Implantable heart pump offers hope for children awaiting heart transplants

A small implantable cardiac pump that could help children wait at home for a heart transplant rather than in hospital has shown good results in a first-stage clinical trial.

The pump, a new type of ventricular assist therapy, or VAT, device, is surgically attached to the heart to boost its blood-pumping function in people with heart failure, buying time to find a donor heart. The new pump could fill an important gap in pediatric heart transplant care.

In a study evaluating the capabilities of seven children who received a new pump to support their weakened hearts, six eventually received heart transplants, and one child's heart recovered, making a transplant unnecessary. The results were published in The Journal of Heart and Lung Transplantation. The study was led by Stanford School of Medicine and involved several medical centers in the United States.

If initial results are confirmed in a larger study of the device, waiting for a heart transplant could become easier for young children and their families. The new pump, called the Jarvik 2015 Ventricular Assist Device, is slightly larger than a AA battery and can be implanted in children as small as 18 pounds. With the pump implanted, children can do many normal activities while they wait for a heart transplant.

By contrast, the only available ventricular assist device to support young children with heart failure, a pump called the Berlin Heart, is not implanted; it is about the size of a large suitcase. It weighs between 60 and 200 pounds, depending on the model, and is attached to the child using two cannulas almost as big as garden hoses.

Berlin Heart also has a fairly high risk of stroke and requires hospitalization in most cases, meaning children often spend months in hospital waiting for a donor heart. As a result, the burden on children waiting for a heart transplant is much higher than for adults with heart pumps, who are typically discharged from the hospital with similar diagnoses.

"While we are extremely grateful for the Berlin Heart, a life-saving device, ventricular assist devices for adults improve every decade, and in pediatrics we are using technology from the 1960s," said Dr. Christopher Almond, lead author of the study, a pediatric cardiologist and professor of pediatrics at Stanford School of Medicine.

Implantable ventricular assist devices have been available to adults for more than 40 years, Almond notes. Not only do these devices fit inside patients’ chests, but they’re also safer and easier to use than external devices like the Berlin Heart. Patients can live at home, go to work or school, and take walks and bike rides.

The lag in pediatric technology is a problem for other devices designed to help children with heart disease, and for pediatrics in general, Almond notes. "There is a huge disparity in the medical technologies available to children and adults, which is an important public health issue that markets are trying to address because conditions like heart failure are rare in children," he says.

The study's senior author is Dr. William Male, chair of cardiology at Children's Healthcare of Atlanta.

Far fewer children than adults need a heart transplant, leaving little incentive for medical companies to develop a miniaturized pump for children. But the lack of a small ventricular assist device for children puts a strain on the medical system, as children assigned to Berlin Heart rack up large medical bills and can take up hospital beds in specialized cardiovascular care units for months, potentially reducing the availability of those beds for other patients.

Promising initial results

The 2015 Jarvik Ventricular Assistance Device trial included seven children with systolic heart failure. The condition affects the heart's largest pumping chamber, the left ventricle, which pumps blood from the heart to the rest of the body. In six children, systolic heart failure was caused by a condition called dilated cardiomyopathy, in which the heart muscle enlarges and weakens and does not pump blood properly. One child's heart was weakened by complete heart block (electrical failure of the heart) due to lupus, an autoimmune disease. All the children in the trial were on a heart transplant waiting list.

Each child had a Jarvik 2015 device surgically implanted in the left ventricle, the heart’s largest pumping chamber. At the same time, each was given medication to prevent blood clots and reduce the risk of stroke. The children were between 8 months and 7 years old when the pumps were inserted, and weighed between 18 and 44 pounds. The pump can be used for children up to 66 pounds.

If the new pump is approved by medical regulators, doctors estimate that about 200 to 400 children worldwide each year could be candidates for its use.

The trial assessed whether the pump could support patients for at least 30 days without stopping working or causing a severe stroke. The researchers also collected preliminary safety and efficacy data to help them design a larger, key trial for possible approval by the Food and Drug Administration (FDA).

Although the pump is initially designed to allow children to wait at home for a heart transplant, as they participated in a clinical trial, participants remained in the hospital for observation until they received a heart transplant or recovered. Researchers monitored the participants’ blood pressure, an indicator of their risk of blood clots and stroke; measured hemoglobin levels to see if the pumps were destroying red blood cells; and monitored the patients for other complications.

The average time the children used the pump was 149 days. Six children underwent heart transplantation, and one child recovered.

Several children had complications with the new pump. A child whose heart recovered had an ischemic stroke (due to a blood clot) when the heart became strong enough to compete with the pump. The pump was removed, and the child continued to recover and was alive a year later. Another patient had failure of the right side of the heart and was switched to a Berlin Heart pump while awaiting a transplant.

For most patients, complications were manageable and generally in line with what doctors expect when a child is connected to the Berlin Heart pump.

Quality of life questionnaires showed that most children were not bothered by the device, did not feel pain from it, and were able to participate in most play activities. One family reported that their toddler with the pump was able to maintain much greater mobility than his older brother, who was previously supported by a Berlin Heart pump.

Larger Trial Planned The National Institutes of Health has awarded funding for an expanded trial that will allow researchers to further test the usefulness of the new pump and collect data to submit to the FDA for approval. The next phase of the study begins now; the researchers plan to enroll the first patient by the end of 2024. The research team plans to enroll 22 participants at 14 medical centers in the United States and two sites in Europe.

"We're excited to begin the next phase of the study," Almond said. "We've overcome a number of challenges to get the work to this point, and it's exciting that there may be better options for children with end-stage heart failure who need a pump that acts as a bridge to transplant."