Effects of metoprolol and amiodarone combination on heart rate, myocardial contractility and coronary flow: Study in isolated perfused rat hearts.

BACKGROUND: Beta-blockers and amiodarone have been used concomitantly to treat arrhythmias associated with congestive heart failure. However, the combination of metoprolol and amiodarone has only been studied restrospectively, and its potential effects in congestive heart failure remain to be properly elucidated in prospective trials. OBJECTIVE: The present investigation focused on evaluating the pharmacological interaction between metoprolol and amiodarone in an isolated perfused rat heart preparation. MATERIALS AND METHODS: Adult male Wistar rats (n=24) were divided into four groups of six animals, and the effects of the metoprolol/amiodarone combination on systolic pressure, myocardial contractility (dP/dt), coronary flow (CF) and heart rate were analyzed, and the interdependent variables were compared. RESULTS: There was a negative chronotropic effect by both metoprolol and the metoprolol/amiodarone combination in isolated rat hearts. However, the acute effects of the metoprolol/amiodarone combination showed no myocardial contractility depression or bradycardia accentuation compared with metoprolol alone. CF increased by 9.2% at minute 1 through minute 5 (P=0.004) with the metoprolol/amiodarone combination. There was no difference in systolic pressure or myocardial contractility among the groups. CONCLUSIONS: The acute effects of the metoprolol/amiodarone combination in the isolated rat heart were an increase in CF, and no myocardial contractility depression or bradycardia accentuation.