Correlative ultrastructural and electrophysiological study of the Purkinje system of the heart.

To delineate major morphological differences between Purkinje and working myocardial fibers, a comparative electrophysiological and ultrastructural study of the Purkinje system and working myocardial cells was undertaken. To this effect, the false tendon, papillary muscle, trabeculae carneae and segments of the Purkinje extramural network from hearts of dogs, rabbits and cats were studied. The cell populations of the false tendon and of the extramural Purkinje network have similar characteristics and can be, therefore, easily differentiated from the papillary muscle, trabeculae carneae and working myocardial fibers of the ventricular wall. The main distinguishing features of Purkinje fibers are the absence of triads and the presence of peculiar small mitochondria. In addition, the intercalated discs are straighter and thus less prominent than in working myocardial fibers. Some of the current discrepancies on the ultrastructure of the Purkinje system and working myocardial fibers have been resolved by this correlated electrophysiological and morphological study.