Bundle Branch Block


The heart has a natural pacemaker called the sinoatrial (SA) node. The SA node is a specialized group of cells at the top of the right atrium. The SA node sends an electrical impulse through the heart to cause it to beat. When the SA node sends an electrical impulse, that impulse first travels through the atria and then passes through a small group of cells called the atrioventricular (AV) node. The AV node checks the impulse and sends it along a track called the bundle of His. The bundle of His divides into a right bundle branch and a left bundle branch, and these branches lead to the ventricles.

The heart's conduction system can become partially blocked, preventing the electrical impulse from traveling along its path. If an impulse is blocked as it travels through the bundle branches, it is called a bundle branch block
.

What Causes Bundle Branch Block?

For the left and right ventricles to simultaneously contract, an electrical impulse must travel down the right and left bundle branches at the same speed. A block in one branch causes the electrical impulse to take a detoured route to the ventricle. When this happens, the rate and rhythm of the heartbeat are not affected, but the impulse is slowed. The two ventricles will not contract at the same time; one ventricle contracts a fraction of a second slower than the other.

The medical terms for bundle branch block are derived from the affected branch; either left or right bundle branch block is specified. The block can be caused by coronary artery disease, cardiomyopathy, or heart valve disease. Right bundle branch block can also occur in a healthy heart.


Symptoms

Patients may not experience any symptoms with bundle branch block, especially if nothing else is wrong with their heart. Some patients have bundle branch block for years and never know they have the condition. Those who do have symptoms may faint or feel as if they are going to faint.

Bundle branch block can be a warning sign for a more serious heart condition. It could mean that a small part of the heart is not getting enough oxygen-rich blood. Researchers have also discovered that people who have left bundle branch block may be at greater risk for developing heart disease.

Diagnosis

Cardiologists use electrocardiogram (ECG) testing to diagnose bundle branch block, which creates a unique tracing. Its electrical pattern also shows whether the block is located in the right or left bundle branch.

Treatment

In most cases, bundle branch block does not require treatment; however, patients who have bundle branch block along with another heart condition may need treatment. For example, a patient who develops bundle branch block during a heart attack may need a pacemaker to help regulate the heart's rhythm afterward. A patient with bundle branch block and dilated cardiomyopathy may need a type of pacing called cardiac resynchronization treatment (CRT). Patients who do not have other conditions should visit their doctor regularly to be monitored for any additional changes.

Resources

American Heart Association www.americanheart.org/presenter.jhtml?identifier=990
Texas Heart Institute www.texasheartinstitute.com/HIC/Topics/Cond/bbblock.cfm
Updated December 2009