Can Class III Antiarrhythmic Drug Improve Electrical Defibrillation Efficacy During Ventricular Fibrillation?

Objectives. We tested whether new class III drug (MS-551) administered during ventricular fibrillation (VF) could decrease the defibrillation threshold (DFT) in anesthetized canine hearts. Background. Pretreatment with class III antiarrhythmic agents is known to enhance electrical defibrillation efficacy. Methods. In preliminary study (n = 10), we ascertained the validity of DFT determination by sequence of incremental defibrillation shocks in single fibrillation/defibrillation episode. We then compared the DFTs after 130 s of VF with and without administration of MS-551 (2 mg/kg body weight) at 10 s after the onset of VF in 12 open chest dogs and 8 closed chest dogs. Results. MS-551 decreased the DFT in both experimental models (open chest [mean ±SD]: from 416 ± 106 to 318 ± 92 V, p < 0.05; closed chest: from 714 ± 75 to 615 ± 112 V, p < 0.05). The change (Δ) in DFT in each heart was inversely correlated with the drug-induced prolongation of VF cycle length before the defibrillation attempt (ΔDFT vs. ΔVF cycle length 10 s before the first discharge: r = −0.58 and −0.81, p < 0.05). Conclusions. MS-551 given after the induction of VF improved defibrillation efficacy. Class III antiarrhythmic agents deserve consideration when VF is resistant to electrical defibrillation during cardiopulmonary resuscitation.