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Drug Eluting Stents
A Brief History of Stenting
The concept of the stent grew directly out of interventional cardiologists' experience with angioplasty balloons in the first decade of use (1977-87). Although the artery would be opened successfully using a balloon, in a significant number of cases, the artery would collapse after the balloon was deflated - sometimes this might not happen until the patient had been moved to the recovery room. Since there was no interventional "fix" available, the only option for this patient was emergency bypass graft surgery to repair the problem

The Dilemma of Restenosis
  A second problem soon became evident as well. Approximately 30% of all coronary arteries began to close up again after balloon angioplasty. By the mid-80's various cardiologists were working on solutions to these problems, designing new devices in hopes they would provide more safety and durability to the procedures. Lasers, tiny "shavers", rotational "polishers" - many tools were miniaturized to be delivered via catheter.
The First Stents
One such device was the stent -- a metal tube or "scaffold" that was inserted after balloon angioplasty. The stent itself was mounted on a balloon and could be opened once inside the coronary artery. Julio Palmaz and Richard Schatz were working on such a stent in the United States; others in Europe were developing their own designs. In 1986, working in Toulouse, France, Jacques Puel and Ulrich Sigwart implanted the first stent into a human coronary artery. In 1994 the first stent was approved for use in the United States. Over the next decade, several generations of bare metal stents were developed, with each succeeding one being more flexible and easier to deliver to the narrowing.
A Persistent Problem
But while stents virtually eliminated many of the complications of abrupt artery closure, restenosis persisted. Although the rates were somewhat lower, metal stents still experienced reblocking (typically at six-months) in about 25% of cases, necessitating a repeat procedure. The interventional cardiology community also learned that restenosis, rather than being a recurrence of coronary artery disease, actually was the body's response to "controlled injury" of angioplasty and was characterized by growth of smooth muscle cells -roughly analogous to a scar forming over an injury.
Development of Coated and Drug-Eluting Stents
The solution moved away from the purely mechanical devices of the 90's and toward pharmacologic advances that were being made. If interventional medicine, using the body's circulatory system as a "highway" to deliver therapy, worked with devices, it could also work with medicines. Cardiologists and companies began testing a variety of drugs that were known to interrupt the biological processes that caused restenosis. Stents were coated with these drugs.
Drug-Eluting Stent Basics
Sometimes referred to as a "coated" or "medicated" stent, a drug-eluting stent is a normal metal stent that has been coated with a pharmacologic agent (drug) that is known to interfere with the process of restenosis (reblocking). Restenosis has a number of causes; it is a very complex process and the solution to its prevention is equally complex. However, in the data gathered so far, the drug-eluting stent has been extremely successful in reducing restenosis from the 15-30% seen with bare metal stents, to single digits with drug eluting stent.
There are three major components to a drug-eluting stent:
  • Type of stent that carries the drug coating
  • Method by which the drug is delivered (eluted) by the coating to the arterial wall (polymeric or other)
  • The drug with which the stent is coated.
In addition, there are several decisions made by the interventional cardiologist that result in a successful placement:
  • Correct sizing of the stent length to match the length of the lesion, or blocked area
  • Correct sizing of the stent diameter to match the thickness of the healthy part of the artery with successful deployment of the stent, making sure that the stent, once placed at the optimum site in the blocked artery, is expanded fully to the arterial wall.

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