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Bundle branch block (BBB) is a condition in which there's a delay or obstruction in the transmission of your heart's electrical impulses. It can occur in people who appear healthy, and it's often a sign of an underlying heart problem.

When your heart functions normally, electrical impulses travel along a specific pathway. Part of this pathway is a bundle of fibers that divides into left and right branches into the heart's left and right lower chambers.

Injury or damage to the heart muscle or blockage of a coronary vessel can slow or obstruct transmission of electrical impulses. Even though interference with the impulses may happen for only a fraction of a second, that may be enough to cause bundle branch block. Bundle branch block impairs your heart's ability to pump blood forcefully and efficiently through your circulatory system and makes your heart work harder.

Although bundle branch block itself often requires no direct treatment, you'll need treatment of any underlying health problem, such as heart disease. In some cases, your doctor may recommend an artificial pacemaker to ensure that your heart beats properly.

In most people, bundle branch block doesn't cause any symptoms. The condition may be present at birth (congenital), and you may have it for years without knowing it. This is particularly true with right bundle branch block, which tends to be less serious than left bundle branch block.

In some people, either left or right bundle branch block may lead to fainting (syncope), or to dizziness and the sensation that you're going to faint (presyncope). Syncope or presyncope is more common in people who have both bundle branch block and other heart conditions.

Bundle branch block causes changes in your heart's electrical activity that can be detected with an electrocardiogram. Although the heart's rate or rhythm is not always affected, some people may have a very slow heart rate (bradycardia) if the block of the bundle branch is severe.

Normally, electrical impulses within your heart's muscle signal it to beat (contract) in a precisely coordinated manner. These impulses travel along a specific pathway, passing from your heart's upper chambers (atria) through a small mass of cells called the atrioventricular (AV) node and then to the lower chambers (ventricles).

As part of this route from the AV node to the ventricles, the impulses move along a slender cluster of cardiac fibers called the "bundle of His" (named after a German physician, Wilhelm His), which divides into two branches — the right and the left bundles — one for each of the heart's ventricles.

If one or both of these branch bundles become injured or damaged — due to a heart attack, for example — this impairment can alter the electrical pathways and interfere with the normal conduction of signals from your heart's upper chambers to the lower chambers. When transmission of these signals is slow or when a complete blockage occurs, the ventricles no longer contract in perfect coordination with one another.

The cause of bundle branch block is often a serious heart condition. Bundle branch block may develop if you have coronary artery disease, and may be the result of:

• A heart attack (myocardial infarction)
• An inflamed or weakened heart muscle (cardiomyopathy)
• A viral infection of the heart muscle (myocarditis)
• High blood pressure (hypertension)
• Scar tissue that develops after heart surgery
• A heart abnormality that is present at birth (congenital), such as atrial septal defect, a hole in the wall separating the upper chambers of the heart

If you have heart disease, or if your doctor has already diagnosed you as having bundle branch block, make regular appointments to be sure that your condition doesn't become worse. Because you may be free of symptoms and yet still have bundle branch block, routine checkups at intervals recommended by your doctor are important.

If you have had a fainting episode, see your doctor for an evaluation. Discuss the advisability of carrying a medical alert card identifying you as having bundle branch block in case you are seen by a doctor who isn't familiar with your medical history.

An electrocardiogram (ECG) is an electrical recording of your heart's activity. It's the most common diagnostic tool for bundle branch block. Abnormalities in the wave patterns on an ECG may indicate the presence of bundle branch block. These electrical patterns can also point to whether the block is affecting the right or the left bundle branch.

Despite the value of an ECG, bundle branch block is often an incidental finding of this test — that is, the ECG may be ordered for other reasons, and bundle branch block may be discovered unexpectedly.

A block of the left bundle branch is more likely to have serious health implications than a right bundle branch block. With left branch involvement, there's a greater likelihood of the presence of heart disease associated with high blood pressure or the accumulation of fatty deposits within the coronary arterial walls (atherosclerosis). People with left branch involvement also have an increased risk of developing heart failure.

A complete block in both the left and right bundle branches can obstruct your heart's normal rhythms, leading to a very slow heart rate or cardiac arrest. People who have heart attacks and develop bundle branch block have a higher chance of complications and death than people with a heart attack who don't have bundle branch block.

Because bundle branch block affects the electrical activity of your heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks, and lead to delays in proper management of those problems.

There's no specific treatment for many cases of bundle branch block, whether it affects the left or the right bundle branch. In fact, in most cases people are symptom-free and there's no need for therapy. Nevertheless, you may benefit from proper management of the underlying heart disease or other heart conditions.

Medications
Treatment of underlying conditions may involve using medications to reduce high blood pressure, or drugs to reduce the effects of heart failure.

The American Heart Association and the American College of Cardiology recommend treatment called reperfusion therapy for people with left bundle branch block who are suspected of having had a heart attack. This treatment involves using drugs such as streptokinase or tissue plasminogen activator to dissolve blood clots and increase the flow of blood to the heart.

Artificial pacemakers
In a minority of people with bundle branch block, doctors may recommend implanting an artificial pacemaker. This pacemaker is a compact battery-operated device, as tiny as a quarter and weighing as little as an ounce, that can be implanted under your skin (internal pacemaker). Although nonimplantable devices are also available for external use, doctors use them less often in people with bundle branch block.

Internal pacemakers are placed near your collarbone during a one- to two-hour surgical procedure performed with local anesthesia. The pacemaker contains an insulated wire or electrode that is secured to the wall of your heart, and that provides electrical stimulus or pulses that keep your heart contracting regularly. These devices have sensors that can detect when your heart needs a signal from the pacemaker to normalize the rate.

Candidates for a pacemaker include people with bundle branch block who are considered to have a high risk of experiencing a complete heart block. The pacemaker can keep your heart beating at the proper rate even if a complete block develops. A pacemaker may also be an option if you have repeated episodes of fainting.

If you need a pacemaker, your doctor can explain any precautions you need to take in order to minimize interference with the device's heart-stabilization activity, and to reduce risks associated with their use.

To reduce your risk of heart-related problems that can lead to or worsen bundle branch block, adopt lifestyle measures to lower your risk of coronary artery disease:

• Stop cigarette smoking
• Reduce the dietary cholesterol and fat in your meals
• Keep your weight at normal levels
• Exercise regularly
• Control diabetes