Abstract 107: Finite Element Models With Patient-Specific Wall Strength Estimations Improve Growth Predictions of Abdominal Aortic Aneurysms

Abstract

OBJECTIVES: Abdominal aortic aneurysms (AAA) grow discontinuously and there is no reliable method to predict growth rate specifically. If AAA growth rate could be predicted, surveillance intervals and elective surgery could be planned in a safe and cost-efficient manner. In this study, we used finite element modeling (FEM) with estimations of patient specific factors including wall strength and wall thickness to find a biomechanical parameter that predicted AAA growth. METHODS: 41 patients (9 women, 32 men) who had undergone two computed tomography angiographies (CT-A) within 9-18 months were included. Two FEM were made per CT-A; one (standard) with and one (matched) without modeling influence of patient specific age, sex, mean arterial pressure and family history. Annual growth of diameter and volume were measured. The baseline AAA volume, diameter, intraluminal thrombus (ILT) volume, mean wall stress (MWS), mean ILT stress (MIS), peak wall stress (PWS) and peak wall rupture risk (PWRR = maximal wall stress/wall strength ratio) were estimated. Linear and non-linear correlations between growth and biomechanical parameters were tested with Pearson product-moment and Spearman’s rank correlation coefficients, respectively. RESULTS: Standard baseline PWRR correlated with diameter growth (r=0.32 P=0.040). Baseline AAA volume (r=0.57 P=0.0001), diameter (r=0.53 P = 0.0003), ILT volume (r=0.50, P=0.0009), standard (r=0.44 P=0.0087) and matched (r=0.32 P=0,043) PWRR and matched MIS (r=0.39 P=0.013) correlated with volume growth. PWS and MWS did not correlate with AAA growth. CONCLUSIONS: PWRR, based on patient specific wall stress and strength estimations, can predict both diameter and volume growth in our small sample. As this parameter previously has been shown to predict rupture, it is promising as a future clinical predictor for AAA progression and outcome. Our results also suggest a role for the ILT in AAA expansion since both the mean stress and volume of the ILT correlated with AAA volume growth.