Pacemakers and implantable cardioverter-defibrillator (ICD) are used to treat cardiac arrhythmias, disorders associated with abnormal electrical activity in the heart. Arrhythmias may occur occasionally in healthy hearts but in other cases, they may indicate a serious problem that may lead to heart disease, stroke or sudden cardiac arrest.

Pacemakers have come a long way. Early models simply supplied a steady electrical impulse to support a malfunctioning heart. However, these early models did not adapt their rate to the physiological needs of the patient, were very large, and were made from unsuitable materials.

In 1981 the first rate-responsive pacemaker, a pacemaker that adapted the rate to the needs of the patient, was implanted. This was a major advancement as the device was able to adapt its pacing even when the sinus node, the natural pacemaker, was damaged. The device used others than the signals from the sinus node to predict the physiological needs of the patient.

Today, pacemakers contain not only electrodes that measure the naturally occurring activity of the heart but include other sensors to measure oxygen and physical activity (measured by an accelerometer) to determine the optimal pacing rate. Central to this development are integrated circuits (computer chips) that combine the flood of measured parameters with an ever-increasing sophistication to predict the optimal pacing rate.

Pacemakers currently under development include even more sensors combined with increased computational power. The goal is to mimic nature by utilizing various bodily parameters to determine the optimal heart rate. Besides measuring oxygen and physical activity, these prototypes include sensors for CO2, body temperature, adrenaline and ATP (the main energy molecule in the cell) to optimize the pacing rate. At the same time, sophisticated algorithms programmed into computer chips do not only react to the measured parameters but also predict the anticipated short-term pacing needs. The most modern devices already contain a wireless emitter that is able to send critical information to the physician. However, more sophisticated information systems are expected in future devices.