Introduction: Endocardial fibroelastosis (EFE) is primarily associated with hypoplastic left heart syndrome but also with congenital heart defects with normal sized ventricles, with the former associated with worse outcome. As we have recently shown, the communality of these congenital diseases irrespective of ventricular size is flow disturbances. Furthermore, we identified endothelial-to-mesenchymal transition (EndMT) as the underlying mechanism of EFE development. EndMT is attributed to atherosclerosis in the vascular system as a consequence of flow disturbances, and has been shown to be amenable to pharmacological treatment with atorvastatin. We sought to determine whether physiological flow and atorvastatin protected healthy endocardial endothelial cells (EECs) and EFE-derived EECs from EndMT. 

Methods: EFE-derived EECs obtained from the OR and healthy EECs were exposed to either flow stagnation (0 dyn/cm²) or physiological flow (10 dyn/cm²) with and without atorvastatin (0.5 ^µmol) for 72 hours, using a flow pump system (ibidi). Determination of EndMT was evaluated through qRT-PCR (endothelial, mesenchymal markers, Snail) and induction of regulatory pathways through SMAD2 (upregulation indicative of EndMT). 

Results: Physiological flow protected healthy EECs (n=5) from EndMT (mean ± SEM, *p<0.05, see Figure). Atorvastatin had an additional beneficial effect (mean ± SEM, *p<0.05, see Figure). In contrast, EFE-derived cells responded to physiological flow with significantly more EndMT and collagen production. When comparing EFE-derived EECs from small (n=4) and normal sized ventricles (n=8), it could be noted that atorvastatin under flow was protective against EndMT only in normal sized ventricles while no effect was observed in small sized ventricles.