Physicians have been limited in their efforts to treat coronary artery disease in narrower vessels. Abbott (Abbott Park, Illinois) is seeking to fill that treatment gap, which accounts for about 10% of all procedures to treat lesions, with the start of a trial evaluating a 2.25 mm size of the Xience V everolimus eluting coronary stent system.

"There are critical aspects in the design of this new Xience platform that represent improvements compared to larger stents," Marco Costa, MD, PhD, director of the Center for Research and Innovation of Harrington-McLaughlin Heart and Vascular Institute, University Hospitals, Case Western Reserve University (Cleveland), and principal investigator of this new trial, told Medical Device Daily.

"The first factor is the thickness of the struts," he said. "It's thinner compared to previous generations. That might translate into a better, more flexible device which is what we've seen in clinical practice. The amount of drug used is less, yet achieving similar or better outcomes. Our ability to treat is enhanced. That's the reason we're embarking on trying to reach small vessel sizes. Until recently we couldn't."

"Abbott's Xience stent in 2.25 mm size received CE-mark approval in March and is available in the majority of European markets and select countries in Asia and Latin America," Jonathon Hamilton, a spokesman for Abbott Vascular, told MDD. "[The] SPIRIT Small Vessel trial is designed to study the 2.25 mm stent system in the U.S."

Abbott won FDA approval of the Xience V stent for the treatment of coronary artery disease in July, making it the second of the 2.0 family of drug-eluting stents to win marketing approval in the U.S. (MDD, July 8, 2008). Medtronic's (Minneapolis) Endeavor DES was the first second-generation DES to hit the U.S. market early this year (MDD, Feb. 4, 2008).

Both stents are expected to take over a market previously dominated by first-generation DES devices, such as the Cypher from Johnson & Johnson's (J&J; New Brunswick, New Jersey) Cordis (Miami Lakes, Florida) unit, and the Taxus from Boston Scientific (Natick, Massachusetts).

Having a smaller stent is good, but is it a more complex or dangerous procedure to access those smaller vessels?

"I wouldn't use the word 'dangerous,'" Costa said. "Usually smaller vessels are in more distant regions in the heart, so you have a longer way to get there. You have to navigate that road. To do that, you need better technology.

"The smaller size makes the procedure more fragile, so you have to be more delicate," he said. "It does require a careful technique."

Costa said the end goal of the procedure is to help patients gain better quality of life.

"For patients with symptoms and small vessel disease and no other options, this stent will offer an opportunity for therapy which we didn't [previously] have," he added.

The SPIRIT trial is designed to study 250 patients at about 50 U.S. centers. The primary endpoint is a composite measure of cardiac death, heart attack (target vessel myocardial infarction) and target lesion revascularization (repeat procedures on the treated vessel) at one year.

Observational data supporting the safety and efficacy of Xience V in the treatment of disease in small vessels was presented at the Transcatheter Cardiovascular Therapeutics scientific symposium in Washington this past October. James Hermiller, MD, director of cardiac cath labs for The Care Group at St. Vincent Hospital (Indianapolis), and an investigator of the SPIRIT III trial, presented subgroup data from the SPIRIT III trial comparing Xience V to the Taxus Express2 system in patients with small vessels.

In this subgroup analysis, patients were treated with a 2.5 mm stent system and had an average reference vessel diameter of 2.36 mm.

"In the SPIRIT III subgroup analysis, Xience V performed extremely well in small vessels. Compared to Taxus, Xience V reduced in-stent late loss, or vessel re-narrowing, by 80% eight months after the procedure, and reduced major adverse cardiac events by 74% at nine months," Hermiller said. "When you consider these trends, the availability of a smaller Xience V stent system specifically designed to treat lesions in small vessels has the potential to significantly improve patient care."

Following FDA approval, Abbott's 2.25 mm stent will be called Xience Nano. When asked what is nanoscale about the Xience Nano or how it was fabricated, Hamilton said the name simply "reflects the indication to treat small vessels as Abbott's smallest-diameter drug-eluting stent."

"It's much smaller than first-generation drug-eluting stents, but I'm not aware of the use of nanotechnology or nanoparticles in the development of Xience," Costa said.

The inclination to associate products with nanotechnology is growing, as is the field. A variety of products on the market, such as Apple's iPod Nano, are using the term nano even though nanotechnology wasn't used to develop it and the product isn't nanosized.

There are, however, more than 150 med-tech products currently in development that incorporate nanotechnology in a rapidly emerging medical device subsector.

(MDD Nanotechnology R&D Report 2009 reports on activity in the nanotechnology sector. For more information, call 800-688-2421 or 404-262-5476.)