Blackwell Publishing Journal Backfiles 1879-2005
Background: This study examined the proarrhythmic potential of the novel antiarrhythmic agent AZD7009 and dofetilide. Methods and Results: The electrophysiological and proarrhythmic effects of AZD7009 and dofetilide were assessed in the arterially perfused canine and rabbit left ventricular wedge preparation. The proarrhythmic potential of AZD7009, dofetilide, and azimilide was further assessed in the methoxamine-sensitized rabbit model of torsades de pointes (TdP) in vivo. AZD7009 lengthened the action potential duration (APD) and the QT interval in a bell-shaped manner (15.9 ± 1.3% in canine wedge and 46.1 ± 2.9% in rabbit wedge) occurring at 3 and 1 μM. In contrast, dofetilide did not show the bell-shaped concentration response and the QT interval was lengthened more extensively (27.7 ± 1.6% and 100.8 ± 10.0%). Furthermore, whereas dofetilide prolonged the midmyocardial and endocardial APD predominantly, resulting in an increased transmural dispersion of repolarization (TDR), AZD7009 prolonged the APD more homogenously in all cell layers. At 1 μM, AZD7009 produced phase 2 early afterdepolarizations (EADs) in 1/4 rabbit preparations but without ventricular R-on-T extrasystoles or TdP. In contrast, starting at 0.03 μM, dofetilide-induced EADs, R-on-T extrasystoles and TdP in 6/6, 5/6, and 4/6 preparations. Following intravenous infusion of AZD7009 (210 nmol/kg/minute), dofetilide (2 nmol/kg/minute) or azimilide (3.33 μmol/kg/minute), TdP was induced in 0/8, 5/8, and 5/8 rabbits (P = 0.026 vs AZD7009), respectively. In 5/5 rabbits, AZD7009 promptly suppressed TdP induced by dofetilide. Conclusions: In animal models of TdP, AZD7009 delays ventricular repolarization in a self-limited way associated with a low risk of repolarization-related proarrhythmia.
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