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The Digital Pacemaker

In the late 1970s, digital technology began to be incorporated into pacemakers. Until that time, analog timing circuits controlled pacemakers. Initially, the digital systems made use of digital memory and counters to more precisely control timing cycles. This was combined with small memories to store programmed parameter values. As memory grew, simple sensed and paced event counters were added as well. However, other systems, such as the sensing amplifiers and filters within the device, remained based on analog technology. A major step into the digital era took place with the introduction of microprocessors in pacemakers (DGP-1, Vitatron Medical B.V., Dieren, the Netherlands) in 1981. Now the pacemaker could not only store data, but also it could make intelligent decisions based on the data acquired on rate and/or rhythm. This opened the door to features like rate smoothing, automatic overdrive pacing, and eventually sensor driven pacing and advanced dual chamber pacing. With only analog circuits, these important features could never have been implemented. Simultaneously, the increase in memory available allowed an expansion of the diagnostic information and other types of information to be stored in the pacemaker memory. Presentation of these data could be enhanced with histogram and Holter functions, accumulating relevant clinical data over longer periods of time. At that stage the further implementation of digital technology paused and mainly focused on more memory and processing power. Little attention was paid to further digitizing the device, primarily because the remaining analog circuits were difficult to digitize. Even if migration to a digital platform could be realized, the clinical application was not always clear. The input and the output stage of a pacemaker will always remain analog, as they must connect with a nondigital, biological interface (comparable to the microphone-amplifier and amplifierspeaker in a mobile digital telephone). Digital Signal Processing (DSP) has been available for more than a decade in many types of consumer elec-