Studies on the spread of excitation through the ventricular myocardium.

The spread of the excitatory process in the ventricular septum of the dog's heart has been studied in the isolated organ perfused by the Langendorfl technic. It has been possible to remove large portions of the free wall of the right and left ventricles and explore the septal surfaces under direct vision. The mean excitatory pathway in the muscular mass of the dog's ventricular septum has been demonstrated to be from apex to base. The left side of the septum is activated before the right side, and the apical part of the right side is activated before its base. W E HAVE previously reported that the spread of the excitatory process in the left ventricular wall appeared to be related to the predominant direction of the muscle fibers.' The present report pertains to the excitation of the ventricular septum studied in the isolated perfused organ. It has been found that the mean axis of excitatory potentials of this preparation was such that the base was positive to the apical portion throughout most of the excitation. Preliminary reports on the time of arrival of the excitation on either side of the septum from directly applied elec-trodes2 and the vectorgrams3 of the isolated sep-tum have been presented. While the present work was in progress, Sodi-Pallares and co-workers,4 using other technics in the intact animal, published investigations leading them to similar conclusions. aid of Dr. Richard Achor, fellow in medicine, Mayo Foundation. 161 METHODS The isolated dog's heart was perfused by the Langendorff technic, the perfusate being Tyrode's solution to which was added glucose to 1 per cent concentration and small amounts of washed red cells, approximated at 25 to 50 cc. of packed cells per liter. After the heart beat had become stabilized, the free walls of right and left ventricles were removed , exposing the septum to direct exploration. A ridge of the ventricular muscle was left along the A-V (atrioventricular) sulcus so that in effect the "removal" of the free walls could be described as the making of very large windows into the ven-tricles. In the early experiments the electrocardiograms were recorded on a Sanborn Tribeam electrocardio-graph; in the later experiments, on a Sanborn "Poly-viso," to two channels of which was attached a cathode ray oscilloscope (Dumont 304H) so that a vectorgram also could be recorded directly. Time intervals were recorded by the incorporation of an intensity modulator (Hewlett Packard …