First the left ventricle receives the electrical impulse, then the right.įigure 4 – Left Bundle Branch Block (LBBB) As a result, the two ventricles no longer receive the electrical impulse simultaneously. Then, from the left ventricle, the electrical impulse finally makes its way to the right ventricle. Therefore, as the electrical impulse leaves the His bundle, it enters left bundle branch only, and is carried to the left ventricle. In RBBB, the right bundle branch no longer conducts electricity. The in this figure, purple arrows indicate the electrical impulse, traveling down the bundle branches and causing the ventricles to beat simultaneously.īBB occurs when one of the bundle branches becomes diseased or damaged, and stops conducting electrical impulses that is, a bundle branch becomes “blocked.” The chief effect of a bundle branch block is to disrupt the normal, coordinated and simultaneous distribution of the electrical signal to the two ventricles. To form this normal QRS complex, the electrical impuse needs to travel to both ventricles at the same time. Since normally both ventricles receive the electrical impulse at the same time, the normal QRS complex is relatively narrow (generally less than 0.1 second in duration.)įigure 3 – Normal Bundle Branch Conduction In this image of a normal ECG, the QRS complex represents the electrical impulse as it is being distributed, via the bundle branch system, throughout the ventricles. When the bundle branches are functioning normally, the right and left ventricles contract nearly simultaneously. The right and left bundle branches send the electrical impulse to the right and left ventricle, respectively. From the His bundle, the electrical impulse enters the two “bundle branches” (the right and the left). Leaving the AV node, the electrical impulse penetrates into the ventricles via the His bundle. To summarize, the heart’s electrical impulse originates in the in the sinus node in the upper right atrium, then spreads across both atria, then travels through the AV node. The bundle branches are an important part of the cardiac electrical system, the system that coordinates muscular contraction to assure that the heart works efficiently as a pump.įigure 1 – The Normal Electrical System: AVN = AV node, His = His bundle, RBB = right bundle branch, LBB = left bundle branch, RA = right atrium, RV = right ventricle, LA = left atrium, LV = left ventricle

What are the bundle branches, and what do they do? In this article, we will review bundle branch block, its significance, and its treatment. Sometimes BBB itself needs to be treated sometimes it indicates significant underlying cardiac disease that needs to be treated and sometimes it has so little significance that no treatment is necessary at all. Fogoros, M.D., Guide, November 26, 2003, that I reprint here:īundle branch block (BBB) is a relatively frequent finding on the electrocardiogram (ECG). It may lead to delays in proper management of those heart conditions.I found this great article written by Richard N. A slowed heart rate may lead to fainting, irregular heart rhythms and other serious complications.īecause bundle branch block affects the electrical activity of the heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks. The lack of signaling can slow the heart rate. If both the right and the left bundles are blocked, the main complication is a complete blockage of the electric signaling from the upper to the lower chambers of the heart. Having high blood pressure or heart disease increases the risk of having bundle branch block. Bundle branch block is more common in older adults than in younger people. Risk factors for bundle branch block include: High blood pressure in the pulmonary arteries (pulmonary hypertension).Heart structure problems that are present at birth (congenital heart defects) - such as a hole in the wall separating the upper chambers of the heart (atrial septal defect).Blood clot in the lungs (pulmonary embolism).Thickened, stiffened or weakened heart muscle (cardiomyopathy).Inflammation of the heart muscle (myocarditis).Sometimes, there is no known cause.Ĭauses can include: Left bundle branch block The cause for bundle branch blocks can differ depending on whether the left or the right bundle branch is affected. As a result, the heart beats irregularly. If one or both of these branch bundles are damaged - due to a heart attack, for example - the electrical impulses can become blocked. These impulses travel along a pathway, including two branches called the right and the left bundles. Electrical impulses within the heart muscle cause it to beat (contract).

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