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Editor's note: This is one in a 10-part series of the top medical research advances as determined by ÃÛÑ¿´«Ã½ volunteer and staff leaders.

How the most disabling strokes are treated is undergoing the biggest transformation in decades after research this year showed dramatic benefits when tiny devices are used to go into the brain and grab large clots.

People with clots blocking a large vessel in the brain are more likely to survive and fully recover if they have the clot removed by a stent retriever, studies found. Experts say qualified stroke centers nationwide are seeing an increase in referrals for stent retrievers.

“This really is the penicillin era in ischemic stroke,” said Alexander Khalessi, M.D., vice chairman of neurological surgery at University of California San Diego Medical Center. Khalessi was among the first doctors in North America to perform the procedure, called mechanical thrombectomy, in patients with severe strokes.

“For patients with large-vessel blockages in the brain, these procedures reverse otherwise fatal or severely disabling strokes. The magnitude of the advance cannot be overstated,” said Khalessi, who was not involved in the studies. 

Each year, more than 690,000 Americans have a clot-caused, or ischemic, stroke. As many as one in four of them have a large-vessel clot, said Jeffrey Saver, M.D., who directs the University of California Los Angeles Stroke Center.

The last major advance in stroke treatment came almost 20 years ago, when the Food and Drug Administration approved the clot-dissolving drug tissue plasminogen activator, or tPA. For smaller clots, the intravenous drug is very effective, but it often fails to break up large clots.

“For these big blockages, tPA probably dissolves the clot less than a third of the time. The stent retrievers reopen the artery 80 to 90 percent of the time,” said Saver, who led , one of the five groundbreaking studies published in the New England Journal of Medicine.

The studies, which also include , , and , were selected as a top 10 research advance in 2015.

Each study produced varying results, but each found that more patients in the stent retriever group were able to function normally three months later compared with patients given only tPA.

The findings convinced the ÃÛÑ¿´«Ã½ to give the treatment its strongest recommendation in new guidelines issued in June.

Khalessi helped write the guidelines and said the discouraging reality has been that patients who survived large-vessel clots were often condemned to a life of paralysis, speech problems or other significant disability.

“Our patients are actually getting back to their regular lives,” he said. “That’s something we couldn’t offer people five years ago.”

The procedure should be done within six hours after the stroke starts, and in most cases after the patient receives tPA, according to the guidelines. To remove the clot, doctors thread a catheter through an artery in the groin up to the blocked artery in the brain. The stent retriever opens and grabs the clot, allowing doctors to remove the stent with the trapped clot.

Stent retrievers are used at all 96 comprehensive stroke centers and some of the nearly 1,100 primary stroke centers certified by the AHA and the Joint Commission, a nonprofit that accredits hospitals.

The FDA has approved two stent retrievers – Solitaire, made by Minneapolis-based Medtronic, and Trevo, made by Stryker Corporation of Kalamazoo, Michigan.

Up to 20,000 stent thrombectomies are expected to be performed this year in the U.S., twice as many as last year, according to estimates from Stryker. The company expects as many as 60,000 acute stroke patients each year will ultimately receive the procedure.

At UCSD, doctors are on pace to do at least 90 stent-retrieval procedures this year, triple the number in recent years.

“We now have to rejigger our systems of care to make sure we deliver,” Saver said.

That will involve counties and states redesigning their regional systems of stroke care to get patients who would benefit from stent retrievers to a hospital that can do it, he said.

But both tPA and stent retrievers are time-sensitive treatments that rely on people calling 911 as soon as they notice facial drooping, arm weakness or speech difficulty, some of the telltale warning signs of a stroke, said Ralph Sacco, M.D., chair of neurology at the University of Miami Miller School of Medicine and a past AHA president.

“People having stroke symptoms – or those around them who notice there’s a problem – need to understand that they could have a nearly complete recovery if they only get to the hospital fast enough,” he said.

Editor’s Note: This story was written when the time limit on mechanical clot removal was six hours. New guidelines released in January 2018 allow some carefully selected patients to receive mechanical thrombectomy up to 24 hours after stroke symptoms begin.

Editor’s note: On Nov. 9, 2020, the Food and Drug Administration issued a recall for the Trevo XP ProVue Retriever due to the risk that the device’s core wire may break or separate during device retraction. Contact your doctor with questions.