1. A method for analyzing at least one cardiac rhythm having an RR interval series, the method comprising: characterizing RR intervals by at least one dynamic parameter, including entropy; combining the at least one dynamic parameter with at least one density parameter, including mean, standard deviation, or coefficient of variation (CV); classifying the at least one cardiac rhythm based on the combination of the at least one dynamic parameter and the at least one density parameter; and generating a diagnostic output based on the classification, wherein the method employs multivariate statistical models.