[An impairment of transmission of the cardiac electrical impulse along the fibers of the right bundle branch. A " complete RBBB pattern" (with QRS duration > 0.11s) does not necessarily reflect the existence of a total conduction block in the right branch. This pattern only indicates that the entire or major parts of both ventricles are activated by the impulse emerging from the left branch. Thus, a significant degree of conduction delay ("high-grade" or "incomplete RBBB) can produce a similar pattern. ( NCI )]