The randomized controlled trial
known as Mechanical Retrieval and Recanalization of Stroke Clots Using
Embolectomy (MR RESCUE) was funded by the National Institute of
Neurological Disorders and Stroke (NINDS), part of the National
Institutes of Health, and was published online Feb. 8 in the New England
Journal of Medicine.
In patients with ischemic stroke (caused by a
blockage in an artery), brain cells deprived of blood die within
minutes to hours. Rapidly opening the artery can halt brain cell death.
Intravenous tissue plasminogen activator (t-PA), a drug that dissolves
clots has been shown to improve outcomes in such stroke patients.
However intravenous t-PA is not effective in many patients with large
clots blocking the major brain arteries that cause the most devastating
strokes. MR RESCUE investigators tested an invasive clot removal
strategy designed to remove clots from these large arteries. Patients
in the study were enrolled at 22 centers in the United States within
approximately 5.5 hours of their stroke onset. Their ability to function
independently was assessed at 90 days.
All MR-RESCUE patients
underwent emergency computed tomography (CT) or magnetic resonance (MRI)
perfusion imaging to identify regions of the brain with decreased blood
flow, as well as regions that could not be salvaged.
investigators hypothesized that patients in whom the scan suggested that
less than 70 percent of the brain with decreased blood flow had already
died would benefit from the clot-removal procedures. Based on the
imaging results, the 118 study patients were randomly assigned to
receive a clot-removal procedure within eight hours of symptom onset (64
patients) or standard therapy (54 patients) according to medical
protocols. The procedure involves threading a special catheter through
an artery in the groin up to the site of a clot in a brain artery, then
removing the blockage.
“Despite a lack of evidence showing that
these clot-removal devices improve outcomes, they are already widely
used in patients who are not able to get to the hospital in time to
receive t-PA,” said Walter J. Koroshetz, M.D., deputy director of NINDS.
“Though some patients have had dramatic improvements with clot removal,
it has not been shown effective in this or another larger study, the
Interventional Management of Stroke (IMS III), which was halted early
because it did not find the procedure to be of significant benefit.”
majority of patients were not eligible to receive intravenous t-PA, the
only drug approved by the Food and Drug Administration for the
treatment of stroke, because they arrived at the hospital too late for
t-PA to be effective,” said one of the primary investigators, Chelsea
Kidwell, M.D., of Georgetown University Medical Center in Washington,
D.C. As brain cells are dying continuously in the minutes and hours
after stroke, the earlier that treatment is given the greater the
likelihood of a good outcome for the patient.
The patients with
the presumed favorable imaging findings had the same level of disability
at 90 days whether or not they had undergone the clot-removal procedure
or had received standard therapy. The researchers hypothesized that the
lack of a treatment effect may reflect the fact that these patients had
enough blood flow to the brain from secondary sources to support the
brain tissue until spontaneous reperfusion occurred. Patients without
the favorable imaging findings did not benefit from the clot-removal
However, the results of MR RESCUE are not consistent with the conclusions of a separate NINDS-funded observational study called DEFUSE-2
that suggested that a slightly different brain imaging strategy could
predict patients who benefited from the clot-removal procedure.
addition to other imaging techniques “it’s possible that newer
intra-arterial devices that were not available when the study started
could improve functional outcomes,” said Scott Janis, Ph.D., program
director, NINDS. “But an important message from MR RESCUE is that those
newer devices still need to go head to head with standard therapy.”
“Advances in neuroimaging are promising and may someday help to identify who will benefit from a device-based approach. But the MR RESCUE results show that more work needs to be done,” Dr. Koroshetz said.
- Kidwell C, Jahan R, Gornbein J, et al. “A trial of imaging selection and endovascular treatment for ischemic stroke intervention,” N. Engl. J. Med. 2013. DOI: 10.1056/NEJMoa1212793.
- NINDS (http://www.ninds.nih.gov) is the nation’s leading funder of research on the brain and nervous system. The NINDS mission is to reduce the burden of neurological disease – a burden borne by every age group, by every segment of society, by people all over the world.