Radiation may help prevent clogging of coronary arteries
Houston medical specialists are testing radiation as a new tool to prevent coronary arteries from clogging again after they have been opened by medical procedures. On Thursday, two patients and the physicians who treated them described the new procedure that involves the Texas Heart Institute and the University of Texas M.D. Anderson Cancer Center.
“This is a promising new procedure that uses radiation delivered locally (directly to the clogged part of the artery) in small amounts to prevent the exuberant wound healing and scarring that led to renarrowing of the artery after angioplasty or stent placement,” said Dr. James T. Willerson, medical director at the Texas Heart Institute.
Percutaneous transluminal angioplasty was developed in the late 1970s as a therapy that might one day challenge coronary artery bypass as a means of restoring blood flow to the heart.
It involves threading a small tube called a catheter up through blood vessels into the narrowed portion of the coronary artery.
A balloon attached to the tube is inflated in that narrowed area, enlarging the diameter of the artery through which blood passed.
But 30 percent to 40 percent of patients who undergo the procedure find that their arteries have closed again within six months.
Development of tiny wire devices called stents has reduced the frequency of such restenosis, or re-clogging.
The stents are placed in the re-opened area of the artery as tiny scaffolds to hold it open. But 20 percent to 30 percent of patients find that within six months, their artery is once again too narrow to allow good blood flow.
This restenosis occurs because angioplasty and stents cause tiny injuries to the wall of the blood vessel. When that injury begins to heal, the inflammatory and smooth muscle cells actually overgrow, renarrowing the artery.
Physicians interested in the problem theorized that if they were able to deliver radiation directly to the area where the overgrowth would occur, they could kill the dividing cells and prevent the restenosis.
A preliminary study at Scripps Clinic in California found that of 26 patients who received radiation after angioplasty and stenting, only 16.7 percent experienced restenosis six months after the procedure while 53.6 percent of the 29 who did not have radiation found that their arteries had narrowed again.
That study gave the backing needed for a larger trial of the procedure.
Texas Heart Institute is one of 12 centers nationwide involved in a study of the new technique called brachytherapy.
Radiation targets cells that are rapidly dividing, such as those involved in repairing injuries to the walls of arteries, said Dr. Anuja Jhingram, an assistant professor of radiation oncology at Anderson.
After the coronary artery is opened with a balloon or other instrument and the wire stent is placed, Jhingram uses the same catheter to deliver a sealed thread of iridium-192 to the area of the artery that had been clogged. The thread of radioactive material is usually 1 to 2 inches long.
The thread is left in place from 15 to 30 minutes so that it can kill the cells that are most likely to cause overgrowth of tissue in that area, said Jhingram.
Dr. David Fish, director of interventional cardiology at the Texas Heart Institute, said he expects to treat 30 patients in the new study. Half of the patients will receive radiation and half will not.
Two of the patients who have undergone the procedure in Houston so far said they are satisfied with it, even though neither knows if he received radiation or not.
“It took me two seconds to make up my mind to do it,” said Donald Gundermann, 66. “I’m interested in the results of all of this. To me, it was not an unpleasant experience at all. We are celebrating life here today instead of a funeral. That’s proof to me.”
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