Bundle Branch Block

What is bundle branch block?

A bundle branch block is either a complete or a partial interruption of the electrical pathways inside the wall of the heart between the two lower chambers (ventricles).

The master pacemaker of the heart is the sinoatrial node, a small mass of muscle cells at the top of the right chamber (atrium) of the heart. It creates an electrical signal that travels through the heart muscle fibers and causes the atria to contract and pump blood into the lower chambers.

Shortly after the sinoatrial node releases its signal, it is received by the atrioventricular node, which in turn sends a signal to the ventricles causing them to contract and pump blood out of the heart. The muscle fibers that carry the signal from the atrioventricular node go into the wall that divides the ventricles and then splits into two branches, the bundle branches. 

A block in the right bundle branch can occur in people who otherwise seem normal. If it happens with a heart attack, it can be a sign of serious heart muscle damage.

In right bundle branch block, there is a problem with the right branch of the conducting system that sends the electrical signal to the right ventricle. The electrical signal can’t travel down this path the way it normally would. The signal still gets to the right ventricle, but it is slowed down, compared to the left bundle. Because of this, the right ventricle contracts a little later than it normally would. This can cause the heart to eject slightly less blood.

Right bundle block happens more often in older people. It is rare in healthy young people. It may occur with natural degeneration of the hearts conduction system that occurs with age. It can also occur in people who have another underlying heart or lung problem. It may also be caused as a result of a heart procedure.

A block of the right bundle branch may cause an electrocardiogram to be distorted. The distortion usually is not enough to make diagnosing a heart attack difficult. It may be a sign of worsening heart conditions. It can also appear after an embolism in the lung.

A block in the left bundle branch can sometimes be benign and not cause problems. However, it always interferes with using an electrocardiogram to diagnose heart disease.

What causes bundle branch block?

Bundle branch block is a common disorder. It occurs in many medical conditions.

A right bundle branch block only occurs in medical conditions that affect the right side of the heart or lungs. Finding a right bundle branch block is a signal to your doctor to look for other conditions, including:

  • Blood clots in the lung
  • Chronic lung disease such as chronic obstructive pulmonary disorder
  • Disease of the heart muscle, known as cardiomyopathy
  • Defects of the wall between the upper chambers or lower chambers of the heart (atrial and ventricular septal defects).

However, right bundle branch block can also occur in normal, healthy individuals, so an examination may reveal no cause.

A left bundle branch block usually is a sign of an underlying heart disease, including dilated cardiomyopathy, hypertrophic cardiomyopathy, high blood pressure, aortic valve disease, coronary artery disease and other heart conditions. While left bundle branch block can appear in healthy people, it most often does not.

What are the symptoms of bundle branch block?

Bundle branch blocks usually do not cause symptoms. They are not considered to be irregular heartbeats or arrhythmias. Rarely, right bundle branch block may make symptoms worse in some people with heart failure. Researchers are not yet sure whether this is the case. Symptoms are more likely to occur if you have other problems in addition to your right bundle branch block.

How is bundle branch block diagnosed?

A bundle branch block is usually diagnosed with an electrocardiogram. Your doctor also may want to test the health and function of your lung. Testing may also include blood work.

How is bundle branch block treated?

Usually no treatment is done for bundle branch blocks directly. Your doctor may address the heart disease, if it is present.

Usually implanting a pacemaker into the heart isn't beneficial. There are exceptions to this, however. If both bundle branches are affected and associated with a heart attack, if the block is associated with a loss of consciousness (syncope) or if you have dilated cardiomyopathy, surgically implanting a pacemaker may be helpful.

Living with bundle branch block

Your doctor may give you additional instructions about how to manage your right bundle branch block and overall heart health. You might need to make lifestyle changes, like losing weight, quitting smoking, or improving your diet.

Monitor your symptoms carefully. Make sure you see a doctor regularly, even if you don’t have any symptoms.

Make sure all your doctors know about your bundle branch block.

When should I call my healthcare provider?

See a doctor right away if you have severe symptoms like chest pain, syncope (fainting), or severe shortness of breath. If you have any new symptoms, plan to see your doctor soon.

Key points

  • A bundle branch block is either a complete or a partial interruption of the electrical pathways inside the wall of the heart.
  • A block in the right bundle branch can occur in people who otherwise seem normal. If it happens with a heart attack, it can be a sign of serious heart muscle damage.
  • A block in the left bundle branch is usually a sign of heart disease.
  • Bundle branch blocks usually do not cause symptoms.
  • Usually no treatment is done for bundle branch blocks directly. Your doctor may address the heart disease, if it is present.
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