Systems and methods for evaluating electrograms are described. An example method of evaluating an electrogram such as an atrial and/or ventricular electrogram containing a plurality of data samples each having a voltage includes selecting an activity interval for the electrogram, calculating an energy level for each window of a plurality of windows of the electrogram based on the voltages of the data samples in each window, assigning the calculated energy levels to a plurality of bins, and calculating an index based at least in part on a number of energy levels assigned to a particular bin of the plurality of bins.
