ACTIVITY-CONTROLLED CIRCADIAN BASE-RATE

The current pacing rates are clustered around a fixed base rate since pacemaker patients are usually sedentary, resting, or sleeping most of the time. This fixed base rate is either too low for daytime hemodyna mic support or too high for nighttime rest and recovery. Multiple Holt er studies involving normal individuals have suggested that the restin g base rate fluctuates during the-course of the day. The circadian bas e rate (CBR) algorithm was designed to provide patients with a circadi an change in paced resting rate and a normal rate distribution. The CB R algorithm, using a sophisticated accelerometer sensor, was developed and tested using the downloaded activity data from patients implanted with Trilogy DR+ pacemakers. Twenty-five patients (19 men, 6 women, a ge 72 +/- 9 years) were studied. Trilogy DR+ is able to record the det ailed sensor and system behavior data for a week. During outpatient vi sits, the pacemaker was interrogated and the data accumulated in the p acemaker memory were downloaded. The CBR algorithm was applied to the activity variance histogram to calculate the base rate and to construc t its histogram. The base rates in the CBR histogram are generally bel ow 100 ppm with a distribution that mimics the natural sinus rate dist ribution of normal subjects. The CBR algorithm provides the highest da ytime rates for hemodynamic support and the lowest nighttime rates for cardiac recovery, with a smoothly changing base rate modeling the nor mal circadian variation in heart rate.