Nickel-Titanium Clot-buster reverses vessel damage

Mar 20 2004

A novel corkscrew-like device that mechanically removes clots from the brain has shown promise in recanalizing occluded vessels and reversing damage caused by ischemic stroke, according to researchers at the 29th International Stroke Conference.

Dr. Sidney Starkman, professor of emergency medicine and neurology at the University of California at Los Angeles, presented the phase I and II findings of the Mechanical Embolus Removal in Cerebral Ischemia (MERCI) trial.

The investigational device consists of a flexible nickel-titanium wire with a coiled tip that is inserted into the femoral artery and guided via standard angiography into the brain to where the clot is located. When the coil snares the clot, the device and the clot are withdrawn into a catheter with a balloon. The balloon is inflated briefly to stop blood flow and allow the clot to be evacuated.

At the conference, the results of 114 patients from 25 centres were reported. The average age was 70 years (range 28 to 93 years), and 46% were women. The average National Institutes of Health Stroke Score at baseline was 19, indicating severe impairment. Patients included in the study were those seen up to eight hours after initial stroke symptoms who were not eligible for standard tissue plasminogen activator (tPA) drug therapy.

"The only approved therapy for stroke is tPA," Dr. Starkman said. "But it has the limitation that it must be administered within three hours of stroke onset."

The MERCI retrieval device successfully restored blood flow in 61 (54%) of the patients, and 23 of these patients recovered with no disability or only minor disability, such as handwriting problems. Only 6% of patients whose vessels were not opened had a good recovery that allowed them to return to their normal activities.

Dr. Starkman said mortality was significantly higher among patients whose vessels were not opened (50%) compared with those whose vessels were cleared (25%).

He said the recovery was instantaneous in some cases, and noted one patient's paralysis and inability to speak were suddenly reversed with the retrieval of the clot. "It's just like putting a corkscrew into a wine bottle—you pull it out and you get flow. It's exhilarating to see it happen."

The U.S. Food and Drug Administration is currently reviewing the MERCI device, which is manufactured by Concentric Medical Inc., of Mountain View, Calif.

The possibility of mechanical thrombolysis is encouraging since it appears to work quickly and may expand the treatment window for stroke beyond the current three hours from onset with tPA.

However, Dr. Larry Goldstein, who chaired the press conference where the MERCI results were discussed, said there are also limitations to consider.

"You have to be able to see the clot to retrieve it, and very often you don't see it, or it is beyond the range of where you could reach it," said Dr. Goldstein, the director of Duke University Medical Centre of Cerebrovascular Disease in Durham, N.C. "And even in cases where they were able to retrieve the clot, 25% still died."

Dr. Goldstein noted that a lot of new devices have appeared promising at first blush but have proved disappointing over the years. But he also said while none is the panacea, it would be beneficial to have a number of techniques to use in combination to protect the brain and buy time until recanalization can be performed.