Far more people than previously thought can benefit from an emergency procedure for acute ischemic stroke, according to a 38-center clinical trial sponsored by the National Institutes of Health and led by researchers at the Stanford University School of Medicine.
The improved outcomes were achieved through the use of brain-imaging software developed at Stanford. The software helps identify stroke patients who could benefit from a clot-removal procedure (thrombectomy) after the closing of the window of time during which it has generally been considered helpful. Some patients showed dramatic improvement even when their brain clots were removed as long as 10 hours after the end of this six-hour window.
"Nearly half of all patients treated between six and 16 hours after the onset of their symptoms were largely spared from the consequences of their stroke," said the trial's principal investigator, Gregory Albers, MD, Director of the Stanford Stroke Center.
Ischemic strokes account for about 85% of the roughly 750,000 strokes suffered annually in the United States. They occur when blood supply to part of the brain is cut off by a clot in a cerebral blood vessel. The resulting lack of oxygen and glucose quickly kills brain tissue in the immediate area, and the affected area continues to expand until blood supply is restored.
Results of the trial were published online in The New England Journal of Medicine January 24 to coincide with Albers' presentation of the results at the American Heart Association (AHA) International Stroke Conference in Los Angeles. At the conference, the AHA issued new acute-stroke treatment guidelines that reflect what the study found. The guidelines recommend more people should be considered to undergo thrombectomy, in some cases up to 24 hours after symptoms begin in carefully selected patients.
Key to the study's findings is a growing understanding that different individuals' strokes spread through brain tissue at different rates, Albers said. It's not so much the amount of time elapsed since a stroke began as the amount of remaining at-risk but salvageable brain tissue that determines who will benefit from stroke therapy, he said.
The investigators used the brain-imaging software to rapidly evaluate blood-flow data generated from incoming patients.
Thrombectomy involves guiding a cagelike stent through the circulatory system to the site of an acute-stroke patient's brain clot, where the stent then encases the clot and physically extracts it. Until the new AHA guidelines were issued, the procedure was recommended only for patients who reach a treatment center within six hours of a stroke. As many as 35% to 40% of all strokes occur during sleep, so the short window of time severely limits the number of stroke patients getting this procedure.
Another treatment, intravenous injection of a clot-dissolving substance, has had an even tighter AHA-recommended time limit for efficacy—4.5 hours. However, the newest AHA guidelines suggest that more people should be considered eligible for the clot-dissolving medication alteplase. The previous guidelines were termed very rigid.
In the thrombectomy trial, patients were evaluated at treatment centers between six and 16 hours after incurring strokes originating in either of two large arteries in the brain: the middle cerebral artery or the internal carotid artery, which together account for about 25% of all strokes and the majority of severely disabling strokes. Patients 90 years of age or younger whose brains showed evidence of substantial amounts of at-risk but salvageable tissue were randomized into two groups. The intervention group received thrombectomies, and the control group, received standard medical therapy. Those who received a thrombectomy had far superior outcomes.
Patients were followed for 90 days after their strokes. By 90 days, 26% of the patients in the control group had died and 16% had devastating disability. In contrast, only 14% of the thrombectomized patients had died, and 8% had severe disability. There was a slight, statistically insignificant increase in bleeding from the spot in the brain where the clot had been extracted. But this effect was dwarfed by the overall reduction in death and disability among those treated.
Albers noted one caveat: "Our trial's excellent results reflect our selection of patients most likely to benefit," he said. "Only about half of the patients we screened with the brain-imaging software had enough salvageable brain tissue to enter the study. For the others, the procedure was considered unlikely to be effective."