Influence of asymmetry and resulting inflection on peak wall stress in abdominal aortic aneurysms

Abdominal aortic aneurysms are a major health concern in the developed world. These aneurysms are often asymptomatic and eventually enlarge to the point of rupture if left untreated. Most surgical intervention is performed when the detected aneurysm has exceeded 5.5cm in maximum diameter. Recently, concerns have been raised over the reliability of this criterion, with calls for other relevant parameters to be included in the decision-making process. Peak wall stress is often deemed the most appropriate value determined using numerical approaches to aneurysm modelling. This work examined the influence of asymmetry on peak wall stress. Idealised models based on a realistic asymmetric case were studied. Twelve models comprising of three forms of aneurysmal sac lengths, with four ratios of asymmetry per sac length, were analysed. All models experienced significant increases (P=0.004) in peak wall stress with increases in asymmetry, with peak stress always occurring at regions of inflection, rather than at regions of maximum diameter. A novel technique of quantifying inflection was also developed and shown to be significant (P=0.023). Asymmetry and inflection play significant roles in wall stress distributions and should be a concern of the clinician when deciding on the timing of surgical repair of abdominal aortic aneurysms.