The automatic rate adjustment pacemaker. The possibilities of rate hysteresis.

Since the first use of pacemakers there have been attempts to regulate the fixed, or basic rate of implanted pulse generators. Earlier models employed the use of magnets or percutaneous needles to change the pacemaker rate after implantation. A recent development is the programmable pacemaker, which utilizes external electromagnetic signals to alter the basic rate. A series of engineering advances have resulted in automatic pacemaker rate changes, as first embodied in the hysteresis pacemaker. Notable modifications of the basic hysteresis concept include gradual pacemaker rate changes, and variable hysteresis or rate changes dependent on electrophysiologic events. Many of these technical advances are unknown to physicians, but are disclosed in patents. In general, negative hysteresis favors emergence of underlying non-pacer rhythms, whereas positive hysteresis suppresses underlying rhythms of any type. The automatic rate adjustment pacemaker represents an attempt to derive the advantages of negative hysteresis while eliminating the disadvantages of abrupt rate changes. The unit automatically searches for a sinus rhythm slower than the basic pacing rate, by periodically gradually slowing its rate to a lower level.