Are biodegradable stents the answer?

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The 12-month results of the BEST-BTK study for Biotronik’s revolutionary new absorbable metal stent (AMS) were presented in January. The results, in terms of primary clinical patency and limb salvage, indicate that the AMS performanced well in the treatment of below the knee lesions in patients with critical limb ischemia.

Commenting on the results the President of the Congress for the Friedrich Olbert workshop, Johannes Lammer, described the absorbable metal stent technology “as a major step forward” and “almost as important as the Palmaz stent”. “If in a 1000 years people were to open up our patients and see all this metal, they might see it as some kind of torture.” However, Dr Lammer also emphasized that more work is needed. “This is the first study. We need larger studies versus PTA in a large group of patients.”

In his presentation on the concept behind this absorbable metal stent technology, Lammer indicated that such a temporary stent could take away the main negatives of using stents which cause neointimal hyperplasia, but still provide the main function of a stent – to prevent elastic vessel recoil (see figure 1).

“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,” said Marc Bosiers, M.D., lead author of the study and head of the Department of Vascular Surgery at A.Z. Sint-Blasius Hospital, Dendermonde, Belgium. “We believe the absorbable metal stent could be a major breakthrough, because it provides a temporary solution to a temporary problem. This is the first bioabsorbable metal stent tested in humans. An absorbable polymer stent has been tested in humans, but doesn’t appear to be as effective as the metal stent in propping open the artery.”The absorbable metal stent is made of an alloy of 90% magnesium (a substance that occurs naturally in the body) and 10% rare earth elements. The absorption process begins within a week to 10 days, and tests have shown the stent is fully absorbed within 60 days, Bosiers said.

The metal stent is completely absorbed into the vessel wall without freeing particles into the blood stream. As soon as the stent is in place, the body begins to cover it with a layer of cells. Once that has occurred, the vessel wall begins absorbing the stent.

From December 2003 to January 2004, 20 patients with Rutherford category 4 or 5 have been treated with AMS as an approach to treat their BTK lesions.

The study included 20 patients with Rutherford category 4 or 5 who received absorbable metal stents to treat severely blocked arteries below the knee. Immediate procedural success, post-procedural vessel run-off and good stent positioning were confirmed by angiography and IVUS. At discharge, 1, 3, and 6-month post-procedure Rutherford category evaluation, duplex ultrasound and blood sample parameter analysis were performed.

“One patient died of pneumonia unrelated to the procedure. Six months after treatment, 15 of 19 arteries (79%) remained open. Typically, about 60% of narrowed below-the-knee arteries treated with standard stents remain open after six months”, said Bosiers. Angiographic procedural success was maintained in all 20 patients. Post-procedural IVUS control confirmed homogenous and complete inflation in all patients. The limited stent visibility under fluoroscopy did not cause any procedural complications. Twelve month post-procedure primary clinical patency rate was 72.4% as (secondary patency was 78.9%) shown on duplex ultrasound. In one case, amputation of the treated limb was necessary, yielding a 12-month limb salvage rate of 94.7%. Comparison of post-procedure and 1-month duplex ultrasound and magnetic resonance images clearly indicated the ongoing absorption process of the AMS. No patient showed any symptoms of allergic of toxic reactions to the stent material.

Researchers have also begun testing the absorbable stents in the coronary arteries and expect to have results later this year. Co-authors of the study Bosiers, Koen Deloose, Patrick Peeters and Jurgen Verbist. Jeroen Hendriks presented the 12-month results of the BEST-BTK study at the Friedrich Olbert workshop on behalf of Marc Bosiers, who could not attend. The following week Koen Deloose presented the study results at ISET in Miami.

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