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Stroke due to Carotid Artery Stenosis
Cause of Carotid Stenosis – Stroke Mechanism – Stroke Prevention in Carotid Stenosis – Carotid Endarterectomy vs. Carotid Artery Stenting
Stroke due to Carotid Artery Stenosis
Atherosclerosis commonly affects carotid arteries. Carotid arteries run in the front of the neck on both sides and supply the frontal two thirds of the brain. Common carotid artery originates at the base of the neck and then divides into two branches: internal carotid artery (supplies the brain) and external carotid artery (supplies tissues on the outside). Common carotid artery widens before it divides. The wide portion is called the bulb.
Atherosclerotic plaques tend to form in the bulb area. Strokes are caused by blockage at the level of the internal carotid artery or the bulb. Technically, narrowing of the common carotid artery can cause strokes as well, but it hardly ever happens. External carotid artery disease does not cause strokes.
Risk factors for carotid atherosclerosis are atherosclerosis elsewhere in the body, older age, smoking, hypertension, diabetes, obesity, lack of physical activity, elevated cholesterol blood level.
Carotid atherosclerosis is responsible for 7% of ischemic strokes. Stroke risk highly correlates with the degree of stenosis (narrowing) and history of prior strokes. Statin (cholesterol lowering medications) wide-spread use in recent years significantly altered stroke risk statistical data.
Let me introduce a couple of terms. Carotid stenosis is called asymptomatic before it has caused a stroke and symptomatic if the stroke has already occurred. Prior to statins invention, less than 75% asymptomatic carotid stenosis carried 1.3% chance of stroke per year. Greater than 75% stenosis had an annual risk of 2.0% to 2.5%. On the other hand, 70% or greater symptomatic carotid stenosis carries an annual stroke risk of 10% to 15%.
Stroke Prevention Strategies in Carotid Stenosis
There are three stroke prevention options in carotid stenosis, which are carotid endarterectomy surgery, carotid stenting, and conservative management with medications.
It is a surgical procedure performed by incision of the carotid artery wall and physical removal of the atherosclerotic plaques obstructing the blood flow.
Carotid Angioplasty (Stenting)
Carotid artery is accessed from the inside. A special flexible catheter is inserted into another artery (usually in the groin). Under fluoroscopy guidance it is pushed along the blood vessel until it reaches the desired part of the carotid artery. The narrow section of carotid artery is widened with inflatable balloon and stent is placed in order to keep the artery open.
Medications in Carotid Atherosclerosis
When it comes to carotid atherosclerosis, statins and anti-platelet agents are both typically employed in stroke prevention (see Atherosclerosis).
Stroke Prevention in Symptomatic Carotid Stenosis
Once carotid stenosis caused a stroke it is considered symptomatic. High grade symptomatic carotid stenosis is normally managed by invasive methods. The choice of procedure is decided on case by case basis.
The major concern is a chance of stroke or death during or shortly thereafter the procedure.
For carotid endarterectomy it is 2.3%, while for carotid stenting is 4.1%. This difference is observed for four years after these procedures: 4.7% vs. 6.2% respectively. Carotid endarterectomy is obviously safer.
When it comes to women, the chance of stroke or death in carotid stenting comes even higher, or 5.5%. Advanced age is strongly associated with increased chance of stroke or death for both types of treatment; more so for carotid stenting. After age of 75 the chance of stroke or death is 7.4% for carotid endarterectomy and 12.7% for carotid stenting!
Basically, in any age group and sex, carotid endarterectomy is a preferred choice of stroke prevention in carotid stenosis, more so in women and patients over 75 yo. So, what is the point for mere existence of carotid stenting?
Carotid endarterectomy carries a higher rate of procedure related heart attack. Patients who cannot tolerate surgical intervention for medical reasons would benefit from carotid stenting. There are multiple factors that might make carotid endarterectomy impractical, such as severe heart or lung disease, occluded opposite carotid artery, previous neck radiation or massive surgeries, severe neck arthritis, obesity, and some anatomical carotid artery variations.
At this point, the number of studies about conservative management (medications) of symptomatic carotid stenosis is limited. Whenever invasive procedure is contraindicated or is undesirable for any reason, aggressive drug therapy with statins and antiplatelet drugs is the next option. Patients of very advanced age and short life expectancy for other reasons would be better managed conservatively. Complication risk, directly related to either procedure, pays off only if the patient lives long enough to benefit from it.
Stroke prevention in Asymptomatic Carotid Stenosis
Treatment choice in asymptomatic carotid stenosis is more challenging. Asymptomatic means lack of carotid artery related strokes in the past. Greater than 75% asymptomatic carotid stenosis carries 2% to 2.5% annual risk of stroke. In male patients younger than 75 years the risk of intervention may often be justified.
In elderly, especially women, taking chances is often unreasonable. Using Trans cranial Doppler Monitoring, it is possible to detect micro-emboli (small plaque fragments) in the brain circulation. It might help to assess the necessity of aggressive management. No statistical data about significance of these findings is available, however.
There is no one-fits-all protocol for carotid artery disease treatment. There are multiple factors, which have to be taken in consideration. Decision regarding individual treatment options is usually made by neurologist.