Abstract
Characteristics of the action potential and stimulus conduction in the A-V nodal region were studied electrophysiologically, especially in connection with the histological findings by means of ultramicroelectrode technique. The intracellular records in each case of normal sinus rhythm and A-V conduction disturbance were obtained. And situation of the tip of the microelectrode was ascertained by using immigration of cobalt ion. The specific muscle fibers were recognized in the vicinity of the A-V node. The action potentials of those fibers represented an inter-mediate type between the nodal type and the ordinary atrial muscle type. When the recording microelectrode was moved from the upper part of the node to the His' bundle, the shape of the action potential changed from the typical nodal type to the His' type, and the onset of the activation was gradually delayed. Disturbances of the A-V conduction were made using the effects of acetylcholine. And incomplete A-V block, complete A-V dissociation, and A-V dissociation with nodal or ventricular capture were observed and the boundary of characteristic changes of the action potential in all cases was found at the atrial margin of the A-V node which is netlike in structure.
