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Engineered Cells Could Control Irregular Heartbeat

Natural tissues might replace implanted pacemakers in children, study suggests

MONDAY, June 19, 2006 (HealthDay News) -- A tissue-engineered implant could someday take the place of implanted pacemakers in children with life-threatening heart blocks, researchers report.

A heart block occurs when the electrical signals that keep the heart beating normally cannot pass from the atria, the heart's upper chambers, to its lower ventricles. When the AV node -- the point through which the signals pass -- does not function, heart blocks can occur. Right now, a pacemaker is the only effective treatment for the condition.

"Young children not infrequently suffer heart block when they undergo major surgery," noted co-researcher Dr. Edward P. Walsh, chief of the cardiac electrophysiology division at Children's Hospital Boston. "They often need to have their chests opened when they have problems."

Reporting in the June 19 online edition of the American Journal of Pathology, Walsh's team said it engineered skeletal muscles in a way that could eliminate the need for pacemakers. The technique has worked well in early animal tests, the researchers said.

"The idea was that rather than using a pacemaker, we could create an electrical conduit to connect the atria and ventricles," Douglas Cowan, a cell biologist at the hospital and leader of the research program, said in a statement.

Cowan's attempt to create a more natural solution for the AV node problem began with rat studies in which he extracted early stage muscle cells called myoblasts.

Those cells were placed on a flexible scaffold made of collagen, a fibrous material found in bone and cartilage. That three-dimensional structure was then implanted into the rats' hearts.

The cells distributed themselves evenly and became oriented in the same direction. Laboratory tests showed that this newly engineered tissue would start beating when stimulated electrically. When the tissue was implanted between the right atrium and right ventricle of the rats, it soon established an "electrical pathway" in one-third of the animals. That pathway remained active over the rats' three-year life span.

The researchers now are planning trials involving larger animals whose cardiac systems more resemble those of humans, Walsh said.

One major advantage of the proposed method is that it would use cells from the patient's own body, he said, eliminating the possibility of rejection by the immune system.

Other researchers are creating new AV nodes in different ways. Several groups are trying to transform embryonic stem cells into heart cells that would transmit the essential electrical signals.

Progress on that line of research has been slower than hoped, Walsh said, "but that approach has not been given up on."

"We have no idea whether this will work or not in these patients, but someone has to look for an alternative," he said.

Total heart block occurs in about one of every 22,000 births. Causes include congenital heart disease, an injury or scar tissue from heart surgery, or as a side effect of medications. While pacemakers work well for adults, the devices carry a greater risk of heart perforation and clot formation in children. In addition, pacemakers typically last just three to five years in children, and the leads must be replaced frequently, which means repeat operations, the researchers said.

More information

For more on heart block, head to the American Heart Association.

SOURCES: Edward P. Walsh, M.D., chief, cardiac electrophysiology division, Children's Hospital Boston; June 19, 2006, statement, Children's Hospital Boston; June 19, 2006, online edition, American Journal of Pathology
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