Aspirin dose in stroke prevention: beautiful hypotheses slain by ugly facts.
Explore the source record for details and available documents.
Aspirin↗
Biomedical subjects
H J Barnett
Publications and source records attributed to H J Barnett.
Do the facts and figures warrant a 10-fold increase in the performance of carotid endarterectomy on asymptomatic patients?
The detailed results of the Asymptomatic Carotid Atherosclerosis Study (ACAS) have been published. Electrifying reports in the media suggested that 53% fewer strokes would occur if individuals with 60% or greater stenosis were submitted to endarterectomy. The burning question is whether the evidence from this trial, and those preceding it, is sufficiently compelling to persuade any or all individuals with carotid stenosis, but free of any hemisphere and retinal symptoms, to have carotid endarterectomy. Based on a variety of population samplings, it is reasonable to estimate that approximately two million people are living in North America and Europe with asymptomatic lesions comparable with those studied in the ACAS.
Carotid Stenosis↗
The dilemma of surgical treatment for patients with asymptomatic carotid disease.
Several case series have suggested that endarterectomy is beneficial in asymptomatic carotid artery disease. Four randomized trials have been done in this area, the most recent of which is the Asymptomatic Carotid Atherosclerosis Study (ACAS). Results of the first three trials were negative, and ACAS produced a tantalizing, statistically significant finding that does not translate into clinical importance. Disabling strokes have not been reduced by surgical therapy, and the benefit for women has not been shown. It is unclear from this study whether persons with the greatest stenosis and the highest vascular risk profiles are appropriate candidates for endarterectomy. In patients in whom carotid artery disease is incidentally discovered, the benefits of the prophylactic addition of carotid endarterectomy to coronary bypass grafting or other major surgical procedure in patients are still unknown. Excellent surgical skill is of paramount importance for the future use of this procedure. Mass population screening to detect asymptomatic carotid disease will only be justified when and if future studies identify patients in whom the risk for disabling stroke after the procedure is clearly reduced.
Carotid Stenosis↗
Drugs and surgery in the prevention of ischemic stroke.
Randomized clinical trials have proved that warfarin therapy decreases the risk of stroke in patients with nonvalvular atrial fibrillation and in those who have had a myocardial infarction. In patients who are not candidates for long-term anticoagulant therapy, aspirin is beneficial, but the reduction in risk is smaller with aspirin than with warfarin. In patients with cerebral ischemic symptoms of noncardiac origin, aspirin and ticlopidine reduce the risk of stroke, but the benefit is modest. Given alone, neither dipyridamole nor sulfinpyrazone prevents stroke. The question remains whether either of these drugs plus aspirin is better than aspirin alone. The optimal dose of aspirin for stroke prevention has not been established. Carotid endarterectomy reduces the risk of stroke in symptomatic patients with at least 70 percent stenosis, as determined by arteriography. Current trials are addressing the question of whether endarterectomy is beneficial for patients with moderate degrees of carotid stenosis. The benefit of endarterectomy for patients with asymptomatic carotid lesions remains unclear.
Anticoagulants↗
Guidelines for carotid endarterectomy. A multidisciplinary consensus statement from the Ad Hoc Committee, American Heart Association.
BACKGROUND AND PURPOSE: Indications for carotid endarterectomy have engendered considerable debate among experts and have resulted in publication of retrospective reviews, natural history studies, audits of community practice, position papers, expert opinion statements, and finally prospective randomized trials. The American Heart Association assembled a group of experts in a multidisciplinary consensus conference to develop this statement. METHODS: A conference was held July 16-18, 1993, in Park City, Utah, that included recognized experts in neurology, neurosurgery, vascular surgery, and healthcare planning. A program of critical topics was developed, and each expert presented a talk and provided the chairman with a summary statement. From these summary statements a document was developed and edited onsite to achieve consensus before final revision. RESULTS: The first section of this document reviews the natural history, methods of patient evaluation, options for medical management, results of surgical management, data from position statements, and results to date of prospective randomized trials for symptomatic and asymptomatic patients with carotid artery disease. The second section divides 96 potential indications for carotid endarterectomy, based on surgical risk, into four categories: (1) Proven: This is the strongest indication for carotid endarterectomy; data are supported by results of prospective contemporary randomized trials. (2) Acceptable but not proven: a good indication for operation; supported by promising but not scientifically certain data. (3) Uncertain: Data are insufficient to define the risk/benefit ratio. (4) Proven inappropriate: Current data are adequate to show that the risk of surgery outweighs any benefit. CONCLUSIONS: Indications for carotid endarterectomy in symptomatic good-risk patients with a surgeon whose surgical morbidity and mortality rate is less than 6% are as follows. (1) Proven: one or more TIAs in the past 6 months and carotid stenosis > or = 70% or mild stroke within 6 months and a carotid stenosis > or = 70%; (2) acceptable but not proven: TIAs within the past 6 months and a stenosis 50% to 69%, progressive stroke and a stenosis > or = 70%, mild or moderate stroke in the past 6 months and a stenosis 50% to 69%, or carotid endarterectomy ipsilateral to TIAs and a stenosis > or = 70% combined with required coronary artery bypass grafting; (3) uncertain: TIAs with a stenosis < 50%, mild stroke and stenosis < 50%, TIAs with a stenosis < 70% combined with coronary artery bypass grafting, or symptomatic, acute carotid thrombosis; (4) proven inappropriate: moderate stroke with stenosis < 50%, not on aspirin; single TIA, < 50% stenosis, not on aspirin; high-risk patient with multiple TIAs, not on aspirin, stenosis < 50%; high-risk patient, mild or moderate stroke, stenosis < 50%, not on aspirin; global ischemic symptoms with stenosis < 50%; acute dissection, asymptomatic on heparin. Indications for carotid endarterectomy in asymptomatic good-risk patients performed by a surgeon whose surgical morbidity and mortality rate is less than 3% are as follows. (1) Proven: none. As this statement went to press, the National Institute of Neurological Disorders and Stroke issued a clinical advisory stating that the Institute has halted the Asymptomatic Carotid Atherosclerosis Study (ACAS) because of a clear benefit in favor of surgery for patients with carotid stenosis > or = 60% as measured by diameter reduction. When the ACAS report is published, this indication will be recategorized as proven. (2) acceptable but not proven: stenosis > 75% by linear diameter; (3) uncertain: stenosis > 75% in a high-risk patient/surgeon (surgical morbidity and mortality rate > 3%), combined carotid/coronary operations, or ulcerative lesions without hemodynamically significant stenosis; (4) proven inappropriate: operations with a combined stroke morbidity and mortality > 5%.
Arterial Occlusive Diseases↗
Lack of relationship between leukoaraiosis and carotid artery disease. The North American Symptomatic Carotid Endarterectomy Trial.
OBJECTIVE: Leukoaraiosis (LA) (white matter changes) is frequently observed on computed tomographic scans of the brain of elderly patients at risk of stroke. A localized vascular-ischemic cause has been suggested for its underlying mechanism. Our aim was to assess whether high-grade carotid stenosis is associated with LA. DESIGN/SETTING: Patients enrolled in the North American Symptomatic Carotid Endareterectomy Trial (also known as NASCET) were evaluated for LA using a recently proposed grading scale. Ordinal regression analysis was used to assess the association between the severity of carotid artery stenosis and the extent of LA observed on computed tomographic scans. The patients' brain hemisphere was selected as the unit of analysis. RESULTS: Of the 2394 brain hemispheres contributed to the analyses, 352 (14.7%) had signs of LA. After controlling for known stroke risk factors in the ordinal regression analysis, only the history of stroke and increasing age were significantly related to LA. Severity of stenosis was observed to be unrelated (odds ratio [severe vs mild stenosis] = 1.08; 95% confidence interval, 0.73-1.62; P = .952) as were a history of hypertension and a history of myocardial infarction. CONCLUSION: Leukoaraiosis is not associated with severe carotid artery stenosis.
Aged↗
The risk of stroke in patients with first-ever retinal vs hemispheric transient ischemic attacks and high-grade carotid stenosis. North American Symptomatic Carotid Endarterectomy Trial.
BACKGROUND: The prognosis of amaurosis fugax has been considered to be favorable compared with that of hemispheric transient ischemic attacks. However, this has remained uncertain for patients with significant carotid stenosis as the assessment of progression of the disease has been confounded when patients undergo carotid endarterectomy. In the North American Symptomatic Carotid Endarterectomy Trial, patients with high-grade (70% to 99%) carotid stenosis were randomized to receive either medical or surgical treatment, thus making an unconfounded analysis possible. METHOD: We identified 129 medically treated patients with high-grade carotid stenosis who had their first-ever transient ischemic attack as the entry event into the trial. Fifty-nine patients with retinal transient ischemic attacks (RTIAs) were compared with 70 patients with hemispheric transient ischemic attacks (HTIAs). RESULTS: Patients with HTIAs were older, with a higher prevalence of most risk factors for stroke. Average time of delay from the onset of transient ischemic attacks to medical treatment was longer for patients with RTIAs than for patients with HTIAs (48.5 vs 15.2 days). Kaplan-Meier estimates of the risk of ipsilateral stroke at 2 years were 16.6% +/- 5.6% for patients with RTIAs and 43.5% +/- 6.7% for patients with HTIAs (P = .002 for the difference in risk between RTIAs and HTIAs). From corresponding Cox's proportional hazards regression analyses, the risk of ipsilateral stroke ranged from 11.2% to 28.9% for patients with RTIAs and from 37.4% to 96.3% for patients with HTIAs across stenoses, spanning 75% to 95%. Overall, the relative risk of ipsilateral stroke (HTIAs compared with RTIAs) was 3.23 (95% confidence interval, 1.47 to 7.12), regardless of the degree of high-grade stenosis. CONCLUSION: To our knowledge, this study is the first report on the expected outcome for medically treated patients with high-grade (70% to 99%) carotid stenosis in whom the first-ever event was either an RTIA or HTIA. The presence of RTIAs carries a considerable risk of ipsilateral strokes, particularly at higher degrees of stenosis. However, in comparison with HTIAs, patients with RTIAs still have a better prognosis.
Aged↗
The identification by imaging methods of patients who might benefit from carotid endarterectomy.
Explore the source record for details and available documents.
Carotid Stenosis↗
Guidelines for carotid endarterectomy. A multidisciplinary consensus statement from the ad hoc Committee, American Heart Association.
BACKGROUND AND PURPOSE: Indications for carotid endarterectomy have engendered considerable debate among experts and have resulted in publication of retrospective reviews, natural history studies, audits of community practice, position papers, expert opinion statements, and finally prospective randomized trials. The American Heart Association assembled a group of experts in a multidisciplinary consensus conference to develop this statement. METHODS: A conference was held July 16-18, 1993, in Park City, Utah, that included recognized experts in neurology, neurosurgery, vascular surgery, and healthcare planning. A program of critical topics was developed, and each expert presented a talk and provided the chairman with a summary statement. From these summary statements a document was developed and edited onsite to achieve consensus before final revision. RESULTS: The first section of this document reviews the natural history, methods of patient evaluation, options for medical management, results of surgical management, data from position statements, and results to date of prospective randomized trials for symptomatic and asymptomatic patients with carotid artery disease. The second section divides 96 potential indications for carotid endarterectomy, based on surgical risk, into four categories: (1) Proven: This is the strongest indication for carotid endarterectomy; data are supported by results of prospective contemporary randomized trials. (2) Acceptable but not proven: a good indication for operation; supported by promising but not scientifically certain data. (3) Uncertain: Data are insufficient to define the risk/benefit ratio. (4) Proven inappropriate: Current data are adequate to show that the risk of surgery outweighs any benefit. CONCLUSIONS: Indications for carotid endarterectomy in symptomatic good-risk patients with a surgeon whose surgical morbidity and mortality rate is less than 6% are as follows. (1) Proven: one or more TIAs in the past 6 months and carotid stenosis > or = 70% or mild stroke within 6 months and a carotid stenosis > or = 70%; (2) acceptable but not proven: TIAs within the past 6 months and a stenosis 50% to 69%, progressive stroke and a stenosis > or = 70%, mild or moderate stroke in the past 6 months and a stenosis 50% to 69%, or carotid endarterectomy ipsilateral to TIAs and a stenosis > or = 70% combined with required coronary artery bypass grafting; (3) uncertain: TIAs with a stenosis < 50%, mild stroke and stenosis < 50%, TIAs with a stenosis < 70% combined with coronary artery bypass grafting, or symptomatic, acute carotid thrombosis; (4) proven inappropriate: moderate stroke with stenosis < 50%, not on aspirin; single TIA, < 50% stenosis, not on aspirin; high-risk patient with multiple TIAs, not on aspirin, stenosis < 50%; high-risk patient, mild or moderate stroke, stenosis < 50%, not on aspirin; global ischemic symptoms with stenosis < 50%; acute dissection, asymptomatic on heparin. Indications for carotid endarterectomy in asymptomatic good-risk patients performed by a surgeon whose surgical morbidity and mortality rate is less than 3% are as follows. (1) Proven: none. (As this statement went to press, the National Institute of Neurological Disorders and Stroke issued a clinical advisory stating that the Institute has halted the Asymptomatic Carotid Atherosclerosis Study (ACAS) because of a clear benefit in favor of surgery for patients with carotid stenosis > or = 60% as measured by diameter reduction. When the ACAS report is published, this indication will be recategorized as proven. (2) acceptable but not proven: stenosis > 75% by linear diameter; (3) uncertain; stenosis > 75% in a high-risk patient/surgeon (surgical morbidity and mortality rate > 3%), combined carotid/coronary operations, or ulcerative lesions without hemodynamically significant stenosis; (4) proven inappropriate: operations with a combined stroke morbidity and mortality > 5%.
Aspirin↗
Accuracy and prognostic consequences of ultrasonography in identifying severe carotid artery stenosis. North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group.
BACKGROUND AND PURPOSE: The accuracy of routine ultrasonography in detecting severe carotid artery stenosis was evaluated in comparison with cerebral angiography. The precision of ultrasonographic criteria in predicting the risk of stroke was also assessed. METHODS: A total of 1011 symptomatic carotid bifurcations were studied in patients from the North American Symptomatic Carotid Endarterectomy Trial (NASCET). Given that all patients were considered for entry into the trial, the chance of a verification bias affecting the analyses was minimized. The ultrasonographic data consisted of peak systolic velocities and frequency changes from both the internal and common carotid arteries. Angiographic stenosis was calculated as in NASCET. Receiver operating characteristic (ROC) curves were constructed from the ultrasonographic data for the detection of 70% or greater stenosis on the basis of an angiographic assessment. Kaplan-Meier stroke-free survival curves were used to predict the risk of stroke. RESULTS: The areas under the ROC curves ranged from 0.74 to 0.75 (95% confidence interval [CI], 0.69 to 0.79). The sensitivities and specificities ranged from 0.65 to 0.71. The risk of stroke at 18 months declined sharply as the degree of angiographically defined stenosis declined from 99% to 70%. No pattern of decline was apparent on the basis of the ultrasonographic data. CONCLUSIONS: The results indicate that the accuracy of ultrasonography is moderate when flow parameters are used to assess the degree of stenosis. Ultrasonography should be used as a screening tool to exclude patients with no carotid artery disease from further testing. Conventional angiography remains an essential investigation before assigning the risk of stroke and deciding appropriate treatment for extracranial carotid artery disease.
Blood Flow Velocity↗
Prognosis for patients following a transient ischemic attack with and without a cerebral infarction on brain CT. North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group.
BACKGROUND: Although cerebral infarctions are commonly observed on brain CTs of patients with TIAs, their prognostic importance is unknown. METHOD: The association between appropriately sited brain infarctions (ie, lesions located in the anterior circulation of the brain and ipsilateral to the symptomatic stenosed carotid artery) visualized on CT and the risk of subsequent stroke was assessed by Cox proportional hazards regression in 164 patients presenting with TIA (and no history of previous stroke) and severe angiographically defined carotid stenosis (70 to 99%) from the North American Symptomatic Carotid Endarterectomy Trial. RESULTS: Patients with a TIA and CT-verified brain lesions were older and were more likely to have higher degrees of carotid stenosis and carotid plaque ulceration, a longer duration of symptoms, and a history of hypertension. With regard to prognosis, after adjusting for all known risk factors (patient characteristics) in a regression analysis, the presence of ischemic lesions observed on CT was not associated with an increased risk of ipsilateral stroke at 2 years (adjusted hazard ratio = 1.00; 95% CI: 0.39 to 2.58; p value = 0.99). CONCLUSION: Considered in combination with other patient characteristics, the mere presence of an appropriately sited cerebral infarction on CT does not alter the prognosis (risk of ipsilateral strokes) of severely stenosed patients with TIA. Therefore, there is no clinical rationale in differentiating patients with TIA on the basis of CT findings alone.
Aged↗
Long-term prognosis and effect of endarterectomy in patients with symptomatic severe carotid stenosis and contralateral carotid stenosis or occlusion: results from NASCET. North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group.
The purpose of this study was to examine how the prognosis of patients who presented with a recent ischemic event referable to a 70% to 99% stenosis of one carotid artery (ipsilateral) was altered by stenosis and occlusion of the contralateral carotid artery. The benefit of performing carotid endarterectomy on the recently symptomatic artery, in the presence of contralateral artery disease, was also examined. A total of 659 patients were grouped into one of three categories according to the extent of stenosis in the contralateral carotid artery: less than 70% (559 patients), 70% to 99% (57 patients), and occlusion (43 patients). Strokes that occurred during the follow-up period were designated as ipsilateral if they arose from the same carotid artery as the symptom for which the patient had been entered into the study. Medically treated patients with an occluded contralateral artery were more than twice as likely to have had an ipsilateral stroke at 2 years than patients with either severe (hazard ratio: 2.36; 95% confidence interval (CI): 1.00-5.62) or mild-to-moderate (hazard ratio: 2.65; 95% CI: 1.43-4.90) contralateral artery stenosis. The perioperative risk of stroke and death was higher in patients with an occluded contralateral artery (4.0% risk) or mild-to-moderate (5.1% risk) contralateral stenosis. Regression analyses indicated that the results were not affected by other risk factors. An occluded contralateral carotid artery significantly increased the risk of stroke associated with a severely stenosed ipsilateral carotid artery. Despite higher perioperative morbidity in the presence of an occluded contralateral artery, the longer-term outlook for patients who had endarterectomy performed on the recently symptomatic, severely stenosed ipsilateral carotid artery was considerably better than for medically treated patients.
Aged↗
Update on carotid endarterectomy.
Progress in therapeutic decision-making for patients with carotid artery disease has come from evaluations made by several major randomized clinical trials. For patients who are symptomatic and have arteriographically proven stenoses of 70% or more, endarterectomy is clearly established as the treatment of choice. Symptomatic patients with stenoses of less than 70% remain the subject of ongoing study. Asymptomatic patients are at low risk of stroke save for those with the highest (80% to 90%) degrees of stenosis, and even for these subjects the annual stroke rate is close to the operative risk. Four trials have been reported but the practicing physician is still without clear guidelines. The appropriateness of endarterectomy remains unsettled for any group of patients with narrowing of the carotid artery in the absence of symptoms. The decision to apply endarterectomy to symptomatic and to asymptomatic patients must attend to not only the prognostic importance of the degree of stenosis, but also to the vascular risk profile of the individual patient.
Carotid Artery Diseases↗
Carotid endarterectomy: emerging indications.
Several randomized trials have recently reported on the benefit of carotid endarterectomy for symptomatic or asymptomatic patients. A positive benefit has been found for symptomatic patients with > or = 70% stenosis measured by angiogram with a particular formula and performed with high surgical skill. Symptomatic patients with < 70% stenosis continue to be randomized and followed. The answer for this group is expected in the next two years. The randomized trials of asymptomatic patients have not established the benefit for carotid endarterectomy clearly. The most recent trial shows the absolute risk reduction at 5 years is only 5.9% or less than 1.5% risk reduction per year. A fifth trial continues in Europe.
Carotid Stenosis↗
Medical treatment for stroke prevention.
PURPOSE: To review the effectiveness of medical treatments for stroke prevention in patients at elevated risk for stroke. DATA SOURCES: English-language articles published after 1977 and indexed in MEDLINE under the following Medical Subject Heading terms: anticoagulants, aspirin, dipyridamole, ticlopidine, or sulfinpyrazone, combined with cerebrovascular disorders. STUDY SELECTION: Randomized controlled trials of anticoagulant or platelet antiaggregant treatment reporting subsequent stroke and myocardial infarction, death, or complications in persons with asymptomatic carotid stenosis or bruit, transient ischemic attack (TIA), previous stroke, nonvalvular atrial fibrillation, or other vascular diseases. DATA EXTRACTION: Of 900 articles identified, 33 were selected by two independent reviewers and abstracted for outcome events and person-years of follow-up. RESULTS: In patients with nonvalvular atrial fibrillation, warfarin is highly effective in reducing stroke and death but may result in more complications. Aspirin appears to be less effective and less risky than anticoagulation. In patients with TIA or minor stroke, both aspirin and ticlopidine reduce the risk for stroke. In patients who have had myocardial infarction, warfarin is effective but had high complication rates in the reviewed studies. Aspirin slightly reduces the risk for stroke. CONCLUSIONS: Warfarin is strongly recommended for persons with nonvalvular atrial fibrillation who are older than 60 years or who have additional risk factors for stroke. Aspirin is recommended for persons at elevated risk for bleeding while receiving anticoagulants. For persons with TIA or minor stroke, aspirin should be used first. Patients who do not respond to or tolerate aspirin or who have had a major stroke are reasonable candidates for ticlopidine. For patients who have had myocardial infarction, aspirin is recommended for the prevention of secondary myocardial infarction but not of stroke.
Aspirin↗
Prevention of functional impairment by endarterectomy for symptomatic high-grade carotid stenosis. North American Symptomatic Carotid Endarterectomy Trial Collaborators.
OBJECTIVE: To determine whether carotid endarterectomy prevents deterioration of functional status among patients with transient ischemic attacks or nondisabling strokes and ipsilateral carotid stenosis of 70% to 99%. DESIGN: Multicentered randomized controlled trial with an average 18-month follow-up. SETTING: Fifty clinical centers in North America. PATIENTS: A total of 659 patients presenting with recent transient attacks of nondisabling stroke and ipsilateral atherosclerotic carotid stenosis of 70% to 99% were included. Patients were stable neurologically at the time of entry. No patient was lost to follow-up. INTERVENTION: Vascular surgeons and neurosurgeons were prescreened for low perioperative complication rates. Patients were randomly allocated to carotid endarterectomy plus continuing medical care (n = 328) or medical care alone (n = 331), including antiplatelet therapy. MAIN OUTCOME MEASURES: All patients were assessed by neurologists for the occurrence of stroke and functional status at scheduled intervals after entry. RESULTS: In addition to a previously reported risk reduction for ipsilateral stroke for patients assigned to carotid endarterectomy, there was an absolute risk reduction (and relative risk reduction [RRR]) for functional status impairment of 5.6% (RRR, 69%) for vision, 4.6% (RRR, 87%) for comprehension of language, 8.3% (RRR, 88%) for fluency of speech, 4.3% (RRR, 84%) for swallowing, 6.0% (RRR, 53%) for lower-limb function, 9.3% (RRR, 75%) for upper-limb function, 7.4% (RRR, 60%) for shopping, and 10.5% (RRR, 50%) for visiting outside usual residence (P < .05, two-tailed, for all items). CONCLUSIONS: Carotid endarterectomy reduced the risk for impairment of function among patients with recent symptomatic cerebral ischemia and ipsilateral high-grade carotid stenosis.
Carotid Artery, Internal↗
Can bruits distinguish high-grade from moderate symptomatic carotid stenosis? The North American Symptomatic Carotid Endarterectomy Trial.
OBJECTIVE: To determine whether cervical bruits, alone or combined with other clinical characteristics, can distinguish high-grade (70% to 99%) carotid artery stenoses from less severe stenoses in patients with symptoms of cerebrovascular disease. DESIGN: Cross-sectional comparison of clinical observations with contemporaneous angiography. SETTING: The North American Symptomatic Carotid Endarterectomy Trial (NASCET), a multicenter randomized controlled trial of carotid endarterectomy. PATIENTS: All patients enrolled in the NASCET from its inception in 1988 to November 1991. RESULTS: A focal ipsilateral carotid bruit had a sensitivity of 63% and a specificity of 61% for high-grade stenosis and, when absent, only lowered the probability for high-grade stenosis from a pretest value of 52% to a post-test probability of 40%. When combined with four other clinical characteristics (an infarction on computed tomography of the head, a carotid ultrasound scan suggesting more than 90% stenosis, a transient ischemic attack rather than a minor stroke as a qualifying event, and a retinal rather than a hemispheric qualifying event), the predicted probabilities of high-grade stenosis ranged from a low of 18% (when none of the features was present) to a high of 94% (when all the features were present. CONCLUSIONS: Cervical bruits alone were not sufficiently predictive of high-grade symptomatic carotid stenosis to be useful in selecting patients for angiography; they were absent in over one third of patients with high-grade stenosis. When combined with other clinical variables, patients with high or low probabilities of 70% to 99% stenoses could be identified, but this prediction model still missed many individuals with high-grade stenosis, even in this training set of selected patients.
Angiography↗
Occurrence of domoic acid in Washington state razor clams (Siliqua patula) during 1991-1993.
The presence of domoic acid in aquatic species was reported for the first time in the United States in the late summer of 1991 in Monterey Bay, California. By October of 1991, domoic acid was found in razor clams (Siliqua patula) and in the viscera of Dungeness crab (Cancer magister) along the coasts of Washington and Oregon. In response to this outbreak, the National Marine Fisheries Service, in cooperation with the Washington State Department of Fisheries began analysis of Washington State razor clams for the period from November 1991 to June 1993. This survey indicated that domoic acid levels in the edible portion of the razor clams peaked in December of 1991 (average of all Washington state coastal sites: 106 ppm) and followed a slow decline to the present day low levels (< 5 ppm). Sixteen months after the maximum level, domoic acid has not completely disappeared from the razor clams from the Washington State beaches. Unlike mussels (Mytilus edulis), where the toxin is found only in the viscera, domoic acid distributes itself throughout the various body parts of the razor clam. The highest concentration occurs in the foot or "digger" and the lowest in the siphon or "neck." The concentration of domoic acid in the razor clam foot reached a high of 230 ppm.
Animals↗