Biomechanical assessment predicts aneurysm-related events in patients with abdominal aortic aneurysm

Objective To test whether aneurysm biomechanical ratio (ABR; a dimensionless ratio of wall stress and wall strength) can predict aneurysm related events. Methods In a prospective multicentre clinical study of 295 patients with an abdominal aortic aneurysm (AAA; diameter ≥ 40 mm), three dimensional reconstruction and computational biomechanical analyses were used to compute ABR at baseline. Participants were followed for at least two years and the primary end point was the composite of aneurysm rupture or repair. Results The majority were male (87%), current or former smokers (86%), most (72%) had hypertension (mean ± standard deviation [SD] systolic blood pressure 140 ± 22 mmHg), and mean ± SD baseline diameter was 49.0 ± 6.9 mm. Mean ± SD ABR was 0.49 ± 0.27. Participants were followed up for a mean ± SD of 848 ± 379 days and rupture (n = 13) or repair (n = 102) occurred in 115 (39%) cases. The number of repairs increased across tertiles of ABR: low (n = 24), medium (n = 34), and high ABR (n = 44) (p = .010). Rupture or repair occurred more frequently in those with higher ABR (log rank p = .009) and ABR was independently predictive of this outcome after adjusting for diameter and other clinical risk factors, including sex and smoking (hazard ratio 1.41; 95% confidence interval 1.09–1.83 [p = .010]). Conclusion It has been shown that biomechanical ABR is a strong independent predictor of AAA rupture or repair in a model incorporating known risk factors, including diameter. Determining ABR at baseline could help guide the management of patients with AAA

Low Shear Stress at Baseline Predicts Expansion and Aneurysm-Related Events in Patients With Abdominal Aortic Aneurysm

Background Low shear stress has been implicated in abdominal aortic aneurysm (AAA) expansion and clinical events. We tested the hypothesis that low shear stress in AAA at baseline is a marker of expansion rate and future aneurysm-related events. Methods Patients were imaged with computed tomography angiography (CTA) at baseline and followed up every six months >24 months with ultrasound measurements of maximum diameter. From baseline CTA, we reconstructed three dimensional models for automated computational fluid dynamics simulations and computed luminal shear stress. The primary composite endpoint was aneurysm repair and/or rupture, and the secondary endpoint was aneurysm expansion rate. Results We included 295 patients with median AAA diameter of 49mm (IQR 43-54mm) and median follow-up of 914 (IQR 670-1112) days. There were 114 (39%) aneurysm-related events, with 13 AAA ruptures and 98 repairs (one rupture was repaired). Patients with low shear stress (0.6 Pa; 29%) shear stress groups (p=0.010). This association was independent of known risk factors (adjusted HR 1.72; 95% CI [1.08, 2.73]; p=0.023). Low shear stress was also independently associated with AAA expansion rate (β=+0.28mm/y; 95% CI [0.02, 0.53]; p=0.037). Conclusions We show for the first time that low shear stress (<0.4 Pa) at baseline is associated with both AAA expansion and future aneurysm-related events. Aneurysms within the lowest tertile of shear stress, versus those with higher shear stress, were more likely to rupture or reach thresholds for elective repair. Larger prospective validation trials are needed to confirm these findings and translate them into clinical management