  Bicuspid aortic valve is the most common congenital heart defect, affecting
1-2% of the global population. Patients with bicuspid valves frequently develop
dilation and aneurysms of the ascending aorta. Both hemodynamic and genetic
factors are believed to contribute to dilation, yet the precise mechanism
underlying this progression remains under debate. Controlled comparisons of
hemodynamics in patients with different forms of bicuspid valve disease are
challenging because of confounding factors, and simulations offer the
opportunity for direct and systematic comparisons. Using fluid-structure
interaction simulations, we simulate flows through multiple aortic valve models
in a patient-specific geometry. The aortic geometry is based on a healthy
patient with no known aortic or valvular disease, which allows us to isolate
the hemodynamic consequences of changes to the valve alone. Four fully-passive,
elastic model valves are studied: a tricuspid valve and bicuspid valves with
fusion of the left- and right-, right- and non-, and non- and left-coronary
cusps. The resulting tricuspid flow is relatively uniform, with little
secondary or reverse flow, and little to no pressure gradient across the valve.
The bicuspid cases show localized jets of forward flow, excess streamwise
momentum, elevated secondary and reverse flow, and clinically significant
levels of stenosis. Localized high flow rates correspond to locations of
dilation observed in patients, with the location related to which valve cusps
are fused. Thus, the simulations support the hypothesis that chronic exposure
to high local flow contributes to localized dilation and aneurysm formation.
