Pacemakers are battery-driven devices, and like all batteries, pacemaker batteries eventually wear out. When that happens, the whole pacemaker — and not just the battery — has to be replaced. A natural question, which cardiologists hear a lot from their patients with pacemakers, is: Why? Why not just replace the battery, instead of the entire, very expensive, pacemaker? Or, alternately, why not make the pacemaker batteries rechargeable?
These are both good questions. Let’s have a look at why pacemaker developers have built devices that need to be discarded and replaced in their entirety when the battery wears out.
What Pacemakers Do
Typically, the purpose of a pacemaker is to prevent symptoms from sick sinus syndrome or heart block, conditions which can slow your heart rate enough to produce symptoms (such as lightheadedness, palpitations or syncope).
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 predetermined value, it “paces” by sending a tiny electrical impulse to your heart through the lead, thus stimulating your heart to beat.
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 Human Body Is a Hostile Place for a Pacemaker
Anyone who as spilled coffee on their laptop knows that fluids and electronic devices don’t mix. Pacemakers are electronic devices that must spend their entire existence in a fluid environment.
In fact, 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, adequate hermetic sealing would be next to impossible.
Instead of being removable, the battery must be permanently sealed within the device, along with all the other delicate electronic components. This explains why pacemaker developers have considered it infeasible to attempt to build 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 pretty often.
But probably more importantly, with human nature being what it is, people with pacemakers occasionally failed to recharge their devices according to 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 was the fault of the company or because the patient neglected to recharge the device — 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 five to 10 years. So the pressing need for rechargeable pacemakers diminished, while the imminent threat of lawsuits did not.
Thanks to both technological advances and the legal profession, the idea of rechargeable pacemakers were quickly abandoned. It is an idea that is reconsidered by pacemaker developers every once and a while, but so far the potential risks (to the companies, at least), have outweighed the potential benefits.
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 plutonium-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 may still be in operation today.
But, as you might imagine, there were some obvious problems with nuclear pacemakers: first, plutonium is a highly toxic substance, and even if a minuscule amount leaks into the bloodstream, death would rapidly ensue. And because plutonium is obviously a substance of great interest to regulators (and to even the darker elements within our civilization), people with these pacemakers faced problems, for instance, when they attempted to travel overseas.
Physicians who implanted these devices were required, under a regulation enforced by the Nuclear Regulatory Commission, to recover the pacemakers upon the death of the patient, a requirement 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. Sooner or later all 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. By making periodic checkups, doctors have several months warning that a battery is wearing down and is likely to need replacement. So an elective pacemaker replacement can be scheduled at a convenient time.
But if your pacemaker were to fail because one of the other of its hundreds of electronic components suddenly stopped working…well, that could be catastrophic. The pacemaker could suddenly stop pacing, without any warning — and its owner could potentially suffer great harm.
If companies began building pacemakers whose batteries lasted substantially longer than five to 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 substantially more robust without being cost-prohibitive. When that day comes, engineers can design batteries that will last substantially longer than they do today.
With today’s technology, a pacemaker that lasts five to 10 years turns out to be the engineering “sweet spot”—for now.
A Word From Get Meds Info
Pacemakers are a marvel of engineering, and have their effectiveness and reliability have improved tremendously since these devices were first invented. But there is still room for improvement. A lot of research and development is being done by pacemaker manufacturers to develop devices that are easier to implant, are even safer, and will last a lot longer than they do today — potentially, for the life of the person who receives one.