1. A method of determining a cardiac event, comprising: determining a plurality of cycle lengths associated with sensed cardiac signals; determining differences between consecutive cycle lengths of the determined plurality of cycle lengths; determining cluster signature metrics in response to the determined differences; identifying the cardiac event in response to the determined cluster signature metrics; generating a plot corresponding to the determined differences; determining a number of the determined differences that are located within a plurality of segments of the plot defined by a range of magnitudes and phases relative to an origin of the plot and corresponding to patterns associated with the cardiac event; and determining a number of the determined differences that are located in a first segment of the plurality of segments relative to a number of the determined differences that are located in a second segment of the plurality of segments to generate a first output.