Deformation and dynamic response of abdominal aortic aneurysm sealing.

Endovascular sealing is a new technique for the repair of abdominal aortic aneurysms. Commercially available in Europe since 2013, it takes a revolutionary approach to aneurysm repair through minimally invasive techniques. Although aneurysm sealing may be thought as more stable than conventional endovascular stent graft repairs, post-implantation movement of the endoprosthesis has been described, potentially leading to late complications. The paper presents for the first time a model, which explains the nature of forces, in static and dynamic regimes, acting on sealed abdominal aortic aneurysms, with references to real case studies. It is shown that elastic deformation of the aorta and of the endoprosthesis induced by static forces and vibrations during daily activities can potentially promote undesired movements of the endovascular sealing structure.

Estimating the error of CT-based measurements of aortic lumen volume used in endovascular planning.

INTRODUCTION: Planning of endovascular sealing of abdominal aortic aneurysms requires measurement of the aortic lumen volume. The aim of this study was to investigate mathematically the effect of intra- and inter-observer variability error, as well as cardiac cycle-related variability, on these measurements. METHODS: Mean (±2SD) intra- and inter-observer error in lumen measurements and mean (+2SD) cardiac cycle-related variability were obtained from published literature and added to the measurement of the flow lumen volume of a 57 mm abdominal aortic aneurysm to calculate average and extreme error possibilities. RESULTS: The aneurysm volume was measured at 165 ml. The calculated possible mean measurement error due to cardiac cycle variation, intra- and inter-observer variability was +11.0%, resulting in a potential measurement of 183.1 ml. The calculated extreme errors were +24.3% (if 2SD of all errors were added to the mean) and +3.5% (if 2SD of all errors, except cardiac cycle, were subtracted from the mean), resulting in potential measurements of 170.8 ml and 205.1 ml, respectively. When considering the errors combined, the proportion of patients who may have volume measurement errors of up to ±2.5 ml, ±2.6 to ±5.0 ml and ±5.1 to ±7.5 ml were 18%, 17% and 15%, respectively. CONCLUSION: Measurement of CT-based aortic lumen volumes in abdominal aortic aneurysms is imprecise. This has practical implications for the planning and the performance of complex endovascular therapies.

Long-term follow-up of fenestrated endovascular repair for juxtarenal aortic aneurysm.

BACKGROUND: Fenestrated endovascular aneurysm repair (FEVAR) is increasingly being used for juxtarenal aortic aneurysms. The aim of this study was to review long-term results and assess the importance of changing stent-graft design on outcomes. METHODS: This was a retrospective review of all patients who underwent FEVAR within a single unit over 12 years (February 2003 to December 2015). Kaplan-Meier analysis of survival, and freedom from target vessel loss, aneurysm expansion, graft-related endoleak and secondary intervention was performed. Comparison between outcomes of less complex grafts (fewer than 3 fenestrations) and more complex grafts (3 or 4 fenestrations) was undertaken. RESULTS: Some 173 patients underwent FEVAR; median age was 76 (i.q.r. 70-79) years and 90·2 per cent were men. Median aneurysm diameter was 63 (59-71) mm and median follow-up was 34 (16-50) months. The adjusted primary technical operative success rate was 95·4 per cent. The in-hospital mortality rate was 5·2 per cent; there was no known aneurysm-related death during follow-up. Median survival was 7·1 (95 per cent c.i. 5·2 to 8·1) years and overall survival was 60·1 per cent (104 of 173). There was a trend towards an increasing number of fenestrations in the graft design over time. In-hospital mortality appeared higher when more complex stent-grafts were used (8 versus 2 per cent for stent-grafts with 3-4 versus fewer than 3 fenestrations; P = 0·059). Graft-related endoleaks were more common following deployment of stent-grafts with three or four fenestrations (12 of 90 versus 6 of 83; P < 0·001). CONCLUSION: Fenestrated endovascular aneurysm repair for juxtarenal aneurysm is associated with few aneurysm-related deaths in the long term. Significant numbers of secondary interventions are required, but the majority of these can be performed using an endovascular approach.

Mapping and uncertainty analysis of energy and pitch angle phase space in the DIII-D fast ion loss detector.

New phase space mapping and uncertainty analysis of energetic ion loss data in the DIII-D tokamak provides experimental results that serve as valuable constraints in first-principles simulations of energetic ion transport. Beam ion losses are measured by the fast ion loss detector (FILD) diagnostic system consisting of two magnetic spectrometers placed independently along the outer wall. Monte Carlo simulations of mono-energetic and single-pitch ions reaching the FILDs are used to determine the expected uncertainty in the measurements. Modeling shows that the variation in gyrophase of 80 keV beam ions at the FILD aperture can produce an apparent measured energy signature spanning across 50-140 keV. These calculations compare favorably with experiments in which neutral beam prompt loss provides a well known energy and pitch distribution.

Using neutral beams as a light ion beam probe (invited).

By arranging the particle first banana orbits to pass near a distant detector, the light ion beam probe (LIBP) utilizes orbital deflection to probe internal fields and field fluctuations. The LIBP technique takes advantage of (1) the in situ, known source of fast ions created by beam-injected neutral particles that naturally ionize near the plasma edge and (2) various commonly available diagnostics as its detector. These born trapped particles can traverse the plasma core on their inner banana leg before returning to the plasma edge. Orbital displacements (the forces on fast ions) caused by internal instabilities or edge perturbing fields appear as modulated signal at an edge detector. Adjustments in the q-profile and plasma shape that determine the first orbit, as well as the relative position of the source and detector, enable studies under a wide variety of plasma conditions. This diagnostic technique can be used to probe the impact on fast ions of various instabilities, e.g., Alfvén eigenmodes (AEs) and neoclassical tearing modes, and of externally imposed 3D fields, e.g., magnetic perturbations. To date, displacements by AEs and by externally applied resonant magnetic perturbation fields have been measured using a fast ion loss detector. Comparisons with simulations are shown. In addition, nonlinear interactions between fast ions and independent AE waves are revealed by this technique.

Enhanced localized energetic-ion losses resulting from single-pass interactions with Alfvén eigenmodes.

We report the first observation of prompt neutral beam-ion losses due to nonresonant scattering induced by toroidal and reversed shear Alfvén eigenmodes in the DIII-D tokamak. The coherent losses are of full energy beam ions expelled from the plasma on their first poloidal orbit. The first-orbit loss mechanism causes enhanced, concentrated losses on the first wall exceeding nominal levels of prompt losses. The loss amplitude scales linearly with the mode amplitude. The data provide a novel and direct measure of the radial excursion or scatter of particles induced by individual modes and may shed light on the mechanism for the scattering of energetic particles in interstellar medium.

Near midplane scintillator-based fast ion loss detector on DIII-D.

A new scintillator-based fast-ion loss detector (FILD) installed near the outer midplane of the plasma has been commissioned on DIII-D. This detector successfully measures coherent fast ion losses produced by fast-ion driven instabilities (≤500 kHz). Combined with the first FILD at ∼45° below the outer midplane [R. K. Fisher, et al., Rev. Sci. Instrum. 81, 10D307 (2010)], the two-detector system measures poloidal variation of losses. The phase space sensitivity of the new detector (gyroradius r(L) ∼ [1.5-8] cm and pitch angle α ∼ [35°-85°]) is calibrated using neutral beam first orbit loss measurements. Since fast ion losses are localized poloidally, having two FILDs at different poloidal locations allows for the study of losses over a wider range of plasma shapes and types of loss orbits.

Patch variability following carotid endarterectomy: a survey of Great Britain and Ireland.

INTRODUCTION: Evidence suggests a clinical benefit with patch angioplasty after carotid endarterectomy (CEA). The UK National Vascular Database has demonstrated variation in practice but does not record technical details. This study was intended to define indications and technique of patching after CEA. METHODS: An electronic questionnaire was emailed to all 402 members of the Vascular Society of Great Britain and Ireland. The email could not be received by 23 and 14 did not perform CEA. Some questions allowed multiple answers. Fisher's exact test was used for statistical analysis. RESULTS: There were 187 responses (51%). Fifteen members (8%) performed eversion CEA, which obviates patching. Of all the respondents, 121 surgeons (65%) always use a patch. Seventy of these (58%) use the full patch width (median: 8 mm, range: 4-10 mm). Fourteen (12%) variably trimmed the patch (median: 7.5 mm, range: 5-10 mm) and 34 (28%) routinely trimmed (median: 6 mm, range: 3-20 mm). Selective patching, dependent on internal carotid artery diameter, was performed by 48 respondents (26%), 23 of whom specified a median artery threshold diameter of 5 mm (range: 3-8 mm). General anaesthesia was always or usually used by 83 surgeons (45%), local anaesthesia by 77 (41%) and the remainder followed patient choice. Obligatory patching is performed by 68 of the 83 respondents (82%) who prefer general anaesthesia whereas only 40 of the 77 surgeons (52%) who use local anaesthesia always patch (p<0.0001). CONCLUSIONS: There is a variable rate of patching after CEA in the UK, which appears dependent on the vessel size and mode of anaesthesia. There are also differences in the patch width adopted.

Fractional resonances between waves and energetic particles in tokamak plasmas.

From numerical simulation and analytical modeling it is shown that fast ions can resonate with plasma waves at fractional values of the particle drift-orbit transit frequency when the plasma wave amplitude is sufficiently large. The fractional resonances, which are caused by a nonlinear interaction between the particle orbit and the wave, give rise to an increased density of resonances in phase space which reduces the threshold for stochastic transport. The effects of the fractional resonances on spatial and energy transport are illustrated for an energetic particle geodesic acoustic mode but they apply equally well to other types of MHD activity.

Anchoring barbs and balloon expandable stents: what is the risk of perforation and failed stent deployment?

PURPOSE: Balloon expandable stents may on occasion be deployed in close proximity to the anchoring barbs of endovascular grafts. The aim of this study was to determine the risk and effect of balloon perforation by anchoring barbs and to assess whether these risks are different if the balloon is protected by a covered stent mounted upon it. METHODS: A bench-top model was developed to mimic the penetration of anchoring barbs into the lumen of medium sized blood vessels. The model allowed variation of angle and depth of vessel penetration. Both bare balloons and those with covered stents mounted upon them were tested in the model to determine whether there was a risk of perforation and which factors increased or decreased this risk. RESULTS: All combinations of barb angle and depth caused balloon perforation but this was most marked when the barb was placed perpendicular to the long axis of the balloon. When the deployment of covered stents was attempted balloon perforation occurred in some cases but full stent deployment was achieved in all cases where the perforation was in the portion of the balloon covered by the stent. The only situation in which stent deployment failed was where the barb was intentionally placed in the uncovered portion of the balloon. This resulted in only partial deployment of the stent. CONCLUSIONS: Balloon rupture is a distinct possibility when deploying balloon-expandable stents in close proximity to anchoring barbs. Care should be taken in this circumstance to ensure that the barb is well away from the uncovered portion of the balloon.

Soft x-ray array system with variable filters for the DIII-D tokamak.

Recent upgrades to the soft x-ray (SXR) array system on the DIII-D tokamak are described. The system consists of two 32-channel arrays at one toroidal location and three toroidally distributed 12-channel arrays. The 32-channel arrays have been completely rebuilt to allow the switching of SXR filters without breaking vacuum. The 12-channel arrays have had upgrades performed to detectors, view slits, and data acquisition. Absolute extreme ultraviolet (AXUV) photodiodes are used as detectors in all arrays, allowing detection of photons ranging in energy from 2 eV to 10 keV. In the fixed-filter arrays, 127 µm Be filters are used. In the variable-filter arrays, filter wheels are used to switch between five different possible pinhole/filter combinations.

Surveillance after EVAR based on duplex ultrasound and abdominal radiography.

INTRODUCTION: Computed tomography angiography (CTA) is considered the gold standard imaging technique for surveillance following endovascular aneurysm repair (EVAR). Limitations of CTA include cost, risk of contrast nephropathy and radiation exposure. A modified surveillance protocol involving annual duplex ultrasound (DUS) and abdominal radiography (AXR) was introduced, with CTA performed only if abnormalities were identified or DUS was undiagnostic. METHODS: Prospective records were maintained on patients undergoing infra-renal EVAR at a UK, tertiary referral centre. All patients enrolled with at least one-year follow-up were reviewed. Primary outcomes identified were aneurysm rupture and aneurysm-related complications. Secondary outcomes included number of CTAs avoided and cost. RESULTS: Median follow-up was 36 months (range 12-57) for 194 patients. The total number of sets of surveillance imaging was 412 of which 70 (17%) required CTA. Abnormalities were found in 30 patients, 18 confirmed by CTA. Eleven patients required secondary intervention, three initially identified by AXR, three by DUS, three by both DUS and AXR, and two by CTA following undiagnostic DUS. No patient presented with rupture or aneurysm-related complications not identified by modified surveillance. Mean annual savings were €223. CONCLUSION: EVAR surveillance based on DUS and AXR is feasible and safe. The complimentary nature of AXR and DUS is demonstrated.

Fascial closure following percutaneous endovascular aneurysm repair.

INTRODUCTION: There are potential benefits of percutaneous over open femoral access for endovascular aneurysm repair (EVAR). Subsequent arterial closure using percutaneous devices is costly, whilst open repair risks potential wound complications and delayed discharge. The technique of fascial closure has perceived advantages but its efficacy is unclear. The aim of this study was to assess the safety and durability of fascial closure after EVAR. METHODS: Patients undergoing EVAR using devices up to 24 French were considered. Exclusion criteria included morbid obesity, high bifurcation, previous surgery, inadvertent high puncture, arteries < 5 mm and surgeon preference. The primary outcome measure was immediate technical success. All patients were followed-up clinically and with duplex at one and twelve months to determine secondary complications. RESULTS: Over a one-year period fascial closure of 69 common femoral arteries was attempted in 38 patients undergoing EVAR. Nine primary failures were due to haemorrhage in eight arteries and thrombosis in one artery; all had immediate, uncomplicated open revision. Of the 60 (87%) successful procedures, all had duplex surveillance at one month. Four pseudoaneurysms were identified, all treated conservatively. At one year, 61 fascial closures (88%) were imaged, four patients had died and two were lost to follow-up. Three of the pseudoaneurysms had resolved, the fourth patient had died (unrelated). No other complication attributable to fascial closure was found at either one or twelve months. CONCLUSION: Fascial closure is a safe, durable and cost-effective method of arterial closure following EVAR. Success and complication rates are comparable to other techniques.

Modeling the response of a fast ion loss detector using orbit tracing techniques in a neutral beam prompt-loss study on the DIII-D tokamak.

A numerical model describing the expected measurements of neutral beam prompt-losses by a newly commissioned fast ion loss detector (FILD) in DIII-D is presented. This model incorporates the well understood neutral beam deposition profiles from all eight DIII-D beamlines to construct a prompt-loss source distribution. The full range of detectable ion orbit phase space available to the FILD is used to calculate ion trajectories that overlap with neutral beam injection footprints. Weight functions are applied to account for the level of overlap between these detectable orbits and the spatial and velocity (pitch) properties of ionized beam neutrals. An experimental comparison is performed by firing each neutral beam individually in the presence of a ramping plasma current. Fast ion losses determined from the model are in agreement with measured losses.

Scintillator-based diagnostic for fast ion loss measurements on DIII-D.

A new scintillator-based fast ion loss detector has been installed on DIII-D with the time response (>100 kHz) needed to study energetic ion losses induced by Alfvén eigenmodes and other MHD instabilities. Based on the design used on ASDEX Upgrade, the diagnostic measures the pitch angle and gyroradius of ion losses based on the position of the ions striking the two-dimensional scintillator. For fast time response measurements, a beam splitter and fiberoptics couple a portion of the scintillator light to a photomultiplier. Reverse orbit following techniques trace the lost ions to their possible origin within the plasma. Initial DIII-D results showing prompt losses and energetic ion loss due to MHD instabilities are discussed.

Traveller's thrombosis: airlines still not giving passengers the WRIGHT advice!

INTRODUCTION: This study has examined the impact of the World Health Organization's Research into Global Hazards of Travel (WRIGHT) Project's phase 1 report on the information given by airlines to their passengers regarding traveller's thrombosis. METHODS: Official websites of all airlines flying from Heathrow (UK) and John F Kennedy (USA) were located through links on the websites of these two busy international airports. In June 2007, each site was scrutinized by three independent researchers to identify if traveller's thrombosis and its risk factors were discussed and what methods of prevention were advised. This exercise was repeated a year after the publication of the WRIGHT report. RESULTS: One hundred and nineteen international airlines were listed in 2007 (12 were excluded from analysis). A quarter (27/107) of airlines warned of the risk of traveller's thrombosis. A year later, five airlines were no longer operational and there had been no increase in the discussion of traveller's thrombosis (23/102). Additional risk factors discussed in June 2007 versus September 2008: previous venous thromboembolism (16%, 15%); thrombophilia (14%, 15%); family history (11%, 9%); malignancy (12%, 14%); recent surgery (19%, 16%); pregnancy (17%, 16%) and obesity (11%, 12%). Prophylaxis advice given in June 2007 versus September 2008: in-flight exercise (34%, 42%); Hydration (30%, 34%); medical consultation prior to flying (20%, 18%); graduated compression stockings (13%, 12%); aspirin (<1%, <1%) and heparin (5%, 7%). CONCLUSIONS: The majority of world airlines continue to fail to warn of the risk of traveller's thrombosis or offer appropriate advice. Alerting passengers at risk gives them an opportunity to seek medical advice before flying.

Wholly endovascular repair of thoracoabdominal aneurysm.

BACKGROUND: The aim was to evaluate a wholly endovascular approach to the repair of thoracoabdominal aortic aneurysm (TAAA). METHODS: Six patients (median age 71 years) underwent wholly endovascular repair of TAAA (maximum diameter 56-85 mm) employing individually customized endografts. Procedures were performed under general anaesthesia, with spinal drainage in five patients. Patients were followed by serial computed tomography, plain radiography and duplex imaging for a median of 17 (range 8-44) months. RESULTS: All grafts were deployed as intended, with preservation of all target vessels. There were no postoperative deaths, strokes or paraplegia. One patient suffered a silent myocardial infarction. In two patients a persistent paraostial endoleak was treated by further balloon dilatation of the stent within the endograft fenestration. Imaging before discharge confirmed aneurysm exclusion in all patients. Two patients required late secondary intervention to abolish endoleaks due to side-branch disconnection. One patient suffered late occlusion of the coeliac axis without clinical sequelae, and late occlusion of a solitary renal artery in another resulted in dependence on dialysis. There have been no late deaths and all aneurysms remain excluded. CONCLUSION: Wholly endovascular TAAA repair is relatively safe, but long-term follow-up is required to establish its durability.