“…Long-term electrocardiographic (Holter) recordings have permitted the appraisal of rhythm during variation of autonomic input throughout the day. Time, (Malik et al, 1996;Shaffer and Ginsberg, 2017) frequency, (Csepe et al, 2016) and geometric (tachograms, histograms, Poincaré plots) (Esperer et al, 2008;Khandoker et al, 2013;Borracci et al, 2018) domain indices are often used in the assessment of heart rate (sinus) variability (Malik et al, 1996;Billman, 2011;Billman et al, 2015b;Shaffer and Ginsberg, 2017). Furthermore, to understand better the complexity of biophysical oscillators like the sinus node, advanced methods have been developed to analyze heart rate variability such as measures of fractal-like behavior (long-term analysis), detrended fluctuation (Stein et al, 2005) (short-term analysis), disorder (approximate and sample entropy), non-linear dynamical systems (multiscale Poincaré plots) (Henriques et al, 2015;Shaffer and Ginsberg, 2017) and chaotic behavior (Nicolini et al, 2012;Sassi et al, 2015;Zhang et al, 2015;Behar et al, 2018b;Valente et al, 2018).…”