Restenosis
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Despite increased sophistication of medical technology to treat heart disease, there remains dramatic room for improvement. From bypass surgery to balloon angioplasty to stenting, the Achilles' heel of all these procedures continues to be the struggle to keep arteries open. Scar tissue often overgrows inside the vessel, leading to a blockage (restenosis) that prevents blood flow to the heart. In gaining a better understanding of heart disease, its current treatments (and drawbacks), one can appreciate the significance of Angiotech's landmark technology - its drug-eluting stents - and the broader applications of this technology.
Restenosis is the re-narrowing of the blood vessel, thereby restricting blood flow. This re-narrowing can be caused by the vessel's response to an injury inflicted during balloon angioplasty.
Small tears develop in the artery wall (A) when the balloon catheter is inflated, initiating an inflammatory cascade, a natural healing response. Platelets and white blood cells from the blood migrate into the injured intima (inner layer of the vessel) (B). Signals stimulate smooth muscle cells (cells from the wall of the artery) to migrate and divide, in an attempt to repair the wound. This process is enabled by the white blood cells releasing and activating tissue-digesting enzymes, forming a path for the smooth muscle cells to move. The dividing and migrating cells can go on to form an overgrown, obstructing scar (C). As the amount of scar develops, blood flow is gradually reduced, leading to a heart attack. The failure rate of angioplasty ranges from approximately 25 to 40 percent.
In-Stent Restenosis
Although bare metal stents have become popular over the past decade, by demonstrating a clear benefit in treating heart disease when compared to balloon angioplasty alone, they can still carry a failure rate of over 25 percent.
In-stent restenosis is the result of a failed bare metal stent. An uncontrollable amount of scar has overgrown, burying the stent and compromising blood flow.