Action of Ryanodine on Mammalian Cardiac Muscle
Histological Determination of the Site of Retrograde Atrioventricular Block
In our previous study, three types of intra-cellular potentials were found in a small area in the region adjacent to the postero-inferior margin of the membranous portion of the interventricular septum of the isolated dog heart. From the electrophysiologieal behavior of these cells, it was presumed that the cells of the third type were the point of block for retrograde conduction in cases of unidirectional A-V conduction, and that those of the first type lay upstream from the point of retrograde conduction block, whereas those of the second type lay- downstream beyond the blocking point. In this study, histological examination was used to find the origins of these three types of potentials. When a potential of one or another type was found the mieroelectrode tip was gently cut off and later localized histologically. It was found that all three types of potential originated from the ventricular portion of the specialized museilar tissue, that the origin of the third type was just above or at the bifurcation of the bundle of His, and that the origin of the first type was distal while that of the second type was proximal to the origin of the third type. Thus, the deduction from the electrophysiological behavior was proved by the histological examination. This gave further evidence for our belief that there is a sensitive point for retrograde conduction block in unidirectional A-V conduction just above the bifurcation of the bundle of His.
- Received July 5, 1961.
- © 1961 American Heart Association, Inc.