Effect of various drugs on spontaneous and surgically induced ventricular fibrillation in hypothermia

The antifibrillary actions of Ambonestyl, quinidine, and mephentermine were studied on spontaneous ventricular fibrillation and on surgically induced ventricular fibrillation in the hypothermic dog. In addition, combinations of these agents were studied on spontaneous ventricular fibrillation in hypothermia. Mephentermine in a dose of 3 mg./Kg. significantly reduced the frequency of spontaneous ventricular fibrillation, whereas Ambonestyl and quinidine were not effective. When combined with either Ambonestyl or quinidine, mephentermine exerted the same antifibrillary effect. Surgically induced ventricular fibrillation in hypothermia was significantly reduced by quinidine (12 mg./Kg.) but not by Ambonestyl or mephentermine. The results indicate that the two situations (spontaneous and surgically induced fibrillation in hypothermia) are not entirely similar, that prevention of one does not imply prevention of the other, and that the factors predisposing the heart to fibrillation are different in the two conditions.