Ascending Aortic Geometry and its Relationship to the Biomechanical Properties of Aortic Tissue

Objective: To evaluate the relationship between the geometry of the ascending aorta and biomechanical properties.
Methods: Pre-operative computed tomography scans from ascending aortic aneurysm patients were analyzed using centreline technique (n=68). Aortic length was measured from annulus to innominate artery, and maximal diameter from this segment was recorded. Biaxial tensile testing of excised aneurysmal tissue was performed to derive biomechanical parameters energy loss (measure of efficiency in performing the Windkessel function) and modulus of elasticity (aortic stiffness). Delamination testing (simulation of dissection) was performed to derive delamination strength (measure of strength between layers of tissue). Biomechanical parameters were correlated with aortic dimensions.
Results: Ascending aortic diameter was weakly correlated with energy loss (r2=0.10, p=0.008), and was not associated with modulus of elasticity (r2=0.04, p=0.13) or delamination strength (r2=0.01, p=0.36). Ascending aortic length was not associated with energy loss (r2=0.004, p=0.87), modulus of elasticity (r2=0.04, p=0.13) or delamination strength (r2=0.0002, p=0.90). Using current diameter guidelines, aortas >55mm (n=33) demonstrated higher energy loss than those <55mm (n=35) (0.09±0.005 vs. 0.08±0.003, p=0.02), but no difference in modulus of elasticity (148.4±9.8 kPa vs. 160.2±6.1 kPa, p=0.30) or delamination strength (33.4±2.4 mN/mm vs. 34.2±2.5 mN/mm). A length cut-off of 110mm was proposed as an indication for repair. Aortas >110mm (n=37) did not exhibit a significant difference in energy loss (0.06±0.004 vs. 0.07±0.005, p=0.37), modulus of elasticity (136.7±7.7 kPa vs. 141.0±8.5 kPa, p=0.71), or delamination strength (32.6±2.4 mN/mm vs. 35.6±2.6 mN/mm, p=0.44) in comparison to aortas <110mm (n=31). Aortas above both diameter (>55mm) and length (>110mm) thresholds (n=21) showed no significant difference in energy loss (0.07±0.006 vs. 0.06±0.004, p=0.33), modulus of elasticity (122.2±8.6 kPa vs. 146.1±7.0 kPa, p=0.06), or delamination strength (32.5±2.9 mN/mm vs. 34.5±2.2 mN/mm) when compared to smaller aortas (n=47). Adjusting dimensions to patient age and sex resulted in similar findings.
Conclusions: Aortic geometry poorly reflects the mechanical properties of aortic tissue. Weak association between energy loss and aortic diameter does support intervention at larger aortic diameters. Further research into biomarkers that better capture aortic biomechanics is needed.

Daniella Eliathamby (1), Melanie Keshishi (2), Maral Ouzounian (1), Thomas Forbes (3), Kongteng Tan (2), Craig Simmons (2), Jennifer C.-Y. Chung (4), (1) Toronto General Hospital, Toronto, ON, (2) University of Toronto, Toronto, Ontario, (3) University Health Network, Toronto, Ontario, (4) Toronto General Hospital - Toronto, ON, Toronto, Ontario

Daniella Eliathamby

Abstract Presenter

As an electrical and biomedical engineer from McMaster University and current MASc canadidate in the Biomedical Engineering department at the University of Toronto, my research focuses on bridging engineering princples in the field of cardiovascular surgery. Specifcally, I aim to characterize the mechanical properties of the ascending aorta and determine the underlaying structural alterations which result in the mechanical failure of the vessel. 

Specialties: Adult Cardiac, Aorta, Imaging, Anatomy and Conditions, Great Vessels, Aorta, Ascending Aorta, Aortic dissection (includes ulcers, hematomas), Multi-Specialty, General Interests of CardioThoracic Surgeons, Guidelines