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Why the New Clot-Removing Devices Are Revolutionary

A new study has confirmed what an earlier one hinted at in 2014--that clot-removing devices have revolutionized treatment for stroke patients who cannot tolerate clot-busting drugs.

Nancy Crotti

Stryker Trevo ProVue Retrieval System
The Stryker Trevo ProVue Retrieval System allows health provides to visualize deployment for accurate placement. (Image courtesy of Stryker)

The new study, by researchers from Loyola University, showed that the Stryker Trevo and Medtronic Solitaire stent retrievers did a remarkably better job of removing clots from blood vessels in the brain than earlier devices that employed different technology.

A stent retriever is a self-expanding mesh tube attached to a wire, which is guided through a catheter. The endovascular specialist inserts the catheter in an artery in the groin and guides it to the brain. The stent pierces the clot and is then expanded, enabling the physician to then pull it out--similar to how the Fogarty catheter works, albeit with a stent rather than a balloon.

Loyola used stent retrievers on 34 patients in 2015, and 21 patients during the first six months of 2016, according to the study published in Expert Review of Neurotherapeutics by Loyola Medicine neurologists Rick Gill, MD, and Michael J. Schneck, MD.

"Stent retrievers are a major advance in acute ischemic stroke care and will have significant impact on the evolution of stroke systems of care," the researchers write. "Endovascular stroke therapy had been an 'unproven' therapy despite numerous trials of intra-arterial pharmacologic thrombolysis and mechanical thrombectomy. With the advent of stent-retriever devices, there has been a paradigm shift in the utilization of endovascular therapies for (acute ischemic stroke)."

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Gill and Schneck foresee future device improvements that will do an even better job of restoring blood flow and increasing the number of patients who could benefit, according to a statement from the university, located near Chicago.

Stent retrievers also will affect where stroke patients are treated, the study says. Paramedics will play an important role in routing higher severity stroke patients, who could benefit from stent retrievers, to hospitals that offer neuroendovascular procedures, Gill and Schneck write.

Research published in 2014 in the New England Journal of Medicine, found that using a stent thrombectomy device within six hours after a stroke benefited patients more than the clot-busting drugs.

The clot-busting drug tissue plasminogen activator (tPA) has been the preferred stroke treatment for two decades, but many stroke patients do not meet strict criteria for its use. The drug must also be given within 4.5 hours of the onset of stroke to be effective and has had less effective in patients with large clots, the study says.

In selected patients, stent retrievers can be used to remove such clots.

The study reference to those earlier thrombectomy devices included Stryker's Merci device and the eponymous Penumbra. Merci is a coil retriever made of Nitinol shape-memory wire that a neurointerventionalist deploys to pull the clot "back into the catheter, like pulling a cork from a wine bottle," according to a 2012 study published in Neurology Clinical Practice. Stryker acquired the Mountain View, CA manufacturer of the Merci, Concentric Medical, in 2011.

A meta-analysis published in the journal Stroke in February found that using the Covidien Solitaire stent retriever in addition to the clot-busting drug tissue plasminogen activator (IV-tPA) significantly improves functional outcomes in stroke patients. Medtronic acquired Covidien in 2015.

Penumbra'saspiration thrombectomy devices use a minimally invasive "vacuum" inside the artery to remove the blood clot en masse, according to the San Francisco company.

Each year in the United States, 795,000 people have a stroke. Blood clots account for 87% of strokes, which are the fifth most common cause of death in the U.S. and the leading cause of adult disability.

Nancy Crotti is a contributor to Qmed.

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