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Identifier 000402296
Title Εκτίμηση των μορφομετρικών εμβιομηχανικών παραμέτρων και των μηχανικών ιδιοτήτων του τοιχώματος για την εκτίμηση του κινδύνου ταχείας αύξησης ή ρήξης των μικρών ανευρυσμάτων της κοιλιακής αορτής
Alternative Title The evaluation of geometric and biomechanical factors to develop a patient -specific model to accurately predict risk of rupture of small abdominal aortic aneurysms
Author Κοντοπόδης, Νικόλαος
Thesis advisor Ιωάννου, Χρήστος
Παπαχαριλάου, Ιωάννης
Τσέτης, Δημήτριος
Reviewer Γιαννούκας, Αθανάσιος
Ζώρας, Οδυσσέας
Χαλκιαδάκης, Γεώργιος
Παπαϊωάννου, Αλεξία
Abstract Abdominal aortic aneurysms (AAAs) represent a focal, balloon-like dilation of the aorta exceeding 1.5 times its normal diameter.1,2 Therefore in clinical practice a 3cm maximum diameter can be used to set the diagnosis of AAA. It is reported that 4-8% of men and 0.5-1% of women above 50 years of age bear an AAA.3,4 Rupture represents the most catastrophic complication of the aneurysmal disease that is accompanied by a striking overall mortality of 80%.5-8 Diagnostic and therapeutic protocols that regard AAAs aim in the prevention of such a disastrous scenario. Elective repair with open surgical intervention is being performed for decades with a continuously declining operative mortality.9,10 Moreover the advent of endovascular aneurysm repair seems to offer further advantages in terms of reduced adverse operative outcomes.11,12 On the other hand, despite the technological progress and accumulated experience, current repair techniques are not without complications and taking into account that most AAA patients are elderly with several co morbidities the clinicians often have to answer the question when the risk of rupture and subsequent mortality justifies the risk of surgical intervention.13-15 Current guidelines for AAA management consider aneurysm size, as it is defined by its maximum diameter as well as aneurysm growth rate as the only variables to determine the need for elective repair. Therefore cut-off points have been set by the European Society for Vascular Surgery (ESVS), the American Heart Association (AHA) and the Society for Vascular Surgery (SVS) (maximum diamete&ge;5.5cm, growth rate&ge;1cm/year) that are generally thought appropriate for intervention to be recommended. Nevertheless these certain cut-off points represent mean values that have emerged by large randomized trials and even though they can provide a general estimation of AAA risk of rupture they often have been proven unreliable and misleading for the treating physician. This is underscored by autopsy studies which indicate that small AAAs can rupture while some larger, well above the threshold for surgical repair remain intact for long time intervals that often exceed life expectancy of patients.18-20 In fact, in the literature it is reported that up to 13% of AAAs with maximum diameter <5cm can rupture whereas the 50% of large AAAs never proceed to rupture.21,22 Subsequently the use of “one-size fits all” variables to evaluate AAAs often fails since it does not take into account each AAAs unique characteristics that may play a significant role in its evolution. Currently with the use of modern imaging modalities and image post-processing with 3Dreconstruction, the maximum diameter can be accurately and reproducibly recorded on an orthogonal plane (meaning perpendicular to the vessel centerline) therefore avoiding inaccuracies due to tortuosity when examining 2D, axial CT slices. Moreover other indices like the AAA volume have become assessable, which may be more appropriate to describe aneurysm size and expansion over time. The difference between axial and orthogoanal maximum diameter measurements as well as the value of volumetric indices during AAA diagnosis and follow-up have not yet been definitively answered in the literature. Futhermore, according to the biomechanical approach rupture occurs when the stress exerted on the aneurysmal wall overwhelms its strength. Therefore wall stress may be a better predictor of rupture than the maximum diameter, an argument which has been supported by many studies in the literature. The aneurysm geometry as well as thrombus load and distribution and aortic wall mechanical properties, have been proposed to significantly affect wall stresses but also strength and therefore may be related to the risk of rupture. The aim of the current analysis is to examine the value of orthogonal in contrast to axial diameter measurements and those of volumetric variables during AAAs examination. More importantly to investigate the role of biomechanic and geometric parameters to AAAs rupture risk and hopefully develop a model which could accurately estimate the risk of AAA rupture on an individualized, patient specific level, beyond the “one-size fits all” maximum diameter criterion.
Language Greek, English
Issue date 2016
Collection   School/Department--School of Medicine--Department of Medicine--Doctoral theses
  Type of Work--Doctoral theses
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