ORLANDO, Fla. (AP) - Zapping heart arteries with radiation fails to keep them flowing smoothly after angioplasty, a strategy many hoped would prevent the kind of complication that hospitalized Vice President Dick Cheney earlier this month.

The tendency of angioplasties to go bad is one of the most vexing and persistent problems in all of cardiology. Doctors can easily open clogged coronary arteries by briefly inflating a balloon, but often they close again, a situation called restenosis.

``Interventional cardiology has changed wildly over the past 20 years, but we still wrestle with the issue of restenosis,'' said Dr. David Holmes of the Mayo Clinic.

Typically after angioplasty fails, doctors simply perform another angioplasty on the reclogged artery. This was the treatment given Mar. 5 to Cheney, who received a new angioplasty after his earlier one clogged up.

However, doctors sometimes take a more aggressive approach. During the redo angioplasty, they briefly expose the artery to radiation. The idea is to kill tissue that fills the artery with clogging scar formation.

But doctors would like to prevent restenosis completely. And one approach is to try giving this radiation during the initial angioplasty rather than using it as a salvage technique after angioplasty fails.

A major study released Sunday at a meeting of the American College of Cardiology found this fails and may even do more harm than good.

The problem of restenosis is sizable, considering that about 1 million Americans are expected to have angioplasties this year. In about 90 percent or more of cases, doctors insert wire tubes called stents to prop open the arteries.

This cuts restenosis in half, to about 20 percent. But stents also make arteries more difficult to reopen once they have clogged.

The radiation study was directed by Dr. Richard E. Kuntz of Brigham and Women's Hospital in Boston and financed by Novoste Corp. of Atlanta, which makes the Beta-Cath radiation system.

The study was conducted on 1,455 patients, who were randomly given plain angioplasty or angioplasty plus radiation. The researchers found that the radiation might actually reduce the risk of restenosis if people do not receive a stent, which is rarely done today.

In this study, stents were reserved for patients considered to be at especially high risk of restenosis. In these patients, radiation actually made it more likely to happen. Forty-five percent had restenosis, compared with 35 percent who got stents without radiation.

``We have a study that is negative. There is no question,'' said Kuntz.

However, he said newer techniques for delivering stents still might make radiation useful. When the study began in 1997, doctors first inflated a balloon inside the artery, then inserted and removed radioactive beads and finally put in the stent.

The problem, Kuntz said, is that doctors sometimes lost their place inside the artery and failed to deliver the angioplasty, the radiation and the stent to exactly the same spot. This could expose damaged sections of artery to low doses of radiation that promote, rather than inhibit, scar growth.

Now, however, doctors can deliver the angioplasty and the stent at the same time. This makes it easy to follow with radiation exactly where it belongs.

Copyright 2001 The Associated Press. All rights reserved.