how serious is left bundle branch block
Left bundle branch block (LBBB) is an abnormality in the heart’s electrical conduction system. Learn about symptoms and treatment

Left bundle branch block (LBBB) may not be serious if you do not have any underlying heart conditions. Many people with LBBB have no symptoms, and some don’t require any treatment at all.

However, whether or not you have symptoms, LBBB requires careful medical assessment. A newly diagnosed left bundle branch block may indicate an underlying health condition that requires medical evaluation and treatment.

LBBB is more serious if you have conditions such as heart failure, heart attack, hypertension, bacterial or viral infection of the heart muscle (myocarditis), or thickened, stiffened, or weakened heart muscle (cardiomyopathy).

What is left bundle branch block?

LBBB is a condition in which there is a problem with the heart’s electrical conduction system. The heart is supplied by a web of nerve tissue that causes the heart to beat. Electrical signals through these nerves help the heart to pump normally.  

Your heart is made up of four chambers: the upper two chambers are called atria, whereas the lower two chambers are called ventricles. The right atrium and right ventricle are called the right heart, and the left atrium and left ventricle are called the left heart. Each chamber of the heart is separated by partitions, each of which is called a septum.

Electrical signals that cause the heart to pump are generated in the sinoatrial node (SA node), which is a small mass of muscle cells at the top of the right chamber atrium. The SA node is also called the master pacemaker of the heart: 

  • Electrical signals from the SA node travel through the heart muscles and cause the atria to contract and pump blood into the ventricles. 
  • Signals from the SA node are received by another structure called the atrioventricular node (AV node) that in turn sends a signal to the ventricles. 
  • Muscle fibers from the AV node split into two branches called the bundle branches. 

If there is a problem with the branch that sends the electrical signal to the left ventricle, this may interfere with the heart’s pumping activity and result in left bundle branch block.

What are symptoms of left bundle branch block?

Left bundle branch block may not cause any symptoms. However, if symptoms are present, they may include:

How is left bundle branch block treated?

Left bundle branch block may not require any treatment, particularly for people with no symptoms or without any underlying heart condition. However, if LBBB causes symptoms or is severe, or if the patient is older, treatment may be necessary:

  • Cardiac resynchronization therapy (CRT):
    • For people who have heart failure and LBBB 
    • CRT helps correct the heart rhythm by using pacemaker therapy that ensures that the ventricles contract at the same time, which helps improve the pumping of blood from the heart and minimizes symptoms
  • Permanent pacemaker:
    • For patients who exhibit symptoms or have another conduction issue in addition to LBBB
    • Helps keep the heart beating at a normal rate
  • Temporary pacemaker:
    • For patients undergoing right heart catheterization or those with acute myocardial infarction (MI) along with a first-degree atrioventricular (AV) block
    • Helps keep the heart beating at a normal rate

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Medically Reviewed on 8/20/2021
References
Sauer WH. Left Bundle Branch Block. UpToDate. https://www.uptodate.com/contents/left-bundle-branch-block