Active implantable medical device for the treatment of heart failure with vagus nerve stimulation

An active implantable medical device for treatment of heart failure with vagus nerve stimulation (VNS), comprising:

• a generator configured to produce bursts of VNS pulses according to of several different selectable VNS therapy configurations;
• a sensor configured to measure a current activity level of a patient and generate an activity signal depending on the current level of activity of the patient;
• and
• a controller for the generator that changes the bursts in response to the activity signal, the controller comprising one or more circuits configured to:
• determine in which class the current activity level is among a plurality of classes of activity, each of the plurality of classes having limits of the level of activity within the class, wherein each class of activity is defined by limits comprising an upper and a lower measurement level of the sensor and the class of the current activity level is determined by comparing the measured current activity level to the limits of the classes;
• select a respective VNS therapy configuration depending on the activity class determined by the one or more circuits using the limits of the classes;
• and
• dynamically re-calibrate the activity class limits by conducting a historical analysis of the current activity levels of the patient over a predetermined period of analysis;
• and
• defining the limits of the classes of activity based on results of said historical analysis;
• wherein the one or more circuits are configured to periodically conduct the re-calibration.