Modeling Aortic Wall Tensile Stress from Imaging-Derived Biomechanical Parameters for Clinical Risk Prediction

Jessica Williams, PhD
Department of Surgery
Division of Cardiac Surgery
Poster Overview

Aortic dissection is a serious and often fatal condition in which the aortic wall tears making the aorta at risk of bursting. Patients with aortic aneurysms -a bulging of the aorta- are considered more at risks of aortic dissection, yet, it is very difficult to predict if or when dissection will occur. Surgical guidelines recommend that patients with a 55mm aortic diameter should undergo open-heart surgery to replace the aortic aneurysm. Yet, over half of aortic dissections occur in patients with aortic size well below this threshold, highlighting the need for better diagnostic methods. To improve upon these guidelines, we compared biological metrics with data derived from routine clinical imaging. CT scans of aneurysmal patients were analyzed using computational modelling to create heatmaps of the mechanical forces exerted onto the aortic wall. These analyses identified areas of high stress and low stress which were further resected during surgery. Aortic specimens were analyzed in the laboratory to assess the level of tissue damage, which were more severe in areas of high stress vs areas of low stress. This work links tissue damage with metrics obtained from routine clinical imaging and will pave the way for the development of new diagnostic tools.

Scientific Abstract

Despite advances in diagnosis and management of ascending aortic disease, current diameter-based guidelines do not reliably predict aortic catastrophe. To improve upon these guidelines, we evaluated the correlation between non-invasive estimation of aortic biomechanical properties and tissue derangements that may precede aortic catastrophe. Wall tensile stress was estimated using computational analyses of computed tomographic angiography (CTA) of aneurysmal patients who underwent ascending aortic replacement. Aortic tissue was resected in regions of low and high biaxiality ratio (B) defined as the ratio of longitudinal to circumferential tensile stress. Patients with a tricuspid (TAV) and bicuspid aortic valve (BAV) were considered. Regions of high B exhibited localized extracellular matrix degeneration with elevated matrix metalloproteinases activity compared to low B regions in TAV patients only. Smooth muscle cells from regions of high B exhibited lower viability in response to oxidative stress in BAV only. SMC contractility and expression of SMC phenotypic markers were similar in regions of low and high B. This work improves our understanding of aortic wall biomechanical properties in relation to tissue alterations in ascending aortic disease. Tensile stress mapping, combined with other non-invasive, dynamic imaging (e.g., ECG-gated CTA), may improve risk stratification for ascending aortic aneurysm.

Clinical Implications
We combined analyses of routine clinical imaging (CT scans) with tissue examination in the lab to develop new methods to predict the risk of aortic dissection.
Research Areas
Authors
Jessica G. Williams, Lauren V. Huckaby, Ronald Fortunato, Leonid V. Emerel, Julie A. Phillippi, Marie Billaud, Thomas. G. Gleason
Principal Investigator
Thomas. G. Gleason

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