MR RESCUE Trial Finds Mechanical Devices No Better Than tPA in Ischemic Stroke Treatment

February 8, 2013—The American Stroke Association (ASA) announced that in the first comparison of mechanical devices versus standard medical care for clot-caused strokes, mechanical clot removal showed no benefit over standard medical care. Furthermore, using advanced CT scans or MRI prior to treatment did not help identify patients most likely to benefit from treatment, researchers found. Findings from the study were presented at the ASA's International Stroke Conference 2013 in Honolulu, Hawaii.

As summarized in the ASA press release, the 22-center MR RESCUE (Mechanical Retrieval and Recanalization of Stroke Clots Using Embolectomy) trial included 118 patients (average age, 65.5) treated within 8 hours after experiencing an ischemic stroke in one of the large blood vessels carrying blood to the front of the brain. The investigators measured regions of the brain that were in danger of dying, but might be salvaged if blood flow was restored quickly, with specialized evaluation of CT scans or MRI.

Patients were divided into those showing a large area of at-risk but salvageable brain tissue near the clot and those without. Patients in both groups were then randomly assigned to receive either standard medical treatment (according to current guidelines) or to have their clot removed by the Penumbra aspiration system (Penumbra, Inc., Alameda, CA) or the Merci Retriever (Stryker Neurovascular, Kalamazoo, MI), which is a first-generation, corkscrew-like device. The Merci Retriever was developed by Concentric Medical, Inc. (Mountain View, CA), which Stryker acquired in October 2011, and received US Food and Drug Administration clearance in 2004.

The ASA reported that the investigators found that the level of disability 90 days after stroke was no different in patients who received medical care or clot removal, the rates of death (21%) and symptomatic brain bleeds (4%) were no different in the two treatment groups, and response to clot removal was no better in the 58% of patients with a favorable imaging pattern suggesting salvageable brain tissue.

MR RESCUE coprincipal investigator Reza Jahan, MD, Associate Professor of Interventional Neuroradiology at the University of California in Los Angeles, commented in the ASA press release, “We found no data that imaging could help select patients for treatment and did not show an overall benefit of physically removing the clot. However, further studies are needed because there are new devices that open up vessels better and faster, and with fewer complications, than the first-generation devices used in our trial.”

According to the ASA, investigators hoped that mechanical clot removal would possibly result in better outcomes for those who arrive later or whose obstructions do not respond to tissue plasminogen activator (tPA), the only US Food and Drug Administration-approved and research-proven treatment for an ischemic stroke, which must be given within 3 to 4.5 hours of the onset of symptoms. Lead investigator Chelsea Kidwell, MD, Professor of Neurology and Director of the Stroke Center at Georgetown University in Washington, DC, stated in the ASA press release, “The hope was, and to some degree still is, that if you pull out the clot within a certain period of time and there is salvageable brain tissue, there will be better outcomes.”

Dr. Kidwell concluded, “The data are encouraging as far as safety, but we really need randomized controlled trials of newer devices to see if they improve outcome. At this point, we can say that the MR RESCUE trial failed to demonstrate that advanced imaging techniques identify patients who will benefit from mechanical clot retrieval for acute ischemic stroke and failed to demonstrate superiority of embolectomy compared with standard medical care. If you experience signs of stroke, the important thing is to get to a stroke center in time to qualify for the only proven treatment—tPA.”