BACKGROUND AND AIM OF THE STUDY: Abnormal flow conditions across aortic bioprosthetic valves may result in degenerative processes. Thus, it is important to implant biological valve prostheses with velocity profiles similar to those of native valves. The study aim was to compare blood velocity and velocity gradient profiles downstream of stented and stentless aortic valves implanted in pigs, and in native porcine valves.

METHODS: Stented valve prostheses (Mitroflow, n = 7) or stentless valve prostheses (Solo, n = 5 or Toronto SPV, n = 7) were implanted into pigs; the native valve was retained in eight animals. After weaning the animals from cardiopulmonary bypass, cardiac magnetic resonance imaging was performed to determine the blood velocities and velocity gradient profiles.

RESULTS: The native valves had a significantly lower peak velocity (92 +/- 26 cm/s) than the artificial valves (Solo: 247 +/- 107 cm/s; Toronto: 252 +/- 41 cm/s; Mitroflow: 229 +/- 18 cm/s). The native valves exhibited a flat velocity profile during systole, whereas the Solo valve, and especially the Toronto SPV valve, displayed more parabola-shaped velocity profiles; velocity profiles downstream of the Mitroflow valve exhibited a flat shape. The native valves had a lower mean velocity gradient at peak systole (p < 0.0001). The velocity gradient percentage above mean was lowest for the native valve (0.14 +/- 0.11; p < 0.0001), while the Mitroflow valve had a percentage of 0.57 +/- 0.09, which was lower than the Solo valve (0.69 +/- 0.12; p = 0.074), and significantly lower than the Toronto valve (0.70 +/- 0.08; p = 0.015). All valves displayed high velocity gradients adjacent to the aortic wall; in particular, the Toronto SPV which also had high velocity gradients at the center of the vessel.

CONCLUSION: All of the artificial valves tested had a significantly higher mean velocity gradient and peak velocity than the native valves. However, the Mitroflow had a mean velocity and a velocity gradient percentage lower than the two stentless valves. The Solo and Mitroflow valves displayed velocity profiles most like native valves, while the Toronto valve had a more irregular asymmetric velocity profile.