Analysing The Cross-Section of The Abdominal Aortic Aneurysm Neck and Its Effects on Stent Deployment

Abstract

Stent graft devices for the treatment of abdominal aortic aneurysms (AAAs) are being increasingly used worldwide. Yet, during modelling and optimization of these devices, as well as in clinical practice, vascular sections are idealized, possibly compromising the effectiveness of the intervention. In this study, we challenge the commonly used approximation of the circular cross-section of the aorta and identify the implications of this approximation to the mechanical assessment of stent grafts. Using computed tomography angiography (CTA) data from 258 AAA patients, the lumen of the aneurysmal neck was analysed. the cross-section of the aortic neck was found to be an independent variable, uncorrelated to other geometrical aspects of the region, and its shape was non-circular reaching elliptical ratios as low as 0.77. These results were used to design a finite element analysis (FEA) study for the assessment of a ring stent bundle deployed under a variety of aortic cross-sections. Results showed that the most common clinical approximations of the vascular cross-section can be a source of significant error when calculating the maximum stent strains (underestimated by up to 69%) and radial forces (overestimated by up to 13%). Nevertheless, a less frequently used average approximation was shown to yield satisfactory results (5% and 2% of divergence respectively).Since 1991, when Parodi 1 first reported endovascular aneurysm repair (EVAR), the implanting of a stent graft inside an abdominal aortic aneurysm (AAA), the procedure has become mainstream, with recent data ranking it the most common technique for repairing AAAs 2 .When compared to open surgical repair, EVAR has shown to have lower short-term rates of death and complications 3 . This initial survival benefit, though, is lost a few years after the operation 3,4 , due to late medical complications. Moreover, EVAR is more expensive 4 and leads to more readmissions 5 . Though it is true that, being a minimally invasive technique, EVAR is significantly more convenient for the patient (shorter operating time, less blood loss and shorter hospitalization), it has still to prove its long term superiority. Current judgment can be found in a recent review 6 by the European Society of Vascular Surgeons, who present a considered and extensive set of guidelines for the management and treatment of AAA's balancing the efficacy of both EVAR and OSR when required.The most common complications of the EVAR procedure are endoleaks, occurring when the aneurysm is not completely excluded from the circulation and device migration, caused by a loss of structural integrity between the endograft and the vessel. Endoleak occurrences range in the literature from 10% to 45% 7 while migration incidents have been reported to be as frequent as 19% 8 . In general, within 4 years post EVAR, it is estimated that 40% of patients will experience some form of a device-related complication and half of them will undergo a secondary intervention 7 . Inadequate anchoring of the device and a decrease in r...

A new two-dimensional blood flow model with arbitrary cross sections

“…We note that we obtain circular cross sections when ℎ(𝜃) is constant. As it is reported in [26], however, we may observe cross sections that have an elliptical-like shape in the aorta. We then choose…”

A new two-dimensional blood flow model with arbitrary cross sections

“…We note that we obtain circular cross sections when h (θ) is constant. As it is reported in [25], however, we may observe cross sections that have an elliptical-like shape in the aorta. We then choose…”

“…The terms ∂ 2 p and ∂ 3 p are given explicitly by equation (25). In that case, one only needs partial derivatives of G o and A o which are approximated as…”

Imaging Predictive Factors of Abdominal Aortic Aneurysm Growth

“…Wall thickness and intraluminal thrombus presence were studied in the included analysis concluding in conflicting results [ 23 , 36 ]. Additional computed analyses regarding the aneurysm neck and iliac arteries alterations during AAA evolution have been providing scarce data [ 49 , 50 ].…”