|Fig. 1: Artificial pacemaker from St. Jude Medical. (Source: Wikimedia Commons)|
A pacemaker functions to monitor and control your heartbeat. Consisting of a computerized generator, electrodes, wires, and a battery (see Fig. 1), pacemakers receive signals from the heart through the electrodes and generate electric pulses to retain normal heart functions.  The pacemakers also record the heart's electrical activity so that doctors can customize the gadgets to better fit the patients. Nowadays, newer and more advanced pacemakers can monitor blood temperature, respiration rate, and other factors that help to adjust our heart rate in response to changes in daily activities.  Therefore, battery life of these intricate machineries has become very important.
In 1993, there were around 120,000 pacemaker implantations made in the US. That number jumped to 180,000 in 2009.  Over that span, nearly three million Americans had pacemakers implanted. Many of the patients had became sicker and older over time. For many of these patients, replacing the batteries on the pacemakers exposes them to a series of serious complications, such as life threatening infections. The resulting cardiac sepsis maybe irreversible and most often will be fatal among patients with numerous preexisting heart-related disabilities.
Whether it's due to the limited technological innovation or the lack of financial incentive for manufacturers, pacemakers have an average lifespan of around 10-15 years. Short battery life means more frequent replacement surgeries, which come with 1-5 percent infection rate.  In addition to pacemakers, implantable cardioverter defibrillators (ICD) have a longevity of at most seven years, which comes with the risk of more possible infections that require extraction of the entire organ system. 
As of now, the main way to increase longevity of pacemakers has been through reducing the amount of pacing and thus minimizing the drain of current from the pacing. Because pacemaker generator longevity is most dependent on the current consumption and resistance of the impedance leads, the usage of high impedance leads seem to lower current waste in implants.  High impedance leads with around 1000 ohms compared to the standard 600 ohms proved to increase the longevity of the pacemaker through the first 6 years of implantation.  The measurements, however, became statistically insignificant afterwards. And, even with this development, there remains the need for accurate battery energy readings. Many of the current pacemakers and ICDs are replaced 3-12 months earlier than they should be, which increases the frequency of replacement surgery. 
Constant efforts need to be made to utilize the energy in the pacemaker batteries more efficiently to reduce the frequency of replacement surgeries. While this can be done through smart programming, full depletion before replacement, and research on rechargeable batteries, the solution may be to incentivize the medical providers and manufacturers to develop devices with better longevity. 
© James Bai. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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