Cardiac Arrhythmia: Five Cases

brought to light by a study of them, but because they will serve as a means for demonstrating the principal facts on which the modern conceptions of cardiac arrhythmia are based. First, certain facts as to the anatomy and physiology of the cardiac muscle must be recalled. The primitive heart is a muscular tube, the powerfully contracting chamber is a later development, and the valves and pericardium are convenient appendages added later still. Traces of this tube are still to be found in the mammalian heart. These are (a) the sino-auricular node, situated at the junction of the sinus venosus, the opening of the superior vena cava, with the right auricle ; (b) the auriculo-ventricular node, situated in the inter-auricular septum, just above the pars membranacea of the interventricular septum ; (c) the auriculo-ventricular bundle, first described by Professor Stanley Kent, which runs from the node into the inter-ventricular septum, and splits into two branches, one for each ventricle, each breaking up again and again for distribution throughout the ventricular musculature. No definite separate muscular connection has yet been proved between the two nodes, which, it must be remembered, are the main points of junction between the nerves and the musculature of the heart. So much for anatomy. Next it is necessary to state the five separate functions of the cardiac muscle, (i) Rhythmicity,