Volume 5, Number 6: June 2002
Angiographic distribution of lower extremity
atherosclerosis in patients with and without diabetes.
The cost-effectiveness of magnetic
resonance angiography for carotid artery stenosis and peripheral vascular
disease: a systematic review.
Branched chain amino acids in heptatic
encephalopathy.
Stroke prevention: Management of
modifiable vascular risk factors.
|
Angiographic distribution of lower extremity atherosclerosis
in patients with and without diabetes. Reference: Diabet Med 2002 May;19(5):366-370. AIMS: To determine differences in the anatomic site of atherosclerosis in the lower extremity between patients with and patients without diabetes. DESIGN: Cross-sectional study of patients who underwent angiography of both legs because of symptoms of intermittent claudication, rest and/or night pain, ulceration or gangrene. METHODS: The angiographies of 37 patients with diabetes and 37 patients without diabetes, matched for age, sex and smoking behaviour, were evaluated using the Bollinger scoring system. RESULTS: The mean (sd) Bollinger score in the upper leg (from the abdominal aorta to and including the superficial femoral artery) was higher (P = 0.01) for patients without diabetes (35.3 (22.8)) than for patients with diabetes (23.3 (16.1)). In the lower leg (from the popliteal artery to the posterior tibial artery) patients with diabetes tended to have a higher score than patients without diabetes: 47.4 (34.2) and 37.6 (32.9), respectively (P = 0.22). CONCLUSION: This angiographic study confirms the clinical notion that lower limb atherosclerosis in diabetes is more severe in distal segments of the lower extremity, while the proximal segments remain less attenuated compared with patients without diabetes.
BACKGROUND: The principal manifestations of carotid and peripheral atherosclerosis, respectively, include transient ischaemic attack and stroke, and lower limb arterio-occlusive disease resulting in intermittent claudication (pain on walking), ischaemic rest pain, ulceration or gangrene. The total costs to the NHS of arterial and venous disease, in hospital and primary care, exceed GBP 350 million; the total costs of stroke have been estimated as substantially higher, at 5.8 per cent of total expenditure. Clinical decision-making relies on evaluation of the vessels in terms of the degree of stenosis, or narrowing. Magnetic resonance angiography (MRA) is a technique for imaging blood vessels that contain flowing blood. It can be performed on most magnetic resonance scanners installed in hospitals today, and represents an alternative to conventional angiographic techniques using X-rays (digital subtraction angiography (DSA)), or more recent imaging developments, including ultrasound. In this review the use of contrast-enhanced MRA and two-dimensional (2D) and three-dimensional (3D) time-of-flight (TOF) MRA for presurgical assessment in carotid artery disease and in peripheral vascular disease is considered. OBJECTIVES: (1) To identify the literature on MRA that is relevant to the use of MRA for presurgical assessment in carotid artery disease and in peripheral vascular disease. (2) To synthesise published evidence about the diagnostic performance of MRA, compared with DSA, in carotid artery disease and in peripheral vascular disease at surgical decision thresholds. (3) To use this evidence, together with other information about costs and outcomes, to model the cost-effectiveness of MRA compared with conventional angiography in carotid artery disease and in peripheral vascular disease. METHODS - DATA SOURCES: (1) Electronic searches of MEDLINE, EMBASE, HealthSTAR, Science Citation Index, Index to Scientific and Technical Proceedings, the Cochrane Library, Inside from the British Library, EconLIT, HEED, the NHS EED and the Online Computer Library Centre, 1990-1999. (2) A limited Internet search for reviews, 1990-1999. (3) A handsearch of ten key journals and the Department of Health databases (Hospital Episode Statistics and Health Related Resource Groups), 1990-1999. METHODS - STUDY SELECTION: Studies of the diagnostic performance of MRA in the relevant clinical conditions and performed on humans were included with two provisos: that sufficient data were reported for the construction of a 2 x 2 contingency table, and that application-specific inclusion criteria were satisfied. Non-English-language studies were included. Studies reporting cost data were included, providing resource use and costs for the UK setting were reported separately, and providing the study did not use expert opinion or charge data to estimate costs. METHODS - DATA EXTRACTION: Checklists that covered study design, patient characteristics, technical details and potential biases in study execution were completed independently by two reviewers. Consensus was reached on any disagreements. One reviewer, who worked with another where difficulty arose, extracted results on diagnostic performance. Summaries were written to describe each article. Cost data were extracted and summarised by two team members. METHODS - DATA SYNTHESIS: Summary receiver operating characteristic methods were used to combine the results of diagnostic performance studies, grouped by MRA technique and diagnostic threshold. The thresholds used were: (1) For carotid artery disease, using the North American Symptomatic Carotid Endarterectomy Trial (NASCET) protocol: (a) 0-69 per cent or 100 per cent versus 70-99 per cent; (b) 0-49 per cent or 100 per cent versus 50-99 per cent; (c) 0-99 per cent versus 100 per cent. (2) For peripheral vascular disease: (a) 0-49 per cent versus 50-100 per cent; (b) 0-49 per cent or 100 per cent versus 50-99 per cent; (c) 0-99 per cent versus 100 per cent. Study validity was investigated using a multiple linear regression analysis. Overall event rates were calculated by pooling patient results from the included studies. A decision analytic model was used to combine information from the literature and cost estimates, in order to determine the relative cost-effectiveness of MRA and DSA in the two clinical applications. The analysis was performed from the perspectives of the healthcare purchaser and clinician. Sensitivity analysis was performed. RESULTS Ten articles on carotid artery stenosis satisfied all the inclusion criteria and a further 24 satisfied at least four inclusion criteria. There were too few articles on the latest contrast-enhanced techniques for quantitative synthesis, but the results appear better than those for 2D and 3D TOF methods. The TOF methods are highly accurate for detecting occlusion and 70-99 per cent stenoses, but are less accurate for 50-99 per cent stenoses. The decision analytic model showed that over 10 years following its use, MRA is expected to cost GBP 194 less than DSA, with no difference in expected quality-adjusted life-years (QALYs). Providing the equipment is used at more than 10 per cent of capacity, MRA is associated with lower expected costs than DSA. Twenty articles on peripheral vascular disease satisfied all the inclusion criteria. Both 2D TOF and contrast-enhanced MRA are highly accurate for distinguishing 0-49 per cent from 50-100 per cent stenoses. The contrast-enhanced techniques show a non-significant trend for improved performance over 2D TOF MRA. The decision analytic model showed that there is no difference in expected QALYs for MRA and DSA. If the equipment is used at under 100 per cent of capacity, 2D TOF MRA is associated with higher expected costs than DSA, but contrast-enhanced MRA has lower expected costs. CONCLUSIONS - IMPLICATIONS FOR HEALTHCARE: In carotid artery disease, 2D and 3D TOF MRA techniques are accurate for identifying both occlusions and 70-99 per cent stenoses as defined by conventional angiography. The evidence does not support their use for identifying 50-99 per cent stenoses. If the utilisation rate for an MRA system to evaluate all patients (with and without carotid artery disease) is greater than 10 per cent, then MRA is likely to be a cost-effective option. In peripheral vascular disease the evidence supports the use of 2D TOF and contrast-enhanced MRA techniques for identifying occlusions and 50-100 per cent stenoses. If both DSA and MRA are already available in the local setting, then MRA is more cost-effective than DSA, especially if contrast-enhanced MRA is available. The conclusions about cost-effectiveness are valid only for high-quality diagnostic studies. Such examinations can only be performed following training and adequate experience. Consequently, there is a case for guidelines, training and accreditation schemes to be established by the relevant professional bodies. CONCLUSIONS - RECOMMENDATIONS FOR FURTHER RESEARCH: (1) The establishment of a multicentre tracker study to determine the accuracy of contrast-enhanced MRA, duplex ultrasound and computed tomography (CT) angiography (singly or in combination) for the investigation of peripheral vascular disease. (2) The establishment of a multicentre tracker study to determine the accuracy of MRA, duplex ultrasound and CT angiography (singly or in combination) for the investigation of carotid artery disease. (3) Support for data from primary studies to be held on web servers is recommended, as it would facilitate future modelling activity. (4) A rapid, structured review focused on contrast-enhanced MRA in 2002. (5) The compilation of general guidelines for designing and presenting trials of diagnostic and imaging technologies. (6) A methodological investigation of publication bias specifically focused on diagnostic literature. (7) Studies on patient preferences for the diagnostic process and expected impact on their health status and health-related quality of life. (8) Monitoring of expert opinion to ensure that trials of new non-invasive MRA techniques are implemented in a timely way. (9) Updating of the peripheral vascular disease model in 2005.
BACKGROUND: Early theories or hepatic encephalopathy focused on ammonia-driven disruption of the Krebs cycle and cellular energy production. The "false-neurotransmitter" theory directed attention toward the interactions of amino acids, metabolism, the blood-brain barrier and neurotransmission. As they evolved, these studies revealed surprising and subtle effects of ammonia on brain amino acid uptake. DATA SOURCES: Research over a 15-year period in Josef E. Fischer's laboratory explored many aspects of these interactions. Subsequent studies by others have confirmed and extended them into other areas. Insights from this work continue to stimulate attempts to confirm or disprove the clinical utility of branched chain amino acids. CONCLUSIONS: Increased understanding of the factors affecting ammonia, amino acid and neurotransmitter disturbances in chronic liver failure have made a significant and ongoing contribution to the study of metabolism in health and disease.
Reference: J Neurol 2002;249(5):507-17. Stroke prevention is a crucial issue because (i) stroke is a frequent and severe disorder, and (ii) acute stroke therapies that are effective at the individual level have only a little impact in term of public health. Stroke prevention consists of the combination of 3 strategies: an optimal management of vascular risk factors, associated when appropriate with antithrombotic therapies, carotid surgery, or both. Primary prevention trials have shown that reducing blood pressure in hypertensive subjects reduces their vascular risk, including stroke. The association of perindopril plus indapamide reduces the vascular risk in patients who have had a stroke or TIA during the last 5 years, irrespective of their baseline blood pressure. Lowering serum cholesterol with statins or gemfibrozil in patients with hypercholesterolemia or coronary heart disease (CHD), reduces the risk of stroke. However, no trial of cholesterol-lowering therapy has been completed in stroke patients. A strict control of high cholesterol levels should be encouraged, because of benefits in terms of CHD. Statins should be prescribed for stroke patients with CHD, or increased cholesterol levels. Cigarette smoking is associated with an increased risk of stroke and should be avoided. Careful control of all risk factors, especially arterial hypertension in type 1 and type 2 diabetics is recommended, together with a strict glycemic control to reduce systemic microvascular complications. Estrogens prescribed in hormone replacement or oral contraceptive therapies are not recommended after an ischemic stroke. It is also recommended to reduce alcohol consumption and obesity, and to increase physical activity in patients at risk for first-ever or recurrent stroke. An optimal management of risk factors for stroke is crucial to reduce the risks of first-ever stroke, recurrent stroke, any vascular event after stroke and vascular death. One of the major public health issues for the coming years will be to focus more on risk factor recognition and management. |
