ABC | Volume 112, Nº5, May 2019

Original Article Gonzaga et al Cardiac autonomic modulation in breast cancer Arq Bras Cardiol. 2019; 112(5):555-563 Figure 1 – Study design: recruitment and analysis. 348 – women registered in the medical record of the encology department 124 – Women with breast cancer evaluated by eligibility criteria 109 – Not eligible for this study and/or refused to participate in the study 15 – Women with breast cancer eligible for this study 189 – Women without breast cancer evaluated by eligibility criteria 156 – Not eligible for this study and/or refused to participate in the study 33 – Women without breast cancer eligible for this study Analysis of premature ectopic beats and artefacts and only series of RR intervals that presented more than 95% of sinus beats were included in the study. Calculations of the HRV indices were performed using Kubios HRV Analysis software version 2.0 (Kuopio University, Finland). 16 The following indices were analyzed in the time domain: Mean RR, which represents the mean RR intervals; Mean HR, which corresponds to mean heart rate; SDNN, which represents the standard deviation of all normal RR intervals; RMSSD, which corresponds to the square root of the sum of the square of the differences between the RR intervals in the record, divided by the number of RR intervals in a given time minus one RR interval; and finally the NN50 (number of pairs of successive NNs that differ by more than 50 ms) and pNN50 (proportion of NN50 divided by total number of NNs), where the NN50 is the counter of the number of times that successive NN intervals present a duration difference greater than 50ms, and the pNN50 is the ratio obtained by the NN50 / n ratio. 17,18 In the frequency domain, low frequency (LF: 0.04 - 0.15 Hz) and high frequency (HF: 0.15 - 0.40 Hz) spectral components were analyzed in ms² as well as the ratio between the components (LF/HF). The spectral analysis was calculated using the Fast Fourier Transform algorithm. 18 In addition, the RRtri (RR triangular), TINN (triangular interpolation of NN interval), and Poincaré plot were also calculated, which was quantitatively and qualitatively analyzed. The RRtri and TINN were calculated by constructing a density histogram of normal RR intervals, which contains the length of the RR intervals on the x-axis and the frequency with which they occurred on the y-axis. 18 The union of the points of the columns of the histogram forms a figure similar to a triangle from which these indices are extracted. 18 The Poincaré plot is the two-dimensional graphical representation of the correlation between consecutive RR intervals, where each interval is plotted against the next interval. For quantitative analysis of the plot, the SD1 (standard deviation of instantaneous beat-to-beat variability) and SD2 indices (long-term standard deviation of continuous RR intervals) were calculated. 18 The qualitative analysis of the plot was carried out through the analysis of the figures formed by its attractor, which demonstrates the degree of complexity of the RR intervals. The following patterns were considered: I) Figure showing an increase in the dispersion of RR intervals, characteristic of a normal plot; II) Figure with small global dispersion, with no increase in the dispersion of RR intervals in the long term, characteristic of a plot with lower variability. 19 Blood samples Blood collection was performed in a private laboratory and for the biochemical analyzes the volunteers respected a 12-hour fast. The collection was performed in a vacuum tube with separator gel without anticoagulant; after collection, the blood was centrifuged for 10 minutes at 3000 rpm to separate the serum from the other blood components, which was used for the analyzes. For the determination of glycemia, triglycerides, and the HDL-cholesterol fraction, a colourimetric enzyme kit was used in an Autohumalyzer A517 device 17 (HUMAN et al., 2004). CRP was measured using an enzyme ELISA kit: Immulite 2000 analyzer (Siemens Healthcare Diagnostics). 20 Statistical analysis The descriptive data for characterization of the sample are expressed as percentage, mean, standard deviation. In order to compare the anthropometric variables, age, and the HRV indices between the groups, the normality of the data was initially tested using the Shapiro-Wilk test. If the normal distribution was accepted, the Student's t-test for unpaired data was applied, while for non-normal distributions the Mann-Whitney test was applied. The continuous variables that did not present normal distribution were described through median and interquartile range and those that presented normal distribution were described through mean and standard deviation. The correlation between the HRV indices and the independent variables CRP, fasting glycemia, triglycerides, and HDL-cholesterol was verified by linear regression in unadjusted and adjusted models, considering the age of the volunteers. For both analyzes, statistically, significant differences were considered when the "p" value was lower than 0.05. The program used for statistical analysis was the "Statistical Package for Social Sciences" version 15.0 (SPSS Inc., Chicago, Illinois, United States of America). 557