Maximal aneurysm diameter (MAD) is currently used as a risk-threshold to determine indication for abdominal aortic aneurysm (AAA) surgery1,2. However, some AAAs rupture before reaching this threshold, and many AAAs may remain stable until large diameters3. Peak wall stress (PWS) and peak wall rupture index (PWRI) are higher in ruptured aneurysms compared to stable controls4. PWRI has also been shown to be higher in aneurysms prior to rupture5,6. These studies have, however, used only small cohorts of pre-rupture AAAs (n<20). The primary aim of this study was to identify morphological and biomechanical rupture risk predictors in the pre-rupture CT of patients who later develop rAAA.

Patients with ruptured AAA in SLL between 2009-2013 who had performed ≥1 CT-A prior to rupture were included. CT-As were analyzed with A4-clinics (VASCOPS) to obtain PWS, PWRI and geometric measurements. Cox Proportional-Hazards model was used for statistical analysis. A sub-analysis of patients with AAAs <70 mm was undertaken, since the wall-strength model included in PWRI is not validated for AAAs >70 mm.

From 293 patients who presented with rupture between 2009-2013, 50 patients (36 male, age 76.1±8.6 years) with a total of 82 CTA examination prior to rupture were identified. In the survival analysis two models were investigated, model A that included MAD, PWS and PWRI and model B that included aneurysm volume, PWS and PWRI. MAD and aneurysm volume were not included in the same model due to a high level of collinearity. For all patients, Model A showed that MAD and PWS were significantly associated with freedom-from-rupture, and in model B Aneurysm volume and PWS in turn showed a significant association. The model that included aneurysm volume (model B) instead of MAD (model A) had a higher R2 value (0.379 vs 0.367). In the analysis that was limited to aneurysms < 70 mm, instead of PWS, PWRI was significant in both model A and B. The R2 value for the model that included volume was again higher. Adjusting the above models for sex did not influence the overall results or statistical significance (results not shown)

For all aneurysms PWS, even when adjusting for MAD or volume showed a clear association with time-to-rupture. In AAAs <70 mm, instead PWRI was associated with time-to-rupture. Further, the inclusion of volume lead to an improved model when compared to MAD.

1 Wanhainen A, Verzini F, Van Herzeele I, Allaire E, Bown M, Cohnert T, et al. European Society for Vascular Surgery (ESVS) 2019 Clinical Practice Guidelines on the Management of Abdominal Aorto-iliac Artery Aneurysms. Eur J Vasc Endovasc Surg 2018;0(0). Doi: 10.1016/j.ejvs.2018.09.020. 2 Chaikof EL, Dalman RL, Eskandari MK, Jackson BM, Lee WA, Mansour MA, et al. The Society for Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm. J Vasc Surg 2018;67(1):2-77.e2. Doi: 10.1016/j.jvs.2017.10.044. 3 Laine MT, Vänttinen T, Kantonen I, Halmesmäki K, Weselius EM, Laukontaus S, et al. Rupture of Abdominal Aortic Aneurysms in Patients Under Screening Age and Elective Repair Threshold. Eur J Vasc Endovasc Surg 2016;51(4):511-6. Doi: 10.1016/j.ejvs.2015.12.011. 4 Khosla S, Morris DR, Moxon J V, Walker PJ, Gasser TC, Golledge J. Meta-analysis of peak wall stress in ruptured, symptomatic and intact abdominal aortic aneurysms. Br J Surg 2014;101(11):1350-7; discussion 1357. Doi: 10.1002/bjs.9578. 5 Erhart P, Roy J, de Vries J-PPM, Liljeqvist ML, Grond-Ginsbach C, Hyhlik-Dürr A, et al. Prediction of Rupture Sites in Abdominal Aortic Aneurysms After Finite Element Analysis. J Endovasc Ther 2016;23(1):115-20. Doi: 10.1177/1526602815612196. 6 Polzer S, Gasser TC, Vlachovský R, Kubíček L, Lambert L, Man V, et al. Biomechanical indices are more sensitive than diameter in predicting rupture of asymptomatic abdominal aortic aneurysms. J Vasc Surg 2020;71(2):617-626.e6. Doi: 10.1016/j.jvs.2019.03.051.