Abdominal aortic aneurysms (AAA) are repaired when they meet diameter criteria or when they become symptomatic or rupture. The use of aortic diameter as the primary criterion in the decision to repair fails address the considerable numbers of AAA that rupture below this operative threshold,
1
particularly in women.2
Improved prediction of AAA behavior is required to prevent significant morbidity and mortality.AAA are thought to rupture when aortic wall mechanical stress exceeds wall strength.
3
,4
Finite element analysis has been used to model the physical characteristics of the AAA wall from computed tomography reconstructions, allowing the determination of peak wall stress (PWS) and the peak wall rupture index (PWRI). PWS is a measure of maximal tensile stress, whereas PWRI is a ratio of maximal wall stress to strength. The PWRI serves as a predictor of AAA rupture risk; however, to date it has yet to consistently predict the outcome for specific AAA geometries.5
,6
This lack of predictability likely reflects the multifactorial involvement of hemodynamics, intraluminal thrombus (ILT), and inflammatory effects of cytokines and proteases (7) and may also reflect constant aortic remodeling associated with growth.3
The current article examined the biomechanical and morphological changes associated with AAA growth using a finite element analysis linear transformation-based comparison. The authors hypothesized that AAA growth would accompanied by significant changes in biomechanical and geometrical characteristics. It was also hypothesized that the PWRI, PWS, and ILT would change location with AAA growth. AAA diameter and volume, neck configuration, α and β angulation, vessel tortuosity, ILT volume, PWS, and PWRI were determined at two time points.
There was a significant increase in AAA and ILT volume, maximal ILT thickness, neck angulation, and iliac tortuosity with AAA growth. The change in PWRI was most correlated with an increase in AAA volume, whereas the change in PWS was best correlated with neck angulation. These findings suggest that AAA wall stresses vary with growth and that AAA volume may be a better predictor of AAA rupture risk than diameter.
The observation that maximum ILT thickness, in comparison with the positions of maximum PWS and PWRI, was the most pronounced with AAA growth suggests that ILT volume may play an important role in predicting AAA behavior. Using a computational fluid dynamics approach, Lasheras et al
7
,8
have previously shown that alterations in aortic length and tortuosity with AAA growth have been associated with the development of turbulent flow vortexes, with changes in wall shear stress. A low wall shear stress is thought to play a role in initiating and propagating ILT deposition in AAA, which may play a role in promoting aortic wall degeneration and rupture.9
Future studies aimed at improving understanding of AAA rupture risk will require both hemodynamic and finite element analyses in a large cohort with patient-specific physiologic and anatomic data.The opinions or views expressed in this commentary are those of the authors and do not necessarily reflect the opinions or recommendations of JVS: Vascular Science or the Society for Vascular Surgery.
References
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- The relationship between aortic wall distensibility and rupture of infrarenal abdominal aortic aneurysm.J Vasc Surg. 2003; 37: 112-117
- A quarter of a century biomechanical rupture risk assessment of abdominal aortic aneurysms. Achievements, clinical relevance, and ongoing developments.Int J Numer Method Biomed Eng. 2022; 28: e3587
- Systematic review and meta-analysis of peak wall stress and peak wall rupture index in ruptured and asymptomatic intact abdominal aortic aneurysms.J Am Heart Assoc. 2021; 10: e019772
- Prediction of rupture risk in abdominal aortic aneurysm during observation: wall stress versus diameter.J Vasc Surg. 2003; 37: 724-732
- In vivo analysis of mechanical wall stress and abdominal aortic aneurysm rupture risk.J Vasc Surg. 2002; 36: 589-597
- Evolution of the wall shear stresses during the progressive enlargement of symmetric abdominal aortic aneurysms.J Fluid Mech. 2006; 560: 19-51
- Hemodynamic changes occurring during the progressive enlargement of abdominal aortic aneurysms.Ann Vasc Surg. 2004; 18: 14-21
- Intraluminal thrombus: innocent bystander or factor in abdominal aortic aneurysm pathogenesis?.JVS Vasc Sci. 2021; 2: 159-169
Article info
Publication history
Published online: November 17, 2022
Footnotes
Author conflict of interest: none.
The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS-Vascular Science policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest.
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- Rupture risk parameters upon biomechanical analysis independently change from vessel geometry during abdominal aortic aneurysm growthJVS-Vascular ScienceVol. 4
- PreviewThe indication for abdominal aortic aneurysm (AAA) repair is based on a diameter threshold. However, mechanical properties, such as peak wall stress (PWS) and peak wall rupture index (PWRI), influence the individual rupture risk. This study aims to correlate biomechanical and geometrical AAA characteristics during aneurysm growth applying a new linear transformation-based comparison of sequential imaging.
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