Improvement of afterload mismatch of left atrial booster pump function with positive inotropic agent.

Abstract OBJECTIVES The objective of this study was to examine the hypothesis that a positive inotropic agent improves left ventricular (LV) filling during left atrial (LA) contraction in the presence of markedly elevated LV filling pressure. BACKGROUND In patients with old myocardial infarction (MI), an increase in the operational LV chamber stiffness reduces LV filling during the LA contraction, resulting from an “afterload mismatch” of the LA booster pump function. METHODS We investigated the effect of dobutamine infusion (3 μg/kg/min) on the LA pump function in the presence of elevated LV filling pressure induced by aortic constriction (Aoc) during acute MI in 10 dogs. Transmitral flow velocity was determined by transesophageal echocardiography, LV pressure by a micromanometer and LV volume by a conductance catheter. We measured the early (E) and late (A) diastolic peak transmitral flow velocities (cm/s) and LV chamber stiffness (ΔP/ΔV: mm Hg/ml; where ΔP is developed pressure and ΔV is the absolute filling volume during LA contraction). RESULTS When the ΔP/ΔV was increased by Aoc during MI (from 1.1 ± 0.8 to 3.1 ± 2.6 mm Hg/ml, p CONCLUSIONS Dobutamine improved the afterload mismatch of the LA booster pump function. This effect may have been due to the reduction in LV operational chamber stiffness, resulting in an increase in the LA forward ejection into the LV.