Cardiac stents are an effective, nonsurgical way of holding a narrowed or blocked artery open to increase blood flow to the heart in people with coronary artery disease (CAD). However, up to 15 percent of people who receive even the most modern type of stents — called drug-eluting stents — will experience restenosis, or re-narrowing of the artery, due to the formation of scar tissue around the stent.
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Now, interventional cardiologists at the Miller Family Heart & Vascular Institute are using a novel approach called intravascular brachytherapy to treat in-stent restenosis. Brachytherapy uses highly specialized protocols to deliver a small amount of radiation to the re-narrowed area of the artery following a procedure to re-open the stent. The goal of the treatment is to limit the overgrowth of normal tissue as the healing process occurs.
Brachytherapy is more commonly used to treat cancerous tumors, so its use in this context is not only uncommon, but innovative. In fact, Cleveland Clinic is one of only a few centers in the country — and the only one in Northeast Ohio — that offers intravascular brachytherapy, says Stephen Ellis, MD, Section Head of Invasive/Interventional Cardiology.
How brachytherapy works
Brachytherapy for in-stent restenosis is performed by an interventional cardiologist in collaboration with a radiation oncologist and radiation physicist, who ensure that precise doses of targeted radiation are delivered.
“The radiation dose is dependent on the size of the blood vessel determined by a specialized diagnostic ultrasound, and the radiation team ensures that everything is exactly calibrated,” Dr. Ellis says.
The brachytherapy is delivered using a special heart catheter, which is a long, narrow tube. The catheter is guided through the blood vessel to the coronary arteries with the aid of a special x-ray machine. The catheter, which contains a radioactive ribbon, is placed across the blockage. Next, the measured dose of Beta radiation is applied for several minutes and the catheter is pulled out.
“This kills or stuns some of the cells that lead to restenosis,” Dr. Ellis says.
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Who’s a candidate?
At Cleveland Clinic, brachytherapy is an advanced therapy that may be considered in certain patients after in-stent restenosis has occurred two or three times.
Patients who experience restenosis following the placement of a drug-eluting stent are carefully assessed to determine if they might benefit from brachytherapy or another type of treatment, Dr. Ellis explains. Other treatments may include re-opening the blockage with cutting balloon angioplasty and placing another stent, or even coronary artery bypass graft (CABG) surgery in extreme cases.
“The approach to addressing restenosis is highly individualized, and includes a number of options based on the principle cause of the restenosis, the size of the blockage, whether the patient has restenosis in multiple spots, and the number of stents the patient may already have in one area,” he says.
Generally, the number of stents placed in one spot should not exceed three, Dr. Ellis explains. When it has, brachytherapy plus preventive drugs can offer a valuable treatment option.
Patient selection matters
While brachytherapy is an important tool in the interventional cardiologist’s tool box, it’s not for everyone, Dr. Ellis says. Careful patient selection is critical and it’s typically not a first-line treatment following a single occurrence of in-stent restenosis. In addition, certain patients, such as those who have received therapeutic radiation to treat breast cancer or cancer in the thoracic (chest) region, are not candidates.
“We do about 10,000 heart catheterizations a year, and we will treat about 10 to 20 patients with brachytherapy in a year,” he says.
What causes restenosis?
Stents are tiny metal mesh tubes that are placed in the artery using balloon angioplasty. “We compress the plaque or blockage against the artery walls to increase blood flow, and the stent acts as a scaffold that supports the inside of the coronary artery,” Dr. Ellis says.
After the placement of a stent, the body begins healing — a process that takes about six months. “Healing around the stent involves the production of scar tissue to certain degree,” Dr. Ellis says. “When in-stent restenosis occurs, it is often due to the growth of smooth muscle cells during healing — not the recurrence of coronary artery disease.” Restenosis also can occur when the balloon used to compress the blockage prior to placing the stent is not adequately inflated prior to stent placement.
Certain risk factors — such as diabetes, longer stents, small blood vessels and multiple stents — may increase the likelihood of restenosis.
“We have learned that restenosis is a very complex process,” Dr. Ellis says.
The role of drug-eluting stents
“Bare metal” cardiac stents have been approved in the United States for about 20 years, and the Food and Drug Administration first approved drug-eluting stents (DES) about 10 years ago. DES have a thin coating of medication that is gradually released at the stent implantation site, which helps reduce the risk of restenosis.
“Drug-eluting stents work both mechanically and pharmacologically, which has decreased the risk of restenosis from about 10 to 30 percent, to 5 to 15 percent,” Dr. Ellis says. “However, restenosis is clearly still an issue.”
After DES came onto the market, Cleveland Clinic put the use of brachytherapy on hiatus, but recently reintroduced the therapy after recognizing that the need was still there. Because Cleveland Clinic’s Heart & Vascular Institute is a referral center, “We were seeing more and more patients with tough blockages that we knew could benefit from brachytherapy,” Dr. Ellis says.
What to expect after brachytherapy
After brachytherapy is performed, patients are placed on an anti-clotting drug regimen such as therapeutic aspirin and/or the drug clopidogrel.
In the short term, the treatment decreases restenosis by about 50 percent. However, brachytherapy may have some limitations as far as durability, or the amount of time it lasts. When performed in conjunction with bare metal (non-drug-coated) heart stents, clinical studies have found that the restenosis may return in the same spot within 5 years of treatment. Dr. Ellis says that more research is needed regarding durability with DES.