The Significance of Endograft Geometry on the Incidence of Intraprosthetic Thrombus Deposits after Abdominal Endovascular Grafting

Left Renal Artery Chronic Occlusion in the Setting of Extensive Intraprosthetic Mural Thrombus in an Abdominal Aortic Endograft

Thrombotic deposits within aortic endograft post-endovascular aortic aneurysm repair (EVAR) is a fairly well-recognized complication, yet their clinical significance remains inadequately understood. We present a rare case of extensive mural thrombus formation in an oncologic patient with a history of EVAR, emphasizing the importance of lifelong surveillance in abdominal aortic aneurysm (AAA)-EVAR patients. A 75-year-old female was admitted with refractory hypertension secondary to a medium-sized AAA, which exhibited an extensive mural thrombus, contributing to atrophic changes in the left kidney and likely chronic occlusion of the left renal artery. Factors contributing to thrombus formation generally include endograft configuration, aneurysm diameter, and patient-specific characteristics, such as a pro-thrombotic status conferred by metastatic lung cancer. This case underscores the necessity for comprehensive surveillance strategies post-EVAR. Recommendations advocate for a 30-day follow-up and lifelong annual surveillance, employing modalities such as color duplex ultrasound for detection of endoleaks and sac enlargement, with selective use of CT imaging. This case underscores the importance of continued vigilance and surveillance in patients undergoing EVAR, particularly those with complex medical histories, to mitigate potential long-term complications and optimize patient outcomes.

A Retrospective Evaluation of Intra-Prosthetic Thrombus Formation After Endovascular Aortic Repair in Cook Zenith Alpha and Medtronic Endurant II Patients

OBJECTIVE

To investigate the occurrence of limb graft occlusion (LGO) and intra-prosthetic thrombus (IPT) formation in Zenith Alpha and Endurant II stent graft limbs.

METHODS

A single centre retrospective study was conducted on patients treated with the Zenith Alpha and Endurant II stent grafts between 2017 and 2019. All post-operative computed tomography angiography images were re-investigated for thrombus formation. Demographic, aneurysm, and stent graft data were collected and compared. LGO was defined as complete occlusion or significant stenosis (≥ 50% lumen diameter reduction). Logistic regression on pro-thrombotic risk factors was conducted. Freedom from LGO and overall limb IPT were compared using Kaplan-Meier analyses.

RESULTS

Seventy-eight Zenith Alpha and eighty-six Endurant II patients were studied. The median follow up was 33 (IQR 25, 44) months for Zenith Alpha patients and 36 (IQR 22, 46) months for Endurant II patients (p = .53). LGO was seen in 15% (n = 12) of Zenith Alpha patients and 5% (n = 4) of Endurant II patients (p = .032), and freedom from LGO was significantly higher among Endurant II patients (p = .024). The Zenith Alpha stent graft was an independent risk factor for LGO (OR 3.9, 95% CI 1.1 - 13.4; p = .032). Among Zenith Alpha patients, limb flare compression within the main body gate was over represented in LGO patients (p = .011). There was no difference in freedom from overall limb IPT between the stent graft systems. For Endurant II limbs, IPT was significantly less common in the integrated ipsilateral limbs (without ETLW/ETEW stent graft limbs) (p = .044). Main endograft body IPT was correlated with overall limb IPT (p = .035).

CONCLUSION

LGO was significantly more common among Zenith Alpha than Endurant II patients. Zenith Alpha limbs was an independent risk factor for LGO. There was no difference between stent grafts in overall limb IPT formation.

Evaluation of factors associated with limb thrombus formation after endovascular aortic aneurysm repair

BACKGROUND

Limb thrombus formation is a complication that can occur after endovascular aortic repair (EVAR), and its clinical significance has continued to be debated. Our objective was to report the incidence of limb thrombus after EVAR and determine the association of specific demographic, anatomic, and/or graft variables.

METHODS

A retrospective analysis of EVAR patients at a single tertiary center between January 2010 and December 2018 was performed to determine the limb thrombus rate. Demographic, graft, and anatomic variables were analyzed for an association with limb thrombus.

RESULTS

A total of 301 patients were included. The average follow-up was 27.6 ± 4.9 months. The mean age was 76.5 ± 0.5 years, and 85% were men. Limb thrombus occurred in 22 patients (7.3%). Of these 22 patients, 11 (50.0%) had had occlusive limb thrombus, 14 (63.6%) were symptomatic, and 17 (77.3%) had required intervention. The patients with limb thrombus were younger (69.8 ± 1.3 years vs 77.1 ± 0.5 years; P < .0001) and more likely to be smokers (10.2% vs 5.2%; P = .10). The incidence of limb thrombus with the Alpha graft (10.7%; Cook Medical Inc, Bloomington, IN) was compared with that with non-Cook grafts (4.0%; P = .07). The average common iliac artery diameter for patients with and without limb thrombus was 14.1 mm and 16.1 mm, respectively (P < .01). Right-sided limb thrombus was more likely in smaller right iliac arteries (14.7 ± 0.9 cm vs 17.0 ± 0.6 cm; P < .05), with a similar finding on the left (13.6 ± 0.9 cm vs 15.2 ± 0.4 cm; P = .13). Unilateral limb thrombus was almost twice as likely on the main body side than on the contralateral side (11 vs 6). Limb thrombus was not associated with aortoiliac disease (odds ratio [OR], 1.31; 95% confidence interval [CI], 0.37-4.62), limb extension (OR, 0.47; 95% CI, 0.06-3.62), or nonmatching limb heights (OR, 1.36; 95% CI, 0.54-3.43). Limb thrombus was also not associated with increased 30-day mortality (P > .05).

CONCLUSIONS

Limb thrombus formation is a complication that can occur after EVAR (7.3%). In our study, limb thrombus was seen more frequently in younger patients and those who smoked. Cook Alpha grafts had a thrombus formation rate of 10.7%, which was not significantly higher than that with other brands. Limb thrombus was more likely in smaller iliac arteries and on the main body side.

Escalation of Antithrombotic Therapy Should Be Considered in the Presence of Intraluminal Prosthetic Graft Thrombus Following Endovascular Aneurysm Repair

Objectives

Intraluminal prosthetic graft thrombus (IPT) following Endovascular Aneurysm Repair (EVAR) can have serious consequences. The aim of this study was to assess the prevalence of IPT and to identify the risk factors for its formation and progression.

Methods

This was a retrospective study of 258 patients who had EVAR between 2015 and 2018. Demographic data, comorbidities, operative data, antithrombotic therapy, CT anatomical data, IPT characteristics (site, regression, and progression), and re-interventions were collected. Univariable analysis followed by multivariable logistic regression and Cox regression were used for data analysis.

Results

The mean age of patients was 76 years (range 55-95) and 27 (10.5 %) were females. IPT was present in 26 patients (10.1%) with a median time to occurrence of six (range 1- - 24) months. Of the group that developed IPT, six (23.1 %) developed symptoms and two (7.7%) had re-interventions. Multivariable logistic regression analysis revealed peripheral arterial disease to be associated with the formation of IPT (OR 7.4, 95% CI 1.6-35.3, p = 0.02) and escalation of antithrombotic therapy was associated with regression or prevention of progression of IPT (OR 0.1, 95% CI 0.0-0.6, p = 0.01).

Conclusion

PAD is associated with the formation of IPT after EVAR and warrants consideration of escalation of antithrombotic therapy to prevent further progression and complications.

Female gender is associated with increased late luminal narrowing within the stent graft after thoracic endovascular aortic repair

BACKGROUND

Luminal narrowing, suspected secondary to thrombus, occurs within stent grafts at an unclear incidence after thoracic endovascular aortic repair (TEVAR). The significance of this phenomenon has not been determined, nor have the risk factors for development of intragraft luminal narrowing. Small graft diameter is hypothesized to be a risk factor for the development of ingraft stenosis.

METHODS

A retrospective analysis was performed of a multicenter healthcare system including all patients who underwent TEVAR between July 2011 and July 2019 with at least 1 year of subsequently available surveillance contrast-enhanced computed tomography imaging. Standard demographic, preoperative, intraoperative, and postoperative variables were collected. Measurements were obtained via direct off-line images from computed tomography scans. Patent intragraft diameters were compared with baseline and interval change values were normalized to time to follow-up. The primary outcome measure was annual rate of intragraft luminal narrowing.

RESULTS

There were 208 patients who met the inclusion criteria (94 women, 114 men) with a median follow-up of 822 days. The mean annual rate of percent intragraft diameter reduction was 10.5 ± 7.7% for women and 7.6 ± 5.6% for men (P = .0026). Multivariate analysis demonstrated female gender (P = .0283), preoperative diagnosis of hypertension (P = .0449), and need for coverage of the left subclavian artery (P = .0328) were all significant predictors of intragraft luminal narrowing. Small aortic diameters were not found to be associated independently with ingraft luminal narrowing nor was the concomitant use of antiplatelet or anticoagulation medications. Significant amounts of ingraft luminal narrowing, defined as a greater than 20% intragraft diameter decrease, were associated with an increased need for any reintervention, including for malperfusion, endoleak, and symptomatic aneurysm (P = .0249). Kaplan-Meier estimates demonstrated a significant gender-associated difference in high rates of intragraft luminal narrowing (P = .00189).

CONCLUSIONS

In this analysis, female gender is shown to be a significant nonmodifiable risk factor for intragraft luminal narrowing after TEVAR. The development of this phenomenon is not benign; as such, these findings were associated with an increased need for reintervention. This finding may be attributable to differences in aortic compliance or gender-associated differences in coagulation pathways and merits further investigation. Surveillance after thoracic stent grafting must account for patient-specific variations in complication risk.

Thoracic endovascular aortic repair for traumatic aortic injuries: insight from literature and practical recommendations

INTRODUCTION

Thoracic endovascular aortic repair (TEVAR) for treatment of blunt traumatic aortic injuries (BTAIs) is nowadays the gold standard technique in adult patients, replacing gradually the use of open repair (OR). Although randomized controlled trials will never be performed comparing TEVAR to OR for BTAIs management, trauma and vascular societies guidelines today primarily recommend the former for BTAI patients with a suitable anatomy. The aim of this review was to describe past and recent data published in literature regarding pros and cons of TEVAR treatment in BTAI, and to analyze some debated issues and future perspectives.

EVIDENCE ACQUISITION

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and Scale for the Assessment of Narrative Review Articles (SANRA) were used to obtain and describe selected articles on TEVAR in BTAI.

EVIDENCE SYNTHESIS

Young (<50 years) men were the most operated population. The use of TEVAR increased over the years, with a progressive reduction in mortality and overall postoperative complication rates when compared with OR. Lack of information remains about the percentage of urgent cases.

CONCLUSIONS

TEVAR is considered nowadays the treatment of choice in BTAI patients. In case of aortic rupture (grade IV) the treatment is mandatory, while intimal tear (grade I) and intramural hematoma (grade II) can be safely managed with no operative management (NOM). Debate is still ongoing on grade III (pseudoaneurysms). Unfortunately, several aspects remain not yet clarified, including disease classification, type and grade to treat, timing (urgent versus elective), priority of vascular injuries in polytrauma patients, and TEVAR use in pediatrics and young patients.

Prevalence, risk factors and clinical impact of intraprosthetic thrombus deposits after EVAR

BACKGROUND

The aim was to define the prevalence, the evolution and the clinical relevance of the intraprosthetic thrombus deposit (IPT) after endovascular abdominal aortic repair (EVAR).

METHODS

Patients treated with EVAR from 2009 to 2017 for abdominal aortic aneurysm were retrospectively considered. Patients with at least one postoperative computed tomography angiography (CTA) performed after a 3-month follow-up were included. Postoperative medical therapy (antiplatelet and/or oral anticoagulant) were recorded. Aorto-iliac anatomical characteristics were measured on pre-operative CTA, while structural and dimensional endograft features were extracted from instructions for use. IPT was defined as intra-endograft thrombus with minimum thickness of 2mm and longitudinally extended for minimum 4 mm, and was assessed in all postoperative CTA. Primary endpoints were freedom from IPT occurrence, risk factors for IPT and evolution of IPT. Secondary endpoints were the prevalence of overall and IPT-related tromboembolic events (TEE: main-body or limb occlusion, distal embolization) during follow-up and its correlation with IPT.

RESULTS

Two-hundred twenty-one patients (mean age 76±7 years; male 94%) were included. Deployed endografts were: aorto-biiliac 96%, aorto-uniiliac 3%, aortic tube 1%; dacron 90%, ePTFE 10%. Mean follow-up was 30±25 months. Overall IPT prevalence was 36% (80/221). At 6, 12, 24 and 48 months, overall estimated freedom from IPT occurrence was 86%, 80%, 60% and 52%, respectively (Kaplan-Meier analysis). At Cox uni-variate analysis, postoperative medical therapy has no influence on IPT; aorto-iliac anatomical risk factors for IPT were larger neck diameter (P<0.001), severe neck thrombus (P=0.043), higher percentage of sac thrombus (P<0.001), hypogastric occlusion/coverage (P=0.040); endograft risk factors were proximal diameter ≥30mm (P<0.001), longer main body (P=0.002), dacron fabric (P=0.025), higher ratio between main body area/gate areas and main body area/distal iliac areas (P<0.001 and P<0.001, respectively). At Cox multi-variate analysis, independent risk factors for IPT were larger neck diameter (P=0.003), higher percentage of sac thrombus (P=0.005) and longer main body (P=0.028). During follow-up, IPT disappeared in 14 cases (18%). Overall TEE prevalence was 4% (8/221) and overall estimated freedom from TEE occurrence at 6, 12, 24 and 48 months was 99%, 99%, 95.3%, 94.1%, respectively (Kaplan-Meier analysis). TEE was IPT-related in 5/8 cases (63%). No statistical correlation were found between IPT and TEE.

CONCLUSIONS

The development of intraprosthetic graft thrombus (IPT) is a frequent event after EVAR. The risk of IPT is closely correlated with the proximal aortic neck size, the presence of intra-aneurysmal sac thrombus, and the length of the endograft main body. However, there was no statistical correlation between the presence of IPT and TEE.

Customized stent-grafts for endovascular aneurysm repair with challenging necks: A numerical proof of concept

Endovascular aortic repair (EVAR) is a challenging intervention whose long-term success strongly depends on the appropriate stent-graft (SG) selection and sizing. Most off-the-shelf SGs are straight and cylindrical. Especially in challenging vessel morphologies, the morphology of off-the-shelf SGs is not able to meet the patient-specific demands. Advanced manufacturing technologies facilitate the development of highly customized SGs. Customized SGs that have the same morphology as the luminal vessel surface could considerably improve the quality of the EVAR outcome with reduced likelihoods of EVAR related complications such as endoleaks type I and SG migration. In this contribution, we use an in silico EVAR methodology that approximates the deployed state of the elastically deformable SG in a hyperelastic, anisotropic vessel. The in silico EVAR results of off-the-shelf SGs and customized SGs are compared qualitatively and quantitatively in terms of mechanical and geometrical parameters such as stent stresses, contact tractions, SG fixation forces and the SG-vessel attachment. In a numerical proof of concept, eight different vessel morphologies, such as a conical vessel, a barrel shaped vessel and a curved vessel, are used to demonstrate the added value of customized SGs compared to off-the-shelf SGs. The numerical investigation has shown large benefits of the highly customized SGs compared to off-the-shelf SGs with respect to a better SG-vessel attachment and a considerable increase in SG fixation forces of up to 50% which indicate decreased likelihoods of EVAR related complications. Hence, this numerical proof of concept motivates further research and development of highly customized SGs for the use in challenging vessel morphologies.

Impact of Stent Graft Design on External Iliac Artery Limb Occlusion Rates After Endovascular Aneurysm Repair: Post-hoc Analysis of a Japanese Multicentre Database

OBJECTIVE/BACKGROUND

It was hypothesised that a helical stent with expanded polytetrafluoroethylene (ePTFE) grafts could provide a preventive effect for external iliac artery (EIA) limb occlusion following endovascular aortic aneurysm repair (EVAR). Therefore, a post-hoc analysis of a Japanese multicentre database was conducted to assess the impact of the stent graft design on EIA limb occlusion rates.

METHODS

Patients who underwent EVAR with EIA limb deployment between 2008 and 2016 were evaluated. The stent graft limbs were divided into two groups: group A comprised stent graft limbs made of a helical stent with ePTFE grafts (Excluder; n = 255), and group B comprised stent graft limbs made of a Z stent with polyester grafts (Zenith, Flex and Endurant; n = 173). The main outcome was the incidence of limb occlusion and severe limb stenosis (EIA related limb complications). The risk factors for EIA related limb complications were analysed and the midterm results between groups A and B compared. Fine-Gray generalisation of the proportional hazards model was used after propensity score matching to calculate the hazard ratio (HR).

RESULTS

One complication occurred in group A and 10 complications occurred in group B. The risk factors for EIA related limb complications for the entire group were a stent graft limb size ≤10 mm (HR 5.41; p = .01) and inclusion in group B (HR 14.9; p = .009). After propensity matching, group A (n = 159) was matched with group B (n = 159). The cumulative incidence function of EIA related limb complications at five years was 0.66% in group A and 7.8% in group B (HR 8.67; p = .039).

CONCLUSION

Stent graft design can affect limb patency in EIA limb deployment. When EIA limb deployment is necessary for patients with a small EIA, such as Japanese patients, stent graft limbs made of a helical stent with ePTFE should be used to reduce the risk of limb occlusion.

Endograft Specific Haemodynamics After Endovascular Aneurysm Repair: Flow Characteristics of Four Stent Graft Systems

OBJECTIVES

The implication of haemodynamics in the occurrence of complications after endovascular aneurysm repair (EVAR) has been raised in the literature. Different aortic stent graft configurations may lead to different haemodynamic properties. The current study deals with the post-operative haemodynamic variability between four stent graft systems with different structure, material, and type of fixation.

METHODS

Computed tomography data of 32 patients were used, equally distributed among the four endograft groups, namely the AFX, Endurant, Excluder, and Nellix. Velocity, wall shear stress (WSS), and helicity statistics were calculated, in regions around the flow division where disturbances are expected. The haemodynamic data were compared between and within the groups.

RESULTS

The morphology of AAAs pre-operatively did not vary significantly among the four groups. Before the flow division, lowest velocity was observed in Endurant cases and highest in Nellix cases. Endurant induced the lowest peak WSS and Nellix the highest (p = .03). The helicity levels were low in AFX and Nellix cases and high in Endurant and Excluder cases. After the flow division, the trend in the results was preserved. Nellix induced the highest velocity and WSS, followed closely by Excluder and AFX. There was a significant increase of helicity before and after flow division in AFX (p <0.001, R² = 0.09) and Nellix (p <0.001) cases.

CONCLUSIONS

It has been shown that different types of endografts induce variable haemodynamic conditions around the flow division. The parallel limb structure, featured by Nellix, seems to induce favourable flow conditions in terms of velocity and WSS, while helical flow before the flow division is suppressed. High WSS is generally considered to be a desirable flow characteristic in endovascular devices, whereas helicity extremes (very low or high) are potentially a negative sign. Endurant, with the stiffer material and the short neck structure, was associated with the lowest blood velocity and WSS values but preserved high helicity levels. The AFX and Excluder, which include the same material, induced similar haemodynamic conditions.

Significance and Risk Factors for Intraprosthetic Mural Thrombus in Abdominal Aortic Endografts: A Systematic Review and Meta-analysis

BACKGROUND

The detection of intraprosthetic thrombus (IPT) deposits is a common finding during follow-up for endovascular abdominal aneurysm repair (EVAR); however, its clinical significance is still debated. The aim of this study was to determine if IPT represents a risk factor for thromboembolic events (TEs; endograft or limb thrombosis, or distal embolization) after EVAR.

METHODS

A systematic review of English literature was undertaken until November 2017. Studies providing 2-group comparison (patients with IPT development on postoperative computed tomography angiography versus patients without IPT) with extractable outcome data (TE related to IPT and/or risk factors for IPT development) were included. Meta-analysis was performed when comparative data were given in 2 or more articles.

RESULTS

Five single-center studies (808 patients) were analyzed. IPT detection at any time during follow-up occurred in 20.8% (168/808) of patients. Extractable data for postoperative TE were available in 4 studies (613 patients): on comparative meta-analysis, IPT was not significantly associated with TE occurrence during follow-up (odds ratio 2.25, 95% confidence interval [CI] 0.50-10.1; P = 0.29). IPT is generally detected during the first year after EVAR (maximum reported median: 12 months, range: 1.2-23). Polyester graft material (odds ratio 2.34, 95% CI 1.53-3.58; P < 0.001) and aorto-uni-iliac configuration of the endograft (odds ratio 3.27, 95% CI 1.66-6.44; P = 0.001) were confirmed as risk factors for IPT formation on meta-analysis. The literature systematic review suggests that IPT formation may be also associated with long main bodies and large necks.

CONCLUSIONS

IPT detection on postoperative computed tomography angiography was not significantly associated with the occurrence of TE over time. The aorto-uni-iliac configuration and the use of polyester fabric for endografts were confirmed as risk factors for IPT development.

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.

Use of Synchrotron Radiation to Accurately Assess Cross-Sectional Area Reduction of the Aortic Branch Ostia Caused by Suprarenal Stent Wires

PURPOSE

To compare in vivo the use of synchrotron radiation to computed tomography angiography (CTA) for the measurement of cross-sectional area (CSA) reduction of the aortic branch ostia caused by suprarenal stent-graft wires.

METHODS

This study was performed with a Zenith stent-graft placed in a phantom of the human aorta to simulate treatment of abdominal aortic aneurysm. Synchrotron radiation scans were performed using beam energies between 40 and 100 keV and spatial resolution of 19.88 μm per pixel. CSA reduction of the aortic branch ostia by suprarenal stent wires was calculated based on these exposure factors and compared with measurements from CTA images acquired on a 64-row scanner with slice thicknesses of 1.0, 1.5, and 2.0 mm.

RESULTS

Images acquired with synchrotron radiation showed <10% of the CSA occupied by stent wires when a single wire crossed a renal artery ostium and <20% for 2 wires crossing a renovisceral branch ostium. The corresponding areas ranged from 24% to 25% for a single wire and from 40% to 48% for double wires crossing the branch ostia when measured on CT images. The stent wire was accurately assessed on synchrotron radiation with a diameter between 0.38±0.01 and 0.53±0.03 mm, which is close to the actual size of 0.47±0.01 mm. The wire diameter measured on CT images was greatly overestimated (1.15±0.01 to 1.57±0.02 mm).

CONCLUSION

CTA has inferior spatial resolution that hinders accurate assessment of CSA reduction. This experiment demonstrated the superiority of synchrotron radiation over CTA for more accurate assessment of aortic stent wires and CSA reduction of the aortic branch ostia.

A new approach for the pre-clinical optimization of a spatial configuration of bifurcated endovascular prosthesis placed in abdominal aortic aneurysms

Complexity of the spatial configuration of an aortic implant with bifurcation in the distal part is related to changes in blood hemodynamic in the area of bifurcation which may disturb blood flow and lead to thrombus formation. This study was designed to characterize parameters which define spatial configuration of an aortic implant for which the risk of thrombus formation is the smallest. We used AngioCT data from 74 patients, aged 55 ±10 years, after endovascular procedure to prepare 3D geometries of stent-grafts. Computational Fluid Dynamics (CFD) simulations were used to reconstruct blood hemodynamic and simulate thrombus formation. Next, geometric parameters of stent-grafts included the ratio of volume of upper part to the bifurcations, the relation of inlet and outlet diameters of a stent-graft and deformations in the iliac part of the stent-graft were analyzed. We also analyzed tortuosities (spiral twisting of the flow around the flow direction) and bends (the largest angulation in distal part of a stent-graft). The CFD results were confronted with AngioCT data to verify if computer generated thrombus appeared in particular patient. Additionally, geometric parameters of analyzed stent-grafts were used to propose a mathematical tool for prediction of thrombus appearance. The results showed that tortuosities and bends of a stent-graft had the highest impact on thrombus formation. Formation of thrombi was observed in 22% to 31% of cases (at blood hematocrit Hct = 40%) even for small values of tortuosities and bends indicating that these parameters are dominant in determining blood clotting. Our calculated results overlapped with clinical data in 80% to 91%. Therefore, we conclude that tortuosities and bends have high impact on thrombus formation and should be under special attention during stent-graft recommendation and patients’ follow-ups.

Computational fluid dynamics evaluation of the cross-limb stent graft configuration for endovascular aneurysm repair

The technique of crossing the limbs of bifurcated modular stent grafts for endovascular aneurysm repair (EVAR) is often employed in the face of splayed aortic bifurcations to facilitate cannulation and prevent device kinking. However, little has been reported about the implications of cross-limb EVAR, especially in comparison to conventional EVAR. Previous computational fluid dynamics studies of conventional EVAR grafts have mostly utilized simplified planar stent graft geometries. We herein examined the differences between conventional and cross-limb EVAR by comparing their hemodynamic flow fields (i.e., in the "direct" and "cross" configurations, respectively). We also added a "planar" configuration, which is commonly found in the literature, to identify how well this configuration compares to out-of-plane stent graft configurations from a hemodynamic perspective. A representative patient's cross-limb stent graft geometry was segmented using computed tomography imaging in Mimics software. The cross-limb graft geometry was used to build its direct and planar counterparts in SolidWorks. Physiologic velocity and mass flow boundary conditions and blood properties were implemented for steady-state and pulsatile transient simulations in ANSYS CFX. Displacement forces, wall shear stress (WSS), and oscillatory shear index (OSI) were all comparable between the direct and cross configurations, whereas the planar geometry yielded very different predictions of hemodynamics compared to the out-of-plane stent graft configurations, particularly for displacement forces. This single-patient study suggests that the short-term hemodynamics involved in crossing the limbs is as safe as conventional EVAR. Higher helicity and improved WSS distribution of the cross-limb configuration suggest improved flow-related thrombosis resistance in the short term. However, there may be long-term fatigue implications to stent graft use in the cross configuration when compared to the direct configuration.

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

Purpose

To evaluate the flow phenomena within an aortic endograft with crossed-limbs, comparing to an endograft with the ordinary limb bifurcation.

Methods

An endograft model with crossed-limbs was computationally reconstructed based on Computed Tomography patient-specific data, using commercially available software. Accordingly, its analogue model was reconstructed in the ordinary fashion (ordinary bifurcation). Computational fluid dynamics analysis was performed to determine and compare the flow fields, velocity profiles, pressure and shear stress distribution throughout the different parts of both endograft configurations, in different phases of the cardiac cycle.

Results

The flow patterns between the “Ballerina” and the classic endograft were similar, with flow disturbance near the inlet zone at late diastole and smooth flow patterns during the systolic phase. Both configurations presented similar pressure distribution patterns throughout the cardiac cycle. The highest and lowest pressures were demonstrated in the inlet-main body area and the iliac limbs, respectively. Marked differences were observed in the velocity profiles of the proximal limb segments between the two configurations, mostly in the peak- and end-systolic phase. The regions of lower velocities correlated well to low shear values. Differences in the shear stress distribution were noted between the two configurations in the systolic and, predominantly, in the diastolic phase.

Conclusions

There are differences in the velocity profiles and shear distribution between the limbs of the two endograft configurations. The pathophysiologic implication of our findings and their possible association with clinical events, such as thrombus apposition, deserves further investigation.

Late renal artery occlusion following endovascular repair of abdominal aortic aneurysm: a possible complication of mural thrombus formation within aortic endografts

Mural thrombus formation within aortic endoprostheses has been described to occur in up to one-third of aortic endografts depending on the device type. Data regarding the clinical significance of such a phenomenon are scarce, but in most cases it is considered to be clinically innocent. The authors describe a rare case of late renal artery occlusion due to intraprosthetic thrombus formation and extension into the right renal orifice 30 months after endovascular abdominal aortic aneurysm repair. Additionally, a brief literature review regarding the incidence and natural history of mural thrombotic deposits within aortic endografts is also conducted.