Patent ID: 7580745

Claim:
A cardiac rhythm management system, comprising: a pacing output circuit to deliver pacing pulses; a sensing circuit to sense a cardiac signal; a heart rate variability (HRV) measurement circuit, coupled to the sensing circuit, to measure an HRV being a variance in cardiac cycle lengths over a predetermined period of time based on the sensed cardiac signal and to produce an HRV parameter based on the HRV measurement, the HRV parameter being a measure of the HRV; and a pacing control circuit coupled to the pacing output circuit, the sensing circuit, and the HRV measurement circuit, the pacing control circuit including: a pacing algorithm execution module to control the delivery of the pacing pulses by executing an atrial tracking pacing algorithm using pacing parameters including a maximum tracking rate (MTR); and an MTR adjustment module including an indication, estimation, or prediction of an activity level coupled to the HRV measurement circuit and the pacing algorithm execution module and including a comparator to compare the HRV parameter to a plurality of threshold HRV levels, the MTR adjustment module adapted to dynamically adjust the plurality of threshold HRV levels using said indication estimation, or prediction of an activity level and adjust the MTR using a result of comparing the HRV parameter to the plurality of threshold HRV levels.