Ultrasound helps break up blood clots

BOSTON -- The same type of sound waves that pulsate from sonar fish-finders and ultrasound fetal monitors can dramatically boost the power of anti-clotting medicine and help it dissolve brain blockages in stroke patients, a study suggests.

This technique may one day offer a safe accessory for helping up to 100,000 U.S. patients a year, or 15 percent of the nation's stroke victims, doctors said.

Imaging specialist Dr. Joseph Polak at New England Medical Center in Boston said more doctors should now consider adopting the technique.

"It's a relatively big impact for a disease where we don't have many options," he said.

The study and Polak's commentary appeared today in The New England Journal of Medicine. The research was conducted by the University of Texas Medical School at Houston with partners in Canada and Spain.

About 700,000 people suffer strokes each year in the United States, making it the leading cause of serious, long-term disability, according to the American Stroke Association. About 163,000 died from a stroke in 2001, third only to heart disease and cancer.

Like a heart attack within the brain, a stroke happens when a clot gets stuck in a blood vessel and cuts off circulation. The anti-clotting drug TPA is sometimes given to break up the clot before brain tissue starves for lack of blood.

Ultrasound has long been used to diagnose strokes. In recent years, research has intensified on whether it can also supercharge the clot-breaking medication.

In this experiment on 126 patients, it did just that -- and impressively so. Within two hours, almost half of the ultrasound patients with blockage of the middle cerebral artery showed restored blood flow or dramatic recovery from symptoms. With TPA alone, only 30 percent of patients did.

Longer-term results were also favorable -- though not statistically significant in this study, because of the way it was designed. After three months, 42 percent of ultrasound patients were symptom-free or living independently, compared with only 29 percent of those treated with TPA alone.

The risk of bleeding in the brain appeared to be small and no greater than with TPA alone.

Exactly how the ultrasound works is not well understood. But researchers believe it may stir up blood near the clot, like a sonic spoon, and thus help mix in the drug. It may also help the drug bind directly to the clot.

"Think about the clot being inside a closed box, and the ultrasound has somehow opened it a bit more," Polak said.

Researchers said it is also possible that the sound waves shake up the clot and help break it up.

The technique, as it is being tested now, is used only in patients who are treated with TPA. And TPA cannot be given to patients suffering bleeding in the brain, and must be administered within three hours of the onset of a stroke.

Researchers in this study hope to take part soon in a more definitive test of the technique.

Dr. Robert Adams, a neurologist at the Medical College of Georgia and adviser to the American Stroke Association, said the findings are especially impressive for the first few hours of recovery, but he would wait for more research on the effects months later before backing wider use of the technique.

The ultrasound equipment, known as transcranial Doppler, is fairly common at major hospitals for diagnosing strokes but is rarely employed as a treatment. That is partly because it can take months to learn how to pinpoint clots with the lipstick-size wand.

The study's lead researcher, Dr. Andrei Alexandrov at the University of Texas Medical School at Houston, is working on a simpler-to-operate device. "There are too few skilled operators to bring this technique to the emergency department where it's necessary," he said. "That's the major problem."

Some scientists are also looking into whether ultrasound, at higher power, can safely blast away clots by itself, without medication.

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On the Net:

New England Journal of Medicine: http://nejm.org

American Stroke Association: http://www.strokeassociation.org