© Copyright by ICR Publishers 2008 Age-Related Changes in the Aortic Valve Affect Leaflet Stress Distributions: Implications for Aortic Valve Degeneration Reetu Singh 1 , Joel A. Strom 1,2 , Leo Ondrovic 1,3 , Babu Joseph 1 , Michael D. VanAuker 1 Departments of 1 Chemical Engineering, 2 Internal Medicine and 3 Surgery, University of South Florida, Tampa, Florida, USA Degenerative aortic stenosis, characterized by leaflet thickening, stiffening and calcification leading to a nar- rowing of the orifice (1), is currently the most common form of the condition (2,3). The prevalence of degener- ative aortic stenosis increases with age (3), with a two- fold increase in the risk for stenosis for each decade of increasing age (4); indeed, almost 5% of patients aged over 75 years are afflicted by moderate to critical forms of the condition (5). During valve opening and closing, the leaflets undergo cyclic loading which leads in turn to flexural and shearing stresses, such that the leaflets sustain ‘repeated stress injury’. If the effects of this injury are not neutralized by tissue repair, valve degeneration may occur due to fatigue (6). Thus, the mechanical stresses encountered during valve motion are the pri- mary cause of calcific stenosis of the native aortic valve, and the structural degeneration of bioprosthetic aortic valves (7-11). The properties of the aortic valve tissue, which undergoes alterations with aging, com- bined with the properties of the aortic wall and the valve anatomy, play an important role in determining the stress distributions and, therefore, valve degenera- tion. Age-related changes to the aortic valve include a loss of leaflet elasticity (12), a reduction in stretch after the age of 40 years (13), an increase in tissue thickness (14) due to the accumulation of adipose tissue between the fibrosa and ventricularis and an accumulation of extra- cellular matrix materials and cellular degradation Presented in part at the Fourth Biennial Meeting of the Society for Heart Valve Disease, 15th-18th June 2007, New York, USA Address for correspondence: Dr. Michael D. VanAuker PhD, 4202 E. Fowler Avenue, ENB 118, Department of Chemical Engineering, University of South Florida, Tampa, FL 33620, USA e-mail: vanauker@eng.usf.edu Background and aim of the study: The degeneration of aortic valve leaflets occurs primarily due to high mechanical stresses in zones of leaflet flexion. Aging, which has been identified as a risk factor for degen- erative aortic stenosis, is associated with reductions in stretch and in compliance, and an increase in tis- sue thickness of the leaflet and root. The study aim was to investigate the effects of age-related tissue changes on valve opening dynamics and leaflet stress patterns, and its implications for valve degeneration. Methods: A three-dimensional finite element model of the aortic valve and root was developed in Ansys®. A transient, non-linear analysis was carried out of the valve opening phase. Three age groups were identified based on leaflet and root tissue prop- erties: group I age <35 years; group II aged 33-55 years; and group III aged >55 years. The valve open- ing dynamics was studied and von Mises stresses in various regions of the leaflet were computed. Results: Maximum leaflet stresses occurred along the leaflet-root attachment, analogous to the spatial dis- tribution of calcific deposits in the aortic valve. With increasing age, the rate of valve opening decreased, and the magnitude of leaflet tip displacement in both radial and axial directions reduced progressively. At the leaflet-root attachment, groups II and III showed 19% and 32.7% increases in average stress over group I, respectively. At the free edge, the stresses in group III increased 2.7% over group I; however, the average stress at the free edge in group II decreased 3.5% over group I. In the leaflet belly, groups II and III showed 27.6% and 60.9% increases in stresses over group I, respectively. Conclusion: Changes in leaflet and root tissue prop- erties lead to altered leaflet dynamics and increased stresses. This not only emphasizes the role of aging on the development and progression of degenerative aortic valve disease, but also has implications in the design of bioprosthetic heart valves. The Journal of Heart Valve Disease 2008;17:290-299