Abstract 2335: Transposition Of The Great Arteries And Double Outlet Right Ventricle Have Related Early Developmental Origins: Fundamental Insights From In Vivo Imaging

Abstract

Congenital heart defects (CHD) are the most common birth defect. Proper retinoic acid (RA) signaling is required for normal development, and RA excess produces conotruncal CHD such as transposition of the great arteries (TGA) and double outlet right ventricle (DORV). We hypothesized that origins and evolution of TGA and DORV follow specific developmental patterns, definable in vivo by noninvasive ultrasound biomicroscopy (UBM)-Doppler imaging. Timed-pregnant ICR mice were injected with 70 mg/kg IP RA at 8.5 days post-conception (E8.5). Individual embryos were tracked with 40 MHz UBM-Doppler longitudinally on 5 consecutive days (E11.5–15.5: N=34 injected, N=8 uninjected controls). CHD included TGA (24%) and DORV (21%, all with right aorta, left pulmonary artery), as well as ventricular septal defect (VSD, defined at E15.5) and double-inlet left ventricle. External gross examination and histology confirmed ~90% concordance of UBM diagnosis of CHD, here (at E15.5) and in separate experiments (E11.5–15.5, N=111). All E11.5 embryos showed normal cardiac looping, with a normal unseptated heart and outflow tract (OFT) - the truncus arteriosus -arising from the right ventricle/bulbus cordis. Of embryos destined for TGA, 7/8 showed partial septation of the distal truncus into parallel OFT at E12.5; 4 showed DORV at E12.5 before evolving into TGA by E13.5. Of embryos destined for DORV, 6/7 showed partial septation of the distal truncus into parallel OFT at E12.5 as well. Thus, abnormal septation commences in the more distal truncus arteriosus as early as E12.5. In contrast, embryos destined for normal OFT development showed partial OFT septation in spiral (non-parallel) fashion, with complete/near-complete OFT septation and morphology at E13.5. All TGA/DORV embryos displayed normal cardiac function. CONCLUSIONS. TGA and DORV are developmentally related, differing only in complete (TGA) vs. incomplete (DORV) leftward truncal shift. Given normal heart, proximal OFT, and cardiac function, flow streams do not explain TGA/DORV morphogenesis. Corresponding to 4–6 weeks’ human gestation, these first in vivo data support longstanding hypotheses of TGA/DORV embryogenesis, and implicate RA signaling in the pathogenesis of abnormal truncal septation and shift.