In Singapore, stroke is the 4th leading cause of death and a major contributor to long term disability. A stroke or "brain attack" can occur when one of the major arteries in the neck (the carotid artery) is narrowed by fatty deposits (plaques). Such "hardening" of the carotid artery can lead to damage to part of the brain, either as a consequence of reduced blood flow or because small pieces of "emboli" break off from the plaque and lodge into arteries in the brain or eye. This ultimately results in an ischaemic type of stroke, which accounts for 75% of all strokes. Carotid endarterectomy (CEA) is a surgical procedure performed to reduce the risk of stroke. It can therefore help prevent an ischaemic stroke in certain patients with carotid artery stenosis.
This procedure does not apply to haemorrhagic strokes (bleeding in the brain), which make up the other 25% of strokes.
Am I a candidate for Carotid Endarterectomy?
You would be a candidate for surgery if you have experienced any of the following symptoms.
How is Carotid Artery Disease diagnosed?
A computed tomography (CT) or magnetic resonance imaging (MRI) of the brain is often done for patients considered for CEA. This is particularly important in patients with persisting symptoms, to rule out other brain pathologies that can mimic an ischaemic stroke, such as a haemorrhagic stroke or a brain tumour.
While carotid artery stenosis can be detected with the use of a stethoscope placed over the side of the neck - a rushing sound called a bruit (pronounced ‘bru-yee’) is heard, a series of confirmatory tests are necessary. These include:
Duplex Ultrasound Imaging
This is a non-invasive test which is fast, risk-free and relatively inexpensive. Sound waves above the range of human hearing are sent into the neck. Echoes bounce off moving blood and tissues in the artery and are formed into an image. In carefully calibrated ultrasound laboratories, duplex ultrasound can be up to 95% accurate. However, it remains operator dependent requiring a high level of skill and can sometimes overestimate the degree of stenosis. The converse is also true. Most clinicians will use duplex ultrasound as the first investigation, moving on a conventional angiogram or a non-invasive test such as an MRA (MR angiography).
Although invasive, conventional angiography remains the gold standard with a high degree of accuracy in measurement of carotid artery narrowing. This is an X-ray of the carotid artery taken when a special dye is injected into the artery though a fine tube introduced through the groin under local anaesthesia. A burning sensation is experienced when the dye is injected. The test cannot be carried out if there is a history of allergy to iodine.
When used in conjunction with duplex ultrasound alone, MR angiography offers a non-invasive approach to the evaluation of carotid artery stenosis. It is increasingly used today with a high degree of sensitivity and specificity. It is being developed and validated to provide the same information as catheter angiography, eliminating the need for an invasive catheter angiogram.
A) What are the benefits of CEA?
Surgery to remove this narrowing in the carotid artery can help prevent a stroke. However, it cannot improve the outcome of a stroke that has already occurred. CEA is more effective than medical management in the prevention of stroke. However, this is true for certain groups of patients under defined circumstances.
In patients with symptomatic and severe disease of >70-99%, such as patients with symptoms of stroke, transient ischaemic attack (TIA or mini-stroke) or amaurosis fugax (transient blindness) due to carotid artery narrowing of > 70-99%, CEA has significant benefit over medical management. The risk-benefit ratio favors surgery only if the perioperative morbidity and mortality is < 6%.
Patients with asymptomatic disease and carotid artery stenosis of >60%, such as patients with carotid artery narrowing of >60% but who experience no symptoms, benefit substantially less from CEA. For any benefit at all, surgery must be performed at very low stroke rates, in the range of 2-3%.
B) What is the evidence for CEA?
In symptomatic severe carotid artery narrowing, several trials have shown CEA to be superior to medical management for the prevention of stroke. The North American Symptomatic Carotid Endarterectomy Trial (NASCET), published in 1991, showed a significant benefit for CEA in patients with severe carotid artery stenosis of >70% demonstrated on angiography. In the NASCET trial, CEA resulted in an absolute risk reduction of stroke by 17% at 2 years. This difference in outcome between medical therapy and surgery plus medical therapy represented a relative risk reduction of 65%. Thus, surgery was beneficial for persons with severe carotid artery narrowing and who had experienced a stroke or its warning signs. The European Carotid Surgery Trial (ECST), published in 1991, also demonstrated a similar benefit in such patients with severe carotid artery stenosis. It is important to realise that the perioperative stroke and death rate has to be < 6% for CEA to be effective.
CEA has been shown to be beneficial in patients without symptoms but this benefit is less substantial. The Asymptomatic Carotid Atherosclerosis Study (ACAS), published in 1995, is the largest and most definitive randomised trial that evaluated the efficacy of surgery in patients with severe stenosis of > 60% detected by ultrasound. The 5-year projected risk of stroke was reduced by surgery from 11% to 5.1%. While this is translated to a relative risk reduction of 53%, the absolute risk reduction at 2 years was only 1.5% (meaning that 67 patients would need to undergo surgery to prevent one non-disabling stroke). Furthermore, surgery did not protect against major stroke and death and the results were not significant when women were analysed as a discrete population. With a modest benefit of surgery in patients were severe stenosis and no symptoms, carotid endarterectomy is not routinely recommended. It should be only considered as a management option by surgeons with very low complication rates of < 3% in the presence of other high risk factors (eg, stenosis of the opposite carotid artery, plaque ulceration etc). Medical management is a sensible alternative for most of such patients.
C) What does the surgical procedure of CEA involve?
A skin incision is placed obliquely across the side of the neck. This is deepened along border of the sternomastoid muscle to reach the carotid artery, its branches and the accompanying internal jugular vein. Care is taken to preserve the nerves in vicinity.
The branches of the artery and the carotid artery before and after the site of narrowing are clamped. This is done under the cover of heparin to prevent the clotting of blood in the clamped arteries. A longitudinal incision (arteriotomy) is then made over the plaque which is then carefully dissected free, resulting in a very smooth inner wall. The arteriotomy is then repaired with very fine sutures. Next, the arterial clamps are removed to restore blood flow to the brain.
This procedure can be done with EEG monitoring or TCD (transcranial Doppler) to monitor the risk of clamping the arteries. If there are signs of inadequate blood supply, a carotid "shunt" tubing is inserted to restore blood flow to the brain during the endarterectomy.
D) What can I expect after a Carotid Endarterectomy?
Postoperatively, you will be monitored closely in the neurointensive high dependency unit for 12-24 hours. You will then return to the general ward where you should be able to eat and drink normally. You should also be up and about on the second day, after the surgical drain (to prevent accumulation of excess blood in the wound site) is removed. Aspirin is continued while pain killers are also prescribed. A subcutaneous absorbable suture is usually used obviating the need to remove the stiches. Patients without any concomitant medical problems can be expected to be discharged after 3-4 days.
You will then be seen at the neuroscience outpatient clinic 2 weeks after discharge. However, please contact your surgeon or physician immediately if you experience any of the following symptoms:
What are the risks of CEA?
To reduce the risk of postoperative stroke, all patients continue to receive their usual dose of aspirin before CEA. The potential complications of surgery include:
What does “Best Medical Treatment for Stroke Prevention” mean?
Besides CEA in specific individuals for whom the surgery is highly beneficial, the mainstay of stroke prevention is risk factor management. This includes the treatment of high blood pressure, diabetes, heart disease, high cholesterol levels and the cessation of smoking. A healthy life-style is sensible. Additionally, the doctor may prescribe aspirin, warfarin, clopidogrel or other drugs.
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