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Page 10 of 13 Sun et al. Vessel Plus 2020;4:13 I http://dx.doi.org/10.20517/2574-1209.2020.02

Figure 7. 3D grid cube presenting the relationship between peak wall stresses in males and females

(including maximum diameter, asymmetry index, and wall thickness), peak stress equations for males
and females were developed to predict AAA rupture. According to these simulation results and the two
equations developed above, some common and sex-specific features have been revealed.

For both sexes, the geometric features of the AAA have an obvious influence on peak wall stress. Among
the three morphological factors, wall thickness is critical for developing a ruptured AAA in both men and
women, which suggests that more attention should be paid to its distribution and change when predicting
the risk of rupture. Regarding the specific equation for males or females, there were some models where
even when the maximum diameter in AAA was relatively small, the corresponding peak wall stress
conversely became large, which demonstrated the limitation of maximal transverse measurement as a
criterion for AAA rupture risk assessment. In turn, this maximum diameter criterion may even result in
delaying AAA repair.

The AAA peak wall stress also has sex differences. When the AAA wall is thin and the asymmetry index is
large, or the vessel wall is thick and the asymmetry index is small, the peak wall stress observed in males
would be higher than that in females with the same maximum diameter. When the asymmetry index was
0.44 and the corresponding wall thickness was 2 mm, AAAs with maximum diameters of 5 cm for women
and 5.5 cm for men posed a comparable risk of rupture. This difference should alert surgeons to consider
the influence of sex when assessing this risk of rupture of an AAA.

For ease of use in a clinical setting, equations to predict peak wall stress and a 3D grid have been developed
in the present study (Equations 3 and 4, Figure 7). Both equations could assess the risk of AAA rupture in
men and women separately. The 3D grid presented in Figure 7 revealed the relationship between peak wall
stress in males and females with different maximum diameters, asymmetry index and wall thickness. Thus,
the present study provides more biomechanical information with respect to the development and rupture
of AAA to help with patient-specific assessment and treatment decision-making, i.e., open surgery or
percutaneous deployment of a stent-graft.

As this is a preliminary study, there are several shortcomings. AAA models were simplified and
idealised. Numerical calculations used unidirectional fluid-solid coupling. Material properties of the
vascular wall were defined as linear, isotropic elastic, and its thickness was assumed to be uniform.
These limitations would result in less accurate results than that using more realistic biomechanical
properties, e.g., anisotropic, nonlinear, which entails residual stresses and implies statistically distributed
heterogeneities [41-43] . Despite these simplifications, the results still have qualitative significance. With the
development of numerical simulation methodologies and further imaging technology, coupled with