A pacemaker is a battery-operated device placed in body to produce electrical pulses that cause the heart to beat at a normal rate. Recent research studies have described the use of energy harvesting to power a pacemaker. The goal for energy harvesting in this case is to eliminate the need for a battery by generating electricity derived from an external source.

Eliminating the battery would get rid of the weakest link in the pacemaker’s reliability chain. Once a pacemaker battery reaches a critically low energy level, physicians must replace a correctly functioning pacemaker in a surgical intervention, which increases costs and adds possible patient complications. In addition, wires from the battery to the pacemaker are prone to fracture.

 

Replacing batteries with an external energy source would spare patients from repeated interventions and make pacemaker wires obsolete. Researchers didn’t have to look far for a good source of energy. The heart is a promising external energy source for energy harvesting in the body because its contractions are repetitive and occur 24 hours a day, 7 days a week around the clock.

Drawing on their clock-making heritage, Swiss scientists from the University of Bern are adapting technology from automatic watches to power pacemakers with nothing more than the motion of the beating heart. The Swiss automatic wristwatch mechanism, invented in 1777, has a good reputation as a reliable technology.

Adrian Zurbuchen of the university of Bern explained that an automatic watch ‘harvests’ its energy from the wrist by transforming mechanical energy into electrical energy. An automatic wristwatch accelerates due to the movement of the wearer’s arm. This rotation progressively winds a mechanical spring that, once fully charged, unwinds again and spins an electrical micro-generator. Thus, attaching a pacemaker to the heart would allow a similar system to be directly exposed to the movement of the heart’s myocardial muscle.

Researchers copied the wristwatch mechanism. They removed unnecessary parts to reduce weight and size and then developed a custom-made housing with eyelets so it could be stitched directly onto the heart muscle tissue. Results showed that the device generated a mean output power of 52 microwatts, which is more than adequate to power a modern pacemaker that consumes only about 10 microwatts. It was implanted into a 60 kg pig where it successfully restored its heartbeat to 130 beats per minute.

To test the prototype, researchers developed an electronic circuit to transform and store the power into a small energy buffer and then sent it to a custom-made cardiac pacemaker. The system works in three steps. First, the harvesting prototype acquires energy from the heart. Then, the energy is temporarily stored in the energy buffer. Next, the buffered energy powers the pacemaker, which applies stimuli to the heart.

“This answers our core question that heart motion can be converted into electrical energy that exceeds power requirements of modern pacemakers,” said Zurbuchen, whose group now plans to reduce the size and weight of the prototype to make it more sensitive to heart motion. Zurbuchen added that the technology has potential for use in a multitude of devices, including defibrillators, loop recorders and drug delivery pumps.