The congenitally bicuspid aortic valve: How does it function? Why does it fail?

Background. The study was intended to investigate the reason why congenitally bicuspid valves (CBAVs), which may function hemodynamically and clinically well, have a high early failure rate. Methods. Observations were made on cryopreserved, then thawed human aortic roots containing CBAVs. Valvular function was studied in the left heart simulator using conventional and 500-frames/second cinematography, intravascular ultrasound, by preparation of silicone molds, and by computerized digital modeling. Results. The function of the clinically "normal" CBAVs is characterized by (a) excessive folding and creasing, which (unlike in the trileaflet valve) persist throughout the cardiac cycle; (b) extended areas of leaflet contact; (c) significant morphologic stenosis; and (d) asymmetrical flow patterns and turbulence. Conclusions. The above features subject the CBAV to abnormally high stresses and may lead to early thickening and eventually calcification and stenosis. The abnormal flow patterns also predilect for dilatation and dissection of the ascending aorta.