Differential elastin degradation and micromechanical properties in ascending aortic aneurysm groups: statistical modelling

Background: Elastin microstructure is an important factor in aortic aneurysms. However, it is unclear whether elastin microstructure varies in different ascending aneurysm aetiologies, and how this relates to micromechanical behaviour. Objective to combine in vitro experimentation and statistical modelling to distinguish between ascending aortic aneurysm groups; bicuspid aortic valve with associated aneurysm (BAV) and idiopathic degenerative aneurysm (DA). The role of micromechanical and biochemical properties as risk factors was explored. Methods: Aortic biopsies were taken from patients undergoing BAV or DA aneurysmal repair (n = 30). Oscillatory nanoindentation was applied to the medial layer [1]. The same tissues were chemically or enzymatically digested and measured for collagen, elastin and glycosaminoglycan (GAG) levels using hydroxyproline, fastin elastin kit and 1-9 dimethylmethylene blue respectively. Elastic fibre numbers and length were measured from Verhoeff-Van Gieson stained images. All measured data and patient clinical characteristics were analysed using least absolute shrinkage and selection operator (LASSO) regression. Results: Micromechanical properties of BAV tissue was found to be significantly higher than DA tissue (p < 0.001). Similarly, this significant trend was also noted for GAG (p = 0.004) and collagen levels (p = 0.02). Although elastin levels were not significant, an increase in the number of long fibres was observed in BAV tissue (p = 0.02). Conclusions: LASSO regression showed that micromechanical and elastin properties were unique predictors for BAV, whereas age, gender, collagen and preoperative aortic diameter were unique for DA. Our statistical approach is the first to show that ascending aortic aneurysm groups can be distinguished using novel in vitro measurements.