Is a thinner stent a better stent? Device makers are trying to find out

The exterior of the human heart contains critical blood vessels thinner than a small headphone jack that ensure the heart gets enough oxygenated blood to keep beating normally.

When those vessels get clogged, interventional cardiologists will often insert a tiny metallic mesh tube into the vessel to keep them open over time. Now a new generation of stents with very thin components are being implanted in patients and monitored for years in clinical trials to see if they offer better results than slightly thicker versions of the same devices.

Long-term study results announced at an industry conference last month show that, indeed, a European stent made by with "ultra thin" components helped patients avoid do-over procedures to "re Biotronik vascularize" the same vessel better than wider stents did.

The Biotronik device had less than half the rate of do-over vascularizations compared to an older Medtronic stent in small vessels, and it also showed better performance on that measure than a premium-priced Boston Scientific stent designed in Minnesota.

Specifically, in about 1,500 patients randomized in the Netherlands as part of the Bio-Resort trial to receive either Berlin-based Biotronik's Orsiro, Medtronic's Resolute Integrity, or Boston Scientific's Synergy stents to treat blockages in small coronary vessels, 2% of the Biotronik patients needed a "revascularization" within three years in those vessels. The three-year revascularization rate compared to 5% for Medtronic's Resolute Integrity. About 4.1% of the Boston Scientific stent patients in the study needed the do-over procedure.

Those results were included as a part of a "subanalysis" of Bio-Resort patients, focusing on the 1,506 participants who had blockages in the narrowest vessels, of no more than 2.5 mm in diameter. (The study looked at differences in the thickness of the metal that makes up springlike devices, not the diameter of the devices themselves.)

Biotronik's Orsiro stent was cleared by the Food and Drug Administration for U.S. sales in February, allowing it to compete with coronary stents from Boston Scientific, Medtronic, Abbott Laboratories and others in the multibillion-dollar U.S. stent market.

"I think it was a well-done study. It had long-term data, and it was all-comers — it was a real-world study. A lot of times you get these studies that have such precise types of patients that you never see those kinds of patients in clinic," Traverse said. (Traverse was not an investigator in Bio-Resort, though he has implanted Orsiro devices in a different clinical study. He has received payments from Abbott Labs, Boston Scientific and Medtronic.)

Medtronic has already released a thinner version of its stent, called the Resolute Onyx, that is performing well on this measure in one-year clinical trials results. A Medtronic spokesman said the Resolute Onyx stent has other features besides thinness that make it desirable, including the shape and unique composition of the metal wire that makes up the structure of the springlike device.

"We applaud the Bio-Resort investigators on the study findings in this unique subgroup of patients with small vessels, as they can be challenging cases for physicians," Medtronic spokesman Joey Lomicky said via e-mail. "It's also important to put these study findings into the proper context."

Boston Scientific officials disputed the notion that Bio-Resort said anything meaningful in comparing its Synergy stent to the Biotronik stent. Company CEO Mike Mahoney has said in the past the company would seek higher prices for its Synergy stent because of its unique design.

In Bio-Resort, patients were randomized on a 1-to-1-to-1 basis to one of the three stents in the trial. But a Boston Scientific spokeswoman asserted that the trial didn't directly compare Biotronik's stent to the Synergy. Also, the study's association of thinner stent materials and lower adverse events does not prove the metal's thinness led to the better results. The stents had other differences, including the type of drug applied to the outside of the devices to cut down on the risk for re-closure.

Dr. Ron Waksman, director of cardiovascular research at the MedStar Heart & Vascular Institute in Washington, D.C., said the Bio-Resort subanalysis on small-diameter vessels adds to the growing body of research showing that when stents are made from thinner metals, patients have better outcomes.

When a stent is left behind in a blood vessel, scar-tissue-like cells called "endothelial cells" begin to cover over the metal, Waksman said. So it makes logical sense that a thinner metal "strut" in a stent would be covered over more quickly than a stent whose struts are taller and stick out farther from the vessel wall.

"As long as you have exposure of the metal to the blood, that can potentially cause problems. So you want to see fast coverage, and thin coverage," said Waksman, a paid consultant to Biotronik who has also served as an adviser to Medtronic and Boston Scientific. "When it is thinner, it is easier and faster to cover with endothelial cells."

Joe Carlson • 612-673-4779