Bundle branch block

Bundle branch block is a condition in which there’s a delay or obstruction along the pathway that electrical impulses travel to make your heart beat. Bundle branch block can occur in people who appear healthy, and it’s often a sign of another underlying heart problem.

Injury or damage to the heart muscle or blockage of a blood vessel in your heart can slow or block the electrical impulses that make your heart beat. Even though interference with the impulses may last for only a fraction of a second, that may be enough to cause bundle branch block. Bundle branch block sometimes makes it harder for your heart to pump blood forcefully and efficiently through your circulatory system.

Although bundle branch block itself often requires no direct treatment, you’ll need treatment of any underlying health condition that could cause bundle branch block, such as coronary heart disease.


In most people, bundle branch block doesn’t cause any symptoms. For those people who do have signs and symptoms, they may include:

  • Fainting (syncope)
  • Dizziness
  • Feeling as if you’re going to faint (presyncope)
  • A slow heart rate (brachycardia)

You may be born with the condition (congenital) and have bundle branch block for years without knowing it. This is particularly true with bundle branch block that occurs on the right side of your heart, which tends to be less serious than is left bundle branch block.


Normally, electrical impulses within your heart’s muscle signal it to beat (contract). These impulses travel along a 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).

Along the route on this pathway, the impulses move along a slender cluster of cardiac fibers called the “bundle of 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 damaged — due to a heart attack, for example — this change can prevent your heart from beating normally. The heart’s electrical impulses that make your heart beat may be slowed down or blocked. When this occurs, the ventricles no longer contract in perfect coordination with one another.

Bundle branch block may be caused by:

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


The complications of bundle branch block are similar whether the blockage is on the right or left side of your heart, but for people who have a left side bundle branch block, complications are often more common. Complications include:

  • Slow heart rate
  • Heart arrhythmia
  • Cardiac arrest or sudden cardiac death

People who have heart attacks and develop bundle branch block have a higher chance of complications and death than do people with a heart attack who don’t have bundle branch block.

In addition, 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.


An electrocardiogram (ECG) is the most commonly used test for bundle branch block. This noninvasive test is an electrical recording of your heart’s activity. In this test, a technician will place probes on the skin of your chest that will show the patterns of electric impulses through your heart as wave patterns. Abnormalities in the waves 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.

It’s also possible your doctor will discover you have a bundle branch block incidentally—meaning the condition could be found while you’re having an ECG to diagnose another heart condition.


There’s no specific treatment for many cases of bundle branch block. Most people with bundle branch block are symptom-free and don’t need treatment. Nevertheless, you may need to treat the underlying heart condition causing bundle branch block.

Treatment of underlying conditions may involve using medications to reduce high blood pressure or lessen 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 have had a heart attack. This treatment, given in an emergency situation, involves using medications called a streptokinase, or a tissue plasminogen activator to dissolve blood clots and increase the flow of blood to the heart. These medications carry a high risk of bleeding, so ask your doctor if you have concerns about taking these medications.

Artificial pacemakers
For some people with bundle branch block and a history of fainting, 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).

Internal pacemakers are placed near your collarbone during a one- to two-hour surgery performed using local anesthesia. The pacemaker provides electrical pulses which keep your heart beating regularly. These devices have sensors that can detect when your heart needs a signal from the pacemaker to normalize your heart rate. Pacemakers can last for many years before the battery (generator) needs to be changed.

If you need a pacemaker, your doctor can explain any precautions you need to take in order to keep the device working properly, and to reduce risks associated with their use.