[Dose-dependent effect of amrinone on hemodynamics, myocardial circulation and myocardial energy requirement. An...

This study was designed to assess the dose-dependent effects of amrinone (1, 2 and 4 mg/kg i.v.) on hemodynamics, myocardial blood flow and myocardial oxygen consumption in anesthetised closed chest dogs (n = 8). Heart rate (HR), cardiac output, mean aortic pressure (MAP), left ventricular end-diastolic pressure (LVEDP), maximum dp/dt (dp/dtmax), myocardial blood flow (MBF) and aorto-coronary sinus oxygen difference (AVDO2 cor) were measured. Cardiac index (CI), stroke volume index (SVI), ejection fraction (EF), total peripheral resistance (TPR), coronary vascular resistance (CVR) and myocardial oxygen consumption (MVO2) were calculated from standard formulas. Amrinone improved myocardial pump function by a direct positive inotropic effect on the myocardium. EF and SVI increased to a maximal degree with 1 mg/kg amrinone (28% resp. 30%). dp/dtmax increased dose dependent (46, 64, 71%). Following a systemic vasodilation due to amrinone, left ventricular filling pressure and TPR decreased significantly. With 1 and 2 mg/kg amrinone MAP remained unchanged. 4 mg/kg produced a distinct fall in MAP accompanied by an increase in HR. The improvement in myocardial contractility did not cause a comparable increase of myocardial oxygen consumption. Due to an unloading of the heart 1 and 2 mg/kg amrinone induced no significant and prolonged augmentation of the myocardial oxygen demand. In the coronary circulation a non energy dependent vasodilation occurred followed by a marked decrease of AVDO2 cor (10, 18, 28%).