EFFECT OF PROPRANOLOL ON CATECHOLAMINE-INDUCED ARRHYTHMIAS DURING NITROUS OXIDE-HALOTHANE ANAESTHESIA IN THE DOG

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Abstract
In dogs under nitrous oxide-halothane anaesthesia, ventricular arrhythmias were produced by intravenous injection of adrenaline and noradrenaline 2–3 μg/kg or isoprenaline 1μg/kg, and completely prevented by propranolol 0.3 mg/kg. Adrenaline or noradrenaline (20–30 μg/kg) produced slow rate ventricular extrasystoles and ventricular bigeminy, without increase in the rate of sinus rhythm. Doses of 100 to 150 μg/kg produced ventricular tachycardia in all and ventricular fibrillation in some experiments. Increase in sinus rate always preceded ventricular tachycardia. Isoprenaline 10 μ/kg produced ventricular tachycardia preceded by an increase in sinus rate. Very large doses (50 μg/kg) produced a greater increase in sinus rate, and later ventricular tachycardia and even ventricular fibrillation resulted in all the experiments. Dosages of catecholamines which did not produce any increase in the rate of sinus rhythm never produced ventricular tachycardia or fibrillation.

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