Can a class III antiarrhythmic drug improve electrical defibrillation efficacy during ventricular fibrillation?

Abstract

We tested whether a new class III drug (MS-551) administered during ventricular fibrillation (VF) could decrease the defibrillation threshold (DFT) in anesthetized canine hearts. Pretreatment with class III antiarrhythmic agents is known to enhance electrical defibrillation efficacy. In a preliminary study (n = 10), we ascertained the validity of DFT determination by a sequence of incremental defibrillation shocks in a 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. 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 (delta) in DFT in each heart was inversely correlated with the drug-induced prolongation of VF cycle length before the defibrillation attempt (delta DFT vs. delta VF cycle length 10 s before the first discharge: r = -0.58 and -0.81, p < 0.05). 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.