Patent ID: 8909331

Claim:
An implantable cardiac system for monitoring or treating a patient's heart, the implantable cardiac system including at least a plurality of implantable electrodes and operational circuitry coupled to the electrodes for performing cardiac signal analysis, in which the operational circuitry is configured to perform a cardiac signal analysis comprising: sensing a signal using the implantable electrodes; detecting events in the sensed signal, the detected events separated by intervals; at a first time, using a first method to estimate a heart rate for the patient using information related to the detected events; comparing the heart rate for the patient estimated using the first method to a rate threshold and determining that the threshold has been crossed; at a second time after determining that the rate threshold has been crossed, using a second, different method to estimate the heart rate for the patient; wherein the operational circuitry is further configured such that: the first method to estimate heart rate comprises averaging a set of intervals between detected events; and the second method to estimate heart rate comprises choosing intervals according to a set of interval selection rules and calculating a rate based upon the chosen intervals.