Regional Differences in Biomechanical Properties of the Ascending Aorta in Aneurysmal and Normal Aortas
Presented During:
Thursday, April 25, 2024: 5:38PM - 7:00PM
Sheraton Times Square
Posted Room Name:
Central Park
Abstract No:
P0278
Submission Type:
Abstract Submission
Authors:
Daniella Eliathamby (1), Sachin Peterson (2), Hayley Yap (2), Malak Elbatarny (3), Maral Ouzounian (1), Melanie Keshishi (4), Rifat Islam (5), Chun-Po Steve Fan (6), Kongteng Tan (5), Craig Simmons (5), Jennifer C.-Y. Chung (7)
Institutions:
(1) Toronto General Hospital, Toronto, ON, (2) University of Toronto, Toronto, NA, (3) TGH / St Michael's, Toronto, ON, (4) University of Toronto, Toronto, ON, (5) University of Toronto, Toronto, Ontario, (6) Toronto General Hospital, Toronto, Ontario, (7) Toronto General Hospital - Toronto, ON, Toronto, Ontario
Submitting Author:
Daniella Eliathamby
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Toronto General Hospital
Toronto General Hospital
Co-Author(s):
Sachin Peterson
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University of Toronto
University of Toronto
Hayley Yap
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University of Toronto
University of Toronto
Malak Elbatarny
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TGH / St Michael's
TGH / St Michael's
*Maral Ouzounian
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Toronto General Hospital
Toronto General Hospital
Melanie Keshishi
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University of Toronto
University of Toronto
Rifat Islam
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University of Toronto
University of Toronto
Chun-Po Steve Fan
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Toronto General Hospital
Toronto General Hospital
Kongteng Tan
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University of Toronto
University of Toronto
Craig Simmons
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University of Toronto
University of Toronto
Jennifer Chung
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Toronto General Hospital - Toronto, ON
Toronto General Hospital - Toronto, ON
Presenting Author:
Daniella Eliathamby
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Toronto General Hospital
Toronto General Hospital
Abstract:
Objectives: To evaluate differences in biomechanical properties between the inner and outer curve of the ascending aorta. To correlate the extent of regional biomechanical differences with clinical markers including asymmetric dilation, age, sex, and bicuspid aortopathy (BAV).
Methods: Normal (n=25) and aneurysmal (n=102) whole aortic rings were collected intraoperatively, and inner (IC) and outer (OC) curvature regions were sectioned. Biaxial tensile tests were performed to derive tissue hysteresis (energy loss), stored elastic energy (EE), tissue stiffness, and stress and strain at onset of the transition zone (TZo). Delamination tests were performed to derive adhesive strength between aortic tissue layers. Higher energy loss and stiffness, and lower EE, stress/strain at the TZo zone, and delamination strength were previously shown to associate with aneurysmal aortic tissue. Preoperative computed tomography (CT) scans from the aneurysm group (n=39) were analyzed for IC, OC, and centerline length (annulus to innominate). Degree of asymmetric dilation was then defined as difference between OC and IC length normalized to centerline length.
Results: In normal aortas, energy loss was higher in the OC compared to the IC (OC: 0.06±0.02 vs. IC: 0.04±0.01, p<0.001), while EE (p=0.01), stiffness (p<0.001), and TZo stress (p<0.001) were lower. The aortic wall was thinner in the OC (OC:2.9±0.5 mm vs. IC: 3.1±0.8 mm, p=0.05), but delamination strength did not differ significantly between regions (p=0.5). In aneurysmal aortas, a similar pattern emerged. Energy loss was higher in the OC (OC: 0.06±0.03 vs. IC: 0.05±0.02, p<0.001), while EE (p<0.001), stiffness (p<0.001), and TZo stress (p<0.001) were lower than the IC. The aneurysmal aortic wall was thinner in the OC (p<0.001), with lower TZo strain (p<0.001) and delamination strength (OC: 29.5±15 mN/mm vs. IC: 32.3±17 mN/mm, p=0.003) compared to the IC. Aneurysmal aortas with greater differences between IC and OC biomechanics were then identified using the interquartile range method (n=15). These patients were not associated with greater asymmetric outer curvature dilation. Additionally, patients with greater biomechanical differences did not differ in age (p=0.06), sex (p>0.99), hypertension (p=0.76), or presence of BAV (p=0.18) from patients with minimal regional biomechanical differences. Correlations between IC and OC biomechanics were also evaluated by linear regression models. In normal aortas, IC biomechanical properties were positively correlated with their counterparts in the OC (0.77>r2>0.20, p<0.05), except for TZo strain (r2=0.02,p=0.56) and delamination strength (r2=0.09, p=0.17). In aneurysms, all biomechanical properties in the IC were positively correlated with their counterparts in the OC (0.67>r2>0.12, p<0.001).
Conclusion: Biomechanical differences between IC and OC regions were observed in both normal and aneurysmal aortas. Patients with greater regional biomechanical differences were not identifiable by clinical variables including asymmetric outer curvature dilation. However, biomechanical properties of the IC and OC regions were linearly correlated. Therefore, while regional biomechanical differences are present in the ascending aorta, these properties remain inter-related.
Methods: Normal (n=25) and aneurysmal (n=102) whole aortic rings were collected intraoperatively, and inner (IC) and outer (OC) curvature regions were sectioned. Biaxial tensile tests were performed to derive tissue hysteresis (energy loss), stored elastic energy (EE), tissue stiffness, and stress and strain at onset of the transition zone (TZo). Delamination tests were performed to derive adhesive strength between aortic tissue layers. Higher energy loss and stiffness, and lower EE, stress/strain at the TZo zone, and delamination strength were previously shown to associate with aneurysmal aortic tissue. Preoperative computed tomography (CT) scans from the aneurysm group (n=39) were analyzed for IC, OC, and centerline length (annulus to innominate). Degree of asymmetric dilation was then defined as difference between OC and IC length normalized to centerline length.
Results: In normal aortas, energy loss was higher in the OC compared to the IC (OC: 0.06±0.02 vs. IC: 0.04±0.01, p<0.001), while EE (p=0.01), stiffness (p<0.001), and TZo stress (p<0.001) were lower. The aortic wall was thinner in the OC (OC:2.9±0.5 mm vs. IC: 3.1±0.8 mm, p=0.05), but delamination strength did not differ significantly between regions (p=0.5). In aneurysmal aortas, a similar pattern emerged. Energy loss was higher in the OC (OC: 0.06±0.03 vs. IC: 0.05±0.02, p<0.001), while EE (p<0.001), stiffness (p<0.001), and TZo stress (p<0.001) were lower than the IC. The aneurysmal aortic wall was thinner in the OC (p<0.001), with lower TZo strain (p<0.001) and delamination strength (OC: 29.5±15 mN/mm vs. IC: 32.3±17 mN/mm, p=0.003) compared to the IC. Aneurysmal aortas with greater differences between IC and OC biomechanics were then identified using the interquartile range method (n=15). These patients were not associated with greater asymmetric outer curvature dilation. Additionally, patients with greater biomechanical differences did not differ in age (p=0.06), sex (p>0.99), hypertension (p=0.76), or presence of BAV (p=0.18) from patients with minimal regional biomechanical differences. Correlations between IC and OC biomechanics were also evaluated by linear regression models. In normal aortas, IC biomechanical properties were positively correlated with their counterparts in the OC (0.77>r2>0.20, p<0.05), except for TZo strain (r2=0.02,p=0.56) and delamination strength (r2=0.09, p=0.17). In aneurysms, all biomechanical properties in the IC were positively correlated with their counterparts in the OC (0.67>r2>0.12, p<0.001).
Conclusion: Biomechanical differences between IC and OC regions were observed in both normal and aneurysmal aortas. Patients with greater regional biomechanical differences were not identifiable by clinical variables including asymmetric outer curvature dilation. However, biomechanical properties of the IC and OC regions were linearly correlated. Therefore, while regional biomechanical differences are present in the ascending aorta, these properties remain inter-related.
Aortic Symposium:
Ascending Aorta
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