MONDAY, Nov. 10 (HealthDay News) -- In a new twist on the concept of renewable energy, British researchers report that harnessing the heart's own energy may provide power for pacemakers and implanted defibrillators to work.

That might lead to devices that last longer and do even more, said the scientists, who presented their findings at the American Heart Association's annual scientific sessions in New Orleans.

"The heart ejecting is doing an awful lot of work. It's a tremendous mechanical force," said Dr. Ann Bolger, a spokeswoman for the American Heart Association (AHA) and William Watt Kerr professor of clinical medicine at the University of California, San Francisco.

Bolger described a "ballistocardiograph," consisting of a table suspended from the ceiling. A patient lies on the table, and doctors measure the heart beat as actual movement of the table.

Capturing part of that force, Bolger added, "may make the difference between ever needing your battery changed."

Implantable pacemakers are battery-run devices that help the heart maintain a regular rhythm. Implantable cardioverter defibrillators (ICDs), also battery-powered, pick up dangerous heart rhythms and then deliver an electric shock to restore normal rhythms.

According to the researchers, adding more power to pacemakers and implantable defibrillators would necessitate bigger devices. That becomes an issue of "patient tolerance and comfort," Bolger said.

The microgenerator developed by inventors at Southampton University Hospital in the United Kingdom is called the self-energizing implantable medical microsystem (SIMM) and was tested by InVivo Technology, Perpetuum and Zarlink Semiconductor using British government funds.

The microgenerator and two "bladders" are mounted on the wire that connects the pacemaker or defibrillator to the heart. The wire, or lead, is attached to the heart's right ventricle. The bladders "pump" energy at each heartbeat to the generator, which turns it into electricity to be used by the battery.

In this case, the device was implanted into a pig by way of the internal jugular vein.

A heart working at the rate of 80 beats per minute generated 4.3 microjoules of energy per cardiac cycle, about 17 percent of the electricity needed to run a pacemaker.

When the heart beat faster, more energy was produced, and when the heart beat slower or blood pressure was reduced, the corresponding energy produced declined.

The device appeared to cause no harm to the heart.

"The study is very preliminary," said American Heart Association spokesman Dr. Gordon Tomaselli, a professor of medicine in the division of cardiology and molecular medicine at the Johns Hopkins University School of Medicine in Baltimore. "People aren't going to change manufacturing based on this data."

But researchers are currently changing the materials of the microgenerator in the hopes of producing all the energy an implanted pacemaker or defibrillator needs.

More information

The American Heart Association has more on pacemakers.