Ultrastructure of the atrial, ventricular, and Purkinje cell, with special reference to the genesis of arrhythmias

An examination of the anatomy of the atrial, ventricular and Purkinje cells reveals that the internal composition of all cardiac myofibers is qualitatively the same: all have a single nucleus, sarcomeric and mitochondrial units, and a well developed sarcoplasmic reticulum. There are important differences, however, in the extent and distribution of the cell membrane and its derivatives in the myofiber. The presence or absence of a transverse tubular system and the variation in the number and type of intercellular linkages explain at least some of the characteristic electrical and functional properties of individual types of cells. The overall pattern of cellular organization in working atrial, ventricular and conducting tissue is reviewed, and possible anatomic bases for current theories of normal and abnormal impulse generation and conduction in the heart are discussed.