Displacement Forces in Stent Grafts: Influence of Diameter Variation and Curvature Asymmetry

Branched Endovascular Aortic Repair After a Migrated EVAR Bypassing a Severely Kinked Previous Endograft

PURPOSE

To describe a novel technique to repair a juxtarenal abdominal aortic aneurysm (JAAA) after failed endovascular aortic repair (EVAR) with severely kinked anatomy.

TECHNIQUE

We present a patient who underwent an EVAR with a Medtronic Talent device 15 years ago and a proximal cuff extension 3 years earlier for an abdominal aortic aneurysm. Computed tomography (CT) done for a known gastritis showed a 12 cm JAAA, with a migrated endograft and a type Ia endoleak (EL). Endovascular repair was performed, accessing and navigating the aneurysmal sac outside the previous graft. The type I EL was reached and the suprarenal aorta catheterized. A 4-vessel inner-branched EVAR device was deployed in the distal thoracic aorta and their target vessels bridged through femoral access. A distal bifurcated component was deployed and both iliac limbs were extended to the native distal iliac arteries. Completion angiogram as well as early and 12-month CT showed a fully patent straight course branched EVAR with no ELs.

CONCLUSION

Complex aortic reinterventions in the presence of previous EVAR can be performed by choosing a straighter course along and parallel to the previous endograft. Several technical aspects must be considered to successfully perform this type of reinterventions.

CLINICAL IMPACT

We present a technique of a complex endovascular aortic repair in a failed EVAR with kinked anatomy, navigating through the thrombosed aneurysmal sac, outside the previously placed endograft and thus obtaining a straighter path for a new branched endograft. The novelty lies in a different approach to repair a failed EVAR with a branched graft through an uncommon access on the side of the previous endograft, avoiding repeated displacement or occlusion of the new endograft. We exemplify the feasibility of such a complex procedure and highlight important steps to perform it, whether in the abdominal or even thoracic Aorta.

Fast and Accurate Computation of the Displacement Force of Stent Grafts after Endovascular Aneurysm Repair

Purpose: Currently, the displacement force of stent grafts is generally obtained using computational fluid dynamics (CFD), which requires professional CFD knowledge to perform the correct simulation. This study proposes a fast, simple, and clinician-friendly approach to calculating the patient-specific displacement force after endovascular aneurysm repair (EVAR). Methods: Twenty patient-specific post-EVAR computed tomography angiography images were used to reconstruct the patient-specific three-dimensional models, then the displacement forces were calculated using CFD and the proposed approaches, respectively, and their numerical differences were compared and analyzed. Results: Based on the derivation and simplification of the momentum theorem, the patient-specific displacement forces were obtained using the information of the patient-specific pressure, cross-sectional area, and angulation of the two stent graft ends, and the average relative error was no greater than 1.37% when compared to the displacement forces calculated by CFD. In addition, the linear regression analysis also showed good agreement between the displacement force values calculated by the new approach and CFD (R = 0.999). Conclusions: The proposed approach can quickly and accurately calculate the patient-specific displacement force on a stent graft and can therefore help clinicians quickly evaluate the post-EVAR displacement force.

Editor's Choice - Structured Computed Tomography Analysis can Identify the Majority of Patients at Risk of Post-Endovascular Aortic Repair Rupture

OBJECTIVE

The main objective was to report mechanisms and precursors for post-endovascular aneurysm repair (EVAR) rupture. The second was to apply a structured protocol to explore whether these factors were identifiable on follow up computed tomography (CT) prior to rupture. The third objective was to study the incidence, treatment, and outcome of post-EVAR rupture.

METHODS

This was a multicentre, retrospective study of patients treated with standard EVAR at five Swedish hospitals from 2008 to 2018. Patients were identified from the Swedvasc registry. Medical records were reviewed up to 2020. Index EVAR and follow up data were recorded. The primary endpoint was post-EVAR rupture. CT at follow up and at post-EVAR rupture were studied, using a structured protocol, to determine rupture mechanisms and identifiable precursors.

RESULTS

In 1 805 patients treated by EVAR, 45 post-EVAR ruptures occurred in 43 patients. The cumulative incidence was 2.5% over a mean follow up of 5.2 years. The incidence rate was 4.5/1 000 person years. Median time to post-EVAR rupture was 4.1 years. A further six cases of post-EVAR rupture in five patients found outside the main cohort were included in the analysis of rupture mechanisms only. The rupture mechanism was type IA in 20 of 51 cases (39%), IB in 20 of 51 (39%) and IIIA/B in 11 of 51 (22%). One of these had type IA + IB combined. One patient had an aortoduodenal fistula without another mechanism being identified. Precursors had been noted on CT follow up prior to post-EVAR rupture in 16 of 51 (31%). Retrospectively, using the structured protocol, precursors could be identified in 43 of 51 (84%). In 17 of 27 (63%) cases missed on follow up but retrospectively identifiable, the mechanisms were type IB/III. Overall, the 30 day mortality rate after post-EVAR rupture was 47% (n = 24/51) and the post-operative mortality rate was 21% (n = 7/33).

CONCLUSIONS

Most precursors of post-EVAR rupture are underdiagnosed but identifiable before rupture using a structured follow up CT protocol. Precursors of type IB and III failures caused the majority of post-EVAR ruptures.

Modified safety techniques for transcatheter repair of superior sinus venosus defects with partial anomalous pulmonary venous drainage using a 100-mm Optimus-CVS® covered XXL stent

We report the first use of a single 100-mm long custom-made version of the Optimus-CVS® balloon-expandable PTFE-covered XXL (15-Zig) stent (AndraTec, GmbH) to eliminate sinus venosus defect left-to-right shunt and redirect anomalous right pulmonary veins blood flow through a new walled channel to the left atrium. Anatomical feasibility and strategy decision were guided by ex-vivo procedure simulation on the patient-specific 3D printed heart model and in-vivo balloon interrogation. Modified procedural and implantation techniques are detailed. Immediate and one-month follow-up showed excellent outcomes.

Modeling and Computational Comparison of the Displacement Forces Exerted between the AFX Unibody Aortic Stent Graft and its Hybrid Combination with a Nitinol-based Proximal Aortic Cuff

BACKGROUND

The bifurcated AFX (Endologix, Inc, Irvine, CA, USA) aortic stent-graft is the sole unibody endograft for the management of Abdominal Aortic Aneurysms (AAA). In order to improve the AFX central sealing and clinical efficacy in challenging cases, a replacement of the central chromium-cobaltium AFX extension with a Nitinol-based proximal aortic cuff has been suggested. Yet, comparative data regarding the hemodynamic performance of this design is missing. Aim of this study was to compare the displacement forces (DF) acting on the hybrid AFX-Endurant design, with the classic AFX and Endurant endografts, in angulated and non-angulated cases based on patient-specific Computational Fluid Dynamics (CFD) simulations.

METHODS

3D endograft models of 11 treated AAA cases were reconstructed from Computed Tomography Angiography (CTA) imaging data: 5 cases of AFX, 3 cases of the combination AFX-Endurant and 3 cases of the classic Endurant design. The DF on the main-body, the iliac limbs, and the entire stent-graft was calculated by processing the velocity and pressure fields generated by pulsatile CFD simulations.

RESULTS

The range of total DF (acting on the whole endograft structure) in the AFX, hybrid AFX-Endurant and Endurant group was 2.5-5.2N, 2.0-5.9N and 1.9-2.9N respectively, with the maximum total DF being lower for Endurant. The DF on the main-body of the classic and hybrid AFX cases were higher than the right and left iliac limbs (2.5-4.9N vs. 0.6-5.3N and 0.7-3.6N respectively). Conversely, the DF on the main-body of the Endurant cases was comparable to the force exerted on the right and left limbs. When separating the cases with respect to their neck angulation, the DF on all endograft parts (main-body, limbs) and on the endograft as a whole were lower for the hybrid AFX-Endurant group compared to the classic AFX and Endurant groups, for cases with almost straight neck.

CONCLUSION

The off-label use of the hybrid AFX-Endurant stent-graft does not seem superior to the conventional AFX or Endurant endografts in angulated cases but was associated with lower DF than AFX or Endurant in non-angulated cases. The clinical value and utility of these findings remain to be elucidated.

Patient-specific computational flow modelling for assessing hemodynamic changes following fenestrated endovascular aneurysm repair

Objective

This study aimed to develop an accessible patient-specific computational flow modelling pipeline for evaluating the hemodynamic performance of fenestrated endovascular aneurysm repair (fEVAR), with the hypothesis that computational flow modelling can detect aortic branch hemodynamic changes associated with fEVAR graft implantation.

Methods

Patients who underwent fEVAR for juxtarenal aortic aneurysms with the Cook ZFEN were retrospectively selected. Using open-source SimVascular software, preoperative and postoperative visceral aortic anatomy was manually segmented from computed tomography angiograms. Three-dimensional geometric models were then discretized into tetrahedral finite element meshes. Patient-specific pulsatile in-flow conditions were derived from known supraceliac aortic flow waveforms and adjusted for patient body surface area, average resting heart rate, and blood pressure. Outlet boundary conditions consisted of three-element Windkessel models approximated from physiologic flow splits. Rigid wall flow simulations were then performed on preoperative and postoperative models with the same inflow and outflow conditions. We used SimVascular's incompressible Navier-Stokes solver to perform blood flow simulations on a cluster using 72 cores.

Results

Preoperative and postoperative flow simulations were performed for 10 patients undergoing fEVAR with a total of 30 target vessels (20 renal stents, 10 mesenteric scallops). Postoperative models required a higher mean number of mesh elements to reach mesh convergence (3.2 ± 1.8 × 10⁶ vs 2.6 ± 1.1 × 10⁶; P = .005) with a longer mean computational time (10.3 ± 6.3 hours vs 7.8 ± 3.5 hours; P = .04) compared with preoperative models. fEVAR was associated with small but statistically significant increases in mean peak proximal aortic arterial pressure (140.3 ± 11.0 mm Hg vs 136.9 ± 8.7 mm Hg; P = .02) and peak renal artery pressure (131.6 ± 14.8 mm Hg vs 128.9 ± 11.8 mm Hg; P = .04) compared with preoperative simulations. No differences were observed in peak pressure in the celiac, superior mesenteric, or distal aortic arteries (P = .17-.96). When measuring blood flow, the only observed difference was an increase in peak renal flow rate after fEVAR (17.5 ± 3.8 mL/s vs 16.9 ± 3.5 mL/s; P = .04). fEVAR was not associated with changes in the mean pressure or the mean flow rate in the celiac, superior mesenteric, or renal arteries (P = .06-.98). Stenting of the renal arteries did not induce significant changes time-averaged wall shear stress in the proximal renal artery (23.4 ± 8.1 dynes/cm² vs 23.2 ± 8.4 dynes/cm²; P = .98) or distal renal artery (32.7 ± 13.9 dynes/cm² vs 29.6 ± 11.8 dynes/cm²; P = .23). In addition, computational visualization of cross-sectional velocity profiles revealed low flow disturbances associated with protrusion of renal graft fabric into the aortic lumen.

Conclusions

In a pilot study involving a selective cohort of patients who underwent uncomplicated fEVAR, patient-specific flow modelling was a feasible method for assessing the hemodynamic performance of various two-vessel fenestrated device configurations and revealed subtle differences in computationally derived peak branch pressure and blood flow rates. Structural changes in aortic flow geometry after fEVAR do not seem to affect computationally estimated renovisceral branch perfusion or wall shear stress adversely. Additional studies with invasive angiography or phase contrast magnetic resonance imaging are required to clinically validate these findings. (JVS–Vascular Science 2021;2:53-69.)

Clinical Relevance

Using a computational flow modelling for assessing the hemodynamic performance of fenestrated endovascular aneurysm repair (fEVAR), this real-world, patient-specific study included 10 participants and found that structural changes in aortic flow geometry after fEVAR did not seem to adversely impact estimated renal or visceral branch perfusion metrics (eg, peak and mean arterial pressure and flow rates) or wall shear stress. These findings overall support the ongoing clinical use of commercially available fEVAR devices for repair of juxtarenal aortic aneurysms, and provides a computational framework for future evaluation of fEVAR configurations in a preoperative or postoperative settings.

Editor's Choice - Mid Term Outcomes of Crossed Limb vs. Standard Limb Configuration in Endovascular Abdominal Aortic Aneurysm Repair: A Propensity Score Analysis

OBJECTIVE

The aim was to compare mid term outcomes between crossed limb (CL) and standard limb (SL) configuration in patients who underwent endovascular aortic aneurysm repair (EVAR).

METHODS

This was a comparative cohort study. Eligible patients who underwent EVAR between September 2011 and March 2019 in a tertiary academic centre were included. Inverse probability of treatment weighting (IPTW) was used to balance the demographic, anatomical and operative baseline characteristics between the two groups. The primary outcome was adverse limb events including type IB endoleak (T1BEL), type III endoleak, and limb occlusion. Cox proportional hazards regression and marginal structural model were performed to compare time to event outcomes.

RESULTS

The study included 729 patients (194 CL and 535 SL) with a median follow up of 34 months (interquartile range 16 - 62 months). The weighted analyses revealed no significant difference between CL and SL EVAR in terms of adverse limb events, type IA endoleak (T1AEL), type II endoleak (T2EL), re-intervention, and overall survival. In the subgroup analysis of large aneurysm sac, the CL configuration was associated with a significantly decreased risk of T1BEL (hazard ratio [HR] 0.31, 95% confidence interval [CI] 0.12 - 0.78, p = .014). Similar results were also observed in the subgroup of tortuous iliac arteries (HR 0.30, 95% CI 0.11 - 0.81, p = .017). After stratification by severe neck angulation, no significant difference was found between CL and SL EVAR for T1AEL, but the CL configuration was associated with a significantly increased risk of re-intervention (HR 2.69, 95% CI 1.31 - 5.51, p = .007). In addition, a trend towards a higher risk of adverse limb events in the CL group with severely angulated proximal neck was observed.

CONCLUSION

CL configuration in EVAR is safe and may be associated with a lower risk of T1BEL in patients with a large aneurysm sac or tortuous iliac arteries. However, it should be applied cautiously to aneurysms with a severely angulated neck due to the potentially higher risk of re-intervention.

Simple Diagnostic Tools May Guide Transcatheter Closure of Superior Sinus Venosus Defects Without Advanced Imaging Techniques

BACKGROUND

There is a recent interest in nonsurgical correction of superior sinus venosus defects. Patient selection is currently based on advanced imaging and printing technologies. Simple clinical tools to select patients will expand its applicability in developing countries.

METHODS

Defects caudally extending toward the oval fossa and right upper pulmonary veins draining beyond the cavoatrial junction on transesophageal echocardiography were excluded. Balloon interrogation of cavoatrial junction confirmed complete occlusion of the defect with unobstructed pulmonary venous drainage to left atrium. Single long covered stents or overlapping covered stents were used to exclude sinus venosus defects. Closure of left-to-right interatrial shunt without causing pulmonary vein occlusion was confirmed on follow-up imaging.

RESULTS

Forty-four patients selected after transesophageal echocardiography underwent balloon interrogation with monitoring of right upper pulmonary vein. Eighteen out of 44 patients were ineligible. Twenty-four eligible patients with closure of left-to-right interatrial shunt without pulmonary vein occlusion underwent covered stent exclusion using single long stents in 15 and overlapping stents in the rest, while 2 patients are awaiting the procedure. Four patients aged 6 to 16 years received stents that were 18 mm or larger. Three patients had stent embolization that required surgical correction in 2 but in the last patient was managed nonsurgically with an overlapping covered stent with good final outcomes. Procedure was successful in 22 patients. At a median follow-up of 20 months (range, 3-54 months), there were no adverse events. Follow-up imaging showed trivial left-to-right shunt in 4 and unobstructed pulmonary veins in all patients.

CONCLUSIONS

Transesophageal echocardiography and balloon interrogation identified 60% of the patients with sinus venosus defects to be eligible for catheter closure. Overlapping stents are an alternative to custom-made long stents. Transesophageal echocardiography confirms procedural success on follow-up. Advanced imaging and printing technologies are not essential for successful outcomes and thus simple tests increase the feasibility in developing countries.

Evolving Concepts, Management, and Treatment of Type 1 Endoleaks after Endovascular Aneurysm Repair

Over the past 20 years, there has been tremendous progress in endovascular aneurysm repair techniques and devices. The application of new third- and fourth-generation devices (from 2003 onward) has led to changes in the incidence and management of endoleaks. This comprehensive review aims to outline the most recent concepts with respect to pathophysiology/risk factors and management of Type 1 endoleaks.

Outcomes of bell-bottom technique compared to standard endovascular aneurysm repair

OBJECTIVE

The bell-bottom technique is a widely used technique to treat aortoiliac aneurysms with preservation of the hypogastric arteries. The published data are scarce with conflicting results regarding the evolution. The aim of this study was to compare the outcomes of patients submitted to endovascular abdominal aortic aneurysm repair with standard technique (S-EVAR) versus bell-bottom technique.

METHODS

This retrospective cohort study compared the outcomes of standard endovascular aneurysm repair (<16 mm iliac limbs) and bell-bottom technique (≥16 mm iliac limbs) in a tertiary vascular center between 2010 and 2015. The end points of this study were type IB endoleak, reintervention and 30-day mortality. The follow-up protocol included CT scans within 30 days of implantation and 12 months. Duplex ultrasound was performed yearly thereafter.

RESULTS

Two hundred and three patients were treated with bell-bottom technique (n = 84, mean age 72.2 ± 8.9) and S-EVAR (n = 119, mean age 72.7 ± 8.4). The overall 30-day mortality was 1.9%, with no significant difference between groups. There was higher prevalence of coronary heart disease in the bell-bottom technique group compared to the S-EVAR group (41.6% vs. 18.4%, p < 0.01). One patient in the S-EVAR group (0.85%) and four patients in the bell-bottom technique (4.6%) developed type IB endoleak. The mean follow-up period was 35.2 ± 30.4 months. By Kaplan-Meier analysis, freedom from type IB endoleak in 80 months was 85.2% in the bell-bottom technique group and 98.7% in the S-EVAR group (p = 0.05). The freedom from reintervention in 80 months was 74.0% in the bell-bottom technique group and 94.1% in the S-EVAR group (p = 0.6).

CONCLUSIONS

This study shows lower freedom from type IB endoleak in the bell-bottom group compared to the standard repair group. There is no significant difference in reoperation rate and 30-day mortality.

The Use of Iliac Branched Devices in the Acute Endovascular Repair of Ruptured Aortoiliac Aneurysms

BACKGROUND

The objective of this study was to evaluate the feasibility and midterm outcomes of iliac branch devices (IBDs) to preserve the internal iliac artery perfusion in emergent endovascular repair of ruptured aorto-iliac aneurysms.

METHODS

Between December 2012 and July 2017, a total of 8 IBDs were implanted in 6 patients (the median age 65 years; all men) in a single tertiary referral center. The indication for IBD implantation was a ruptured abdominal aortic aneurysm with a concomitant common iliac artery aneurysm (n = 4) or isolated CIA aneurysms (n = 2). The main outcome measures were technical and clinical success. The secondary outcomes were primary and primary assisted patency, the occurrence of type I/III endoleaks, and reinterventions.

RESULTS

All patients were hemodynamically stable during the procedures, which were performed under local anesthesia. Technical success was achieved in all cases (the median total procedure time of 188 min and the median IBD procedure time of 28 min). The median follow-up was 34 months (interquartile range 19-78). There were no deaths during the follow-up and no major complications unrelated to the IBD. Two (25%) secondary interventions were performed for IBD occlusion in patients with bilateral IBDs. The other reintervention was a type II endoleak embolization in 1 of these 2 patients. The freedom from reintervention estimate was 75% through 2 years. The overall primary assisted patency was 100% through 3 years.

CONCLUSIONS

The use of IBDs in the acute setting is feasible to exclude ruptured aortoiliac aneurysms while maintaining pelvic circulation. The secondary intervention rate is considerable; however, the midterm assisted primary patency rates are promising. Further studies are needed to guide patient selection and to evaluate longer term outcomes.

Evolving concepts and management of endoleaks after endovascular aneurysm repair: where do we stand in 2019?

In recent years, there has been tremendous progress in endovascular aneurysm repair (EVAR) techniques and devices. This process has seen a change in incidence, risk factors, and treatment of endoleaks as well as in follow-up protocols after EVAR. In particular, recent literature has highlighted new concepts in the evaluation and prevention/treatment of type I and II endoleak after standard EVAR. There is also recent evidence regarding new imaging protocols for follow-up after EVAR, which include magnetic resonance imaging and contrast-enhanced ultrasound. This comprehensive review aims to outline the most recent concepts on imaging follow-up, pathophysiology/risk factors, and management of endoleaks.

Endovascular Treatment of Aorta-Iliac Aneurysms with a Flared Iliac Limb

Endovascular abdominal aneurysm repair (EVAR) relies on the quality of the proximal and distal landing zone. Reinterventions are higher in patients with suboptimal landing zone. The study aimed to evaluate reintervention rate after endovascular treatment of an aorta-iliac aneurysm using the flared iliac limbs. The retrospective study included 179 patients treated with EVAR at a single university hospital institution from January 2011 to January 2014 of which 75 patients (42%) were treated with flared iliac limb stent graft and 104 patients (58%) were treated with a nonflared iliac limb stent graft. There were 165 male patients (92%), mean age was 75.8 ± 6.6 years. Thirty-six patients underwent secondary treatment accounting for overall reintervention rate of 20%. Endoleak type 1b occurred in 13 patients (7%), followed by endoleak type 1a in six patients (3%). Endoleak type 2 occurred in seven patients (4%) requiring the treatment due to abdominal aortic aneurysm (AAA) enlargement, endoleak type 3 in three patients (2%), and leg stent graft thrombosis in seven patients (4%). In 143 patients (80%), there were no secondary interventions during the follow-up period. Reintervention due to endoleak type 1b was statistically significantly higher in a flared iliac limb group ( p  < 0.02) with the rate of 7.2% compared with 1.9% rate in nonflared iliac limb group. The mean follow-up was 44.3 ± 20.4. Overall mortality was 33%. Flared iliac limb with a distal diameter of ≥ 20 mm, show a higher rate of iliac limb reintervention in a follow-up period due to endoleak type 1b.

Numerical and Experimental Investigation of Novel Blended Bifurcated Stent Grafts with Taper to Improve Hemodynamic Performance

The typical helical flow within the human arterial system is widely used when designing cardiovascular devices, as this helical flow can be generated using the “crossed limbs” strategy of the bifurcated stent graft (BSG) and enhanced by the tapered structure of arteries. Here, we propose the use of a deflected blended bifurcated stent graft (BBSG) with various tapers, using conventional blended BSGs with the same degree of taper as a comparison. Hemodynamic performances, including helical strength and wall shear stress- (WSS-) based indicators, were assessed. Displacement forces that may induce stent-graft migration were assessed using numerical simulations and in vitro experiments. The results showed that as the taper increased, the displacement force, helicity strength, and time-averaged wall shear stress (TAWSS) within the iliac grafts increased, whereas the oscillating shear index (OSI) and relative residence time (RRT) gradually decreased for both types of BBSGs. With identical tapers, deflected BBSGs, compared to conventional BBSGs, exhibited a wider helical structure and lower RRT on the iliac graft and lower displacement force; however, there were no differences in hemodynamic indicators. In summary, the presence of tapering facilitated helical flow and produced better hemodynamic performance but posed a higher risk of graft migration. Conventional and deflected BBSGs with taper might be the two optimal configurations for endovascular aneurysm repair, given the helical flow. The deflected BBSG provides a better configuration, compared to the conventional BBSG, when considering the reduction of migration risk.

Pitfalls of stenting coarctation of an angulated right circumflex aortic arch in Goldenhar syndrome

We report stenting of coarctation of an angulated right circumflex aortic arch (RCAA) using four Cheatham Platinum stents in a child with Goldenhar syndrome. Difficulties in measuring the accurate length of the curved and narrowed transverse aortic arch marked discrepancy between the luminal diameters of the long narrow transverse arch and wide descending thoracic aorta, increased displacement force caused by the 90° bend between the two parts resulted in repeated stent migrations. We discuss the tips to avoid distal stent migration in the setting of an angulated RCAA.