Bundle branch block left

Definition: An impairment of transmission of the cardiac electrical impulse along the fibers of the left main bundle branch, or both the left anterior fascicle and left posterior fascicle. This conduction disturbance is characterized by wide (greater than 0.11s) QRS complexes. The diagnostic criteria consist of prolongation of the QRS complexes (over 0.11s) with neither a Q wave nor an S wave in lead V1 and in the properly placed V6. A wide R wave with a notch on its top (plateau) is seen in these leads. In hearts with an electrical (and anatomic) vertical position a small Q wave may be seen in AVL in the absence of MI. Right chest lead V1 may or may not show an initial R wave, but the latter should be present in lead V2. (NCI)

Synonyms (terms occurring on more labels are shown first): bundle branch block left, left bundle branch block, LBBB

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