Effects of sodium nitroprusside upon cardiac work, efficiency, and substrate extraction in severe left ventricular failure.

In nine patients with severe left ventricular failure caused by coronary artery disease or congestive cardiomyopathy, left ventricular pressure, cardiac output, coronary sinus blood flow, and myocardial substrate extraction were measured before and during infusion of sodium nitroprusside. Infusion of 55 ,ug/min reduced left ventricular systolic and end-diastolic pressures, peripheral resistance, coronary sinus flow, and myocardial oxygen consumption. Left ventricular minute work increased slightly, but the large improvement in myocardial efficiency was mainly the result of decreased oxygen consumption. Doubling the infusion rate to 110 ,ug/min caused no further decrease in ventricular pressures depite further reduction of peripheral resistance; as myocardial oxygen consumption did not change, the further improvement in efficiency was due to increased external work, the result of increased stroke volume. Thus, nitroprusside appears to improve efficiency in low dose by reducing load (ventricular pressure and volume decrease) and in high dose by increasing work at constant load.