THE INOTROPIC AND HEMODYNAMIC-EFFECTS OF INTRAVENOUS MILRINONE WHEN REFLEX ADRENERGIC-STIMULATION IS SUPPRESSED BY BETA-ADRENERGIC-BLOCKADE

Milrinone is an inotropic and vasodilator agent proven to be effective in the treatment of heart failure. This study evaluated whether milri none produces inotropic and hemodynamic effects independent of reflex adrenergic stimulation. Eleven stable heart failure patients (New York Heart Association class II to III) undergoing cardiac catheterization received intravenous (IV) milrinone (50 mug/kg for 10 minutes followe d by 0.5 mug/kg/min for 50 minutes) during beta-adrenergic blockade. A fter beta-blockade with a 50-mg oral dose of metoprolol, heart rate de creased by a mean of 16.6%. The peak inotropic response to IV milrinon e measured using the maximum rate of rise of left ventricular pressure (LV dP/dt) was fully developed at 20 minutes. Mean absolute inotropic response of LV dP/dt from baseline was statistically significant at 1 0, 20, 30, and 40 minutes (P < 0.05). Mean percentage increase in card iac index from baseline was statistically significant at 20 and 30 min utes, and mean absolute decline from baseline for pulmonary capillary wedge pressure was statistically significant at 20 and 40 minutes (P < 0.05). The inotropic and hemodynamic effects of IV milrinone were thu s preserved during beta-adrenergic blockade. This finding is consisten t with a mechanism of action of IV milrinone-myocardial phosphodiester ase inhibition-that is independent of reflex adrenergic stimulation.