What is Strokes, Carotid Artery Disease ?
The goal of carotid surgery and carotid artery stenting is to prevent strokes. Strokes lasting less than 24 hours are referred to as transient ischaemic attacks.
There are two main types of stroke:
ischaemic and haemorrhagic. As per the available worldwide data, 80% of strokes are ischaemic.
A high proportion of ischaemic strokes results from embolisation from diseased carotid arteries in the neck. Embolisation means a blood clot forms in one place then breaks off and travels through the circulation to lodge in another site. The carotid arteries in the neck supply the brain, and they are prone to localised atheromatous plaque formation. Small blood clots form on the surface of the rough plaque then break off and lodge in the brain. This gives rise to different symptoms depending on how large the embolus is and which part of the brain it ends up in.
Problems that may result from carotid artery disease.
Asymptomatic: CT and MRI scanning often reveal evidence of multiple small strokes with no history of preceding symptoms. These patients may have no obvious symptoms like mini-stroles, but over time may develop impaired brain function which may progress to a form of dementia (so-called multi-infarct dementia).
Amaurosis Fugax: Small blood clots from the carotid artery may flow through the circulation to the retinal artery in the eye cause the characteristic symptom of a greying-out of the vision in one eye. Patients often describe it as a curtain coming down. The vision returns to normal within a few minutes.
A transient ischaemic attack (TIA) is a small stroke that resolves within 24 hours.
Strokes result from blockages is middle cerebral artery in the brain and cause paralysis on the opposite side to the damaged artery. Strokes lasting less than 3 weeks are said to be transient strokes. Persistent deficits after 3 weeks are established strokes and subsequent recovery may be good, moderate or poor. These clinical distinctions are important since prognosis after carotid surgery is related to the presenting symptom.
What is the best way of testing for carotid artery disease?
Any patient presenting with one of the above symptoms should have a carotid duplex scan. This identifies whether the internal carotid artery is deseased and if so, what the degree of narrowing (stenosis) is present. The percentage stenosis is the best predictor currently available of likelihood of subsequent stroke.
What is the risk of major stroke after a min-stroke?
A patient who presents with amaurosis fugax, TIA or stroke associated with a stenosis of the relevant internal carotid artery greater than 70% has a high risk of major stroke in the following 3 months. Correcting vascular risk factors (stopping smoking, treating hypertension, instigating aspirin and statin therapy) go some way to reduce this risk but correcting the underlying carotid artery disease by operation or stenting is highly effective at reducing subsequent stroke risk down to normal levels.
What is carotid endarterectomy?
Carotid endarterectomy is an operation to unblock damaged arteries supplying the brain which cause strokes if left untreated. The operation involves exposing the carotid arteries, opening the vessel and carefully removing the diseased plaque leaving a smooth internal lining. The artery is usually closed with a patch to avoid narrowing. A shunt may be used during the operation to preserve cerebral blood flow while the artery is open but this is not always necessary. The operation can be performed under local or general anaesthetic. We generally prefer the local anaesthetic technique so the patient remains conscious throughout. Transcranial doppler is also used to monitor brain blood flow during the operation.
The operation takes about 60-90 minutes and most patients are discharged home 24 to 48 hours post-op. The long term results are excellent, recurrence of the problem is extremely rare.
Side effects and problems of carotid surgery
Carotid endarterectomy has a risk of death and stroke of around 2-3% depending on the operating surgeon and the patient's risk factors. This is much less than the risk of stroke or death from leaving the artery untreated. The other main complication is damage to important nerves in the area. The most important ones are the hypoglossal nerve which controls the tongue, mouth, and branches of the vagus nerve which supply the voice box. Some patients notice their voice is a little hoarse afterwards, or that their tongue feels clumsy. Fortunately these problems are fairly uncommon, and usually temporary. It is also quite usual for the skin around the scar to feel numb in places. This sometimes feels a little odd when shaving but is of no great consequence and returns to normal eventually.
Carotid artery stenting
Carotid artery stenting is a relatively new way of correcting blockages of the carotid arteries with the same goal as carotid endarterectomy; to reduce risk of stroke. The procedure is done under local anaesthetic. A fine wire and catheter are inserted into the femoral artery in the groin and passed up into the neck under Xray guidance.
A balloon is inserted along the wire across the blocked artery, and the balloon inflated to open up the area of narrowing. A stent (fine metal mesh tube) is then inserted to hold the artery open after the balloon has been withdrawn. The procedure takes about an hour and discharge is within 24 hours.
Potential side effects of carotid artery stenting
The problem with passing wires, catheters and balloons past a diseased artery is that it may cause debris to break off and lodge in the brain causing a stroke. For this reason, most carotid artery stenting devices are equipped with a so-called cerebral protection device which is a filter to catch any debris before it can pass to the brain and do damage.
Carotid artery stenting has the advantages of avoiding any incisions, and there is no risk of damage to nerves in the neck. There is uncertainty over whether the risk of stroke during carotid stenting is greater than carotid surgery. Numerous trials have compared the two techniques but there is still considerable controversy over which one is better. The choice of technique is influenced by individual patient factors including the exact anatomy and nature of the carotid artery block.
Asymptomatic carotid artery stenosis
The carotid arteries often become furred-up without any warning signs. The risk of these blockages causing strokes is much less than those which have caused blood clots to form, but nonetheless they are associated with an increased risk of stroke. There are now very good quality trials which prove that correcting carotid artery stenosis (narrowing) even when there have been no preceding symptoms significantly reduces the long-term risk of fatal or disabling stroke. The benefit depends on the degree of narrowing, and the age and gender of the patient.