Objectives: AVE0118 is a novel blocker of the K(+) channels K(v)1.5 and K(v)4.3 which are the molecular basis for the human cardiac ultrarapid delayed rectifier potassium current (I(Kur)) and the transient outward current (I(to)). The objective of this study was to investigate the effect of AVE0118 on atrial refractoriness (ERP), left atrial vulnerability (LAV) and on left atrial monophasic action potentials (MAP) in pentobarbital anesthetized pigs in comparison to the selective I(Kr) blocker dofetilide in order to assess the therapeutic potential of the novel K(+) channel blocker for atrial fibrillation.
Methods: Atrial ERP was determined with the S1-S2-stimulus method in the free walls of left and right atrium at 240, 300 and 400 ms basic cycle length (BCL). The inducibility of mostly nonsustained atrial tachyarrhythmias by the premature S2 extrastimulus, which is very high in the left pig atrium and referred to as LAV, was evaluated before and after drugs. Left atrial epicardial MAP was recorded to study the influence of the potassium channel blockers on the time course of repolarization. Left ventricular epicardial MAP, ERP and QT interval were measured to investigate a possible effect of AVE0118 on ventricular repolarization.
Results: ERPs determined at 240, 300 and 400 ms BCL were significantly shorter in the left vs. right atrium (99+/-3, 106+/-4 and 113+/-3 ms vs. 133+/-4 ms, 142+/-4 and 149+/-5, respectively; p<0.001; n=21). AVE0118 administered i.v. dose-dependently prolonged the atrial ERP independent from rate and inhibited LAV (100% at 0.5 and 1 mg/kg) while having no effect at all on the corrected QT (QTc) interval. At 1 mg/kg (n=5) AVE0118 prolonged left vs. right atrial ERP by 49.6+/-4.1 ms vs. 37.7+/-9.7 ms (means+/-SEM of changes at 240, 300, and 400 ms BCL), respectively, corresponding to a relative increase of 53.2+/-6.2% vs. 27.6+/-6.8% (p<0.05 for percent increase of left vs. right atrial ERP). In a separate group of pigs (n=5) AVE0118 had no effect on left ventricular ERP at 333, 400 and 500 ms BCL and no effect on MAP duration and QT at 600 ms BCL. After 1 mg/kg of AVE0118 the atrial MAP was significantly prolonged already at 10% repolarization (P<0.05; n=7) reaching the maximum at 40% repolarization. In contrast to AVE0118 the effect of dofetilide (10 microg/kg) on atrial MAP started to become significant only at 60% repolarization (n=6) with a maximum increase at 90%. Dofetilide, which prolonged the QTc interval by 16.9% (P<0.001), had a significantly stronger effect on right (34.7+/-5 ms) vs. left atrial ERP (23.5+/-7 ms) at 300 ms BCL, respectively, but did not significantly inhibit LAV (14%; n=6).
Conclusion: The novel K(+) channel blocker AVE0118 prolonged atrial ERP and showed strong atrial antiarrhythmic efficacy with no apparent effect on ventricular repolarization in pigs in vivo.