F. Bello, E. Edwards (Eds.): ISBMS 2008, LNCS 5104, pp. 119–126, 2008. © Springer-Verlag Berlin Heidelberg 2008 Mechanism and Localization of Wall Failure During Abdominal Aortic Aneurysm Formation Dominik Szczerba 1 , Robert McGregor 1 , Krishnamurthy Muralidhar 2 , and Gábor Székely 1 1 Department of Electrical Engineering, ETH Zürich, Switzerland 2 Department of Mechanical Engineering, IIT Kanpur, India Abstract. Our previously presented model of abdominal aneurysm formation allowed to simulate aneurysm dynamics relying on a postulated initial wall fail- ure without being able to predict the actual location of such weakening. In this study we investigate what factors can trigger pathology progression at positions eventually observed in reality. We consider mechanical effects inside the arte- rial wall and their possible contributions to the formation of an aneurysm. Using a computer model we demonstrate the existence of wall regions susceptible to failure due to increased oscillatory mechanical loading. We find these regions to be uniquely correlated with actually observed aneurysm locations. We dem- onstrate that wall fatigue and failure are probable factors influencing the forma- tion of an abdominal aortic aneurysm. Keywords: Abdominal Aortic Aneurysm, aneurysm formation, arterial wall mechanics, fluid-structure interaction, computational fluid dynamics. 1 Introduction Abdominal aortic aneurysm (AAA) is a major cause of mortality in developed coun- tries. It kills fifteen thousand people every year in the United States alone, where it is the 13th leading cause of death [1] and these numbers are likely to further increase due to ageing population. The precise causes of the disease are still not fully identified and subject to ongoing research. Its pathogenesis is complex and multifactorial, de- pending on many parameters such as genetic predispositions, age, lifestyle and indi- vidual aortic geometry. It occurs most frequently distal to the renal arteries and proximal to the bifurcation, suggesting that the complex flow patterns at this location may have an influence on aneurysm development. Hemodynamic forces exerted on the arterial wall are known to induce its remodel- ing [2], which is usually a healthy process but can become pathological in regions with disturbed flows, such as at bifurcations. Wall shear stress (WSS) in particular and its spatial and temporal variations affect the cells of the endothelium which can lead to biochemical responses modifying wall properties, making it less able to with- stand the loading imposed by the flow pressure waves. There is some debate as to whether it is low WSS, high spatial or temporal gradients of WSS or a combination of these which leads to wall lesions [3]. Much work has been done to identify areas of low or oscillating WSS in both healthy, [4] and aneurysmal [5], [6] abdominal aortic