Provided herein are implantable devices, and methods for use therewith, that perform at least one of a cardiac assessment and an autonomic assessment. An implantable device is used to sense a cardiac electrogram (EGM) signal, and cardiac intervals are measured within a portion of the sensed EGM signal. Anchor points are identified based on the measured cardiac intervals, and for each identified anchor point, a segment of at least three consecutive said cardiac intervals that is generally centered about the anchor point is defined. The segments defined for the anchor points are averaged to produce an average segment. At least one of a cardiac assessment and an autonomic assessment is performed based on the average segment. This can include assessing a patient's autonomic tone based on the average segment, assessing a patients risk of SCD based on the average segment and/or detecting a myocardial ischemic event based on the average segment. This abstract is not intended to describe all of the various embodiments of the present invention.