"The advantage of using myoblasts is that they can be taken from skeletal muscle rather than the heart itself--which will be important for newborns whose hearts are so tiny they cannot spare any tissue for the biopsy--and that they're resistant to ischemia, meaning they can go without a good blood supply for a relatively long period of time," Cowan says.

Cowan and his team are now working with a large-animal model that more closely simulates pediatric heart block. Further studies will seek to create tissue-engineered grafts that behave more like a natural AV node, for example by providing a built-in delay before sending electrical signals to the ventricles. The team is investigating whether other cell types, such as stem cells derived from muscle or bone marrow, might be made to behave more like AV node cells.
Complete heart block is present in about 1 in 22,000 births. It can also result from congenital heart disease, through an injury or scar tissue from heart surgery, or as a side effect of medications. In adults, pacemakers are a good solution, but in children, they carry a greater risk of heart perforation and clot formation. In addition, pacemakers only last 3 to 5 years in children, and the leads must be replaced frequently, requiring many repeat operations. In very small babies, the pacemaker leads must be positioned on the heart surface, resulting in even greater failure rates.
Cowan envisions a future in which a child with heart block would receive a conventional pacemaker, but also receive an implant of engineered, electrically conducting tissue that would grow along with the child. The pacemaker, acting as a backup, would start functioning only if the biological implant failed, prolonging its useful life.

The research was funded by the National Institutes of Health and a private family donation.

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