Since tissue plasminogen activator (tPA) was approved by the Food and Drug Administration in 1996 for the dissolution of blood clots in the brain that cause strokes, it has been the primary treatment for stroke victims. But it has several limitations. In most cases, it must be used within three hours after the stroke to be effective, although in some cases the crucial window can be extended to 4.5 hours. It is also often not effective in dissolving larger blood clots.
On 2004, the FDA approved the first mechanical system for removing clots from the brain, the Merci Retrieval System. In this approach, a corkscrew-like wire is threaded through the vascular system from the groin to the brain, where the wire is screwed into the clot. When the retriever is removed, it takes the clot with it. The device can be used after the initial three-hour window and with larger clots, but surgeons have concluded that it still leaves much to be desired.
Two new systems address those issues. Both are expandable wire-mesh systems much like the wire stents that are used to hold blood vessels open after balloon angioplasty. The collapsed mesh is threaded through blood vessels to the site of the clot, where it is opened and moved forward to engulf the clot. It is then collapsed again and withdrawn, taking the clot with it.
Two new studies released this week in the journal Lancet and at the European Society of Cardiology Congress in Munich show that both devices are more effective and safer than the Merci device.
The first device, the Solitaire Flow Restoration Device, was developed at UCLA and is now marketed by Covidien of Mansfield, Mass. A team headed by Dr. Jeffrey L. Saver of the UCLA Stroke Center studied 113 stroke patients at 18 hospitals. The patients were randomly assigned to receive treatment with either the Solitaire or Merci devices within eight hours of stroke onset. Forty percent of the patients had not improved with tPA therapy, while the rest had not received it.
Saver and colleagues reported that, three months after treatment, 58% of those treated with the Solitaire device were assessed as having a good neurological outcome, compared to 33% of those treated with the Merci device; 17% of those treated with Solitaire died, compared to 38% of those treated with the Merci device. "We are going from our first generation of clot-removing procedures, which were only moderately good in reopening target arteries, to now having a highly effective tool," Saver said.
The second, similar device is Trevo, marketed by Stryker Neurovascular of Kalamazoo, Mich., which also sells the Merci device. A team headed by Dr. Raul Nogueira of the Marcus Stroke and Neuroscience Center at the Emory University School of Medicine in Atlanta studied 178 patients with large blood clots at 26 U.S. centers and one in Spain, comparing the Trevo device to the Merci device within 8 hours after stroke onset. They reported that 40% of the patients treated with the Trevo device had a fully independent life after treatment, compared to 22% of those treated with the Merci device. Fifteen percent of the patients treated with Trevo had an adverse event, compared to 23% in the Merci group.
Both devices have been approved by the Food and Drug Administration for clinical use in the United States.
In an editorial accompanying the Lancet articles, Dr. Philip Gorelick of the Hauenstein Neuroscience Center in Grand Rapids, Mich., noted that the two studies "are major steps forward in the successful treatment of acute ischemic stroke, and pave the way for new treatment options and further validation by additional trials."