An implantable medical device is configured determine a numerical value of a variable that is monitored by the implantable medical device and convert the numerical value to a data sequence of modulated electrical stimulation rate intervals. The implantable medical device delivers electrical stimulation pulses according to the data sequence of modulated stimulation rate intervals to cause a modulated rate of activation of excitable tissue of a patient corresponding to the modulated stimulation rate intervals. The modulated rate of activation is detectable by a rate monitor for demodulation to the numerical value of the monitored variable data value. In some examples, the implantable medical device is a pacemaker delivering cardiac pacing pulses according to modulated pacing rate intervals to cause a modulated heart rate of the patient detectable by a heart rate monitor for demodulation to the numerical value of the monitored variable.
