IJCS | Volume 33, Nº4, July and August 2020

DOI: https://doi.org/10.36660/ijcs.20200192 TheAutonomic Nervous System (ANS) consists of two opposite pathways (sympathetic and parasympathetic) that have action both on the atrial and ventricular myocardium, as well as on atrioventricular and sinus nodes, thus exerting influence on the variation of heart rate (HR). The increase in HR is a consequence of the greater action of the sympathetic pathway and the lower parasympathetic activity (vagal inhibition), while its reduction basically depends on predominance of vagal activity. The influence of ANS on the heart is dependent on information that departs, among others, from baroceptors, chemoreceptors, changes in the respiratory system, vasomotor system, renin-angiotensin- aldosterone system and thermoregulatory system. The discovery of the relationship between ANS and mortality from cardiovascular diseases has led to several studies, which have proven the existence of reduced parasympathetic and increased sympathetic activity in several pathologies of the cardiovascular system. These findings made it necessary to develop quantitative markers of cardiac autonomic activity, and heart rate variability (HRV) is the most promising autonomic marker 1 . Historically, their clinical interest arose in 1965, when Hon and Lee demonstrated a well-defined clinical application of HRV in the area of fetal distress monitoring. In 1977, Wolf et al., 2 showed an association between low HRV and higher risk of mortality after acute myocardial infarction and Kleiger et al., 3 in 1987, confirmed that HRV was a potent and independent predictor of mortality after acute myocardial infarction. In 1996, in an age-stratified cross-sectional study, Barbosa et al., 4 reported >18 % per decade reduction in HRV in healthy adults and >25%per decade reduction in subjects two years post-myocardial infarctionwith persevered left ventricular systolic function. 5 Additionally, the authors observed that aging related HRV decrease was mainly related to reduction in spontaneous vagal activity. In 2002, Nunes studiedHRV variability in preschool healthy children, defining normality ranges for HRV variables in this population. 6 HRV represents the spontaneous and continuous variation of cardiac interbeat interval. Therefore, HRV comprises the oscillations between the RR intervals of heartbeat, which reflect the changes resulting from the action of the ANS on the behavior of HR. HRV's analyses, from linear methods, can be performed as a function of two parameters: time domain (analysis of records deriving from times greater than 10 minutes, expressed in milliseconds, through variation of the duration of intervals between normal QRS complexes resulting from sinus depolarization and its mathematical indices) and frequency domain (records of wave intensity verified in time intervals of up to 4 minutes and it’s unit is determined by Hertz). In the time domain, SDNN and SDNNi are indexes taken through individual RR intervals and represent sympathetic and parasympathetic activities, while rMSSD and pNN50 are obtained through adjacent RR intervals and reflect parasympathetic activity. The parameters obtained by the frequency domain are: HF (High Frequency): values between 0,15 a 0,4Hz, related to respiratory activity and it is an indication 368 EDITORIAL International Journal of Cardiovascular Sciences. 2020; 33(4):368-370 Mailing Address: Nágela Nunes Universidade Federal Fluminense - UFF HUAP - R. Marquês de Paraná, 303. Postal Code: 24220-900, Centro, Niterói, RJ – Brazil. E-mail: nvinhosa@me.com Identification of Preclinical Markers Related to Hereditary Diseases: Expanding the Horizons of the Study of Cardiac Autonomic Modulation Nágela Nunes 1, 2 a nd Paulo R. Benchimol-Barbosa 1, 3 Complexo Hospitalar de Niterói, 1 Niterói, RJ – Brazil. Hospital Universitário Antônio Pedro, 2 Niterói, RJ – Brazil. Hospital Universitário Pedro Ernesto, 3 Rio de Janeiro, RJ – Brazil. Editorial related to the article: Influence of Family History of Diabetes on Cardiac Autonomic Dysfunction of Adolescents Autonomic Nervous System/complications; Diabetes Mellitus/complications; Autonomic Denervation; Genetic Diseases, Inborn; Adolescent. Keywords