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Cardiologists in USA, Europe more willing to use bioabsorbable stents than those in Japan, Latin America

Cardiologists in USA, Europe more willing to use bioabsorbable stents than those in Japan, Latin America

Majority of cardiologists in USA, Europe, China, India, Middle East and Africa would use a bioabsorbable stent for the treatment of coronary angioplasty. In contrast, majority of cardiologist in Japan and Latin-America would not use a bioabsorbable stent, as per a report released by iData Research on the interventional cardiology market. Bioabsorbable stents are expected to enter the European market by 2013 and the U.S. thereafter. The U.S. market is estimated to quickly reach almost US$750 mln with companies such as Abbott Laboratories, Biosensors International and REVA Medical emerging as leaders. The survey provided dramatic differences between geographical regions in usage trends of bioabsorbable, bifurcated and drug-eluting stents, stent-grafts and vulnerable plaque treatment. Cardiologists in the U.S. and Europe are more willing to use new technologies such as bifurcated and bioabsorbable stents, while Japanese and Latin American cardiologists are more resistant, citing the lack of long-term clinical data, early recoil and technical challenges as drawbacks to these technologies. The U.S. market for interventional cardiology is expected to reach almost US$5 bln by 2017, with increasing drug-eluting stent sales and the emergence of bioabsorbable and bifurcated stents fueling market growth. Development of a bioabsorbable stent would obviate the permanent metal implant in vessels. Bioabsorbable stents would allow late expansive luminal and vessel remodeling in the absence of a metallic cage and leave only healed native vessel tissue after the full absorption of the stent. This could reduce surgical procedures to remove implanted devices, and could perhaps reduce the possibility for additional interventions at sites of device implantation without concerns for the generation of jailed side-branches. Consequently, the lack of a foreign object in the body might reduce the risk of potential long-term complications and of late thrombosis, and would facilitate non-invasive diagnostic MRI/CT imaging. Bioabsorbable materials are an exciting class of compounds due to their ability to be absorbed by the body over time. This allows the lifetime of a stent to be tailored to the clinical needs of a disease or condition. A material candidate for bioabsorbable stents should possess enough mechanical strength to hold open the blocked vessel and provide mechanical support without significant recoil, or bioactive remodeling. Candidates should also have a certain degree of fracture toughness to avoid cracks and broken struts. One other minimum requirement is that the degradation products are non-toxic. Materials that have potential use for bioabsorbable stent preparation include various biodegradable polyesters, polyanhydrides, poly(orthoesters), polyurethanes, poly(ether amides), poly(amino acids) and tyrosine-derived polycarbonates. Among these polymers, polyesters have been used in a wide range of medical devices with an astonishing number of different applications including bioabsorbable.
Coronary artery disease affects millions of Americans. It occurs when arteries are blocked or narrowed by cholesterol or plaque which reduces blood flow to the heart. It can lead to heart attacks. Currently minimally invasive procedures are used to unblock these arteries. One of the methods is to install a stent- a tiny wire mesh tube expanded in the damaged artery using a balloon catheter. After stent installation the balloon is deflated and removed which restores blood flow. Some stents deliver drugs to the artery which reduce the scar tissue formation. There are several bioabsorbable stents in development and in clinical trials. The stents are made from a variety of biodegradable polymer materials, such as organic biopolymers and corrodible metals. One of the first bioabsorbable stents, the Igaki-Tamai stent, used a poly-L-lactide polymer but was not coated with a drug and is no longer in development. Two other companies, Bioabsorbable Therapeutics and Reva Medical, are testing bioabsorbable stents coated with sirolimus and paclitaxel, respectively. The sirolimus-eluting stent uses a poly (anhydride ester) salicylic acid polymer, while the paclitaxel stent uses a poly desaminotyrosyl-trypsine ethyl ester polymer. A magnesium-alloy stent made by Biotronik, one that does not elute any drug, had been tested in the PROGRESS-AMS study, with results reported by heartwire. That first-generation stent was absorbed too quickly, losing radial strength, which resulted in high rates of restenosis. Several experts noted that the everolimus-eluting stent made by Abbott Vascular is furthest along in development. That stent, which also uses a poly-L-lactide polymer, was tested in the ABSORB trial, with lead investigator Dr Patrick Serruys and colleagues showing the feasibility of the device and the durability of its antirestenotic properties, at least over the first 12 months. Late loss and higher-than-expected restenosis rates, however, were believed to be caused by "shrinkage" of the stent, which led to some speculation that the bioabsorption rate might be occurring too fast for the necessary radial strength of the stent to keep restenosis at bay. Two-year imaging results showed that at least one-third of the stent has been absorbed by the vessel wall, a result reported by heartwire. Reva Medical Inc. (financially supported by Boston Scientific, Inc.) is developing a bioabsorbable drug eluting stent made from tyrosine-derived polycarbonate material and will start its clinical trial in 2007. Reva Medical utilizes a unique �slide and lock� geometry for its stent designs. When expanded, the stent elements slide from the compact state and lock into an expanded state, similar to safety lockouts on extension ladders. Thus, the expansion is not dependent on material deformation, and will provide steel-like scaffolding. The Reva stent is delivered by standard balloon deployment and is made radiopaque by a proprietary method. An example of this metal scaffold stent is Abbott�s Xience V everolimus eluting coronary stent system. A disadvantage of the metal stent is that it stays in your body for life. After the vessel heals and hardens the scaffold actually becomes a liability as it blocks X-rays and MRI and can form blood clots. Abbott is currently finishing up a 3 year trial for a bioresorbable stent, properly known as a bioresorbable vascular scaffold (BVS). This stent is made of the bioplastic PLA (poly-L-lactic acid) with an additional coating of a mix of a different kind of PLA (poly-D,L-lactic acid) and antiproliferative agent everolimus (a drug that prevents the formation of scar tissue). Over the course of time the stent is slowly reabsorbed by the body as the artery heals. This starts happening within the first 6 months.

Early clinical studies are encouraging and have shown that bioabsorbable stents, especially coronary bioabsorbable stents, offer potential to dramatically improve acute and long term results of percutaneous revascularization. Although more long-term beneficial outcomes in controlled clinical studies have yet to be demonstrated, it is anticipated that biodegradable stents offer the possibility for integration with local drug delivery, genetic transfer, and radiation. Furthermore, once proven, the use of drug/gene-loaded biodegradable stents in revascularization has enormous translational impact. Geometrically modified biodegradable implants can act as potential therapeutic carriers for treatment of diseases such as cancers, where specific tissue targeting and high local dosage possibilities could offer an alternative to conventional systemic therapies. The success of bioabsorbable stents applied in coronary arteries will also prompt the expansion to peripheral arteries, the urethra, trachea, esophagus and GI tract. One of the more speculative hypotheses with the bioabsorbable stents is that a stent that leaves nothing behind might prove useful in patients with vulnerable plaques/arteries. Rather than wait for the disease to advance to a stage of plaque rupture, some experts envision the stent as preventive, which would expand use of the stents to more and more patients.
 
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