Bioabsorbable Magnesium Stent Shows Short Term Efficacy But Lacks Legs

ESSEN, Germany, June 1 -- An investigational bioabsorbable magnesium coronary stent worked as advertised for several months but led to a higher revascularization rate at one year.

It effectively enlarged lumen diameter in de novo coronary lesions, completely degraded within four months, and yielded no evidence of stent thrombosis, reported Raimund Erbel, M.D., of the West German Heart Center, and colleagues, in the June 2 issue of The Lancet.

But at one year the target lesion revascularization rate was almost six times higher than the rate reported for drug-eluting stents and almost twice the revascularization rate reported with bare metal stents, according to results of the PROGRESS-AMS trial.

Ischemia-driven target lesion revascularization rate at four months was 23.8% and at one year the overall target lesion revascularization rate was 45%. The comparable historical one-year revascularization rate is 28% for bare metal stents and 6% for drug-eluting stents.

Likewise, in-stent late lumen loss was 1.08 mm versus average rates of 0.85 mm for bare metal stents and 0.10 to 0.20 for drug eluting stents in published trials.

Nonetheless, the early improvement in diameter stenosis and the lack of toxicity associated with the degrading process, suggest support for continued development with modifications to lengthen degrading time and incorporate drug eluting technology, concluded Dr. Erbel and colleagues.

Although promising, the magnesium stent also was not as effective as a bioabsorbable everolimus-eluting coronary stent tested in 26 patients.

At the American College of Cardiology meeting in March, Patrick Serruys, M.D., Ph.D., of Thoraxcenter-Erasmus University in Rotterdam, reported that the everolimus-eluting biodegradable stent had a late loss of 0.44 mm at six months and a restenosis rate of 11.5%.

In an editorial that accompanied the Lancet study, John Ormiston, M.D., and Mark Webster, M.D., of Mercy Angiography and Auckland City Hospital in Auckland, New Zealand, wrote that the mechanism of restenosis with the magnesium stent-"excessive healing response" contributing to chronic wall recoil-was similar to that seen with balloon angioplasty.

"The current magnesium stent might be absorbed too quickly (in weeks), so that the artery is not supported for long enough to prevent negative remodeling. If these problems are resolved by slower stent absorption, the excessive healing response could be limited by the controlled release from the stent of an antiproliferative drug," Dr. Ormiston and Dr. Webster wrote.

The PROGRESS-AMS (Clinical Performance and angiographic Results of Coronary Stenting with Absorbable Metal Stents) trial enrolled 63 patients mean age 61 at eight participating centers in the United States and Europe.

Forty-four of the patients were men. Angiographic and intravascular ultrasound follow-up were conducted at four months and clinical assessment was done at six months and 12 months.

The primary endpoint was cardiac death, non-fatal myocardial infarction, or clinically driven target lesion revascularization at four months.

Among the findings:

• Seventy-one stents-10-15 mm in length and 3.0 to 3.5 mm in diameter-were implanted following successful pre-dilatation.
• Diameter restenosis was reduced from 61.5% to 12.6% with an average acute gain of 1.41 mm.
• The absence of residual metal was confirmed by intravascular ultrasound at four months.

The authors concluded that the "absence of a rigid cage inside the vessel after absorption is expected to restore vasomotion, and is the target of an ongoing study."