The purpose of this study was to assess the factors involved in the development of the right-to-left (R-L) shunt in patients with atrial septal defect (ASD), especially the role of tricuspid regurgitation (TR). Thirty-one consecutive patients with ASD underwent transesophageal Doppler echocardiography to determine the size of ASD, the shunt flow, and the TR flow, and they were compared with hemodynamics examined by cardiac catheterization. Sixteen patients with the R-L shunt were older (53 ± 11 vs 34 ± 9 years; p < 0.001) and had higher pulmonary arterial pressure (36 ± 17 vs 25 ± 5 mmHg; p < 0.05) and a greater Qp Qs (3.6 ± 1.2 vs 2.4 ± 0.9 L/min; p < 0.01) as compared with 15 patients with the pure left-to-right shunt. In six of 21 patients with TR, the regurgitant flow oriented toward ASD and blew into the left atrium through the defect. Besides the deviation of TR flow, the prevalences of the maximum diameter of ASD >2.5 cm and the maximal TR flow area >4 cm2 were significantly higher in the six patients as compared with patients with TR not related to the R-L shunt (p < 0.05), despite the pulmonary arterial pressure being similar in the two groups. Reversal of pressure gradient between the left and right atrium was not observed during the cardiac cycle in all patients. In conclusion, TR is a determinant of the R-L shunt in patients with ASD even in the absence of the reversal of pressure gradient between the left and right atrium.
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