Abstract
In six cases when dog's heart were used the unipolar lead ECG simultaneously recorded was taken over the surface of the right and left atria after the atrial septum was ligated, to study possible variation that might take place in the P-Q interval before and after the ligation, that is, to study any effect that the septum ligation might have on the stimulus conduction between the sinus node and the Tawara's node.Here again Osawa worked out a minute histological research on the ligated portion by way of finding its relation with the four pathways, which he had previously reported as activation pathways between the sinus node and the Tawara's node.Summarized below are the results of all these studies.1) In two of the six above cases, when, out of the four pathways assumed by Osawa in his histological research, the two running through the atrial septum were completely ligated, no impediment was found done to either the Tawara's node or His's bundle. In each of these two cases a remarkable prolongation of 0.025-0.050 second immediately after ligation was noted in P-Q interval as compared with that before ligation.2) In each of the other four cases, after a histological research, impediments to various extents were found done to Tawara's node and His's bundle causing in these cases an extraordinary prolongation of 0.067-0.217 second in the P-Q interval immediately after ligation, as compared with that before ligation, and in three out of the four cases a-v block and ventricular fibrillation occurred within three minutes.From what have been said above, two cases may be looked into concerning the prolongation of the P-Q interval in the clinical ECG; one when there is an injury done on the conducting pathway connected between sinus node and the Tawara's node, and the other when there is an injury done on the Tawara's node or the His's bundle.It is however, almost impossible to tell, by means of the length of the prolongation of the P-Q interval, which cause may be taken to account, when it is taken into consideration that the injuries done to the pathways must differ every way in extent. Be that as it may, the theory, that the stimulus conduction between the sinus node and the Tawara's node is performed through the definite stimulus conducting pathways, could undoubtedly be said to have been proved as a result of all above experiments.
