Influence of positive inotropic therapy on pulsatile hydraulic load and ventricular-vascular coupling in congestive heart failure

The aortic input impedance spectrum provides a description of the total hydraulic load imposed on the left ventricle and may be used to assess the coupling of the ventricle to the vasculature. The adaptation of the vasculature to positive inotropic intervention was examined in 10 patients with idiopathic dilated cardiomyopathy to test the hypothesis that increased myocardial contractility is matched by complementary changes in aortic impedance that optimize ventricular-vascular coupling and maximize power transfer to the circulation. High fidelity intravascular recordings of aortic pressure and flow were obtained at baseline study and during infusion of dobutamine to derive the aortic input impedance spectrum. In eight patients in whom increased staged infusion of dobutamine resulted in a significant increase in stroke volume (22.3 ± 14.5 ml/beat increase over baseline), the significant (p < 0.05) increase in the maximum of the first derivative left ventricular pressure pulse (dP/dt) was accompanied by significant decreases in characteristic impedance of the aorta (138 ± 88 to 92 ± 44 dyne·s·cm^-5) wave reflection index (238 ± 144 to 109 ± 59 dyne·s·cm^-5), and low frequency moduli of impedance. Effective positive inotropic therapy with dobutamine in the setting of congestive heart failure is accompanied by complementary changes in the aortic impedance spectrum, which represent a matching of impedance to the increased contractile state of the ventricle and facilitation of ventricular-vascular coupling.