Hemodynamic effects of noninvasive systolic unloading (nitroprusside) and diastolic augmentation (external counterpulsation) in patients with acute myocardial infarction

Abstract

The two major beneficial hemodynamic effects of invasive circulatory assistance (intraaortic balloon pumping) are (1) left ventricular systolic unloading, and (2) diastolic augmentation of aortic pressure. In this study, these effects were produced noninvasively in 17 patients (13 with acute myocardial infarction, 5 of whom had cardiogenic shock). Systolic unloading produced by the constant intravenous infusion of sodium nitroprusside (16 to 200 μg/min) caused a reduction in pulmonary capillary wedge pressure (27 to 19 mm Hg), a rise in cardiac index (1.71 to 2.25 liters/min per m 2), and a reduction in mean arterial pressure (81 to 73 mm Hg). Diastolic augmentation with external counterpulsation produced a 20 mm Hg increase in peak, and a 7 mm Hg increase in mean diastolic arterial pressure. Cardiac index rose 14 percent after external counterpulsation in the patients with acute myocardial infarction. The results of combined use of these two modes of therapy (nitroprusside plus external counterpulsation) were better than those of either alone, in that external counterpulsation reversed the decrease in diastolic arterial pressure produced by nitroprusside, and also increased cardiac index further in six of nine patients. Thus it is feasible to utilize the principles of invasive circulatory assistance in a noninvasive way to produce hemodynamic improvement in patients with acute myocardial infarction.