It sounds almost like a perpetual motion machine: A pacemaker that’s powered by the very beating of the heart that it’s regulating. Of course, such a device wouldn’t really be a fantasy of engineering, as the heart would receive energy to power its beats from both the pacemaker and the body’s natural systems. But it’s still a nifty idea.
The idea for a piezoelectric-powered pacemaker, which generates electricity in response to mechanical stress, comes from M. Amin Karami, an assistant professor of mechanical engineering at the University of Buffalo. He’s working on two prototypes, and tells IEEE Spectrum that he’s talking to device-makers about collaborating on a commercial product. “I would guess that in two years we will have the animal tests done, and be ready for human tests” as part of the FDA approval process, he says.
Today’s typical pacemaker is a small flat device that fits easily in the palm of a hand, yet it could be smaller still, Karami said earlier this month in a talk at the MD&M medical device conference. Only about 40 percent of a pacemaker consists of the pulse generator and related electronics, he said; about 60 percent is devoted to the battery. And because the battery eventually gives out, surgeons have to swap out the whole device every seven to ten years. Doing away with the battery would do away with the inconvenience, medical risks, and costs of those replacement surgeries, Karami said.
Karami’s first design is for an energy-harvesting module that could replace the batteries on a conventional pacemaker, which sits in the chest cavity and connects to the heart via insulated wires called leads. His second idea takes the work a step further, and would power a tiny lead-less pacemaker that nestles inside the heart itself. Such miniature devices are just starting to make it to market in Europe.
To power a conventional pacemaker, Karami designed a flat ceramic piezoelectric structure [pdf] that oscillates in response to the vibrations in the chest cavity, which are generated with every heartbeat. He has tested his device with heartbeat rates ranging from 7 to 700 beats per minute, and found that it generated more than enough power to keep a pacemaker running.
But Karami told Spectrum that powering leadless pacemakers would be the best use of his technology. “Conventional pacemakers are a very mature technology,” he says. “But with leadless pacemakers, power is still a big challenge.” To design the piezoelectric power source for these tiny devices, Karami had to come up with a 3D structure that would fit inside the lozenge-shaped device.
A leadless pacemaker doesn’t require surgeons to open up the chest cavity, but can instead be delivered to the heart’s interior through a catheter in a vein. “It’s a simple surgery that can be done easily in developing countries,” Karami notes. Getting rid of the leads also removes a potential point of failure (various cardiac leads have been recalled over the years when their insulation eroded or cracked). “Every time the heart moves, it pulls on the leads,” he says. “And the heart moves significantly. You would be awestruck to see the heart in motion.”