Modified Ehlers´ index for improved detection of heart rate asymmetry in Poincaré plot

Heart rate asymmetry (HRA) is a quantifiable and visible phenomena in e¿ plot which is defined with respect to line of identity (RR(i) = RR(i+1)). In general, third moment measure (skewness) is most appropriate for quantifying asymmetry of any time series signal. Existing Elhers´ index (E1) is the third moment measure but it is defined based on the actual time series signal. The aim of this study is to redefine E1 as EI_R in view of stated HRA definition. The new index calculated as a third moment along the minor axis of the plot from the derived signal along this axis. To show the benefit of EI_R over EI, we have calculated both index values of 54 Normal Sinus Rhythm (NSR) and 272 Arrhythmia subjects taken from Physionet NSR and Arrhythmia databases. The results showed that EI_R (ROC area = 0.80) discriminates NSR from Arrhythmia subjects better than EI (ROC area = 0.59). This study could be useful for quantifying HRA in Poincare¿ plot and classifying different pathology conditions.