Objectives: The purpose of this study was to evaluate left ventricular contractility, arterial loading conditions and the way their interaction affects myocardial energetics.
Background: Ventriculoarterial coupling, defined as the ratio of effective arterial elastance to left ventricular end-systolic elastance, is known to reflect the mechanoenergetic performance of the heart. However, relations between the coupling and efficiencies of energy transfer from oxygen consumption to hydraulic energy have not been fully investigated in failing hearts.
Methods: Pressure-volume data were measured in 23 patients with idiopathic dilated cardiomyopathy by using a conductance catheter, and myocardial oxygen consumption was obtained simultaneously in 16 patients by a double-thermistor coronary sinus catheter. End-systolic elastance was determined by transient inferior cava occlusion.
Results: Data are reported as mean value +/- SE. Ventriculoarterial coupling at baseline was 3.24 +/- 0.28. It decreased from 3.12 +/- 0.43 to 1.86 +/- 0.15 (p < 0.05) for the group receiving dobutamine infusion and from 3.16 +/- 0.45 to 1.78 +/- 0.22 (p < 0.01) for the group receiving the oral phosphodiesterase inhibitor MS-857. The ratio of pressure-volume area to myocardial oxygen consumption had a positive correlation with ventriculoarterial coupling. The ratio of external work to pressure-volume area had a hyperbolic correlation with the coupling. The mechanical efficiency defined as the ratio of external work to myocardial oxygen consumption remained within a narrow range (16.4 +/- 1.2%).
Conclusions: The degree of ventriculoarterial coupling is far from optimal and the cardiovascular performance is severely depressed mechanically and energetically in patients with idiopathic dilated cardiomyopathy. Although inotropic agents improve the coupling, they have a minimal effect on mechanical efficiency.