Methods and systems are provided for discriminating rhythm patterns in cardiac activity. The method and system obtain cardiac activity data for multiple cardiac beats over a predetermined period of time. Multi-beat segments within the cardiac activity data exhibit different rhythm patterns of interest including fast and slow rhythm patterns. The method and system calculate a cardiac beats timing relation representative of intervals between the cardiac beats within a measurement window, wherein the measurement window is configured to overlap the corresponding multi-beat segment. The method and system designate the cardiac beats timing relation to have one of the rhythm patterns of interest based on a rate threshold, identifies when successive multi-beat segments exhibit rhythm patterns that transition between the fast and slow irregular rhythm patterns and records the irregular rhythm pattern transition in connection with the cardiac activity data.