LONDON: Removing a stroke-causing clot from a large blood vessel in the brain can improve outcomes in some patients, even when extraction occurs six to 24 hours after symptoms develop, according to results of a large new test of the technique.
Until now, studies have suggested that the extraction needs to be performed within six hours of the stroke.
The old time limit may still provide the best outcome, but the new findings of the DAWN trial open the door to clot removal for other patients, particularly people who don't discover their symptoms until they wake up, making the precise time of onset unknown.
The study was financed by Michigan-based Stryker Neurovascular, which made the clot-removal device used in the trial, maintained the database for the study, and analysed the data.
"The stroke community is going to embrace these results very easily because many believe you can benefit beyond six hours," co-author Tudor Jovin of the University of Pittsburgh Medical Center Stroke Institute told Reuters Health in a telephone interview.
But the results, presented at the Society of Vascular and Interventional Neurology's annual meeting in Boston and online by the New England Journal of Medicine, are not going to apply to all stroke patients.
The DAWN study only considered testing the technique, known as thrombectomy, on people with a blockage in a large blood vessel of the brain that had produced symptoms six to 24 hours earlier.
In about one third of those cases, symptoms were far more severe than a CT scan or an MRI of the brain might suggest, and that mismatch made them candidates for clot extraction, said Jovin. That meant some degree of blood was still getting to the affected areas of the brain.
Those criteria would apply to only about 2 per cent to 3 per cent of the roughly 800,000 strokes in the United States each year, according to Jovin.
The results of the study are "strikingly positive," said Werner Hacke, a neurologist at the University of Heidelberg in a Journal editorial.
At 90 days, 49 per cent of the 107 patients who received a thrombectomy along with standard care were functionally independent versus 13 per cent of the 99 who received standard care alone.
The rate of neurological deterioration was 14 per cent in the clot-extraction group versus 26 per cent with standard care.
"For every 2.8 patients who underwent thrombectomy, one additional patient had functional independence at 90 days," the researchers concluded. The benefits were seen regardless of age, stroke severity, time to treatment, the site of the blockage and whether the stroke happened when the person was awake or asleep.
Delayed removal did not, however, reduce mortality, which occurred at rates of 19 per cent with clot extraction and 18 per cent without.
The patients, all of whom had an occlusion of the intracranial internal carotid or proximal middle cerebral artery, were treated at 26 centres in the US, Europe, Canada and Australia. The trial was stopped after the first interim analysis because the benefit was so dramatic.
The median time between inclusion in the trial and when the patient was last known to be free of new stroke symptoms was 12.2 hours in the thrombectomy group and 13.3 hours in the control group. It typically took another 1.4 hours to remove the clot and restore blood flow to the brain.
But the key element in deciding whether to go ahead with clot removal once more than six hours has expired is whether there is a sizable "area of reversible damage that's severely under-supplied with blood and not functioning well, but still alive", said Jovin. "It's not the time; it's that mismatch."
If the clot isn't removed, "the area that's threatened but not dead will eventually become dead," he explained.
Hacke cautioned that the findings do not mean doctors can relax the six-hour treatment window.
"Reducing the time from the onset of stroke to treatment remains essential and results in the best outcomes," he said.
"It is likely that a limited proportion of patients with occlusion of a large vessel who present late after the onset of stroke will have a small infarct core and a large volume of tissue at risk, as did the patients in the DAWN trial.
"For those patients, late thrombectomy works - but as of now, as far as we know, it works only for them."