The carotid arteries carry oxygen-rich blood from the heart to the front half of the brain. But these crucial arteries can become narrowed by the cholesterol-laden plaques of atherosclerosis. Blood clots, or thrombi, can form on the plaques, then break off and travel as emboli to the brain, where they lodge in small arteries, interrupting the vital flow of blood to brain cells. If the interruption is partial or brief, the brain cells recover; the patient experiences a transient ischemic attack (TIA) with no permanent damage. But if the blockage is complete, brain cells die, producing a stroke.
In many cases, a TIA warns of a future stroke, giving doctors time to perform a carotid ultrasound test to see if the artery is mildly (less than 50%), moderately (50% to 69%), or severely (70% to 99%) narrowed. Once the diagnosis of carotid stenosis (narrowing) is established, several treatment options must be considered.
Reporting warning symptoms
Patients hold the key to preventing strokes caused by carotid artery stenosis; their task is to recognize warning symptoms (see “The first decision,” below) and to report them promptly to their doctors. How well do patients perform as reporters? To find out, investigators surveyed 1,662 patients enrolled in the Asymptomatic Carotid Atherosclerosis Study. At the start of the study, each patient received extensive instruction about warning symptoms and the need for speedy reporting. Despite these educational efforts, fewer than 40% of patients who experienced symptoms reported them within three days, and fewer than 25% reported them within 24 hours. It’s a dangerous delay that can have shocking consequences.
Carotid stenosis can be treated with medication or with a procedure to open the narrowed artery. In both cases, the goal is to prevent strokes. Medical therapy does this by administering drugs that prevent clot formation and improve vascular health. Artery-opening options involve either surgery to remove the atherosclerotic plaques clogging the artery or angioplasty with stenting, which uses a tiny balloon in a catheter to open the artery and a wire mesh stent to hold it open. Patients who undergo either procedure take anticlotting medication afterward, and all patients should work to correct the risk factors responsible for their basic disease, atherosclerosis.
The first decision: Medical therapy or an artery-opening procedure
Decisions like this are always hard, but in the case of carotid stenosis, two key factors can help make the right choice: first, the presence or absence of symptoms; and second, the degree of arterial narrowing.
The symptoms of carotid artery narrowing that warn of a high risk of stroke take the form of TIAs. They begin abruptly and resolve in less than 24 hours, often clearing up within an hour or two. The most common warning symptom is temporary visual loss in one eye; it may be complete blindness (amaurosis fugax) or partial loss “like a shade before my eye.” Other typical symptoms of carotid TIAs include slurred speech or an inability to use or understand words (aphasia), and weakness, clumsiness, and numbness or tingling of the face, hand, or leg on one side of the body. Visual symptoms point to a blockage in the carotid artery on the same side of the body as the affected eye. Aphasia suggests the blockage is in the artery that carries blood to the dominant half of the brain, usually the left side. Symptoms elsewhere in the body point to the narrowing of the carotid on the opposite side of the body.
Every patient with a TIA should have an urgent medical evaluation; at a minimum, this should include an electrocardiogram (ECG) to check for an abnormal heart rhythm that could send blood clots (emboli) to the brain and a Doppler ultrasound test to check the carotid artery. The ultrasound will answer the second key question: is the artery narrowed, and if so, how much? If a significant blockage is present, most medical centers recommend a more detailed imaging study (magnetic resonance angiography or computed tomographic angiography) before moving on to an invasive, artery-opening procedure.
As a result of careful clinical trials dating back to the early 1990s, doctors can now provide clear guidelines for symptomatic patients with narrowed carotids, but the treatment of patients who do not have carotid TIA symptoms remains controversial.
Patients with carotid TIA symptoms or minor strokes should be considered for invasive therapy if they have a carotid artery that is narrowed by more than 50%. Patients with severe narrowing (70% to 99%) stand to benefit the most, but patients with moderate narrowing (50% to 69%) may also gain some protection against future strokes. Because men are at higher risk for stroke than women with a similar degree of stenosis, they are more likely to benefit from invasive therapy. But artery-opening procedures carry their own risks; patients will only benefit when the risk of severe complications (stroke, death) is 6% or less. Invasive therapy is most effective when performed soon after the onset of symptoms, ideally within two weeks.
Patients who haven’t had carotid TIA symptoms face a more difficult set of decisions, which often arise because of “routine” ultrasound screening tests. Those who have narrowing of less than 60% should be treated medically. Asymptomatic patients with more severe narrowing can be treated with medication or with an artery-opening procedure; the latter provides a small advantage, reducing the risk of stroke from about 2% a year to about 1% a year, but the benefit is lost if the risk of severe complications is above 3%. Patients over age 75 and those with serious underlying illnesses are better off with medical therapy. But if a patient on medical therapy develops carotid TIA symptoms, he should be evaluated for an artery-opening procedure.
The second decision: Surgery or stenting?
It took years of research to establish the relative merits of medical and surgical therapy, and even with all this study, uncertainties and controversies persist. Since angioplasty with stenting is a much newer way to open blocked carotids, the controversy about this option is even more intense.
Surgery for carotid stenosis is called carotid endarterectomy, which is performed under general anesthesia. The surgeon makes a small incision in the patient’s neck to expose the diseased carotid. He opens the artery, “scoops out” the plaque, and sews the artery back together, sometimes introducing a patch taken from one of the patient’s veins to make the channel wider. Carotid endarterectomy is a delicate operation that should be performed by highly experienced surgical teams. Stroke and death are among the risks of carotid endarterectomy; in the hands of a highly skilled surgeon and an experienced team, the risk of major complications is below 3%, but it can be much higher.
Carotid artery angioplasty with stenting is a relatively new technique that uses the same technology that’s been so successful in opening blocked coronary arteries. Under local anesthesia, the doctor inserts a thin tube, or catheter, into the patient’s femoral artery in his groin. Using x-rays to show the way, he then threads the catheter up to the carotid blockage in the patient’s neck (see figure). Next, he passes a wire through the catheter; when the tip of the wire is beyond the blockage, the doctor opens a tiny filter at the end of the wire to catch debris and clot fragments that might otherwise travel to the brain during the angioplasty itself. The next step is to insert a second tube that carries a tiny, collapsible wire mesh, or stent, over an inflatable balloon. When the apparatus is in place, the doctor inflates the balloon, which both expands the stent and “squashes” the plaque to open the artery. When the procedure is finished, the catheter, balloon, and filter are removed through the groin and pressure is applied to the femoral artery to prevent bleeding as the puncture closes. The stent remains in place to help keep the carotid artery open. Like endarterectomy, carotid stenting is a delicate procedure that requires a skilled and experienced medical team. In good hands, the risk of major complications, including bleeding, stroke, and death, is below 3%.
Carotid artery angioplasty with stenting
A. Using x-rays to show the way, the doctor threads a guidewire and filter up to the carotid blockage. B. The filter is opened and a catheter is passed to the blockage. C. A tiny balloon in the catheter is inflated to “squash” the blockage and open the stent. D. Finally, the catheter, balloon, and filter are removed, leaving the stent in place to hold the artery open.
When researchers evaluate the relative merits of the two ways to open a blocked carotid artery, they must remember that rapidly developing technical improvements make comparison a moving target. Carotid endarterectomy has been in use since the 1950s and is still the gold standard. But stenting has improved substantially since it was first employed in the 1990s, and its much shorter recovery time has obvious appeal.
As things now stand, which procedure is best? It’s a simple and important question, but the answer is long and complex, in part because both techniques are effective and both are improving. A 2011 meta-analysis of 13 randomized clinical trials involving 7,477 patients may offer the best summary of the available evidence. In the days and weeks following the procedure, surgery has the edge. Carotid endarterectomy produces fewer serious complications, including stroke and death, than stenting, though stenting is followed by fewer mild complications such as nonfatal heart attacks and damage to certain nerves. In the long run, over months and years, the differences narrow, but surgery still appears more successful.
Does this mean endarterectomy is the best choice for every patient? Not necessarily. In fact, individualized decisions are best, and four factors come into play:
The first is the age and general health of the patient. In general, surgery is preferable for people 70 and above, while patients with medical problems that boost the risks of surgery may do better with stenting.
The second factor is the nature of the carotid blockage. Carotid plaques that extend far up the artery toward the brain may be more suitable for stenting, while plaques that are ulcerated on the surface or laden with clots might be best treated with surgery.
A third factor is the skill and experience of the team that will be performing the procedure; national statistics from clinical trials may not apply to the real-world results in your hospital.
Finally, each patient’s preference should be considered; some will favor the faster recovery associated with stenting, while others may opt for the greater safety of surgery.
Before a doctor recommends surgery or stenting, he should remember that medical therapy is another effective treatment that has also improved substantially. Medical treatment is preferred for symptomatic patients with mild narrowing and also for many asymptomatic patients with moderate or even severe narrowing. And even patients who undergo artery-opening procedures need long-term medical therapy.
Medical therapy is necessary to help prevent dangerous clots from forming in the carotid artery and to fight atherosclerosis, the process that blocks arteries in the first place.
The key drug for preventing clots is aspirin; it inhibits platelets, the tiny blood cells that trigger the clotting process. Because platelets are so sensitive to aspirin, small doses will do this big job. Most doctors recommend 81 to 325 milligrams (mg) of aspirin a day, starting as soon as the carotid blockage is diagnosed. Clopidogrel (Plavix) and prasugrel (Effient) are newer antiplatelet drugs that may be prescribed for patients who cannot take aspirin. A less powerful antiplatelet drug, dipyridamole, can also be administered with aspirin in a single tablet (Aggrenox) for enhanced protection.
Another essential aspect of medical therapy is blood pressure control — but while aspirin should be started as soon as possible, elevated blood pressures should be lowered gently and gradually. Angiotensin-converting–enzyme (ACE) inhibitors, angiotensin-receptor blockers (ARBs), and thiazide diuretics are particularly desirable antihypertensive medications in these circumstances. A long-term goal of maintaining blood pressure below 130/80 millimeters of mercury is probably best.
Nearly every patient with carotid stenosis should receive a statin drug, with a goal of reducing LDL (“bad”) cholesterol to 100 milligrams per deciliter (mg/dL) or less; 70 mg/dL or less may be even better. In addition to lowering LDL cholesterol, statins help by stabilizing carotid artery plaques; they even improve the outcome of patients who have had carotid endarterectomy operations.
Lifestyle modification is also vital both to prevent further damage to the diseased carotid arteries and to protect against atherosclerosis in other arteries. Patients must eliminate all tobacco products, including exposure to secondhand smoke. Regular exercise reduces the risk of carotid stenosis and slows the progression of atherosclerosis. Walking for 30 to 40 minutes a day is a fine place to start. Because patients with carotid stenosis are at risk for coronary artery disease, they should get their doctor’s okay before attempting intense exercise. People with diabetes should aim for good blood sugar control. Last but not least, all overweight patients should work toward girth control; a study reported that weight loss can actually help reverse carotid artery narrowing over a two-year period.
A good diet can help. That means reducing saturated and trans fats by cutting down sharply on whole-fat dairy products, red meat, fried foods, and products made with trans fat. Because salt raises blood pressure, it is important to restrict sodium, ideally to less than 1,500 mg a day. Eat lots of fish, fruits, vegetables, and whole grains. Cut back on portion size and calories if you need to lose weight, but don’t swear off all liquid calories if you enjoy alcohol and can drink responsibly. In fact, low-dose alcohol has been linked to a reduced risk of carotid stenosis, but large amounts have an adverse effect on the crucial artery. That makes one to two drinks a day ideal for vascular health in men, counting 5 ounces of wine, 12 ounces of beer, or 1 ounces of spirits as one drink.
Comprehensive medical and lifestyle therapy is effective; it slows the progression of carotid atherosclerosis, lowers the risk of stroke, and reduces the need for artery-opening procedures.
Stress and the carotid artery
A person’s susceptibility to disease depends on many things, from genetics to health habits, environmental exposures, and even luck. Psychological factors, too, play a role in many illnesses, with heart disease topping the list. Although the link between stress and the heart is well established, the coronary arteries are not easily accessible for direct study. But ultrasound can accurately measure carotid artery thickness and plaques. Can the carotid artery provide information about stress and atherosclerosis?
A series of reports says it can. A Canadian study evaluated 351 adults for atherosclerosis risk factors such as smoking, hypertension, high cholesterol, diabetes, and obesity. Each person was also given the Stroop Color–Word Interference Test, a computerized system for producing frustration and stress during mental tasks. Subjects were monitored during the test to determine whether or not they responded to frustration with stress. Each person also underwent a carotid artery Doppler ultrasound test. Even after taking other risk factors into account, high-stress individuals were more likely to have carotid artery atherosclerosis than low-stress people. And when 136 of the subjects were restudied after two years, high stress was associated with the progression of carotid artery disease.
A joint European–American investigation looked at the question another way. It measured job stress, cardiovascular risk factors, and carotid artery thickness and plaques in 591 men ages 42 to 60. The carotid artery ultrasounds were repeated after four years to evaluate disease progression. When the findings were analyzed, stress was linked to progression of carotid artery disease, even after accounting for the impact of other risk factors.
Similar results were reported by a Finnish study of 901 men between the ages of 42 and 60. Each man underwent a battery of tests to evaluate his blood pressure’s response to mental stress, and each had a carotid ultrasound. The results suggest that stress can take a toll on the carotid arteries: the men whose blood pressures shot up the highest in response to mental stress were the most likely to have abnormally thickened carotid arteries.
Psychological factors appear to affect the carotid arteries of women, too. A study of 209 healthy middle-aged women found that pessimists were more likely to have progressive thickening of their carotids than optimists. Finally, researchers from the Netherlands and Germany linked high levels of the stress hormone cortisol to carotid artery atherosclerosis.
Past, present, and future
Carotid artery blockages pose a substantial risk of stroke. Decades ago, doctors discovered that low-dose aspirin can inhibit platelets, prevent clot formation, and reduce that risk. Surgeons have improved carotid endarterectomy, the operation that removes carotid blockages. The operation should be strongly considered for patients with carotid TIA symptoms and severe (70% to 99%) narrowing, and it may help selected symptomatic patients with 50% to 69% narrowing and some symptom-free individuals with 60% to 99% narrowing. More recently, carotid artery angioplasty with stenting has emerged as another less invasive way to open blocked carotids, particularly for certain patients with serious medical conditions.
More progress is sure to follow. But the best outcome for all requires a return to the basics. Medications can control blood pressure, cholesterol, and diabetes, and a good diet, regular exercise, and eliminating tobacco exposure can control these risk factors and improve vascular health. A drink or two may also help. All in all, it’s a time-honored package of prevention for protecting all arteries — and that’s something we can all toast.