Abstract
BackgroundRanolazine inhibits late Na+ and K+ currents. Earlier studies have reported an antiarrhythmic effect. The aim of the present study was to understand whether ranolazine could still preserve its antiarrhythmic properties in the settings of chronic heart failure (CHF). Methods and ResultsIn 12 female rabbits, CHF was induced by 4 weeks of rapid ventricular pacing leading to a decrease in ejection fraction. Twelve rabbits underwent sham operation. Isolated hearts were Langendorff perfused and demonstrated a significant QT prolongation after induction of heart failure. Ranolazine caused a concentration-dependent (10 and 30 μmol/L) increase of action potential duration (APD90) in sham-operated and failing hearts. Eight endo- and epicardial monophasic action potentials revealed a nonsignificant increase in spatial and temporal dispersion of repolarization. The increase in APD90 was accompanied by a greater increase in refractory period, resulting in a significant increase in postrepolarization refractoriness in sham-operated (+29 ms and +55 ms; P < .01) and failing (+22 ms and +30 ms; P < .05) hearts. In control conditions, programmed ventricular stimulation and a burst pacing protocol led to ventricular fibrillation (VF) in 5 of the 12 sham-operated (6 episodes) and in 7 of the 12 failing (18 episodes) hearts. In the presence of ranolazine, VF was inducible in only 2 of 12 failing hearts (5 episodes). In the presence of low [K+], only 1 ranolazine-treated sham-operated heart developed early afterdepolarizations and ventricular tachyarrhythmias despite significant QT prolongation. ConclusionsRanolazine decreases inducibility of VF in the presence of a significant increase in postrepolarization refractoriness. This antiarrhythmic effect in the intact heart is preserved in CHF and is not associated with drug-induced proarrhythmia.
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