Artificial pacemakers, also called pacemakers, discharge electrical impulses in two ways. They can be programmed to emit electrical impulses at a steady rate that does not respond to the activity of the heart. These are known as fixed-rate pacemakers. Alternatively, demand pacemakers can discharge electrical impulses when the heart rate falls outside of a predetermined zone or skips a beat. Demand pacemakers are thus used to regulate arrhythmias, which are heart rhythms that are irregular, where the heart beats either too rapidly or too slowly.
Pacemakers that work on demand are known as permanent pacemakers. They are implanted to regulate heart-rate problems that occur over extended periods of time. In 1958, Wilson Greatbatch and W.M. Chardack created the first implantable permanent pacemaker. Just six years later in 1964, Greatbatch designed the demand pacemaker, which became available for use in 1966. The advantages of using demand pacemakers were realized shortly after this.
One advantage of a demand pacemaker is that they prevent the occurrence of what are known as competitive beats. They occur when the heart’s intrinsic pace-making mechanism and an fixed-rate pacemaker stimulate a heartbeat at the same time. This simultaneous firing usually happens because arrhythmias are only intermittent. When they are not occurring, the heart’s intrinsic pacemaker fires and the heart beats normally. A fixed-rate pacemaker cannot detect intrinsic heartbeats and will emit electrical impulses at the same time that the hearts own pacemaker fires, causing the competitive beats. Once thought to be harmless, competitive beats have been associated with higher mortality rates and health problems in pacemaker patients.
The demand pacemaker senses the activity of the heart, which allows it to refrain from emitting electrical impulses while the heart is intrinsically firing. This eliminates the possibility for competitive beats to occur. Doing so has increased the clinical applicability of pacemaker treatment for conditions that would elicit a competitive beat from a fixed-rate pacemaker, but would benefit from some sort of pacing nonetheless.
Another advantage of the demand pacemaker is that firing less often allows it to reserve its battery power for a much longer period of time than fixed rate pacemakers. Demand pacemakers are also advantageous because they protect against a condition known as ventricular asystole. Ventricular asystole refers to the lack of mechanical and electrical activity in the heart—a condition that can cause a person to faint and is in many cases fatal. In sensing the absence of a heartbeat, the demand pacemaker sends an electrical impulse to catalyze the heart to prevent fainting or death from occurring.
