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.

Endograft Conformability in Fenestrated Endovascular Aneurysm Repair for Complex Abdominal Aortic Aneurysms.

Purpose: To compare the impact of 2 commercially available custom-made fenestrated endografts on patient anatomy. Materials and Methods: The records of 234 patients who underwent fenestrated endovascular aneurysm repair for abdominal aortic aneurysm from March 2002 to July 2016 in 2 hospitals were screened to identify those who had pre- and postoperative computed tomography angiography assessments with a slice thickness of ≤2 mm. The search identified 145 patients for further analysis: 110 patients (mean age 72.4±7.1 years; 94 men) who had been treated with the Zenith Fenestrated (ZF) endograft and 35 patients (mean age 72.3±7.3 years; 30 men) treated with the Fenestrated Anaconda (FA) endograft. Measurements included aortic diameters at the level of the superior mesenteric artery (SMA) and renal arteries, target vessel angles, target vessel clock positions, and the target vessel tortuosity index. Variables were tested for inter- and intraobserver agreement. Results: There was a good agreement between observers in all tested variables. The native anatomy changed in both groups after endograft implantation. In the ZF group, changes were seen in the angles of the celiac artery (p=0.012), SMA (p=0.022), left renal artery (LRA) (p<0.001), and the right renal artery (RRA) (p<0.001); the aortic diameter at the SMA level (p<0.001); and the LRA (p<0.001) and RRA (p<0.001) clock positions. In the FA group, changes were seen in the angles of the LRA (p=0.001) and RRA (p<0.001) and in the SMA tortuosity index (p=0.044). Between group differences in changes were seen for the aortic diameters at the SMA and renal artery levels (p<0.001 for both) and the LRA clock position (p=0.019). Conclusion: Both custom-made fenestrated endografts altered vascular anatomy. The data suggest a higher conformability of the Fenestrated Anaconda endograft compared with the Zenith Fenestrated.

Partial renal coverage in endovascular aneurysm repair causes unfavorable renal flow patterns in an infrarenal aneurysm model.

OBJECTIVE: To achieve an optimal sealing zone during endovascular aneurysm repair, 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 investigated the consequences of partial coverage on renal flow patterns and wall shear stress (WSS). METHODS: In vitro models of an abdominal aortic aneurysm were used to visualize pulsatile flow using two-dimensional particle image velocimetry under physiologic resting conditions. One model served as control and two models were stented with an Endurant endograft (Medtronic Inc, Minneapolis, Minn), 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 WSS, 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 WSS, not present in the control model. A region with very low WSS (<0.1 Pa) was present in the model with partial coverage over a length of 7 mm compared with 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%). CONCLUSIONS: In this flow model, partial renal coverage after endovascular aneurysm repair causes low and marked oscillations in WSS, 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.

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 (p<0.001). Gutters and endoleaks were observed in all configurations. The largest gutter volume (232.8 mm3) and change in volume (20.7 mm3) between systole and diastole were observed in the Endurant-Advanta configuration. These values were 2.7- and 3.0-fold higher, respectively, compared to the Endurant-Viabahn configuration and 1.7- and 1.6-fold higher as observed in the Endurant-BeGraft configuration. The Endurant-Viabahn configuration had the highest D-ratio (right, 1.26-1.35; left, 1.33-1.48), while the Endurant-BeGraft configuration had the lowest (right, 1.11-1.17; left, 1.08-1.15). Assessment of the interobserver variability showed a high correlation (intraclass correlation >0.935) 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.

Benchtop quantification of gutter formation and compression of chimney stent grafts in relation to renal flow in chimney endovascular aneurysm repair and endovascular aneurysm sealing configurations.

BACKGROUND: The chimney technique has been successfully used to treat juxtarenal aortic aneurysms. The two main issues with this technique are gutter formation and chimney graft (CG) compression, which induce a risk for type Ia endoleaks and stent thrombosis, respectively. In this benchtop study, the geometry and renal artery flow of chimney endovascular aneurysm repair configurations were compared with chimney configurations with endovascular aneurysm sealing (ch-EVAS). METHODS: Seven flow phantoms were constructed, including one control and six chimney endovascular aneurysm repairs (Endurant [Medtronic Inc, Minneapolis, Minn] and AFX [Endologix Inc, Irvine, Calif]) or ch-EVAS (Nellix, Endologix) configurations, combined with either balloon-expandable or self-expanding CGs with an intended higher positioning of the right CG in comparison to the left CG. Geometric analysis was based on measurements at three-dimensional computed tomography angiography and included gutter volume and CG compression, quantified by the ratio between maximal and minimal diameter (D-ratio). In addition, renal artery flow was studied in a physiologic flow model and compared with the control. RESULTS: The average gutter volume was 343.5 ± 142.0 mm3, with the lowest gutter volume in the EVAS-Viabahn (W. L. Gore & Associates, Flagstaff, Ariz) combination (102.6 mm3) and the largest in the AFX-Advanta V12 (Atrium Medical Corporation, Hudson, NH) configuration (559.6 mm3). The maximum D-ratio was larger in self-expanding CGs than in balloon-expandable CGs in all configurations (2.02 ± 0.34 vs 1.39 ± 0.13). The CG compression had minimal influence on renal volumetric flow (right, 390.7 ± 29.4 mL/min vs 455.1 mL/min; left, 423.9 ± 28.3 mL/min vs 410.0 mL/min in the control). CONCLUSIONS: This study showed that gutter volume was lowest in ch-EVAS in combination with a Viabahn CG. CG compression was lower in configurations with the Advanta V12 than with Viabahn. Renal flow is unrestricted by CG compression.

Feasibility and Technical Aspects of Proximal Nellix-in-Nellix Extension for Late Caudal Endograft Migration.

PURPOSE: To describe the feasibility and technical aspects of a proximal Nellix-in-Nellix extension to treat caudal stent-graft migration after endovascular aneurysm sealing (EVAS) in the in vitro and in vivo settings. METHODS: In vitro studies were designed (1) to assess inner diameters of Nellix-in-Nellix extensions after postdilation with 12-mm balloons and (2) to test wall apposition in tubes with different diameters using a Nellix-in-Nellix stent-graft that extended out of the original Nellix stent-graft lumen by 10, 20, 30, and 40 mm. Simulated-use experiments were performed using silicone models in conjunction with a pulsatile flow pump. In the clinical setting, 5 patients (median age 74 years, range 73-83) presented at 2 centers with type Ia endoleak secondary to caudal Nellix stent-graft migration measuring a median 9 mm (range 7-15) on the left and 7 mm (range 0-11) on the right. Median polymer fill volume at the initial EVAS procedure was 42.5 mL (range 25-71). The median time to reintervention with a proximal Nellix extension was 15 months (range 13-32). RESULTS: In vitro, the inner diameters of the Nellix-in-Nellix extensions were consistent after postdilation. Cases with 10 and 20 mm of exposed endobag resulted in a poor seal with endoleak, while cases with 30 and 40 mm of exposed endobag length exhibited angiographic seal. Fill line pressures of the second Nellix were higher than expected. In the 5 clinical cases, chimney grafts were required in each case to create an adequate proximal landing zone. The Nellix-in-Nellix procedure was successful in all patients. There were no procedure-related complications, and no endoleaks were observed during a median 12-month follow-up. Reinterventions were performed in 2 patients because of in-stent stenosis and chimney graft compression, respectively. CONCLUSION: Proximal Nellix-in-Nellix extension can be used to treat caudally migrated Nellix stent-grafts and to treat the consequent type Ia endoleak, but the technique differs from primary EVAS. The development of dedicated proximal extensions is desirable.

EndoAnchors to Resolve Persistent Type Ia Endoleak Secondary to Proximal Cuff With Parallel Graft Placement.

PURPOSE: To describe 2 patients with a distally migrated endograft causing a type Ia endoleak and treatment with a proximal cuff and chimney grafts that required EndoAnchors to finally seal the leak. CASE REPORT: Two men, ages 86 and 72 years, presented with stent-graft migration and type Ia endoleak at 5 and 15 years after endovascular repair, respectively. Both were treated with a proximal cuff in combination with a chimney graft to the left renal artery. In both cases, the type Ia endoleak persisted, likely due to gutter formation. Both patients were treated in the same setting with EndoAnchors that instantly resolved the endoleak. At 1-year follow-up, there was no recurrent endoleak or migration, with patent chimney grafts and renal arteries and stable renal function. CONCLUSION: EndoAnchors may effectively resolve a persistent type Ia endoleak arising from gutter formation after placement of a proximal cuff and chimney grafts.