What is the significance of bundle branch block?īBB is quite common, and occurs in a variety of medical conditions. The QRS complex is said to “widen.” Also, since the pattern of the spreading of the electrical impulse is abnormal in BBB, the pattern of the QRS complex is also abnormal. Because with BBB the ventricles receive the electrical impulse one after another instead of at the same time, it takes longer to form the QRS complex on the ECG. Why does the QRS complex change in BBB? The QRS represents the spread of the heart’s electrical impulse across the right and left ventricles. The characteristic shapes of the QRS complex allow doctors to determine whether the right or the left bundle branch is blocked. Note that with both kinds of bundle branch block, the QRS is wide and misshapen. The middle figure shows RBBB, and the bottom figure shows LBBB. In Figure 5, the top image shows a normal QRS complex. This sequential spread of the impulse (i.e., first the right ventricle, then the left – or vice versa) means that it takes longer for the impulse to reach throughout the ventricles. With either type of BBB, therefore, the electrical signal spreads across the ventricles sequentially, as opposed to simultaneously. First the right ventricle receives the electrical impulse, then the left. Once again, the two ventricles no longer receive the electrical impulse simultaneously. From there, it finally spreads to the left ventricle (second panel). The electrical impulse thus enters right bundle branch, and is carried to the right ventricle (first panel). Here, the left bundle branch no longer conducts electricity.
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). I found this great article written by Richard N.
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