DAWN Trial Yields Strong Results

Cathy Sila, MD

A new study examining the use of mechanical thrombectomy to treat stroke patients will help to expand the population of patients who can benefit from this treatment.

The international DAWN trial – a multi-center, blinded endpoint assessment, randomized study – compared outcomes of 206 stroke patients who presented with symptoms after at least six hours from onset. Patients in the study were either treated using mechanical thrombectomy with Stryker’s Trevo® Retriever plus medical management or they received only medical management. All patients had last been seen well between six and 24 hours (average 13 hours) before treatment.

EARLY SUCCESS

Study researchers found that slightly more than 48 percent of stroke patients who received the thrombectomy treatment had a “good” outcome, defined as functional independence at 90 days later, compared to about 13 percent of patients receiving medical management alone, says Cathy Sila, MD, Director of the Comprehensive Stroke Center, University Hospitals Neurological Institute, Vice Chairman, Department of Neurology, UH Cleveland Medical Center and Case Western Reserve University School of Medicine; Professor of Neurology, Case Western Reserve University School of Medicine.

“In patients for whom this treatment works, it’s a miracle,” Dr. Sila says. “They literally can go home again and experience an independent recovery. Many of them walk out of the hospital within days.”

The treatment itself is not experimental, Dr. Sila notes, only the expanded time frame in which it was utilized. In the study, thrombectomy was only used after magnetic resonance imaging determined a patient had enough salvageable brain tissue to warrant opening the artery and removing the clot.

UH entered seven patients in the DAWN trial, which was designed to facilitate up to 500 patients. However, interim analysis of data conducted after 200 patients showed sufficient positive results, and Stryker suspended further enrollment.

SUCCESS AFTER THE SIX-HOUR WINDOW

Dr. Sila compares the retrieval devices used in the study to a Chinese finger puzzle ? very thin if pulled straight but wider when compressed. They are deployed via a catheter into the affected artery and held there briefly in the “wide” position to allow the clot to migrate into it. The surgeon then straightens the device, trapping the clot, and retracts it from the catheter.

Several studies conducted in 2015 demonstrated that doing this kind of mechanical thrombectomy procedure within six hours, particularly coupled with IV tissue plasminogen activator treatment, yielded dramatically improved outcomes after a major stroke within an intracranial artery. A few of those studies extended treatment beyond the six-hour window, but they didn’t have enough patients enrolled in them to be definitive, Dr. Sila says.

UH doctors have now adopted the DAWN protocol. Before, they were working with the internally created “Wake-Up Stroke Protocol,” which utilizes magnetic resonance scans to determine if patients whose strokes occurred at an unknown time, most often during the night, could still benefit from treatment.

“We considered the time on the clock to be a surrogate marker for what is actually going on the brain, and that brain cells can survive for a while with minimal blood flow,” Dr. Sila explains. “If you took an average group of patients with average circulation, the six-hour timeframe was a pretty average estimate of when a stroke had evolved to the point where the brain cells were dead.”

Under the Wake-Up Protocol, UH doctors proceeded with revascularization procedures despite the time window if they saw a very small core infarction with a significant clinical deficit or large area of the brain at risk. “We believed that, radiographically, this was the right thing to do,” she says. “We had many successes with it.”

For this work, Dr. Sila and her colleagues were invited to be part of the original steering committee for the DAWN study. The committee brought together 26 centers worldwide, all capable of performing the advanced imaging needed to identify patients who could benefit from the approach.

Though about 15 percent of all stroke patients are of the “wake-up” variety, patients may also present later because they had an unwitnessed stroke or they were initially taken to a facility that is not equipped to treat them, Dr. Sila explains. “We wanted to demonstrate that we have more options to offer patients in these situations, and we did just that,” she says.

Dr. Sila expects that the American Stroke Association will incorporate the DAWN trial’s findings into its formal guidelines soon. “These results will have major implications for a lot of centers,” she concludes. 

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