ArticlesPrediction of benefit from carotid endar terectomy in individual patients: a risk-modelling study
Section snippets
Background
Carotid endarterectomy lowers the risk of carotid territory ipsilateral ischaemic stroke, and is the treatment of choice, in patients with recently symptomatic 70–99% carotid stenosis. However, the 3-year risk of stroke on medical treatment alone is only about 20%. We investigated whether the efficacy of endarterectomy would be improved if patients with a high risk of stroke on medical treatment and a low risk of operative stroke or death could be identified.
Methods
We developed two prognostic models from data on patients with 0–69% carotid stenosis in the European Carotid Surgery Trial (ECST). The medical model predicted risk of ipsilateral carotid territory major ischaemic stroke (fatal or lasting longer than 7 days) on medical treatment and the surgical model predicted risk of major stroke and death within 30 days of endarterectomy. From these models we developed a prognostic score to identify patients with a high risk of stroke on medical treatment but
Findings
When patients with 70–99% stenosis were stratified by the scoring system, which was based on seven independent prognostic factors, endarterectomy was beneficial in only 162 (16%) patients. The 5-year absolute risk of carotid territory ipsilateral major ischaemic stroke, operative major stroke, or death was lowered by 33% in the 16% of patients with a score of 4 or more (odds ratio 0·12 [95% CI 0·05–0·29], p<0·0001), but not in the other 828 (84%) patients (1·00 [0·65–1·54], p=0·7).
Interpretation
Many patients with recently symptomatic 70–99% carotid stenosis may not benefit from carotid endarterectomy. Validation of the predictive score is needed on external datasets, but risk-factor modelling could be useful to identify those patients in whom endarterectomy will be beneficial.
Patients
We used clinical data and carotid angiograms from the ECST.2, 19 Briefly, patients were recruited to ECST if they had had a carotid distribution transient ischaemic attack, minor ischaemic stroke, non-disabling major ischaemic stroke, or a retinal infarction in the previous 6 months, and had evidence of ipsilateral carotid stenosis on angiography. Patients from 100 centres in 14 European countries were randomly assigned immediate surgery (60%) or medical treatment only (40%). Clinicians were
Methods and statistical analysis
We developed models from baseline clinical and angiographic data. The medical model, which predicted the risk of ipsilateral carotid territory ischaemic stroke on medical treatment, was derived from data on patients with 0–69% stenosis who had been assigned no surgery in ECST. The outcome was the first major ipsilateral ischaemic stroke (fatal or lasting longer than 7 days) on follow-up. If no CT brain scan was available, or if the scan was done more than 30 days after stroke, the stroke was
Development and validation of models
2060 ECST patients had 0–69% stenosis. 1203 (58·4%) were randomly assigned surgery and 857 (41·6%) no surgery. There were 78 first ipsilateral carotid territory major ischaemic strokes on follow-up in the medicaltreatment group and 84 major strokes or deaths within 30 days of endarterectomy in the surgery group. Four baseline clinical and angiographic variables were predictive of ipsilateral carotid territory major ischaemic stroke in the medical-treatment group (table 1). We derived the
Stratification by predictive score
The score predicting likely overall benefit from endarterectomy (ie, high medical risk and low surgical risk) is shown in table 1. The scores for patients in the 70–99% stenosis group in ECST ranged from 0 to 5·0. The overall effect of surgery in patients with 70–99% stenosis is shown in figure 1 (absolute risk reduction 7%, p=0·003). Figure 2 shows the decrease in the 5-year actuarial risk of ipsilateral carotid territory major ischaemic stroke, surgical major stroke or death in the surgery
Non-validated models
Table 5, Table 6 show the results of the non-validated models that were derived from all the surgery and medicaltreatment groups (ie, patients with 0–99% stenosis). Both of these models require external validation. The medical model contained nine variables that were independent predictors of the risk of ipsilateral carotid territory ischaemic stroke. Each of the four variables in the validated model (based on the 0–69% stenosis group) remained significant independent predictors in the more
Discussion
Although carotid endarterectomy lowers the risk of stroke in patients with recently symptomatic 70–99% carotid stenosis, the cost-effectiveness of the procedure is still questioned.20 Surgery is needed in about 14 patients to prevent one having an ipsilateral carotid territory major ischaemic stroke lasting longer than 7 days over the next 5 years. The number of operations required to prevent one stroke might be lowered substantially by the use of riskfactor modelling to identify patients who
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