P22.08: Characteristics of interventricular shunt flow in fetuses with isolated ventricular septal defect assessed by dual Doppler imaging

Abstract

Prenatal diagnosis of ventricular septal defect (VSD) can be difficult, even using colour Doppler imaging. One reason is that the interventricular shunt flow of fetuses is not as prominent as that of children because of the low pressure difference between ventricles. This study aimed to elucidate the characteristics of the interventricular shunt flow associated with the cardiac phase in fetuses with isolated VSD using dual Doppler imaging. We prospectively studied 18 consecutive fetuses that were prenatally diagnosed with isolated VSD. We simultaneously recorded shunt flow across VSD and mitral/aortic flow using dual Doppler. The cardiac cycle was divided into five phases isovolumetric relaxation time (IRT), early or late filling time, isovolumetric contraction time (ICT), and ejection time by the mitral/aortic flow waveforms; further, shunt flow direction and phase were decided. One fetus with muscular VSD was not evaluated due to difficulty in simultaneous recording of flow signals. The remaining 17 fetuses (11 perimembranous and 6 muscular) were assessed. During IRT, peak right-to-left shunt flow was demonstrated in 16 (94%) fetuses. In ICT and/or early ejection time, 15 (88%) fetuses showed peak left-to-right shunt flow. This study revealed a commonality of the interventricular shunt flow in isolated VSD fetuses. Right-to-left flow during IRT and left-to-right flow in ICT and/or early ejection time were consistently observed. These shunt flow characteristics can help in prenatal diagnosis of isolated VSD and in understanding the physiology of fetal circulation.