A patient monitor in communication with ECG leads is configured to monitor physiological parameters over time to indicate an abnormal condition. The physiological parameters can include an ST parameter and/or action potential, and the abnormal condition can be an anaerobic state. To identify the abnormal condition, the patient monitor identifies a reference physiological parameter measurement of a patient at a first time and determines expected physiological parameter measurements based on different heart rates. The patient monitor compares an expected physiological parameter measurement of a patient at a current heart rate with an actual physiological parameter measurement at the current heart rate. The patient monitor indicates an abnormal condition if the difference between the expected and actual physiological parameter measurement is greater than a threshold amount.
