Radioactivity is tried to keep `stents' clear

New treatment used in cases like Cheney's when clogs re-form

March 10, 2001|By Jonathan Bor | Jonathan Bor,SUN STAFF

Vice President Dick Cheney's recent problem with a clogged "stent" didn't surprise doctors who use the devices to reopen arteries of the heart. Many said they wouldn't be surprised if the stent clogs again, sending him back to the hospital for further treatment.

But if that happens, it is likely that doctors will treat Cheney's problem with radioactive pellets, a new therapy for the heart borrowed from the world of oncology.

The pellets have been used for many years to shrink tumors of the prostate and brain. Last year, the U.S. Food and Drug Administration approved the use of pellets to irradiate coronary arteries from within. Using a long, hollow tube, doctors direct a column of 10 seeds to the clogged stent and hold it in place for three of four minutes before withdrawing the tube and seeds from the body.

The radiation triggers biological changes that, in most cases, keep the stent from clogging again.

"This is the latest and most promising technology we've heard about in the last 15 years," said Dr. Warren Lasky, associate director of cardiology at the University of Maryland Medical Center.

The University of Maryland School of Medicine and the Johns Hopkins School of Medicine were among 50 institutions taking part last year in a nationwide trial of a system that uses so-called beta radiation to treat clogged stents.

The treatment addresses the very problem that Cheney faced Monday, when he was admitted to the George Washington University Hospital after experiencing several bouts of chest pain over a four-day period.

The vice president has a long history of coronary artery disease, a chronic illness in which the vessels of the heart become narrowed and hinder blood flow. Over the years, Cheney has had four heart attacks and a quadruple bypass operation.

His last heart attack, in November, stemmed from a narrowing in a small branch artery. Doctors treated it by inserting a long tube into his upper leg and threading it to his heart, where they inflated a tiny balloon that flattened the obstruction.

The treatment, called balloon angioplasty, is done 700,000 times each year in the United States. In Cheney's case, doctors also implanted a mesh stent into the troubled area. The stent holds the artery open, helping to reduce the chances that it will close again.

Studies have shown that about 40 percent of arteries treated with angioplasty alone develop new clots, compared with 20 percent of arteries also treated with stents.

But at that rate, more than 100,000 stents inserted every year will close again. The phenomenon, called restenosis, is exactly what happened to Cheney. And studies have shown that once this occurs, the artery becomes harder to treat.

Doctors treated Cheney's stent with another angioplasty, but he runs about a 40 percent chance that the same problem will return.

Most stents don't develop the types of fatty clots that afflict arteries, Instead, tissue from the wall of the artery grows into the stent, narrowing the path for blood flow. Doctors liken the tissue to a keloid, a scar that forms after a wound or surgical incision.

"Of all the devices to clean out the vessels, none have been shown to be really good at preventing this keloid from reoccurring, except [the radiation therapy]," said Dr. Jeffrey Brinker, a Hopkins cardiologist.

Cheney's cardiologist, Dr. Jonathan Reiner, said Monday that he might consider treating the vice president with the radiation seeds if the problem recurs.

In the large clinical trial, brachytherapy, the radiation treatment, produced about a 60 percent reduction in the incidence of restenosis within eight months and a 40 percent reduction within a year.

The procedure has just begun to enter the practice of medicine. The University of Maryland, Johns Hopkins and St. Joseph's Hospital in Towson are among the hospitals using it. Not all hospitals provide it because the procedure requires not just a cardiologist, but a radiation oncologist and shielded containers and rooms to store the radioactive material.

Just as radiation shrinks tumors by stopping the multiplication of abnormal cells, it halts restenosis by turning off the growth of cells around the stent, said Lasky.

Dr. Mohan Suntha, vice chairman of radiation oncology at Maryland, said doctors are not greatly concerned that the low-dose radiation will cause cancer. A greater concern is that the radiation will produce scar tissue years later that could interfere with blood flow. "It could cause the kind of problem you've just prevented," he said.

So far, the studies show that patients go four years without developing such problems. It is theoretically possible that the problem could crop up after nine or 10 years - but even that might represent an improvement, he said.

Though excited about brachytherapy, doctors agree it is not the ultimate treatment.

"This is a road to the final goal," said Dr. Benjamin Dubois, a cardiologist with a large practice called Midatlantic Cardiovascular Associates. "The ultimate goal would be a stent that doesn't have a high restenosis rate."

Doctors envision a number of possibilities, including stents covered with medications to prevent further blockages. Another strategy is to irradiate arteries during the original angioplasty, a strategy that could prevent new blockages from forming in the first place.

In the meantime, doctors appear reasonably certain that Cheney will have further problems with his heart.

"This is his first go-round with the stent," said Lasky. "But the ominous feature is that it happened so quickly. Usually when it happens quickly, it's a bad thing and it's likely to happen again."

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