Antiarrhythmic properties of ivabradine in an experimental model of Short-QT- Syndrome

The I-f channel inhibitor ivabradine is recommended for treatment of chronic heart failure. However, ivabradine also inhibits human ether-a-go-go (hERG) mediated potassium currents. The aim of the present study was to assess the electrophysiologic effects of ivabradine in an experimental model of short-QT-syndrome. Twelve rabbit hearts were isolated and Langendorff-perfused. After obtaining baseline data, pinacidil, an IK-ATP channel opener, was infused (1mol/L). Eight endo- and epicardial monophasic action potentials and a 12-lead ECG showed a significant abbreviation of QT interval (-32ms, P<.05) and shortening of action potential duration at 90% of repolarization (APD90; -22ms, P<.05). The shortening of ventricular repolarization was accompanied by a reduction of effective refractory period (ERP; -20ms, P<.05). Thereafter, hearts were additionally treated with ivabradine (5mol/L) leading to an increase of QT interval (+31ms, P<.05), APD90 (+15ms, P<.05) as well as of ERP (+38ms, P<.05) and post-repolarization refractoriness (PRR, +33ms, P<.05) as compared with sole pinacidil infusion. Under baseline conditions, ventricular fibrillation (VF) was inducible by a standardized pacing protocol including programmed stimulation and burst stimulation in 3 of 12 hearts (6 episodes). After application of 1mol/L pinacidil, 6 of 12 hearts were inducible (22 episodes). Additional infusion of 5mol/L ivabradine led to a significant suppression of VF. Only two episodes could be induced in 1 of 12 hearts. In the present study ivabradine reversed the electrophysiologic effects of pharmacologically simulated short-QT syndrome. Ivabradine demonstrated antiarrhythmic properties based on an increase of both ERP and PRR.