When Not to Implant the Multilayer Flow Modulator: Lessons Learned From Application Outside the Indications for Use in Patients With Thoracoabdominal Pathologies

Management of acute aortic syndrome with evolving individualized precision medicine solutions: Lessons learned over two decades and literature review

Background

Thoracoabdominal acute aortic syndrome is associated with high morbidity and mortality. We aim to scrutinize our evolving strategies for acute aortic syndrome (AAS) management using minimally invasive and adaptive surgical techniques over two decades.

Methods

This is a longitudinal observational study at our tertiary vascular centre from 2002 to 2021. Out of 22,349 aortic referrals, we performed 1,555 aortic interventions over twenty years. Amongst 96 presented with symptomatic aortic thoracic pathology, 71 patients had AAS. Our primary endpoint is combined aneurysm-related and cardiovascular-related mortality.

Results

There were 43 males and 28 females (5 Traumatic Aortic Transection (TAT), 8 Acute Aortic Intramural Hematoma (IMH), 27 Symptomatic Aortic Dissection (SAD) and 31 Thoracic Aortic Aneurysm (TAA) post-SAD) with a mean age of 69. All the patients with AAS received optimal medical therapy (OMT), but TAT patients underwent emergency thoracic endovascular aortic repair (TEVAR). Fifty-eight patients had an aortic dissection, of which 31 developed TAA. These 31 patients with SAD and TAA received OMT initially and interval surgical intervention with TEVAR or sTaged hybrId sinGle lumEn Reconstruction (TIGER). To increase our landing area, we performed a left subclavian chimney graft with TEVAR in twelve patients. The average follow-up duration was 78.2 months, and eleven patients (15.5%) had combined aneurysm and cardiovascular-related mortality. Twenty-six percentage of the patients developed endoleaks (EL), of which 15% required re-intervention for type II and III. Four patients who had paraplegia (5.7%) and developed renal failure died. None of our patients had a stroke or bowel ischaemia. Twenty patients had OMT, eight of these were patients with acute aortic hematoma, and all eight died within 30 days of presentation.

Conclusion

Acute aortic hematoma is a sinister finding, which must be closely monitored, and consideration is given to early intervention. Paraplegia and renal failure result in an increased mortality rate. TIGER technique with interval TEVAR has salvaged complex situations in young patients. Left subclavian chimney increases our landing area and abolishes SINE. Our experience shows that minimally invasive techniques could be a viable option for AAS.

Aneurysm Sac Pressure during Branched Endovascular Aneurysm Repair versus Multilayer Flow Modulator Implantation in Patients with Thoracoabdominal Aortic Aneurysm

Open thoracoabdominal repair is the gold standard in the TAAA treatment. However, there are endovascular techniques, that sometimes may be an alternative, such as branched endovascular aneurysm repair (BEVAR) or implantation of the multilayer flow modulator (MFM). In this study, we aimed to assess differences in the aneurysm sac pressure (ASP) between patients undergoing BEVAR and MFM implantation. The study included 22 patients with TAAA (14 patients underwent BEVAR, while eight MFM implantation). The pressure sensor wire was placed inside the aneurysm. A measurement of ASP and aortic pressure (AP) was performed during the procedure. The systolic pressure index (SPI), diastolic pressure index (DPI), and pulse pressure index (PPI) were calculated as a quotient of the ASP and AP values. After the procedure, SPI and PPI were lower in the BEVAR group than in the MFM group. During a procedure, a drop in SPI and PPI was noted in patients undergoing BEVAR, while no changes were revealed in the MFM group. This indicates that BEVAR, but not MFM, is associated with a reduction in systolic and pulse pressure in the aneurysm sac in patients with TAAA.

The contemporary design of endovascular aneurysm stent-graft materials: PTFE versus polyester

Endovascular aneurysm repair of the abdominal aorta (EVAR) and of the thoracic aorta (TEVAR) have revolutionised therapeutic strategies in the management of aortic pathology, and endovascular repair is now an established and attractive alternative to open surgical repair (OSR) due to its superior short-term safety profile. However, opinions are divided regarding its long-term cost-effectiveness, which is reflected in the controversial NICE guidelines on abdominal aortic aneurysm (AAA) repair published in 2018, which advised against EVAR for elective aortic repair due to high secondary intervention rates and resultant associated costs. There is no doubt that OSR continues to have a valuable role to play in aortic repair, but it is not universally applicable, especially in older and sicker patients. Therefore, we should not dismiss EVAR and TEVAR without examining the reasons for long-term failure, and the most obvious starting point is stent graft material properties. Polytetrafluoroethylene (PTFE) and polyester are the two most common stent-graft materials; however, there has been no objective comparison of PTFE and polyester stent-graft post-procedural outcomes in EVAR and TEVAR, or even OSR. This lack of definitive data on different stent-graft materials and their configuration necessitates a comprehensive review to elucidate the post-procedural outcome in terms of endograft failure, cardiovascular events, and aortic-related mortality and morbidity.

A Finite Element Based Analysis of a Hemodynamics Efficient Flow Stent Suitable for Different Abdominal Aneurysm Shapes

This research aimed to examine the impact of a proposed flow stent (PFS) on different abdominal artery shapes. For that purpose, a finite element-based model using the computational fluid dynamics (CFD) method is developed. The effect of PFS intervention on the hemodynamic efficiency is estimated by all of the significant criteria used for the evaluation of aneurysm occlusion and possible rupture; the flow velocity, pressure, wall shear stress (WSS), and WSS-related indices. Results showed that PFS intervention preserves the effects of high flow rate and decreases irregular flow recirculation in the sac of the aneurysm. The flow velocity decreases inside the aneurysm sac in the range of 55% to 80%. The time-averaged wall shear stress (TAWSS) was reduced from 42% to 53% by FPS deployment. The simulation results implies that PFS could heal an aneurysm efficiently with a mechanism that causes the development of thrombus and ultimately leads to aneurysm resorption.

Late surgical conversion of failed Multilayer Flow Modulator stenting in thoraco-abdominal aneurysms

OBJECTIVES

The aim of this study was to report the outcomes of open or hybrid repair of failed thoraco-abdominal aortic aneurysm endovascular treatment with Multilayer Flow Modulator (MFM) stents.

METHODS

All patients who underwent open or hybrid repair of a failed MFM aortic treatment were retrospectively analysed. Perioperative and postoperative data, as well as midterm survival, were assessed.

RESULTS

Between 2013 and 2020, 39 patients received an open or hybrid conversion after endovascular treatment. Five of them [13%; 4 males; median age 68 years (interquartile range 66-76)] were previously treated with aortic MFM stents (Cardiatis, Isnes, Belgium). Among these, the median interval between index repair and conversion was 84 months (interquartile range 75-84). The median aneurysm diameter was 9.6 cm (interquartile range 8-10). Renovisceral vessels steno-occlusion was highly prevalent: 2 renal arteries were occluded; 3 coeliac trunks, 2 renal arteries and 1 superior mesenteric artery had a >70% ostial stenosis. Open standard thoraco-abdominal aneurysm conversion was performed in 3 fit patients, while a hybrid approach with visceral debranching and tube endografting was performed in 2 high-risk patients. Two patients (2 open repairs) died intraoperatively, and 1 (hybrid repair) postoperatively. The 2 successfully treated patients are alive at 4- and 34-month follow-up, respectively, with patent visceral branches.

CONCLUSIONS

Open or hybrid thoraco-abdominal aortic aneurysm treatment after failed endovascular aortic repair with MFM stents might be the only surgical option to address sac enlargements and ruptures or branch-related failures. However, both procedures had a poor prognosis due to both the impaired preoperative patient's status and the surgical complexity in the presented series.

Influence of shape-memory stent grafts on local aortic compliance

The effect of repair techniques on the biomechanics of the aorta is poorly understood, resulting in significant levels of postoperative complications for patients worldwide. This study presents a computational analysis of the influence of Nitinol-based devices on the biomechanical performance of a healthy patient-specific human aorta. Simulations reveal that Nitinol stent-grafts stretch the artery wall so that collagen is stretched to a straightened high-stiffness configuration. The high-compliance regime (HCR) associated with low diastolic lumen pressure is eliminated, and the artery operates in a low-compliance regime (LCR) throughout the entire cardiac cycle. The slope of the lumen pressure–area curve for the LCR post-implantation is almost identical to that of the native vessel during systole. This negligible change from the native LCR slope occurs because the stent-graft increases its diameter from the crimped configuration during deployment so that it reaches a low-stiffness unloading plateau. The effective radial stiffness of the implant along this unloading plateau is negligible compared to the stiffness of the artery wall. Provided the Nitinol device unloads sufficiently during deployment to the unloading plateau, the degree of oversizing has a negligible effect on the pressure–area response of the vessel, as each device exerts approximately the same radial force, the slope of which is negligible compared to the LCR slope of the native artery. We show that 10% oversizing based on the observed diastolic diameter in the mid descending thoracic aorta results in a complete loss of contact between the device and the wall during systole, which could lead to an endoleak and stent migration. 20% oversizing reaches the Dacron enforced area limit (DEAL) during the pulse pressure and results in an effective zero-compliance in the later portion of systole.

A systematic review and meta-analysis of the streamliner multilayer flow modulator stent for treatment of complex aortic lesions

OBJECTIVE

We evaluated the safety and efficacy of multilayer flow modulator (MFM) stents (Cardiatis, Isnes, Belgium) for the treatment of complex aortic lesions.

METHODS

A systematic electronic research was conducted for studies reported from December 2008 to May 2020. Data extracted from 15 eligible case series (CS) were appropriately pooled and analyzed in a meta-analysis. The patient baseline characteristics were recorded, and 16 outcomes of interest were studied. The primary end points included 30-day all-cause and aneurysm-related mortality, aneurysm-related mortality at 1 year, vessel patency, and any endoleaks, ruptures, reinterventions, and aneurysm exclusion at the end of follow-up.

RESULTS

A total of 39 studies (15 CS and 24 case reports), involving 429 patients, met the inclusion criteria. Overall, 436 lesions were treated, and 1521 aortic branches were covered by the multilayer stent. The mean follow-up for the 15 CS with 404 patients was 14.6 months. Compliance with the instructions for use was reported by eight CS, with 75% of the procedures performed within the instructions for use. However, 41% of the patients reported by 12 CS had undergone a previous aortic intervention. The pooled 30-day all-cause and 30-day aneurysm-related mortality rates were 0.56% (95% confidence interval [CI], 0.00%-2.54%) and 0.00% (95% CI, 0.00%-0.80%), respectively. The pooled aneurysm-related mortality at 1 year of follow-up was 5.25% (95% CI, 0.07%-14.91%). The pooled vessel patency at the end of follow-up was 99.12% (95% CI, 97.73%-99.93%). The pooled reintervention and endoleak rates at the end of follow-up were 10.94% (95% CI, 3.64%-20.67%) and 10.70% (95% CI, 4.45%-18.66%), respectively. The crude spinal cord ischemia and renal failure rates were 0.69% and 1.8%, respectively.

CONCLUSIONS

The results from the present review and meta-analysis have indicated the safety and efficacy of MFM stents for treating challenging aortic pathologic lesions when used as first-line treatment and within the instructions for use. The almost zero pooled 30-day all-cause and aneurysm-related mortality rates combined with the low crude spinal cord ischemia and renal failure rates indicate the use of MFM stents is a good treatment option for complex aortic lesions in the short- and mid-term periods. The lack of long-term follow-up warrants further research concerning the efficacy of the device in the long term.

Multilayer stents affect the final diameter of aortic aneurysms and maintain renal artery patency for a short time in a swine experimental model

OBJECTIVES

We sought to analyze the hemodynamic effects of the multilayer flow-modulated stent (MFMS) in Thoracoabdominal aortic aneurysms (TAAAs).

METHODS

The hemodynamic effects of MFMS were analyzed in aortic thoracoabdominal aneurysms in experimental swine models. We randomly assigned 18 pigs to the stent or control groups and underwent the creation of an artificial bovine pericardium transrenal aneurysm. In the stent group, an MFMS (Cardiatis, Isnes, Belgium) was immediately implanted. After 4 weeks, we evaluated aneurysm sac thrombosis and renal branch patency by angiography, duplex scan, and morphological analysis.

RESULTS

All the renal arteries remained patent after re-evaluation in both groups. Aneurysmal sac thrombosis was absent in the control group, whereas in the stent group it was present in 66.7% of aneurysmal sacs (p=0.061).The mean final aneurysm sac diameter was significantly lower in the stent group (mean estimated reduction, 6.90 mm; p=0.021). The proximal neck diameter decreased significantly in the stent group (mean difference, 2.51 mm; p=0.022) and grew significantly in the control group (mean difference, 3.02 mm; p=0.007). The distal neck diameter increased significantly in the control group (mean difference, 3.24 mm; p=0.017). There were no significant findings regarding distal neck measurements in the stent group.

CONCLUSION

The MFMSs remained patent and did not obstruct the renal arteries within 4 weeks. In the stent group, the device was also associated with a significant decrease in aneurysmal sac diameter and a large proportion (albeit non-significant) of aneurysmal sac thrombosis.

A systematic review and meta-analysis of the performance of flow-diverting stents in the treatment of peripheral and visceral artery aneurysms

OBJECTIVE

This meta-analysis aims to evaluate the safety and efficacy of flow-diverting stents (FDS) in treating peripheral and visceral artery aneurysms (PAA/VAAs).

BACKGROUND

Though rare, PAA/VAAs can represent a life-threatening condition due to their propensity of rupture. The FDS emerges as a new solution to exclude these aneurysms while maintaining collateral branches, but convincing evidence is lacking on its clinical effectiveness.

METHODS

A systematic literature search was performed to identify studies related to FDS in treating PAA/VAAs. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement was applied to guide the data extraction, quality assessment, and synthesis of outcomes of interest. Random effect models were applied to calculate the event rates of major endpoints. OpenMeta[Analyst] software was used for statistical analysis.

RESULTS

Of 130 records screened, 10 cohort studies (including 220 patients, average age: 66.0 years, 78.4% male) were enrolled in the meta-analysis. Pooled data suggested a technical success rate of 98.5% (95% CI: 97.0-100%). During a mean follow-up period of 14.1 months, 93.6% (95% CI: 88.6-98.5%) side branches remained patent, 89.8% (95% CI: 84.3-95.3%) aneurysms were totally thrombosed, whereas shrinkage/stabilization of the aneurysm was documented in 93.4% (95% CI: 88.4-98.4%) cases. The primary stent patency rate was estimated to be 87.9% (95% CI: 81.0-94.8%). Overall clinical success was achieved in 83.2% (95% CI: 74.4-92.0%) patients.

CONCLUSIONS

The FDS features a potential advantage of preserving side branches while inducing sac thrombosis and aneurysm shrinkage/stabilization. Further prospective, comparative studies in larger patient cohorts are anticipated to draw a robust conclusion.

Current status on aortic endografts

Endovascular treatment has become widespread to treat aneurysmal disease, especially located in the aorta. The modern era of abdominal aortic aneurysm repair started between 1986 and 1991, and in the last 30 years, Endovascular Treatment for abdominal aortic aneurysms evolved both due to the development of new materials and devices and the increasing appeal and effectiveness of the endovascular therapy itself. Vascular surgeons are using nowadays different solutions of Endovascular Treatment to treat all the expressions of aortic pathology (aneurysms, dissections and trauma) both in the acute and elective setting. Despite its use in every location of the aorta (the ascending aorta, the aortic arch, the thoracic aorta, thoraco-abdominal aorta, pararenal, iuxtarenal and infrarenal aortic aneurysms and iliac aneurysms), its safety and efficiency, endovascular treatment for aortic aneurysms presents some drawbacks: despite a lower short-term morbi-mortality, reinterventions and long-term patency are higher compared to open repair. In this review, we detail the most used types of endografts according to location, their performances and durability for each device. We conclude by discussing options to overcome ET limitations. Therefore, an obvious question arises: what we need in the future? What can the technological progress gives to physicians to further improve this new way of treating aorta?

Treatment of High Surgical Risk Thoracoabdominal Aortic Aneurysms with Stent Graft and Multilayer Bare Stents Joint Technique: Mid-Long-Term Clinical Results

BACKGROUND

This study aims to present the performance data on stent-graft and multilayer bare stents (MBS) joint technique in the treatment of high-risk thoracoabdominal aortic aneurysm (TAAA).

METHODS

From May 2012 to December 2015, 8 selective TAAA cases (ages 46-75 years) ineligible for surgical repair underwent the stent-graft and MBS joint procedure, and were closely followed up for a median of 32 months (range 14-58). Using computed tomography images, the aneurysm size, luminal blood flow diameter, and the covered visceral branches were analyzed.

RESULTS

Technical success was achieved in all patients (100%, 8/8). Twenty-four visceral branches were covered by MBS in total. There was no complication or death during hospital stay. During follow-up period, no death or complication occurred. Aneurysm shrinkage (maximum diameter decrease ≥5 mm) was observed in 7 patients. No aneurysm expansion was observed. Total aneurysm sac thrombosis was observed in all patients. The majority of covered side branches (23/24) were successfully preserved. No visceral ischemia or bleeding complications was observed during follow-up.

CONCLUSIONS

Total endovascular repair of TAAA using stent-graft and MBS joint technique may be a safe and effective alternative in high surgical risk patients. More approving clinical evidences about the safety and efficacy of this procedure are anticipated.

Contemporary strategies for repair of complex thoracoabdominal aortic aneurysms: real-world experiences and multilayer stents as an alternative

Thoracoabdominal aortic aneurysms (TAAA) present special challenges for repair due to their extent, their distinctive pathology, and the fact that they typically cross the ostia of one or more visceral branch vessels. Historically, the established treatment for TAAA was open surgical repair, with the first procedure reported in 1955. Endovascular repair of TAAA with fenestrated and/ or branched endografts, has been studied since the beginning of the current century as a means of mechanical aneurysm exclusion. More recently, flow modulator stents have been employed with the aim at reducing shear stress on aortic aneurysmal wall. In this review we present technical and main results of these techniques, based on literature review and personal experience.

Influence of overlapping pattern of multiple overlapping uncovered stents on the local mechanical environment: A patient-specific parameter study

BACKGROUND

Multiple overlapping uncovered stents (MOUS) system has shown potentials in managing complex aortic aneurysms with side branches involvement. It promotes the development of thrombus by modulating local flow pattern that reduces the wall tension, while maintaining patency of side branches. However the modulation of local hemodynamic parameters depends on various factors that have not been assessed comprehensively.

METHODS

Aneurysm 3D geometry was reconstructed based on CT images. One-way fluid-structure interaction analysis was performed to quantify structural stress concentration in the wall, and changes of blood velocity, wall shear stress (WSS), oscillatory shear index (OSI), relative residence time (RRT) and pressure in the sac due to the stent deployment.

RESULTS

High structural stress concentration due to stent deployment was found in the landing zone and it increased linearly with the number of stents deployed. The wall tension in the sac was unaffected by the stent deployment. Stress within the wall was insensitive to the different overlapping pattern. After one stent was deployed, the mean flow velocity in the sac reduced by 36.4%. The deployment of the 2nd stent further reduced the mean sac velocity by 10%. WSS decreased while both OSI and RRT increased after stent deployment, however pressure in the sac remained nearly unchanged. Except for the cases with complete stents struts alignment, different overlapping pattern had little effect on flow parameters.

CONCLUSIONS

Mechanical parameters modulated by the MOUS are insensitive to different overlapping pattern suggesting that endovascular procedure can be performed with less attention to the overlapping pattern.

Is endovascular treatment with multilayer flow modulator stent insertion a safe alternative to open surgery for high-risk patients with thoracoabdominal aortic aneurysm?

A best evidence topic in cardiothoracic and vascular surgery was written according to a structured protocol. The question addressed was whether endovascular treatment with multilayer flow modulator stents (MFMS) can be considered a safe alternative to open surgery for high-risk patients with thoracoabdominal aortic aneurysm (TAAA). Altogether 27 papers were identified using the reported search, of which 11 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes, results, and study limitations are tabulated. The outcomes of interest were all-cause survival, aneurysm-related survival, branch vessel patency and major adverse events. Aneurysm-related survival exceeded 78% in almost all studies, with the exception of one where the MFMS was inserted outside the instructions for use. In that study the aneurysm-related survival was 28.9%. The branch vessel patency was higher than 95% in 10 studies and not reported in one. At 12-month follow-up, several studies showed a low incidence of major adverse events, including stroke, paraplegia and aneurysm rupture. We conclude that MFMS represent a suitable and safe treatment for high-risk patients with TAAA maintaining branch vessel patency when used within their instructions for use. However, a number of limitations must be considered when interpreting this evidence, particularly the complete lack of randomised controlled trials (RCTs), short follow-up in all studies, and heterogeneity of the pathologies among the different populations studied. Further innovative developments are needed to improve MFMS safety, expand their instructions for use, and enhance their efficacy.

Multilayer Flow Modulator Treatment of Abdominal and Thoracoabdominal Aortic Aneurysms With Side Branch Coverage: Outcomes From a Prospective Single-Center Moroccan Registry

PURPOSE

To evaluate endovascular repair of thoracoabdominal aortic aneurysms (TAAA) and abdominal aortic aneurysms (AAA) using the Multilayer Flow Modulator (MFM) in high-surgical-risk patients with at least one covered branch vessel.

METHODS

In this prospective single-center nonrandomized trial, 18 patients (mean age 61.1 years; 16 men) with TAAA (n=10, mean diameter 74.4 mm) and AAA (n=8, mean diameter 67.8 mm) were treated with the MFM between June 2009 and September 2012. The primary safety endpoints were all-cause mortality at 30 days and 12 months and neurological complications. The primary efficacy endpoint was overall procedure success, defined as patency of covered branch vessels, reductions in aneurysm diameter, and sac thrombus formation.

RESULTS

The technical success rate was 100% (53 study devices implanted, mean stented length 273 mm). Through mean follow-up of 13.4 months, all 61 covered branch vessels remained patent; there were no neurologic complications, ruptures, or instances of device migration, kinking, or fracture. Three patients died, 2 of unrelated causes and one of an undetermined cause. Only one reintervention with an additional MFM implanted at 5 years was required for a type I endoleak in a young patient with natural growth. Carefully planned and executed diameter and volume measurements demonstrated aneurysm shrinkage and progressive sac thrombus formation for both patient groups.

CONCLUSION

Through midterm follow-up, treatment of high-surgical-risk TAAA and AAA patients with the MFM appears to be safe and effective, maintaining branch vessel patency and reducing rupture risk through reduction of aneurysm diameter and modulation of flow dynamics. Longer term follow-up is needed.

Insights from complex aortic surgery with a Streamliner device for aortic arch repair (STAR)

OBJECTIVE

Aortic arch aneurysms and thoracoabdominal aortic arch aneurysms are technically challenging to manage by established surgical and endovascular methods. The Streamliner Multilayer Flow Modulator device (Cardiatis, Isnes, Brussels, Belgium) offers an unorthodox option for these high-risk cases. The Streamliner device for aortic arch repair (STAR) study investigated complex aneurysm cases managed by the Streamliner Multilayer Flow Modulator device and offers an analytic solution for a clinical dilemma.

METHODS

Six cases were included, with a 1-year follow-up, comprising 4 pure arch aneurysms and 2 thoracoabdominal aortic arch aneurysms Crawford type I, from a multicenter database hosted by the Streamliner Multilayer Flow Modulator Global Registry. A total of 50% of cases were performed under instructions for use. All were American Society of Anesthesiology IV and originated from zone 0. All cases were computationally analyzed, which consisted of (1) simulating the treatment on the basis of the postoperative data, (2) repositioning the stents for the failed technical cases, and (3) assessing the effects of overlapping devices on branch patency.

RESULTS

Correct device placement induced aneurysm flow streamlining, which reduced the dynamic pressure by 23% to 66%, whereas incorrect placements promoted Failure Mode I with 58% and 16% dynamic pressure increases and aneurysm volume expansion up to 23%. Overlapped devices improved distal perfusion by increasing arch branch outflows from 5% to 24%. The Streamliner Multilayer Flow Modulator device does not benefit a sac volume greater than 400 cm³.

CONCLUSIONS

The Streamliner Multilayer Flow Modulator device is a new technology that can manage complex aortic arch aneurysms and thoracoabdominal aortic arch aneurysms with favorable clinical outcomes if it is performed under instructions for use. Careful procedure planning and perioperative virtual stent placement will avoid foreshortening, prevent inadequate stent overlap lengths, and provide insight into the sufficient numbers of required implanted devices.

Hemodynamic Study of Flow Remodeling Stent Graft for the Treatment of Highly Angulated Abdominal Aortic Aneurysm

This study investigates the effect of a novel flow remodeling stent graft (FRSG) on the hemodynamic characteristics in highly angulated abdominal aortic aneurysm based on computational fluid dynamics (CFD) approach. An idealized aortic aneurysm with varying aortic neck angulations was constructed and CFD simulations were performed on nonstented models and stented models with FRSG. The influence of FRSG intervention on the hemodynamic performance is analyzed and compared in terms of flow patterns, wall shear stress (WSS), and pressure distribution in the aneurysm. The findings showed that aortic neck angulations significantly influence the velocity flow field in nonstented models, with larger angulations shifting the mainstream blood flow towards the center of the aorta. By introducing FRSG treatment into the aneurysm, erratic flow recirculation pattern in the aneurysm sac diminishes while the average velocity magnitude in the aneurysm sac was reduced in the range of 39% to 53%. FRSG intervention protects the aneurysm against the impacts of high velocity concentrated flow and decreases wall shear stress by more than 50%. The simulation results highlighted that FRSG may effectively treat aneurysm with high aortic neck angulations via the mechanism of promoting thrombus formation and subsequently led to the resorption of the aneurysm.

Endovascular management of renal artery aneurysms using the multilayer flow modulator

OBJECTIVE

Our aim was to describe our experience of the Multilayer Flow Modulator (MFM, Cardiatis, Isnes, Belgium) used in the treatment of type III renal artery aneurysms (RAA).

METHODS

This is a single-centre study. 3 patients (2 men and 1 woman; mean age 59 years; range 41-77 years) underwent treatment of a type III renal artery aneurysm using the MFM. The indications were a 23.9 mm type III RAA at the bifurcation of the upper and lower pole vessels, with 4 side branches; a 42.4 mm type III saccular RAA at the renal hilum; and a 23 mm type III RAA at the origin of the artery, supplying the upper pole.

RESULTS

Patients had a mean follow-up of 27 months, and were assessed by perioperative renal function tests, and repeat postoperative CT scan. There were no immediate postoperative complications or mortality. The first patient's aneurysm shrank by 8.6 mm, from 23.9 to 15.3 mm over 19 months, with all 4 side branches remaining patent. The largest aneurysm at 42.4 mm completely thrombosed, while the renal artery remained patent to the kidney. The final patient refused to have any follow-up scans but had no deterioration in renal function below 30 mL/min, and no further symptoms reported.

CONCLUSIONS

The MFM is safe and effective in the management of patients with complex renal artery aneurysms. The MFM can be used to treat branched or distal renal artery aneurysms with exclusion of the aneurysm from the circulation, while successfully preserving the flow to the side branches and kidney. Initial results are promising, however, longer follow-up and a larger cohort are required to prove the effectiveness of this emerging technology.

Systematic Review and Patient-Level Meta-analysis of the Streamliner Multilayer Flow Modulator in the Management of Complex Thoracoabdominal Aortic Pathology

Purpose:

To examine the safety and short-term efficacy of the Streamliner Multilayer Flow Modulator (SMFM) in the management of patients with complex thoracoabdominal aortic pathology who are unfit for alternative interventions.

Methods:

Biomedical databases were systematically searched for articles published between 2008 and 2015 on the SMFM. A patient-level meta-analysis was used to evaluate aneurysm-related survival. Secondary outcomes were all-cause survival, stroke, spinal cord ischemia, renal impairment, and branch vessel patency. Other considerations were the impact of compliance with the instructions for use (IFU) on clinical outcome. Mean values and Kaplan-Meier estimates are presented with the 95% confidence interval (CI).

Results:

Fifteen articles (3 multicenter cohort studies, 3 observational cohort studies, and 9 case reports) were included, presenting 171 patients (mean age 68.8±12.3 years; 139 men). The mean aneurysm diameter was 6.7±1.6 cm (95% CI 6.4 to 6.9 cm). Technical success reported in 15 studies was 77.2%. Aneurysm-related survival at 1 year was 78.7% (95% CI 71.7% to 84.4%). One-year all-cause survival was 53.7% (95% CI 46.0% to 61.3%). There were no reported cases of spinal cord ischemia, renal insult, or stroke.

Conclusion:

The SMFM can be safely utilized in some patients with complex thoracoabdominal pathologies provided operators adhere to the IFU. The SMFM is a novel technology with no long-term published data on its sustained effectiveness and a lack of comparative studies. Randomized clinical trials, registries, and continued assessment are essential before this flow-modulating technology can be widely disseminated.

Multi-layer Flow-modulating Stents for Thoraco-abdominal and Peri-renal Aneurysms: The UK Pilot Study

OBJECTIVE

There remains a population of patients with aortic aneurysms that cannot be treated by conventional endovascular means. Multi-layer flow modulating stents (MFMS) are a novel approach for the treatment of aortic aneurysm; this study reports outcomes of a UK pilot study of first-generation MFMS in thoraco-abdominal (TAAA) and perirenal aneurysms (PAA) in patients who were also unfit for open surgery.

METHODS

Patients with TAAA and PAA unfit for open surgery and with no conventional options for endovascular repair were recruited. Follow-up included CTA at 1, 3, 6, and 12 months, then annually. Outcome measures included 30 day mortality, growth-free survival, branch vessel patency, complications, re-intervention, and maximal aortic diameter.

RESULTS

MFMS were implanted in 14 patients (6 PAA, 8 TAAA) between October 2011 and March 2014 with one (7%) 30 day death and 11 (79%) surviving to 12 months. The median aneurysm growth was 9 mm in the first 12 months following implantation. On mean follow-up of 22.8 months, seven (50%) patients had died including one confirmed rupture. AAA diameter remained stable in only two of the surviving patients. Fifty of 51 covered aortic branches remained patent with no embolic episodes or symptoms of ischaemia in any patient. MFMS dislocation occurred in four patients, leading to re-intervention in two. A total of six re-interventions were performed in five patients (35%) with one post-re-intervention death.

CONCLUSION

These first-generation MFMS were unstable and dislocated frequently. It is uncertain whether MFMS implantation influenced the natural history of these aneurysms as none decreased in size, but two remain stable after a mean of 22.8 months. Although side branch patency was maintained, our results do not support the continued use of these first-generation devices. Further development is needed if this technology is to have a role in treatment of aortic aneurysm.

Multilayer flow modulator stent technology: a treatment revolution for US patients?

Thoracoabdominal aortic repair is a high-risk procedure in most experienced centers, not only because of anatomical complexity but also due to the fragility of the patients in whom these aneurysms occur. Such repairs are complex, time-consuming and impose a systemic injury upon the patients, regardless of whether the repair is performed by open surgery or via a fenestrated/branched technique. The substantive risks associated with such repairs include death, dialysis and paralysis. The multilayer flow modulator (MFM) is a disruptive technology which promises a minimally invasive reproducible treatment option, with clinical results demonstrating physiological modulation of the aortic sac with abolition of spinal injury. The mode of action of MFM forces us to completely rethink aneurysm pathogenesis and, consequently, it has been met with much cynicism. We aim to uncloak some of the mystery surrounding the MFM, clarify its mode of action and explore the truth behind its clinical effectiveness.

Management of complicated aortic aneurysms using multiple overlapping uncovered stents: mid-term outcome from a cohort study

This study sought to report the mid-term outcome of a modified flow-diverting strategy in the treatment of complicated aortic aneurysms of different morphology. Historical data suggested aortic aneurysm expansion and rupture after endovascular treatment with current commercial flow-diverters, indicating the essentiality of further investigation of this technique prior to its large-scale clinical application. An alternative flow-diverting strategy using layer-by-layer assembled multiple overlapping uncovered stents was employed in this study. The treatment outcome in aneurysms of different morphology (saccular, fusiform, and dissecting) was assessed during a mid-term follow-up period.Of 42 patients enrolled in this study (30 male, mean age: 63.3 years), technical success was achieved in 40 cases. During an average follow-up period of 20.9 months, mean aneurysm diameter shrunk from 53.4 ± 13.6 mm to 48.8 ± 13.9 mm (P < 0.001), while stent-induced sac thrombosis ratio increased significantly (18.1 ± 14.9% to 93.6 ± 9.5%, P < 0.001). The majority of side branches (74/76 major visceral branches, 237/244 minor segmental arteries), covered by 3.3 stents on average, maintained their patency after stenting. Saccular aneurysms manifested the highest thrombus deposition speed (18/20 were totally thrombosed within 12 months) and most significant shrinkage (51.4 ± 13.3 mm pre-operatively vs 43.5 ± 10.2 mm during follow-up, P < 0.001) compared with fusiform and dissecting aneurysms. This modified flow-diverting strategy could be a feasible alternative in the management of complicated aortic aneurysms where vital branches need to be preserved. The treatment outcome may depend on the aneurysm type. Further studies with larger patient cohort and longer follow-up are required to substantiate these results.

Total endovascular repair of thoracoabdominal aortic aneurysms with non-customized stent grafts

BACKGROUND

Total endovascular repair of thoracoabdominal aortic aneurysms with customized branched or fenestrated endografts could be technically challenging outside large-volume centers. This study aims to describe a new endovascular strategy for use of both noncustomized stent grafts and flow-diverting stents in treating complicated thoracoabdominal aortic aneurysms.

METHODS

Patients diagnosed with thoracoabdominal aortic aneurysms and deemed unfit for open surgical repair were recruited. The aim of the procedure was to cover the renovisceral segment of the aorta with flow-diverting uncovered stents, while covering the remaining aneurysm with stent grafts. Aneurysm morphologic evolution and the patency of the visceral branches were assessed at follow-up.

RESULTS

Between February 2012 and August 2013, 6 selective patients (4 men, mean age 58 years) underwent the novel joint procedure. During mean follow-up of 14 months, aneurysm shrinkage (maximum diameter decrease ＞5 mm) was demonstrated in 4 patients and aneurysm stabilization (maximum diameter decrease ＜5 mm) was observed in 2 patients. No aneurysm expansion was observed in any participants. Mean aneurysm diameter decreased from 65.0±8.8 mm to 58.5±12.2 mm (p=0.054), with a significant increase in average sac thrombus deposition volume (sac thrombosis ratio increased from 23.3%±7.4% to 98.0%±3.3%, p＜0.001). The majority of side branches (23 of 24) were successfully preserved.

CONCLUSIONS

Complete endovascular repair of thoracoabdominal aortic aneurysms with this novel joint procedure may be a feasible alternative in high surgical risk patients. Further validation of this technique is required to substantiate these results.

Endovascular repair of a juxtarenal saccular aneurysm using the Multilayer Flow Modulator: report of the first case performed in a Public Hospital in Brazil

Endovascular treatment of abdominal aortic aneurysms (AAA), involving the exits of the renal and visceral arteries still constitutes a considerable challenge. Many different techniques have been developed over the years in attempts to surmount the difficulties presented by these cases. Techniques that have gained prominence include fenestrated or branched stents, methods involving parallel prostheses, such as the chimney, periscope and sandwich techniques, and, more recently, flow modulation with Multilayer stents. We describe a case of a complex juxtarenal saccular AAA with a high surgical risk, both according to cardiological assessment and because the patient had a difficult airway caused by a total laryngectomy for early stage laryngeal neoplasm. In view of the technical simplicity of using Multilayer stents, the presence of chronic obstructive aortoiliac disease, ostial stenosis of the renal artery and a small diameter suprarenal aorta, options involving fenestrated/branched stents and techniques involving parallel prostheses were ruled out, because of the need for multiple accesses. In view of the dilemma it presented, we describe this case as a therapeutic challenge and present the treatment option employed, which has been successful over the short term.