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).

A normal heart is a masterpiece of muscles, electrical signals, valves and circulation working together in a coordinated way to pump blood through the heart, lungs and body.

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.


Bundle branch blocks usually do not cause symptoms. They are not considered to be irregular heartbeats or arrhythmias.

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 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.

Causes and Risk Factors

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 to the lung, chronic lung disease, cardiomyopathy and 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.


A bundle branch block is usually diagnosed with an electrocardiogram.


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.

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