Computational Modeling of Shear-Based Hemolysis Caused by Renal Obstruction

Abstract

As endovascular treatment of abdominal aortic aneurysms (AAAs) gains popularity, it is becoming possible to treat certain challenging aneurysmal anatomies with endografts relying on suprarenal fixation. In such anatomies, the bare struts of the device may be placed across the renal artery ostia, causing partial obstruction to renal artery blood flow. Computational fluid dynamics (CFD) was used to simulate blood flow from the aorta to the renal arteries, utilizing patient-specific boundary conditions, in three patient models and calculate the degree of shear-based blood damage (hemolysis). We used contrast-enhanced computed tomography angiography (CTA) data from three AAA patients who were treated with a novel endograft to build patient-specific models. For each of the three patients, we constructed a baseline model and endoframe model. The baseline model was a direct representation of the patient's 30-day post-operative CTA data. This model was then altered to create the endoframe model, which included a ring of metallic struts across the renal artery ostia. CFD was used to simulate blood flow, utilizing patient-specific boundary conditions. Pressures, flows, shear stresses, and the normalized index of hemolysis (NIH) were quantified for all patients. The overall differences between the baseline and endoframe models for all three patients were minimal, as measured though pressure, volumetric flow, velocity, and shear stress. The average NIH across the three baseline and endoframe models was 0.002 and 0.004, respectively. Results of CFD modeling show that the overall disturbance to flow caused by the presence of the endoframe struts is minimal. The magnitude of the NIH in all models was well below the accepted design and safety threshold for implantable medical devices that interact with blood flow.

Flow and wall shear stress characterization after endovascular aneurysm repair and endovascular aneurysm sealing in an infrarenal aneurysm model

“…An increase in WSS was found only close to the stent struts. 19 An intended lower positioning of the EVAS stents in this study may have improved the renal flow profile, and this will be the subject of a future study. That position, however, could reduce the sealing zone and thus increase the risk of other problems, including migration and type IA endoleak.…”

Spiral blood flow in aorta–renal bifurcation models

“…Along with the above-mentioned in vitro and in vivo investigations, several computational fluid dynamics (CFD) studies have been also undertaken to investigate the role of haemodynamic forces in the progression of ARAS (Ku et al 1989;Cheer et al 1998;Yim et al 2004;Hassani et al 2007;Kagadis et al 2008;Segalova et al 2012;Albert et al 2014;Zhang et al 2014). All these studies have confirmed the inevitable roles of haemodynamic parameters and anatomic and physiological features of the renal artery bifurcation in the progression of ARAS.…”

The Influence of Positioning of the Nellix Endovascular Aneurysm Sealing System on Suprarenal and Renal Flow: An In Vitro Study

“…This phenomenon was also observed in a previous flow study on EVAS with the 28-mm IFU model, 26 showing that maximum shear rate associated with this increase in peak velocity in the RA is well below the pathological threshold for acute thrombosis, so this event should not be expected. 26 The computational fluid dynamics study conducted by Segalova and coauthors 27 has demonstrated that the proximal bare stent had almost no influence on the renal flow profile when positioned across the RA orifice, and it is not likely that the proximal bare metal stent will cause large disturbances in RA flow profile. An intended positioning with the bare metal stent across the RA ostium (proximal 4 mm) should be a safe margin for positioning of the endosystem with reference to the RA orifice.…”