Effects of antiarrhythmic drugs (verapamil, propranolol and lignocaine) on the electrocardiogram and haematology in adrenaline-induced arrhythmias in dogs anaesthetized with halothane.

Twenty adult (1-3 year old) mongrel dogs of either sex were used to study the effects of antiarrhythmic drugs in adrenaline-induced arrhythmias. The dogs were divided randomly into four groups of five dogs each (n = 5), anaesthetized with halothane and pretreated intravenously (i.v.) with verapamil 0.1 mg kg-1, propranolol 0.06 mg kg-1, or lignocaine 4 mg kg-1 while the controls received sterile physiological saline. Adrenaline (4 micrograms kg-1) was administered i.v. 10 min after drug pretreatments. Lead II of the ECG was recorded and blood collected for haematology. Ventricular fibrillations preceded by ventricular tachycardia occurred in the control dogs and three died within one minute of adrenaline administration. The predominant arrhythmias were ventricular premature beats, ventricular tachycardia, and second degree heart block. A significant increase (P < 0.05) in T wave amplitude was observed in the control group from 0.16 +/- 0.05 mV to 0.43 +/- 0.09 mV while only minimal increases were noted in the drug pretreated groups and there were no deaths. Data obtained from this study suggest that verapamil when administered early compares well with propranolol in the control of adrenaline-induced ventricular arrhythmias in the dog. Lignocaine when administered early prior to the induction of the arrhythmias protected against death but not arrhythmias. Drug pretreatments did not have any clinically significant effects on electrocardiographic parameters.