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Biomedical subjects

A R Naylor

Publications and source records attributed to A R Naylor.

At least 19 recordsLinked to original sources
PubMed2006

High risk plaque, high risk patient or high risk procedure?

SAPPHIRE, a randomised trial of endarterectomy versus angioplasty in 'high-risk' patients, concluded that angioplasty was 'not inferior' to surgery. This has subsequently been translated to mean that angioplasty was 'preferable' or 'advisable' in patients considered high-risk for surgery, with no further discrimination between symptomatic and asymptomatic individuals. Moreover, there have been suggestions that the accepted procedural risks may have to be increased in these patients. In fact, 71% of patients in SAPPHIRE were asymptomatic in whom there was an average 6% 30-day death/stroke rate. At this level of risk, neither surgery nor angioplasty could ever prevent long-term stroke. The concept of identifying high-risk patients is laudable, but they should be high risk for stroke (i.e. symptomatic). There is currently little systematic evidence to include asymptomatic patients within this definition.

Angioplasty↗
PubMed2006

Ultrasound based measurement of 'carotid stenosis >70%': an audit of UK practice.

OBJECTIVES: To determine velocity thresholds for diagnosing 'carotid stenosis >70%' and whether Vascular Studies Units in the United Kingdom used ECST or NASCET measurement methods. DESIGN: Questionnaire to 102 members of the Society of Vascular Technology of Great Britain and Ireland. RESULTS: One quarter (26%) of respondents reported that their unit used the NASCET measurement method, 31% used the ECST method, while 43% did not know. When all velocity criteria were pooled and compared, an almost equal proportion of ECST, NASCET and 'do not know' respondents used a peak systolic velocity threshold of >230 cm/s as being diagnostic of a 'stenosis >70%'. Interestingly, this velocity is now the threshold proposed by a North American consensus group for diagnosing a NASCET stenosis of >70%. CONCLUSIONS: This audit suggests that there is considerable confusion about what constitutes an ultrasound based diagnosis of 'stenosis >70% in the United Kingdom.

Blood Flow Velocity↗
PubMed2006

Cerebral protection during open retrograde angioplasty/stenting of common carotid and innominate artery stenoses.

BACKGROUND: This was a retrospective study of the effectiveness of open, retrograde angioplasty/stenting of supra-aortic arterial stenoses combined with transcranial Doppler-directed dextran therapy in preventing perioperative embolization. METHODS: Eight patients underwent angioplasty/stenting of the proximal common carotid (synchronous carotid endarterectomy (CEA) in six), while four underwent angioplasty/stenting of the innominate artery (synchronous CEA in one). Open exposure of the carotid bifurcation enabled temporary carotid clamping to protect the brain from procedural embolization. Dextran was administered to patients with a high rate of embolization on transcranial Doppler after the operation. RESULTS: No emboli were recorded in the cerebral circulation during the actual angioplasty procedure when the internal carotid artery was clamped. After operation three patients developed high-rate embolization and received dextran. No strokes or deaths occurred within 30 days of treatment. One patient developed symptoms and a recurrent stenosis greater than 50 per cent during follow-up and was treated by redo angioplasty. CONCLUSION: Retrograde angioplasty/stenting with or without synchronous CEA offers an alternative approach to treating patients with supra-aortic inflow disease.

Adult↗
PubMed2005

Patch corrugation on duplex ultrasonography may be an early warning of prosthetic patch infection.

Four of 10 patients presenting with prosthetic patch infection after carotid endarterectomy (CEA) were noted to have Duplex evidence of 'corrugation' of the prosthetic patch, without false aneurysm formation. In three, corrugation preceded diagnosis of overt patch infection by up to 11 months. In the fourth patient, awareness of the potential significance of patch corrugation enabled timely treatment of an otherwise unrecognized patch infection. Even if other imaging modalities are normal, the presence of patch corrugation on Duplex should prompt the surgeon to (at least) consider the possibility of patch infection.

Aged↗
PubMed2005

Identification of patients at risk for ischaemic cerebral complications after carotid endarterectomy with TCD monitoring.

OBJECTIVES: Transcranial Doppler (TCD) monitoring for micro embolic signals (MES), directly after carotid endarterectomy (CEA) may identify patients at risk of developing ischaemic complications. In this retrospective multicentre study, this hypothesis was investigated. METHODS: Centres that monitored for MES after CEA were identified by searching Medline. Individual patient data were obtained from centres willing to collaborate. The number of emboli in 1h was computed. Uni- and multivariate logistic regression analyses were performed for the variables gender, age and number of MES. Discriminative ability of MES monitoring was investigated in a ROC curve. RESULTS: Nine hundred and ninety-one patients were monitored in the first 3h after CEA. Two percent developed ischaemic cerebral complications. Univariate analysis revealed statistically significant associations between ischaemic cerebral complications and both gender and MES, but not age. In a multivariate analysis, > or =8 MES/h showed a statistically significant relationship with cerebral complications (OR 8.1, 95% CI 1.8-36), in contrast to gender (OR 2.2, 95% CI 0.9-5.5). The ROC curve yielded an AUC of 0.83 for monitoring of MES. CONCLUSIONS: These results support the use of TCD monitoring for MES shortly after CEA in order to identify patients at risk of developing ischaemic cerebral complications.

Aged↗
PubMed2005

Duplex imaging immediately prior to carotid endarterectomy.

INTRODUCTION: In this centre, angiography is used only in selected cases, whilst duplex ultrasound (DU) is the main imaging method prior to carotid endarterectomy (CEA). DU has no associated morbidity and so can be repeated immediately before surgery to detect changes in the carotid plaque or degree of stenosis. PATIENTS AND METHODS: We retrospectively examined our Vascular Surgery Audit database for the last 500 patients admitted for CEA. In each case, the DU scan was repeated immediately before surgery. RESULTS: From 500 admissions, repeat DU immediately prior to surgery detected 8 (1.6%) situations where CEA would no longer have been an appropriate intervention. In four cases, the degree of stenosis was found to be less than 70% on the repeat scan - in three cases the internal carotid artery (ICA) had occluded or sub-occluded and in one case there was a dissection of the ICA plaque. CONCLUSIONS: DU can be repeated, with no associated morbidity, immediately prior to surgery. Such a practice changes management decisions in 1.6% of admissions for CEA, allowing surgery unjustified by current evidence to be avoided. This policy also serves several other important purposes: it is a method of internal validation, provides a means of improving training of vascular technologists and of achieving quality assurance in DU techniques.

Carotid Artery, Internal↗
PubMed2004

Unstable carotid plaques exhibit raised matrix metalloproteinase-8 activity.

BACKGROUND: The fibrous cap of atherosclerotic plaques is composed predominantly of type I and III collagen. Unstable carotid plaques are characterized by rupture of their cap, leading to thromboembolism and stroke. The proteolytic mechanisms causing plaque disruption are undefined, but the collagenolytic matrix metalloproteinase (MMP) -1, -8, and -13 may be implicated. The aim of this study was to quantify the concentrations of these collagenases in carotid plaques and to determine their relationship to markers of plaque instability. METHODS AND RESULTS: Atherosclerotic plaques were collected from 159 patients undergoing carotid endarterectomy. The presence and timing of carotid territory symptoms were ascertained. Preoperative embolization was recorded by transcranial Doppler. Each plaque was assessed for histological features of instability. Plaque MMP concentrations were quantified with ELISA. Significantly higher concentrations of active MMP-8 were observed in the plaques of symptomatic patients (20.5 versus 11.4 ng/g; P=0.0002), in plaques of emboli-positive patients (22.7 versus 13.5 ng/g; P=0.0037), and in those plaques showing histological evidence of rupture (20.8 versus 14.7 ng/g; P=0.0036). No differences were seen in the levels of MMP-1 and MMP-13. Immunohistochemistry, in situ hybridization, and colocalization studies confirmed the presence of MMP-8 protein and mRNA within the plaque, which colocalized with macrophages. CONCLUSIONS: These data suggest that the active form of MMP-8 may be partly responsible for degradation of the collagen cap of atherosclerotic plaques. This enzyme represents an attractive target for drug therapy aimed at stabilizing vulnerable plaques.

Aged↗
PubMed2004

Patch angioplasty versus primary closure for carotid endarterectomy.

BACKGROUND: Carotid patch angioplasty (with either a venous or a synthetic patch) may reduce the risk of carotid artery restenosis and subsequent ischaemic stroke. OBJECTIVES: The objective of this review was to assess the safety and efficacy of routine or selective carotid patch angioplasty compared to carotid endarterectomy with primary closure. SEARCH STRATEGY: We searched the Cochrane Stroke Group Trials Register (last searched November 2002). In addition, we searched the Cochrane Controlled Trials Register (The Cochrane Library, Issue 4, 2001), MEDLINE (1966 to December 2001), EMBASE (1980 to December 2001) and Index to Scientific and Technical Proceedings (1980 to 2001). We also handsearched eight journals and five conference proceedings. Reference lists were checked and we contacted experts in the field to identify further published and unpublished studies. SELECTION CRITERIA: Randomised and quasi-randomised trials comparing carotid patch angioplasty with primary closure in any patients undergoing carotid endarterectomy. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed eligibility, trial quality and extracted the data. MAIN RESULTS: The previous review included six trials involving 794 patients undergoing 882 operations. Since the last review only one study of adequate quality to be included has been reported. This added 399 operations randomised to either primary closure, vein patch or synthetic patch groups resulting in 1127 patients undergoing 1307 operations being available for analysis. The quality of trials was generally poor. Follow-up varied from hospital discharge to five years. Carotid patch angioplasty was associated with a reduction in the risk of stroke of any type (OR = 0.33, p = 0.004), ipsilateral stroke (OR = 0.31, p = 0.0008), and stroke or death, during the perioperative period (OR = 0.39, p = 0.007) and long term follow-up (OR = 0.59, p = 0.004). It was also associated with a reduced risk of perioperative arterial occlusion (odds ratio 0.15, 95% confidence interval 0.06 to 0.37 p = 0.00004), and decreased restenosis during long-term follow-up in five trials, (odds ratio 0.20, 95% confidence interval 0.13 to 0.29 p < 0.00001). These results are more certain than those of the previous review since the number of operations and events have increased. However, the sample sizes are still relatively small, data were not available from all trials, and there was significant loss to follow-up. Very few arterial complications, including haemorrhage, infection, cranial nerve palsies and pseudo-aneurysm formation were recorded with either patch or primary closure. No significant correlation was found between use of patch angioplasty and the risk of either perioperative or long-term all-cause death rates REVIEWERS' CONCLUSIONS: Limited evidence suggests that carotid patch angioplasty may reduce the risk of perioperative arterial occlusion and restenosis. It would appear to reduce the risk of combined death or stroke and there is a non significant trend towards a reduction in all-cause mortality.

Blood Vessel Prosthesis↗
PubMed2004

Real-time identification and archiving of micro-embolic Doppler signals using a knowledge-based DSP system.

Identification of micro-emboli in the cerebral circulation using transcranial Doppler ultrasound provides valuable clinical information, but, currently, embolic signal detection and analysis are significantly limited because they mainly rely on costly off-line analysis by human experts. In this study, a reliable, high-resolution, real-time automated system for the detection and archiving of embolic signals was designed and implemented using expert system theory and modern DSP technology. Preliminary tests were conducted to evaluate the functions and the performance of the system using data from ten carotid endarterectomy patients and two normal volunteers. Using the widely accepted 7 dB threshold for human reliability and a human expert, majority-decision gold standard, the real-time system reached sensitivity and specificity of 93.6% and 99.3%, respectively, which were close to the results obtained by three human experts under ideal laboratory conditions (90.1% and 99.8%, 98.4% and 99.9%, 98.9 and 99.9%). The new system has the potential to be used either as a bedside monitoring and signal acquisition device, or as a laboratory investigation tool.

Endarterectomy, Carotid↗
PubMed2004

An in vitro model to compare the antimicrobial activity of silver-coated versus rifampicin-soaked vascular grafts.

In situ replacement of infected vascular grafts is an accepted alternative to total graft excision and extraanatomic replacement. Its success relies upon the ability of the newly inserted graft to resist recurrent infection. This study compares the efficacy of two methods used to reduce the risk of graft reinfection: rifampicin soaking versus silver bonding of grafts. The grafts' resistance to infection was tested in vitro in two protocols, each using a panel of seven common bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The length of time the grafts remained free of organisms was compared between the groups. Both the silver graft and the rifampicin-soaked graft were significantly better than control graft at preventing bacterial growth on the graft surface. The rifampicin inhibited the growth of the gram-positive organisms, including MRSA, significantly better than the silver graft on days 2 and 3 (p < 0.001). Conversely, the silver graft was significantly more effective against the gram-negative organisms until day 4 (p < 0.0001). Both types of graft inhibit the in vitro growth of bacteria more effectively than controls, with rifampicin being most effective against gram-positive organisms and silver being best against the gram-negative organisms.

Acetates↗
PubMed2004

Does the sequence of clamp application during open abdominal aortic aneurysm surgery influence distal embolisation?

BACKGROUND: Embolisation of atherosclerotic debris during abdominal aortic aneurysm (AAA) repair is responsible for significant peri-operative morbidity. Reports have suggested that preferential clamping of the distal vessel(s) before the proximal aorta may decrease the number of emboli passing distally and hence reduce complications. METHODS: Forty patients undergoing AAA repair were randomised to have either first clamping of the proximal aorta or the iliac vessels. Emboli passing through the Superficial Femoral Arteries were detected with a Transcranial Doppler ultrasound system. RESULTS: There was no difference between the two groups in the number of emboli detected (p=0.49) and no significant correlation between number of emboli and dissection time (r=0.0008). However, there was a significantly higher number of emboli in the patient sub-group that were current smokers (p=0.034). CONCLUSIONS: There appears to be no difference in the numbers of emboli detected when the first vascular clamp is applied to the proximal aorta or iliacs.

Aged↗
PubMed2004

Elevation in plasma MMP-9 following carotid endarterectomy is associated with particulate cerebral embolisation.

OBJECTIVES: To study plasma MMP-9 levels before and after carotid endarterectomy (CEA). DESIGN: Observational study. METHODS: Pre-operative (morning of surgery) and post-operative (48 h) plasma samples were obtained from 75 consecutive patients undergoing CEA. MMP-9 concentrations were quantified using ELISA. Transcranial Doppler monitoring was performed on each patient to detect particulate embolisation during the dissection phase of the CEA, until the application of carotid clamps. RESULTS: The median post-operative plasma MMP-9 level of emboli-positive patients was significantly higher than their median pre-operative value (14.9 ng/ml vs. 8.8 ng/ml; p=0.038). However, no significant difference was seen in the plasma MMP-9 level of emboli-negative patients (7.7 ng/ml vs. 7.1 ng/ml; p=0.364). A greater rise was seen in the median plasma MMP-9 levels of those patients suffering >2 emboli (from 3.4 to 19.3 ng/ml; p=0.041) than those patients suffering 1 or 2 emboli (from 10.1 to 12.8 ng/ml; p=0.340). CONCLUSIONS: Plasma MMP-9 only rises after CEA in patients with evidence of embolisation. This increase is more pronounced in those with high numbers of emboli. These data suggest that the increase in MMP-9 is due to cerebral damage caused by embolisation.

Aged↗