Non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus

The objective of this work was to determine the linear and non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus and to study the changes in mechanical properties throughout the thickness of the thrombus. Samples are gathered from thrombi of seven patients. Linear viscoelastic data from oscillatory shear experiments show that the change of properties throughout the thrombus is different for each thrombus. Furthermore the variations found within one thrombus are of the same order of magnitude as the variation between patients. To study the non-linear regime, stress relaxation experiments are performed. To describe the phenomena observed experimentally, a non-linear multimode model is presented. The parameters for this model are obtained by fitting this model successfully to the experiments. The model cannot only describe the average stress response for all thrombus samples but also the highest and lowest stress responses. To determine the influence on the wall stress of the behavior observed the model proposed needs to implemented in the finite element wall stress analysis

Feasibility of determination of mechanical properties of abdominal aortic aneurysms by simultaneous pressure and volume measurements in-vivo

In an effort to better predict the risk of rupture of an abdominal aortic aneurysm (AAA), methods have been developed that comprise more than diameter information alone. Wall stress calculations demonstrated superior results compared to the diameter criterion [1]. Accurate wall stress calculations require patient specific geometry, load, and wall properties of the aneurysm [2]. Usually, values for mechanical properties obtained from in-vitro tensile tests of excised aneurysmal wall material are used for wall stress calculations [3]. For obvious reasons such experiments to obtain vessel properties are impossible to perform in patient specific cases for risk assessmen

Collective experience with hybrid procedures for suprarenal and thoracoabdominal aneurysms

Not every patient is fit for open thoracoabdominal aortic aneurysm (TAAA) repair, nor is every TAAA or juxtarenal abdominal aortic aneurysm suitable for branched or fenestrated endovascular exclusion. The hybrid procedure consists of debranching of the renal and visceral arteries followed by endovascular exclusion of the aneurysm and might be an alternative in these patients. Between May 2004 and March 2006, 16 patients were treated with a hybrid procedure. The indications were recurrent suprarenal or thoracoabdominal aneurysms after previous abdominal and/or thoracic aortic surgery (n = 8), type I to III TAAAs (n = 3), proximal type I endoleak after endovascular repair (n = 2), penetrating ulcer of the juxtarenal aorta (n = 1), visceral patch aneurysm after type IV open repair (n = 1), and primary suprarenal aneurysm (n = 1). Eight (50%) of 16 patients were judged to be unfit for open TAAA repair. The hospital mortality rate was 31% (5 of 16). Four of five deceased patients were unfit for thoracophrenic laparotomy. Two patients died from cardiac complications and three from visceral ischemia. No spinal cord ischemia was detected, and temporary renal failure occurred in four patients (25%). The mean follow-up was 13 months (range 6-28 months). During follow-up, no additional grafts occluded and no patients died. Hybrid procedures are technically feasible but have substantial mortality (31%), especially in patients unfit for open repair (80%). They might be indicated when urgent TAAA surgery is required or when vascular anatomy is unfavorable for fenestrated endografts in patients with extensive previous open aortic surger