Increased Brachial Artery Compliance After Arteriovenous Fistula Creation as Measured by Shear Wave Elastography: Results From a Feasibility Study.

OBJECTIVES: Arterial stiffness has been proposed as a marker of arteriovenous fistula failure and can be measured locally by using ultrasound shear wave elastography (SWE). This preliminary study aimed to assess whether SWE measurements of the brachial artery were associated with arteriovenous fistula failure. METHODS: Data were collected on patients who were indicated for fistula creation. Preoperative and postoperative vessel diameters from B-mode ultrasound, brachial artery SWE maps, and demographic data were collected. Logistic and linear regression analyses were used to determine whether any of these variables were related to the outcome of the fistula 3 months after creation. RESULTS: Data were acquired for 33 patients. Shear wave velocity values decreased after fistula creation (mean ± SD, -1.2 ± 1 m/s; P < .05). No parameters were associated with failure of the fistula in the logistic regression analysis. CONCLUSIONS: No markers were related to fistula failure, but a decrease in the shear wave velocity was observed in the brachial arteries after fistula creation, indicating increased compliance.

Non-contrast MRI methods as a tool for the pre-operative assessment and surveillance of the arterio-venous fistula for haemodialysis.

OBJECTIVE: To compare non-contrast enhanced MRI with ultrasound (US) for measurement of arm blood vessel geometries and flow velocities in volunteers and patients with end-stage renal disease. MATERIALS AND METHODS: Subjects were scanned using US (reference standard), and MRI 2D time-of-flight (ToF), 2D phase contrast (PC), and 3D multi-echo data image combination (MEDIC). Patients were also scanned after arteriovenous fistula (AVF) surgery. RESULTS: For mean vessel diameters (radial and brachial arteries; cephalic vein) MEDIC measurements were similar to US (p > 0.05). However, ToF underestimated the mean diameter of the cephalic vein relative to US (p < 0.05). For arterial velocity measurements, the mean values derived by PC-MR and US were similar (p > 0.05). Post-operatively, the intra-luminal signal intensity was hypo-intense at the anastomosis site using ToF and MEDIC. At the same site the outer boundary of the vessel was consistently lost on ToF, but remained clearly delineated on the MEDIC images. DISCUSSION: With the exception of ToF, the MRI data demonstrated excellent agreement with US for measurements of vessel geometry and flow velocity. Further, the ability to clearly delineate the post-surgery vessel edges with MEDIC MRI suggests that the technique may be useful for surveillance after AVF creation or for patient-specific modelling studies.

The aneurysmal arteriovenous fistula - morphological study and assessment of clinical implications. A pilot study.

Aneurysmal dilation of arteriovenous fistulae used for haemodialysis is a recognised complication but its clinical significance is a contentious issue. Our aims were to describe aneurysmal fistulae morphologically and clinically.Sixty patients underwent duplex scanning to measure the maximum diameter and skin thickness of their fistula. Haemodialysis function and bleeding risk were assessed clinically.The 75th percentile of maximum diameter was 2.05 cm. In addition to conventional diameter measurement, we describe a novel volume measurement technique which may be of value. No relationship was found between maximum diameter or volume and function, skin thickness or bleeding.Some studies define aneurysm at 2 cm (75th percentile); however, this definition and other arbitrary definitions lack clinical significance. This work suggests that fistula dilation should be considered together with clinical issues when determining the clinical significance of an aneurysm. Our finding that haemodialysis function, skin thickness and bleeding were not associated with diameter needs further study.

Bisoprolol versus celiprolol on dynamic hyperinflation, cardiopulmonary exercise and domiciliary safety in COPD: a single-centre, randomised, crossover study.

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is frequently associated with cardiovascular disease. The utility of beta-blockers for treating patients with COPD may be beneficial, but their safety remains uncertain, including worsening of dynamic hyperinflation (DH) during exercise. We hypothesised that among cardioselective beta-blockers celiprolol, due to its partial beta-2 agonist activity, may be safer than bisoprolol on exercise DH. METHODS: We measured isotime inspiratory capacity (IC) during cycle endurance testing in eleven moderate-severe COPD subjects, alongside other non-invasive cardiopulmonary exercise, bioreactance cardiac output, pulmonary function, biomarkers and daily domiciliary measures. Participants received titrated doses of either bisoprolol (maximim 5 mg) or celiprolol (maximum 400 mg) in randomised crossover fashion, each over 4 weeks. RESULTS: Clinically relevant DH occurred between resting and exercise isotime IC but showed no significant difference with either beta-blocker compared with post-run-in pooled baseline or between treatments. There were no other significant differences observed for remaining exercise ventilatory; non-invasive cardiac output; resting pulmonary function; beta-2 receptor and cardiac biomarkers; domiciliary pulmonary function, oxygen saturation and symptom outcomes, either between treatments or compared with baseline. No significant adverse effects occurred. CONCLUSIONS: Significant DH in moderate-severe COPD subjects was no different between bisoprolol or celiprolol or versus baseline. A broad spectrum of other non-invasive cardiopulmonary and domiciliary safety outcomes was equally reassuring. Bronchoprotection with a concomitant long-acting muscarinic antagonist might be an important safety measure in this context. TRIAL REGISTRATION NUMBER: NCT02380053.

Spiral Laminar Flow is Associated with a Reduction in Disturbed Shear in Patient-Specific Models of an Arteriovenous Fistula.

PURPOSE: Areas of disturbed shear that arise following arteriovenous fistula (AVF) creation are believed to contribute to the development of intimal hyperplasia (IH). The presence of helical flow can suppress areas of disturbed shear, which may protect the vasculature from IH. Therefore, the aim of this study is to determine if helical flow, specifically spiral laminar flow (SLF), is present in patient-specific AVF models and is associated with a reduction in exposure to disturbed shear. METHODS: Four AVF were imaged using MRI within the first two weeks following fistula creation. Patient-specific boundary conditions were obtained using phase-contrast MRI and applied at the inlet and outlets of each model. Computational fluid dynamics was used to analyse the hemodynamics in each model and compare the helical content of the flow to the distribution of disturbed shear. RESULTS: BC-1 and RC-2 are characterised by the presence of SLF, which coincides with the lowest distribution of disturbed shear. Contrastingly, SLF is absent from BC-2 and RC-1 and experience the largest amount of disturbed shear. Interestingly, BC-2 and RC-1 developed an anastomosis stenosis, while BC-1 and RC-2 remained stenosis free. CONCLUSION: These findings are in agreement with previous clinical studies and further highlight the clinical potential of SLF as a prognostic marker for a healthy AVF, as its presence correlates with an overall reduction in exposure to disturbed shear and a decrease in the incidence of AVF dysfunction, albeit in a small sample size.

Does exclusive enteral nutrition reduce the rate of stoma formation in patients requiring ileocolic resection for Crohn's disease? A single center experience.

BACKGROUND AND AIM: Nutrition has a role in achieving and maintaining remission in Crohn's disease. The aim of this study was to determine the impact of a strategy of steroid-avoidance and Exclusive Enteral Nutrition (EEN) for 6 weeks (with a minimum of 4 weeks) in adult patients presenting with acute small bowel Crohn's disease followed by an interval ileocolic resection 4-6 weeks later. METHODS: Retrospective review of prospectively collected data. Patients were administered exclusive enteral nutrition (EEN) for at least 4 weeks prior to surgery. RESULTS: 24 EEN patients included. Median age of 45 (range 23-73). 17/24 patients tolerated Modulen for at least 4 weeks, 5 were switched to Ensures and 2 a liquid diet. 6 patients underwent surgery earlier than planned. Prior to surgery, there was no change in the mean BMI, albumin increased from a mean of 36 g/L (range 25-43) to 40 g/L (range 30-48). CRP levels decreased by a mean of 35.8 mg/L overall. 19 (79%) of operations were performed laparoscopically. 6 of the cases were re-do operations. All but 3 patients avoided a stoma at the time of the original operation. There were 5 post-operative complications: 1 anastomotic leak in a patient with a BMI of 42, 3 cases of paralytic ileus and 2 wound infections. Median length of stay was 7 days (range 3-76 days). Only 2 patients were readmitted within the 30-day post-operative period. CONCLUSION: The pre-operative use of EEN appears to avoid unnecessary stoma formation with acceptable clinical outcomes.

The role of exclusive enteral nutrition in the pre-operative optimisation of adult patients with Crohn's disease. A systematic review.

AIM: To conduct a systematic review in order to bring together the current knowledge about the use of exclusive enteral nutrition (EEN) in the pre-operative optimisation of adult patients with Crohn's disease undergoing intestinal resection. METHODS: We searched Pubmed, Cochrane Library, ClinicalTrials.gov and the EU clinical trial register to identify experimental and observational studies on the effect of pre-operative EEN on nutritional and clinical outcomes of patients undergoing surgery. Methodological quality was assessed using the Downs and Black checklist. RESULTS: Seven studies were included in the final analysis. Of these 5 were retrospective cohort studies and 2 were retrospective case-control studies. There were 4 ongoing RCTs, however they have not reported data to analyse. Overall the 7 retrospective studies, support that with EEN; body mass index (BMI) does not increase, C-reactive protein decreases (CRP), albumin usually increases and haemoglobin does not significantly change. There were fewer infectious complications in patients who had taken EEN. There was a trend towards fewer stomas but only one of the studies was powered enough to demonstrate significance. There was no significant difference in recurrence rates of Crohn's disease at 12 months in any of the studies. Quality of the studies were either medium or poor. CONCLUSION: The current data on the use of EEN in pre-operative optimisation is of poor quality and underpowered to demonstrate significance. Randomised controlled trials are needed to demonstrate whether or not EEN can improve outcomes and reduce stoma formation in adult patients undergoing intestinal resection.

Assessment of brachial artery mechanics using velocity vector imaging does not predict arteriovenous fistula failure; a feasibility study.

Strain measurements by US have been suggested as a method of assessing arterial elasticity prior to arterio venous fistula creation. This pilot study sought to develop an imaging protocol to measure strain in the brachial artery via velocity vector imaging (VVI) and determine if differences in strain could be observed between a healthy group and a group with end-stage renal disease (ESRD), and if VVI measurements were associated with arterio-venous fistula malfunction. 40 healthy volunteers and 33 patients with ESRD were included in this study. All participants underwent US assessment of brachial artery strain via VVI. Peak velocity, strain, strain-rate and velocity were assessed. Patients with and without AVF failure at 3-months were assessed for differences in VVI measurement. Mean VVI measurements between the patient and volunteer groups were similar, and no significant differences were observed. Measurements were reproducible. No significant differences were observed in patients with or without AVF dysfunction. The results from this pilot study suggest VVI measurements of brachial artery mechanics are feasible and that VVI measurements may be used to assess age related changes of the brachial artery.

Imaging in Vascular Access.

This review examines four imaging modalities; ultrasound (US), digital subtraction angiography (DSA), magnetic resonance imaging (MRI) and computed tomography (CT), that have common or potential applications in vascular access (VA). The four modalities are reviewed under their primary uses, techniques, advantages and disadvantages, and future directions that are specific to VA. Currently, US is the most commonly used modality in VA because it is cheaper (relative to other modalities), accessible, non-ionising, and does not require the use of contrast agents. DSA is predominantly only performed when an intervention is indicated. MRI is limited by its cost and the time required for image acquisition that mainly confines it to the realm of research where high resolution is required. CT's short acquisition times and high resolution make it useful as a problem-solving tool in complex cases, although accessibility can be an issue. All four imaging modalities have advantages and disadvantages that limit their use in this particular patient cohort. Current imaging in VA comprises an integrated approach with each modality providing particular uses dependent on their capabilities. MRI and CT, which currently have limited use, may have increasingly important future roles in complex cases where detailed analysis is required.

Natural history of upper limb arterio-venous fistulae for chronic hemodialysis.

PURPOSE: Arterio-venous fistulae (AVF) for hemodialysis are prone to problems, ultimately leading to failure of the fistulae. Our aim was to determine the site and time to first stenosis and time to and factors influencing AVF failure for radio-cephalic (RC), brachio-cephalic (BC), and transposed brachio-basilic (BB) AVF. METHODS: Retrospective analysis of native AVF constructed within a single vascular unit between January 2002-December 2008. Patients followed up to the end points of death, AVF failure or end of study period. Data collected included: age, sex, AVF type, time and site of first stenosis and time to failure. The relationship between fistula type, stenosis, and failure were examined. RESULTS: In total, 398 native AVF were included in the study (91 RC, 208 BC, and 99 BB), with a mean age of 66 years. A total of 215 (54%) AVF developed a flow limiting stenosis, and over time 151 (40%) AVF failed. Stenoses developed significantly earlier in RC AVF (median 113 days) compared to BC (median 277 days), compared to BB (median days 414), P=.029. There was no statistically significant difference in time to failure (RC median 1344 days; BC median 1576 days; BB median 1159 days), P=.673. The presence of stenosis was the only variable found to have a significant impact on AVF failure in multivariate analysis. CONCLUSIONS: Type of upper limb fistula did not impact on failure rates. Flow limiting stenoses impacted on fistula failure.

Long-term results after placement of aortic bifurcation self-expanding stents: 10 year mortality, stent restenosis, and distal disease progression.

PURPOSE: To retrospectively evaluate the 10 year follow-up results in patients who had "kissing" self-expanding stent aortic bifurcation reconstruction. METHODS: Forty-three patients were treated with "kissing" self-expanding stents for aortoiliac occlusive disease. Early follow-up with clinical and ankle brachial pressure indices (ABPI) was performed at 3, 6, 12, and 24 months and with intra-arterial digital subtraction angiography at 12-24 months; clinical and angiographic follow-up was performed for symptom recurrence up to 10 years after treatment. Retrospective record review was performed to assess mortality, clinical patency, angiographic patency, and secondary assisted patency of both stents and downstream peripheral vessels at 5 and 10 years follow-up. RESULTS: The 2 year primary angiographic and secondary assisted stent patencies were 89% and 93%, respectively. At 10 years follow-up in 40 patients the mortality was 38% (due to myocardial infarction, stroke, chronic renal failure, malignancy, and liver failure). At 5 and 10 years follow-up the primary clinical stent patency was 82% and 68%, and the secondary assisted stent patency 93% and 86%, respectively. At 5 and 10 years, the distal vessel patency was 86% and 72%, and the secondary assisted distal vessel patency treated by surgical or endovascular techniques was 94% and 88%, respectively. At 10 years there was no limb loss. CONCLUSION: The long-term (10 year) results of aortic bifurcation arterial self-expanding stent placement in patients with arterial occlusive disease show a 10 year primary stent patency rate of 68% but a secondary assisted patency rate of 86%. In addition there is a high overall mortality due to other cardiovascular causes and the rate of distal disease progression and loss of patency is similar to the loss of stent patency rate.

Cutting balloon angioplasty versus standard balloon angioplasty for failing infra-inguinal vein grafts: comparative study of short- and mid-term primary patency rates.

PURPOSE: To evaluate the results of a recent change in practice in our institution using cutting balloon angioplasty instead of standard balloon angioplasty as the primary treatment for failing infra-inguinal vein bypass grafts. METHODS: In this nonrandomized cohort study with a historical control, failing infra-inguinal vein grafts were identified at duplex surveillance or clinical examination. Patients had confirmatory arteriography and balloon angioplasty at the same attendance. Interventions proximal or distal to the graft itself and prosthetic grafts were not included. Patients were entered into a duplex graft surveillance program. Initial assessment of technical success was duplex or improvement 4-6 weeks after the primary angioplasty. RESULTS: Twenty-seven consecutive patients were treated with standard balloon angioplasty, then 11 consecutive patients were treated with cutting balloon angioplasty. Initial technical success was 74% for the standard balloon versus 82% for the cutting balloon. The primary patency rate at 6 months was 16/26 (62%) for standard balloon angioplasty and 8/10 (80%) for cutting balloon angioplasty (p = 0.44). The primary patency rate at 12 months was 9/25 (36%) for standard balloon angioplasty and 5/10 (50%) for cutting balloon angioplasty (p = 0.47). CONCLUSION: The use of cutting balloons for primary angioplasty of infra-inguinal vein grafts offers no definite advantage over standard balloon angioplasty in this institution or compared with patency rates after standard balloon angioplasty reported elsewhere. Larger multicenter studies would be required to demonstrate whether there was any real difference between the two techniques.