Detecting or validating a detection of a state change from a template of heart rate derivative shape or heat beat wave complex

A medical device system, comprising:

• a cardiac data collection module configured to obtain a time series of cardiac data from a patient;
• a parameter selection module configured to select at least one parameter from the cardiac data time series;
• a reference parameter value determination module configured to determine a magnitude, a duration, a direction and a rate of change of a characteristic of the heart's beat contractility during a reference state;
• a state change determination module configured to indicate an occurrence of a brain state change when at least one value relating to the characteristic of the heart's beat contractility is different than at least one reference value for a selected time period;
• and
• a therapy device configured to initiate an electrical stimulation based on the occurrence of the brain state change.