Type 2 Diabetes: Preventing Complications
Advances for Carotid Disease
By Neil Goyal, MD, Instructor in Clinical Medicine, Columbia University and William A. Gray, MD, Director of Endovascular Services New York -Presbyterian Hospital, Columbia University.
Stroke is a leading cause of severe disability and the third leading cause of death in the U.S. Despite medical advances, about 700,000 Americans suffer a stroke each year. When a stroke occurs, people may feel sudden onset of weakness in a limb, numbness, difficulty speaking or even a generalized change in behavior.
Rapid medical attention is needed to deliver therapy to help allow brain recovery and prevent recurrent strokes. Physicians now have a variety of options, both medical and surgical, to treat and prevent this potentially devastating complication of cardiovascular illness.
Sources of stroke
Most strokes are caused by emboli, small blood clots that travel to the brain and prevent the normal delivery of oxygen-containing blood. Sources of emboli include the heart itself, the aorta, and the carotid arteries. In some people with an irregular heart rhythm called atrial fibrillation, clots can form in a chamber of the heart and then travel to the brain causing a stroke. The aorta, the largest artery in the body, can develop plaque accumulation that can also break off and travel to the brain.
The carotid arteries: Vital vessels to the brain
An important cause of stroke is the carotid arteries. Arising from the aorta and its branches (see figure 1), the carotid arteries serve as conduits for oxygenated blood to reach the brain. If atherosclerosis occurs in the carotid arteries, small emboli can dislodge and travel to the smaller brain arteries and clog blood flow, thereby resulting in a stroke. Severe narrowing (stenosis) can completely interrupt blood flow to the brain supplied by that artery.
An insidious danger
Narrowing in the carotid arteries generally occurs over many years without producing symptoms. Often, the first indication of a problem is a sudden neurologic event. This can be relatively mild with transient weakness, a vision or speech disturbance, or other motor or sensory abnormality. If the symptoms resolve over a few minutes to hours, the event is called a transient ischemic attack, or TIA. Unfortunately, the initial symptom of carotid disease can also be a devastating stroke, which results in major loss of function, aralysis or even death.
There is a clue to carotid narrowing that can be detected on physical examination. A carotid bruit is a “whooshing” sound, heard with the stethoscope placed over the neck. It is important to note that not everyone with a carotid bruit has significant disease. Similarly, not every patient with major carotid stenosis will have an audible bruit. Another clue to carotid disease may be detected during a funduscopic (eye) examination.
Finding the blockage
In order to detect the presence and extent of disease in the carotid arteries, imaging studies are performed. The most commonly available technique is duplex ultrasound sonography, which uses sound waves to create images of the arteries and measure the severity of stenosis. Other imaging modalities include MRA (magnetic resonance angiography), CTA (computerized tomographic angiography) and catheterization. The gold-standard test is angiography, in which catheters are inserted into the carotid artery and contrast is injected under x-ray guidance to determine the degree of blockage.
Stroke risk related to carotid narrowing and symptoms
The risk of stroke in patients with carotid stenosis is related both to the degree of narrowing and the presence of symptoms. In general, the risk of a stroke rises when the blockage is greater than 80%. If a patient has already suffered a stroke, even a 50% stenosis confers a significant risk of recurrent stroke with medical therapy alone.
Potential treatments to reduce the risk of stroke include medicines to control risk factors for atherosclerosis, blood thinners to prevent clots and mechanical means to restore blood flow (revascularization). Revascularization can either be performed surgically with carotid endarterectomy (CEA), or by insertion of a stent via a catheter.
Medical management
Risk factors for developing plaque buildup in the carotid arteries include hypertension, diabetes, high cholesterol, and smoking. All patients with evidence of any degree of carotid disease need aggressive medical management. Antiplatelet therapy with aspirin reduces the risk of stroke and heart attack. Tobacco cessation is vital. Control of cholesterol with medications called statins reduces the risk of both heart attack and stroke. Diabetes management is instrumental in preventing stroke and progression of disease.
Perhaps the most important risk factor to control is hypertension. The risk of stroke increases threefold when the systolic blood pressure exceeds 160 mmHg. According to recent reviews, even a modest lowering in blood pressure of 10 mmHg systolic and 3-6 mmHg diastolic reduces the risk of stroke by 30% and 42%.
Despite excellent medical management some patients continue to have strokes. This tends to occur in those patients who have had strokes in the past and those with more extensive carotid blockages.
Carotid surgery reduces stroke risk
Medical therapy alone may not be sufficient to reduce the risk of stroke. In patients who have already suffered a stroke and have a carotid stenosis greater than 50%, the two-year risk of recurrent stroke is 26%. Carotid endarterectomy can reduce the two-year risk of stroke to 9% after the surgical correction.
For patients with carotid disease who have not had previous symptoms, the risk of stroke increases significantly when the stenosis is greater than 80%. For these individuals, CEA reduces the risk of stroke from 11% down to 5% after 2-3 years.
While surgical revascularization has shown benefit, not all patients can tolerate anesthesia and surgery because they have other major illnesses. Furthermore, the above benefits are present only in the hands of skilled surgeons. Patients with coronary heart disease, chronic obstructive pulmonary disease, and prior neck surgery are examples of those at increased risk from carotid surgery. Because of the need for less invasive revascularization, carotid stenting technology was developed.
Stents right for some patients
Recently, carotid stenting has been developed as an alternative to carotid surgery in selected patients. Performed under x-ray guidance, a catheter is advanced from an artery in the leg, through the aorta, and into the carotid artery. Awire with a protective filter or mesh is placed beyond the blockage. The narrowing is opened with a balloon and a stent placed to keep the artery open (see figure 2). The protective apparatus traps any debris that may have been dislodged during the procedure. One study in patients at highrisk for surgery showed that carotid stenting is at least equivalent and likely better than surgery because of a decreased risk of heart attacks.
This article first appeared in the January/February 2007 issue of Heart & Health Reports. For a subscription, call 1-877-HEART-12.