Stiffness Matters: Improved Failure Risk Assessment of Ascending Thoracic Aortic Aneurysms

BackgroundRupture 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. MethodsTo 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. ResultsOur 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. ConclusionsIn 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 PerspectiveO_ST_ABSWhat is new?C_ST_ABSThe distensibility coefficient, which reflects the capacity of the vessel to expand during pressure changes, outperforms purely geometrical predictors when assessing the rupture or dissection risk of ascending thoracic aortic aneurysms. Not only the change in diameter, but also the change in axial length is important to assess the risk of aneurysm failure. Both dimensions are considered when the change in aneurysm volume is measured. What are the clinical implications?To quantify the distensibility when determining the need for surgery, the aneurysm should be visualized at two phases, i.e. at diastole and systole. Therefore, ECG-triggered scans with at least two phases need to be included in clinical practice. Clinicians can add this new metric to their risk stratification process, where it can gradually replace purely geometrical predictors as the database and hence confidence in a cut-off value grows.