Helical flows and asymmetry of blood jet in dilated ascending aorta with normally functioning bicuspid valve

Bicuspid aortic valve (BAV) is associated with aortic dilatation and aneurysm. Several studies evidenced an eccentric systolic flow in ascending aorta associated to increased wall shear stresses (WSS) and the occurrence of an helical systolic flow. This study seeks to elucidate the connections between jet asymmetry and helical flow in patients with normally functioning BAV and dilated ascending aorta. We performed a computational parametric study by varying, for a patient-specific geometry, the valve area and the flow rate entering the aorta and drawing also a tricuspid valve (TAV). We considered also phase contrast magnetic resonance imaging of four BAV and TAV patients. Measurement of normalized flow asymmetry (NFA) index, systolic WSS and of a new index (positive helic fraction, PHF) quantifying the presence of a single helical flow, were performed. In our computation, BAV cases featured higher values of all indices with respect to TAV in both numerical and imaged-based results. Moreover, all indices increased with decreasing valve area and/or with increasing flow rate. This allows us to identify two groups for BAV: the former with valve/root area ratio Aval/Aroot = 0.29 and systolic flow rate F > 18 l/min, or for Aval/Aroot < 0.29, featuring high indices values (NFA > 0.45 and PHF > 0.8), and the latter featuring intermediate values (0.2 < NFA < 0.4, 0.5 < PHF < 0.7).