Bundle branch block
Bundle branch block (BBB) is a disruption in the normal flow of electrical pulses that drive the heart beat. Bundle branch block belongs to a group of heart problems called intraventricular conduction defects (IVCD). There are two bundle branches, right and left. The right bundle carries nerve impulses that cause contraction of the right ventricle (the lower chamber of the heart) and the left bundle carries nerve impulses that cause contraction of the left ventricle. The two bundles
initially are together at a junction called the bundle of His. Nerve impulses come through the sinus node of the heart to the bundle of His and then move into the right and left bundle branches. Bundle branch block is a slowing or interruption of nerve impulses. A problem may exist in any of the three bundles.
Patients with BBB are generally without symptoms unless the disease is severe enough to cause a complete infranodal A-V block and very slow heart rate. In patients with right bundle branch block (RBBB), the nerve impulse is conducted slowly or not at all. The right ventricle finally receives the impulse through muscle-to-muscle spread, outside the regular nerve pathway. This mechanism of impulse transmission is slow and results in a delayed contraction of the right ventricle. There are several types of left bundle branch block (LBBB), each producing its own characteristic mechanism of failure. In each case, the nerve impulse is blocked or delayed. Patients with LBBB may have left ventricular disease or cardiomyopathy.
Bundle branch block is usually found incidentally on an electrocardiogram (ECG) done for some other reason. It often causes no symptoms. Bundle branch block results from a slowing or complete blockage of one pathway (branch) taken by the electrical impulses that cause your heart to beat. Normally, these electrical impulses originate in the upper-right (atrial) chamber of your heart. They move through the middle of your heart to the lower chambers through right and left electrical conducting branches. These electrical impulses activate the lower chambers, allowing your heart to pump blood to your body and lungs.
If a blockage occurs in one of the branches, the electrical impulse takes a detour to its destination. When this happens, it doesn't affect the rate and rhythm of your heartbeat. But the alternative pathway that the electrical impulse takes shows up on an ECG. Bundle branch block almost never needs treatment. But more severe blockage of the electrical pathways, such as complete heart block, may lead to a very slow heart rate (bradycardia). In this case, a doctor may recommend a pacemaker. It's important to understand that blockage of the electrical system isn't the same as narrowing or blockage of the coronary arteries, which provide blood to the heart.
Usually a person with bundle branch block shows no symptoms, but this block shows up on the EKG as an abnormality. If you have bundle branch block, it may have only been noticed when you had an EKG. You may feel fine, although some people may either faint (syncope) or feel as if they're going to faint (presyncope).
If both bundles are diseased, heart block may result, producing syncope or presyncope. When this happens, the heartbeat may be so slow that an artificial pacemaker is implanted.
Bundle heart block may be caused by damage to the heart muscle resulting from a heart attack. In most cases, bundle branch block does not need treatment. But patients who have bundle branch block along with another heart condition may need treatment. For example, if bundle branch block develops during a heart attack, you may need a pacemaker. After a heart attack, your heart is fragile, and bundle branch block may cause a very slow heart rhythm (bradycardia). A pacemaker will help regulate the heart's rhythm after a heart attack.
For patients with both bundle branch block and dilated cardiomyopathy, a new type of pacing called cardiac resynchronization treatment (CRT) may be used. Normally, pacemakers pace only one of the lower heart chambers (the ventricles) at a time. But CRT re-coordinates the beating of the two ventricles by pacing them at the same time. Recent studies have shown that CRT works for certain patients with both bundle branch block and dilated cardiomyopathy. Even if you do not have other conditions, you should still see your doctor regularly so that he or she can be sure there are no other changes in your heart.