Updates on bioabsorbable stents: ABSORB and PROGRESS-AMS trials

Shelley Wood

May 31, 2007

Barcelona, Spain and London, UK - Updates from bioabsorbable-stent trials suggest that investigators are making incremental improvements to devices that might one day be used for coronary revascularization procedures and then dissolve when their job is done. But there are hurdles ahead.

At last week's EuroPCR2007 meeting in Barcelona, Dr Darius Dudek (Institute of Cardiology, Jagiellonian University, Krakow, Poland) presented nine-month clinical results from the ABSORB trial using Abbott's bioabsorbable everolimus-eluting stent, known as the BVS stent; in this week's Lancet, Dr Raimund Erbel (University Clinic, Essen, Germany) and colleagues report four-month angiographic and 12-month clinical results for the PROGRESS-AMS trial of Biotronik's absorbable magnesium stent[1].

ABSORB nine-month clinical results

Dudek's EuroPCR presentation updated the results that Dr Patrick Serruys (Thoraxcenter, Rotterdam, the Netherlands) presented earlier this year at the American College of Cardiology (ACC) 2007 Scientific Sessions, as reported by heart wire . In all, 26 patients at one of six centers were treated with the poly-L-lactic-acid BVS stent, which also boasts a bioabsorbable polymer for drug elution. At six months, as previously reported, in-stent late loss was 0.44 mm, a finding that Dudek attributed to bioactive remodeling or mechanical late recoil. Promisingly, however, as of nine months there have been no additional major adverse cardiovascular events (MACE) since the six-month follow-up reported at the ACC. At that time, there had been one non-ST-elevation MI requiring a single target lesion revascularization (TLR), but no ischemia-driven TLR subsequently.

During his EuroPCR presentation, Dudek explained how the BVS stent is being redesigned in the hopes of chipping away at late-loss results and reducing the need for TLR: the stent material and thickness will remain the same, but the new overall design will have a more uniform strut distribution, permitting more even support of the arterial wall and a lower maximum circular unsupported surface area.

PROGRESS-AMS published

Results from PROGRESS-AMS appearing in the June 2, 2007 issue of the Lancet update and expand upon the early clinical data presented at the ACC i2 Summit in March 2007. As Erbel et al report, MACE, defined as cardiac death, nonfatal MI, or clinically driven TLR (the primary end point of the study), in the 63 patients who received the non-drug-eluting magnesium stent was 26.7% at 12 months, up from 23.8% at four months. Secondary end points, however, included all target vessel and target lesion revascularizations (some of which were not ischemia-driven), plus standard angiographic end points at four months. As such, overall TLR rates were high, while angiographic results at four months, in the words of Drs John Ormiston and Mark Webster (Mercy Angiography and Auckland City Hospital, New Zealand), in an accompanying Comment, approached rates "similar to, or higher than, those reported with balloon angioplasty alone"[2].

Clinical and angiographic results with the magnesium stent

End point Rate
4-mo TLR (%) 39.7
12-mo TLR (%) 45.0
4-mo diameter stenosis (%)* 48.37
4-mo binary restenosis (%) 47.5
4-mo late-loss (mm)* 1.08

Investigators say the study results suggest that absorbable magnesium stents can indeed be delivered and expanded at high pressure and provide support/lumen gain similar to that seen with metal stents, while the lack of ischemic episodes suggests that the stents do not embolize as they dissolve but rather are absorbed into the vessel wall, the authors write.

In their Comment, Ormiston and Webster suggest that arterial lumen renarrowing is likely due in part to shrinking of the vessel (negative remodeling) and partly an excessive healing response similar to that seen following 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," they hypothesize. "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."

Erbel and colleagues concede that the current version of the stent requires "further development" but the early results underscore the safety and feasibility of the device.



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