Purkinje fibers of sheep papillary muscle: Occurrence of discontinuous fibers

Abstract Mapping of the peripheral specialized conducting system of the heart could contribute to an understanding of normal and abnormal impulse propagation. In this study, a sheep right anterior papillary muscle was sectioned serially and stained for Purkinje fibers with the periodic acid Schiff and hematoxylin procedure. The subendocardial Purkinje fibers entered the papillary muscle through its base and extended nearly to its apex. Except for one “mixed” fiber group, the subendocardial fibers did not connect to the deep Purkinje fibers, and both groups contained discontinuous Purkinje fibers. The fibers of the moderator band radiated in such a complex fashion that they could not be reconstructed exactly, but they generally disappeared in the ventricular wall through the base of the papillary muscle and false tendons. No direct connections between the subendocardial Purkinje fibers and those of the moderator band could be found within the boundaries of the papillary muscle, and this may form the basis for the relatively late activation of the papillary muscle as compared to the surrounding myocardial wall. The discontinuous fibers we observed are compatible with a current concept regarding the embryology of the ventricular specialized conducting system, and are not in conflict with normal impulse propagation.