• Fanny Vaillant, Quadiri Timour, Jacques Descotes, Waheed Manati, Dalila Belhani, Bernard Bui-Xuan, Alain Tabib, Giampiero Bricca, and Philippe Chevalier.
• Laboratory of Medical Pharmacology, INSERM ERI 22, Grange Blanche Medical School, Claude Bernard University, Lyon, France.
• J. Cardiovasc. Pharmacol. 2008 Dec 1; 52 (6): 548-54.

BackgroundTachycardia often facilitates ischemic ventricular fibrillation (VF).ObjectiveThis study assessed the impact of ivabradine (IVA), a selective inhibitor of the cardiac pacemaker If current, on ventricular fibrillation threshold (VFT) during acute myocardial ischemia.MethodsThe experiments were conducted on a total of 54 domestic pigs. Myocardial ischemia was induced in anesthetized pigs by total 1-minute coronary occlusion at baseline and then on 2 occasions after intravenous administration of saline or 0.5 mg/kg of IVA. VF was triggered by electrical stimuli of increasing intensity at a fixed rate. Heart rate (HR), VFT, monophasic action potential duration, and peak of the time derivative of left ventricular pressure (LV dP/dt max) were monitored on each occasion. The activity of mitochondrial succinodehydrogenase was measured on heart sections.ResultsCompared with controls, IVA induced a 31% reduction in HR, a 2.9-fold increase in VFT, and prevented ischemia-induced monophasic action potential duration shortening (+1 +/- 12 vs. -14 +/- 11 milliseconds) without affecting peak LV dP/dt. This beneficial effect on VFT was mainly due to HR reduction and was accompanied by a significant reduction in the hypoxic area (26% +/- 1% vs. 38% +/- 1%, P < 0.0001).ConclusionHR reduction and the decrease in myocardial damage induced by IVA protected against primary ischemic VF without altering myocardial contractility.

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