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Our data suggest that AAA rupture is associated with aortic wall weakening, but not with wall stiffening. A widely accepted indicator for risk of aneurysm rupture is the maximum transverse diameter. Our results suggest that AAA wall strength, in large aneurysms, is not related to the maximum transverse diameter. Rather, wall thickness or stiffness may be a better predictor of rupture for large AAAs.

Abstract-Rupture of abdominal aortic aneurysm (AAA) represents a significant clinical event, having a mortality rate of 90% and being currently ranked as the 13th leading cause of death in the US. The ability to reliably evaluate the susceptibility of a particular AAA to rupture on a case-specific basis could vastly improve the clinical management of these patients. Because AAA rupture represents a mechanical failure of the degenerated aortic wall, biomechanical considerations are important to understand this process and to improve our predictions of its occurrence. Presented here is an overview of research to date related to the biomechanics of AAA rupture. This includes a summary of results related to ex vivo and in vivo mechanical testing, noninvasive AAA wall stress estimations, and potential mechanisms of AAA wall weakening. We conclude with a demonstration of a biomechanics-based approach to predicting AAA rupture on a patient-specific basis, which may ultimately prove to be superior to the widely and currently used maximum diameter criterion. Key Words: abdominal aortic aneurysm Ⅲ biomechanics Ⅲ rupture Ⅲ strength Ⅲ stress A bdominal aortic aneurysm (AAA) is a focal enlargement of the infrarenal aorta, which occurs over a time course of several years. This condition is present in Ϸ2% of the elderly population, with Ϸ150 000 new cases diagnosed each year, and the incidence is increasing. 1,2 If left untreated, AAA will gradually expand until rupture; it is an event that carries a mortality rate of 90% and that is ranked as the 13th most common cause of death in the US. 3 Current AAA repair procedures are expensive and carry significant morbidity and mortality risks.Open repair of AAA is a major surgical procedure that requires patients to be hospitalized typically for 1 week and to recuperate at home for several more weeks. The mean postoperative mortality for elective repair is Ϸ5% and for emergency operations 47% (range 27% to 69%). 4 The major drawback of open repair is the compromised quality of life after surgery because of postoperative pain, the prolonged recovery period, and the high costs associated with both the surgery and the recovery.An alternative approach that avoids the extensive tissue dissection associated with open repair is the minimally invasive endovascular repair procedure. The potential advantages of endovascular AAA repair include reductions in mortality, morbidity, blood loss, hospital stay, intensive careOriginal

The spatial distributions of both wall stress and wall strength are required to accurately evaluate the rupture potential for an individual abdominal aortic aneurysm (AAA). The purpose of this study was to develop a statistical model to non-invasively estimate the distribution of AAA wall strength. Seven parameters--namely age, gender, family history of AAA, smoking status, AAA size, local diameter, and local intraluminal thrombus (ILT) thickness--were either directly measured or recorded from the patients hospital chart. Wall strength values corresponding to these predictor variables were calculated from the tensile testing of surgically procured AAA wall specimens. Backwards-stepwise regression techniques were used to identify and eliminate insignificant predictors for wall strength. Linear mixed-effects modeling was used to derive a final statistical model for AAA wall strength, from which 95% confidence intervals on the model parameters were formed. The final statistical model for AAA wall strength consisted of the following variables: sex, family history, ILT thickness, and normalized transverse diameter. Demonstrative application of the model revealed a unique, complex wall strength distribution, with strength values ranging from 56 N/cm2 to 133 N/cm2. A four-parameter statistical model for the noninvasive estimation of patient-specific AAA wall strength distribution has been successfully developed. The currently developed model represents a first attempt towards the noninvasive assessment of AAA wall strength. Coupling this model with our stress analysis technique may provide a more accurate means to estimate patient-specific rupture potential of AAA.