By: Jean Johnson for Veins1
Leave to the Californians – opening a bottle of wine with a corkscrew one day and pioneering medical technology that uses a corkscrew device to removed blood clots from stroke patients the next.
Initial Trials Enjoy 54 Percent Success Rate
It didn’t happen over night, of course. It was in 1999 that researchers and entrepreneurs at Concentric Medical in Mountain View, California, first hung out their shingle. Then another five years elapsed until 2004 when the first report of their progress reached the American Stroke Association’s (ASA) 29th International Stroke Conference. By then, a device known as the Merci Retriever had been tested in preliminary investigative trials and demonstrated to be 54 percent effective in removing clots and reversing damage to the brain caused by ischemic stroke. More than 100 patients participated in these first trials.
An ischemic stroke occurs when a blood vessel feeding the brain – like a carotid artery – is blocked by a blood clot and the associated tissue is deprived of blood flow. Brain function deteriorates rapidly causing severe disability or death. Of the more than 700,000 strokes in the United States yearly, 85 percent are ischemic or caused by blood clots. Stroke is the leading cause of disability and the third leading cause of death in United States.
Why Time is Critical
“The analogy I use with patients is, you hit your hand with a hammer, and the injury is done, but you look at your hand and it looks the same, even if it hurts,” neurologist at the Yale School of Medicine, Lawrence M. Brass, M.D., told Newsweek. “But 48 hours later it’s black and blue and swollen.” Indeed, because tissue dies rapidly when deprived of blood flow, people who have had a stroke need timely medical intervention.
That’s why the anti-stroke drug, tPA which can dissolve clots if administered within the first three hours after a stroke (and the earlier the better) can help reverse the effects of stroke. Once that window of opportunity passes, however, the medical world has had little to offer patients. The Merci system has possibly extended this timeframe to eight hours, during which appropriate candidates can experience significant, and even dramatic, reversal of symptoms if they can reach physicians versed in the use of the technology.
“Our belief has been that restoring blood flow quickly is key in a devastating stroke,” said Gary Curtis, president and CEO of Concentric Medical. “Restoration of flow correlated with good outcomes for many of these patients. We are committed to changing the way in which ischemic stroke patients are treated and continue our efforts on newer generation devices.”
Merci Retriever Goes Global
Since 2004 approximately 200 centers throughout the world have used the Merci Retriever mechanical corkscrew-type system to treat an estimated 3,000 patients. The U.S. Food and Drug Administration has cleared the device for testing.
“How often do we get a chance to reverse a patient’s stroke on the table?” said Sidney Starkman, M.D., professor of emergency medicine and neurology at the University of California, Los Angeles and co-director of the UCLA Stroke Center who helped present the first report of Merci Retriever to the ASA. “We have had patients completely paralyzed on one side of their body, who were made normal almost instantaneously when the clot was retrieved.”
One hundred and fourteen patients participated in the pre-2004 trials on which Starkman reported. Of the 61 patients whose arteries were unblocked with the device, he noted that “23 have no disability or have minor disability such as hand writing problems.”
How It Works
For the techies in the crowd, the Merci Retriever is used in conjunction with a microcatheter and balloon-guided catheter. The balloon-guided catheter is inserted in the femoral artery in the groin, and using guided imaging circulation experts maneuver the spaghetti-sized line through the body to the site just beyond the clot. Then the physician deploys the Merci Retriever device to engage and ensnare the clot. Once the clot is captured, the Merci balloon-guided catheter is inflated to temporarily arrest forward flow while the clot is being withdrawn. The clot is pulled into the balloon-guided catheter and completely out of the body. The balloon is then deflated, and blood flow is restored.
Since the 2004 trial, Concentric Medical has sponsored further clinical trials and evidence has mounted that its system has application for a range of stroke patients.
“These interim results offer further support of the Merci Retriever’s ability to safely restore blood flow for these patients with devastating strokes, including those patients where prior clot dissolving drug treatment (IV tPA) was not effective,” principal investigator of one trial and associate professor of neurology at the University of California, San Francisco, Wade Smith, M.D., PhD, told attendees at the International Stroke Conference in Florida in February 2006.
“This restoration of flow provides them with the potential of favorable clinical outcomes and over a third of these patients are not living functionally independent lives,” added Smith.
Concentric Medical has not rested on its laurels solely in California, though, and expectedly the progressive and innovative Swedes have entered into the action. In May 2006 Concentric Medical joined forces with the SITS (Safe Implementation of Thrombolysis in Stroke) Network, an academic-drive, non-profit, international collaboration covering more than 500 stroke centers in 30 countries. The collaboration of private, academic, and professional partners is undertaking a study called THRUST (Thrombectomy in Unsuccessful Stroke Thrombolysis).
Nils G. Wahlgren, M.D., PhD, professor in Stockholm and chairman of SITS International, said: “The THRUST study is an important step in providing practitioners with additional treatments in stroke. There has been a high interest from members within the SITS Network to participate which shows the importance of the study.”
Meanwhile Concentric Medical has continued to improve its technology and recently announced the release of its upgraded Merci L5 Retrieval System for use throughout Europe. Not to be left behind, the Americans are also looking with close interest at ways to use the corkscrew-like medical device so that it benefits as many patients as possible.
Toward that end, researchers at the Weill Cornell Medical College in New York are studying whether using MRI (magnetic resonance imaging) can help determine which patients are good candidates to have clots removed mechanically. Director of Interventional Neuroradiology, Pierre Gobin, M.D., and Dana Leifer, M.D., director of the Stroke Unit, both at New York Presbyterian Hospital/Weill Cornell Medical Center, are looking at using imaging to determine whether or not stroke patients that arrive in emergency rooms within eight hours of being stricken can benefit from the Merci Retriever procedure.
According to a Weill Cornell press release, “In this trial, doctors will use MRI scans to determine if there is a blocked artery that the device can potentially open. They will also use the MRI to estimate the amount of tissue that has already been irreversibly damaged and the amount of tissue that is at risk but can be salvaged if blood flow is restored. The results from the trial will help establish guidelines for use of the Merci Retriever.”