In a system and method for reconstructing cardiac activation information, an analysis cardiac signal and a reference cardiac signal are accessed and processed to determine a first point of change in the analysis cardiac signal at which a derivative of the analysis cardiac signal diverges with respect to a derivative of the reference cardiac signal. The signals are processed to determine a second point of change in the analysis cardiac signal at which a different derivative of the analysis cardiac signal with respect to a different derivative of the reference cardiac signal. An activation onset time is assigned in the analysis cardiac signal at a point based on a mathematical association of the first point of change and the second point of change to define cardiac activation indicating a beat in the analysis cardiac signal.