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March 24, 2009 -- 1:55pm EDT

Is The Scaffolding Coming Down?
Today's good news about Abbott's bioabsorbable stent brings the following analogy to mind.

Scaffolding on Building

A stent is often described as a "scaffold" inside the artery. Indeed, in the era of POBA (Plain Ol' Balloon Angioplasty) elastic recoil of the arterial plaque could reblock the freshly-opened artery, or the ragged interior surface left after the balloon fractured the plaque would lead to increased rates of restenosis.

So angioplasty pioneers developed the stent, a scaffold to hold the artery open. Recoil virtually disappeared. Abrupt closure, which led to emergency CABG 3-5% of the time, was reduced by a factor of 20. And while stents reduced restenosis, these devices produced their own unique brand of complications.

Scaffolding in Artery

Unlike their construction counterpart, scaffolding inside the artery cannot be removed when the job is finished. Metal stents are permanent. They (hopefully) get covered over by endothelial cells and are incorporated into the lining of the artery, but cell growth can occur inside the stent, reblocking the blood flow (in-stent restenosis) or in the case of drug-eluting stents, the endothelial healing can be delayed, causing platelets to aggregate around the bare metal structure, causing a blood clot and possible heart attack (late stent thrombosis).

These complications are small in number (very small in the case of late stent thrombosis) but they complicate what should be a simple task. Fix the arterial wall until it heals and then "Take Down The Scaffolding!"

There's also the issue of the "straight-jacket", as Dr. Charles Simonton of Abbott calls it. A metal stent must, by its presence, restrict the normal natural flexibility of the coronary artery (which is beating and moving all the time). Certainly the newer stents with thinner struts are better, but patients with 7, 8 or more stents can get into the realm of what's called a "full-metal jacket". And too much metal can compromise future therapy as well -- bypass surgery, for example.

Enter (or exit!) the bioabsorbable stent. As recent results have shown, the stent, having done its job, disappears after two years. Normal motion is restored to the artery which, in many ways, acts like it did before the stent was placed, except that the blockage is gone.

These are, of course, hopes. The early trial was only 30 patients. Abbott announced a second phase today which will bring the total to 110. All agree that larger trials with more patients and more complex anatomy must be done. All also agree that this technology, if it proves as safe and effective as the small trial, could revolutionize the treatment of coronary artery disease yet again.

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