This is the VOA Special English Health Report. (来源：英语杂志 http://www.EnglishCN.com)

Today we have the second half of a report about some concerns with the use of drug-treated coronary stents. These are small metal tubes designed to be placed inside arteries in heart patients. The stent is usually left in permanently after doctors clean out a narrowed artery with angioplasty treatment. Doctors expand the stent to hold the passage open so blood can flow normally to the heart.

Medicine on the stent is released slowly over time to stop the development of scar tissue. Scar tissue can cause the artery to become narrow again.

These devices have been approved in the United States for the past four years for patients with simple blockages and no history of heart attack. But some doctors use drug-eluting stents, as they are called, for patients with more serious heart problems. This is known as "off-label use" and is permitted.

But two recent studies questioned the safety of off-label use of drug-treated stents. Both found that some patients with more serious conditions were more likely to suffer a renarrowing of the artery. This is called restenosis.

So far, researchers have mostly investigated the stents themselves and how they are made. But now attention is turning also to the way they are being used.

The question is how much of the problem of stent failure may be the result of stents not being put in right. Or maybe they are not being expanded enough to fit firmly in the artery.

One recent study found that stents were incorrectly placed in almost seventy percent of the patients in that study.

Now a heart research organization hopes to solve the mystery. The Cardiovascular Research Foundation is a big supporter of the use of drug-treated stents. The foundation is going to carry out a large study. Spokeswoman Irma Damhuis says it will involve eleven thousand patients at ten centers in the United States and two in Germany. A heart doctor with the foundation will be one of the lead investigators.

Researchers will examine how doctors implant and expand stents and how the methods they use might affect outcomes. The study will deal especially with serious artery blockages that have been found a year or more after a stent was put in place.

And that's the VOA Special English Health Report, written by Caty Weaver. The first part of our report can be found at voaspecialenglish.com. I'm Katherine Cole.

coronary stent :冠状动脉支架