Comparative hemodynamic effects of intravenous nitroprusside and oral prazosin in refractory heart failure

Abstract

Beneficial effects of vasodilator therapy in heart failure have been amply described. Afterload reduction with intravenous nitroprusside improves hemodynamic values in patients with left ventricular dysfunction. The oral vasodilator prazosin was given to 10 patients with refractory heart failure, and its hemodynamic effects were compared with those of intravenous nitroprusside in the same patients. With prazosin, heart rate remained unchanged, mean arterial pressure decreased 13 percent ( P < 0.01), left ventricular filling and mean pulmonary arterial pressures decreased 31 and 24 percent, respectively (both P < 0.01) and cardiac index and left ventricular stroke work increased by 31 and 30 percent, respectively (both P < 0.01). Resistance levels in the systemic and pulmonary vascular beds declined by 29 and 27 percent, respectively (both P < 0.01). The hemodynamic changes appeared 1 hour after administration of a single dose of oral prazosin and persisted for 6 hours. Intravenous infusion of nitroprusside resulted in similar changes in heart rate and arterial pressure but greater reduction in left ventricular filling and mean pulmonary arterial pressures ( P < 0.05). Left ventricular stroke work index increased more with nitroprusside ( P < 0.01); however, changes in cardiac index and systemic and pulmonary vascular resistance levels were identical. Further, systolic pressure-heart rate product (index of myocardial oxygen demand) decreased significantly with oral prazosin as well as nitroprusside. These results suggest that prazosin has salutary effects on cardiovascular hemodynamics in heart failure, probably because of its vasodilator properties. These effects are qualitatively similar to those observed with intravenous infusion of nitroprusside. However, quantitatively, intravenous nitroprusside is slightly more potent.