Endovascular AAA exclusion: will stents with hooks and barbs prevent stent-graft migration?

FIXATION STUDY OF SINGLE AND DOUBLE STENT GRAFTS FOR ENDOVASCULAR AORTIC REPAIR

Application of double-barreled cannon stent grafts aortic repair (DoBAR) was reported in 2011 for extremely large aortic aneurysms of patients when there was no proper size of grafts for the emergent treatment. Fixation characteristics of the double stent grafts are obtained in a laboratory setting, and are incorporated with those of single Zenith TX2 grafts of sizes from 34 to 42[Formula: see text]mm. Radial stress and shear increase linearly with the oversizing parameter but decrease with increasing stent diameter. The slope of the linear relationship is practically the same for this group of grafts. When the original circular stent grafts of diameter 36 and 38[Formula: see text]mm are deformed to form DoBAR of diameter 44 or 46.4[Formula: see text]mm, the formation could provide higher radial stress and shear to secure fixation for endo-aortic repair. The experimental results of single and DoBAR grafts can be incorporated for clinical application of DoBAR for emergent treatment.

A novel, ring-connected stent versus conventional GI stents: comparative study of physical properties and migration rates in a canine colon obstruction model

BACKGROUND

Migration of stents is one of the most common adverse events in covered stent placement in GI tract obstruction.

OBJECTIVE

To compare physical property and migration rates in a canine colon obstruction model among a novel stent and conventional stents.

DESIGN

Comparative physical test and animal study.

SETTING

Medical device testing laboratory and animal laboratory.

SUBJECTS

Mongrel dogs (N=26).

INTERVENTIONS

Surgical colon obstruction followed by placement of a novel (n=13) or conventional (n=13) stent.

MAIN OUTCOME MEASUREMENTS

Physical properties, migration, and adverse events.

RESULTS

The novel stent showed better flexibility, as in a physical test of longitudinal compressibility and axial force, than did conventional stents, and it withstood the fatigue test for 10 days. In terms of radial force and tensile strength, the novel stent showed the same or better results than conventional stents. In a canine colon obstruction model, the migration rate of a novel stent was significantly lower than that of a conventional stent (2/13, 15.4% vs 8/13, 61.5%; P=.008).

LIMITATIONS

Animal study of limited size.

CONCLUSION

The novel, ring-connected stent is more flexible and more resistant to migration than the conventional stents.

An in Vitro Twist Fatigue Test of Fabric Stent-Grafts Supported by Z-Stents vs. Ringed Stents

Whereas buckling can cause type III endoleaks, long-term twisting of a stent-graft was investigated here as a mechanism leading to type V endoleak or endotension. Two experimental device designs supported with Z-stents having strut angles of 35° or 45° were compared to a ringed control under accelerated twisting. Damage to each device was assessed and compared after different durations of twisting, with focus on damage that may allow leakage. Stent-grafts with 35° Z-stents had the most severe distortion and damage to the graft fabric. The 45° Z-stents caused less fabric damage. However, consistent stretching was still seen around the holes for sutures, which attach the stents to the graft fabric. Larger holes may become channels for fluid percolation through the wall. The ringed stent-graft had the least damage observed. Stent apexes with sharp angles appear to be responsible for major damage to the fabrics. Device manufacturers should consider stent apex angle when designing stent-grafts, and ensure their devices are resistant to twisting.

Role of graft oversizing in the fixation strength of barbed endovascular grafts

PURPOSE

The role of endovascular graft oversizing on risk of distal graft migration following endovascular aneurysm repair for abdominal aortic aneurysm is poorly understood. A controlled in vitro investigation of the role of oversizing in graft-aorta attachment strength for endovascular grafts (EVGs) with barbs was performed.

METHODS

Barbed stent grafts (N = 20) with controlled graft oversizing varying from 4-45% were fabricated while maintaining other design variables unchanged. A flow loop with physiological flow characteristics and a biosynthetic aortic aneurysm phantom (synthetic aneurysm model with a bovine aortic neck) were developed. The stent grafts were deployed into the aortic neck of the bio-synthetic aortic aneurysm phantom under realistic flow conditions. Computed tomography imaging of the graft-aorta complex was used to document attachment characteristics such as graft apposition, number of barbs penetrated, and penetration depth and angle. The strength of graft attachment to the aortic neck was assessed using mechanical pullout testing. Stent grafts were categorized into four groups based on oversizing: 4-10%; 11-20%; 21-30%; and greater than 30% oversizing.

RESULTS

Pullout force, a measure of post-deployment fixation strength was not different between 4-10% (6.23 +/- 1.90 N), 11-20% (6.25 +/- 1.84 N) and 20-30% (5.85 +/- 1.89 N) groups, but significantly lower for the group with greater than 30% oversizing (3.67 +/- 1.41 N). Increasing oversizing caused a proportional decrease in the number of barbs penetrating the aortic wall (correlation = -0.83). Of the 14 barbs available in the stent graft, 89% of the barbs (12.5 of 14 on average) penetrated the aortic wall in the 4-10% oversizing group while only 38% (5.25 of 14) did for the greater than 30% group (P < .001). Also, the stent grafts with greater than 30% oversizing showed significantly poorer apposition characteristics such as eccentric compression or folding of the graft perimeter. The number and depth of barb penetration were found to be positively correlated to pullout force.

CONCLUSION

Greater than 30% graft oversizing affects both barb penetration and graft apposition adversely resulting in a low pullout force in this in vitro model. Barbed stent grafts with excessive oversizing are likely to result in poor fixation and increased risk of migration.

[Aortic stent migration: a rare complication after endovascular repair]

Migration of an aortic stent is one of the most serious complications that can occur during follow-up after endovascular repair of an abdominal aortic aneurysm. We report the case of a 75-year-old man who underwent endovascular treatment for an infra-renal aortic aneurysm using an aorto-mono-iliac stent associated to a femoro-femoral bypass. The angiography performed at the end of procedure showed complete exclusion of the aneurysm. The postoperative course was uneventful. CT scans at 1, 6 and 12 months were normal. The CT scan at the 18th month showed a proximal migration of the stent, which was complicated by a type 1 endoleak and a stent disjunction with a type 3 endoleak. Revision surgery was indicated but the patient died from aneurismal rupture pending treatment. The migration of an aortic stent is a rare but serious complication of endovascular aneurysmal repair. Prevention requires a precise anatomical selection and adequate deployment of the stent graft.

A computational framework for investigating the positional stability of aortic endografts

Endovascular aneurysm repair (Greenhalgh in N Engl J Med 362(20):1863-1871, 2010) techniques have revolutionized the treatment of thoracic and abdominal aortic aneurysm disease, greatly reducing the perioperative mortality and morbidity associated with open surgical repair techniques. However, EVAR is not free of important complications such as late device migration, endoleak formation and fracture of device components that may result in adverse events such as aneurysm enlargement, need for long-term imaging surveillance and secondary interventions or even death. These complications result from the device inability to withstand the hemodynamics of blood flow and to keep its originally intended post-operative position over time. Understanding the in vivo biomechanical working environment experienced by endografts is a critical factor in improving their long-term performance. To date, no study has investigated the mechanics of contact between device and aorta in a three-dimensional setting. In this work, we developed a comprehensive Computational Solid Mechanics and Computational Fluid Dynamics framework to investigate the mechanics of endograft positional stability. The main building blocks of this framework are: (1) Three-dimensional non-planar aortic and stent-graft geometrical models, (2) Realistic multi-material constitutive laws for aorta, stent, and graft, (3) Physiological values for blood flow and pressure, and (4) Frictional model to describe the contact between the endograft and the aorta. We introduce a new metric for numerical quantification of the positional stability of the endograft. Lastly, in the results section, we test the framework by investigating the impact of several factors that are clinically known to affect endograft stability.

Human ex-vivo model of Stanford type B aortic dissection

OBJECTIVE

To report a new human ex vivo model of type B aortic dissection (TBAD) and to assess if the locations of the primary entry tear determine the patterns of dissection propagation.

METHODS

Twenty fresh human aortas were harvested. TBADs were surgically initiated 2 cm below the left subclavian artery at four different locations (lateral, n = 5; medial, n = 5; anterior, n = 5; posterior, n = 5). Aortas were thereafter connected to a bench-top pulsatile flow model to induce antegrade propagation of the dissection.

RESULTS

Antegrade propagation of the dissection was achieved and reached at least the celiac trunk (CT) in all the cases. Dissection was propagated to the renal aorta in 16 (80%) and infrarenal aorta in seven cases (35%). Left renal artery with or without the CT originated more often from the false channel when primary entry tear was lateral. Right renal artery and the CT most often originated from the false channel when primary entry tear was medial. When the CT was the only one originating from the false channel, primary entry tear was more often anterior, whereas when it originated from the true channel, it was more often posterior.

CONCLUSIONS

This human ex vivo model of TBAD is reproducible, since, in all the aortas, extended dissection was achieved and provides the first model of human aortic dissection with infrarenal aorta extension allowing future assessment of endovascular devices developed for human use. Furthermore, it allows clarification of the patterns of aortic dissection propagation and visceral and renal artery involvement according to the site of the primary entry tear.

Respiration-induced deformations of the superior mesenteric and renal arteries in patients with abdominal aortic aneurysms

PURPOSE

To quantify respiration-induced deformations of the superior mesenteric artery (SMA), left renal artery (LRA), and right renal artery (RRA) in patients with small abdominal aortic aneurysms (AAAs).

MATERIALS AND METHODS

Sixteen men with AAAs (age 73 y ± 7) were imaged with contrast-enhanced magnetic resonance angiography during inspiratory and expiratory breath-holds. Centerline paths of the aorta and visceral arteries were acquired by geometric modeling and segmentation techniques. Vessel translations and changes in branching angle and curvature resulting from respiration were computed from centerline paths.

RESULTS

With expiration, the SMA, LRA, and RRA bifurcation points translated superiorly by 12.4 mm ± 9.5, 14.5 mm ± 8.8, and 12.7 mm ± 6.4 (P < .001), and posteriorly by 2.2 mm ± 2.7, 4.9 mm ± 4.2, and 5.6 mm ± 3.9 (P < .05), respectively, and the SMA translated rightward by 3.9 mm ± 4.9 (P < .01). With expiration, the SMA, LRA, and RRA angled upward by 9.7° ± 6.4, 7.5° ± 7.8, and 4.9° ± 5.3, respectively (P < .005). With expiration, mean curvature increased by 0.02 mm(-1) ± 0.01, 0.01 mm(-1) ± 0.01, and 0.01 mm(-1) ± 0.01 in the SMA, LRA, and RRA, respectively (P < .05). For inspiration and expiration, RRA curvature was greater than in other vessels (P < .025).

CONCLUSIONS

With expiration, the SMA, LRA, and RRA translated superiorly and posteriorly as a result of diaphragmatic motion, inducing upward angling of vessel branches and increased curvature. In addition, the SMA exhibited rightward translation with expiration. The RRA was significantly more tortuous, but deformed less than the other vessels during respiration.

Respiratory-induced 3D deformations of the renal arteries quantified with geometric modeling during inspiration and expiration breath-holds of magnetic resonance angiography

PURPOSE

To quantify renal artery deformation due to respiration using magnetic resonance (MR) image-based geometric analysis.

MATERIALS AND METHODS

Five males were imaged with contrast-enhanced MR angiography during inspiratory and expiratory breath-holds. From 3D models of the abdominal aorta, left and right renal arteries (LRA and RRA), we quantified branching angle, curvature, peak curve angle, axial length, and locations of branch points.

RESULTS

With expiration, maximum curvature changes were 0.054 ± 0.025 mm(-1) (P < 0.01), and curve angle at the most proximal curvature peak increased by 8.0 ± 4.5° (P < 0.05) in the LRA. Changes in maximum curvature and curve angles were not significant in the RRA. The first renal bifurcation point translated superiorly and posteriorly by 9.7 ± 3.6 mm (P < 0.005) and 3.5 ± 2.1 mm (P < 0.05), respectively, in the LRA, and 10.8 ± 6.1 mm (P < 0.05) and 3.6 ± 2.5 mm (P < 0.05), respectively, in the RRA. Changes in branching angle, axial length, and renal ostia locations were not significant.

CONCLUSION

The LRA and RRA deformed and translated significantly. Greater deformation of the LRA as compared to the RRA may be due to asymmetric anatomy and mechanical support by the inferior vena cava. The presented methodology can extend to quantification of deformation of diseased and stented arteries to help renal artery implant development.

Role of aortic stent graft oversizing and barb characteristics on folding

OBJECTIVE

To evaluate folding in infrarenal stent grafts in relation to oversizing, barb angle, and barb length using computed tomography images of stent grafts deployed in explanted bovine aortas.

METHODS

Computed tomography data from an in vitro investigation on the effect of oversizing of 4% to 45% (n = 19), barb length of 2 to 7 mm (n = 11), and barb angle of 10° to 90° (n = 7) on device fixation were examined for instances of folding. Folding was classified as circumferential or longitudinal and quantified on an ordinal scale based on codified criteria. Cumulative fold ranking from 0 (no fold) to 6 (two severe folds) for each deployment was used as the measure of folding observed.

RESULTS

Of the 37 cases, cumulative mean ± standard deviation fold ranking for stent grafts oversized >30% (n = 5) was significantly greater than the rest (3.4 ± 1.7 vs 0.5 ± 1.2, respectively; Mann-Whitney U test; P < .005). When barb length was varied from 2 to 7 mm (oversizing held at 10%-20%), folding was noted in one of 11 cases. Similarly, when barb angle was varied from 0° (vertical) to 90° (horizontal), folding was not noted in any of the seven cases. The pullout force was not significantly different between stent grafts with and without folding (5.4 ± 1.95 vs 5.12 ± 1.89 N, respectively; P > .5). At least one instance of folding was noted in the seven of seven (100%) stent grafts with oversizing >23.5% and in only five of 30 (14%) stent grafts with oversizing <23.5%.

CONCLUSIONS

Stent graft folding was prevalent when oversized >30%. Large variations in barb length and angle did not aggravate folding risk when oversized within the recommended range of 10% to 20%.

Determination of coefficient of friction for self-expanding stent-grafts

Migration of stent-grafts (SGs) after endovascular aneurysm repair of abdominal aortic aneurysms is a serious complication that may require secondary intervention. Experimental, analytical, and computational studies have been carried out in the past to understand the factors responsible for migration. In an experimental setting, it can be very challenging to correctly capture and understand the interaction between a SG and an artery. Quantities such as coefficient of friction (COF) and contact pressures that characterize this interaction are difficult to measure using an experimental approach. This behavior can be investigated with good accuracy using finite element modeling. Although finite element models are able to incorporate frictional behavior of SGs, the absence of reliable values of coefficient of friction make these simulations unreliable. The aim of this paper is to demonstrate a method for determining the coefficients of friction of a self-expanding endovascular stent-graft. The methodology is demonstrated by considering three commercially available self-expanding SGs, labeled as A, B, and C. The SGs were compressed, expanded, and pulled out of polymeric cylinders of varying diameters and the pullout force was recorded in each case. The SG geometries were recreated using computer-aided design modeling and the entire experiment was simulated in ABAQUS 6.8/STANDARD. An optimization procedure was carried out for each SG oversize configuration to determine the COF that generated a frictional force corresponding to that measured in the experiment. The experimental pullout force and analytically determined COF for SGs A, B, and C were in the range of 6-9 N, 3-12 N, and 3-9 N and 0.08-0.16, 0.22-0.46, and 0.012-0.018, respectively. The computational model predicted COFs in the range of 0.00025-0.0055, 0.025-0.07, and 0.00025-0.006 for SGs A, B, and C, respectively. Our results suggest that for SGs A and B, which are exoskeleton based devices, the pullout forces increase upto a particular oversize beyond which they plateau, while pullout forces showed a continuous increase with oversize for SG C, which is an endoskeleton based device. The COF decreased with oversizing for both types of SGs. The proposed methodology will be useful for determining the COF between self-expanding stent-grafts from pullout tests on human arterial tissue.

Biomechanical and histologic analysis in aortic endoprosthesis using fibrin glue

BACKGROUND

The absence of incorporation between endoprosthesis (EP) and the arterial wall may lead to device migration and endoleaks around the stent graft. Alternatives have been tested aiming to improve this incorporation. Fibrin glue is used in many operating procedures promoting adhesion and tissue regeneration; however, its use to improve EP incorporation by arteries is unknown.

OBJECTIVE

The objective of this study was to analyze dislodgement forces needed to extract the EPs implanted in pig aorta, compare different oversizing and fibrin glue injections, and to analyze histologic changes among groups.

METHODS

Straight EPs were implanted in the thoracic aorta of pigs using 10% oversizing plus fibrin glue in the interface between the EP and the artery (group 1), using 20% oversizing (group 2), and 10% oversizing (group 3). Fourteen days after the implant, the animals were killed to enable biomechanical analysis of the EP and to verify histologic changes of the aortic wall and its interface with the EP.

RESULTS

Group 1 showed a dislodgement force of 21.9 ± 5.3 Newton (N) being higher than the other groups and statistically significant when compared to group 3 (15.6 ± 3.6N), P = .003%. Group 2 had a higher dislodgement force and statistically more significant than group 3 (19.5 ± 7.8N). Histologic analysis showed tissue reaction with inflammatory cells and fibroblasts higher in group 1 and group 2 compared to group 3.

CONCLUSION

This study reports a large animal survival model of thoracic aortic stent graft placement by testing the impact of fibrin glue on EP incorporation. Compared to oversizing alone, fibrin glue placed between the stent graft and the arterial wall increases EP incorporation. Additional studies are needed to determine the potential utility of fibrin glue in the setting of human arterial endografts.

The effect of vessel material properties and pulsatile wall motion on the fixation of a proximal stent of an endovascular graft

Migration is a serious failure mechanism associated with endovascular abdominal aortic aneurysm (AAA) repair (EVAR). The effect of vessel material properties and pulsatile wall motion on stent fixation has not been previously investigated. A proximal stent from a commercially available stent graft was implanted into the proximal neck of silicone rubber abdominal aortic aneurysm models of varying proximal neck stiffness (β=25.39 and 20.44). The stent was then dislodged by placing distal force on the stent struts. The peak force to completely dislodge the stent was measured using a loadcell. Dislodgment was performed at ambient pressure with no flow (NF) and during pulsatile flow (PF) at pressures of 120/80 mmHg and 140/100 mmHg to determine if pulsatile wall motions affected the dislodgement force. An imaging analysis was performed at ambient pressure and at pressures of 120 mmHg and 140 mmHg to investigate diameter changes on the model due to the radial force of the stent and internal pressurisation. Stent displacement forces were ~50% higher in the stiffer model (7.16-8.4 N) than in the more compliant model (3.67-4.21 N). The mean displacement force was significantly reduced by 10.95-12.83% from the case of NF to the case of PF at 120/80 mmHg. A further increase in pressure to 140/120 mmHg had no significant effect on the displacement force. The imaging analysis showed that the diameter in the region of the stent was 0.37 mm greater in the less stiff model at all the pressures which could reduce the fixation of the stent. The results suggest that the fixation of passively fixated aortic stents could be comprised in more compliant walls and that pulsatile motions of the wall can reduce the maximum stent fixation.

Fatores envolvidos na migração das endopróteses em pacientes submetidos ao tratamento endovascular do aneurisma da aorta abdominal

A migração da endoprótese é complicação do tratamento endovascular definida como deslocamento da ancoragem inicial. Para avaliação da migração, verifica-se a posição da endoprótese em relação a determinada região anatômica. Considerando o aneurisma da aorta abdominal infrarrenal, a área proximal de referência consiste na origem da artéria renal mais baixa e, na região distal, situa-se nas artérias ilíacas internas. Os pacientes deverão ser monitorizados por longos períodos, a fim de serem identificadas migrações, visto que estas ocorrem normalmente após 2 anos de implante. Para evitar migrações, forças mecânicas que propiciam fixação, determinadas por características dos dispositivos e incorporação da endoprótese, devem predominar sobre forças gravitacionais e hemodinâmicas que tendem a arrastar a prótese no sentido caudal. Angulação, extensão e diâmetro do colo, além da medida transversa do saco aneurismático, são importantes aspectos morfológicos do aneurisma relacionados à migração. Com relação à técnica, não se recomenda implante de endopróteses com sobredimensionamento excessivo (> 30%), por provocar dilatação do colo do aneurisma, além de dobras e vazamentos proximais que também contribuem para a migração. Por outro lado, endopróteses com mecanismos adicionais de fixação (ganchos, farpas e fixação suprarrenal) parecem apresentar menos migrações. O processo de incorporação das endopróteses ocorre parcialmente e parece não ser suficiente para impedir migrações tardias. Nesse sentido, estudos experimentais com endopróteses de maior porosidade e uso de substâncias que permitam maior fibroplasia e aderência da prótese à artéria vêm sendo realizados e parecem ser promissores. Esses aspectos serão discutidos nesta revisão.

AAA stent-grafts: past problems and future prospects

Endovascular aneurysm repair (EVAR) has quickly gained popularity for infrarenal abdominal aortic aneurysm repair during the last two decades. The improvement of available EVAR devices is critical for the advancement of patient care in vascular surgery. Problems are still associated with the grafts, many of which can necessitate the conversion of the patient to open repair, or even result in rupture of the aneurysm. This review attempts to address these problems, by highlighting why they occur and what the failings of the currently available stent grafts are, respectively. In addition, the review gives critical appraisal as to the novel methods required for dealing with these problems and identifies the new generation of stent grafts that are being or need to be designed and constructed in order to overcome the issues that are associated with the existing first- and second-generation devices.

Endovascular stent graft repair of abdominal aortic aneurysms: Current status and future directions

Endovascular stent graft repair of abdominal aortic aneurysm (AAA) has undergone rapid developments since it was introduced in the early 1990s. Two main types of aortic stent grafts have been developed and are currently being used in clinical practice to deal with patients with complicated or unsuitable aneurysm necks, namely, suprarenal and fenestrated stent grafts. Helical computed tomography angiography has been widely recognized as the method of choice for both pre-operative planning and post-operative follow-up of endovascular repair (EVAR). In addition to 2D axial images, a number of 2D and 3D reconstructions are generated to provide additional information about imaging of the stent grafts in relation to the aortic aneurysm diameter and extent, encroachment of stent wires to the renal artery ostium and position of the fenestrated vessel stents. The purpose of this article is to provide an overview of applications of EVAR of AAA and diagnostic applications of 2D and 3D image visualizations in the assessment of treatment outcomes of EVAR. Interference of stent wires with renal blood flow from the hemodynamic point of view will also be discussed, and future directions explored.

The proximal fixation strength of modern EVAR grafts in a short aneurysm neck. An in vitro study

OBJECTIVES

The study aims to measure the strength of the proximal fixation of endografts in short and long necks.

DESIGN

Three types of endografts were compared: Gore Excluder, Vascutek Anaconda and Medtronic Endurant.

MATERIALS AND METHODS

The proximal part of the stent grafts was inserted in bovine arteries and the graft was then attached to a tensile testing machine. The force to obtain dislodgement (DF) from the aorta was recorded for each graft at proximal seal lengths of 10 and 15 mm.

RESULTS

The median DF (interquartile range, IQR) for the Excluder, the Anaconda and the Endurant with a seal length of 15 mm was: 11.8 (10.5-12.0) N, 20.8 (18.0-30.1) N and 10.7 (10.4-11.3) N. With the shorter proximal seal of 10mm, DF was, respectively: 6.0 (4.5-6.6) N, 17.0 (11.2-36.6) N and 6.4 (6.1-12.0) N.

CONCLUSIONS

The proximal fixation of the Anaconda is superior to the Excluder and the Endurant at short necks of 10 and 15 mm in an experimental set-up. There is a statistically significant decrease of proximal fixation for the Excluder stent graft, when decreasing the length of the proximal neck from 15 to 10 mm.

Fluid-Structure Interaction Analyses of Stented Abdominal Aortic Aneurysms

Rupture of abdominal aortic aneurysms (AAAs) alone is the thirteenth leading cause of death in the United States. Thus, reliable AAA-rupture risk prediction is an important advancement. If repair becomes necessary, the minimally invasive technique of inserting a stent-graft (SG), commonly referred to as endovascular aneurysm repair (EVAR), is a viable option in many cases. However, postoperative complications, such as endoleaks and/or SG migration, may occur. Computational fluid-structure interaction simulations provide physical insight into the hemodynamics coupled with multi-wall mechanics' function as an assessment tool for optimal SG placement and improved device design.

Transrenal Fixation of Aortic Stent-Grafts: Short- to Midterm Effects on Renal Function—A Systematic Review

PURPOSE

To perform a systematic review of the short- to midterm effects of transrenal fixation of aortic stent-grafts on renal function in patients with abdominal aortic aneurysms.

MATERIALS AND METHODS

A search of the PubMed, MEDLINE, and EMBASE databases for English-language literature was performed. Studies with at least 10 patients were included for data analysis. Only studies on transrenal fixation of aortic stent-grafts that included follow-up results for renal function were included. A log-linear model was used for meta-analysis to compare transrenal fixation with infrarenal fixation.

RESULTS

Twenty-two studies met the inclusion criteria. Because two studies analyzed the same group of patients, one was excluded, for a total of 21 studies. Comparisons between transrenal fixation and infrarenal fixation were found in seven studies. For transrenal versus infrarenal fixation, the combined odds ratio, 95% confidence interval, and P value were found to be statistically significant with respect to postprocedural renal infarction only (combined odds ratio, 5.189; 95% confidence interval: 3.198, 8.420; P < .001). No significant difference was found between transrenal and infrarenal fixation with respect to renal dysfunction, renal artery occlusion, or endoleaks (P > .05).

CONCLUSION

Transrenal fixation of aortic stent-grafts seems to be a relatively safe alternative compared with infrarenal fixation in terms of short- to midterm follow-up. Postprocedural renal infarction, however, was significantly higher for transrenal fixation.

Three-dimensional visualization of suprarenal aortic stent-grafts: evaluation of migration in midterm follow-up

PURPOSE

To investigate the midterm results of transrenal fixation of abdominal aortic stent-grafts with regard to device migration and encroachment of stent wires on the renal and visceral branches.

METHODS

Imaging data from 18 patients (15 men; mean age 75 years, range 63-84) undergoing transrenal stent-graft fixation for abdominal aortic aneurysm (AAA) were included in the study. Computed tomographic angiographic data acquired within 1 week of stent-graft implantation were compared to the latest follow-up images. Postprocessing methods generated 3-dimensional (3D) maximum intensity projections (MIP) and virtual intravascular endoscopy (VIE) for evaluation of the relationship between suprarenal stents and aortic branches. Aortic neck angulation was measured in each patient for correlation with the incidence of stent migration.

RESULTS

The mean follow-up period was 40 months. 3D image visualizations showed that the stent-graft moved caudally in all patients (range 2.6-14.2 mm), with migration (>10 mm) observed in 4 (22%) patients. Corresponding VIE images documented changes in stent wire encroachment on the aortic branch ostia in 11 patients, including the number and position of crossing stent wires. There was no close relationship between aortic neck angulation and stent migration.

CONCLUSION

The current study demonstrated that migration occurs at midterm follow-up in transrenally deployed stent-grafts. 3D images were valuable for the assessment of stent migration, as well as its relationship with aortic branch ostia. Long-term follow-up of transrenal fixation deserves to be investigated, especially after observing stent migration relative to aortic ostial encroachment.

Effects of flat, parabolic and realistic steady flow inlet profiles on idealised and realistic stent graft fits through Abdominal Aortic Aneurysms (AAA)

Computational fluid dynamics modelling of bifurcated stent grafts positioned across Abdominal Aortic Aneursysms (AAAs) is influenced significantly by the boundary conditions and geometry. To assess these influencing factors, simulations using three different steady inlet profiles and two geometries were run. The steady velocity inlet profiles (flat, parabolic and realistic) were used as input boundary conditions with a constant pressure outlet for each model. The geometry of an out-of-plane realistic stent graft model, fitted to the internal geometry of an AAA (a realistic geometry generated from CT scans) was compared to an idealised geometry of an in-plane model. It was found that the realistic boundary condition when applied to the idealised model had a 5% difference in outlet flow rates when compared to flat and parabolic inlet profiles, while the realistic models had an 11-16% difference. The blood flowed in a parallel streamlined fashion for all the idealised models with slight recirculation for the realistic boundary condition. All realistic models had significant recirculation and flowed in a left-handed helix motion in the proximal end and left leg and in a right-handed helix motion in the right leg. The drag force was unidirectional in the idealised models, while it was found to act in all three directions for the realistic models with a 26% increase over the idealised models. It was concluded that geometry has the greatest influence on the outlet flow rates, flow patterns and drag forces. Input boundary condition cause variations in the skewness and recirculation of the flow throughout the models.

Endoleakage after endovascular treatment of abdominal aortic aneurysms: diagnosis, significance and treatment

Endoleak, also called leakage, leak and Perigraft leak, is a major complication and its persistence represents a failure of endovascular aortic aneurysm repair. Its detection and treatment is therefore of primary importance, since endoleak can be associated with pressurization (increase in pressure) of the sac, resulting in expansion and rupture of the aneurysm. The aim of this paper is to discuss the definition, significance, diagnosis and different options to treat endoleak.

Introduction to biomechanics related to endovascular repair of abdominal aortic aneurysm

Biomechanical issues of practical relevance to the physician in the clinical management of patients undergoing endovascular repair (EVR) of their abdominal aortic aneurysms (AAA) is discussed. Following a brief description of key terms in vascular biomechanics, background on the current state of knowledge in the biomechanics of AAA pathogenesis and rupture is provided. This is followed by a discussion of key issues of biomechanical relevance in EVR such as the mechanics of endotension, the notion of intraaneurysmal sac pressure and potential pitfalls of techniques used to measure them, mechanics of graft fracture/kinking, and graft migration. The discussions are intended to provide an overview of this field to physicians.

Initial and Midterm Results for Repair of Aortic Diseases With Handmade Stent Grafts

BACKGROUND

The purpose of this study was to determine the initial and midterm results for repair of thoracic and abdominal aortic diseases using handmade stent-grafts (SGs).

METHODS AND RESULTS

Between 1999 and 2004, 41 consecutive patients (31 patients with thoracic and 10 patients with abdominal aortic disease) underwent endovascular stent-graft repair using handmade SGs. The follow-up averaged 24.8+/-17.6 months. The technical and initial clinical success rates were 82.9% (34/41) and 80.5% (33/41), respectively. Primary type I or III endoleaks occurred in 12.2% (5/41) of the patients. The hospital mortality rate was 4.9% (2/41). Persistent type I or III endoleaks occurred in 9.8% (4/41) and SG migrations occurred in 4.9% (2/41) of the patients. Open surgical conversion was undertaken in 12.2% (5/41) of the patients because of an endoleak and/or migration. The mean change observed in the aneurysm diameter was -6.2+/-10.5 mm, and shrinkage in the diameter occurred in 51.4% (18/35) of the cases. There was 1 patient death because of aneurysm rupture. Neither stent fracture nor graft hole was observed. The overall clinical success rate during follow-up was 78.0% (32/41).

CONCLUSION

The initial and midterm results obtained after repair of the aortic diseases using handmade SGs were considered to be satisfactory. More surgical experience and long-term patient follow-up are both required to further reassess the effect of this treatment.