Chicago – Mechanical thrombectomy, a treatment to remove a stroke-causing blood clot in the brain, is effective in some patients even when performed within six to 24 hours after a stroke, according to the results of an international, randomized controlled research study.
The findings of the study were presented in late May at the European Stroke Organization Conference 2017 in Prague.
“There already is overwhelming evidence supporting clot removal as the standard of care for eligible patients with acute stroke within the first six hours after symptom onset,” said Dr. Michael Chen, neurointerventionalist and lead investigator of the study at Rush University Medical Center. "This was the most statistically powerful study evaluating clot removal beyond the six-hour time window for stroke.”
Rush is the only Illinois site, one of seven sites in the United States and one of only 22 sites in the world to participate in the international study, called the DAWN trial.
The study looked at patients who suffered a severe ischemic stroke (that is, a clot in an artery that blocks the flow of blood to the brain) and who underwent a thrombectomy six to 24 hours after the onset of stroke.
Moving beyond one size fits all treatment guideline
“The study results indicate that patients with a severe stroke (large vessel occlusion) can still have salvageable brain based on patient-specific imaging information, rather than the crude, one-size-fits-all, six-hour time window,” Chen said.
In addition, the study findings show that ischemic stroke patients who received clot dissolving medications but did not improve also benefited from mechanical thrombectomy.
During a mechanical thrombectomy procedure, neurovascular surgeons make a 1-centimeter incision at the patient’s groin crease to gain access to the system of arteries in the body. Guided by real-time imaging of the blood vessels, the surgeon then carefully navigates a catheter within the blood vessels up to the arteries in the brain. The doctor then can carefully removes the clot using a variety of devices, including suction and/or a stent-like device, and remove it from the body.
The DAWN study enrolled a total of 206 patients in the U.S. and internationally. Patients in the study who underwent thrombectomy had significantly less post-stroke disability and improved functional independence 90 days later, compared to those who received medical management alone.
Almost half of the patients (48.6 percent) receiving the thrombectomy therapy were independent after 90 days, as opposed to only 13.1 percent of the patients treated medically or with clot-busting drugs alone.
“That is a 35 percent absolute difference in the primary outcome measure, which may be greater than any prior thrombectomy stroke trial," Chen said.
Not only did the patients treated with mechanical thrombectomy dramatically improve during hospitalization, but there was also a much lower risk of subsequent neurological worsening because of the poor blood flow to the brain.
Results may help doctors decide which patients past six hour window to treat
In the DAWN trial,, researchers used neuroimaging to determine which patients would likely benefit from thrombectomy. The imaging helped doctors determine how much brain tissue had suffered irreversible damage and how much tissue they might be able to save. If the amount of damaged tissue were no bigger than the size of a small apricot, researchers believed the patient could benefit from the therapy.
On average, providing thrombectomy between six and 24 hours after the onset of stroke produced a good outcome in one out of every 2.8 patients. This ratio is a much greater rate of response than what was seen in trials that did not routinely use advanced brain imaging to guide treatment.
"The results of the DAWN trial provide physicians who treat stroke with evidence of the benefits of thrombectomy even when it is administered out as far as 24 hours,” Chen said. “This could help to make decisions clearer as to which patients to treat.”
"These positive outcomes of the DAWN trial represent a paradigm shift that allows physicians to more accurately select patients for thrombectomy and ultimately offer more treatment options for stroke patients than what is currently available."
‘These patients may have a better chance of independent life’
"Until this study, for patients presenting with stroke symptoms beyond six hours, the benefit of clot retrieval using a stent retriever was unknown," said Chen. "Now we have evidence that thrombectomy after six hours may offer certain patients a better chance for an independent life.”
“Although this is great news, earlier treatment is always better because with stroke 'time is brain,” Chen said.
‘The clock starts ticking the second a person suffers a stroke’
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.
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, causing brain cells to stop receiving oxygen, which after a few hours usually causes brain tissue to die.
Most of the time, the brain territory affected by the blocked artery goes from stunned to irreversibly injured after six hours.
“The clock starts ticking the second a person suffers a stroke, as the brain is essentially holding its breath,” said Chen. “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 tPA, a clot-dissolving medication. This therapy, administered intravenously, has to be provided within the first four-and-a-half hours after a stroke 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 who suffer a large vessel occlusive stroke will die or be severely disabled afterwards. Past studies have found that mechanical thrombectomy within six hours reduced the incidence of death and severe disability by half.
Contact: Deb Song