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Widening Stroke Treatment's Window

Rush studying if procedure helps when too late for other care

Dr. Michael Chen, expert who is leading the DAWN study for stroke intervention.

By Deb Song
July 19, 2016

Quick and appropriate medical or surgical intervention within the first six hours after a person suffers a stroke can greatly enhance that person’s chance of recovery. Nearly half of stroke patients who have their blood flow restored within this time window experience little to no physical or speech deficit afterwards. 

However, less than 2 percent of stroke patients actually get the treatment they need within the time window, for reasons that include not recognizing the symptoms or transportation delays. Many wake up with a stroke and don’t know when the symptoms first began.

Now a new clinical study may give hope to stroke patients who reach physicians past the six-hour time window. Rush University Medical Center is the only hospital in Illinois participating in the study, which is evaluating a new intervention for these stroke patients.

The clock is ticking

A stroke occurs when blood flow to the brain stops due to a clot, causing brain cells to stop receiving oxygen. Up to 85 percent of strokes are ischemic strokes, which usually are caused by a clot that blocks a blood vessel carrying blood to the brain. The blockage cuts off the brain’s blood supply, which after a few hours usually causes brain tissue to die. 

Stroke is the No. 1 cause of disability and the fifth-leading cause of death in the United States. On average, someone has a stroke every 40 seconds. 

Most of the time, the brain territory affected by the blocked artery goes from stunned to irreversibly injured brain after six hours. “The clock starts ticking the second a person suffers a stroke, as the brain is essentially holding its breath,” says Michael Chen, MD, an associate professor of neurosurgery and neurology at Rush. “Many patients develop speech difficulty and/or significant paralysis on one side of the body.”

When a stroke occurs, it’s crucial that clots be dissolved as quickly as possible, returning normal blood flow to the brain. The first proven treatment for ischemic stroke is recombinant tissue plasminogen activator, or rtPA, a clot-dissolving medication. This therapy, adminstered intravenously, has to be provided within the first four-and-a-half hours and has been shown to be less effective for larger clots. 

Large vessel occlusive strokes involve the major arteries in the brain and cause the greatest disability. Three out of every four patients with a large vessel occlusive stroke will be dead or severely disabled. A procedure called mechanical thrombectomy within six hours was shown to reduce the incidence of death and severe disability by half. 

DAWN outside the window

The new study, called the DAWN trial, is evaluating mechanical thrombectomy for ischemic stroke patients who have had symptoms for more than six hours and were not able to receive rtPA or did not improve with the drug. Rush is one of only 22 clinical sites in the world participating in this international study.

In the procedure, neurovascular surgeons make a 1-centimeter incision at the patient’s groin crease, and carefully navigate catheters within the blood vessels up to the arteries in the brain. The doctor can then carefully remove the clot using a variety of devices, including suction and/or a stent-like device, and pull it back out through the blood vessels and the groin incision.

"This is the first study we have offered that looks beyond the six-hour time window for stroke thrombectomy by using imaging rather than time for patient selection,” says Chen, lead investigator of the study at Rush.

The purpose of the study is to see if thrombectomy with medical management is superior to medical management alone in improving clinical outcomes at 90 days in appropriately selected “wake up” and late-presenting acute ischemic stroke subjects.

“This clinical trial may be particularly beneficial for people who wake up from sleep with a stroke and do not know when the symptoms first occurred,” Chen says.

Patients brought to Rush by ambulance, transferred to Rush with stroke symptoms or referred by a physician who are past the six-hour window will be evaluated using a CT scan that provides reliable imaging to help specialists decide where there is salvageable brain regardless of time.

Both groups randomized in the study will receive medical management, including blood pressure control, aspirin, and general medical care to prevent known complications such as deep vein thrombosis, urinary tract infections, skin ulcers and pneumonia.

The main outcome measure for the study will be the participant’s level of disability at 90 days using the modified Rankin score, which has been the standard for all stroke intervention studies.

“The DAWN study will determine whether a patient with a severe stroke (large vessel occlusion) still has salvageable brain based on patient-specific imaging information, rather than the crude, one-size-fits-all, six-hour time window,” Chen says.

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