RESUMO
After instantaneous left atrial volume was defined as the net difference between the forward-flowing blood from the lungs and the blood flowing through the mitral valve, we constructed the left atrial volume curve by sampling the Doppler mitral valve and the right upper pulmonary vein velocity from an apical four-chamber view in eight normal subjects and 11 patients with heart disease. The instantaneous mitral valve flow was estimated as mitral valve velocity x annular area (derived from the same view), whereas the pulmonary venous flow was obtained as right upper pulmonary vein velocity x pulmonary vein area, where pulmonary vein area = mitral valve velocity integral x mitral valve area) divided by pulmonary vein velocity integral. The left atrial volume curve can then be derived as: [(instantaneous pulmonary venous flow - mitral valve flow) + left atrial volume assessed at end diastole by two-dimensional echocardiography]. Biplane angiographic left atrial volume curves, available in four of 11 patients, compared morphologically very closely with the noninvasive curves, whereas the correlation coefficient for maximum (end-systolic) and filling (maximum minus minimum) left atrial volumes obtained from the Doppler-derived curve and the corresponding two-dimensional echocardiographic estimates was 0.95 (p < 0.001, standard error of the estimate = 11.9 ml), the dispersion of the data increased with decreasing volumes. These data demonstrate that combined Doppler mitral valve and pulmonary vein velocities can be used to construct the left atrial volume curve in human beings. The approach described, besides providing a tool for further noninvasive evaluation of the left atrial function, offers the opportunity for relating the continuous pulmonary venous flow to the intermittent filling of the ventricle through the mitral orifice in diastole, underlining the complex role that the left atrial cavity plays in this process.
