A pacemaker consists of a tiny but sophisticated computer, software instructions for that computer, various delicate electronic components, and a battery—all enclosed within a small metal container. (A typical pacemaker today is about the size of a 50-cent piece, and about three times as thick.) Pacemakers are usually implanted under the skin, just below the collarbone, and are connected by leads—or insulated wires—to your cardiac chambers. The pacemaker monitors your heart rhythm, beat-by-beat, and makes moment-to-moment decisions about whether or not it should pace your heart. If your heart rate falls below a pre-determined value, it "paces" by sending a tiny electrical impulse to your heart through the lead, thus stimulating your heart to beat.
Why Don't Pacemakers Have Replaceable Batteries?The engineers who design pacemakers had to solve several difficult problems, one of the most difficult being how to keep the pacemaker functioning perfectly, inside the human body, for several years. The inside of the human body is a warm, wet, and salty place -- a very hostile environment for any electronic device. So among other things, a pacemaker must be hermetically sealed (to keep moisture and body fluids out), and its delicate electronic components must be designed to survive and function in this hostile environment for a long time. Engineers have become very good at building these devices to last for many years, and the failure rate for pacemakers, in general, is well under 1% after five years of use.
It's critically important for pacemakers to be hermetically sealed in order to protect these devices from the hostile environment in which they must function. If pacemakers were capable of being opened so that the battery could be replaced, hermetic sealing would be impossible. Instead, the battery must be permanently sealed within the device, along with all the other delicate electronic components. This explains why it's impossible to make pacemakers with replaceable batteries.
Why Aren't Pacemaker Batteries Rechargeable?The technology for recharging batteries wirelessly (a process also known as inductive charging) has been around for several decades, and you can buy wireless rechargers for your cell phones today. So why don't pacemaker companies build rechargeable pacemakers?
You may be surprised to learn that the original implantable pacemakers from 1958 had rechargeable nickel-cadmium (NiCad) batteries, and most people believed that the use of rechargeable batteries would always be necessary for implantable electronic devices. These pacemakers were recharged by holding an inductive coil up against the skin, near the pacemaker, for several hours. This procedure had to be repeated every few days.
Rechargeable pacemakers ultimately failed for two reasons. First, even though they're rechargeable, NiCad batteries have a relatively short service life, so these pacemakers still needed to be replaced often. But probably more importantly, with human nature being what it is, patients often failed to recharge their pacemakers according the rigorous schedule that was imposed upon them. Lawyers informed the pacemaker companies that if a patient suffered harm because his/her pacemaker stopped working—whether the failure to recharge the device was the "fault" of the patient or the company—subsequent lawsuits would likely produce bankruptcy.
Within a few years, mercury-zinc batteries were developed that could keep a pacemaker going for up to two years. Soon thereafter, lithium-iodide batteries were developed which could power a pacemaker far longer than that: for 5 to 10 years. So the pressing need for rechargeable pacemakers disappeared, while the imminent threat of lawsuits did not.
Thanks to both technological advances and the legal profession, rechargeable pacemakers were quickly abandoned.
Why Can't They Make Pacemaker Batteries Last Much Longer Than They Do Now?The fact is, they could make pacemaker batteries that last substantially longer than they do now. In fact, in the 1960s and 1970s, a few pacemaker companies made nuclear-powered pacemakers which were powered by plutinium-238—which has a half-life of 87 years—so these pacemakers were virtually guaranteed not to run out of "juice" during the lifetime of the patient. Indeed, a few of these pacemakers are said to still be in operation today.
There were some obvious problems with nuclear pacemakers: first, plutonium is a highly toxic substance, and even if a miniscule amount leaks into the bloodstream, death would rapidly ensue. And because plutonium is obviously a substance of great interest to both regulators, and even the darker elements within our civilization, people with these pacemakers faced problems when they attempted to travel overseas, or even to certain states. Physicians who implanted these devices were required, under a law enforced by the Nuclear Regulatory Commission, to recover the pacemakers upon the death of the patient, which (because patients move away and doctors retire) proved entirely impractical.
There's also a less obvious problem with pacemakers whose batteries last "forever": the fact is that all electronic devices eventually fail. Electronic components break, or just wear out. When a pacemaker fails because the battery wears out, at least that's a gradual and predictable event. As you yourself have said, your doctor knows that your pacemaker battery is going to fail in the next year or so, and he's therefore scheduling an elective pacemaker replacement at your convenience. But if your pacemaker were to fail because one of the other hundreds of electronic components within it suddenly stopped working . . . well, that pacemaker failure could be catastrophic. It could suddenly, without warning, stop pacing—and you could potentially suffer great harm.
If companies began building pacemakers whose batteries lasted substantially longer than 5 - 10 years, with the kinds of electronic components that exist today, too many pacemakers would suffer sudden, catastrophic failure. Rather, pacemakers are designed so that the first component that is likely to "fail" is the battery, and since that "failure" can be predicted ahead of time, the device can be replaced before it stops working altogether.
It is possible, of course—and even likely—that in the future, other electronic components needed for building pacemakers will be made that are more robust, and are also at a reasonable cost. When that day comes, engineers can design batteries that will last substantially longer than they do today.
But with today's technology, a pacemaker that lasts 5 - 10 years turns out to be the engineering "sweet spot."
Mallela VS, Ilankumaran V, Rao NS. Trends in Cardiac Pacemaker Batteries. Indian Pacing and Electrophysiology Journal 2004; 4(4):201.
Maisel WH, Moynahan M, Zuckerman BD, et al. Pacemaker and ICD generator malfunctions: analysis of Food and Drug Administration annual reports. JAMA 2006; 295:1901.