Analysis of the design and dynamics of aortic bioprostheses in vivo

An understanding of the in vivo design and dynamics of the present bioprosthetic valves should provide the information necessary for an improvement in their efficiency and durability. Three types of commercially available bioprostheses were prepared with radiopaque markers and implanted in the aortic position in calves. One week later, under light general anesthesia, the animals were studied to determine the in vivo design, shape, configuration, and motion of the bioprostheses. This information was then compared to that previously obtained from the natural aortic valve in vivo. The following observations were made: (1) In all three types of bioprostheses, the three leaflets opened and closed simultaneously in less than one thirtieth of a second; (2) there was no detectable flexion of the stent posts in any of the three types of valves; (3) in all of the bioprostheses studied, the greatest flexion occurred along the attachment of the leaflets; (4) the systolic and the diastolic geometry of the three types of valves was completely different for each type of valve, and none duplicated the geometry of the natural aortic valve; (5) the open configuration of the leaflets was different for each type of prosthetic valve and different from the natural aortic valve; (6) the zone of leaflet bending varied in size and extent for each of the valves. It is concluded that the differences between the design of bioprosthetic valves and that of natural valves are probably a major factor in increasing the stresses in bioprostheses. Hence stress failures could be reduced and durability increased by redesigning bioprostheses to duplicate more closely the design of the natural aortic valve.