Electrophysiology of Endocardial Intraventricular Conduction: The Role and Function of the Specialized Conducting System

Abstract

When a cardiac impulse propagates from the A-V node to ventricular muscle, it must excite in temporal sequence: 1. the bundle of His; 2. the bundle branches; 3. the peripheral ramifications of the specialized intraventricular conducting system; 4. the terminal subendocardial Purkinje network; and 5. the junctions between Purkinje fibers and ventricular muscle cells (i.e., PF-VM junctions) (572,575). Impulses cannot excite muscle cells lateral to the orientation of the specialized conducting fibers unless PF-VM junctions are present (575), thereby limiting spread in the system to a functionally longitudinal orientation. Thus, the pattern of intraventricular conduction, and the functional electrophysiologic properties of the specialized intraventricular conducting system, are determined at least partially by the following factors: 1. the anatomy of the various portions of the intraventricular conducting system; 2. the functional relationship between intraventricular specialized conducting fibers and the ventricular muscle (PF-VM junctions); 3, the electrophysiologic properties of single units at various levels of the system; and 4. the interactions of groups of cells within the specialized conducting system. Each of these interactions and influences must be considered as one attempts to determine the mechanisms of normal and abnormal impulse conduction, and the nature of functional and pathologic intraventricular block.