Abstract
In sixteen adult mongrel dogs, cardiac arrest was induced experimentally by administration with digitalis or acetylcholine, electroshock of the right atrium, hyper- or hypothermia, or asphyxia. Resuscitation was carried out just before and/or after cardiac arrest. Electrocardiograms were recorded with A-B lead in each experiment and analyzed. From the results obtained from the present experiments, it was presumed that cardiac arrest might be classified into two categories, reversible and irreversible. It was very difficult to bring to life animals in which there was a shift from extrasystole to flutter or fibrillation, or in which fibrillation suddenly appeared. As the mechanism of heterotopic stimulus formation in these animals, it was assumed that the exciting level of the secondary pacemaker might be higher than that of the primary one. On the contrary, it was not impossible to resuscitate dogs in which sinus bradycardia progressed or shifted to atrio-ventricular block. These arrhythmias were caused mainly by disturbances in excitatory conduction. Although the arrhythmias caused by the heterotopic ritimulus formation were observed in several dogs of the second category. As the mechanism for their occurrence, it was assumed that the exciting level of the primary pacemaker was disturbed to an abnormal extent.
