Manner of Stimulus Conduction in Atria

(1) The manner of the stimulus conduction was investigated for both left and right atria of the canine heart through analysis of the configuration of unipolar electrograms and the arrival times of the activation wave. Langendorff's method of irrigating the heart was used.(2) In the right atrium, the stimulus spreaded from the S-A node to the orifice of the I.V.C. with higher conduction velocity along the sulcus terminalis. The stimulus coming along the sulcus terminalis spreaded over the atrium through the muscle bundles which branched from the sulcus terminalis. The apex of the atrial appendage was found to be the last portion to become activated.(3) In the left atrium, the stimulus originating in the S-A node, spreaded through Bachmann's bundle, first of all. The stimulus coming along Bachmann's bundle spreaded over the atrium through the muscle bundles which branched from Bachmann's bundle. The region between the left lower pulmonary vein and the A-V ring was found to be the last portion of activation in both left and right atrium.(4) In some cases, there was an area in which the stimulus originating in the S-A node might reach directly from the right atrium without passing through Bachmann's bundle. This area was located in a small region of the posteroinferior portion of the left atrium near the I.V.C.