcare provider will want to do regular evaluations of your heart to make sure it remains healthy.
Is LBBB Reversible?
LBBB doesn’t resolve on its own. In some cases, treatment can help correct the problem, but many people continue to live with LBBB long term.
Preventing LBBB
Left bundle branch block can’t always be prevented. However, you may be able to reduce your chances of developing left bundle branch block by building healthier habits. For example:
- Eat heart-healthy foods like fruits and vegetables, whole grains, and fish.
- Exercise at least 30 minutes a day five times each week.
- Monitor your blood pressure and reduce high blood pressure.
- Lose weight if you need to.
- If you smoke, quit.
- Keep your cholesterol levels under control.
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