Left bundle branch block (LBBB) occurs when transmission of the cardiac electrical impulse is delayed or fails to be conducted along the rapidly conducting fibers of the main left bundle branch or in both left anterior and posterior fascicles. Thus, the left ventricle slowly depolarizes by means of cell-to-cell conduction that spreads from the right ventricle to the left ventricle. This results in the characteristic ECG pattern shown in the image below.
