Stent-Graft Migration:A Reappraisal of Analysis Methods and Proposed Revised Definition

Real world experience with the TREO device in standard EVAR: Mid-term results of 150 cases from a German Multicenter study

Background: The objective of the study was to analyze mid-term results of unselected patients treated with the TREO (Terumo Aortic, Florida, USA) device at six German hospital sites. Methods: A multicenter, retrospective analysis of patients treated within and outside instructions for use (IFU) from January 2017 to November 2020 was performed. Primary outcomes were technical success, mortality and endograft related complications according to IFU status. Secondary outcomes were aneurysm/procedure related re-interventions. Results: 150 patients (92% male, mean age 73 ±8 years) were treated (within IFU 84% vs. outside IFU 16%) with the TREO device for abdominal aortic aneurysms (n=127 intact, n=17 symptomatic and n=6 ruptured; p=0.30). Technical success was achieved in 147/150 (within IFU 99% vs. outside IFU 92%, p=0.08). 30-day mortality was 2%, one year and overall mortality was 3% and 5%. During a mean follow-up of 28.4 months (range: 1-67.4 months), 35 (25%; within IFU 23% vs. outside IFU 35%, p=0.23) patients suffered from endoleaks. The majority were endoleaks type II (n=33), the remaining type Ia (n=5) and type Ib (n=3). No endoleaks type III-V, migrations or aneurysm ruptures occurred. Overall, 19 patients (13%; within IFU 13% vs. 15% outside IFU, p=0.70) received a secondary intervention: nine endoleak related endovascular procedures, three open conversions, two endograft limb related interventions, four surgical revisions of the femoral access sites and two bowl ischemia related procedures, respectively. Conclusions: This non industry-sponsored, multicenter trial indicates that using the TREO device in a real-world setting (both within and outside IFU) seems feasible in the treatment of patients suffering from AAA. While the rate of complications and secondary interventions is in line with previously published data, the findings highlight the fact that standard EVAR is associated with serious adverse events.

Treatment of Complete Displacement of the Bilateral Legs into an Aortic Aneurysm Using an Iliac Branch Device

PURPOSE

Migration is a major cause of reintervention after endovascular aneurysm repair (EVAR). In patients with common iliac artery (CIA) dilation due to proximal migration of the iliac limb, internal iliac blood flow can be preserved by implanting an iliac branch device (IBD).

CASE REPORT

In this report, we discuss the case of a patient in whom the bilateral limbs were completely displaced into the aortic aneurysm due to proximal migration of the iliac limb after EVAR. By taking advantage of the characteristics of this migration, we formed a pull-through wire through the native terminal aorta without passing through the flow divider of the stent graft, and the IBD was deployed safely.

CONCLUSION

The present case indicates that the preservation of at least 1 internal iliac artery is possible in patients with CIA dilation due to proximal migration of the iliac limb. However, the unique features of each case must be considered to determine the appropriate approach.

Endovascular Outcomes in Aortic Arch Repair with Double and Triple Parallel Stent Grafts

PURPOSE

To report early and midterm outcomes of treating thoracic aortic aneurysm (TAA) and aortic dissection (AD) involving zone 1 and zone 0 with multiple parallel stent grafts (PSGs).

MATERIALS AND METHODS

From February 2011 to August 2018, 31 of 1,806 patients (1.7%) who underwent thoracic endovascular aortic repair (TEVAR) with double PSGs (DPSGs) (n = 20) or triple PSGs (TPSGs) (n = 11) were retrospectively reviewed. Procedures were performed in high-risk patients who had TAA or AD involving zone 1 or zone 0.

RESULTS

Fifteen patients (48.4%) who presented with symptomatic or impending rupture underwent urgent or emergent TEVAR with DPSGs or TPSGs. Nineteen patients (61.3%) were treated for zone 0 disease. Technical and clinical success rates were 70.0% for DPSG cohort and 45.5% for TPSG cohort. Intraoperative type Ia endoleak was observed in 30% of DPSG cohort and 45.5% of TPSG cohort. One patient in the DPSG cohort died of aortic sinus rupture intraoperatively. Minor stroke during the 30-day postoperative period was more frequent in the TPSG cohort (P = .042). Mean duration of follow-up was 28.9 months ± 17.7. The TPSG cohort had a higher incidence of major adverse events (72.7% vs 25.0%, P = .021). The most common adverse events were endoleaks (12.9%), endograft migration (9.7%), PSG stenosis or occlusion (6.5%), retrograde dissection (6.5%), and stroke (3.2%). Endograft migrations were more common in TPSG cohort (27.3%, P = .037). Overall mortality rate was 16.1% (5/31) perioperatively and during follow-up. There were no statistical differences in overall survival and reintervention-free survival.

CONCLUSIONS

In the context of TEVAR with multiple PSGs for aortic arch repair, TPSGs may have a high risk of major complications.

g. Scholten G, Kuipers H, Slump CH, de Vries JPPM. Effect of Different EndoAnchor Configurations on Aortic Endograft Displacement Resistance: An Experimental Study

Purpose: This study investigated the effect of different EndoAnchor configurations on aortic endograft displacement resistance in an in vitro model. Materials and Methods: An in vitro model was developed and validated to perform displacement force measurements on different EndoAnchor configurations within an endograft and silicone tube. Five EndoAnchor configurations were created: (1) 6 circumferentially deployed EndoAnchors, (2) 5 EndoAnchors within 120° of the circumference and 1 additional, contralateral EndoAnchor, (3) 4 circumferentially deployed EndoAnchors, (4) 2 rows of 4 circumferentially deployed EndoAnchors, and (5) a configuration of 2 columns of 3 EndoAnchors. An experienced vascular surgeon deployed EndoAnchors under C-arm guidance at the proximal sealing zone of the endograft. A constant force with increments of 1 newton (N) was applied to the distal end of the endograft. The force necessary to displace a part of the endograft by 3 mm was defined as the endograft displacement force (EDF). Two video cameras recorded the measurements. Videos were examined to determine the exact moment 3-mm migration had occurred at part of the endograft. Five measurements were performed after each deployed EndoAnchor for each configuration. Measurements are given as the median and interquartile range (IQR) Q1, Q3. Results: Baseline displacement force measurement of the endograft without EndoAnchors resulted in a median EDF of 5.1 N (IQR 4.8, 5.2). The circumferential distribution of 6 EndoAnchors resulted in a median EDF of 53.7 N (IQR 49.0, 59.0), whereas configurations 2 through 5 demonstrated substantially lower EDFs of 29.0 N (IQR 28.5, 30.1), 24.6 N (IQR 21.9, 27.2), 36.7 N, and 9.6 N (IQR 9.4, 10.0), respectively. Decreasing the distance between the EndoAnchors over the circumference of the endograft increased the displacement resistance. Conclusion: This in vitro study demonstrates the influence EndoAnchor configurations have on the displacement resistance of an aortic endograft. Parts of the endograft where no EndoAnchor has been deployed remain sensitive to migration. In the current model, the only configuration that rivaled a hand-sewn anastomosis was the one with 6 EndoAnchors. A circumferential distribution of EndoAnchors with small distances between EndoAnchors should be pursued, if possible. This study provides a quantification of different EndoAnchor configurations that clinicians may have to adopt in clinical practice, which can help them make a measured decision on where to deploy EndoAnchors to ensure good endograft fixation.

Determination of Stent Frame Displacement After Endovascular Aneurysm Sealing

Purpose: To describe and validate a new methodology for visualizing and quantifying 3-dimensional (3D) displacement of the stent frames of the Nellix endosystem after endovascular aneurysm sealing (EVAS). Methods: The 3D positions of the stent frames were registered to 5 fixed anatomical landmarks on the post-EVAS computed tomography (CT) scans, facilitating comparison of the position and shape of the stent frames between consecutive follow-up scans. Displacement of the proximal and distal ends of the stent frames, the entire stent frame trajectories, as well as changes in distance between the stent frames were determined for 6 patients with >5-mm displacement and 6 patients with <5-mm displacement at 1-year follow-up. The measurements were performed by 2 independent observers; the intraclass correlation coefficient (ICC) was used to determine interobserver variability. Results: Three types of displacement were identified: displacement of the proximal and/or distal end of the stent frames, lateral displacement of one or both stent frames, and stent frame buckling. The ICC ranged from good (0.750) to excellent (0.958). No endoleak or migration was detected in the 12 patients on conventional CT angiography at 1 year. However, of the 6 patients with >5-mm displacement on the 1-year CT as determined by the new methodology, 2 went on to develop a type Ia endoleak in longer follow-up, and displacement progressed to >15 mm for 2 other patients. No endoleak or progressive displacement was appreciated for the patients with <5-mm displacement. Conclusion: The sac anchoring principle of the Nellix endosystem may result in several types of displacement that have not been observed during surveillance of regular endovascular aneurysm repairs. The presented methodology allows precise 3D determination of the Nellix endosystems and can detect subtle displacement better than standard CT angiography. Displacement >5 mm on the 1-year CT scans reconstructed with the new methodology may forecast impaired sealing and anchoring of the Nellix endosystem.

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.

Systematic review and meta-analysis of migration after endovascular abdominal aortic aneurysm repair

Aim

To identify patients who are under higher threat for migration because of an old generation stent graft application.

Methods

A systematic review and meta-analysis of the literature was undertaken to identify all studies which included older generation endografts and data reporting on graft migration after EVAR. Outcome data were pooled and combined, and were calculated using fixed or random effects models.

Results

From 2000 to 2014, 22 retrospective studies were identified reporting on stent- graft migration after EVAR (8.6%). From those patients, 39% received re-intervention with the mean time of identification ranging from 12 to 36 months. Six of these retrospective nonrandomized studies were eligible for meta-analysis. AAA diameter (AAA diameter: 0.719 mm; 95% confidence interval [CI]: 0.00065–1.4384 mm; p = 0.00497) and neck length (neck length: 4.36 mm; 95% CI: 1.3277–7.394; p = 0.0048) were the only significant factors associated with stent- graft migration. Neck diameter and neck angulation did not have any important influence on stent-graft migration.

Conclusions

Patients with large AAA and short necks who were treated with older generation stent grafts such as AneurX and Talent are in higher risk for endograft migration than others. Stent- graft migration consists of an insidious and underestimated threat.

Active Proximal Sealing in the Endovascular Repair of Abdominal Aortic Aneurysms

Purpose: To investigate the performance of a new device that uses the STRATA polytetrafluoroethylene graft material and a mechanism that provides active proximal sealing in order to prevent type Ia endoleak during endovascular aneurysm repair (EVAR). Methods: Between April 2013 and July 2014, 21 consecutive patients (all men; median age 71 years, range 60–84 years) with abdominal aortic aneurysm (median diameter 5.9 cm, range 4.9–7.8 cm) and suitable anatomy were offered elective EVAR using the AFX endograft. These patients had an irregular, conical, tapered, or bulging proximal neck, for which this specific device was considered appropriate. Aneurysm exclusion and incidence of type Ia endoleak were the primary outcomes; secondary outcomes included mortality, morbidity, migration, and other graft-related complications. Results: Primary technical success was 90%; 2 intraoperative type Ia endoleaks due to low endograft deployment were treated with additional proximal cuffs. During a median follow-up of 10 months (range 2–15 months), no type I endoleak was observed. One type II endoleak was encountered, with no associated sac enlargement. There was no stent-graft migration or any other device-related complication. One patient had a nonfatal myocardial infarction and another developed renal failure requiring transient dialysis. No deaths occurred. Conclusion: In this early experience, this newly available device appears to be safe and efficient in providing seal along irregularly shaped necks over the short term.

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.

Endovascular device design in the future: transformation from trial and error to computational design

Endovascular devices have been designed by trial and error, with bench and animal testing followed by human clinical trials to determine whether the devices are safe and effective. Despite remarkable advances over the past 15 years, there are persistent concerns regarding the long-term durability of endovascular devices. This may be due to deficiencies in device design, which has lagged behind other industries in adopting computational methods that are now routinely used to design, develop, and test new aircraft and automobiles. Similar computational design and failure mode simulations that evaluate performance under stress conditions have not been widely applied in the development of endovascular devices. Advances in medical imaging and computational modeling now allow simulation of physiological conditions in patient-specific 3-dimensional vascular models, which can provide a framework to design and test the next generation of endovascular devices. This modeling will allow the prospective design of devices that can withstand the force variations in the cardiovascular system that occur during bending, coughing, and varying degrees of exercise, as well as the extremes encountered during sudden impact in contact sports. Utilization of computational design methodology that takes into consideration the physiology of the cardiovascular system will improve future endovascular devices so that they are safer and more effective and durable.

Secondary Endovascular and Conversion Procedures for Failed Endovascular Abdominal Aortic Aneurysm Repair: Can We Still Be Optimistic?

The purpose of this study was to evaluate the incidence, etiology, and outcome of secondary endovascular and “open” conversion procedures after failed endovascular abdominal aortic aneurysm repair (EVAR). From January 1997 until December 2005, 625 patients with an infrarenal abdominal aortic aneurysm were treated by elective EVAR, with 98.7% ( n = 617) primary EVAR success. The mean follow-up of the 617 patients was 46.7 ± 11.2 months. One hundred of these patients (16.2%) required secondary endovascular or peripheral procedures, and 39 (6.3%) patients underwent a secondary abdominal conversion. There were 5 acute conversions (0.8%) and 34 elective conversions (5.5%). The pre-EVAR anatomic suitability data, the main cause of the secondary procedure, and stent graft type were compared between patients with primary EVAR success, patients in need of a secondary endovascular or peripheral procedure, and patients with abdominal conversion. The overall main causes for reinterventions were proximal migration ( n = 60; 9.7%), progressive kinking of the stent graft ( n = 59; 9.6%), and late type III endoleak ( n = 12; 1.9%). Multivariate logistic regression analysis showed that factors significantly correlated with secondary procedures were the abdominal aortic aneurysm's maximum diameter, the proximal neck's width and length, and particularly the commercial withdrawal of the stent graft ( p < .001). The morbidity and mortality rates of secondary endovascular or peripheral interventions were 0%. The mortality rate of acute secondary conversions was 20% ( n = 1) and of elective secondary conversions was 8.8% ( n = 3). The morbidity rates for acute and elective conversions were 0% and 65%, respectively. The aneurysm-related mortality rate in our series was below 1%. Abdominal conversion surgery still carries a high mortality rate, but the overall EVAR-related mortality rate remains low. Early pitfall detection and proper reintervention are crucial to long-term EVAR success.

Measurement of pulsatile haemodynamic forces in a model of a bifurcated stent graft for abdominal aortic aneurysm repair

The longitudinal haemodynamic force (LF) acting on a bifurcated stent graft for abdominal aortic aneurysm repair has been estimated previously using a simple one-dimensional analytical model based on the momentum equation which assumes steady flow of an inviscid fluid. Using an instrumented stent-graft model an experimental technique was developed to measure the LF under pulsatile flow conditions. The physical stent-graft model, with main trunk diameter of 30mm and limb diameters of 12 mm, was fabricated from aluminium. Strain gauges were bonded on to the main trunk to determine the longitudinal strain which is related to the LF. After calibration, the model was placed in a pulsatile flow system with 40 per cent aqueous glycerol solution as the circulating fluid. The LF was determined using a Wheatstone bridge signal-conditioning circuit. The signals were averaged over 590 cardiac cycles and saved to a personal computer for subsequent processing. The LF was strongly dependent on the pressure but less so on the flowrate. The measured forces were higher than those predicted by the simplified mathematical model by about 6-18 per cent during the cardiac cycle. The excess measured forces are due to the viscous drag and the effect of pulsatile flow. The peak measured LF in this model of 30 mm diameter may exceed the fixation force of some current clinical endovascular stent grafts.

Infrarenal Aortic Devices: Failure Modes and Unmet Needs

Endovascular repair of abdominal aortic aneurysms has become part of the standard of care for those patients with appropriate anatomy. Since its initial reporting in 1991, numerous devices have been manufactured and undergone various stages of clinical trials and subsequent postmarket use. Currently, there are four commercially available devices. Without exception, all of the devices are subject to late failure and complications, and, therefore, diligent postoperative surveillance is mandatory. Some of the failure modes apply to the therapy itself and some are device-specific. These failure modes shed light into the unmet needs of the current technology and directions for further improvement.

Are aortic endograft prostheses fully hemo-compatible? A dielectric spectroscopy investigation of the electrical alterations induced on erythrocyte cell membranes

In this paper we present a new approach directed to ascertain the full hemo-compatibility of aortic endograft prostheses based on the measurement of the passive electrical parameters of the erythrocyte cell membrane. The red blood cell membrane, from an electric point of view, is characterized by an electrical permittivity, (s), which takes into account the structural charged organization of the lipid double layer, and by the electrical conductivity, sigma(s), which accounts for the ionic transport processes across the membrane. These parameters can be easily measured by means of a radiowave dielectric spectroscopy technique, analyzing the dependence of the electrical impedance of an erythrocyte suspension on the frequency of the applied electric field. In this preliminary report, we investigate the alterations induced, at a membrane level, by two different devices commonly employed for endovascular abdominal aortic aneurysm exclusion, i.e., Excluder and Zenith devices, implanted in ten patients. We observe, in all the cases investigated, a statistically significant increase of both the permittivity (s) and electrical conductivity sigma(s) of the erythrocyte membrane upon the prosthesis implant, this increase being higher than about 20% of the un-treated values. Moreover, these alterations remain roughly unaffected 30 days after surgery. These findings suggest that a complete hemo-compatibility of these prostheses is lacking, even if the observed alterations may not have a clinical relevance.

Effect of challenging neck anatomy on mid-term migration rates in AneuRx endografts

OBJECTIVE

To establish the effect of challenging neck anatomy on the mid- and long-term incidence of migration with the AneuRx bifurcated device in patients treated after Food and Drug Administration approval and to identify the predictive factors for device migration.

METHODS

Prospectively maintained databases at the University of North Carolina (UNC) and Washington University (WU) were used to identify 595 patients (UNC, n = 230; WU, n = 365) who underwent endovascular repair of an infrarenal abdominal aortic aneurysm with the AneuRx bifurcated stent graft. Those patients with at least 30 months of follow-up were identified and underwent further assessment of migration (UNC, n = 25; WU, n = 59) by use of multiplanar reconstructed computed tomographic scans.

RESULTS

Eighty-four patients with a mean follow-up time of 40.3 months (range, 30-55 months) were studied. Seventy percent of the patients (n = 59) met all inclusion criteria for neck anatomy (length, angle, diameter, and quality) as defined by the revised instructions for use guidelines and are referred to as those with favorable neck anatomy (FNA). The remaining 25 patients retrospectively fell outside of the revised instructions for use guidelines and are referred to as those with unfavorable neck anatomy (UFNA). Life-table analysis for FNA patients at 2 and 4 years revealed a migration rate of 0% and 6.1%, respectively. For UFNA patients, it was 24.0% and 42.1% at 2 and 4 years, respectively (P < .0001). The overall (FNA and UFNA) migration rate was 7.1% and 17.1% at 2 and 4 years, respectively. Overall, late graft-related complications occurred in 38% of patients (FNA, 27%; UFNA, 64%; P = .003; relative risk, 1.7). There was no incidence of late rupture or open conversion. The relative risk of migration for UFNA patients was 2.5 compared with FNA patients (P = .0003). A larger neck angle and a longer initial graft to renal artery distance were predictors of migration, whereas shorter neck length approached but did not reach statistical significance.

CONCLUSIONS

Patients who have unfavorable aneurysm neck anatomy experience significantly higher migration, device-related complication, and secondary intervention rates. However, there was no incidence of open conversion, rupture, or abdominal aortic aneurysm-related death, thereby supporting the AneuRx device as a feasible alternative to open repair even in patients with challenging neck characteristics. Enhanced surveillance should be used in these high-risk patients.

Aortic Aneurysm, Thoracoabdominal Aneurysm, Juxtarenal Aneurysm, Fenestrated Endografts, Branched Endografts, and Endovascular Aneurysm Repair

The development of endovascular devices to treat aneurysms that abut or involve the visceral vessels has occurred in an effort to reduce the significant procedural morbidity and mortality associated with conventional repair. To accomplish this, three systems have been trialed. The first technique was developed to treat juxtarenal aneurysms and involves the placement of customized fenestrations strategically placed within the fabric of the graft. These are aligned with the ostia of the visceral vessels incorporated by the repair and supplemented by the placement of a balloon expandable stent. In a similar fashion, aneurysms that involve the visceral vessels can be treated with a fenestrated graft where the fenestration is reinforced with a nitinol ring. This is then mated with a balloon-expandable stentgraft, allowing the devices to seal at the level of the nitinol ring. An alternative means of incorporating the visceral vessels is to use directional branches where one or more additional limbs (typically 8 mm) are anastomosed to the aortic graft, through which access into the visceral vessel is attained. Mating stentgrafts for the later design can be of a self-expanding or balloon expandable nature. The experience with fenestrated devices is mature and associated with a low perioperative mortality (<2%) without many long-term complications. The treatment of thoracoabdominal aneurysms with branches has provided us with optimism regarding the technique, but results are only short term in nature. Further device development is ongoing and dissemination of this technology is now occurring in Europe, Australia and Canada.

A Prospective Analysis of Fenestrated Endovascular Grafting: Intermediate-term Outcomes

PURPOSE

To assess the intermediate-term outcomes following fenestrated grafting for juxtarenal aneurysms.

MATERIALS AND METHODS

A prospective trial was conducted on patients with short proximal necks, who were considered to be high-risk for open repair and unacceptable for conventional endovascular repair. Devices were designed from reconstructed CT data. Follow-up studies included CT, duplex ultrasound, and KUB and occurred at hospital discharge, 1, 6, and 12 months and annually thereafter.

RESULTS

One hundred and nineteen patients were treated (2001-2005). Mean age and aneurysm size were 75 years and 65 mm, respectively, and 82% were male. A total of 302 visceral vessels were inferior to the fabric seal (a mean of 2.5 vessels per patient), with the most common design incorporating two renal arteries and the SMA (58%). All prostheses were implanted successfully without any acute visceral artery loss. The mean follow-up was 19 months (0-42 months). One patient died within 30 days of device implantation. Kaplan-Meier estimates of survival at 1, 12, 24, and 36 months are 0.99, 0.92, 0.83 and 0.79. There were no ruptures or conversions. Pre-discharge imaging noted 11 type I and type III endoleaks. The 30-day endoleak rate was 10% (all type II). Aneurysm sac size decreased (>5 mm) in 51, 79 and 77% at 6, 12 and 24 months, respectively. One patient had sac enlargement within the first year, associated with a persistent type II endoleak. In-stent stenoses occurred in 12 renal arteries and one SMA. Six renal arteries and the SMA stenosis were treated and two renal stenoses are awaiting treatment. Ten of 231 stented renal arteries occluded (three prior to discharge), one of which was recanalized. One component separation was treated with an extension at 2 years.

CONCLUSIONS

The placement of endovascular prostheses with graft material incorporating the visceral arteries is safe and appears to be effective at preventing rupture. Continued follow-up to assess the long-term benefit, aneurysm sac behavior and effect of stenting upon the visceral ostia remains critical.

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.

An evaluation of centerline of flow measurement techniques to assess migration after thoracic endovascular aneurysm repair

OBJECTIVE

To validate a means by which migration of thoracic stent grafts can be reliably detected and quantified.

METHODS

Patients treated for thoracic aneurysms (without dissections) with either the Cook Zenith TX1/TX2 or the Gore TAG device were retrospectively reviewed. Patients with digital imaging data at a baseline study (discharge or 1-month computed tomographic scan) and a minimum of 6 months' follow-up were evaluated on a three-dimensional workstation. Centerline of flow (CLF) calculations were used to determine length measurements to establish distances from native vascular landmarks (left common carotid artery, left common carotid artery, and celiac artery) to the proximal and distal aspects of the fixation systems of stent grafts. Patients with evidence of fixation system migration (>10 mm of movement) or increasing thoracic aortic lengths (left common carotid artery to celiac artery distance) were subjected to more detailed reviews.

RESULTS

Of 194 patients evaluated (133 Zenith and 61 TAG), 46 were treated for dissections and excluded. Fifty-seven patients did not have a digital baseline study and available DICOM data for follow-up imaging at 6 months or later or had died before such follow-up imaging. The remaining 91 patients underwent assessment for device migration. Analyses were conducted on 19 patients at 6 months, on 42 at 12 months, on 12 at 24 months, on 13 at 36 months, and on 5 at 48 months. CLF analysis noted more than 10 mm of caudal movement of the proximal device in 10 patients and cranial movement of the distal device in 3 patients. When this subset was further scrutinized with regard to morphologic changes remote from the prosthesis and in the context of the overall aortic repair (such as elephant trunk grafts), only four patients had movement of the proximal or distal fixation system with respect to the initially deployed location. Two-dimensional axial image analysis identified migration in only one of the four patients with CLF-detected fixation system movement.

CONCLUSIONS

The importance of early migration detection cannot be overstated given the potential to avert consequences as evidenced by analyses of counterpart abdominal aortic aneurysm devices. In vivo thoracic device analysis is more complex than that for devices used for infrarenal aneurysms. Distance calculations based on CLF measurements may overestimate the frequency of true migration, yet they serve as a reasonable initial screening tool. The resultant subset of patients then must undergo a more detailed evaluation of device position in the context of the aortic morphology to differentiate true migration from devices that maintain stable fixation system positions.

The importance of iliac fixation in prevention of stent graft migration

OBJECTIVE

Secure proximal fixation of endografts to the infrarenal aortic neck is known to be important in the short- and long-term success of endovascular aneurysm repair. We sought to determine the relative importance of distal iliac fixation in preventing endograft migration and adverse clinical events after endovascular aneurysm repair.

METHODS

We reviewed the outcome of 173 patients treated from 1996 to 2003 at Stanford University Medical Center with an externally supported stent graft. Quantitative image analysis of the postimplantation computed tomography scan was performed to determine the proximal aortic and distal iliac fixation lengths and the proximity the distal end of the stent graft to the iliac bifurcation. Subsequent follow-up computed tomography scans were reviewed for evidence of stent graft migration. Patients were grouped according to good (>15 mm), intermediate, or bad (<10 mm) aortic fixation and good (iliac fixation length > or =25 mm and iliac limbs <10 mm from iliac bifurcation), intermediate, or bad (<25-mm fixation length) iliac fixation.

RESULTS

Stent graft migration of 10 mm or more was seen in 17 patients (10%) during the 23 +/- 19-month follow-up period. Patients with no migration had a greater iliac fixation length (30 +/- 12 mm) than those with migration (22 +/- 8 mm; P = .01), and the distal ends of the iliac limbs were closer to the iliac bifurcation (15 +/- 12 mm) than in patients with migration (25 +/- 10 mm; P < .001). Patients with no migration also had a greater proximal aortic fixation length (23 +/- 12 mm) than migration patients (13 +/- 7 mm; P = .001). There were no migrations among patients with good iliac fixation whether aortic fixation was good, intermediate, or bad (0/63; 0%). Among patients with bad/intermediate iliac and good aortic fixation, there were 5 (9%) of 58 patients had migrations. Patients with both bad/intermediate iliac and bad/intermediate aortic fixation had the highest migration rate (12/52; 23%). Cox proportional hazards regression modeling revealed that the significant factors predicting migration were poor proximity of the distal end of the iliac limbs to the iliac bifurcation (odds ratio 17.2; P = .01) and aortic fixation length (odds ratio 2.0; p = 0.007 for each centimeter). Iliac extender modules were placed in 9 patients with bad iliac fixation and migration, with no further migration during a mean follow-up of 12 months. Patients with good iliac and aortic fixation and no endoleak on the initial postprocedure computed tomography scan (n = 43) had no migrations, secondary procedures, or adverse clinical events over a 2-year follow-up period.

CONCLUSIONS

Iliac fixation, along with proximal aortic fixation, is an important factor in preventing the migration of stent grafts that have longitudinal columnar support. Patients with good iliac fixation did not experience migration even in the presence of suboptimal proximal aortic fixation. Close proximity of the distal end of the stent graft to the iliac bifurcation seems to provide stability against migration.

Late Stent-Graft Migration Secondary to Separation of the Uncovered Segment From the Main Body of a Zenith Endoluminal Graft

PURPOSE

To report a case of type I endoleak secondary to complete disruption of the sutures uniting the uncovered and covered segments of a bifurcated Zenith endoluminal graft, causing displacement and distal migration of the graft main body.

CASE REPORT

A 76-year-old man had successful exclusion of an abdominal aortic aneurysm with a Zenith endoluminal graft in 1999. He continued to do well until the 4-year surveillance imaging [computed tomography (CT) and plain abdominal radiography] showed device migration and proximal endoleak, with consequent expansion of the aneurysm. A proximal extension stent-graft was inserted with good seal. The 1-month follow-up CT angiogram showed reduced aneurysm size and no evidence of any leak.

CONCLUSION

This case shows that the failure of an endoluminal graft occurs at weak points in the construction of the graft, reinforcing the need for long-term surveillance. If detected promptly, such events can often be treated by another endovascular procedure.

Current Status of Branched Stent-Graft Technology in Treatment of Thoracoabdominal Aneurysms

Endovascular aortic aneurysm repair has been established as an alternative to open surgical reconstruction in appropriately selected patients. Until recently, this approach has been limited to aneurysms not involving critical aortic branches due to the complex nature of designing devices that would preserve important end-organ flow. This article reviews the current status of endovascular approaches to aneurysms involving the thoracoabdominal aorta. The evolution of fenestrated devices and further developments, including reinforced fenestrated branched grafts and directional branches for more complex aneurysms are discussed.

Hybrid Approaches to Thoracic Aortic Aneurysms

Background— Thoracic aortic aneurysm affecting the arch and proximal descending thoracic aorta requires 2-stage repairs that include proximal elephant trunk graft placement and completion of thoracic or thoracoabdominal repair. The application of endovascular grafting to complete the proximal procedure avoids a thoracotomy and may improve the morbidity and mortality of the patient population at risk.

Methods and Results— A retrospective review of 399 thoracic endovascular grafts at our institution between 2000 and 2004 identified 22 patients who required elephant trunk and endovascular completion. Three patients underwent mesenteric bypass in addition to their proximal repairs. Mean follow-up was 10 months (range 1 to 42 months); there were no ruptures, and all patients returned for follow-up. Technical success was achieved in all patients. The 1-, 12-, and 24-month mortality rates (by Kaplan-Meier analysis) were 4.5%, 15.8%, and 15.8%, respectively. Caudal migration of the endograft occurred in 1 patient, and all but 2 aneurysms decreased or remained stable in size. The 2 patients with growth included a type III endoleak (which resolved after treatment) and pressurization through an expanded PTFE stentgraft. Three cases of transient paraparesis occurred (all in patients requiring mesenteric bypass or abdominal aortic aneurysm repair), and there were no paraplegias or strokes.

Conclusions— Endovascular completion of elephant trunks is feasible and can be accomplished with minimal mortality. Meticulous imaging follow-up is required to detect persistent aneurysm pressurization and to verify the integrity of the repair. Improvements in implant design and delivery systems will further simplify the second-stage portion of these complex aneurysm repairs.