09 March 2009

Vacuum cleaner for the brain

A new treatment for stroke victims aims to suction out clogged arteries in hopes of stopping the brain attack before it does permanent harm.

It is a tiny "vacuum cleaner" for the brain: a new treatment for stroke victims aims to suction out clogged arteries in hopes of stopping the brain attack before it does permanent harm.

Called Penumbra, the newly approved device is the latest in a series of inside-the-artery attempts to boost recovery from stroke, which kills many.

Identifying candidates
Now the question is how to determine which patients are good candidates - because, illogical as it may sound, unclogging is not always the best option.

"Is the patient at a stage of stroke where you're going to hurt them by pulling a clot out, or show benefit?" asks Dr Walter Koroshetz of the US National Institutes of Health. "It's good we have devices. Now we have to learn how to use them."

Most strokes occur when blood vessels feeding the brain become blocked, starving delicate brain cells of oxygen until they die. For those, the clot-busting drug TPA can mean the difference between permanent brain injury or recovery - but only if patients receive intravenous TPA within three hours of the first symptoms.

Yet fewer than 5 percent of stroke sufferers get TPA, because they do not get specialized care in time. And of those treated, it only helps about 30 percent, because the clot is often too big or tough for TPA to break.

Enter Penumbra, an option for patients who miss out on early care - it can be tried up to eight hours after a stroke strikes - or if standard TPA treatment fails.

How it works
Specialists thread a tiny tube inside a blood vessel at the groin and push it up the body and into the brain until it reaches the clog.

Just like a vacuum cleaner, it sucks up the clot bit by bit to restore blood flow.

For the right patient, Penumbra can produce dramatic help, says Dr Demetrius Lopes of Chicago's Rush University Medical Centre, one of two dozen hospitals that tested the device in 125 severe stroke patients.

He points to 45-year-old Aretha Streeter, whose left side remained paralysed almost an hour after a big dose of TPA. Lopes scanned her brain and spotted a key artery completely blocked. She agreed to the Penumbra experiment, and started moving as Lopes suctioned out the clot. Streeter was walking the next day, and was left with weakness in her arm instead of paralysis.

The study's full results will be presented next month at a meeting of the American Stroke Association.

But the device vacuumed out clots well enough to earn California-based Penumbra Inc. a surprise speedy approval from the Food and Drug Administration in late December. Rush's Lopes says it caused few serious side effects, and that about 42 percent of successfully treated patients showed significant recovery a month later.

Alternative methods
Penumbra is not the only mechanical clot-buster. Doctors also can try threading a corkscrew-shaped wire, called the Merci Retriever, through the clot and tugging it out. Researchers also are experimenting with dripping TPA directly on the clot instead of the old IV method, and even beaming the clog with ultrasound waves for an extra jolt.

Here's the rub: Unclogging sometimes does more harm than good in bad strokes, says Koroshetz, deputy director of NIH's National Institute for Neurological Disorders and Stroke.

When the dam is broken and blood rushes into oxygen-deprived brain tissue, it sometimes triggers swelling or a brain haemorrhage. Either can kill.

So treatment is a balancing act: Using brain scans to estimate if the stroke already has killed all the brain tissue it is going to, or if enough still could be salvaged that it's worth the risk of this injury, Koroshetz explains.

"Your ability to succeed with taking the clot out depends on what's going on in the brain," he cautions.

The NIH is funding a 900-patient study comparing standard therapy with different inside-the-artery treatments - the TPA drip, ultrasound, and the Merci Retriever - to tell if and how they should be used.

Researchers will decide soon whether to include the new Penumbra device in that study. – (Sapa-AP)

Read more:
Stroke Centre

January 2008


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