bundle branch block (BBB), an inability of cardiac impulses to be conducted down the bundle branches, causing a broad and abnormally shaped QRS complex. BBB is commonly seen in high-risk, acute, anterior wall myocardial infarction. It may be caused by ischemia or necrosis of the bundle branches, trauma (as in surgical manipulation), or mechanical compression of the branches by a tumor. A pacemaker may be inserted if further deterioration of conduction is anticipated. See also left bundle branch block, right bundle branch block.
