Preoperative Evaluation of Endarterectomy Patients
Abstract & Commentary
Source: Rothwell PM, Warlow CP. Prediction of benefit from carotid endarterectomy in individual patients: A risk-modelling study. Lancet 1999;353:2105-2110.
Carotid endarterectomy is the treatment of choice in patients with recently symptomatic severe carotid stenosis. Two randomized controlled trials, the European Carotid Surgery Trial (ECST) (European Carotid Surgery Trialists’ Collaborative Group. Lancet 1991;337:1235-1243) and the North American Symptomatic Carotid Endarterectomy Trial (NASCET) (North American Symptomatic Carotid Endarterectomy Trial Collaborators. N Engl J Med 1991;325:445-453), showed that endarterectomy lowers the risk of major ischemic stroke by 50% over the next three years in patients with symptomatic 70-99% carotid stenosis. Nevertheless, the three-year stroke risk on best medical therapy alone is only about 20%. Therefore, surgery is not necessary and may be harmful in 80% of patients.
In fact, ECST found that surgery is harmful in patients with less than 70% stenosis (ECST Collaborative Group. Lancet 1998;351:1379-1387). NASCET reported a small benefit from surgery in patients with 50-69% stenosis, but no benefit in those with 30-49% stenosis (NASCET Collaborative Group. N Engl J Med 1998;339:1415-1425). Because of different methodologies, a 50-69% stenosis in NASCET is equivalent to a 70-80% stenosis in ECST (Barnett HJM, Warlow CP. Stroke 1993;24:1281-1284; Rothwell PM, et al. Stroke 1994;25:2435-2439).
Based on data from ECST patients with 0-69% carotid stenosis, Rothwell and Warlow developed two prognostic models (see Table 2), a medical model that predicted risk of major ischemic stroke on medical treatment and a surgical model that predicted risk of stroke or death within 30 days of endarterectomy. The predictive score is based on seven independent factors. Risk points were derived by rounding the hazard ratio to the nearest whole number and subtracting one. In order to identify patients most likely to benefit from endarterectomy, the predictive score adds points for the presence of factors associated with a high stroke risk despite medical treatment. It then subtracts points for the presence of variables that increase operative stroke or death risk. Since the risk of stroke on medical treatment in ECST or NASCET patients with 70-99% stenosis was double the operative risk of stroke or death, surgical risk points are subtracted from the predictive score and their weighting is decreased by 50% (see Table 2).
| Table 2-Prognostic Model | ||||
| Medical Model | Hazard Ratio (95% C7) | P | Risk Points | Predictive Score |
| 1. Cerebral vs. ocular events | 2.45 (1.09-3.71) | 0.02 | 1 | 1 |
| 2. Irregular plaque | 2.09 (1.21-3.62) | 0.008 | 1 | 1 |
| 3. Event within past 2 months | 1.82 (1.02-3.18) | 0.04 | 1 | 1 |
| 4. Carotid stenosis | 1.30 (1.10-1.40) | 0.001 | 0-2* | 0-2 |
| Surgical Model | ||||
| 5. Female | 2.05 (1.29-3.24) | 0.002 | 1 | -0.5 |
| 6. Peripheral vascular disease | 2.48 (1.51-4.13) | 0.0004 | 1 | -0.5 |
| 7. Systolic BP > 180 mmHg | 2.21 (1.29-3.79) | 0.004 | 1 | -0.5 |
| *Carotid Stenosis 70-79% = 0; 80-89% = 1; 90-99% = 2. | ||||
When ECST patients in the 70-99% stenosis group were stratified using the scoring system, scores ranged from 0-5.0 (see Table 3). Endarterectomy was significantly beneficial in only the 16% of patients who had risk scores of 4 or more. In these patients, there was a 33% absolute reduction in the five-year actuarial risk of stroke.
| Table 3-Stratification of ECST Patients | |||||
| Risk Score | Patients | Total | Adverse Events | ||
| Surgery | Medical Treatment | Surgery* | Medical Treatment** | ||
| 0-3.5 | 495 | 333 | 828(84%) | 58 | 39 |
| 4.0-5.0 | 101 | 61 | 162(16%) | 7 | 24 |
| Total | 596 | 394 | 990(100%) | 65 | 63 |
| *Operative stroke or death | |||||
| **Ipsilateral major ischemic stroke | |||||
Rothwell and Warlow conclude that the use of risk- factor modeling can be used to identify patients with a high risk of stroke and a low operative risk in whom endarterectomy will be beneficial.
Commentary
The overall positive result of a multicenter clinical trial may at times obscure substantial unevenness of therapeutic effect across groups of patients. In fact, patients may appear to be homogenous, but actually have differing risks of poor outcome. Rothwell and Warlow have tried to analyze the heterogeneity of effect of endarterectomy in the ECST population by developing a predictive model to stratify patients according to both risk of stroke and of surgical complications. As they acknowledge, their predictive score needs validation by application to other data such as the NASCET results. Nevertheless, their scoring system is clear, logical, and apparently easy to apply. Neurology Alert thinks clinicians might well test its predictive power in their own patients. —jjc
Each of the following is associated with an increased risk of stroke or death following endarterectomy except:
a. female sex.
b. peripheral vascular disease.
c. uncontrolled hypertension.
d. male sex.
e. systolic hypertension more than 180 mmHg.
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