Implantable medical device with chemical sensor and related methods

A method for providing cardiac arrhythmia therapy to a patient comprising:

• optically measuring a physiological concentration of an ion in a bodily fluid of the patient with chronically implanted chemical sensor, the chemical sensor comprising
• a sensing element comprising a potassium ion selective complexing moiety, the potassium ion selective complexing moiety selected from the group comprising cryptands, crown ethers, bis-crown ethers, calixarenes, noncyclic amides, and hemispherands;
• an excitation assembly configured to illuminate the sensing element;
• a detection assembly configured to receive light from the sensing element;
• an opaque cover layer disposed over a side of the sensing element;
• and
• a battery in communication with the excitation assembly, wherein all components of the chemical sensor are implanted within the patient;
• transmitting data regarding the physiological concentration of the ion to an implanted pulse generator;
• measuring temperature with an implanted temperature sensor;
• calculating a compensated physiological concentration measurement of the ion using the measured temperature and the transmitted data regarding the physiological concentration of the ion;
• storing the compensated physiological concentration measurement of the ion with an associated time stamp in a memory of the implanted pulse generator;
• and
• delivering cardiac arrhythmia therapy from the implanted pulse generator to the patient based in part on the compensated physiological concentration of the ion.