| 1. |
- Roos, Håkan, 1967, et al.
(författare)
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Displacement Forces in Stent Grafts: Influence of Diameter Variation and Curvature Asymmetry
- 2016
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 52:2, s. 150-156
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Long-term durability after endovascular aortic repair is influenced by stent graft migration causing types I and III endoleaks. Flow induced displacement forces have been shown to have the potential to cause migration. In this study, the influence of the distal diameter of iliac limb stent grafts and the shape of graft curvature on flow induced displacement forces, were investigated. Methods: In an experimental pulsatile flow model mimicking aortic conditions in vivo, flow induced displacement forces at the proximal and distal ends of iliac limb stent grafts were studied at different angles (0-90 degrees) and perfusion pressures (145/80, 170/90, 195/100 mmHg). Bell-bottomed, tapered, and non-tapered stent grafts and also asymmetric stent graft curvatures at 90 bend were studied. Measurements of graft movement were performed at all studied angulations and graft shapes. Results: For all stent graft diameters, flow induced displacement forces increased with higher pressure and increased stent graft angulation. Forces in the bell-bottom graft were considerably higher than in tapered and non-tapered grafts, with a markedly elevated peak force at the distal end (proximal end, 2.3 +/- 0.06 N and distal end, 6.9 +/- 0.05 N compared with 1.7 +/- 0.08 N and 1.6 +/- 0.08 N in non-tapered grafts; p <.001 both). Peak forces in tapered and non-tapered grafts were not significantly different between the proximal and distal end. In asymmetric stent graft curvatures, a significant increase in displacement forces was observed in the attachment zone that was closest to the stent graft bend. Graft movement increased with greater displacement forces. Conclusion: Flow induced displacement forces in iliac limb stent grafts are significant and are influenced by distal stent graft diameter and the shape of the graft curvature. The displacement forces are particularly high at the large distal end of bell-bottom grafts. Wide iliac arteries treated with bell-bottom stent grafts may require more vigilant surveillance and improved stent graft fixation.
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| 2. |
- Tokarev, Mikhail, 1982, et al.
(författare)
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DIC for Surface Motion Analysis Applied to Displacement of a Stent Graft for Abdominal Aortic Repair in a Pulsating Flow
- 2015
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Ingår i: PIV15; 11th International Symposium on Particle Image Velocimetry, Santa Barbara, California, USA, September 14-16, 2015. ; , s. 1-12
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Stent graft migration has been recognized to influence the long-term durability of endovascular aortic repair. Flow-induced displacement forces acting on the attachment zones may contribute to this migration. An experimental perfusion model consisting of the flow loop described by Roos et al. 2014 was used for further characterization of the pulsating flow induced stent graft movements with monocular and stereoscopic configurations of an optical imaging system. This paper adds new information on displacement measurement accuracy and 3D deformation analysis of the stent graft, which is used for abdominal aortic aneurysm treatment. The work describes used modification of Soloff’s Stereo PIV reconstruction algorithm for surface motion analysis. It was found that the oscillation of the stent graft’s body in the perpendicular direction to the front plane was 5 times less than side movements of the bent stent graft. These results can be used for further studies on different stent graft geometrical configurations and CFD simulations using fluid-structure interaction approach.
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| 3. |
- Nordanstig, Joakim, et al.
(författare)
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Deep Femoral Vein Reconstruction of the Abdominal Aorta and Adaptation of the Neo-Aortoiliac System Bypass Technique in an Endovascular Era.
- 2019
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Ingår i: Vascular and endovascular surgery. - : SAGE Publications. - 1938-9116 .- 1538-5744. ; 53:1, s. 28-34
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Tidskriftsartikel (refereegranskat)abstract
- Primary infection of the abdominal aorta is a rare pathology that may threaten the integrity of the aortic wall, while secondary aortic prosthesis infection represents a devastating complication to open surgical and endovascular aortic surgery. Curative treatment is achievable by removal of all infected prosthetic material followed by a vascular reconstruction.Twelve consecutive patients treated with the neo-aortoiliac system bypass (NAIS) procedure were reviewed. Nine were treated for a secondary aortic prosthesis infection (tube graft n = 3, bifurcated graft n = 4, endovascular aortic repair (EVAR) stent graft n = 1, and fenestrated EVAR [FEVAR] stent graft n = 1), while 3 patients underwent NAIS repair due to an emergent primary mycotic aortoiliac aneurysm. Primary Results: Ten of 12 patients survived 30 days. Three patients were operated on acutely, and 9 patients had elective or subacute NAIS surgery. Two of 3 patients operated acutely died within 30 days, whereas no 30-day or 1-year mortality was observed in patients undergoing elective or subacute surgery. The median time from primary reconstruction to the NAIS procedure was 11 months (range: 0-201 months). Stent grafts (n = 5 of 12) were in 4 cases explanted using endovascular balloon clamping. Of the explanted endografts, 2 patients presented with a secondary graft infection after EVAR/FEVAR, while 3 patients had been emergently treated with endovascular cuffs as a "bridge-to-surgery" procedure due to aortoenteric fistula (AEF). Patients who received a "bridge-to-surgery" regimen were treated with the NAIS procedure within 8 weeks (median 27 days, range: 27-60) after receiving emergency stent grafting.Aortic balloon-clamping during explantation of infected aortic prosthetic endografts is feasible and facilitates complete endograft removal. Endovascular bridging procedures could be beneficiary in the treatment of AEF or anastomotic dehiscence due to graft infection, offering a possibility to convert the acute setting to an elective definitive reconstructive procedure with a higher overall success rate.
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| 4. |
- Roos, Håkan, 1967, et al.
(författare)
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Predisposing Factors for Re-interventions with Additional Iliac Stent Grafts After Endovascular Aortic Repair.
- 2017
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Ingår i: European journal of vascular and endovascular surgery : the official journal of the European Society for Vascular Surgery. - : Elsevier BV. - 1532-2165. ; 53:1, s. 89-94
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Tidskriftsartikel (refereegranskat)abstract
- Endoleaks of type Ib and III are relatively common causes of re-intervention after EVAR. The aim was to determine underlying causes and identify anatomical factors associated with these re-interventions.A total of 444 patients with standard bifurcated stent grafts were included in a retrospective observational study. Patients requiring additional iliac stent grafts (n=24) were compared to those who did not (n=420). Pre- and post-operative CT examinations were reviewed in patients with additional iliac stents. Reasons for re-interventions were defined as migration (>5mmat the distal end or at interconnections), progression of disease (iliac artery diameter exceeding graft diameter), inadequate distal seal length at primary repair, or a combination of these factors.Twenty-four patients received 31 additional grafts in 30 limbs after a median 46 months (range 2-92 months). Five re-interventions (21%) were due to rupture. Re-intervened limbs had a larger iliac artery diameter 18mm (25th and 75th percentile 20-25) versus 15mm (13-18mm), p<.001. The degree of iliac limb oversizing at primary EVAR was lower in re-intervened patients (11% (8-18%) versus 18% (12-26%), p=.003). In re-intervened patients, iliac attachment zones were shorter in treated limbs than in untreated 23mm (11-34) versus 34mm (25-44), p<.001). Sixteen of 31 re-interventions (51%) were caused by migration (10at the distal landing site, 6at interconnections), nine of 31 (29%) by disease progression, and nine of 31 (29%) had inadequate initial stent graft placement. Three of 31 re-interventions (10%) were done as proactive procedures.Additional iliac stent grafting occurred late after primary repair; a considerable number were caused by rupture. A low degree of oversizing, migration at the distal landing site, separation of stent graft interconnections, disease progression at the distal landing site, and inadequate initial stent graft placement may all contribute. Patients with large iliac dimensions and short attachment zones may need a larger degree of oversizing and more vigorous surveillance.
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| 5. |
- Roos, Håkan, 1967
(författare)
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Re-interventions after endovascular aortic repair: clinical and experimental studies
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Endovascular aortic repair (EVAR) has lower morbidity and mortality than open surgery. Late complications and re-interventions are more common, however, and the timing of different re-interventions and their respective underlying causes are not fully understood. Aims: The overall aim was to describe re-interventions after EVAR and to identify possible underlying causes. Specific aims were as follows: 1. To describe re-interventions after EVAR, including incidence, indications, procedures, and outcome, concentrating especially on non-access-related re-interventions. 2. To determine underlying causes and to identify anatomical factors associated with additional iliac stent grafting. 3. To study flow-induced displacement forces in iliac limb stent grafts and the influence of stent graft angulation, fluid pressure, pulsation frequency, distal diameter of the stent graft, and asymmetric graft curvatures in an experimental aortic model. 4. To describe a new endovascular technique to close small entries that persist in the aortic arch. Materials and methods: Studies 1 and 2 were retrospective single-centre cohort studies of re-interventions after standard EVAR, focusing especially on non-access-related re-interventions. In Study 1, incidence, indications, procedures, and outcome were analyzed in 405 patients. In Study 2, 24 patients with additional iliac stent grafts after EVAR were studied. Computed tomography examinations were reviewed in detail regarding causes of re-intervention and underlying anatomic factors. These patients were compared with 420 patients treated with bifurcated EVAR during the same time period who did not require additional iliac stent grafts during follow-up, regarding patient characteristics and preoperative anatomic measurements. Studies 3 and 4 involved investigation of flow-induced displacement forces in iliac limb stent grafts in an experimental flow model mimicking physiologic conditions. In Study 3, the forces on a tubular stent graft with symmetric curvature were studied in relation to graft angulation, fluid pressure, and stroke rate. In Study 4 tapered, non-tapered, and bell-bottom grafts were studied at symmetric graft curvature and non-tapered grafts were studied at asymmetric curvature. Study 5 involved a new endovascular technique for closure of persistent small entries in selected patients with aneurysmal dilatation of chronic aortic dissections. Results: Study 1 showed that embolization of endoleak type II and placement of additional iliac stent grafts were the most common re-interventions after EVAR. These interventions were performed long after the initial intervention. Medium-term outcome in patients with re-intervention was comparable to that in patients without re-intervention. Study 2 showed that a considerable number of additional iliac stent grafting were caused by rupture. Migration at the distal landing site or graft interconnections was the most common cause, followed by disease progression. Study 3 demonstrated that flow-induced displacement forces were of similar magnitude at both ends of a non-tapered iliac stent graft, and the force increased with increasing graft angulation and fluid pressure but not with increasing pulse frequency. There was a high correlation between pulsatile graft movement and displacement forces. Study 4 showed that there were particularly high displacement forces in bell-bottom grafts, and that the forces were dependent on distal graft diameter and shape of the curvature. Study 5 showed that endovascular closure of persistent entries in chronic dissections is feasible, and in selected patients it may be an alternative to open surgery. Conclusions: Re-interventions are still common after EVAR, but most are percutaneous procedures and outcomes are generally good. Additional iliac stent grafting is one of the more frequent re-interventions, and in most cases it is related to stent graft migration, with a higher risk in patients with large iliac diameters and short attachment zones. Flow-induced displacement forces may have a role in the increased risk of migration. Patients with EVAR landing zones in wide iliac arteries may need improved graft fixation and more vigorous surveillance.
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