Erik Groot Jebbink

Hemodynamic comparison of stent configurations used for aortoiliac occlusive disease

Background: Endovascular treatment of aortoiliac occlusive disease entails the use of multiple stents to reconstruct the aortic bifurcation. Different configurations have been applied and geometric variations exist, as quantified in previous work. Other studies concluded that specific stent geometry seems to affect patency. These variations may affect local flow patterns, resulting in different wall shear stress (WSS) and oscillating shear index (OSI). The aim of this study was to compare the effect of different stent configurations on flow perturbations (recirculation and fluid stasis), WSS, and OSI in an in vitro setup. Methods: Three different stent configurations were deployed in transparent silicone models: bare‐metal kissing (BMK) stents, covered kissing (CK) stents, and the covered endovascular reconstruction of the aortic bifurcation (CERAB) configuration. Transparent covered stents were created with polyurethane to enable visualization. Models were placed in a circulation setup under physiologic flow conditions. Time‐resolved laser particle image velocimetry techniques were used to quantify the flow, and WSS and OSI were calculated. Results: The BMK configuration did not show flow disturbances at the inflow section, and WSS values were similar to the control. An area of persistent low flow was observed throughout the cardiac cycle in the area between the anatomic bifurcation and neobifurcation. The CK model showed recirculation zones near the inflow area of the stents with a resulting low average WSS value and high OSI. The proximal inflow of the CERAB configuration did not show flow disturbances, and WSS values were comparable to control. Near the inflow of the limbs, a minor zone of recirculation was observed without changes in WSS values. Flow, WSS, and OSI on the lateral wall of the proximal iliac artery were undisturbed in all models. Conclusions: The studied aortoiliac stent configurations have distinct locations where flow disturbances occur, and these are related to the radial mismatch. The CERAB configuration is the most unimpaired physiologic reconstruction, whereas BMK and CK stents have their typical zones of flow recirculation. Clinical Relevance: Aortoiliac occlusive disease involving the aortic bifurcation is treated with kissing stents on a regular basis. The midterm and long‐term results cannot compete with open aortic repair, possibly because of disturbed blood flow. In response to the varying clinical results, several stent configurations have been introduced, most of them promoting a more physiologic reconstruction of the aortic bifurcation to ensure undisturbed blood flow. However, the hemodynamic differences between frequently used aortoiliac stent configurations have never been quantified. Insight into the local hemodynamics expands the knowledge on the interaction between stent geometry and blood flow. Furthermore, the results complement current clinical results and aid vascular specialists in their choice of stent configuration.

Validation of the Simbionix PROcedure Rehearsal Studio sizing module: A comparison of software for endovascular aneurysm repair sizing and planning

An important determinant of successful endovascular aortic aneurysm repair is proper sizing of the dimensions of the aortic-iliac vessels. The goal of the present study was to determine the concurrent validity, a method for comparison of test scores, for EVAR sizing and planning of the recently introduced Simbionix PROcedure Rehearsal Studio (PRORS). Seven vascular specialists analyzed anonymized computed tomography angiography scans of 70 patients with an infrarenal aneurysm of the abdominal aorta, using three different sizing software packages Simbionix PRORS (Simbionix USA Corp., Cleveland, OH, USA), 3mensio (Pie Medical Imaging BV, Maastricht, The Netherlands), and TeraRecon (Aquarius, Foster City, CA, USA). The following measurements were included in the protocol: diameter 1 mm below the most distal main renal artery, diameter 15 mm below the lowest renal artery, maximum aneurysm diameter, and length from the most distal renal artery to the left iliac artery bifurcation. Averaged over the locations, the intraclass correlation coefficient is 0.83 for Simbionix versus 3mensio, 0.81 for Simbionix versus TeraRecon, and 0.86 for 3mensio versus TeraRecon. It can be concluded that the Simbionix sizing software is as precise as two other validated and commercially available software packages.

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

Background: Endovascular aneurysm repair (EVAR) with a modular endograft has become the preferred treatment for abdominal aortic aneurysms. A novel concept is endovascular aneurysm sealing (EVAS), consisting of dual endoframes surrounded by polymer‐filled endobags. This dual‐lumen configuration is different from a bifurcation with a tapered trajectory of the flow lumen into the two limbs and may induce unfavorable flow conditions. These include low and oscillatory wall shear stress (WSS), linked to atherosclerosis, and high shear rates that may result in thrombosis. An in vitro study was performed to assess the impact of EVAR and EVAS on flow patterns and WSS. Methods: Four abdominal aortic aneurysm phantoms were constructed, including three stented models, to study the influence of the flow divider on flow (Endurant [Medtronic, Minneapolis, Minn], AFX [Endologix, Irvine, Calif], and Nellix [Endologix]). Experimental models were tested under physiologic resting conditions, and flow was visualized with laser particle imaging velocimetry, quantified by shear rate, WSS, and oscillatory shear index (OSI) in the suprarenal aorta, renal artery (RA), and common iliac artery. Results: WSS and OSI were comparable for all models in the suprarenal aorta. The RA flow profile in the EVAR models was comparable to the control, but a region of lower WSS was observed on the caudal wall compared with the control. The EVAS model showed a stronger jet flow with a higher shear rate in some regions compared with the other models. Small regions of low WSS and high OSI were found near the distal end of all stents in the common iliac artery compared with the control. Maximum shear rates in each region of interest were well below the pathologic threshold for acute thrombosis. Conclusions: The different stent designs do not influence suprarenal flow. Lower WSS is observed in the caudal wall of the RA after EVAR and a higher shear rate after EVAS. All stented models have a small region of low WSS and high OSI near the distal outflow of the stents. Clinical Relevance: Most endografts for endovascular aortic aneurysm repair involve a modular stent design, and the design could vary in the location of the flow divider. Endovascular aneurysm sealing based on polymer filling of endobags surrounding dual stent frames was recently introduced. This study focuses on effects of a dual‐lumen configuration in the abdominal aorta after endovascular aneurysm sealing on flow and wall shear stress proximal and distal to the stents in comparison with two endovascular aneurysm repair endografts and an aneurysm control by in vitro flow visualization.

Three-year outcome of the covered endovascular reconstruction of the aortic bifurcation technique for aortoiliac occlusive disease

Objective: The objective of this study was to demonstrate the 3‐year outcome of the covered endovascular reconstruction of the aortic bifurcation (CERAB) technique for the treatment of extensive aortoiliac occlusive disease (AIOD). Methods: Between February 2009 and July 2016, all patients treated with the CERAB technique for AIOD were identified in the local databases of two centers and analyzed. Demographics and lesion characteristics were scored. Follow‐up consisted of clinical assessment, duplex ultrasound, and ankle‐brachial indices. Patency rates and clinically driven target lesion revascularization were calculated by Kaplan‐Meier analysis. Results: Of 130 patients (69 male and 61 female) treated, 68% were diagnosed with intermittent claudication and 32% suffered from critical limb ischemia. The majority (89%) were TransAtlantic Inter‐Society Consensus II D lesions, and the remaining were B and C lesions (both 5%). Median follow‐up was 24 months (range, 0‐67 months). The technical success rate was 97%, and 67% of cases were performed completely percutaneously. The ankle‐brachial index improved significantly from 0.65 ± 0.22 preoperatively to 0.88 ± 0.15 after the procedure. The 30‐day minor and major complication rate was 33% and 7%. The median hospital stay was 2 days (range, 1‐76 days). At 1 year and 3 years of follow‐up, 94% and 96% of the patients clinically improved at least one Rutherford category (2% and 0% unchanged, 4% and 4% worsened). Limb salvage rate was 98% at 1 year and 97% at 3 years of follow‐up. Primary, primary assisted, and secondary patency was 86%, 91%, and 97% at 1 year; 84%, 89%, and 97% at 2 years; and 82%, 87%, and 97% at 3 years. Freedom from clinically driven target lesion revascularization was 87% at 1‐year follow‐up and 86% at both 2‐year and 3‐year follow‐up. Conclusions: The CERAB technique is a safe and feasible technique for the treatment of extensive AIOD with good 3‐year results regarding patency and clinical improvement.

A phantom study for the comparison of different brands of computed tomography scanners and software packages for endovascular aneurysm repair sizing and planning

Objectives Correct sizing of endoprostheses used for the treatment of abdominal aortic aneurysms is important to prevent endoleaks and migration. Sizing requires several steps and each step introduces a possible sizing error. The goal of this study was to investigate the magnitude of these errors compared to the golden standard: a vessel phantom. This study focuses on the errors in sizing with three different brands of computed tomography angiography scanners in combination with three reconstruction software packages. Methods Three phantoms with a different diameter, altitude and azimuth were scanned with three computed tomography scanners: Toshiba Aquilion 64-slice, Philips Brilliance iCT 256-slice and Siemens Somatom Sensation 64-slice. The phantom diameters were determined in the stretched view after central lumen line reconstruction by three observers using Simbionix PROcedure Rehearsal Studio, 3mensio and TeraRecon planning software. The observers, all novices in sizing endoprostheses using planning software, measured 108 slices each. Two senior vascular surgeons set the tolerated error margin of sizing on ±1.0 mm. Results In total, 11.3% of the measurements (73/648) were outside the set margins of ±1.0 mm from the phantom diameter, with significant differences between the scanner types (14.8%, 12.1%, 6.9% for the Siemens scanner, Philips scanner and Toshiba scanner, respectively, p-value = 0.032), but not between the software packages (8.3%, 11.1%, 14.4%, p-value = 0.141) or the observers (10.6%, 9.7%, 13.4%, p-value = 0.448). Conclusions It can be concluded that the errors in sizing were independent of the used software packages, but the phantoms scanned with Siemens scanner were significantly more measured incorrectly than the phantoms scanned with the Toshiba scanner. Consequently, awareness on the type of computed tomography scanner and computed tomography scanner setting is necessary, especially in complex abdominal aortic aneurysms sizing for fenestrated or branched endovascular aneurysm repair if appropriate the sizing is of upmost importance.

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.

Native blood speckle vs ultrasound contrast agent for particle image velocimetry with ultrafast ultrasound - in vitro experiments

Ultrafast contrast enhanced ultrasound, combined with echo particle image velocimetry (ePIV), can provide accurate, multidimensional hemodynamic flow field measurement. However, the use of ultrasound contrast agent (UCA) still prevents this method from becoming a truly versatile and non-invasive diagnostic tool. In this study, we investigate the use of native blood instead of UCA backscatter for ePIV measurements and compare their accuracy in vitro. Additionally, the effect of measurement depth is experimentally assessed. Blood mimicking fluid (BMF) was pumped through a 10 mm diameter tube producing parabolic flow profiles, adding UCA in the case of contrast imaging. Plane wave imaging at 5000 frames-per-second was performed with a Verasonics Vantage system and a linear array. The tube was imaged at three different depths: 25, 50 and 100 mm. Singular value decomposition (SVD) was assessed for clutter suppression against mean background subtraction. PIVlab was used as a PIV implementation. With SVD, BMF provided almost equal ePIV accuracy as UCA, except at 100 mm depth where UCA provided better accuracy. Use of clutter suppression greatly improved ePIV results, but minimal differences in ePIV accuracy were noted between mean and SVD filtered groups (BMF or UCA). Accuracy decreased with increasing depth, likely due to reduced elevation resolution, resulting in out-of-plane smoothing of velocity gradients.

High-Frame-Rate Contrast-enhanced US Particle Image Velocimetry in the Abdominal Aorta: First Human Results

Purpose To study the feasibility of high-frame-rate (HFR) contrast material-enhanced (CE) ultrasound particle image velocimetry (PIV), or echo PIV, in the abdominal aorta. Materials and Methods Fifteen healthy participants (six men; median age, 23 years [age range, 18-34 years]; median body mass index, 20.3 kg/m2 [range, 17.3-24.9 kg/m2]) underwent HFR CE US. US microbubbles were injected at incremental doses (0.25, 0.5, 0.75, and 1.5 mL), with each dose followed by US measurement to determine the optimal dosage. Different US mechanical index values were evaluated (0.09, 0.06, 0.03, and 0.01) in a diverging wave acquisition scheme. PIV analysis was performed via pairwise cross-correlation of all captured images. Participants also underwent phase-contrast MRI. The echo PIV and phase-contrast MRI velocity profiles were compared via calculation of similarity index and relative difference in peak velocity. Results Visualization of the aortic bifurcation with HFR CE US was successful in all participants. Optimal echo PIV results were achieved with the lowest contrast agent dose of 0.25 mL in combination with the lowest mechanical indexes (0.01 or 0.03). Substantial bubble destruction occurred at higher mechanical indexes (≥0.06). Flow patterns were qualitatively similar in the echo PIV and MR images. The echo PIV and MRI velocity profiles showed good agreement (similarity index, 0.98 and 0.99; difference in peak velocity, 8.5% and 17.0% in temporal and spatial profiles, respectively). Conclusion Quantification of blood flow in the human abdominal aorta with US particle image velocimetry (echo PIV) is feasible. Use of echo PIV has potential in the clinical evaluation of aortic disease.

Effect of abdominal aortic endoprostheses on arterial pulse wave velocity in an in vitro abdominal aortic flow model

OBJECTIVE Aortic pulse-wave-velocity (aPWV) is a measure for arterial stiffness, which is associated with increased cardiovascular risk. Recent evidence suggests aPWV increases after endograft-placement for aortic aneurysms. The aim of this study was to investigate the influence of different aortic endoprostheses on aPWV and structural stiffness in vitro. APPROACH Three different abdominal aortic endoprostheses (AFX, Endurant II, and Nellix) were implanted in identical silicone aneurysm models. One model was left untreated, and another model contained an aortic tube graft (Gelweave). The models were placed in an in vitro flow set-up that mimics physiological flow. aPWV was measured as the transit time of the pressure wave over the flow trajectory of the suprarenal to iliac segment. Structural stiffness corrected for lumen diameter was calculated for each model. RESULTS aPWV was significantly lower for the control compared to the AFX, Endurant, Nellix and tube graft models (13.00  ±  1.20, 13.40  ±  1.17, 18.18  ±  1.20, 16.19  ±  1.25 and 15.41  ±  0.87 m s-1, respectively (P  <  0.05)). Structural stiffness of the AFX model was significant lower compared to the control model (4718 N m-1 versus 5115 N m-1 (P  <  0.001), respectively), whereas all other models showed higher structural stiffness. SIGNIFICANCE Endograft placement resulted in a higher aPWV compared to a non-treated aortic flow model. All models showed increased structural stiffness over the flow trajectory compared to the control model, except for the AFX endoprosthesis. Future studies in patients treated with an endograft are needed to evaluate the current results in vivo.

In vivo geometry of the kissing stent and covered endovascular reconstruction of the aortic bifurcation configurations in aortoiliac occlusive disease

Objectives Various configurations of kissing stent (KS) configurations exist and patency rates vary. In response the covered endovascular reconstruction of the aortic bifurcation configuration was designed to minimize mismatch and improve outcome. The aim of the current study is to compare geometrical mismatch of kissing stent with the covered endovascular reconstruction of the aortic bifurcation configuration in vivo. Methods Post-operative computed tomographic data and patient demographics from 11 covered endovascular reconstruction of the aortic bifurcation and 11 matched kissing stent patients were included. A free hand region of interest and ellipse fitting method were applied to determine mismatch areas and volumes. Conformation of the stents to the vessel wall was expressed using the D-ratio. Results Patients were mostly treated for Rutherford category 2 and 3 (64%) with a lesion classification of TASC C and D in 82%. Radial mismatch area and volume for the covered endovascular reconstruction of the aortic bifurcation group was significantly lower compared to the kissing stent configuration (P < 0.05). The D-ratio did not significantly differ between groups. Measurements were performed with good intra-class correlation. There were no significant differences in the post-procedural aortoiliac anatomy. Conclusions The present study shows that radial mismatch exists in vivo and that large differences in mismatch exist, in favour of the covered endovascular reconstruction of the aortic bifurcation configuration. Future research should determine if the decreased radial mismatch results in improved local flow profiles and subsequent clinical outcome.