Carotid Stenting: A Minimally Invasive Technique for Stroke Prevention

What Is Carotid Stenting?

Carotid stenting is a minimally invasive procedure in which the same techniques used to open blocked arteries near the heart are used to improve the flow of blood to the brain and help prevent stroke.

Carotid Stenosis and Stroke

The carotid arteries are the major arteries that supply blood to the brain. They carry blood from the heart along both sides of the front of the neck. When the carotid arteries become narrowed or blocked by fatty plaques such as cholesterol, a condition known as arteriosclerosis, or "hardening of the arteries," is the result. While most people think of arteriosclerosis as a coronary ailment that may lead to heart attacks, fewer are aware that it is also a leading cause of stroke.

Stroke occurs when one or both of the carotid arteries becomes blocked and the flow of blood to the brain is interrupted, depriving the brain of its supply of oxygen. This lack of oxygen can damage or kill brain cells, causing a variety of physical and mental disabilities or death.

Stroke is the third leading cause of death in the United States and the leading cause of disabling brain damage, making the detection and prevention of potential strokes a high priority for physicians.

Physicians usually first detect a dangerous blockage or "stenosis" of the carotid arteries by listening through a stethoscope for a distinctive sound caused by uneven blood flow, called a "bruit" (pronounced "bru-ee"). The physician may then prescribe a series of imaging tests including an ultrasound scan, Doppler ultrasound flow exam, and magnetic resonance imaging (MRI) to determine the location and size of the blockage.

Correcting the blockage

Until recently, the only accepted surgical method for correcting a blockage of the carotid arteries was a traditional open surgical procedure known as carotid endarterectomy. After administering general or regional anesthesia, surgeons would stop the flow of blood through the carotid artery (usually by means of a surgical clamp), carefully remove plaque from the artery, and then restore the flow of blood to the brain.

While carotid endarterectomy is usually successful and has been the standard of care for the past forty years, its critics point out that the procedure still has significant risks. First, general anesthesia has increased risks compared to local anesthetics. Also, because the carotid artery is clamped to prevent bleeding, the flow of blood to the brain is interrupted, creating the risk of brain injuries.

In carotid stenting, the physician, often an interventional radiologist, inserts a thin plastic tube called a catheter through a tiny incision in the neck and threads it through the artery. A balloon at the tip of the catheter is inflated, widening the artery, then deflated. To prevent the newly widened artery from closing again, a wire mesh tube called a "stent" is put in place to hold the artery open.

Supporters of carotid stenting point out the same advantages as found in most minimally invasive interventional procedures:

• less trauma on the body because no general anesthesia is used;
• smaller incisions and less pain;
• shorter hospital stays; and
• less recovery time.

Because the flow of blood to the brain is not interrupted there is reduced risk of stroke from the procedure itself. Additionally, because there are no major incisions in the body, there is less risk of facial paralysis from damage to the cranial nerves.

Potential Complications

All surgeries in or near the brain and cerebrovascular system are potentially risky, and most of the potential complications of carotid stenting are due to its delicate location in the body.

Because physicians are working so close to the brain, there is the danger of blood clots or tiny pieces of fatty plaque coming loose during the procedure and traveling to the brain where they could cause a stroke. To prevent this, interventional radiologists use various forms of embolic protection, such as tiny filters placed in the artery to trap debris and prevent it from reaching the brain.

Who Should Have Carotid Stenting?

The most important considerations in determining whether or not stenting is the best method for correcting a carotid blockage are the age and health of the patient.

A recent study, known as the SAPPHIRE trial (Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy) indicates that older patients and patients with additional health problems are at high risk for stroke and death during carotid endarterectomy. For this group of patients, carotid stenting may be the preferred method for correcting stenosis.

"The patients who benefit from stenting are those who are considered at high risk for carotid endarterectomy," says interventional radiologist Dr. Barry Katzen, founder and medical director of Baptist Cardiac and Vascular Institute and clinical professor of radiology at the University of Miami School of Medicine. "If they are at low risk for carotid endarterectomy, stenting has not been proven to be of benefit for them." (These studies are still underway)

Some patients are more at risk of complications from carotid endarterectomy and may be candidates for carotid stenting. This includes patients who:

• have had previous heart surgery.
• have already had carotid surgery.
• have had cancer of the neck and radiation therapy in the neck.
• have stenosis (or narrowing) located very high in the carotid artery.
• are over the age of 80.

Many physicians disagree about the best course of treatment for patients who are at low risk of complication from carotid endarterectomy.

"Some of us believe in the end that carotid stenting will turn out to be superior for both groups," says Dr. Katzen, "But right now, based on today's data, we can't say that stenting is beneficial for low-risk groups."

Still, there are those who believe that neither traditional surgery nor stenting is the best treatment for low-risk patients, and that treatment with drugs like anticoagulants and antiplatelets may be the best course of action.

"For the low-risk group, the issue is not whether stenting is appropriate or inappropriate," says Dr. Katzen, "It's whether any surgical approach is appropriate. There are people who feel very strongly about this, and it is a source of great controversy right now."

Which method is best for correcting carotid stenosis may also depend on the degree of blockage. Some studies suggest that patients with the most extreme or advanced blockages of 70 percent or more can benefit most from carotid endarterectomy. For patients with the least degree of blockage—less than 50 percent—the risk of stroke can be effectively reduced non-surgically with the use of drugs like anticoagulants and antiplatelets.

Another important factor in deciding if carotid stenting should be used is whether the patient is "symptomatic" and shows objective symptoms of carotid stenosis, or is "asymptomatic" with symptoms that can only be detected during in-depth medical testing.

According to the results of the SAPPHIRE trial, patients with asymptomatic stenosis are at greater risk for stroke and death during surgical carotid endarterectomy and carotid stenting. Because of this, some physicians recommend that patients with asymptomatic carotid stenosis be treated with drugs alone, and that carotid stenting should be performed only on symptomatic patients.

The American Society of Neuroradiology, the American Society of Interventional and Therapeutic Neuroradiology and the Society of Interventional Radiology have all recommended that carotid stenting be used on patients with asymptomatic carotid stenosis only as part of controlled clinical trials and not as a generally available procedure.

New Policy and Current Trials

The Federal Drug Administration (FDA) approved the first carotid stenting system in 2004. In March 2005, the Centers for Medicare and Medicaid Services (CMS) announced that Medicare would cover the procedure for asymptomatic patients as part of ongoing clinical trials and certain patients at high risk of stroke during carotid surgery who have had symptoms.

Studies performed in the United States and Europe indicate that the long term effects of carotid stenting are comparable to carotid endarterectomy, and that both procedures effectively correct carotid blockage and restore normal blood flow to the brain.

A number of studies are currently underway to further examine the effectiveness of carotid stenting. In particular, the National Institutes of Health (NIH) supports the Carotid Revascularization: Endarterectomy vs. Stent Trial (CREST), a national trial comparing the benefits and risks of carotid stenting versus carotid endarterectomy. These trials will contribute greatly to what is known about this innovative treatment.