Overall results of a pooled analysis of individual patient data from trials of endarterectomy for symptomatic carotid stenosis
Carotid endarterectomy (CEA) is beneficial for severe symptomatic stenosis, but trial results for moderate stenosis have been conflicting. This may be due to the differences between trials in the method of measurement of carotid stenosis, differences in outcome definitions, or chance. We used the same definitions of outcomes and the same method of measurement of stenosis to pool individual patient data on over 95% of patients ever randomised in trials of CEA for symptomatic stenosis: European Carotid Surgery Trial (ECST); North American Symptomatic Carotid Endarterectomy Trial; Veterans Administration trial #309. The degree of stenosis was remeasured on the 3018 pre-randomisation ECST angiograms by the method used in the other two trials. Remeasurements correlated well with the original measurements (r=0.94, P<0.00001). Data were merged on 6092 patients with 1711 strokes and 1493 deaths during 35,000 patient years of follow-up. Patients were categorised according to the degree of symptomatic stenosis: <30% (n=1755); 30–49% (n=1441); 50–69% (n=1547); 70–99% (n = 1338); occlusion (n = 9); unknown (n=2). Surgery was harmful in patients with <30% stenosis, and was of no benefit in patients with 30–49% stenosis. Surgery reduced the risk of any stroke or surgical death in patients with 50–69% stenosis (NNT = 14, 95% CI = 8–30), and this was consistent across the individual trials. Surgery was highly beneficial in patients with 70–99% stenosis (NNT = 8, 95% CI = 5–12), but had no effect on overall survival. Operative mortality was 1.1% (95% CI = 0.9–1.4) and the operative risk of stroke and death was 7.0% (95% CI = 6.2–8.0). In contrast to interpretations of the original trial reports, by using the same outcome definitions and the same method of measurement of stenosis we have demonstrated that the trial results are entirely consistent. By combining all available trial data we have determined the effect of surgery with greater precision. CEA reduces the risk of any stroke or death in patients with 50–99% carotid stenosis, although benefit is less than for 70–99% stenosis.