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The crucial, controversial carotid artery Part I: The artery in health and disease

You don’t have to be a brain surgeon to know it is vitally important for your brain to receive an uninterrupted supply of blood. That’s because nerve cells require a constant supply of oxygen. Even a brief disruption stuns nerve cells, impairing their function, while more prolonged oxygen deprivation kills the cells. If only a small, noncritical area of your brain is affected, you may not notice the damage. Unfortunately, however, the damage is often very noticeable indeed. Brief or partial interruptions of blood flow cause transient ischemic attacks (TIAs), while prolonged or complete blockages are the major cause of cerebrovascular accidents — strokes.

Shocking statistics

Stroke is the fourth leading cause of death in the United States, taking about 136,000 lives annually. Another 660,000 Americans survive strokes each year, but many are so disabled that they cannot return to work. In human terms, it’s an enormous burden of suffering; in dollar terms, it costs $74 billion a year to care for stroke victims and make up for their lost productivity.

Strokes are uncommon in young people, but they become progressively more common with age. Because women live longer than men, the overall risk of stroke is higher in women than men. Between ages 55 and 84, however, men have the dubious distinction of being at higher risk than women.

Different strokes

A stroke may occur when a blood vessel in the brain bursts (hemorrhagic stroke), but the vast majority, nearly nine of every 10, are caused by a blocked artery (ischemic stroke). The blockage can occur right in an artery in the brain (thrombotic stroke), but it is more commonly caused by blood clots that break off from the heart or from an artery that carries blood to the brain (embolic stroke).

That’s where the carotid arteries come in. In health, they carry blood to the front part of the brain, but when diseased, they are a major cause of TIAs and strokes. Simple, noninvasive tests can diagnose carotid artery disease, and treatment can reduce the risk of stroke. That’s where the controversy comes in, as doctors debate who should be tested for carotid disease and who should be treated with medication or with procedures that open narrowed arteries. And if that’s not controversial enough, doctors are now debating the relative merits of using surgery or angioplasty with stenting to open partially blocked carotids.

The normal carotids

The brain gets its blood from four arteries that travel up from the body’s main artery, the aorta, and its branches. The two smaller vertebral arteries (see figure) are located deep in the back of the neck, where their pulses can’t be felt; they join at the base of the brain to form the basilar artery that supplies blood to the rear portions of the brain. The two common carotid arteries carry blood up the front of the neck, where their pulses can be felt on either side of the trachea, or windpipe. When they near the jaw, at about the level of the thyroid cartilage (“Adam’s apple”), each common carotid artery divides into the internal and external carotid arteries. The external carotids supply blood to the face. But it’s the internal carotids that really count; they carry blood to the front part of the brain, and the first portion of the internal carotid is the main site of disease that leads to TIAs and strokes.

The right internal carotid artery carries blood to the right side of the brain, which is responsible for strength and sensation on the left side of the body. As a result, disease of the right carotid can cause neurologic symptoms on the left half of the body. Similarly, disease of the left internal carotid can produce neurological symptoms on the right side of the body. But since each carotid supplies blood to the eye on its own side, disease of the left carotid can cause visual symptoms in the left eye, while the right carotid affects the right eye.

Brain at risk: The carotid circulation

illustration showing brain and carotid arteries

The internal carotid artery carries blood to the brain. Cholesterol-laden plaques can narrow the artery, allowing clots to form. If the clots break off and travel to the brain, they can cause transient ischemic attacks (TIAs) or strokes.

Carotid stenosis

In a healthy man, the internal carotid artery is about 5 millimeters wide, the diameter of a pencil eraser. That’s more than wide enough to bring the brain all the blood it needs. Narrowing, or stenosis, of the carotid is considered mild when it reduces the width of the artery by less than 50%; narrowing of 50% to 69% is considered moderate, while 70% to 99% is considered severe carotid stenosis.

What narrows the carotid artery? In nearly all cases, it’s atherosclerosis, the same disease that causes heart attacks by blocking coronary arteries. In atherosclerosis, cholesterol-laden plaques build up in the artery wall, gradually narrowing the vessel. But in most cases, it’s not the plaque itself that does the final damage. Instead, the culprit is a blood clot, or thrombus, that forms on the ulcerated, irregular surface of the plaque. In the heart, the clot blocks a coronary artery, thus causing a heart attack. But in carotid stenosis, the clot breaks away from the plaque and is carried by the blood to the brain or eye, where it lodges in a smaller artery. If the clot breaks into tiny fragments that are carried away, the brain cells recover — that’s why the symptoms of a TIA resolve within 24 hours. But if the clot stays put, brain cells die, causing the irreversible damage of stroke.

Vertebral artery TIAs

The carotids are just two of the four arteries that carry blood from the heart to the brain. The other two are the vertebral arteries that join to form a single basilar artery, then branch out to supply blood to the rear portion of the brain (see figure).

TIAs caused by abnormalities of the vertebral, or basilar, circulation are more complex than carotid TIAs, and they are harder to recognize. Abrupt, transient dizziness may occur, usually accompanied by loss of balance, double vision, or slurred speech. Visual loss is another symptom, but unlike the problem produced by carotid disease, it usually involves both eyes simultaneously, producing complete blindness or loss of sight in one half of each eye. Weakness, clumsiness, or tingling of the face, hands, or legs can also occur, usually involving both sides of the body. Tingling of the cheeks, gums, and tongue are particularly likely to result from disease in the vertebral artery system. Headaches are also common and especially likely to occur at the back of the head. In rare cases, patients have drop attacks, abruptly losing muscle strength and falling to the floor without losing consciousness.

Routine maintenance

The best way to prevent TIAs and strokes is to keep your blood vessels healthy. Like coronary artery disease, carotid artery disease is most often caused by smoking, hypertension, high cholesterol, lack of exercise, diabetes, and obesity. Stress may also contribute. All these risk factors can be controlled. The key is smoking cessation, a healthy diet (low in saturated and trans fats, cholesterol, and salt, but high in fish, fiber, fruits, and vegetables), regular exercise, and regular check-ups to detect and treat high blood pressure and abnormal cholesterol levels.

In the United States, strokes have declined by about 70% since 1950, largely because of blood pressure control. It’s good news, but it could — and should — be much better. And if you already have carotid stenosis, you may need to take additional steps to prevent a stroke. Two approaches are available: medication to prevent clots from forming on plaques, and surgery or angioplasty with stenting to open the narrowed artery.

Detecting carotid stenosis

You can feel your carotid artery simply by placing a finger on your neck. You might guess that it would be simple for the trained finger of a doctor to detect a diseased vessel, but it’s not; the carotid pulse doesn’t provide reliable information about the internal carotid’s health.

Atherosclerosis narrows arteries. Narrowing produces turbulent blood flow; like white water in a bubbling brook, turbulent flow in a vessel is noisy. Your doctor can hear that noise, called a bruit, simply by listening to your carotid arteries through his stethoscope. Unfortunately, when it comes to detecting carotid stenosis, the ear isn’t much better than the finger. Many arteries with audible bruits have perfectly adequate blood flow, and some that are severely narrowed carry blood silently. All in all, the presence or absence of a carotid bruit does little to predict your risk of stroke. But since carotid stenosis is a symptom of widespread atherosclerosis, a bruit may indicate an increased risk for a heart attack.

Although carotid stenosis can’t be detected reliably by physical examination, it can be diagnosed with medical tests. The most widely used test, carotid ultrasound, is quick, safe, and inexpensive. Many companies offer free or very low-cost ultrasounds, and some even come to your community to make screening easy (“scan-in-a-van”). This makes screening very tempting — but before you sign up, consider that most authorities, including the American Stroke Association and the U.S. Preventive Services Task Force, recommend against carotid screening for people who don’t have symptoms of carotid disease. Instead, they suggest that people understand the symptoms of carotid disease, then report them to a doctor who will order necessary tests. This strategy is based on two observations. First, carotid stenosis often produces a TIA before it causes a stroke, giving doctors enough time to act. Second, diagnosis of asymptomatic carotid stenosis often leads to invasive treatments that have the potential to do more harm than good.

Symptomatic carotid stenosis is an altogether different matter. In this case, early diagnosis and treatment are essential. The first step is to spot warning symptoms.

Snoring and stenosis

Smoking, hypertension, high cholesterol, diabetes, lack of exercise, obesity, and stress are well-known risk factors for atherosclerosis of the carotids and other arteries. And one study raises the possibility that snoring belongs on the list of risk factors for carotid stenosis.

Australian scientists evaluated 110 volunteers; each underwent a detailed sleep study, ultrasound evaluations of carotid arteries in the neck and femoral arteries in the groin, and measurements of standard cardiovascular risk factors. None of the subjects had significant obstructive sleep apnea (OSA), which often triggers snoring and increases the risk of stroke and heart attacks.

The subjects were classified as mild, moderate, or heavy snorers. The prevalence of carotid atherosclerosis was 20% for mild, 32% for moderate, and 64% for heavy snorers. The link between snoring and carotid stenosis persisted even after the researchers took age, sex, smoking, and blood pressure into account.

There was no link between snoring and blockages in the femoral artery, suggesting that the neck vibrations that occur with snoring may contribute to carotid artery damage. Other possibilities include surges in blood levels of stress hormones such as adrenaline, high blood levels of carbon dioxide, and nighttime spikes in blood pressure. More research is needed; if nothing else, the study emphasizes the impact of bad vibrations.

Warning symptoms

Everyone should understand the importance of TIAs, which indicate vascular abnormalities that could lead to a stroke.

TIAs begin abruptly and they also resolve relatively fast. A typical TIA lasts just two to 15 minutes, and half of all patients are back to normal in less than an hour. The longer the symptoms last, the less likely they are to resolve on their own; by definition, symptoms that persist for more than 24 hours are not due to TIAs, but strokes.

TIAs caused by carotid stenosis often produce visual abnormalities. The most dramatic is amaurosis fugax, an abrupt, painless loss of vision in one eye. Often, the visual loss is complete, but some patients complain of partial loss of sight “like looking through ground glass” or “like a shade coming down before my eye.” Vision is restored to its previous state when the TIA resolves. Because visual loss usually occurs without other neurological symptoms, patients often consult an ophthalmologist rather than a neurologist or primary care physician. Amaurosis fugax suggests carotid stenosis on the same side of the body as the affected eye.

TIAs due to carotid stenosis can also affect other parts of the body, producing temporary clumsiness, weakness, or numbness and tingling. The face, hand, or leg can be affected, but symptoms are always restricted to just one side of the body. Slurred speech is very common, often occurring along with other symptoms. Some patients experience transient aphasia, a severe or complete inability to understand or use words. Aphasia indicates impaired circulation to the dominant half of the brain, usually the left. Except for vision, symptoms on one side of the body suggest carotid stenosis on the opposite side. Note, though, that many common neurological symptoms such as brief, nonspecific visual symptoms (blurring, floaters, flashing), dizziness or lightheadedness, or generalized weakness do not qualify as carotid TIA symptoms.

Although TIAs resolve within 24 hours, that doesn’t mean they aren’t serious. On the contrary, they should be taken seriously because they warn of a possible future stroke. And TIAs must be diagnosed and treated promptly because the risk of stroke is highest within the first 30 days, but urgent treatment can reduce that risk by up to 80%.

Every patient with a TIA should have a medical evaluation as soon as possible. At a minimum, this should always include both an electrocardiogram (ECG) to check for cardiac abnormalities that could be responsible for emboli and a carotid ultrasound to check for carotid stenosis. If carotid stenosis is detected, the severity of the blockage predicts the likelihood of stroke and is the key factor in deciding if artery-opening treatment is needed. But while your doctor waits for the ultrasound results, he can use a simple scoring system to estimate your risk of stroke:

According to this system, patients with a score of 0–3 have just a 1.2% risk of stroke within seven days; but risk rises progressively with scores of 4 and higher, indicating the need for prompt evaluation and treatment.

Factor

Points

Age 60 or above

1

Blood pressure 140/90 or above

1

Weakness on one side of the body

2

Impaired speech without weakness

1

Duration of TIA symptoms

10–59 minutes

1

60 minutes or longer

2

Diabetes

1

What’s causing your symptoms?

The first step is for your doctors to determine if your symptoms are actually due to a TIA. Because carotid stenosis can be detected quickly and safely, a carotid ultrasound is usually the next step. But if you don’t have a narrowed artery, your doctor will consider other conditions such as migraine or seizure disorder. In an older person, a subdural hematoma (blood clot on the outside of the brain) is a possibility; in a younger patient, multiple sclerosis could be the diagnosis. In diabetics who take insulin, hypoglycemia (low blood sugar) can mimic a TIA.

Testosterone and the carotids

The relationship between testosterone and atherosclerosis is controversial; reversing old beliefs, studies suggest that testosterone may do more good than harm, at least in normal amounts of the male hormone.

A study from Finland linked low levels of testosterone to an increased risk of carotid artery blockages. The subjects were 239 men between the ages of 40 and 70; men with low testosterone levels had thicker carotid arteries, a sign of atherosclerosis, than men with normal levels of the hormone. The link persisted even after the scientists accounted for age, cholesterol, blood pressure, obesity, and smoking.

Testing for carotid stenosis

Ultrasound is the standard way to diagnose carotid stenosis; in most centers, older techniques have been replaced by carotid duplex ultrasonography. Involving neither injections nor dye, the test is fast and completely safe. While you’re lying on your back, a technician places an ultrasound probe on the side of your neck. The probe beams sound waves at your artery, and a computer uses the waves that are reflected back to construct an image of your artery and the blood flowing through it.

Carotid ultrasonography is a good way to evaluate severe carotid stenosis, but it’s less accurate for milder blockages. Reliable results depend on good equipment, an experienced technician, and a skilled interpreter, but even with all three, patients who are being considered for surgery or angioplasty should have more detailed imaging studies.

Magnetic resonance angiography (MRA) and computed tomography angiography (CTA) can produce detailed images of carotid blockages. As you lie on a table in the scanner, a technician injects contrast material in an arm vein so the scanner can obtain information that a computer uses to construct high-quality images of the carotid. CTA involves radiation but MRA does not; both are safe and accurate.

Carotid angiography is an invasive test that requires an injection of dye into the carotid artery. X-rays are taken after the injection, producing detailed pictures of the blockage. Unfortunately, fragments of clot or plaque may be dislodged from a diseased carotid by the injection, sometimes causing a stroke. Some patients also experience kidney problems or allergic reactions caused by the dye. In experienced hands, the risk of complications is low, and angiography is the time-honored gold standard to test for carotid stenosis. In many centers, though, it has been replaced by MRAs or CTAs.

Working together

Detecting a narrowed carotid artery depends on cooperation between patient and physician. In most cases, the patient raises the alarm by reporting symptoms of a TIA, and the doctor confirms the diagnosis by ordering a carotid ultrasound test. But making the correct diagnosis is only half the job; next comes the crucial — and often controversial — problem of deciding which treatment is best.

Posted by: Dr.Health

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