Published On May 7, 2015
Each year, nearly 800,000 Americans suffer a stroke, the majority of which are caused by a clot blocking blood flow to the brain. Several therapies in the past two decades have led to advances in treatment, but none has made quite the splash as a recently adopted “stent retriever” method for eliminating clots quickly and safely. Lee H. Schwamm, executive vice-chairman of the department of neurology at Massachusetts General Hospital, explains how this technology may change stroke care.
Q: How have strokes historically been treated?
A: Since 1996, neurologists have prescribed a drug called tPA (tissue plasminogen activator) for stroke patients. Using tPA is like pouring Liquid Plumber in your drain—when there is a small clog it works great, but unfortunately when there is a big clog you have to call the Roto-Rooter guy. It was also discovered that tPA can only be administered within a time window of about three hours.
Then about a decade ago, we started using a series of wires and catheters to engage the clot. That reopened arteries nearly 70% of the time, compared with 30% to 40% after tPA. But we still weren’t preventing disabilities in any more patients. And the reason is most likely that physicians just couldn’t do the procedure quickly or effectively enough.
Q: What is a stent retriever, and how does it help?
A: It’s similar to the stents inserted to prop open clogged arteries in the heart, but used for a slightly different purpose. Instead of leaving the stent in the artery, the physician sticks the stent into the middle of the clot, pops it open and then removes the clot with the stent.
Q: What makes that such a breakthrough technology?
A: It accomplishes three important things. First, it fully engages the clot—this stent gets stuck in the middle of the clot like a slinky in a big piece of chewing gum. And because of that it has a very high success rate, removing the clot more than 80% of the time.
Second, popping the stent open re-creates a smaller channel inside the blood vessel by creating a hole in the clot, allowing fresh blood to restore equilibrium to the cells on the other side. So you don’t have to wait until the end of the procedure to start getting blood flow back to the brain. It happens right away.
Lastly, this procedure can be done using an intravenous sedative instead of general anesthesia (where the patient is paralyzed, put to sleep and a breathing tube is put in). For this time-sensitive condition, using the IV sedative allows the treatment to start faster and end quicker. It also reduces exposure of the injured brain to anesthetic agents, which we are starting to believe might be harmful.
Q: How has this performed in clinical studies?
A: When tPA is given within the first three hours of stroke, the absolute benefit—a research term comparing the percentage difference in how many patients are disability-free patients after the treatment compared with those who didn’t get it—is around 14%.
Here at MGH we have been using stent retriever technology and its predecessor devices, all Food and Drug Administration approved, for many years. The results from recent studies show that patients who are treated with this approach after tPA fails to fully dissolve the clot do better than those who do not undergo the stent retriever procedure by an absolute benefit of close to 25%, even up to six hours after stroke. That’s a shocking degree of benefit. We don’t have very many treatments in medicine that have an absolute benefit that large.