Corkscrew-like device that removes blood clots from the brains of stroke sufferers

Aug 18 2004

A corkscrew-like device that removes blood clots from the brains of stroke sufferers may someday become the standard for treating severe forms of the disease, Oregon Health & Science University neurologists say.

But experts at the Oregon Stroke Center, OHSU School of Medicine, say work must continue to further demonstrate the safety and effectiveness of the Merci Retriever, manufactured by Mountain View, Calif.-based Concentric Medical. It has received federal Food and Drug Administration clearance, the company announced today.

The device "appears fairly safe and has the potential to make dramatic differences in stroke therapy," said Wayne Clark, M.D., professor of neurology and director of the Oregon Stroke Center.

Clark cautions the device has "not been proven to work yet" since it's only been tested on 141 patients nationwide, compared with the thousands of patients typically tested in clinical trials for drug therapies, but "we've had some dramatic cases." He said a larger sampling of patients needs to be tested, and the treatment should be compared to other common therapies, such as tPA, or tissue plasminogen activator, a clot-busting drug approved for intravenous use in some stroke patients.

"The current phase is to get the bugs out," Clark said.

The Oregon portion of the Merci trial is being conducted at OHSU and Providence St. Vincent Medical Center in Portland. Twenty-five patients suffering from acute ischemic strokes - those with symptoms of "medium to large" strokes that include aphasia, the inability to lift arms and legs, and difficulty walking - have been treated to date.

Stanley Barnwell, M.D., Ph.D., associate professor of neurological surgery and diagnostic radiology, OHSU School of Medicine, used the Merci device on several cases and said the procedure was successful in about half the Oregon patients. The technique involves guiding a catheter through the femoral artery from the groin area to the brain, extending the corkscrew, drilling it into a clot and pulling the blockage out.

"It's not the miracle cure, but it's a lot better than anything else" for opening blood vessels and restoring flow, he said.

For one, the Merci - mechanical embolus removal in cerebral ischemia - device can be used at up to six hours after a stroke compared with the three hours in which tPA must be administered to be effective, Barnwell notes. Even if it's given within the three-hour window, tPA doesn't always work on the larger occlusions the corkscrew is capable of opening.

"If things go well, for some patients, it's a pretty miraculous cure," he said. "Patients come in paralyzed and minutes after opening their blood vessels (with the Merci device), they start to regain function." For other patients, brain damage is limited so patients recover over weeks or months rather than suffer from lifelong impairment.

"It's a major improvement. It's very exciting," Barnwell said. "It's the first treatment for stroke that's safe and effective for large vessel occlusions. But it's not for every stroke patient."

For starters, now that the device has FDA approval, it can cost patients and their insurance companies $9,000 just for the device.

"If it really works, and you're walking and playing golf because of it, that's certainly worth it. But if you don't have insurance or if it doesn't work, it may not be worth it," said Clark, who emphasized that further studies on the device must show unequivocally "whether it's better than tPA."

Whatever the outcome of future studies, the contributions made by OHSU scientists in the Merci device's development will have been extensive. Clark cited the efforts of Helmi Lutsep, M.D., associate professor of neurology, who worked on the trial's testing protocols and outcome scales, and of Gary Nesbit, M.D., assistant professor of diagnostic radiology, and Barnwell, who performed preclinical development work and insight on the testing protocols.

"We've been working on it for years," Barnwell said.

According to the American Stroke Association, a division of the American Heart Association, stroke killed an estimated 163,538 people in 2001 and is the nation's third leading cause of death, ranking behind diseases of the heart and all forms of cancer. It's also a leading cause of serious, long-term disability in the United States.

Stroke symptoms include sudden numbness, weakness, or paralysis in face, arm, or leg, especially on one side of the body; sudden blurred or decreased vision in one or both eyes; sudden difficulty speaking or understanding simple statements; and sudden loss of balance or coordination when combined with another sign.