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EXPERIMENTAL STUDY

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

^a Second Department of Internal Medicine, Yamaguchi University School of Medicine, Yamaguchi, Japan

Manuscript received February 28, 2000; revised manuscript received July 24, 2000, accepted September 11, 2000.

Reprint requests and correspondence: Dr. Masunori Matsuzaki, Second Department of Internal Medicine, Yamaguchi University School of Medicine, 1-1-1 Minamikogushi, Ube, 755-8505, Yamaguchi, Japan

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 (P/V: mm Hg/ml; where P is developed pressure and V is the absolute filling volume during LA contraction).

RESULTS

When the P/V was increased by Aoc during MI (from 1.1 ± 0.8 to 3.1 ± 2.6 mm Hg/ml, p < 0.01), A decreased significantly (from 30 ± 5 to 22 ± 8 cm/s, p < 0.01), and the ratio of E to A increased (from 1.0 ± 0.3 to 1.4 ± 0.8, p < 0.05) compared with MI without Aoc, showing the pseudonormal transmitral flow pattern, the so called "LA afterload mismatch." Dobutamine under this condition significantly reduced the P/V (to 1.7 ± 1.2 mm Hg/ml, p < 0.05), resulting in an increase in A (to 31 ± 8 cm/s, p < 0.01) and a decrease in E/A (to 1.0 ± 0.3, p < 0.05), and the transmitral flow became a prolonged relaxation pattern as in MI without Aoc in all dogs. There was an inverse correlation between the P/V and the time-velocity integral of A (r = –0.70, p < 0.01).

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.

Abbreviations and Acronyms   A = late diastolic transmitral flow velocity   Aoc = aortic constriction   DOB = dobutamine   E = early diastolic transmitral flow velocity   LA = left atrium/left atrial   LV = left ventricle/left ventricular   MI = myocardial ischemia/myocardial infarction   PV = pulmonary vein/pulmonary venous   (+) = with   (–) = without

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