The power problem
A pacemaker’s job is simple in principle: deliver a small electrical pulse, about once a second, for years. In practice, the energy source was the main limit on the first implanted devices. The battery had to be small, safe inside the body, reliable and long-lasting, and it also determined how often a patient had to return to the operating room. Pacemaker batteries therefore shaped the size, shape, sealing and even the follow-up schedule of the devices.
The first cells: short lives
The first implanted units of 1958 and 1960 used small cells available at the time. The Swedish unit of Elmqvist and Senning used rechargeable nickel-cadmium cells, which were topped up by a coil placed on the skin that transferred energy by induction, and the patient had to remember to recharge. Electronic failures and sealing problems limited that first device’s life in any case.
The American unit by Wilson Greatbatch and William Chardack used mercury-zinc cells, a common type in the 1950s hearing aids and other small electronics. They provided a steady voltage and were compact, but they were generally limited to a couple of years in a pacemaker, with variation between units. A significant weakness was that mercury-zinc cells could produce hydrogen gas, so the case could not be completely sealed in the way later devices would be, and body fluid sometimes seeped in. Replacing a pacemaker meant another operation, which carried its own risks.
Rechargeable ideas
Because replacement surgery was a burden, designers tried rechargeable systems in the 1960s, using nickel-cadmium cells and external charging. Some were used in patients. They offered the promise of a device that would not need to be replaced for battery reasons. In practice, they had problems: charging was inconvenient, the cells and charging circuits could fail, and the technology of the time did not deliver long enough life. Rechargeable pacemakers declined in clinical use, though the idea has returned for other implants such as nerve stimulators, where power demand is higher. Developments in lithium-ion batteries for consumer electronics later renewed interest in rechargeable implant power, and the broader history of energy storage shows how long it took for compact cells to improve.
Nuclear power
Another approach used radioactive isotopes. In the 1970s, a number of pacemakers were powered by a small amount of plutonium-238, which produces heat as it decays, converted to electricity. They were designed to last a decade or longer. Some were implanted in patients, and the concept is a minor chapter of the history, although it was tied to the same nuclear technology as the nuclear reactor. The devices raised issues of radiation shielding, disposal and regulation, and they fell out of use as lithium batteries became available.
The lithium revolution
The change that mattered most came in the 1970s with lithium cells. Lithium-iodine batteries, developed for pacemakers with Wilson Greatbatch playing an important role, provided higher energy density and a very slow, predictable decline in voltage. Another advantage was that the chemistry did not produce gas, so the device could be hermetically sealed in a welded metal case, usually titanium, which protected the electronics from body fluids. The battery’s gradual decline also meant doctors could detect approaching depletion during routine checks and schedule a replacement ahead of time.
Pacemakers using lithium batteries commonly lasted many years, and manufacturers’ estimates for modern devices are often in the range of roughly 5 to 15 years depending on settings and how much the device paces. Those figures vary with the device, the patient’s needs and the model, so they should be taken as rough ranges rather than guarantees.
How battery life shaped design
Power had a direct effect on the design of the electronics. As integrated circuits replaced discrete transistors, devices used less current, so batteries could be smaller or last longer. Designers learned to save energy by pacing only when needed. A pacemaker that senses the heart’s own beat and inhibits itself, a design introduced in the 1960s, avoids wasting energy and also avoids competing with the natural rhythm. Later devices could adjust the strength and duration of each pulse to the minimum that reliably captured the heart. Such features, together with improved leads and the silicon chips used in modern controllers, allowed longer service.
Batteries also affected other aspects. The size of the device was largely determined by the cell, which is why many pacemakers are shaped to fit a battery. Follow-up routines, including checking for an “elective replacement indicator” that signals the battery is approaching the end of its useful life, grew from the way lithium cells behave. Replacement still involves surgery on the generator, though not necessarily new leads.
Looking back
The pacemaker is often described as an electronic invention, but its history shows how much depended on chemistry and sealing. The same lessons applied later to defibrillators, which need large bursts of energy, and to artificial hearts, which need far more power than any pacemaker. This article is history only and is not medical advice about any device.