Increased ventricular contractility is not sufficient for effective positive inotropic intervention.

ABSTRACT

Positive inotropic intervention with dobutamine in patients with congestive heart failure is accompanied by complementary vascular changes, as measured by the aortic input impedance spectrum, that promote the efficient transfer of augmented myocardial contractile power. It is unknown whether this is a nonspecific response to increased ventricular contractility or is a function of the properties of the positive inotropic agent employed. Therefore, the influence of two different positive inotropic interventions, dobutamine and dopamine, on ventricular-vascular coupling was examined in 15 patients with congestive heart failure. Significant reductions in characteristic aortic impedance, wave reflection, and low-frequency impedance moduli were noted with dobutamine and were not seen with dopamine. Consequently, a significantly (P = 0.0008) greater increase in pulsatile, rather than steady-state, power output was noted with dopamine that was reflective of a significantly diminished efficiency of power transfer. Therefore, optimal transfer of increased ventricular contractile power in patients with congestive heart failure requires increases in large vessel compliance and complementary changes in ventriculoarterial coupling.