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Diagnosis and treatment of carotid artery disease.

After completing this article, the reader should be able to:

* Define carotid artery disease (CAD) and list its signs and symptoms.

* Identify the risk factors for CAD.

* Differentiate between controllable and uncontrollable risk factors and explain how controllable risks can be reduced or eliminated.

* Describe the anatomy of the carotid arteries and blood flow within them.

* Describe several common abnormalities involving the carotid arteries.

* Compare and contrast imaging techniques used to diagnose CAD.

* Explain established treatments for CAD.

* List the medical specialists who evaluate and treat CAD.

* Discuss some new or controversial stroke treatments.

Carotid artery disease (CAD) is 1 reason why millions of people are watching their cholesterol levels today. It is also why they are exercising more, choosing to eat fish and chicken instead of beef, and why some have decided to quit smoking. But millions of others aren't changing their lifestyle, even though they are well informed about health issues. Physicians counsel patients about what could damage their health, but if people can't see immediate proof of the damage, they sometimes ignore the advice. Patients often think that what they can't see won't hurt them, but that isn't the case with CAD. The damage isn't apparent until it is too late.

What Is Carotid Artery Disease?

CAD narrows or blocks the blood flow in the arteries in the neck. This blockage prevents the arteries, known as the carotids, from supplying blood flow to the face and brain. (1) CAD is similar to coronary artery disease, which blocks blood flow in the arteries of the heart. Narrowing or blockage of the carotids, also known as stenosis, can cause symptoms, a stroke or even death. Stenosis is a result of plaque buildup on the lining of the arteries. Plaque is made up of cholesterol, calcium and fibrous tissue. (1) When the plaque gets thick enough, it clogs or partially blocks the arteries. If severe, the plaque can totally obstruct an artery. Plaque also makes the walls of the arteries stiff and rigid, a condition known as atherosclerosis or "hardening of the arteries." (1)

CAD can start to develop in a person's 20s or 30s, but it is more likely to develop at older ages. One percent of adults aged 50 to 59 years have significantly narrowed carotid arteries, whereas 10% of adults aged 80 to 89 years have this problem. (1) How fast CAD progresses depends on the individual's risk factors and behaviors.

Plaque is not the only reason for a partially blocked or obstructed carotid artery. Thrombus, also known as a blood clot, can block an artery enough to slow or stop blood flow to the brain) When an artery is blocked by plaque or a thrombus, it can cause a stroke. Stroke is the leading cause of adult disability in the United States, (2,3) and the third-leading cause of death after heart disease and cancer in the United States, Canada and Japan. (2) One in 5 people is affected by stroke. Approximately 700 000 strokes occur each year in the United States, with 150 000 deaths resulting from them. (2)

Risk Factors for Carotid Artery Disease

The risk factors for CAD are similar to those for coronary artery disease. Some can be controlled and others can't. Uncontrollable risk factors include age, sex, race and genetics. There is a greater risk for men than for women before the age of 75 years. After age 75, women have a higher risk of CAD. (4) Race or ethnicity plays a role in CAD, too; black, Hispanic and Asian patients have a higher risk of CAD than whites. (5) Genetics are involved; people with a family history of CAD or coronary artery disease are at higher risk.

Controllable risk factors include hypertension, diabetes, high cholesterol, obesity and sedentary lifestyle, alcohol consumption, smoking and air pollution. Each of these is discussed below.

Hypertension

It is estimated that I in every 4 American adults has high blood pressure. A blood pressure level of 140/90 mmHg or higher is considered high. (6) Normal blood pressure is 120/80 mmHg. (7) Hypertension can speed up atherosclerosis if it is not controlled. (7) The constant force or hard pounding of blood against the artery wall damages the vessel and makes the heart work harder. Hypertension also can cause heart failure, kidney disease and blindness if not managed. (6) Changes in vision can be caused by hypertension if the arteries around and in the eyes are narrowed or blocked by atherosclerosis. High blood pressure also can cause a blood vessel to burst or bleed in the eye, again causing loss of vision. Renal failure can result when high blood pressure narrows the blood vessels leading to and in the kidneys.

Diabetes

Diabetes, a chronic incurable disease, occurs when the pancreas does not produce enough insulin to regulate glucose levels. A person's glucose level is checked by monitoring the blood and urine. If the glucose level is high, the patient is given insulin injections (for insulin-dependent patients) or oral medication (for noninsulin-dependent patients) to bring the glucose under control. One of the long-term effects of uncontrolled diabetes is damage to blood vessels from atherosclerosis. A patient with diabetes is at a greater risk for stroke, heart attack and gangrene of the feet, as well as problems with the eyes, kidneys and nerves when blood vessels are damaged. (8)

High Cholesterol

Cholesterol, like other fats found in the blood, protects nerves, makes cell tissues and produces certain hormones. Cholesterol is synthesized in the liver, but humans also acquire cholesterol through certain foods, such as egg yolks, meat, various oils, cheese and other dairy products. (9) There are 2 types of cholesterol: low density lipoprotein (LDL) and high density lipoprotein (HDL). Considered the "bad" lipoprotein, LDL delivers cholesterol to the body but any excess builds up on the walls of the arteries, which can lead to atherosclerosis. LDL makes up most of the cholesterol circulating in the blood, about 60% to 75%, and therefore is the majority of the total cholesterol measurement. HDL is considered the "good" lipoprotein. If HDL levels are high enough, it prevents harmful buildup of cholesterol in the arteries. HDL removes excess cholesterol from the cells and the walls of the arteries and disposes of it in the liver. HDL can slow or even reverse the development of atherosclerosis. (10) Unfortunately, HDL only makes up about 20% to 30% of the cholesterol in the blood.

Everyone should know their cholesterol levels to monitor themselves and their diet. The National Cholesterol Program published the following guidelines in 1988, and they still are used today for evaluating total cholesterol measurements:

* Normal total cholesterol is less than 200 mg/100 mL.

* Borderline cholesterol is 200 to 239 mg/100 mL. Dietary changes are advised for those whose value is in this range.

* Abnormal total cholesterol is 240 mg/100 mL or higher. Drug therapy might be recommended if a patient's measurement remains above 240 mg/100 mL in spite of diet modification. (7)

Other blood fats physicians monitor are triglycerides. Triglycerides combine with cholesterol and proteins to make lipoproteins. (10) Like cholesterol, triglycerides are produced in the liver and are absorbed from food. The body uses triglycerides for quick energy. However, any extra calories, whether from fats, carbohydrates or proteins, are stored in fat cells. People who routinely overeat and don't burn off excess calories can have high triglyceride levels. According to the American Heart Association, a normal triglyceride level is less than 150 mg/dL. Borderline-high is 150 to 199 mg/dL and high is 200 to 499 mg/dL. Very high is 500 mg/dL or higher. (11)

Obesity and Sedentary Lifestyle

Obesity is considered a risk factor if a person also has a high blood cholesterol level. Obesity can be associated with other risk factors, such as high blood pressure and diabetes. Most overweight people have low HDL cholesterol, which can increase the risk of CAD. Regular exercise can decrease heart rate, lower blood pressure, control weight and decrease the level of fats in the blood, all of which in turn decrease the risk of CAD. (7)

Alcohol Consumption

Alcohol can contribute to high blood pressure, which can speed up atherosclerosis. Even a moderate amount of alcohol daily might increase the possibility of CAD and heart disease. (7) Moderate intake is defined as 1 to 2 drinks per day for men and 1 drink per day for women. A drink is defined as 1 oz of 100 proof spirits, 1.5 oz of 80 proof spirits, 4 oz of wine or 12 oz of beer. (12) Heavy drinking can lead to high blood pressure, malfunction of the heart muscle and ultimately heart failure. (7) However, if the problem has not advanced to the point of heart failure, cessation of alcohol consumption might halt progression of the disease. (7)

Smoking

Smokers are at particular risk for atherosclerosis. The chemicals in cigarettes irritate the inner lining of the arteries, which causes inflammation of the artery walls. Smoking also increases the platelets' tendency to clot, which allows cholesterol to accumulate on the artery walls. Furthermore, smoking causes the adrenal glands to secrete a hormone that temporarily increases blood pressure and makes the heart work harder. As a result, the heart speeds up and blood pressure rises. (7)

Air Pollution

Air pollution is a risk factor that is controllable to a certain extent. The American Heart Association has stated that exposure to air pollution contributes to the development of cardiovascular disease, including heart disease and stroke. Air pollution includes many environmental agents, such as carbon monoxide, nitrates, sulfur dioxide, ozone, lead, secondhand tobacco smoke and particulate matter. Particulate matter, also known as particle pollution, is generated from vehicle emissions, tire fragmentation and road dust, power generation and industrial combustion, smelting and other metal processing, construction and demolition activities, residential wood burning, windblown soil, pollens, molds, forest fires, volcanic emissions and sea spray. (13)

Secondhand smoke is the single largest contributor to indoor air pollution. Studies of secondhand smoke indicate that air pollution in general can affect the heart and circulatory system. Previous research has established that exposure to the secondhand smoke of just 1 cigarette per day accelerates the progression of atherosclerosis. (13)

Normal Carotid Anatomy and Blood Flow

The walls of the carotid arteries have 3 layers. (See Fig. 1.) The innermost layer is called the tunica intima. It is a smooth, single-cell-thick layer made up of endothelial tissue that covers a base membrane and connective tissue and provides a slick lining for the artery. The middle layer is a fairly thick layer called the tunica media. The tunica media consists of smooth muscle tissue, elastic tissue and white fibrous tissue. It maintains blood pressure and flow by expanding and contracting its muscle layer. It also strengthens the artery so that the artery can withstand the pumping action of the heart. Plaque develops between the intimal and medial layers. The outermost layer is called the tunica adventitia, or externa. The tunica adventitia is made up of strong white fibrous tissue that helps the vessel retain its shape and keeps it from collapsing. (14)

[FIGURE 1 OMITTED]

Most individuals have a right and left common carotid artery (CCA). (See Fig. 2.) These arteries have different origins, but after the origin they take the same course up the neck to the carotid bulb. The right common carotid artery originates from the innominate or brachiocephalic artery, which is the first artery branching from the aortic arch. The left common carotid artery starts directly at the aortic arch and is the second branch off the arch in most patients. These arteries travel in a fairly straight line up the neck along each side of the trachea and then bifurcate into their terminal branches at about the level of the thyroid cartilage. There is an area just before the bifurcation where the common carotid arteries get larger. This area is called the carotid bulb. It is a common site for plaque to form. After the bulb, the CCA terminates as it divides into 2 branches, the internal and external carotid arteries. The internal carotid artery (ICA) supplies blood to the brain, and the external carotid artery (ECA) supplies blood to the face, scalp and skin. (15) (See Fig. 3.)

[FIGURES 2-3 OMITTED]

The external carotid artery has approximately 8 major branches, which then branch into many smaller arteries. The first branch off the ECA from the bulb is the superior thyroid artery. It is followed by the ascending pharyngeal, lingual, occipital, facial and internal maxillary branches. After the internal maxillary artery branches off the ECA, the ECA becomes known as the superficial temporal artery. The superficial temporal artery terminates in the capillaries of the forehead. (15)

The internal carotid artery has no branches until it enters the skull. The first branch off the ICA is the ophthalmic artery. The ophthalmic artery supplies blood to the eyes and in turn branches off into the supraorbital artery, frontal artery and the nasal artery. After the ICA's second branch, the anterior cerebral artery, it is called the middle cerebral artery. The right- and leftsided arteries then are connected by the anterior communicating artery, which forms the anterior half of the circle of Willis, the system of arteries that nourishes and oxygenates the brain. (15)

The posterior half of the circle of Willis starts inside the cranium with the right and left vertebral arteries coming off of the right and left subclavian arteries, respectively. Then the vertebral arteries join to form the basilar artery, which divides into the right and left posterior cerebral arteries. Finally, the posterior cerebral arteries join the right and left posterior communicating arteries that connect to the internal carotid arteries, all forming the posterior circle of Willis. (15)

Abnormal Carotid Anatomy and Blood Flow

Plaque

Specific terms are used to characterize the location of plaque within the artery. For example, circumferential means the plaque is around the entire circumference of the artery, not just along a single side. Scattered or diffuse means the plaque occurs at multiple spots along the vessel. Extensive means the plaque is distributed along quite a bit of the artery's length. Focal means the plaque is specific to 1 area. (16)

There are also terms to describe the surface of the plaque. For example, a smooth surface on plaque develops when smooth muscle cells grow from the medial layer into the intima and deposit fat in the intima. The intimal layer that lies over the plaque is intact. (See Fig. 4.) An irregular surface is present when the surface of the plaque breaks open, fractures or ruptures as the plaque grows or expands. (See Fig. 5.) The hemorrhage from this rupture can form fibrosis or calcification, which causes surface irregularity as it heals. An ulcerative surface is similar to an irregular surface. Ulceration is a gap within the plaque that extends into the collagen of the artery wall, causing platelet aggregates to embolize. Irregularities and ulcerations on the surface of plaque are important because they are thought to cause emboli that produce transient ischemic symptoms and cerebral infarction. (17,18)

[FIGURES 4-5 OMITTED]

Plaque also can be characterized by grading carotid stenosis. For example, intimal thickening or fatty streaking is a minimal amount of plaque on the artery wall. The plaque is considered mild if the artery is less than 20% stenosed by diameter. As the arteries become more narrow, the category changes:

* Moderate--20% to 50% stenosed.

* Moderately severe--50% to 80% stenosed.

* Severe--more than 80% stenosed.

* Complete stenosis--total occlusion. (19)

In addition to plaque, carotid lesions also can be caused by arteritis, carotid dissection, fibromuscular dysplasia, radiation and vasospasm. All of these result in thickening or irregularities in the lining of the vessels and can block blood flow.

Alternative Routes

When an artery is obstructed by plaque or a clot, it can develop a different route to deliver the blood to its appropriate destination. A new vascular route is called collateral circulation, and it is formed by an anastomosis, or joining of vessels. For example, if the internal carotid artery were blocked, the external carotid artery on the same side could provide a new route for blood flow through the supraorbital or frontal artery. Shunts are a natural connection from 1 side of the brain to the other or from the front of the brain to the back and vice versa. For example, collateral circulation can be accomplished by alternate flow through the circle of Willis. The body compensates by creating these alternate pathways naturally. (15)

Aneurysms

Another type of abnormal anatomy is a carotid aneurysm. An aneurysm is an outpouching or ballooning of a weak area in the artery wall. It usually develops where vessels divide or branch off and is caused by constant blood pressure. The presence of 1 aneurysm is associated with a 15% to 20% chance of having at least 1 additional aneurysm. Smaller aneurysms usually have no symptoms. As an aneurysm enlarges, however, it can produce headaches or localized pain. If an aneurysm becomes very large, it can produce pressure on the brain tissue or adjacent nerves. This pressure can cause difficulty with vision, numbness or weakness in an arm or leg, impaired memory or speech, or seizures. (20) As the aneurysm enlarges over time, the wall grows weaker and rupture becomes a possibility. Atherosclerosis is the most common cause of aneurysms in the United States. However, carotid artery aneurysms are very rare. They usually occur after trauma or develop in elderly people who have atherosclerosis.

Arteriovenous Malformation (AVM)

An AVM is an abnormal connection of blood vessels that can occur anywhere in the vascular system. When an AVM develops in the brain, a cluster of blood vessels bypasses the brain tissue and directly diverts blood from the arteries to the veins. An AVM consists of weakened blood vessels that dilate over time and can eventually burst from the high pressure of blood flow through the arteries, causing bleeding into the brain. AVMs occur in less than 1% of the general population and are more common in men than women. (21)

Stroke

Stroke can result from blockage of the carotid arteries that disrupts blood flow to the brain. There are 2 major types of stroke: ischemic and hemorrhagic. Ischemic stroke is the more common type, accounting for 88% of strokes. It occurs when a blood clot blocks an artery that supplies blood and oxygen to the brain. Hemorrhagic strokes account for the remaining 12% of strokes. A hemorrhagic stroke takes place when very high blood pressure causes a weakened blood vessel to rupture and bleed into the brain. (5) High blood pressure is the most important risk factor for stroke. (5,17)

It is believed that the carotid circulation is involved in 80% of ischemic strokes. In these cases, an atherosclerotic plaque in a carotid artery blocks blood flow to the brain. The other 20% of ischemic strokes are thought to be related to emboli from the heart. In these cases, a blood clot that forms in the heart, such as those caused by atrial fibrillation, travels to the brain and blocks blood flow. In half of strokes and transient ischemic attacks (TIAs), the lesion in the internal carotid artery has caused less than a 50% narrowing of the lumen diameter. A blood clot that travels into the brain is called a cerebral embolus, whereas a clot that builds up inside the brain and blocks off a blood vessel is called a cerebral thrombus. (5)

The risk of stroke increases with each of the following factors: age, hypertension, diabetes, smoking, atrial fibrillation, obesity, hyperlipidemia and elevated homocysteine levels. (3) Homocysteine is an amino acid in the blood that is correlated with a higher risk of heart disease, stroke and peripheral vascular disease.

According to the American Stroke Association, about 24% of strokes are fatal, 50% to 70% of survivors will have only a mild disability or will improve, and 15% to 30% who survive will be permanently disabled. Institutional care is required by 20% of survivors 3 months following a stroke. (5)

A cerebrovascular accident (CVA), or stroke, occurs when the signs and symptoms of a stroke last more than 24 hours, causing a temporary or permanent loss of blood and oxygen to the brain. There are 3 types of CVA. The first type is an acute CVA, in which the symptoms come on suddenly and the patient is unstable. The second type is stroke in evolution, in which the symptoms come and go, but the patient is still considered unstable. The last type of CVA is a completed stroke, in which there is no progression or resolution of the symptoms and the patient is considered stable. A TIA or "mini-stroke" is a temporary blockage of blood vessels to the brain or eye lasting from just a few seconds to several hours. A reversible ischemic neurologic deficit (RIND) usually lasts longer than a TIA (at least 24 hours) but the patient completely recovers from any symptoms. (21)

Symptoms of a stroke include:

* Numbness, weakness or paralysis of the face, arm or leg, especially on I side of the body.

* Confusion, slurred speech, trouble talking or understanding spoken or written words.

* Blurred vision or loss of vision in 1 or both eyes.

* Trouble walking, dizziness, loss of balance or coordination.

* Severe headache.

* Trouble swallowing.

* Memory loss.

* Loss of consciousness.

* Drooping on 1 side of the mouth or face. (2,5,22)

Clinical signs or predictors of stroke include:

* Carotid bruit. This is a sound created by turbulent blood flow in a carotid artery. A patient with an asymptomatic bruit has a stroke risk of 1.5% in 1 year and 7.5% in 5 years. About 4% of adults have asymptomatic neck bruits. To listen for a bruit, the physician places a stethoscope over the carotid arteries to hear a rushing sound. Unfortunately, severe levels of disease do not always produce the rushing sound, and some blockages with a low risk can make the same sound. Therefore, a neck bruit is a poor indicator of extracranial CAD or high-grade stenosis.

* Polycythemia, or excess red blood cells.

* Increased fibrinogen level. Fibrinogen is a protein present in the blood that is essential for clotting.

* High plasma homocysteine level.

* Microalbuminuria or serum protein in the urine.

* Oral contraceptive use. (23)

Cerebrovascular Signs and Symptoms Correlated To Carotid Anatomy

Some signs and symptoms tend to be associated with a specific vessel or circulation. If a problem occurs in the:

* Internal carotid artery, the symptoms are contralateral weakness, paralysis, numbness, ipsilateral amaurosis fugax (temporary loss of vision in 1 eye due to insufficient blood flow to the eye), bruit, aphasia in the dominant hemisphere and occasionally altered level of consciousness.

* Middle cerebral artery, the symptoms are difficulty with speech, numbness of face and arms, behavioral changes, confusion and agitation.

* Anterior cerebral artery, the symptoms are contralateral hemiparesis (especially in the leg), incontinence, loss of coordination and impaired motor and sensory functions.

* Vertebrobasilar circulation, the symptoms are numbness around the lips and mouth, diplopia (double vision), poor coordination, dysphagia, vertigo, amnesia and ataxia (muscle incoordination, lack of gait control).

* Posterior cerebral artery, the symptoms are dyslexia and coma.

* Posterior circulation, the symptoms are vertigo, ataxia, visual blurring bilaterally, double vision, bilateral tingling of the skin or loss of sensation, and drop attack (falling to the ground without other symptoms or loss of consciousness). (24)

Carotid Imaging

Many different tests can be performed to diagnose plaque in the carotid arteries. Accurately determining the degree of carotid artery stenosis is important because this helps determine whether surgery or other interventions are needed.

Ultrasound

Ultrasound images can demonstrate both the carotid arteries and blood flow in the vessels. A painless and noninvasive imaging modality, ultrasound uses high-frequency sound waves to show plaque in the carotid arteries. Audible sounds are in the frequency range of 20 Hz to 18 kHz. Because ultrasound uses frequencies higher than 18 kHz, the sound waves are not audible. (25)

The patient lies on his or her back for the examination, and a water-soluble gel or lotion is applied to the neck. This gel prevents air from getting between the transducer and the patient's skin and deflecting the sound waves. As the sonographer glides the transducer over the patient's neck, it sends sound waves through the neck tissues and then receives the sound waves that are reflected off the tissues. These reflected echoes create an image on the screen. A disadvantage of ultrasound is that sometimes the sonographer cannot tell if an artery is totally occluded or if there is a trickle of blood flowing through the vessel. Also, if calcification is present in the vessel, the sonographer cannot see behind the calcification or through it.

Ultrasound uses unique terminology to describe plaque. Plaque that appears to be the same texture throughout is described as homogeneous. This type of plaque is usually a fibrofatty lesion without hemorrhage and is associated with a low incidence of stroke. Its appearance is typically smooth. Heterogeneous plaque is made up of multiple textures and has an irregular appearance. These lesions can be part soft plaque, part hemorrhage and part calcification and are associated with a higher incidence of neurologic deficits. Calcifications can be identified in either homogeneous or heterogeneous plaques, but alone they are considered benign. (18)

Ultrasound uses 3 types of display modes to evaluate the carotid arteries: grayscale, Doppler and duplex. The first 2 modes provide information to diagnose the carotid anatomy and blood flow; duplex ultrasound is a combination of the first 2 modes.

Grayscale ultrasound creates a 2-D view of carotid artery anatomy. The technique uses shades from black to white to display different densities of tissues. The more dense or white the tissue is, the brighter the echo. Anatomy that is not very dense lacks echoes and is called sonolucent. Because blood in a vessel is not very dense, it appears black or sonolucent on the screen. Artery walls are denser than the blood so they appear as a gray color. Very dense tissue is echogenic, or produces a lot of echoes, and displays as white on the screen. Calcifications in vessels appear white and have an echogenic texture.

There are several types of Doppler ultrasound in use. The standard types used to evaluate the carotid arteries are duplex and color Doppler. It is important to first explain Doppler. Doppler ultrasound displays blood flow in a wave form on the screen. From this waveform, the sonographer can detect blood flow and its speed, direction and the amount of turbulence in it. All of these characteristics help determine if plaque is present and how much of the carotid artery is narrowed or obstructed. The technique uses the Doppler effect, or Doppler shift, a physical principle proposed by Christian Doppler in 1889. First used clinically in the 1960s, the Doppler shift is the difference between the frequency transmitted by the transducer and the frequency received by the transducer after being reflected by the red blood cells. A positive shift, depicted as a waveform above the line, occurs when the received frequency exceeds the transmitted frequency. This means the blood is moving toward the transducer. A negative shift, depicted as a waveform below the line, occurs when the received frequency is less than the transmitted frequency. This means the blood is moving away from the transducer. (26)

The amplitude of the waveform represents the velocity of blood traveling through the artery. Velocity is only I criterion Doppler uses to determine whether plaque is present and how much narrowing has occurred in the vessel. A normal internal carotid artery has a peak systolic velocity less than 125 cm/sec. When a plaque covers more than 50% of the artery lumen, it causes a significant change in the blood flow velocity. The peak systolic velocity in an abnormal carotid artery is 125 cm/sec or higher.

Duplex ultrasound combines the anatomic information from grayscale and the physiological information from Doppler on the screen at the same time. If there is plaque, the sonographer usually can see whether the vessel is totally or partially obstructed. (1,4)

Color Doppler ultrasound converts the Doppler waveform into colors that are overlaid on the grayscale image of the blood vessel to show the direction and speed of the blood flow through that vessel.

Radiography

When calcified plaque is present in the carotid arteries, it shows up on cervical radiographs as calcification lateral to either side of the vertebrae. The amount of information that can be obtained from radiographs alone is extremely limited. Radiographs can reveal calcified plaque, but they cannot show if the plaque obstructs the vessel or if there is any soft plaque present. However, radiographs can show if any bone spurs (ie, growths on the cervical vertebrae) are compressing the carotid vessels. They also show arthritis or misalignment of the spine, which could affect the carotid and vertebral arteries. When a significant amount of calcified plaque is seen on the radiograph, physicians usually order additional tests.

Carotid Angiography

Carotid angiography is the most accurate test for examining the entire carotid artery. If CAD is suspected, an arteriogram might be performed before treatment or surgery. Angiography is an invasive imaging procedure in which a catheter is inserted into an artery in either the groin or arm and guided into the carotid artery using fluoroscopy. Contrast then is injected through the catheter. The contrast helps demonstrate the blood flow through the carotids and show any narrowing or abnormality. (See Fig. 2.) Angiography carries some risks, including a small incidence of stroke, which is a reason that physicians do not always use it as the first test to diagnose or evaluate treatment for CAD. Digital subtraction angiography is a special technique to eliminate bone and other confusing shadows from the image so the contrast in the vessels is even more visible. (26)

Magnetic Resonance Imaging

Magnetic resonance (MR) imaging does not use ionizing radiation, but instead uses magnetism and radio waves to produce images. MR is based on the magnetic properties of the nucleus of atoms. Radio waves are directed to a specific part of the body, which causes the nuclei of atoms to give off energy. The pattern of energy is detected, and a computer translates the magnetic energy into an image for the radiologist to read.

MR imaging is excellent for diagnosing soft-tissue abnormalities. All symptomatic patients should have a scan of the head to check for other intracranial lesions and to identify old and new cerebral infarcts. MR imaging also can be used to evaluate how much damage has already occurred to the brain tissue and function. On cross-sectional MR images, the carotid arteries appear as black holes, or void of flow. On a frontal scan, the arteries appear as black tubes. The test is painless and takes approximately 20 to 30 minutes to complete. (5)

Magnetic Resonance Angiography

MR angiography (MRA) is a new imaging technique that avoids most of the risks associated with angiography. Like other types of MR imaging, MRA uses radio waves and harmless but powerful magnetic fields to create detailed images. Some forms of this test can show blood flow and might help evaluate CAD. An injection of gadolinium can improve the test's accuracy by making the arteries more visible. (1,2)

Computed Tomography Angiography

Computed tomography angiography (CTA) uses radiation to create cross-sectional images of the brain and neck. It is performed by injecting a contrast agent through a vein in the arm. When the contrast is concentrated in the vessels, multiple sections of anatomy are imaged. The computer receives this data and reconstructs it into frontal or lateral views. The contrast makes the blood vessels in the brain and neck visible and helps identify areas of narrowing or blockage. (1,4)

Preventing and Treating CAD

The goal of CAD treatment is to restore adequate blood flow in the blocked artery and to stabilize the fatty plaque, preventing it from coming loose and causing an embolus that could lead to a stroke. In addition to receiving treatment for atherosclerosis, it is also important for patients to prevent, limit or eliminate risk factors as much as possible.

Prevention

The best way to prevent stroke is to control or manage its risk factors. For some patients, this requires very difficult lifestyle changes. The National Stroke Association recommends these measures:

* Stop smoking.

* Control high blood pressure. If using less salt in food doesn't help, medication may be prescribed.

* Avoid a sedentary lifestyle. Exercise 30 minutes per day.

* Control cholesterol and triglycerides. Eat foods low in saturated fats and cholesterol. Medication may be necessary to reach a lipid goal of LDL less than 100 and HDL greater than 45.

* Reduce blood sugar levels and control diabetes. Fasting blood sugar levels should be below 100 mg/dL. If blood sugar levels are not controlled by diet, oral hypoglycemics (drugs to lower blood sugar) or insulin is needed.

* Avoid excess alcohol. Experts say that moderate alcohol intake is an average of 1 or 2 drinks per day for men and 1 drink per day for women. (12,27,28)

* Maintain a healthy weight. The more overweight a person is, the higher the risk for stroke. Women should maintain a waist measurement of 35 inches or less and men should maintain a waist measurement of 40 inches or less. (28) A person who has a body mass index (BMI) of 25 or greater is considered overweight, and a person with a BMI of 30 or greater is considered obese. It is important to maintain a BMI of less than 25. (29)

* Control cardiac arrhythmias such as atrial fibrillation (a fast, irregular heartbeat), which can increase the risk of clotting and lead to a stroke. Arrhythmias can be treated with medication.

Medical Therapy

Acute treatment is administered within 24 hours of stroke onset and can include the use of thrombolytics, antiplatelet agents, anticoagulants, antihypertensives and neuroprotectants.

Blood-thinning medications, called anticoagulants, are used in patients with CAD to decrease the risk of blood clots and thereby prevent strokes. Aspirin is the most well-known anticoagulant. If warfarin (Coumadin) is prescribed, blood work should be checked regularly to make sure the dosage is correct. In most cases, patients will be on these medications for the rest of their lives. (3)

Antiplatelet medications are similar to anticoagulants. They inhibit the synthesis of platelets, thus preventing blood from coagulating or forming clots. Aspirin, ticlopidine hydrochloride and clopidogrel bisulfate are types of antiplatelet drugs. (3)

Tissue plasminogen activator (tPA) is a thrombolytic, or clot-dissolving drug, approved by the U.S. Food and Drug Administration to treat ischemic strokes. This drug must be used within the first 3 hours of stroke symptom onset for a chance of complete or a near-complete recovery. Certain criteria must be met before tPA can be administered: ACT or MR head scan must be performed to rule out hemorrhage as the cause of symptoms. Blood pressure should be less than 185/100 mmHg. In addition, platelet count must be greater than 100 x 109/L, thromboplastin time must be less than 40 seconds and glucose levels should be between 50 and 400 mg/dL. Recent surgery, trauma and bleeding diatheses (predisposition to certain diseases) should be screened in the history. (30)

The protocol for treatment with tPA is:

1. tPA (0.9 mg/kg, up to a maximum of 90 mg) is administered intravenously.

2. The first 10% is given as a bolus over 1 minute. The remaining 90% is delivered over the next hour.

3. No anticoagulants or antiplatelet agents are used for the next 24 hours.

4. Blood pressure is monitored closely over the next 24 hours and aggressively managed.

5. Opportunities for neurosurgical consultation and reversal of bleeding should be available in case intracerebral hemorrhage complicates treatment. (30)

Percutaneous Intervention

If surgery is considered too risky or the plaque blocking the carotid artery is in an area not suitable for surgery, then carotid angioplasty, stent placement or both are needed.

High-risk patients include those with severe coronary artery disease, congestive heart failure, chronic obstructive pulmonary disease or those who have undergone previous carotid endarterectomy, radical neck surgery or radiation therapy. Other surgical risks are associated with general anesthesia, injury from cranial nerve damage and neck scarring. (31)

Carotid angioplasty and stenting usually are performed in a catheterization lab or interventional angiography suite. The femoral or brachial artery first is accessed by a needle puncture. A guidewire then is inserted through the needle, and an introducer sheath is placed over the guidewire after the needle is removed. The sheath helps to stabilize the artery at the access site during the angioplasty and stenting procedure.

A guiding catheter is inserted through the sheath over the guidewire, and the catheter tip is placed at the area of carotid stenosis. Once the catheter is in place, the guidewire is removed and contrast media is injected through the catheter. Images are taken to identify and map the stenosis. The stenosis is measured to determine the balloon and stent size needed to complete the procedure.

The guidewire then is reinserted and the guiding catheter is removed. An embolic protective device or filter is placed over the guidewire and positioned above the stenotic area to protect distal brain vessels from emboli that could be dislodged during the angioplasty procedure. Once the filter is in place, a balloon catheter is inserted, positioned over the stenosis and inflated to dilate the artery wall. The balloon then is removed and a catheter loaded with a stent is inserted over the guidewire. The stent is deployed over the recently dilated area to fully expand the artery wall and correct the stenosis. Sometimes a second angioplasty is performed inside the stent to ensure that the stent's struts are fully expanded. Contrast media is injected again and images are taken to confirm the success of the procedure. All medical devices except the stent are removed at the end of the procedure and pressure is applied to the puncture site to achieve hemostasis.

Surgical Treatment

Carotid endarterectomy is the standard surgical procedure for removing plaque from the carotid arteries. The procedure was first described in the mid 1950s and began to be used increasingly as a stroke prevention measure in the 1960s and 1970s. Its use peaked in the mid 1980s, when some authorities began to question the risk-benefit ratio for some groups of patients. According to the American Heart Association and the American Stroke Association, about 98 000 carotid endaterectomies were performed in 2004. (32)

The National Institute of Neurological Disorders and Stroke supports 2 clinical trials that have identified specific individuals for whom carotid endarterectomy is beneficial when performed by surgeons and in institutions that can match the standards set in those studies. The surgery has been found highly beneficial for people who already have had a stroke or experienced the symptoms of a stroke and who have severe stenosis of 70% to 99%. In this group, surgery reduces the estimated 2-year risk of stroke or death by more than 80%. For patients who already have had transient or mild stroke symptoms caused by moderate carotid stenosis (50% to 69%), surgery reduces the 5-year risk of stroke or death by 6.5%. (2)

In another trial, the procedure was found to be highly beneficial for people who were symptom free but had a carotid stenosis of 60% to 99%. In this group, endarterectomy reduced the estimated 5-year risk of stroke by more than half, from about 1 in 10 to less than 1 in 20. (2)

Contraindications for a carotid endarterectomy include a severe neurologic deficit following a cerebral infarction, an occluded carotid artery or a concurrent illness that significantly limits the patient's life expectancy.

Patients younger than 70 years with normal electrocardiogram findings and without diabetes or cardiac symptoms can undergo carotid endarterectomy without further cardiac work-up. (3) However, the American Heart Association recommends a preoperative cardiac evaluation for all prospective carotid endarterectomy patients who have a history of new-onset angina or new symptoms following coronary angioplasty or bypass.

Carotid endarterectomy can be performed using either local or general anesthesia. Local anesthesia has the advantage of allowing direct evaluation of the patient's neurologic status without sophisticated monitoring. This enables the surgeon to operate on the majority of patients without the need for a shunt, which can raise the risk of stroke. General anesthesia has the advantage of improved airway control and patient comfort during prolonged operations. However, it requires the use of routine or selected shunting, and shunting requires electroencephalography, stump pressure measurements and transcranial Doppler ultrasound or some other form of cerebral monitoring to assess the need for a shunt.

During this procedure, the blood flow either must be stopped or rerouted while the surgeon works on the artery. In rerouting, a tube can be placed to connect blood flow from above the area of blockage to below the area. In other cases, the surgeon stops the blood flow just long enough to peel the blockage away from the artery.

After the anesthesia has taken affect, the vascular surgeon makes a vertical incision in the neck along the anterior border of the sternocleidomastoid muscle. The surgeon does not cut into the plaque; instead, a dissection plane is made around the plaque. The plaque and diseased portion of the artery are removed from the inner lining of the artery, which leaves a smooth, wide-open vessel. (See Fig. 6.)

[FIGURE 6 OMITTED]

Finally, the artery is sewn back together, sometimes with a patch, and blood flow returns to the brain. A patch graft is used if it appears that the vessel lumen would be constricted. The patch graft is either made from 1 of the arm veins or constructed from prosthetic material. The technical results of the endarterectomy should be verified by angiography or duplex ultrasound. Patients leave the hospital the same day as the procedure or the following day, depending on how they feel. (3,12)

Possible complications of carotid endarterectomy are cardiac ischemia, cranial nerve injury, hematoma with or without airway compromise, hypertension and hypotension, perioperative stroke and recurrent stenosis. (3) Postoperative care consists of a complete blood count, an electrocardiogram, neurologic assessment, blood pressure readings and observation for hematoma that may compromise the airway. Antiplatelet therapy also is necessary. (3) Follow-up care consists of evaluating the patient 2 weeks postoperatively for wound and neurologic complications. Carotid duplex ultrasound should be performed at 6 months and then annually thereafter. (3)

Specialists Trained To Evaluate and Treat Stroke Patients

The procedures and therapies used to diagnose and treat strokes can be prescribed or performed by different kinds of specialists:

* Emergency room physicians specialize in the rapid evaluation of medical emergencies. Patients should inform the emergency room physician if they believe they may be having a stroke so he or she can make a rapid and thorough assessment. If a patient arrives within 3 hours of the stroke's onset, clot-dissolving drugs might be prescribed.

* Stroke neurologists specialize in evaluating and medically managing ischemic and hemorrhagic strokes. They have special training to recognize and treat strokes and effectively manage clot-dissolving drugs, blood pressure medication and other required medical therapies.

* Neurosurgeons can specialize in surgically managing strokes. If a stroke is due to a ruptured aneurysm, vascular malformation or cerebral bleeding, surgery may be necessary to clip the aneurysm or remove a blood clot in the brain.

* Vascular surgeons specialize in surgically treating carotid artery disease due to atherosclerosis. If 1 of the major blood vessels to the brain such as the carotid artery is blocked, treating the blockage might require a carotid endarterectomy.

* Neuroradiologists specialize in the rapid diagnostic evaluation and treatment of stroke and brain and spinal cord diseases using imaging techniques. Special tests may be performed to quickly and accurately diagnose the cause of a stroke, including CT, MR and diagnostic cerebral angiography. A diagnostic neuroradiologist has special expertise and training to interpret these examinations and diagnose the underlying condition. (5) Neuroradiologists also assist in the interventional treatment of stroke by using radiographic techniques to demonstrate the damage and assess treatment.

* Endovascular neurosurgeons perform delicate operations in the brain to treat acute strokes. These physicians have additional specialized training required to navigate the delicate brain blood vessels, open blocked arteries and close off aneurysms that may have ruptured and bled.

Future Advances in Treatment Options

Numerous drugs are being studied for the prevention and treatment of stroke. For example, a Wake Forest University School of Medicine research team has been investigating 2 drugs used to treat lupus that might also stabilize atherosclerotic plaque in the walls of arteries and help avert heart attacks and strokes. At an American College of Rheumatology meeting in Washington, Mishra and colleagues reported that the drugs trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA) decreased cholesterol deposits in the walls of arteries. Atherosclerosis is in part an inflammatory disease; Mishra noted that physicians might be able to take advantage of the anti-inflammatory effects of TSA and SAHA. (33)

A new experimental drug from bat venom can be used beyond the 3-hour mark for busting a clot. Desmoteplase is a genetically engineered version of a clot-busting agent found in the saliva of the vampire bat. It can treat stroke patients up to 9 hours after the onset of symptoms. Today only about 5% of stroke patients are treated with intravenous tPA because they don't get to the hospital within 3 hours of onset. In studies thus far, 60% of patients who received desmoteplase improved enough to live on their own within 90 days. (34)

In addition to drug treatments, acupuncture therapy is being studied to treat stroke patients in China, Scandinavia and Japan. Acupuncture is used for patients with conditions such as paralysis, speech and swallowing problems, and depression. It is believed that acupuncture opens blood vessels for better flow and decreases clotting and inflammation. In these studies, patients got well faster, performed better in self-care activities, required less nursing and rehabilitation therapy and had lower health care expenses. In China acupuncture is started as soon as possible after a stroke and is used on a daily basis; in Western countries, acupuncture treatment 3 times a week is considered optimal. More than 1 approach is used in acupuncture, including scalp therapy, hand therapy and the ear approach. However, most physicians in the United States, including rehabilitation experts, are unwilling to use acupuncture therapy because the studies that have been published so far do not meet rigorous research criteria. More studies are needed before skeptics will be convinced that acupuncture is a legitimate therapy for stroke patients. (35)

Conclusion

Medical science has discovered quite a lot about CAD, not only what CAD is and how it develops, but also how to slow its progression and treat it. To minimize risk for CAD, individuals must control their risk factors. Everyone should know his or her blood pressure, cholesterol, triglycerides and blood sugar levels, as well as weight, waist measurement and body mass index. Managing CAD risk factors requires keeping these values within normal ranges. When an individual develops signs and symptoms of CAD, the disease has progressed and medical or surgical treatment might be needed. Tests are performed to diagnose the location and amount of plaque in the carotid arteries. Many types of drugs are available for a patient at high risk for surgery, including anticoagulants, antiplatelets and thrombolytic medicines. An angioplasty is another option for patients who are at high risk of complications from surgery. If a patient is a good candidate for surgery, then a carotid endarterectomy can be performed. Although new therapies and medicines for CAD are being studied continuously, the best option is prevention.

Directed Reading Continuing Education Quiz

Diagnosis and Treatment Of Carotid Artery Disease

To receive Category A continuing education credit for this Directed Reading, read the preceding article and circle the correct response to each statement. Choose the answer that is most correct based on the text. Transfer your responses to the answer sheet on Page 445 and then follow the directions for submitting the answer sheet to the American Society of Radiologic Technologists. You also may take Directed Reading quizzes online at www.asrt.org. Effective October 1, 2002, new and reinstated members are ineligible to take DRs from journals published prior to their most recent join date unless they have purchased a back issue from ASRT.

* Your answer sheet for this Directed Reading must be received in the ASRT office on or before this date.

1. Plaque is made up of:

1. cholesterol.

2. calcium.

3. fibrous tissue.

a. 1 and 2

b. 1 and 3

c. 2 and 3

d. 1, 2 and 3

2. Controllable risk factors for carotid artery disease (CAD) include:

a. age and exposure to air pollution.

b. obesity and high cholesterol.

c. race and smoking.

d. sex and genetics.

3. According to this Directed Reading, normal blood pressure is -- mmHg.

a. 140/90

b. 130/60

c. 120/80

d. 110/40

4. Borderline cholesterol is considered -- to -- mg/mL.

a. 160, 179

b. 180, 199

c. 200, 239

d. 240, 279

5. According to the American Heart Association, a normal triglyceride level is -- mg/dL.

a. less than 150

b. 160

c. 170

d. more than 180

6. How many major branches does the external carotid artery (ECA) have?

a. 2

b. 4

c. 6

d. 8

7. What is the first arterial branch off the ECA from the bulb?

a. lingual

b. facial

c. superior thyroid

d. ascending pharyngeal

8. When plaque is described as specific to 1 area, it is:

a. extensive.

b. circumferential.

c. focal.

d. diffuse.

9. Astenosis of 50% to 80% is considered:

a. moderate.

b. moderately severe.

c. severe.

d. complete.

10. An outpouching or ballooning of a weak area in the artery wall is:

a. an arteriovenous malformation.

b. an aneurysm.

c. collateral circulation.

d. a stroke.

11. According to the American Stroke Association, what percentage of strokes are fatal?

a. 12

b. 16

c. 20

d. 24

12. What type of stroke has symptoms that come and go, but the patient is considered unstable?

a. completed stroke

b. stroke in evolution

c. acute cerebrovascular accident

d. transient ischemic attack

13. Symptoms of stroke can include:

1. numbness, weakness or paralysis.

2. confusion or slurred speech.

3. blurry vision or loss of vision.

a. 1 and 2

b. 1 and 3

c. 2 and 3

d. 1, 2 and 3

14. A neck bruit is a poor indicator of extracranial carotid artery disease or high-grade stenosis.

a. true

b. false

15. Which imaging modality uses high-frequency sound waves to show plaque in the carotid arteries?

a. magnetic resonance (MR) imaging

b. radiography

c. ultrasound

d. computed tomography angiography (CTA)

16. Which imaging modality uses radio waves and powerful magnetic fields to create images of the coronary arteries?

a. MR angiography (MRA)

b. angiography

c. CTA

d. ultrasound

17. The National Stroke Association's recommendations for managing stroke risk factors include:

1. stop smoking.

2. control blood pressure.

3. maintain a body mass index greater than 30.

a. 1 and 2

b. 1 and 3

c. 2 and 3

d. 1, 2 and 3

18. Which of the following is a thrombolytic medicine approved by the U.S. Food and Drug Administration (FDA) to dissolve clots?

a. ticlopidine

b. warfarin

c. aspirin

d. tissue plasminogen activator (tPA)

19. An FDA-approved thrombolytic drug must be used within the first hours of stroke symptom onset for the patient to have a chance of near or complete recovery.

a. 10

b. 7

c. 5

d. 3

20. When surgery is considered too risky or the plaque blocking the carotid artery is in an area not suitable for surgery, what treatments are needed?

1. carotid endarterectomy

2. stent placement

3. carotid angioplasty

a. 1 and 2

b. 1 and 3

c. 2 and 3

d. 1, 2 and 3

21. Carotid endarterectomy has been found beneficial for people:

1. who have already had a stroke.

2. with severe neurologic deficits.

3. with stenosis of 70% to 99%.

a. 1 and 2

b. 1 and 3

c. 2 and 3

d. 1, 2 and 3

22. Which imaging examination should be performed 6 months after carotid endarterectomy and then annually thereafter?

a. duplex ultrasound

b. carotid angiography

c. MRA

d. CTA

23. Stroke neurologists specialize in:

a. surgically managing strokes.

b. medically managing strokes.

c. using radiologic techniques to visualize damage caused by strokes.

d. rapid diagnostic evaluation of strokes.

24. Two drugs currently under investigation by a research team from Wake Forest University School of Medicine for their ability to stabilize atherosclerotic plaque also are used to treat:

a. breast cancer.

b. osteoporosis.

c. lupus.

d. fibromyalgia.

25. Desmoteplase, a genetically engineered version of a clot-busting agent found in bat saliva, can be used to treat stroke victims up to -- hours after the onset of symptoms.

a. 3

b. 6

c. 9

d. 12

26. According to some studies, stroke patients treated with -- got well faster, performed better in self-care activities and required less nursing care.

a. herbal remedies

b. massage therapy

c. acupuncture

d. aromatherapy

DRI0007011

Expiration Date: June 30, 2009* Approved for 1.5 Cat. A CE credits

References

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(2.) National Institute of Neurological Disorders and Stroke. Questions and answers about carotid endarterectomy. Available at: www.ninds.nih.gov/disorders/stroke/carotid_ endarterectomy_backgrounder.htm. Accessed July 31, 2006.

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(19.) Ridgway DE The common studies. In: Introduction to Vascular Scanning A Guide for the Complete Beginner. 2nd ed. Pasadena, Calif: Davies Publishing; 1998:64.

(20.) Higashida RT. What you should know about cerebral aneurysms [undated patient handout]. Dallas, Texas: American Heart Association Cardiovascular Radiology Council, Cerebrovascular Imaging and Interventions Committee.

(21.) Higashida RT. What is an arteriovenous malformation? [undated patient handout]. Dallas, Texas: American Heart Association Cardiovascular Council, Cerebrovascular Imaging and Intervention Committee.

(22.) St. Luke's Episcopal Health System. Carotid artery disease. Available at: www.sleh/Section004/index.cfm?pagename= Carotid%20Artery%20Disease. Accessed July 31, 2006.

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(34). Empowered Hospital. Bat venom stroke drug. Available at: www.Empoweredhospital.com/story_475.html. Accessed January 16, 2007.

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Pamela Jones, B.A., R.T.(R)(M), RDMS, RVT, is a staff sonographer at the University of Pittsburgh Medical Center McKeesport Hospital, in McKeesport, Penn. She has worked in diagnostic imaging for more than 25 years. She was formerly a radiographer, mammographer, chief technologist, office manager and technical director. She also has taught ultrasound classes at the Community College of Allegheny County in Pennsylvania.

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Title Annotation:CE: DIRECTED READING
Author:Jones, Pamela J.
Publication:Radiologic Technology
Article Type:Disease/Disorder overview
Geographic Code:1USA
Date:May 1, 2007
Words:9774
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