A system for determining a health status of a patient using an implantable medical device configured for subcutaneous implantation outside of a thorax of the patient, the system comprising: the implantable medical device comprising at least one optical sensor; and processing circuitry configured to: determine a current tissue oxygen saturation value of the patient based on a first signal received from the at least one optical sensor; determine a current pulsatile oxygen saturation value of the patient based on a second signal received from the at least one optical sensor; compare the current tissue oxygen saturation value and the current pulsatile oxygen saturation value to corresponding ones of a baseline tissue oxygenation saturation value and a baseline pulsatile oxygen saturation value; determine a heart failure status of the patient at least based on the comparison of the current tissue oxygen saturation value to the baseline tissue oxygen saturation value; determine a pulmonary status of the patient at least based on the comparison of the current pulsatile oxygen saturation value of the patient to the baseline pulsatile oxygen saturation value; and determine the health status of the patient based on a combination of the heart failure status and the pulmonary status of the patient. the implantable medical device comprising at least one optical sensor; and processing circuitry configured to: determine a current tissue oxygen saturation value of the patient based on a first signal received from the at least one optical sensor; determine a current pulsatile oxygen saturation value of the patient based on a second signal received from the at least one optical sensor; compare the current tissue oxygen saturation value and the current pulsatile oxygen saturation value to corresponding ones of a baseline tissue oxygenation saturation value and a baseline pulsatile oxygen saturation value; determine a heart failure status of the patient at least based on the comparison of the current tissue oxygen saturation value to the baseline tissue oxygen saturation value; determine a pulmonary status of the patient at least based on the comparison of the current pulsatile oxygen saturation value of the patient to the baseline pulsatile oxygen saturation value; and determine the health status of the patient based on a combination of the heart failure status and the pulmonary status of the patient. determine a current tissue oxygen saturation value of the patient based on a first signal received from the at least one optical sensor; determine a current pulsatile oxygen saturation value of the patient based on a second signal received from the at least one optical sensor; compare the current tissue oxygen saturation value and the current pulsatile oxygen saturation value to corresponding ones of a baseline tissue oxygenation saturation value and a baseline pulsatile oxygen saturation value; determine a heart failure status of the patient at least based on the comparison of the current tissue oxygen saturation value to the baseline tissue oxygen saturation value; determine a pulmonary status of the patient at least based on the comparison of the current pulsatile oxygen saturation value of the patient to the baseline pulsatile oxygen saturation value; and determine the health status of the patient based on a combination of the heart failure status and the pulmonary status of the patient.