Projects plant hope for littlest hearts

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The numbers are small, but the payoff could be big.

That's the message from scientists who are working on the development of miniaturized heart pumps for children, known technically as PVADs, or pediatric ventricular assist devices.

There are just 240 children waiting for heart transplants in the United States today, according to the United Network for Organ Sharing, which is less than 10 percent of the total heart transplant list and nowhere near the 78,220 people waiting for kidneys.

But if current trends continue, more than a fifth of them will die before they get a transplant, and those deaths will not be just a personal tragedy for their families, but the loss of decades of productive years that the child could have contributed.

"The story I try to sell is the ripple in a pond from a single drop," said Dr. Peter Wearden, a heart surgeon at Children's Hospital of Pittsburgh who is developing one of the heart pump prototypes. While the number of children who die from heart failure is small, "each one of these kids would have had an impact upon society."

Despite that sentiment, there are simply not enough cases needing pediatric heart pumps to encourage a U.S. company to invest the money necessary to develop a federally approved device, the experts say.

"From purely a market perspective, nobody in their right mind would develop a pediatric device that needs to be available in 10 sizes for something that will be a tiny fraction of the adult market," said Dr. David Rosenthal, a pediatric heart specialist at Stanford University.

That's why the federal government stepped in five years ago to offer contracts to develop pediatric assist devices.

Of the five projects that were funded with a total of $22.5 million, three are based in Pennsylvania.

One, headed by Dr. Wearden, involves Children's Hospital of Pittsburgh, the University of Pittsburgh's McGowan Institute for Regenerative Medicine, Carnegie Mellon University, an engineering firm called LaunchPoint Technologies, and WorldHeart Corp., a California company that has made the Novacor brand of heart pumps.

The consortium is working on an implantable pump the size of a battery that would use a magnetically levitated rotor to propel the blood. The levitation would cut down on clotting and damage to blood vessels by eliminating bearings and valves.

Another group involves Ension Corp., a Harmar bioengineering firm that is working with the University of Louisville and the University of Tennessee, along with Canonsburg-based Ansys Inc.

Unlike the other projects, Ension has developed a miniaturized version of ECMO, which stands for extracorporeal membrane oxygenation, which not only circulates blood but oxygenates it as well.

The key to their device, said Ension president Mark Gartner, is using a forest of tiny, hollow fibers, coated with biocompatible material, to infuse oxygen into the blood and eliminate carbon dioxide.

The third Pennsylvania effort is based at Penn State University, which is working on a pediatric version of its well-known adult heart pump, which uses air pressure to pump blood. Where the Children's and Ension pumps would provide a continuous blood flow, the Penn State device would mimic the heart's pumping rhythm.

The other two developmental projects are spearheaded by the Cleveland Clinic, which is developing a magnetically-driven device similar to the one at Children's, and Jarvik Inc., which is downsizing its Jarvik 2000 adult ventricular assist device.

Each of the designs is taking a slightly different approach to aiding the weak hearts of tiny children, but all of them are designed to go inside children's bodies to minimize the risks of infection from tubes piercing the skin.

All of them have been through animal testing -- Children's is using sheep, for instance, while Ension's partners are using calves and piglets -- but none is close to being ready for human testing yet.

That is why the National Heart, Lung and Blood Institute is planning to fund another round of research to get some of the devices ready for testing in children.

Timothy Baldwin, a biomedical engineer at the institute who heads up the pediatric device program, said the government hopes to start clinical trials by 2013 and have working devices by 2016.

And he doesn't expect all five of the current projects to survive. "I've been very honest with the contractors from day one," he said. "I don't expect all five to make it into clinical practice."

While the children who need heart support while waiting for a transplant number only in the hundreds nationally, truly effective mini-pumps might one day help thousands of other pediatric patients, said Stanford's Dr. Rosenthal.

Just as the pumps being used today sometimes allow the hearts of children waiting for transplants to recover their normal function, the same thing might be possible one day for children whose hearts have been attacked by viruses or weakened by other causes, he said.

Another large group is children who have chronically weak hearts. Most of them now take medication, Dr. Rosenthal said, but if reliable heart pumps could one day take over part of the heart's pumping load, they might be a viable therapy for those patients. "It wouldn't substitute for medicine," he said, "but it would represent an improvement on medications alone, which are presently rather imperfect."

Finally, there are some children who are born with only one pumping chamber instead of the normal two, and mechanical pumps might be of vital assistance to them.

When all those children are grouped together, Dr. Rosenthal said, it could amount to tens of thousands of children who could benefit from pumps each year.

There is one other potential spillover benefit, Pittsburgh's Dr. Wearden said. "I think just the process of making things smaller will allow us to have smaller, less [injurious] devices for adults."

Scientists are years away from developing pediatric pumps that will work truly well, Dr. Rosenthal said, but it's helpful to take the long view.

The history of pacemakers is a good case in point, he said. "The first pacemakers were the size of refrigerators, cost a fortune and lasted two weeks. Today, you couldn't find an insurer who wouldn't pay for a pacemaker."

Dr. Baldwin, of the Heart, Lung and Blood Institute, points out one other rationale.

Children with failing hearts are "one of the most vulnerable populations we have. Ethically, morally, we have an obligation to take care of them.

"And in a relative sense, we're doing this on a shoestring budget. There's a lot more money spent on other clinical trials than we're spending on this program."


Mark Roth can be reached at mroth@post-gazette.com or at 412-263-1130. First Published February 4, 2009 5:00 AM


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