CIRCADIAN RATE VARIATION IN RATE-ADAPTIVE PACING SYSTEMS

By mimicking the natural rate slowdown during sleep, a pacing system can enhance patient comfort while improving device longevity. A new family of rate-adaptive pacemakers accomplishes this circadian rate variation by modeling the patient's sleep-wake cycle using a time-of-day clock inside the device. Furthermore, to account for minor variations in the patient's sleep-wake cycle, sensor data can be used to automatically adapt the starting and stopping points of this change in rate. Using the model, the device begins to gradually reduce the pacing rate beginning one-half hour before the selected bed time. Similarly, the rate begins to increase one-half hour before the selected waking time. Sensor data indicating the presence or absence of patient activity are used to adapt the selected bed and wake times, enabling the system to maintain an appropriate schedule despite changes in the patient's actual schedule. The model approximates natural human adaptation times for time zone or work shift changes. This circadian rate adaptation does not preclude the system's rate response to patient activity; even during sleep time the response to moderate or heavy exercise is essentially unchanged.