Drug-eluting stent (DES) technology is the current state of the art in propping open, and keeping open, coronary and peripheral vessels. But DES doesn't equal the "Holy Grail" in treating restenosis. That goal most likely will be achieved with a stent device that, after placement, disappears from the vasculature, leaving in place no material that is foreign to the body.
Details concerning a version of such a stent were unveiled at last month's 17th annual International Symposium on Endovascular Therapy (ISET) in Miami Beach, Florida.
The product is the Lekton Magnesium Bioabsorbable Metal Stent from Biotronik (Berlin, Germany), with Belgian researchers presenting data concerning its use in treating blocked lower leg arteries. The Lekton is an absorbable bare-metal stent made of an alloy of 90% magnesium a substance that occurs naturally in the body and 10% rare earth elements. Bioabsorption begins in a week to 10 days after implantation, and tests have shown the stent is fully absorbed within 60 days, according to Marc Bosiers, MD, lead author of the study presented at ISET.
Typically, about 60% of narrowed below-the-knee arteries treated with standard stents remain open after six months, said Bosiers, head of the department of vas-cular surgery at A.Z. Sint-Blasius Hospital (Dendermonde, Belgium). Lekton stents were implanted to treat 20 patients who suffered with severely blocked arteries below the knees. Six months after treatment, 15 of 19 arteries (79%) remained open. One patient died of pneumonia unrelated to the procedure.
The stents were completely absorbed into the walls of the vessels without freeing particles into the bloodstream, Bosiers said. The absorption, he said, actually begins with implantation, with the body immediately beginning to cover it with a layer of cells.
Bosiers said the Lekton is the first biosabsorbable metal stent tested in humans. He acknowledged that an absorbable polymer stent has been implanted in humans but said it doesn't appear to be as effective for propping open the arteries as a metal device. "A stent is really only needed for a couple of weeks, to allow the blood vessel to reshape and get strong, and after that time it is useless," Bosiers said. "We believe the absorbable metal stent could be a major breakthrough, because it provides a temporary solution to a temporary problem."
Koen DeLoose, a co-investigator in the study, told Cardiovascular Device Update that the next step in the group's research is the launch of a randomized study of 120 patients to compare the use of percutaneous intervention against the Lekton absorbable metal stent. "If results are as promising [in the larger study] as our results, at this moment, on our 20 patients," it will clearly support commercialization, he said.
DeLoose acknowledged the preliminary nature of the 20-patient study, but said, "at this moment, [the absorbable stent] looks very promising." He added: "When in the future it is possible to make a combination drug-eluting/absorbable stent, in my opinion it is the absolute future for small-artery treatments." While he granted the need for such a stent in larger vessels, such as coronary arteries, he said that "the problem of restenosis is most important in arteries below the knee. The key point is to prove [the Lekton's] value in small-caliber vessels."
At last October's annual Transcatheter Cardiovascular Therapeutics (TCT) conference in Washington, Biotronik released preliminary positive data for the Lekton in treating blocked coronary arteries in a 65-patient trial, noting 50% absorption of the stent in all patients after three weeks. Study results should be released sometime this year, with larger studies also to be launched in both the U.S. and Europe this year, Biotronik said at the TCT gathering.
CryoPlasty treats blocked leg arteries
Fully 100% of people facing almost certain amputation were successfully treated with a new non-surgical therapy that cools and opens leg arteries clogged with plaque, according to preliminary data on 22 patients presented at ISET. First available in August to treat patients with arteries that are blocked below the knee, the new CryoPlasty therapy is now offered at nearly 800 sites in the U.S., including most major hospitals. The therapy is delivered by the PolarCath System developed by CryoVascular Systems (Los Gatos, California).
CryoPlasty therapy offers hope to people with lower leg arteries severely blocked as a result of peripheral arterial disease (PAD). These blockages, common in diabetic patients, can put people at risk for infection, leg ulcers, gangrene and amputation, the company said. PAD affects about 10 million people in the U.S. and is a strong risk factor for other cardiovascular diseases, including heart attack or stroke. CryoPlasty fits into the treatment spectrum before the use of angioplasty and appears to avoid some of the complications seen in that procedure, researchers said. It also can be used to treat other vessels affected by PAD, including arteries in the thighs and abdomen.
"Previously, amputation was the only option for some people with such advanced disease in arteries below the knee, many of whom are diabetic," said James Joye, DO, director of the cardiac catheterization lab at El Camino Hospital (Mountain View, California), and co-inventor of the CryoPlasty technique. "CryoPlasty is a 'no harm' treatment that offers early, conservative management and can be used repeatedly not only avoiding or delaying amputation, but postponing the use of more invasive procedures."
The data presented by Joye at ISET are the first results from Below the Knee Chill, an ongoing multi-center study at 30 hospitals across the U.S., which will enroll 100 patients likely facing amputation of a foot or leg within six months. All of the patients in the study have critical limb ischemia, causing extremely poor blood flow. Treatment in all 22 patients resulted in procedural success, defined as artery blockages (stenoses) being 50% or less after CryoPlasty therapy. After treatment, the average blockage was 19%, compared to 87% before treatment. Immediately after the procedure, ankle or toe pulses improved in 17 of 20 patients (85%), meaning blood flow increased. Pulses were not measured in two patients. There were no procedural complications or adverse events. Other data, on 102 patients who received CryoPlasty therapy to treat blocked upper leg or knee arteries, have shown 83% of the arteries still open after nine months, compared to the typical rate of 59% of blocked blood vessels treated with traditional angioplasty remaining open after one year, and 89% of people reported an improvement in leg pain while walking.
CryoPlasty therapy involves the use of nitrous oxide, rather than saline, to inflate the balloon and cool it to -10 degrees. This in turn prompts several physical responses that open the artery and cause less scarring than occurs with traditional angioplasty. Repeat procedures for patients treated with standard balloon angioplasty and stent technology of the arteries below the knee are reported as high as 45%. The below-the-knee CryoPlasty procedure is performed using one of several new smaller-sized catheters, which received clearance from the FDA.
"While this is a relatively new technology, the process is very familiar to physicians who perform angioplasty, and its use is rapidly spreading in hospitals across the country," according to Joye.
CryoVascular Systems has a partnership with Boston Scientific (Natick, Massachusetts) to distribute the PolarCath System globally.
Other studies presented at ISET
Frank Veith, MD, professor and vice chairman of the department of surgery at Albert Einstein College of Medicine (Bronx, New York), presented data demonstrating the successful use of a minimally invasive alternative to open surgery to repair aortic aneurysms. The data covered 476 patients worldwide who received endovascular repair for burst aneurysms, of whom 385 survived and the remainder (19%) died. This compares to an average of 40% to 50% typically who die when open surgery is used to treat a ruptured aortic aneurysm. He also reported on 37 patients treated with the endograft endovascular system at Montefiore Medical Center (New York), where he holds the William J. von Liebig Chair in vascular surgery. Of these, five (15%) died.
Veith emphasized that endograft repair avoids many risks of surgical repair, which involves making a large chest incision and replacing the weakened portion of the aorta with a graft. The risks involve greatly increased blood flow, dangerously decreased body temperature and potential injury to other organs. "Before and during endograft repair, we allow the patient's blood pressure to fall to low levels by restricting fluid resuscitation. This limits the bleeding, and we have found this approach which we call hypotensive hemostasis to be very effective," he said. Veith estimated that "as many as two-thirds of people who need treatment for a ruptured aortic aneurysm could be candidates" for the endovascular surgery as opposed to open surgery.
Endologix (Irvine, California) reported clinical data suggesting that three years following treatment of abdominal aortic aneurysm (AAA) with the company's Powerlink System, patients from a premarket application study experienced decreases in aneurysm sac diameter and volume, and less angulation of the aorta. The paper was presented by Rodney White, MD, professor of vascular surgery at Harbor-UCLA Medical Center (Torrance, California).
"These results are based on our retrospective study that investigated changes in aneurysm sac anatomy, including maximum diameter of the aneurysm, volume of the aneurysm sac, length from the renal arteries to the aortic bifurcation and angulation of the abdominal aorta, during a three-year period in patients treated with a Powerlink System," said White. "The design features of the Powerlink device, including its long main body and single-wire stent cage that provide for column strength, may positively influence the aortic sac remodeling that we found during this study."
Endologix received approval last October to mar-ket the Powerlink in the U.S. Paul McCormick, president and CEO, said, "In spite of the success of minimally invasive treatment of AAA, there remain 50,000 to 60,000 patients who still undergo the traditional surgery, many due to concerns about the long-term results of the stent graft procedure itself. With our Powerlink System, we are addressing the failings of first-generation endoluminal stent grafts in deliverability of the device, dependability of the clinical results and durability of the materials."