Seeing through the maze of complete left bundle branch block.

LBBB obscures many cardiovascular diagnoses, but it is now possible to diagnose LVH and MI in the presence of LBBB. It is possible from accumulated data to synthesize a new clinical entity: The Complete Left Bundle Branch Block Syndrome. This encompasses the following: Uncomplicated LBBB: (1) the abnormal ECG configuration with normal QRS axis; (2) reversed splitting of the cardiac second sound due to delay of aortic valve closure; (3) significant left ventricular systolic and diastolic dysfunction due to the abnormal sequence of left ventricular activation and relaxation; (4) ventricular septal hypokinesis, and during thallium stress testing ventricular septal perfusion defects which tend to invalidate the results of the test; (5) the vast majority of patients with LBBB have organic heart disease, but 16% have structurally normal hearts except for the conduction system disease; Complicated LBBB: (6) left or right axis deviation or QRS duration greater than 0.14 secs. indicates a greater degree of left ventricular disease and dysfunction than LBBB alone and nearly excludes the presence of conduction disease only; (7) disordered function of the SA node, AV node and right bundle branch.