VENTRICULAR LOAD OPTIMIZATION BY UNLOADING THERAPY IN PATIENTS WITH HEART-FAILURE

The effects of unloading a depressed heart were assessed in terms of optimal coupling between the ventricle and arterial system. To assess the effects of preload on ventricular load coupling, preload was reduced with a lower body negative pressure of -20 mm Hg. Nitroprusside was used to evaluate the effects of afterload on the coupling under the condition that preload reduction was comparable to that with lower body negative pressure. In 13 patients with heart failure (ejection fraction 32 +/- 3%, mean +/- SE), direct arterial pressure was simultaneously recorded with the left ventricular echocardiogram as the pressure was elevated by phenylephrine. Left ventricular contractile properties were defined by the slope (Ees) of the end-systolic pressure-volume relation. The effective arterial elastance (Ea) was expressed by the slope of the end-systolic pressure-stroke volume relation. Left ventricular external work, end-systolic potential energy and work efficiency, defined as external work per pressure volume area (external work + potential energy), were determined. Baseline ventricular load coupling in these patients was characterized by an increase in the ratio of arterial elastance to ventricular elastance (Ea/Ees) (1.96 +/- 0.31). This ratio decreased significantly, to 1.45 +/- 0.22, with nitroprusside, and increased to 2.37 +/- 0.34 with lower body negative pressure. Therefore, end-systolic potential energy was decreased by nitroprusside but was unaltered by lower body negative pressure while external work was comparably decreased by both manipulations, indicating that work efficiency was significantly augmented with nitroprusside but declined with lower body negative pressure. It is concluded that reduction in afterload rather than in preload plays an important role in restoring optimal ventricular load coupling in patients with heart failure.