An example system and method of reconstructing cardiac activation information are disclosed. An analysis signal and a reference signal are processed to determine whether there is a first point of change in a first selected-order derivative of the analysis signal with respect to a first selected-order derivative of the reference signal above a first threshold. The analysis signal and the reference signal are processed to determine whether there is a second point of change in a second selected-order derivative of the analysis cardiac signal with respect to a second selected-order derivative of the reference cardiac signal above a second threshold. 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.