How the Purkinje system determines the ventricular activation sequence

Conduction of the cardiac action potential in a spatially and temporally defined excitation sequence involves regional differences in cell membrane properties and intercellular coupling. This produces a sequence which in some regions is nearly continuous while other regions have discontinuous conduction. The Purkinje-Ventricular junction sites on the endocardial surface seem specifically designed to use discontinuous conduction as a means of effectively increasing the spread of activation through the endocardial surface while preserving a high safety factor for conduction. We present a historical survey of studies on this junctional region. Because of the specialized nature of the action potential properties of the Purkinje and ventricular as well as the localized electrical coupling, these sites may serve to originate arrhythmias as regions of after-depolarizations or may serve as important sites within endocardial reentrant circuits. In addition, the changes in the spatial pattern of junctional conductance following myocardial ischemia may produce other sites within the atrium or ventricle with properties of discontinuous conduction.