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Ask Dr. K: March 12, 2014

DEAR DOCTOR K: Two friends recently had stents put in. What exactly is a stent? How does it work?

DEAR READER: A stent is a small metal cylinder that opens up a blockage in the arteries. It looks like a miniature chain-link fence rolled into a tube. Stents have helped revolutionize the treatment of the most common form of heart disease, coronary artery disease. To understand how, we’ll have to take a few steps back.

Coronary artery disease is atherosclerosis of the arteries that supply blood to the heart. Atherosclerosis causes cholesterol-filled plaques — growths in the wall of the artery that block the flow of blood through the artery. Those plaques can cause symptoms like angina (chest pain caused by coronary artery disease). They also can suddenly rupture, causing a clot to form that completely blocks blood flow and causes a heart attack.

Stents are used during a procedure called angioplasty. Angioplasty allows doctors to open narrowed or blocked coronary arteries that could lead to a heart attack.

During angioplasty, a cardiologist uses a needle to guide a plastic tube called a catheter into an artery (usually in the groin). Using X-rays as a guide, and a guide wire, the cardiologist pushes the tip of the catheter through the arteries that lead to the heart.

Once the catheter tip reaches the heart, it is guided into the coronary arteries. Dye squirted through the catheter shows the location and severity of any blockages. Near the tip of the catheter is an inflatable balloon. Once the catheter reaches the narrowed section of blood vessel, the cardiologist inflates the balloon. This pushes the plaque back against the wall of the artery and widens the channel through the artery, allowing more blood to flow through it.

The stent surrounds the catheter, on top of the uninflated balloon. When the balloon is inflated, the stent also expands. After the procedure is done, the doctor withdraws the catheter and the deflated balloon from the body. But the expanded stent remains in place, keeping that artery open and blood flowing through it. (I’ve put an illustration of stent placement on my website, AskDoctorK.com.)

The stent serves as a scaffold to hold the artery open. Most stents are coated with drugs that prevent cells from growing over and around the stent. Such growth occurred with older stents, and that caused a new blockage to occur where the old one had been.

But drug-coated stents can create some problems of their own. The drugs they exude can make it easier for clots to form on the stent. That’s why anyone with a drug-coated stent must also take blood-thinning drugs.

Researchers are continually trying to improve the design of stents. Stents also are used to open blocked arteries in other parts of the body, such as the kidney. Even 50 years ago, who would have imagined that you could open up a blocked artery deep inside the body without performing surgery? Today this procedure has become a welcome reality for millions of people.

With colleagues at Orca Health, we have recently published inexpensive iBooks for the Apple iPad and iPhone on angioplasty and stent, and on CABG surgery. They show you — with spectacular videos — what happens during these procedures. You can learn more about them at my website, AskDoctorK.com.

Dr. Komaroff is a physician and professor at Harvard Medical School. Send questions to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.

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