Stiffness matters: Improved failure risk assessment of ascending thoracic aortic aneurysms

Background Rupture and dissection are feared complications of ascending thoracic aortic aneurysms caused by mechanical failure of the wall. Currently, the largest aortic diameter is used to predict the risk of wall failure and to determine the need for surgical resection. However, this criterion lacks accuracy, and other prospective parameters are required to predict aneurysm rupture or dissection. Methods To identify better predictors, we performed a retrospective personalized failure risk analysis, including clinical, geometrical, histological and mechanical data of 33 patients. Uniaxial tensile tests until failure were performed to determine the wall strength. Material parameters were fitted against ex vivo planar biaxial data and in vivo pressure-diameter relationships at diastole and systole. Using the resulting material properties and in vivo data, the maximal in vivo stress at systole was calculated, assuming a thin-walled axisymmetric geometry. The retrospective failure risk, defined as the ratio between the maximal stress and maximal strength, was correlated with prospective parameters to find the best failure risk predictor. Results Our results show that the distensibility coefficient, which reflects aortic compliance and is derived from pressure measurements and multiphasic scans, outperforms other predictors in assessing the risk of aneurysm failure. Conclusions In a clinical setting, multiphasic CT-scans followed by the calculation of the distensibility coefficient can be of added benefit in patient-specific, clinical decision making. Additionally, the distensibility derived from the aneurysm volume has the best predictive power as it also takes the axial stretch into account. Clinical trial URL: https://clinicaltrials.gov/ct2/show/NCT03142074?cond=Aneurysm+Ascending+Aorta&cntry=BE&city=Leuven&draw=2&rank=1} Clinical trial ID: NCT03142074