[Efficacy of isoproterenol, magnesium sulfate and verapamil for torsade de pointes].

The efficacy of isoproterenol, MgSO4 and verapamil for torsade de pointes was evaluated in 60 dogs. Torsade de pointes was induced in 28 out of 60 dogs (46.7%) by ventricular stimulation after administration of quinidine sulfate (30 mg/kg). The electrophysiologic effect of isoproterenol (0.5 micrograms/min drip infusion) was studied in 9 dogs with torsade de pointes, in 9 dogs with MgSO4 (30 mg/kg), and in 10 dogs with verapamil (0.1 mg/kg bolus injection followed by 0.01 mg/kg/min drip infusion). If the first dose of these drugs was ineffective, ventricular stimulation was performed after the additional administration of the same dose. Isoproterenol significantly decreased QTc, ERP and dispersion of ERP but increased ERP/QT. MgSO4 significantly increased ERP and ERP/QT, however dispersion of ERP did not change. Verapamil induced no electrophysiologic changes in ventricular refractions . Isoproterenol prevented the occurrence of torsade de pointes in all dogs (100%), MgSO4 in 7 of 9 dogs (77.8%, 30 mg/kg in three and 60 mg/kg in four) and verapamil in 4 of 10 dogs (40%, 0.1 mg/kg in two and 0.2 mg/kg in two). These findings suggest that isoproterenol and MgSO4 increased ERP/QT, showing one of their antiarrhythmic effects. It also shows that isoproterenol and MgSO4 may be useful in the treatment of torsade de pointes.