Partial renal coverage in EVAR causes unfavorable renal flow patterns in an infrarenal aneurysm model

Objective: To achieve an optimal sealing zone during EVAR, the intended positioning of the proximal end of the endograft fabric should be as close as possible to the most caudal edge of the renal arteries. Some endografts exhibit a small offset between the radiopaque markers and the proximal fabric edge. Unintended partial renal artery coverage may thus occur. This study investigates the consequences of partial coverage on renal flow patterns and wall shear stress. Methods: In-vitro models of an abdominal aortic aneurysm were used to visualize pulsatile flow using 2D particle image velocimetry under physiologic resting conditions. One model served as control and two models were stented with an Endurant endograft, one without and one with partial renal artery coverage with 1.3 mm of stent fabric extending beyond the marker (16\% area coverage). The magnitude and oscillation of wall shear stress, relative residence time and backflow in the renal artery were analyzed. Results: In both stented models, a region along the caudal renal artery wall presented with low and oscillating wall shear stress, not present in the control model. A region with very low wall shear stress (<0.1 Pa) was present in the model with partial coverage over a length of 7 mm, compared to a length of 2 mm in the model without renal coverage. Average renal backflow area percentage in the renal artery incrementally increased from control (0.9%) to the stented model without (6.4%) and with renal coverage (18.8%). Conclusion: In this flow model partial renal coverage after EVAR causes low and marked oscillations in wall shear stress, potentially promoting atherosclerosis and subsequent renal artery stenosis. Awareness of the device-dependent offset between the fabric edge and the radiopaque markers is therefore important in endovascular practice.Comment: 8 pages, 6 figures, supplementary video at publishe

In Vitro Quantification of Gutter Formation and Chimney Graft Compression in Chimney EVAR Stent-Graft Configurations Using Electrocardiography-Gated Computed Tomography

Purpose: To assess the dynamic behavior of chimney grafts during the cardiac cycle. Methods: Three chimney endovascular aneurysm repair (EVAR) stent-graft configurations (Endurant and Advanta V12, Endurant and Viabahn, and Endurant and BeGraft) were placed in silicone aneurysm models and subjected to physiologic flow. Electrocardiography (ECG)-gated contrast-enhanced computed tomography was used to visualize geometric changes during the cardiac cycle. Endograft and chimney graft surface, gutter volume, chimney graft angulation over the center lumen line, and the D-ratio (the ratio between the lengths of the major and minor axes) were independently assessed by 2 observers at 10 time points in the cardiac cycle. Results: Both gutter volumes and chimney graft geometry changed significantly during the cardiac cycle in all 3 configurations (p0.935) between measurements. Conclusion: Gutter volumes and stent compression are dynamic phenomena that reshape during the cardiac cycle. Compelling differences were observed during the cardiac cycle in all configurations, with the self-expanding (Endurant–Viabahn) chimney EVAR configurations having smaller gutters and less variation in gutter volume during the cardiac cycle yet more stent compression without affecting the chimney graft surface

Electrocardiography-gated computed tomography angiography analysis of cardiac pulsatility-induced motion and deformation after endovascular aneurysm sealing with chimney grafts

Objective: To evaluate the proximal stability of the chimney endovascular aneurysm sealing configuration (chEVAS) during the cardiac cycle by investigating the cardiac pulsatility-induced movement and deformation. Methods: We retrospectively analyzed postoperative electrocardiogram-gated computed tomography angiography scans of 11 chEVAS cases (9 primary chEVAS plus 2 chEVAS-in-chEVAS). ChEVAS procedures were conducted between September 2013 and June 2016. Motion and deformation of the EVAS stents, the chimney grafts, and the stented branch vessels were evaluated during the cardiac cycle using an established combination of image registration and segmentation techniques. Results: Electrocardiogram-gated computed tomography angiography scans of 11 chEVAS configurations including 22 EVAS stents and 20 chimney grafts were analyzed. The three-dimensional displacement was at most 1.7 mm for both the EVAS stents and the chimney grafts. The maximum change in distance between components was no more than 0.4 mm and did not differ between EVAS-to-EVAS stent and EVAS stent-to-chimney stent (0.2 ± 0.1 mm vs 0.2 ± 0.1 mm; P = .823). The mean change in chimney deflection angle was 1.2 ± 0.7°; the maximum change was greatest for the superior mesenteric artery (SMA) (2.6°). The EVAS stent-to-chimney angles for the left renal artery, right renal artery, and SMA varied on average by 0.7 ± 0.3° (range, 0.4°-1.3°), 1.0 ± 0.3° (range, 0.5°-1.7°), and 0.8 ± 0.4° (range, 0.3°-1.3°), respectively, during the cardiac cycle. The end-stent angles for the left renal artery, right renal artery, and SMA varied on average by 1.7 ± 0.9° (range, 0.5°-3.3°), 1.9 ± 0.8° (range, 0.7°-3.3°), and 1.3 ± 0.4° (range, 0.7°-1.6°), respectively, during the cardiac cycle. Overall, the end-stent angles varied on average by 1.7 ± 0.8° (range, 0.5°-3.3°). Conclusions: The chEVAS configuration proved to be stable during the cardiac cycle, as demonstrated by minimal cyclical changes in distance between device components and angulation between the EVAS stents and the chimney grafts. The limited deflection angles of the chimney grafts decrease the risk of bending fatigue, but the more apparent change in end-stent angle distal to the chimney graft may raise concerns regarding late branch occlusion or stenosis