Ventricular outputs, central blood flow distribution and flow pattern through the aortic isthmus of fetuses with simple transposition of the great arteries.

ABSTRACT

INTRODUCTION: Our objective was to determine the impact of simple transposition of the great arteries (TGA) on fetal left ventricular (LV) and right ventricular (RV) performances and central circulatory dynamics including the aortic isthmus. MATERIAL AND METHODS: Ventricular stroke volumes were calculated as the product of the cross-sectional area of the corresponding semi-lunar valve and the flow velocity integral through these valves. Volume flow in ductus arteriosus (QDA ) was evaluated using the same technique. Flow through the lungs (QLUNGS ) was calculated by subtracting net QDA from flow in main pulmonary artery [net QDA = QDA minus retrograde ductus arteriosus (DA) diastolic flow]. Relative performance of each ventricle expressed as percentage of combined cardiac output was also indirectly assessed by the aortic isthmus systolic index (ISI) (nadir of incisura/peak systolic of the Doppler waveforms in the isthmus); the relation between ISI and QLUNGS was investigated. RESULTS: Fifty-one fetuses with TGA were compared with 74 normal controls matched for gestational age. TGA fetuses had higher QLV at T2 (58.6 ± 9.4% vs. 43.4 ± 5.0%, p < 0.001) and T3 (53.7 ± 8.9% vs. 43.9 ± 5.7%, p < 0.001). QLUNGS was higher in fetuses with TGA, in the second (50.4 ± 16.3% vs. 39.0 ± 16.8%, p = 0.007) and third trimesters of gestation (52.8 ± 22.0% vs. 37.1 ± 16.3%, p = 0.005). No difference was found between ISI values from normal and TGA groups. A significant inverse correlation was observed between ISI and QLUNGS (r = -0.55, p = 0.006). CONCLUSIONS: Central distribution of combined cardiac output of fetuses with simple TGA is characterized by a greater QLUNGS leading to a dominant LV. In prenatal TGA, changes in QLUNGS could be monitored by measuring ISI. The clinical importance of this last observation deserves further investigations.