Dofetilide induced Torsade de Pointes in 100% of dogs with ventricular hypertrophy at 3-10 μg/kg, compared to 16.7% of control dogs at 30 μg/kg, driven by increased dispersion of repolarization.
Does dofetilide increase the incidence of Torsade de Pointes and transmural dispersion of repolarization in hypertrophied hearts compared to normal hearts?
Ventricular hypertrophy increases susceptibility to drug-induced Torsade de Pointes due to baseline and drug-accentuated increases in transmural dispersion of repolarization.
Absolute Event Rate: 100% vs 16.7%
Background — Cardiac hypertrophy is associated with increased incidence of sudden death and susceptibility to proarrhythmic effects of antiarrhythmic agents. However, the in vivo electrophysiologic mechanism of the arrhythmias has not been investigated in detail. Methods and Results — Dose-dependent susceptibility to Torsade de Pointes (TdP) by class III drug dofetilide, 3, 10, and 30 μg/kg, was compared in 6 control dogs (C) and in 5 dogs 6 to 8 weeks after induction of complete atrioventricular block (AVB) that resulted in ventricular hypertrophy (H). Tridimensional ventricular activation and repolarization (R) patterns were simultaneously analyzed from unipolar extracellular electrograms, and local R was measured from activation recovery intervals. Both R and transmural dispersion of R (TDR) were significantly greater in dogs with H compared with C. Dofetilide resulted in cycle length–dependent and dose-dependent prolongation of R, which was more marked in left ventricular endocardium/midmyocardium compared with epicardium, resulting in significant increase of TDR. These changes were more accentuated in dogs with H compared with C. All 5 dogs with H developed TdP at a dose of 3 to 10 μg/kg, whereas only 1 of 6 C dogs developed TdP at 30 μg/kg. TdP was initiated by subendocardial focal activity that infringed on TDR, resulting in functional conduction block and reentrant excitation. Conclusions — Enhanced susceptibility of hypertrophied heart to class III drugs is attributable to baseline increased TDR and greater dose-related accentuation of TDR compared with nonhypertrophied heart. This provides the electrophysiologic substrate for drug-induced TdP.
Kozhevnikov et al. (Tue,) conducted a other in Ventricular hypertrophy and Torsade de Pointes (n=11). Dofetilide vs. Control dogs (nonhypertrophied) was evaluated on Development of Torsade de Pointes (TdP). Dofetilide induced Torsade de Pointes in 100% of dogs with ventricular hypertrophy at 3-10 μg/kg, compared to 16.7% of control dogs at 30 μg/kg, driven by increased dispersion of repolarization.