Graeme Houston

Spiral Laminar Flow Prosthetic Bypass Graft: Medium-Term Results From a First-In-Man Structured Registry Study

BACKGROUND A number of surgical strategies and graft enhancements have been trialled to improve the performance of prosthetic grafts. Neointimal hyperplasia may, in part, be a normal cellular response to an abnormal (turbulent) flow environment. This first-in-many study assesses the safety and medium-term patency performance of a new graft designed to induce stable laminar flow through the distal anastomosis. METHOD Forty patients who required an infrainguinal bypass graft were recruited/registered from a number of centers in Belgium and The Netherlands. Thirty-nine received a Spiral Laminar Flow graft as part of a standard treatment protocol (23 above-the-knee and 16 below-the-knee bypasses). Kaplan-Meier analyses were used to calculate primary and secondary patency rates. RESULTS The 12-, 24-, and 30-month primary patency rates were 86%, 81%, and 81% for above-the-knee bypasses and 73%, 57%, and 57% for below-the-knee bypasses, respectively. In the case of secondary patency rates, numbers were unchanged for above-the-knee bypasses and were 86%, 64%, and 64%, respectively, for below-the-knee bypasses. There were no amputations in the study population. CONCLUSION This first-in-man series shows potential for the idea of spiral flow-enhanced prosthetic grafts. As always, randomized studies are required to explore the role of different enhanced prosthetic grafts.

Early cannulation grafts for haemodialysis: a systematic review

Purpose Arteriovenous grafts have advantages compared with central venous catheters for dialysis access and guidelines suggest their use as second choice after arteriovenous fistulas. Standard practice with expanded polytetrafluoroethylene (ePTFE) grafts has been to avoid cannulation for 2 weeks following placement, but new generation grafts have been marketed for their early cannulation properties allowing use as an alternative to central venous catheters for prompt access. The aim of this review is to search the current literature for evidence of early cannulation of new generation grafts and to assess their patency and complication rates. Methods Electronic databases were searched for studies assessing the use of early cannulation grafts for dialysis in accordance with PRISMA. The primary outcomes for this study were primary patency rate, primary-assisted patency rate and secondary patency rate. Secondary outcomes were timing of first cannulation, rates of access thrombosis, steal syndrome, pseudo-aneurysm and infection. Results Following strict inclusion/exclusion criteria by two reviewers, 15 studies were included in our review and divided into the different types of graft. Flixene, Avflo, Rapidax and Acuseal grafts showed that early cannulation within 72 h was possible; there was no evidence of the use of Vectra within 2 weeks of placement. All grafts showed similar patency and complication rates as previously published data on standard ePTFE grafts. Conclusion Our review showed that early cannulation is possible without detriment, but data did not allow specific graft recommendations. Therefore, we feel that a multicentre, randomised controlled trial is necessary to compare early cannulation grafts.

Blood vessel segmentation and width estimation in ultra-wide field scanning laser ophthalmoscopy

Features of the retinal vasculature, such as vessel widths, are considered biomarkers for systemic disease. The aim of this work is to present a supervised approach to vessel segmentation in ultra-wide field of view scanning laser ophthalmoscope (UWFoV SLO) images and to evaluate its performance in terms of segmentation and vessel width estimation accuracy. The results of the proposed method are compared with ground truth measurements from human observers and with existing state-of-the-art techniques developed for fundus camera images that we optimized for UWFoV SLO images. Our algorithm is based on multi-scale matched filters, a neural network classifier and hysteresis thresholding. After spline-based refinement of the detected vessel contours, the vessel widths are estimated from the binary maps. Such analysis is performed on SLO images for the first time. The proposed method achieves the best results, both in vessel segmentation and in width estimation, in comparison to other automatic techniques.

Hemodynamic effects of spiral ePTFE prosthesis compared with standard arteriovenous graft in a carotid to jugular vein porcine model

Introduction The primary patency rate of arteriovenous (AV) grafts is limited by distal venous anastomosis stenosis or occlusion due to intimal hyperplasia associated with distal graft turbulence. The normal blood flow in native arteries is spiral laminar flow. Standard vascular grafts do not produce spiral laminar flow at the distal anastomosis. Vascular grafts which induce a spiral laminar flow distally result in lower turbulence, particularly near the vessel wall. This initial study compares the hemodynamic effects of a spiral flow–-inducing graft and a standard graft in a new AV carotid to jugular vein crossover graft porcine model. Methods Four spiral flow grafts and 4 control grafts were implanted from the carotid artery to the contralateral jugular vein in 4 pigs. Two animals were terminated after 48 hours and 2 at 14 days. Graft patency was assessed by selective catheter digital angiography, and the flow pattern was assessed by intraoperative flow probe and color Doppler ultrasound (CDU) measurements. The spiral grafts were also assessed at enhanced flow rates using an external roller pump to simulate increased flow rates that may occur during dialysis using a standard dialysis needle cannulation. The method increased the flow rate through the graft by 660 ml/min. The graft distal anastomotic appearances were evaluated by explant histopathology. Results All grafts were patent at explantation with no complications. All anastomoses were found to be wide open and showed no significant angiographic stenosis at the distal anastomosis in both spiral and control grafts. CDU examinations showed a spiral flow pattern in the spiral graft and double helix pattern in the control graft. No gross histopathological effects were seen in either spiral or control grafts. Conclusion This porcine model is robust and allows hemodynamic flow assessment up to 14 days postimplantation. The spiral flow–-inducing grafts produced and maintained spiral flow at baseline and enhanced flow rates during dialysis needle cannulation, whereas control grafts did not produce spiral flow through the distal anastomosis. There was no deleterious effect of the spiral flow–-inducing graft on macroscopic and histological examination. The reducing effect of spiral flow on intima hyperplasia formation will be the subject of further study using the same AV graft model at a longer period of implantation.

An Increased B-Type Natriuretic Peptide in the Absence of a Cardiac Abnormality Identifies Those Whose Left Ventricular Mass Will Increase Over Time

Objectives The purpose of this study was to identify the relationship of B-type natriuretic peptide (BNP) with evolution of left ventricular mass (LVM) in optimally treated primary prevention patients. Background Patients who have an elevated BNP no cardiac abnormality on echocardiography are common and at increased risk of adverse events. One hypothesis is that an elevated BNP is an early sensitive indicator of who will develop future structural abnormalities such as left ventricular (LV) hypertrophy. Methods We identified optimally treated primary prevention patients with no cardiac abnormality at baseline. In particular, they had no myocardial ischemia, LV hypertrophy, LV dysfunction, or left atrial enlargement. They had a diverse range of plasma BNP levels and underwent cardiac magnetic resonance at baseline and 3 years later on a 3-T scanner. Results Fifty patients with a diverse range of BNP were studied (with BNP ≤10 pg/ml in 25 patients and >10 pg/ml in 25 patients). LVM increased (+4.7 ± 3.5 g) in 24 patients and decreased (–4.9 ± 2.8 g) in 26 patients (p < 0.01). Blood pressure by 24-h monitoring was virtually identical between those whose LVM increased (systolic blood pressure 122 ± 14 mm Hg) and those whose LVM decreased (systolic blood pressure 121 ± 11 mm Hg, p = 0.77). Plasma BNP was nearly 3 times higher in those whose LVM increased versus those in whom LVM decreased (21 ± 9.6 pg/ml vs. 7.9 ± 3.9 pg/ml, p < 0.01). The c-statistic for BNP was 0.88. Conclusions In optimally treated primary prevention patients, plasma BNP levels are able to distinguish between those whose LVM will increase during the next 3 years versus those whose LVM will decrease during the next 3 years. This may explain why individuals with high BNP are at increased risk even if no cardiac abnormality can be detected initially.

Framework for detailed workflow analysis and modelling for simulation of multi‐modal image‐guided interventions

Purpose – The purpose of this paper is to provide a framework for analysing and modelling detailed workflow of image‐guided interventions to facilitate simulation and the re‐engineering process for the development of new procedures in multi‐modal imaging environments.Design/methodology/approach – The methodology presented includes a literature review on workflow simulation in surgery, focussing on radiology environments, an assessment of simulation tools, a data gathering and management framework and research on methods for conceptual modelling of the processes.Findings – The literature review reveals that few authors attempted to analyse the phases within image‐guided interventions, and those that did, only did so partially. The framework developed for this work intends to fill the gap found in the survey. It allows the maintenance and management of large amounts of data, one of the most critical factors when modelling detailed workflow. In addition, selecting the appropriate simulation software plays an...

An animal paired crossover ePTFE arteriovenous graft model

PurposePreviously, we developed a porcine model for Arterio Venous Graft (AVG) failure to allow assessment of new access strategies. This model was limited concerning graft length. In the present technical report, we describe a modification of our model allowing the assessment of long AVGs.TechniqueIn 4 pigs, AVGs of 15 cm length were created bilaterally in a cross-over fashion between the carotid artery and the contralateral jugular vein. Two days (2 pigs) and two weeks (2 pigs) after AV shunting, graft patency was evaluated by angiography, showing all four grafts to be patent, with no sign of angiographic or macroscopic narrowing at the anastomoses sites.ConclusionsIn this modified pig AVG failure model, implantation of a bilateral cross-over long AVG is a feasible approach. The present model offers a suitable tool to study local interventions or compare various long graft designs aimed at improvement of AVG patency.

Brown-Séquard syndrome due to noncompressive disc prolapse and spinal cord infarction

A 36-year-old female presented with acute onset right mid thoracic pain. Over the subsequent 30 min, she developed weakness of the right lower limb and contralateral numbness and paraesthesia. On examination, there was increased tone in the right lower limb with pyramidal type weakness grade 1–2/5, hyperreflexia and an extensor plantar response. Pyramidal function on the left was normal. In relation to her sensory examination, there was a patch of sensory loss to pain on the right at T7. Below this, there was contralateral pain and temperature loss distal to the knee. Proprioception and vibration were lost on the right to the knee. These signs and symptoms were consistent with a partial Brown-Sequard syndrome on the right at T7. …

Effect of renal artery revascularization upon cardiac structure and function in atherosclerotic renal artery stenosis: cardiac magnetic resonance sub-study of the ASTRAL trial

Background Cardiac abnormalities are frequent in patients with atherosclerotic renovascular disease (ARVD). The Angioplasty and Stenting for Renal Artery Lesions (ASTRAL) trial studied the effect of percutaneous renal revascularization combined with medical therapy compared with medical therapy alone in 806 patients with ARVD. Methods This was a pre-specified sub-study of ASTRAL (clinical trials registration, current controlled trials number: ISRCTN59586944), designed to consider the effect of percutaneous renal artery angioplasty and stenting on change in cardiac structure and function, measured using cardiac magnetic resonance (CMR) imaging. Fifty-one patients were recruited from six selected ASTRAL centres. Forty-four completed the study (medical therapy n = 21; revascularization n = 23). Full analysis of CMR was possible in 40 patients (18 medical therapy and 22 revascularization). CMR measurements of left and right ventricular end systolic (LV and RVESV) and diastolic volume (LV and RVEDV), ejection fraction (LVEF) and mass (LVM) were made shortly after recruitment and before revascularization in the interventional group, and again after 12 months. Reporting was performed by CMR analysts blinded to randomization arm. Results Groups were well matched for mean age (70 versus 72 years), blood pressure (148/71 versus 143/74 mmHg), degree of renal artery stenosis (75 versus 75%) and comorbid conditions. In both randomized groups, improvements in cardiac structural parameters were seen at 12 months, but there were no significant differences between treatment groups. Median left ventricular changes between baseline and 12 months (medical versus revascularization) were LVEDV -1.9 versus -5.8 mL, P = 0.4; LVESV -2.1 versus 0.3 mL, P = 0.7; LVM -5.4 versus -6.3 g, P = 0.8; and LVEF -1.5 versus -0.8%, P = 0.7. Multivariate regression also found that randomized treatment assignment was not associated with degree of change in any of the CMR measurements. Conclusions In this sub-study of the ASTRAL trial, renal revascularization did not offer additional benefit to cardiac structure or function in unselected patients with ARVD.

Workflow Analysis, Design, Modeling and Simulation for the Multimodality Imaging Therapy Operating System (MITOS)

Image-guided therapy has the great benefit for patients by reducing invasiveness of procedures to avoid complications and improve effectiveness and efficacy and carries the potential to improve the outcome for the patients. However, it is utilizing very costly and complex technologies such as imaging, navigation, and robotics. Although there should be no price tag of any of the mentioned improvements, we must face an increasing pressure on the healthcare systems to be more economic. It is therefore mandatory to utilize expensive equipment as efficient as possible and to reduce unnecessary staff involvement handling complex equipment instead of serving the patients personal needs. This chapter describes the attempt to apply state-of-the-art industrial modeling and simulation tools to optimized workflow, equipment, and staff allocation for more efficient, effective, and economic image-guided therapy.