Abstract: There is provided a pacemaker system with an SRD detection and intervention feature, which enables a simple way of initiating confirmation of SRD, i.e., looking for an AS/AP transition in a DDD or DDI pacemaker, or a transition from a VS to a VP in a DDI pacemaker. This simple initiation of SRD confirmation is made possible by use of a relatively wide hysteresis band which is normally operative when a spontaneous rate is present, and which tracks physiological changes in the patient's natural rate, across the pacemaker rate range. Transitions which result from a gradual decrease in natural rate and thus represent physiological bradycardia are not interpreted as suggesting SRD. The detection is confirmed only after a predetermined number of pace pulses are delivered at the hysteresis rate, i.e., 1-5 pulses.

Abstract: An implantable pacemaker system is provided with a conditional hysteresis feature, whereby a hysteresis value is added to the pacing escape interval only when the prior spontaneous rate corresponded to a rate below the top of a predetermined hysteresis band. This feature limits the lengthening of the escape interval when there are sudden drops in the natural rate thereby avoiding excessive changes in rate. In a preferred embodiment, the pacemaker defines a hysteresis band around a given pacing rate, e.g., lower rate limit, the band having an upper hysteresis limit and a lower hysteresis limit. No hysteresis lengthening of the escape interval is utilized for spontaneous heartbeats having rates above the upper hysteresis limit; for spontaneous heartbeats having rates between the lower rate limit and the upper hysteresis limit, an escape interval is set to have a value corresponding to a rate between the pacing limit and the lower rate limit of the hysteresis band which is, e.g.