Facilitation of cardiac defribillation by aminophylline in the conscious, closed-chest dog

The effects of intravenous aminophylline, 10 mg/kg , on the ventricular defibrillation threshold (DFT) were studied in two groups of closed-chest, conscious dogs; truncated monophasic waveforms were delivered between an intravascular catheter electrode (anode) and a left ventricular epicardial electrode (cathode). In group 1 (N = eight dogs, ten experiments), aminophylline produced a decrease in DFT from 11.0 ± 7.0 J (mean ± SD) at baseline to 5.3 ± 2.9 J at an average time of 31 minutes after the infusion of aminophylline (p < 0.005). DFT returned to 10.4 ± 7.2 J at an average time of 174 minutes after drug infusion. In group 2, eight dogs were given aminophylline alone 10 mg/kg (13 experiments) and, on alternate days, aminophylline was preceded by propranolol 0.4 mg/kg (14 experiments). Propranolol increased DFT from 23.8 ± 12.1 J at baseline to 27.2 ± 11.9 J (p < 0.05); aminophylline after propranolol decreased DFT from 27.2 ± 11.9 J to 20.9 ± 12.0 J (p < 0.001). Neither aminophylline nor propranolol produced significant changes in transcardiac impedance. These results demonstrate a facilitation of ventricular defibrillation by aminophylline in the conscious, closed-chest dog, an effect that was not blocked by pretreatment with propranolol.