OP04.02: Ultrasound approach to differential diagnosis of a single inflow tract at 11–14 week scan

Screening for major cardiac anomalies is now included as a protocol at 11-14 week scan. Visualisation of two inflow tracts in 4 chamber colour view and the two arches in 3 VT colour view has proven to increase the detection of major cardiac anomalies. A single inflow tract in 4 chamber colour view is the common finding seen in major cardiac malformations. The aim of the study is to identify an algorithmic approach in these cases which would help in arriving at the final diagnosis. 43 cases which showed a single inflow tract in 4 chamber colour view were assessed by transvaginal route using the following protocols. After confirming the situs, the first step was to evaluate the 4 chamber B mode. Interventricular septum and the two atrioventricular valves along with the crux of the heart was evaluated. Ventricular chamber discrepancy was then assessed. Further 3 VT colour was used to narrow down the differential diagnosis in cases with chamber discrepancy. Further in 3 cases, a diagnosis could not be arrived at first trimester and were excluded from the study. In cases with a CRL of less than 65mm at initial scan, a repeat scan after 2 weeks was done. Using this protocol 27% of cases were identified as AVSD by evaluating the AV valves and the crux in 4 chamber B mode. Complete absence of the IV septum was seen in 4% of cases in univentricular heart.44% showed a very small or an absent LV which were confirmed as HLHS by evaluating flow reversal in aortic arch in 3 VT view. 14% of cases with a small RV had flow reversal in ductal arch, thus arriving at the diagnosis of PA with IVS. Single inflow tract in 4 chamber colour is a pointer towards major cardiac anomalies and needs a detailed evaluation of the heart. The 4 chamber B mode plays a key role in evaluating such cases. Evaluating the IV septum and crux helps in differential diagnosis of AVSD and univentricular heart. Chamber discrepancy with flow reversal in 3 VT view is a hallmark of HLHS and pulmonary atresia.