Studying the Flow Dynamics in an Aortic Endograft with Crossed-limbs

A Comparative Study on the Hemodynamic Performance Within Cross and Non-cross Stent-Grafts for Abdominal Aortic Aneurysms With an Angulated Neck

Objectives: Cross-limb stent grafts for endovascular aneurysm repair (EVAR) are often employed for abdominal aortic aneurysms (AAAs) with significant aortic neck angulation. Neck angulation may be coronal or sagittal; however, previous hemodynamic studies of cross-limb EVAR stent grafts (SGs) primarily utilized simplified planar neck geometries. This study examined the differences in flow patterns and hemodynamic parameters between crossed and non-crossed limb SGs at different spatial neck angulations.

Methods: Ideal models consisting of 13 cross and 13 non-cross limbs were established, with coronal and sagittal angles ranging from 0 to 90°. Computational fluid dynamics (CFD) was used to capture the hemodynamic information, and the differences were compared.

Results: With regards to the pressure drop index, the maximum difference caused by the configuration and angular direction was 4.6 and 8.0%, respectively, but the difference resulting from the change in aneurysm neck angle can reach 27.1%. With regards to the SAR-TAWSS index, the maximum difference caused by the configuration and angular direction was 7.8 and 9.8%, respectively, but the difference resulting from the change in aneurysm neck angle can reach 26.7%. In addition, when the aneurysm neck angle is lower than 45°, the configuration and angular direction significantly influence the OSI and helical flow intensity index. However, when the aneurysm neck angle is greater than 45°, the hemodynamic differences of each model at the same aneurysm neck angle are reduced.

Conclusion: The main factor affecting the hemodynamic index was the angle of the aneurysm neck, while the configuration and angular direction had little effect on the hemodynamics. Furthermore, when the aneurysm neck was greatly angulated, the cross-limb technique did not increase the risk of thrombosis.

Meta-Analysis of the Crossed Versus Standard Limb Configuration in Endovascular Aneurysm Repair

OBJECTIVE

To investigate whether the crossed-limb technique confers better or worse clinical outcomes compared to the standard straight limb configuration in standard endovascular aneurysm repair (EVAR).

METHODS

We conducted a systematic review to identify studies comparing outcomes of EVAR with the crossed versus standard limb configuration. MEDLINE, EMBASE, CINAHL, and CENTRAL were searched in March 2021 using the Healthcare Databases Advanced Search interface developed by the National Institute for Heath and Care Excellence. The risk of bias was assessed with the Newcastle-Ottawa scale (NOS) and the Risk Of Bias In Non-randomized Studies - of Interventions (ROBINS-I) tool. Summary estimates were calculated using the odds ratio (OR), risk difference (RD), or mean difference (MD) and 95% confidence interval (CI), applying the Mantel-Haenszel or inverse variance statistical method. Random-effects models were employed.

RESULTS

Four observational studies qualified for inclusion, reporting a total of 1132 patients. All presented contemporary experiences. Baseline clinical characteristics were largely similar between patients with and without the crossed-limb configuration, but the anatomy tended to be less favourable in patients treated with the crossed-limb technique. No statistically significant difference was found in the primary outcomes: limb occlusion (OR 1.44, 95% CI 0.65 - 3.19), type Ib endoleak (RD 0.01, 95% CI -0.03 - 0.04), type III endoleak (RD 0.01, 95% CI -0.01 - 0.03); or secondary outcomes: perioperative mortality (RD 0.00, 95% CI -0.03 - 0.03), type Ia endoleak (RD 0.00, 95% CI -0.03 - 0.02), type II endoleak (OR 1.38, 95% CI 0.51 - 3.74), procedure duration (MD 18.07 min, 95% CI -1.14-37.29). Inconsistency across studies was low for all outcomes. The studies were judged to be of high quality on the NOS. The main bias identified using the ROBINS-I tool was due to confounding.

CONCLUSIONS

The crossed-limb technique was not found to confer inferior clinical outcomes in the medium term compared to the standard limb configuration in patients who undergo standard EVAR.

Abdominal aortic aneurysm endovascular repair: profiling post-implantation morphometry and hemodynamics with image-based computational fluid dynamics

Endovascular aneurysm repair (EVAR) has disseminated rapidly as an alternative to open surgical repair for the treatment of abdominal aortic aneurysms (AAAs), because of its reduced invasiveness, low mortality and morbidity rate. The effectiveness of the endovascular devices used in EVAR is always at question as postoperative adverse events can lead to re-intervention or to a possible fatal scenario for the circulatory system. Motivated by the assessment of the risks related to thrombus formation, here the impact of two different commercial endovascular grafts on local hemodynamics is explored through 20 image-based computational hemodynamic models of EVAR-treated patients (N=10 per each endograft model). Hemodynamic features, susceptible to promote thrombus formation, such as flow separation and recirculation, are quantitatively assessed and compared with the local hemodynamics established in image-based infrarenal abdominal aortic models of healthy subjects (N=10). The hemodynamic analysis is complemented by a geometrical characterization of the EVAR-induced reshaping of the infrarenal abdominal aortic vascular region. The findings of this study indicate that: (1) the clinically observed propensity to thrombus formation in devices used in EVAR strategies can be explained in terms of local hemodynamics by means of image-based computational hemodynamics approach; (2) reportedly pro-thrombotic hemodynamic structures are strongly correlated with the geometry of the aortoiliac tract postoperatively. In perspective, our study suggests that future clinical follow up studies could include a geometric analysis of the region of the implant, monitoring shape variations that can lead to hemodynamic disturbances of clinical significance.

Studying the Interaction of Stent-Grafts and Treated Abdominal Aortic Aneurysms

Since the advent of endovascular repair of aortic aneurysms (EVAR), clinical focus has been on preventing loss of sealing at the level of the infrarenal neck, which leads to type I endoleak and repressurization of the aneurysm sac. Enhanced mechanisms for central fixation and seal have consequently lowered the incidence of migration and endoleaks. However, endograft limb thrombosis and its causal mechanisms have not been addressed adequately in the literature. This article reviews the pathophysiological mechanisms associated with limb thrombosis in order to facilitate better clinical judgment to prevent iliac adverse effects.