1. A method for use with an implantable medical device having a detection system that detects an abnormal physiological condition within a patient in which the device is implanted by comparing at least one morphological parameter against a detection threshold, wherein the morphological parameter is derived from signals sensed within the patient, the method comprising: sensing signals within the patient and deriving values of the morphological parameter from the signals; monitoring the values of the morphological parameter to detect a possible occurrence of the abnormal physiological condition; collecting information representative of a range of variation in the morphological parameter within the patient; adjusting the detection threshold based on the information representative of the range of variation in the morphological parameter collected within the patient to improve detection accuracy; and wherein collecting information representative of a range of variation in the morphological parameter within the patient includes: selectively incrementing a plurality of counters based on the plurality of measurements, wherein the counters are representative of different ranges of measurements.