Vessel wall heterogeneity is an important factor in abdominal aortic aneurysm rupture risk prediction

Objective: Current indications for repair of abdominal aortic aneurysms (AAA) emphasize aortic diameter as marker for risk of rupture, overlooking the role played by wall heterogeneity. This study uses pre-operative CT... [ view full abstract ]

Objective: Current indications for repair of abdominal aortic aneurysms (AAA) emphasize aortic diameter as marker for risk of rupture, overlooking the role played by wall heterogeneity. This study uses pre-operative CT scanning to compute mechanical and fluid-mechanical stress profiles on the aortic wall for patients undergoing open AAA repair, and correlate these characteristics with aortic wall histopathology and mechanical properties obtained via a sampling grid during surgery.
Methods: Three patients with non-ruptured AAA underwent routine CTA-scan examination two weeks prior surgery. Pre-operative mechanical wall stress (MWS) and time averaged wall shear-stress (TAWSS) were predicted by means of finite element analysis (FEA) and computational fluid dynamics (CFD), respectively. The derived stress maps (figure1) served as guide during surgery to collect specimens from diseased aortas for elastin fragmentation and collagen content evaluation. Local mechanical properties of the tissue were assessed from uniaxial and planar biaxial tensile tests.
Results: The macroscopic MWS and TAWSS were distributed non-uniformly over the wall and large variability of collagen content and elastin fragmentation was observed. There was a moderate negative correlation between thrombus thickness (TT) and MWS and between TT and TAWSS. Elastin fragmentation was strongly correlated with the percentage of collagen content in the media. Large variability in the mechanical properties was observed. Collagen content was correlated with the material strength of aortic wall.
Conclusions: Observed regional differences are consequence of local response of tissue to mechanical and biological triggers. Non-invasive methods to infer local properties would increase the reliability of pre-operative risk of rupture prediction.