1. A computer readable program storage unit encoded with instructions that, when executed by a computer, perform a method for indicating an occurrence of a state change, comprising: obtaining a time series of cardiac data from a patient; determining a reference heart rate parameter from said cardiac data; determining a heart rate derivative shape from said time series of cardiac data, wherein said heart rate derivative shape comprises at least one characteristic selected from a number of phases relative to said reference heart rate parameter, a number of extrema of said heart rate derivative, a number of directions of change of said heart rate derivative, an area under the curve of at least one phase, a number of positive phases, or a number of negative phases; and, indicating an occurrence of a state change based upon a determination that said heart rate derivative shape matches a state change template in said at least one characteristic, wherein said at least one characteristic of said state change template comprises two or more phases relative to said reference heart rate parameter, two or more extrema of said heart rate derivative, three or more directions of change of said heart rate derivative, a number of positive phases, or a number of negative phases, provided the total number of positive phases and negative phases is two or more.