What Is a Left Bundle Branch Block?

Left bundle branch block (LBBB) is a disorder which affects the heart. Normally, the electrical signals which cause cardiac muscle to contract pass through specialized heart tissue called the Bundle of His before dividing into right and left branches. Each branch rapidly supplies electrical impulses to one side of the heart and, when the left branch is obstructed, this can delay contraction in the left side of the heart. Depending on the degree of LBBB, there may be no symptoms or a slowed heart beat or fainting may occur. Treatment is not always necessary, but drugs, artificial pacemakers and a procedure known as coronary angioplasty may be used in some patients.

There are a number of causes of left bundle branch block. Most involve an underlying heart condition, such as cardiomyopathy, where the heart muscle is abnormally weak or thick, or congestive cardiac failure, where the heart no longer pumps blood efficiently. Bundle branch block can also affect the heart's right side, and causes here include structural abnormalities, cardiac scar tissue, heart muscle infections and heart attacks. High blood pressure can be a cause of left or right bundle branch block.

Symptoms of left bundle branch block may be absent in some patients, so that the condition remains undiagnosed for years. When symptoms are experienced, they can include having the feeling that a faint is about to occur, as well as actual fainting. Diagnosis of left bundle branch block involves a test known as an electrocardiogram (ECG). In an ECG, electrodes which detect the heart's electrical impulses are attached to the chest, and wires run from these to a machine. The machine records the pattern of the heart's electrical activity, and the doctor can see whether the pattern typically associated with LBBB is present.

Treatment of left bundle branch block often involves attending to an underlying heart condition. Drugs can be used to treat heart failure, lower blood pressure and improve blood flow to the heart. Patients who experience fainting may have an artificial pacemaker fitted under the skin of the chest, with a wire that connects it to the heart. This device is able to regulate the heart's rhythm.

Patients with blocked coronary arteries, which reduce the heart's blood supply, may need to have those arteries widened using a procedure known as angioplasty. A tube called a stent may be inserted to keep an artery open. The outlook for patients who develop left bundle branch block is often positive. When left bundle branch block arises following a heart attack, the risk of dying or experiencing complications is higher in these patients than it is for heart attack survivors who do not develop LBBB.