Effects of lignocaine, propranolol and bretylium on ventricular fibrillation threshold

The threshold for electrically induced ventricular fibrillation was measured by external transthoracic shocks in dogs weighing from 18 to 35 kg, anesthetized with morphine and pentobarbitone. The duration of the vulnerable period was determined for shocks of 10 joules. The administration of lignocaine, 10 mg/kg followed by an intravenous infusion of 1 mg/kg per min, raised the ventricular fibrillation threshold; smaller doses did not. Neither propranolol nor bretylium in the doses used raised the ventricular fibrillation threshold. None of the drugs affected the duration of the vulnerable period.