title: Medical management versus investigate-and-operate strategy in asymptomatic carotid stenosis: a decision analysis.
abstract: OBJECTIVE
  The objective of this study was to determine whether asymptomatic patients at high risk for carotid stenosis should undergo screening Duplex ultrasound (DUS), with a view to offering carotid endarterectomy (CE) to those patients with significant stenosis.
  
  
  METHODS
  We constructed a decision analysis model to evaluate the impact of an investigate-and-operate strategy, compared with medical management alone, on the risk of stroke in patients at high risk for carotid stenosis. We studied five investigate-and-operate models addressing different thresholds for intervention (in terms of degree of stenosis) and the effects of using or not using preoperative angiography.
  
  
  RESULTS
  For each of the strategies, under the base case conditions (30% prevalence of >50% carotid stenosis), the number needed to screen (NNS) and the number needed to treat (NNT) are high (213 to 769 and 13 to 144, respectively). The strategy of angiography for >50% stenosis and CE for >70% stenosis was harmful. Other strategies were unattractive because of unacceptably high NNT (no angiography, CE >50% stenosis), or because of unacceptably high NNS (angiography >70%, CE >70% stenosis), or both (angiography >50% stenosis, CE >50% stenosis; no angiography, CE > 70% stenosis). At 50% prevalence of >50% stenosis, two models produced more reasonable combinations of NNT and NNS: 11 and 370, respectively, for angiography >70%, CE >70% stenosis; and 27 and 286, respectively, for no angiography, CE >70% stenosis. Within the range of clinically plausible values for sensitivity and specificity of DUS, results were not greatly influenced by the measurement properties of DUS. However, angiographic or surgical rates of stroke or death were critical to the outcomes with any strategy. Only 3% to 12% of strokes in the studied population were prevented.
  
  
  CONCLUSIONS
  Screening is acceptable only in populations at >40% to 50% risk for >50% carotid stenosis, who are surgical candidates, and who would undergo surgery if recommended. Acceptable investigate-and-operate strategies include angiography for DUS stenosis >70%, with CE if this level of stenosis is confirmed, and CE for DUS-measured stenosis >70% without angiographic confirmation. Surgery for asymptomatic carotid stenosis is unlikely to have a large impact upon the burden of stroke in society.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: C M
authors.initials: CM
authors.lastname: Clase
authors.forename: C S
authors.initials: CS
authors.lastname: Cinà
mesh_terms: D016893:Carotid Stenosis / Q000150:complications / Q000000981:diagnostic imaging* / Q000601:surgery*; D003661:Decision Support Techniques; D016894:Endarterectomy, Carotid; D006801:Humans; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D020521:Stroke / Q000209:etiology / Q000517:prevention & control*; D018616:Ultrasonography, Doppler, Duplex