Ventricular-load Optimization by Inotropic Stimulation in Patients with Heart Failure

To evaluate the effects of inotropic stimulation on ventriculo-arterial coupling, we determined both the slope of the end-systolic pressure-volume relationship (ventricular elastance) and the slope of end-systolic pressure-stroke volume relationship (arterial elastance) at rest and during dobutamine infusion (5 micrograms/kg/min). We also determined stroke work, end-systolic potential energy and the ventricular work efficiency defined as stroke work per pressure volume area (stroke work + potential energy). In the resting state, ventricular elastance was lower than arterial elastance and work efficiency was about 59.7 +/- 9.3% (mean +/- SD). This condition is remote from the point where stroke work or mechanical efficiency is optimal. Enhanced ventricular elastance by 41% with dobutamine resulted in a significant reduction in both left ventricular end-diastolic and end-systolic volumes and was accompanied by the reduction in arterial elastance by 23%. Consequently, the ratio of arterial elastance to ventricular elastance decreased from 1.43 +/- 0.57 to 0.82 +/- 0.47, which resulted in an increase in stroke work, a decrease in potential energy and hence a marked increase in work efficiency. Thus, inotropic stimulation of depressed hearts could modulate ventriculo-arterial coupling towards optimization of either stroke work or mechanical efficiency.