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Biomedical subjects

A R Naylor

Publications and source records attributed to A R Naylor.

At least 91 records · Page 5Linked to original sources
PubMed1998

Time domain analysis of embolic signals can be used in place of high-resolution Wigner analysis when classifying gaseous and particulate emboli.

The sample-volume length (SVL) of an embolic signal has previously been used to differentiate between gaseous and particulate emboli and has been calculated using high-resolution Wigner analysis. Although successful, this method of analysis is not widely available to other groups using transcranial Doppler ultrasound (TCD) to classify emboli. The SVL of embolic signals can also be calculated using time domain analysis, which is a far simpler method and potentially available to all TCD users. The aim of this study was to compare the SVL of embolic signals calculated using Wigner analysis and time domain analysis to assess whether or not time domain analysis can replace Wigner analysis to classify emboli. In total, 215 particulate and 100 gaseous emboli were recorded onto digital audiotape and analysed off-line. Two SVLs for each embolic signal were calculated by measuring embolic duration and velocity in the time domain and with Wigner analysis. Receiver operator characteristic (ROC) curves were plotted to assess the optimum SVL threshold for each method, and levels of sensitivity and specificity were defined. The optimum SVL threshold using Wigner analysis was 1.28 cm, yielding 93% sensitivity and 97% specificity. Using time domain analysis, the optimum threshold was 1.12 cm, yielding 90% sensitivity and 96% specificity. The methods were compared statistically (chi2) using their optimum thresholds, and were found not to be statistically different for classifying particles p=0.283) or gaseous emboli (p=0.700). This study has shown that the SVL of embolic signals, used to differentiate particulate from gaseous emboli, can be calculated more simply in the time domain, which yields as accurate results as calculating the SVL using Wigner analysis.

Blood Flow Velocity↗
PubMed1998

Randomized study of carotid angioplasty and stenting versus carotid endarterectomy: a stopped trial.

BACKGROUND: Carotid angioplasty (CA) has been suggested to be a safer and more cost-effective alternative to carotid endarterectomy (CEA) in the management of symptomatic severe internal carotid artery (ICA) disease. METHODS: The study was conducted as a prospective consecutive randomized trial of CEA versus CA for symptomatic severe ICA disease in a university teaching hospital. All patients were assessed before and after surgery by a neurologist. The study consisted of 23 patients with focal carotid territory symptoms and severe ICA stenosis (> 70%) who were randomized to either CEA or CA. However, only 17 had received their allocated treatment before trial suspension. CEA with patching or CA with stenting were used as interventions. The main outcome measures were death or disabling or nondisabling stroke within 30 days. RESULTS: All 10 CEA operations proceeded without complication, but 5 of the 7 patients who underwent CA had a stroke (P=.0034), 3 of which were disabling at 30 days. CONCLUSIONS: After referral, the Data Monitoring Committee invoked the stopping rule and the trial was suspended. The investigators and the Ethics Committee subsequently concluded that the trial could not be restarted--even in an amended format-primarily because of problems with informed consent. We review many of the ethical dilemmas encountered in the performance of this study. If future trials do suggest a selected role for CA, it is essential that both the inclusion and the exclusion criteria are fully documented.

Aged↗
PubMed1998

The increasing workload required to maintain infrainguinal bypass graft patency.

BACKGROUND: To assess the impact upon the provision of a vascular service of the workload associated with maintaining infrainguinal bypass graft patency. DESIGN: A computerised prospective audit. MATERIALS AND METHODS: Between January 1990 and December 1995, all patients with infrainguinal bypass grafts were entered into a prospective computerised audit to monitor interventions for the maintenance of graft patency. Excluded from the study were interventions during the first 30 postoperative days and procedures not directly related to the graft. A graft surveillance programme was in operation throughout. RESULTS: During the study period a total of 131 patients with 144 grafts were admitted on 330 occasions and required 401 separate interventional procedures. There were 227 procedures in 72 femorodistal grafts, 116 in 38 below-knee femoropopliteal grafts and 58 interventions in the group of 34 above-knee femoropopliteal grafts. Radiological interventions accounted for almost 70% of this workload. CONCLUSION: The workload associated with the maintenance of infrainguinal bypass grafts increased considerably during the study period, and seems likely to increase further. Such interventions should therefore be considered when planning for vascular service provision.

Anastomosis, Surgical↗
PubMed1998

The increasing activity of a vascular ultrasound service.

OBJECTIVES: To examine the change in activity of a vascular ultrasound service over 7 years. DESIGN: Retrospective review. SETTING: Vascular studies unit, University hospital. METHOD: Audit of the number of vascular ultrasound tests carried out over the last 7 years using a prospective computerised database. RESULTS: Data shows that the overall workload has tripled over the 7-year period. In addition the complexity of investigations has increased during this time. The number of carotid scans has increased four-fold while the number of graft surveillance scans and vein scans has increased seven-fold. Assessment of lower limb arteries has developed from simple pressure measurements to detailed ultrasound scans and, as a consequence, the number of diagnostic angiograms has fallen by 75%. The factors that have influenced these changes are discussed. CONCLUSIONS: There has been an important increase in the role of colour Doppler ultrasound as it becomes the "first line" vascular diagnostic test. However this trend can only continue if vascular ultrasound services are appropriately resourced. It is therefore essential to maintain an efficient audit system.

Angiography↗
PubMed1998

A clinical and haemodynamic investigation into the role of calf perforating vein surgery in patients with venous ulceration and deep venous incompetence.

OBJECTIVE: To determine the clinical efficacy and local haemodynamic effects of perforating vein surgery in ulcerated limbs with combined deep and perforating vein incompetence. DESIGN: Prospective, interventional study. MATERIALS AND METHODS: Seven ulcerated limbs with combined primary deep and perforating vein incompetence were studied. Clinical efficacy was determined by ultimate ulcer healing and reduction in ulcer area, local haemodynamics were assessed at three sites with photoplethysmographic 90% venous refilling times (PPG RT90); both assessments were performed pre- and 1-month postoperatively. RESULTS: None of the ulcers healed following perforating vein surgery, the median (range) ulcer areas pre- and postoperatively were 31 (7-685) cm2 and 35.5 (7-796) cm2 (Wilcoxon p = 0.07). Preoperative PPG RT90 demonstrated a global abnormality of venous function at all sites examined that persisted after perforating vein surgery. CONCLUSION: In the presence of deep venous incompetence perforating vein surgery had no influence on venous function or ulcer healing. We conclude that perforating vein surgery is not indicated for the treatment of venous ulceration in limbs with primary deep venous incompetence.

Aged↗
PubMed1998

Bilateral infrainguinal vein grafts and the incidence of vein graft stenosis.

OBJECTIVES: To elucidate the incidence of significant vein graft stenosis in patients who have undergone bilateral infrainguinal vein grafts. MATERIALS: Between 1987 and 1996, 22 patients were identified from our vascular studies database as having undergone bilateral infrainguinal vein bypass grafting. METHODS: Data was obtained from the vascular studies database and by case note review. All patients had been part of a vein graft surveillance programme. RESULTS: Of the 22 patients with bilateral vein grafts, eight were excluded from further analysis because one or more of their grafts failed within 30 postoperative days. In the remaining 14 patients (28 vein grafts) there were 15 primary vein graft stenoses. Six patients (43%) had bilateral vein graft stenoses, which is significantly higher (p = 0.0008) than the predicted value of 9%, for developing bilateral vein graft stenoses. For those patients who developed a vein graft stenosis in their first grafted limb (9/14), 67% (6/14) subsequently developed a vein graft stenosis in their second grafted limb. CONCLUSION: Patients who develop vein graft stenosis in one limb are at a greater risk of developing a contralateral vein graft stenosis if that limb is grafted. This may well be due to individual vein morphology or unidentified systemic factors that play a role in the aetiology of vein graft stenosis.

Aged↗
PubMed1998

At what peak velocity ratio value should duplex-detected infrainguinal vein graft stenoses be revised?

OBJECTIVES: To determine the peak velocity ratio (PVR) threshold at which to intervene and correct duplex detected vein graft stenoses. DESIGN: Prospective study. MATERIALS: Infrainguinal vein grafts in patients attending the vascular studies for routine postoperative surveillance. METHODS: Colour duplex detected stenotic vein graft lesions with a peak velocity ratio (PVR) between 2.0 and 2.9 were identified and monitored by serial duplex scans performed monthly for 3 months and then at 3-monthly intervals thereafter. At the end of the study period, the outcome of these lesions were analysed. RESULTS: Thirty-eight lesions were identified from 32 grafts. Of these lesions, sixteen (42%) resolved, 11 (29%) remained stable and 11 (29%) progressed to a PVR of > or = 3.0 and underwent angioplasty. There were no occlusions in any of the grafts during the period of study. CONCLUSIONS: Colour duplex detected vein graft stenoses with a PVR of less than 3.0 can be treated expectantly if grafts with stenoses with a PVR 2.0-2.9 are scanned every month for at least 3 months after detection.

Angioplasty, Balloon↗
PubMed1998

The effect of perioperative embolisation on visual function in patients undergoing carotid endarterectomy.

OBJECTIVES: To investigate the effect of carotid artery embolisation detected by transcranial Doppler (TCD) monitoring during carotid endarterectomy (CEA) on visual function. DESIGN: A prospective study. Visual function was assessed by an independent ophthalmalogist. MATERIALS: One hundred consecutive patients undergoing carotid endarterectomy. METHODS: All patients underwent pre- and postoperative retinal fundoscopy and automated visual field analysis. Intraoperative emboli were detected by continuous TCD monitoring of the middle cerebral artery. RESULTS: Preoperatively, six patients had fundoscopic evidence of silent retinal embolisation, five patients had visible emboli associated with amaurosis fugax. Visual field analysis found no significant difference between ipsi- and contralateral eye scores. Only patients with occlusions of major retinal vessels had clinically reduced visual function. Intraoperatively TCD identified embolisation in 83/91 of monitored operations. Postoperatively, ipsilateral visual field scores deteriorated while contralateral eye scores remained unchanged, however only one new retinal embolus was detected. The incidence of TCD detected embolisation was not associated with a corresponding deterioration in postoperative visual function. CONCLUSIONS: (1) A group of patients can be identified who experience "silent" retinal embolisation prior to CEA. (2) Clinically significant retinal embolisation resulting from CEA is uncommon. (3) CEA is associated with a deterioration in the visual field scores for the ipsilateral eye compared with the contralateral eye but the mechanism for this small but significant deterioration remains unclear.

Blindness↗
PubMed1998

Carotid endarterectomy without angiography does not compromise operative outcome.

OBJECTIVES: Carotid angiography is associated with a 2% risk of stroke and, since the advent of colour-duplex ultrasound, its role in the assessment of patients with carotid disease has been the subject of debate. The aim of this study was to evaluate a policy of adopting routine duplex supplemented by selective angiography on operative outcome over a 5-year period. METHODS: A prospective audit of the results of carotid endarterectomy without routine angiography from January 1992 to December 1996. Angiography was performed only if the ultrasonography was concerned about the distal or proximal extent of disease or to assess subocclusion. RESULTS: During the study period, 494 carotid endarterectomies were performed but only 35 patients underwent carotid angiography. The indications for angiography were subocclusion/string sign in 22 patients, to assess the limits of proximal or distal disease in 12 and abnormal anatomy in one. During the 5-year study period the overall perioperative death and/or stroke rate was 4.2%. By 1997, the perioperative stroke rate had fallen to 1.3%. In no case in this series was the operation abandoned due to unexpected findings. CONCLUSION: Although concerns exist about the precise duplex criteria for diagnosing a severe stenosis, this study has shown that a policy of selective angiography does not compromise patient safety or operability and avoids the unnecessary mortality, morbidity and costs associated with routine angiography.

Angiography↗
PubMed1998

Experience with transcranial Doppler monitoring reduces the incidence of particulate embolization during carotid endarterectomy.

BACKGROUND: The aim of this study was to investigate whether the introduction of routine transcranial Doppler (TCD) ultrasonography during carotid endarterectomy reduces the incidence of microembolization by altering operative technique. METHODS: The number and nature of microemboli detected during the first 75 consecutive carotid endarterectomies performed with TCD monitoring during 1992-1993 (group 1) were compared with those in a similar series of 75 consecutive patients undergoing carotid endarterectomy in 1995 (group 2), after substantial experience (210 patients) with TCD monitoring. Emboli were classified as either particulate or gaseous. RESULTS: In patients with evidence of particulate emboli during the dissection phase of the operation, the total number of particulate emboli fell significantly in patients in group 2 (P = 0.019). Similarly, in patients in whom microembolization was detected on immediate opening of the shunt, the total number of microemboli also fell significantly in group 2 (P = 0.003). Overall, the median (95 per cent confidence interval) number of particulate emboli detected during the entire procedure fell significantly from 21 (16-29) in group 1 to 9 (7-14) in group 2 (P = 0.0008). CONCLUSIONS: TCD monitoring plays an important role in the training and quality control of carotid endarterectomy and helps significantly to reduce the amount of microembolization.

Aged↗
PubMed1998

Role of saphenous vein surgery in the treatment of venous ulceration.

BACKGROUND: This paper describes local anaesthetic saphenous disconnection in elderly patients for the treatment of venous ulceration in legs with either saphenous venous reflux alone or in combination with deep venous reflux. METHODS: Ambulatory venous pressure was measured in 16 legs with saphenous vein reflux alone and in nine legs with combined deep and saphenous venous reflux before, immediately after and 3 months after saphenofemoral or popliteal disconnection. Ulcer area was measured by computerized planimetry before surgery and at 1 and 3 months after operation. No compression bandages or hose were applied after surgery unless the ulcers had not begun to heal after 1 month. RESULTS: In legs with saphenous reflux alone all ulcers healed without compression bandages at a median of 81 (range 14-253) days and the pressure relief index (PRI) improved significantly both after surgery and at follow-up. None of the ulcers in the nine limbs with saphenous and deep venous reflux healed without compression bandaging and the PRI was unchanged immediately following surgery and at follow-up. CONCLUSION: Saphenous vein disconnection improves venous function and heals venous ulcers without compression bandaging if the deep veins are normal. This procedure under local anaesthetic may be particularly suitable for elderly patients, but long saphenous vein stripping should be added in young patients.

Aged↗
PubMed1998

Provision of training in carotid surgery does not compromise patient safety.

BACKGROUND: Vascular surgeons perceive that carotid endarterectomy carries a higher risk of stroke if performed by a surgical trainee. Accordingly, some trainees consider that they receive a less than adequate training in carotid surgery before taking up a consultant position. The aim of this study was to establish whether the stroke rate was adversely affected if carotid endarterectomy was performed by a surgical trainee under consultant supervision. METHODS: This was a prospective study of 151 consecutive patients undergoing carotid endarterectomy between 1 January and 31 December 1996 using a standardized technique including intraoperative and postoperative transcranial Doppler monitoring and completion angioscopy. RESULTS: The overall mortality and/or disabling stroke rate was 0.7 per cent (one of 151 patients), whereas the mortality and/or any stroke rate was 1.3 per cent (two of 151). Surgical trainees performed 82 of 151 carotid endarterectomies, with a mortality rate of 1 per cent and a mortality and/or any stroke rate of 2 per cent. There was no significant difference in the incidence of retained thrombus or intimal flaps between trainees and consultants as detected by angioscopy. CONCLUSION: Vascular surgical trainees can receive a comprehensive training in carotid artery surgery without incurring an unacceptable increase in operative risk.

Aged↗
PubMed1998

Predischarge duplex imaging of infrainguinal vein grafts does not predict the development of stenoses.

BACKGROUND: The aim of this study was to determine whether predischarge duplex imaging of an infrainguinal vein graft could predict the subsequent development of graft stenosis. METHODS: Patients with infrainguinal vein grafts underwent a duplex scan of the entire graft before discharge from hospital. Grafts were classified as abnormal or normal based on the presence or absence of flow abnormalities (peak velocity ratio 1.5 or greater). All grafts were re-examined 1 month after surgery, at 3-monthly intervals for the first year and then every 6 months thereafter. A significant stenosis requiring correction was defined by a duplex-derived peak systolic velocity ratio of 3.0 or more. The relationship between the predischarge scan and subsequent development of stenosis was examined. RESULTS: Forty-four grafts were recruited. Two occluded soon after a normal predischarge scan and were excluded from subsequent analysis. Predischarge abnormalities were found in 16 grafts. The abnormality in one graft required immediate correction. A further four grafts subsequently developed significant stenoses and required angioplasty. Of the 26 grafts with no predischarge abnormalities, 11 developed significant stenoses and underwent angioplasty. Abnormal predischarge duplex scans had a sensitivity and specificity of 31 and 58 per cent respectively for the development of stenoses. The positive and negative predictive values were 31 and 58 per cent respectively. CONCLUSION: Predischarge duplex imaging cannot be used to predict the development of stenoses in infrainguinal vein grafts.

Blood Flow Velocity↗
PubMed1998

Lower limb surveillance following autologous vein bypass should be life long.

BACKGROUND: The aim of the study was to investigate whether infrainguinal vein graft surveillance can be stopped at 1 year without prejudicing graft or leg survival. METHODS: Data were collected prospectively on 351 infrainguinal vein bypass grafts (326 patients) that had been entered into a vein graft surveillance programme between 1988 and 1997. RESULTS: Some 104 grafts (30 per cent) developed significant new vein graft stenoses, 95 (91 per cent) of which occurred within 12 months. After 1 year, the risk of developing a significant graft stenosis was 3 per cent per year. Sixty-nine grafted limbs (20 per cent) developed new arterial inflow or run-off stenoses that required intervention, but only 37 (54 per cent) occurred within the first year, after which the risk was 9 per cent per year. The overall risk of developing a new vein graft or arterial stenosis after 1 year was 10 per cent per year. CONCLUSION: The incidence of vein graft stenosis decreases significantly 1 year after operation but there is still at risk of developing potentially graft-threatening arterial stenoses. Legs that have undergone infrainguinal vein bypass grafting should continue to be monitored in a surveillance programme for life.

Adolescent↗