Scientists say they've successfully used gene therapy to create a "biological pacemaker" that could one day replace electronic pacemakers currently used to treat human heart conditions.

Normal heart cells in pigs have been transformed into so-called pacemaker cells, the type of cells a normal heart uses to keep its rhythm in time and its beat consistent, researchers at Cedars-Sinai Heart Institute in Los Angeles are reporting.

"Pacemaker" cells reside in the heart in a small area known as the sinoatrial node, where they act as the heart's overall timekeeper.

When they can't do their job, the heartbeat can become too slow or its rhythm can become irregular, risking symptoms ranging from slight fatigue to complete circulatory collapse, the researchers said.

The researchers strategy, reported in the journal Science Translational Medicine, was to create fresh pacemaker cells that would work from a different location within the heart.

"We have been able, for the first time, to create a biological pacemaker using minimally invasive methods and to show that the biological pacemaker supports the demands of daily life," says research team leader Eduardo Marbán. "We also are the first to reprogram a heart cell in a living animal in order to effectively cure a disease."

The study suggests the possibility of clinical trials, possible in 3 years, for humans suffering from heart rhythm disorders plagued by side effects from implanted electronic pacemakers, such as infection caused by the leads used to connect a pacemaker to the heart, the researchers said.

In laboratory pigs in the experimental study, a gene known as TBX18 was injected into the heart using a minimally invasive procedure involving a catheter, they said.

Once the gene was conveyed into the pigs' hearts, in a different location outside of the sinoatrial node, those animals that received it had appreciably faster heartbeat rhythms than the ones that did not receive it, the researchers reported.

The stronger, more regular heartbeat also persisted during the complete period of the 14-day study, they said.

"Originally, we thought that biological pacemaker cells could be a temporary bridge therapy for patients who had an infection in the implanted pacemaker area," Marbán says. "These results show us that with more research, we might be able to develop a long-lasting biological treatment for patients."

In the United States an estimated 300,000 patients are fitted with pacemakers annually and around 2 percent of them develop infections, he says.

A biological pacemaker could someday see patients "cured of the slow heart rate forever," he says.