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We estimated the magnitude of the left atrial contraction in 28 patients with ischemic heart disease by calculating the biplane cineangiographic volumes of the left atrium. The left atrial contraction contribution to the left ventricular stroke volume (ml/m2, Y axis) correlated inversely with the left ventricular ejection fraction (%, X axis), yielding an equation: Y = -0.31X + 43.7 (n = 28, r = -0.56, p less than 0.001). The result indicates that the left ventricular filling is compensated by the augmented atrial contraction in case of impaired left ventricular function. We defined the left atrial volume at the beginning of the atrial contraction (LAVd, ml/m2) as the "preload" of the left atrium, and we also defined the volume expelled by the active atrial contraction (delta LAVa, ml/m2) as the stroke volume of the left atrium. The stroke volume (Y) correlated positively with the "preload" (X), yielding an equation: Y = 0.48X - 1.3 (n = 28, r = 0.80, p less than 0.001). We then defined the left ventricular end-diastolic pressure, the peak of the a-wave, as the "afterload" of the left atrium, and we studied the "afterload"-stroke volume relations in the left atrium. However as expected, a reasonable relationship between them was difficult to form. Consequently, we showed that an increase in the "preload" of the left atrium augmented the stroke volume of the left atrium, which means that Frank-Starling mechanism is operative in the left atrium.

Study on left atrial contractile performance. Participation of Frank-Starling mechanism.