Abstract P184: Following Long Duration Ventricular Fibrillation, Flunarizine Greatly Reduces the Defibrillation Threshold and the Incidence of Refibrillation
Introduction: Following long duration ventricular fibrillation (LDVF) during sudden cardiac arrest, some individuals have a high defibrillation threshold (DFT) and many individuals refibrillate following successful defibrillation. This study determined if the delayed after depolarization (DAD) blocker flunarizine affected either of these two outcomes.
Methods: VF was electrically induced in 6 control dogs with 64 electrode basket catheters in the left and right ventricles. After 20 s of VF, the short duration VF (SDVF) DFT was determined by initially giving a 10 J shock through external patches on the thorax and increasing the shock strength until VF was halted. VF was then reinduced and after 7 min of LDVF the DFT was determined as before. Basket electrode recordings were then made for 20 min to document any refibrillation episodes, each of which was defibrillated. In another 6 dogs, after determination of the SDVF DFT, Flunarizine was given (loading dose 2 mg/kg over 10 min, maintenance dose 4 mg/kg/hr) and SDVF DFT, LDVF DFT and refibrillation incidence were determined as before.
Results: In controls, LDVF DFT was higher than SDVF DFT (Figure⇓, p<0.05). SDVF DFT before and after flunarizine was not significantly different, but LDVF DFT after flunarizine was only 18% of control LDVF DFT (p<0.05). The number of refibrillation episodes per animal after flunarizine (0.8±1.2) was only 21% of that for controls (3.8±2.3, p<0.05).
Conclusion: Flunarizine markedly reduced LDVF DFT and refibrillation incidence. These findings, besides having possible clinical significance, raise the possibility that defibrillation failure as well as refibrillation following LDVF are caused by DADs.