Does Carotid Endarterectomy
Reduce Stroke Risk?
The Evidence

European Carotid Surgery Trial (ECST)
In this randomized multicenter trial patients with non-disabling stroke, TIA, or retinal infarct in the carotid territory were randomized to best medical care vs carotid endarterectomy plus best medical care. Every one had angiography to demonstrate the culprit lesion.

For patients with mild stenosis (0-29%) surgery was harmful due to the upfront risk of a stroke within 30 days secondary to the procedure, and a lack of benefit in the long term.

For patients with severe stenosis (70-90%) there was clear longterm benefit. At 3 years the risk of stroke or death was 12.3%in the surgery group vs. 21.9% in the control group. (RR56%, RRR 44%, p<0.01, ARR 9.6%, NNT 10.4) There was a 7.5% risk of stroke or death in the first 30 days in the surgery group, which is an important point to remember. Interestingly in the control group, disability or death was also front loaded, happening much more frequently in the first year after the qualifying event, suggesting delay of surgery for more than a few months would negate the benefits of subsequent surgery.

For the patients with moderate stenosis (30-69%) the trial was neutral. The upfront risk of surgery balanced the subsequent benefit, such that there was no difference out to 5 years in the 50-69% group and 7 years in the 30-49% group.

North American Symptomatic Carotid Endarterectomy Trial (NASCET)
This large multicenter randomized trial was coordinated in Canada at McMaster University. The qualifying event was a retinal or hemispheric TIA or non-disabling stroke within the last 120 days. It looked at 2 pre-specified groups based on the severity of the ipsilateral carotid stenosis: 30-69% (moderate) and 70-99% (severe). Patients were randomized to best medical care vs. carotid endarterectomy plus best medical care.

In the 659 patients with a severe stenosis the results were dramatic. At 2 years the cumulative risk of any ipsilateral stroke was 9% in the surgery group and 26% in the medical group. (RR 35%, RRR 65%, ARR 17%, NNT 5.9, P<.001)

The moderate stenosis group was divided farther into the high moderate (50-69%) and low moderate (30-49%) groups. The high moderate group randomized 858 patients. At 5 years any ipsilateral stroke was 15.7% in the surgical group vs. 22.2% in the medical group. (RR 71%, RRR 29%, ARR 6.5%, NNT 15, p=0.45). For any stroke or death at 5 years the numbers were 33.2% in the surgical group vs. 43.3% for the medical group. (RR 77%, RRR 23%, ARR 10.1%, NNT 10, p=0.005) The low moderate group randomized 1,368 patients. For ipsilateral stroke there was a 20% RRR but the p=0.16 was insignificant. There was no difference at all in the all stokes and deaths group.

There are several caveats here. The surgeons chosen for the NASCET were the best available. Their surgical risk for disabling stroke or death in the perioperative period was only 2%. Also the method of measuring the stenosis is critical and was different between ECAS and NASCET, such that an 80% stenosis in ECAS was equivalent to a 60% stenosis in NASCET. Relying solely on ultrasound examinations of the neck to make surgical discussions is not recommended, as they do not correlate exactly with angiographic data.

What about asymptomatic carotid stenosis? This has been looked at in the: Asymptomatic Carotid Atherosclerosis Study (ACAS)⁵ In this multicenter trial 1,662 patients who were healthy enough to be candidates for surgery and had greater than 60% stenosis of the internal carotid artery, were randomized to best medical treatment vs. medical treatment plus carotid endarterectomy. After a median of 2.7 years of follow up, with 4,657 years of patient observation, the trial was stopped early due to demonstration of a clear benefit. The aggregate risk over 5 years for ipsilateral stroke, or any perioperative stroke or death was estimated to be 5.1% in the surgical group vs. 11% in the medical group. (RR 46%, RRR 54%,ARR 5.9% NNT 17, p<0.05). For this result to be obtained, the angiography and perioperative stroke and death rate has to be less than 3%.

These studies highlight the importance of having any patients presenting with non-disabling stroke, TIA, or retinal infarct in the carotid territory, evaluated quickly for the possibility of surgical intervention. This is especially important when you consider that there is a 10% risk of stroke in the first 90 days following TIA, and half of this risk occurs in the first 2 days.

- Farokh Buhariwalla

1. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. North American Symptomatic Carotid Endarterectomy Trail Collaborators. N Engl J Med. 1991 Aug 15;325(7):445-53
    
2. Barnet, H et al, Benefit of Carotid Endarterectomy in Patients with Symptomatic Moderate or Severe Stenosis. N Engl J Med. 339(20):1415-25
    
3. MRC European Carotid Surgery Trial: Interim Results for Symptomatic Patients with Severe (70-99%) or with mild (0-29%) Carotid Stenosis. European Carotid Surgery Trialists' Collaborative Group. Lancet. 1991 May 25;337(8752):1235-43
    
4. Endarterectomy for Moderate Symptomatic Carotid Stenosis: Interim Results from the MRC European Carotid Surgery Trail. Lancet. 1996 Jun 8;3447(9014):1591-3
    
5. Endarterectomy for Asymptomatic Carotid Artery Stenosis. JAMA. 1995 may 10;273(18):1421-8