Clogged Arteries? Not All Arterial Plaque is Equally Dangerous
Many people know that plaque can build up in the walls of arteries and cause a heart attack. As the core of the blood vessel gradually grows narrower, blood flow is increasingly restricted. If the plaque grows large enough to obstruct blood flow, a heart attack will occur. Many people who have this type of plaque, called stable plaque, receive a warning sign in the form of angina—chest pain that accompanies exertion but disappears with rest.
But there’s a different type of plaque—a soft, unstable form—that is far more dangerous.
“Stable plaque can be compared to a callus and unstable plaque to a blister. A blister is likely to pop; a callus is not,” says Weill Cornell cardiologist Robert J. Kim, MD.
Unstable plaques are prone to sudden rupture, triggering a heart attack. They are thought to be responsible for at least half of all heart attacks, which tend to occur without warning in arteries that are blocked less than 50 percent.
WHAT YOU SHOULD KNOW
Lower your risk of developing any type of arterial plaque by:
➤ Not smoking
➤ Keeping blood pressure below 140/90 mm Hg
➤ Following a heart-healthy diet
➤ Exercising for 30 minutes on five or more days a week
Inside the arteries
A healthy blood vessel wall (endothelium) is smooth, alive, and actively working to maintain good blood flow. But smoking, air pollution, diabetes, hypertension, and other cardiac risk factors can irritate and roughen the surface, opening the door for cholesterol and white blood cells to invade the vessel wall and begin generating substances such as calcium and toxic byproducts.
Stable plaques are composed primarily of calcium and have grown slowly over time.
Unstable plaques have a soft, cholesterol-rich core covered by a thin, fibrous cap. Exactly what causes these plaques to rupture is unknown, but inflammation is the prime suspect. Enzymes contained in inflammatory cells appear to degrade the fibrous cap, causing its cells to die and the cap to tear. When the underlying contents are exposed to the bloodstream, a cascade of events is triggered that causes a clot to form. If the clot is large enough to block blood flow, a heart attack occurs.
Some unstable plaques never rupture, but become hard and calcified. Others cause a minor or “silent” heart attack, and then heal. As yet, there’s no practical way to tell whether a plaque is stable or unstable, or how a plaque will develop.
“That’s the Holy Grail of cardiology,” says Dr. Kim.
Challenges in diagnosing plaque type
Angiography is the gold standard for diagnosing or ruling out coronary artery disease. However, the test reveals only the inner core (lumen) of the artery. Narrowed areas indicate the presence of plaque “squeezing” the lumen.
Cardiac stress tests evaluate blood flow through the coronary arteries during exercise. The test is designed to identify arteries that are blocked 75 percent or more. At this point, intensified medical therapy, angioplasty, stenting, or even bypass surgery may be advised to help prevent a heart attack from occurring.
The only technologies that can reveal the composition of plaque are CT angiography, intravascular ultra-sound (IVUS), and optical coherence tomography (OCT). A new investigational technology, PET/CT used with radiolabeled sodium fluoride, is showing promise in clinical trials.
“This exciting technology does what others cannot—it identifies ‘hot,’ actively inflamed plaque. In other words, it allows us to not only see the plaque, but to tell whether it is danger-ous,” says Dr. Kim.
However, the likelihood that any of these technologies will ever be used for screening purposes is small, since CT and PET/CT emit radiation, and IVUS and OCT are invasive. “Even if we find the right tool, the harder question is, who would we choose to use it on?” says Dr. Kim.
Until there’s an answer, people who experience stable angina or are at risk for developing plaques will continue to undergo stress tests and angiograms. If your test reveals plaques, what does it mean for you?
“It means you should talk to your doctor about ways to minimize plaque growth,” says Dr. Kim. “Coronary artery disease is a common diagnosis, and we’re learning more about it every day. It is certainly not a death sentence.”
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