Termination of ouabain-induced ventricular tachycardia by flunarizine in conscious dogs.

The ability of flunarizine to terminate ouabain-induced ventricular tachycardia was investigated in conscious dogs. These arrhythmias result from triggered activity based on delayed afterdepolarizations. Sustained ventricular tachycardia was induced by ouabain (48 +/- 6 micrograms/kg) and pacing in 13 animals with surgically induced complete atrioventricular block. Flunarizine was administered i.v. when the arrhythmia had persisted for at least 20 min. Flunarizine induced an increase of the R-R interval from 300 +/- 30 to 410 +/- 50 ms (P less than or equal to 0.001) in all dogs. Flunarizine (2 mg/kg) terminated ventricular tachycardia with long R-R intervals (330 +/- 20 ms) in seven dogs. An additional dose of flunarizine (1 mg/kg) resulted in termination of the faster tachycardias (280 +/- 15 ms). The arrhythmias were not induced again by pacing for 27 +/- 18 min. Reinitiated tachycardias could be suppressed again by flunarizine. In conclusion, flunarizine (1) slows and terminates arrhythmias resulting from delayed afterdepolarizations, and (2) prevents their reinitiation.