Abstract 17475: High Throughput Screening and Diagnosis of Structural Heart Defects in Newborn Mice Using High Resolution Micro-Computed Tomography

Abstract

Background: We are conducting a high-throughput chemical mutagenesis screen in mice to recover mutations causing congenital heart defects (CHD) using fetal echocardiography. Mutant fetuses identified to have cardiac defects by ultrasound screening must be further examined by time-consuming necropsy and histological analysis to confirm the CHD. We hypothesize post-mortem micro-CT may be used as a high throughput secondary screening tool for phenotyping CHD in fetal/newborn mice. Methods: Formalin fixed fetuses and neonatal mice were soaked with iodine for soft tissue visualization. Micro-CT scanning was carried out at 15 or 45μ m using the Siemens Inveon with a custom 12-pup cradle. Micro-CT diagnoses of suspected CHD were validated using episcopic fluorescence image capture (EFIC), a 3D high resolution histological imaging technique that provides registered image stacks suitable for digital resectioning in any imaging plane (Figure). Results. We micro-CT scanned 938 newborn mice and 58 late term fetuses and found a spectrum of CHD. This included ventricular septal defects (VSDs; 14.7%, n=146), endocardial cushion defects (0.9%, n=9), transposition of the great arteries (TGA; 1.2%, n=12), double outlet right ventricle (DORV; 2.2%, n=22), pulmonary atresia (PA; 0.1%, n=1), tricuspid atresia (0.5%, n=5), right aortic arch (RAA; 0.3%, n=3), interrupted aortic arch (0.2%; n=2), and dextrocardia (0.5%; n=5). Subsequent necropsy/EFIC imaging of 45 pups confirmed all RAA diagnoses (100%; n=3), 91% of the VSD (n=29/32), 90% of the TGA/DORV/PA (n=9/10) and 100% of the dextrocardia (n=5/5). We had false positive rate of 6% (n=2) for VSD and 10% (n=1) for TGA/DORV, while a false negative rate of 3% (n=1) was observed for VSD. Conclusions: Our studies showed micro-CT has a low false negative CHD detection rate, thus making it a valuable secondary imaging tool for enhancing the diagnosis of structural heart defects in large-scale mutagenesis screens.