CHICAGO (Reuters) - A miniaturized heart pump helped keep eight out of nine severely ill children alive long enough to receive a heart transplant, US researchers said on Monday.

Heart assist devices are widely available for adults with severely damaged hearts who need the help of an artificial heart pump while waiting for a heart transplant.

But the devices approved for sale in the United States, made by companies including Thoratec Corp, are too large for many children. And while devices tailored for a child's smaller anatomy are approved in Europe and other parts of the world, no such devices are approved in the United States.

"Research and development on pediatric pumps has been woefully lacking," said Dr. Sanjiv Gandhi of the Saint Louis Children's Hospital in Missouri, whose research appears in the journal Circulation.

"Up until now there were no available pumps for children who are in end stage heart failure and in need of some sort of bridge while waiting for a suitable donor organ to come along," he said in a telephone interview.

Gandhi and colleagues tested one such device, the Excor pediatric ventricular assist device made by Berlin Heart GmbH, in seven girls and two boys ranging from 12 days to 17 years.

All had severe heart failure and weighed less than 88 pounds. One child died from kidney failure before receiving a heart transplant. After 19 months of follow up, the other eight were alive with new hearts.

"The potential benefits are huge," Gandhi said.

"A lot of the children in whom they were implanted would probably not have made it with conventional therapy while waiting for a suitable heart."

Gandhi said there were complications along the way, but all were easily managed, and the children who survived and received a heart transplant are faring well.

Because fewer than 100 US children need a heart assist device a year, the pediatric market has been too small to attract the attention of US makers of adult heart pumps, he said.

Gandhi's hospital is now among several centres taking part in a three-year, US Food and Drug Administration-approved clinical trial started late last year to test the Excor in children needing heart transplants.

Before the start of the trial, pediatric hospitals in the United States used the Berlin Heart under the FDA's emergency or "compassionate use" regulations. But that meant each case had to be approved by the FDA before use and the device could not be stored in the United States.

"I presume based on our work and other people's work, the results will pan out — that this this is a better way to treat kids with heart failure than we've done in the past," he said.

"Once that proof exists, I would hope availability of these things would be much easier."