Approximately 85 percent of strokes are ischemic. A new generation of devices that remove clots from blocked brain arteries while restoring blood flow could dramatically increase survival and recovery rates for acute ischemic stroke patients, according to new research.
While clot-busting thrombolytic drugs are often the first treatment option in acute ischemic stroke, they are not suitable for all patients and aren’t always effective. In those cases, mechanical clot removal is another option.
The standard mechanical clot remover, the Merci Retrieval System, from Stryker in Kalamazoo, Mich., uses a small, corkscrew-shaped coil to remove blood clots. However, a new generation of devices that rely on a self-expanding stent are outperforming the mechanical system, according to two studies published in the August 26 online edition of The Lancet.
In the new generation of systems, the stent is inserted into the blocked artery via a thin catheter and compresses and traps the clot. The entire device is then removed—and with it, the clot—thereby reopening the blocked blood vessel.
Although other systems are on the market, The Lancet studies focused on the Solitaire Flow Restoration Device from Covidien of Mansfield, Mass., and Stryker’s Trevo Pro Retrieval System, which received approval from the U.S. Food and Drug Administration in March 2012 and August 2012 respectively. Findings from both studies were reported at the 2012 European Society of Cardiology meeting in Munich.
One study featured findings from the Solitaire With the Intention for Thrombectomy (SWIFT) trial, which compared the Solitaire device to the Merci in 113 stroke patients at 18 hospitals. Patients received either Solitaire or Merci therapy within eight hours of stroke onset.
The Solitaire device opened more vessels when used as the first line of treatment, necessitating fewer subsequent attempts with other devices or drugs, said Reza Jahan, M.D., an associate professor of radiology at the University of California, Los Angeles (UCLA), and a researcher on the study. Led by Jeffrey L. Saver, M.D., director of the UCLA Stroke Center, the SWIFT trial was conducted at 21 sites including the stroke center. (See sidebar)
“Solitaire was much better at successfully pulling the clot out,” Dr. Jahan said. “No other retrievers have a design that allows immediate resumption of blood flow.”
In the second study, 86 percent of patients treated with Stryker’s Trevo device achieved the targeted reperfusion rate compared with 60 percent of those treated with the company’s Merci. Patients’ chances of having a fully independent life after a stroke was 40 percent for Trevo-treated patients treated and 22 percent for those treated with Merci. The study comprised 178 patients with large vessel occlusions.
Another researcher who investigated Solitaire also discovered the device to be highly effective. “A main advantage of the Solitaire is that it enables fast recanalization with a high success rate,” said researcher Pasquale Mordasini, M.D., of the Department of Diagnostic and Interventional Neuroradiology, University of Bern in Bern, Switzerland.
In findings published in the June 21, 2012 online issue of the American Journal of Neuroradiology, Dr. Mordasini and colleagues studied the device in 14 patients with basilar artery occlusion (BAO), a type of stroke associated with a poor clinical outcome and high mortality. Recanalization is a major prognostic factor for good outcome in BAO.
Successful recanalization was achieved in all patients in the study. Median procedure time to maximal recanalization was 47 minutes and there were no device-related complications, he said.
“Our study and other research has shown a procedure time of less than 60 minutes with recanalization success in 80 percent to 100 percent of cases, which has not been achieved with previous mechanical devices,” Dr. Mordasini said. “Therefore, I think stent retrievers will become a mainstay of mechanical thrombectomy in acute stroke treatment.”
While Solitaire is becoming more common in practice as interventionists receive training, additional studies are needed, researchers say. A second-stage study by Dr. Jahan and colleagues will use multimodality imaging techniques to learn more about patient selection for the device.
“In our next study, SWIFT PRIME, we’re going to use multimodality CT-MR imaging to select patients who might benefit from Solitaire, just as we would in everyday practice,” Dr. Jahan said. “If the at-risk area of the brain has died, it’s too late to intervene with Solitaire. However, if the area of the brain is still viable, that’s a patient we would want to treat.”
Stent retrievers are just one way that medical researchers are working to speed lifesaving treatment to stroke victims.
German researchers have demonstrated the effectiveness of Mobile Stroke Units (MSUs)—specialized ambulances equipped with a CT scanner, a point-of-care laboratory and a telemedicine connection that transmits information to the hospital—in getting critical treatment to stroke victims already at the emergency site.
A study examining MSUs in the May 2012 edition of The Lancet Neurology found a dramatic advantage of pre-hospital stroke diagnostic work up and treatment.
“Treatment success is strongly dependent on the time frame of drug administration,” said lead researcher Silke Walter, M.D., senior physician in the Department of Neurology at the University Hospital of the Saarland in Homburg, Germany. “The earlier the therapy is applied, the more patients can be saved from permanent disability.”
To that end, MSUs have the potential to cut the time from the initial emergency call to treatment decision in half, according to new research.
In the study of 100 patients, Dr. Walter and colleagues found that median time from the emergency call to the therapy decision was 35 minutes for stroke patients who had pre-hospital treatment in MSUs compared with 76 minutes for patients who received conventional hospital treatment. Safety endpoints were similar across the groups.
“The halved time until therapy decision results in a much earlier beginning of thrombolysis which is directly linked to a better outcome with reduced disability,” Dr. Walter said.
Although cost is an obstacle to widespread adoption of MSUs, the long-term cost benefits are substantial, she said.
“It is important to invest in the first hour after stroke symptom onset in order to rescue stroke patients and save money by preventing lifelong disability.”
Access an abstract of the study at www.thelancet.com/journals/lanneurol/article/PIIS1474-4422%2812%2970057-1/abstract.
Stroke is the focus of Volume 2 of Radiology Select, a continuing series of Radiology articles that highlight developments in imaging science, techniques and clinical practice. For information on obtaining the print, online and tablet editions of Radiology Select, go to www2.rsna.org/timssnet/radiologyselect/index.cfm.
To view a video of Radiology Senior Deputy Editor and Radiology Select Series Editor Deborah Levine, M.D., discussing the Stroke series, click Video - Levin Stroke Intro.
To view a video of Radiology Deputy Editor David Kallmes, M.D., discussing the Radiology study, “Evaluation of Dual-energy CT for Differentiating Intracerebral Hemorrhage from Iodinated Contrast Material Staining,” with authors Rajiv Gupta, M.D., Ph.D., and Catherine M. Phan, M.D., and the Radiology editorial, “CT Perfusion Imaging of Acute Stroke: The Need for Arrival Time, Delay Insensitive, and Standardized Postprocessing Algorithms?” with Radiology Select Stroke Series Editor Michael Lev, M.D., click Video - Gupta Lev Phan.
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