Electrocardiographic manifestations: bundle branch blocks and fascicular blocks.

Intraventricular conduction block is the general name given to a varied group of electrocardiographic entities. All share a common finding of some degree of delay in ventricular activation; recognition of these blocks hinges upon analysis of the QRS complex, as well as the ST-T changes associated with them. Bundle branch block (right or left), and fascicular block (left anterior or left posterior) are all examples of intraventricular conduction block. Causation of intraventricular conduction block may be cardiac or noncardiac; early recognition of the etiology may be of clinical importance. This article reviews the basic anatomy and physiology related to intraventricular conduction blocks, and then examines each in terms of electrocardiographic definition and clinical correlation.