Observations Upon Refractory Period of Auricular Extrasystoles in the Mammalian Heart

Abstract

By means of an adaptation of the method reported by Andrus and Carter, 1 the authors have determined the refractory period of extrasystoles induced at various points in the cardiac cycle in the normally beating dog's auricle. A typical experiment in which extrasystoles were induced soon after the end of the refractory period of the spontaneous excitation is summarized in Table I.

Columns I and II depict the determination of the refractory period of the spontaneous beat. The intervals, which are given in seconds, were measured between a spontaneous excitation and the induced stimulus which followed (R₁-S₁ interval). Those stimuli represented above the “refractory period” line were followed by auricular extrasystoles; those below were not. The refractory period, therefore, lay between the shortest interval which was followed by a response and the longest which was not.

Each series is made up of consecutive observations; those of Column I with successively decreasing, and those of Column II with successively increasing, R-S intervals. Identical supra-maximal stimuli were used throughout.

Columns III and IV illustrate the estimation of the refractory period of extrasystoles induced 0.1470 sec. ± 0.0031 sec. after spontaneous excitations. The intervals are those between a stimulus which produced an extrasystole and a succeeding identical stimulus (S₁-S₂ interval). The stimuli above the “refractory period” line were followed by a second auricular systole, those below were not. The refractory period of the auricular extrasystoles, therefore, lay between the extremes as defined above. These results are also from consecutive observations with successive S₁-S₂ intervals shorter in column III and longer in column IV.