The maximum circumferential force imparted on a material at the point of failure is known as the hoop strength. Tensile strength is the maximum longitudinal force that a material can withstand. Mathematical models have been designed to assess the hoop strength and tensile strength of blood vessels—in particular aortic aneurysms-to predict the point at which rupture is likely to occur. Intense calculations and eloquent in-vitro experimental models have been the topics of research theses and volumes of scientific journals. Indeed, to predict which aneurysm will rupture would revolutionize therapeutic strategies. Relying on the archaic “one-size-fits-all” approach of using size criteria to predict aneurysm rupture leads to countless events of morbidity and mortality in treating patients who may never go on to rupture or undertreating aneurysms that rupture at sizes smaller than those treated based on size alone. To the frustrations of many, the disorganized degeneration of aortic aneurysms with complex layers of mural thrombus, intimal obliteration, medial necrosis, and adventitial thinning makes predicting which aneurysm will rupture an impossibility based on current technologies. While estimates of these elements can be used to model stresses experienced by the vessel walls and predict where ruptures may occur in the aneurysm, another important property, wall shear stress, is less predictable. It is a function of the drastic, dynamic forces of cardiac output and peripheral vascular resistance. These changing forces that impart pressure on the weakened aortic walls are not easily accounted for in these models. The goal of endovascular stent grafts is to reduce the shear stress of flowing blood and remove the requirements of tensile and hoop strength from the aortic wall. Although current devices and techniques are modeled to provide this goal, degeneration of the aneurysm neck, failure of materials used, limitations of the seal zones, and occurrence of endoleaks result in sometimes disappointing results. Mitigating these avenues of failure requires optimal techniques and a keen understanding of the mechanical properties of available devices. Described in detail in the following articles is the current state-of-the-art in endovascular aneurysm repair. With foundations of stent-grafts dating back to the 1960s, iterations of these devices have progressed slowly with few technical achievements going beyond the original platform. The general concept of diverting blood flow through the endograft and allowing the aneurysm sac to thrombose and hopefully involuted has been the principle paradigm. Modifications have focused on lower-profile devices, better materials and methods, and the ability to treat smaller necks through fenestrations and parallel grafts. The most recent advancement and truly novel idea is the concept of endovascular aneurysm sealing. In this technique, the space inside of the aneurysm is filled with a polymer encased by an endobag. This theoretically eliminates the possibility of a type II endoleak. However, the current technique is in its early iterations in design, lacks long-term data, and has experienced a number of challenges, including treatment of type I endoleaks. Given the imperfections in current devices, the endovascular community thirsts for innovation in the field of aneurysm repair. Until such time, optimal understanding of the use of current devices and optimal patient selection will ensure the best and safest outcomes for our patients. What follows in this issue are techniques described by some of the masters in the field of endovascular aneurysm repair designed to instruct the reader on how to achieve those outcomes. Each article provides unique insight into the complex realm of endovascular aneurysm repair. As guest editor, I have had the privilege of reviewing these articles and hope that they are as informative and instructive to you as they have been to me. I would like to thank the authors of the articles as well as the editors of the journal for this unique opportunity.
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Feb 6, 2019
Sebastian Mafeld + 9
Open Access
