Abstract: An implantable medical device monitoring method and system monitors chronic data representative of at least one physiological parameter. The chronic data is monitored to detect changes in state of the at least one physiological parameter. Data associated with detected changes in state is stored within the implantable medical device. The detection of changes in state of the at least one physiological parameter is performed by establishing a baseline (e.g., a center reference line and upper and lower control limits), and then determining if the chronic data being monitored satisfies predetermined conditions (e.g., conditions based on the center reference line and the upper and lower control limits) indicative of a change in state of the at least one physiological parameter. The data stored in memory associated with the detected change in state of the at least one physiological parameter may, for example, include data representative of the center reference line and/or upper and lower control limits.