Intra-subject covariates of QT variability indices: influence of ECG noise

Figures

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  Figure 1. Results of regression analyses relating SDNN and RMSSD-NN values to mean NN intervals. For both univariable regressions, Panels (A, B) show scatter diagrams of p-values of β coefficients, and of β coefficients, respectively. Red circles and blue squares correspond to individual female and male subjects, respectively. Panels (C, D) show cumulative frequences of data shown in the scatter diagrams [p-values of β coefficients in Panel (C) and β coefficients in Panel (D)]. Bold lines correspond to the SDNN/mean NN regressions, dashed lines to the RMSSD-NN/mean NN regressions; red and blue lines correspond to the distributions in female and male subjects, respectively. Panel (C) also shows the threshold of statistical significance (vertical green line). Note that the graphical interpretation of Panel (C) is potentially counter-intuitive: the lower the curve, the more frequent strongly significant results.

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  Figure 2. Results of regression analyses relating SDNN and RMSSD-NN values to ECG noise. The layout and meaning of individual panels correspond to the layout and meaning of Figure 1.

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  Figure 3. Results of the univariable regression analyses relating SDQT and RMSSD-QT values to mean NN intervals (A), SDNN and RMSSD-NN (B), mean QT intervals (C) and ECG noise (D). The layout of all panels and meaning of symbols correspond to the layout and symbols of Panel (A) of Figure 1.

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  Figure 4. Results of the univariable regression analyses relating SDQT and RMSSD-QT values to mean NN intervals (A), SDNN and RMSSD-NN (B), mean QT intervals (C) and ECG noise (D). The layout of all panels and meaning of symbols correspond to the layout and symbols of Panel C of Figure 1. Bold and dashed lines correspond to the regression results of SDQT and to the regression results of RMSSD-QT, respectively.

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  Figure 5. Results of the univariable regression analyses relating SDQT and RMSSD-QT values to mean NN intervals (A), SDNN and RMSSD-NN (B), mean QT intervals (C) and ECG noise (D). The layout of all panels and meaning of symbols correspond to the layout and symbols of Panel B of Figure 1.

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  Figure 6. Results of the univariable regression analyses relating SDQT and RMSSD-QT values to mean NN intervals (A), SDNN and RMSSD-NN (B), mean QT intervals (C) and ECG noise (D). The layout of all panels and meaning of symbols correspond to the layout and symbols of Panel D of Figure 1. Bold and dashed lines correspond to the regression results of SDQT and to the regression results of RMSSD-QT, respectively.

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  Figure 7. Results of the bivariable regression analyses relating SDQT values to the combination of ECG noise with mean NN intervals (A), SDNN (B), RMSSD-NN (C), and mean QT intervals (D). The layout of all panels and meaning of symbols correspond to the layout and symbols of Panel A of Figure 1. In all panels, the regression contributions of ECG noise are shown on the vertical axis, the contributions of the other covariate on the horizontal axis.

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  Figure 8. Results of the bivariable regression analyses relating SDQT values to the combination of ECG noise with mean NN intervals (A), SDNN (B), RMSSD-NN (C), and mean QT intervals (D). The layout of all panels and meaning of symbols correspond to the layout and symbols of Panel C of Figure 1. In all panels, the dashed lines correspond to the contributions of ECG noise, the full lines to the contributions of the other covariate.

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  Figure 9. Results of the bivariable regression analyses relating SDQT values to the combination of ECG noise with mean NN intervals (A), SDNN (B), RMSSD-NN (C), and mean QT intervals (D). The layout of all panels and meaning of symbols correspond to the layout and symbols of Panel B of Figure 1. In all panels, the regression contributions of ECG noise are shown on the vertical axis, the contributions of the other covariate on the horizontal axis.

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  Figure 10. Results of the bivariable regression analyses relating SDQT values to the combination of ECG noise with mean NN intervals (A), SDNN (B), RMSSD-NN (C), and mean QT intervals (D). The layout of all panels and meaning of symbols correspond to the layout and symbols of Panel D of Figure 1. In all panels, the dashed lines correspond to the contributions of ECG noise, the full lines to the contributions of the other covariate.

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  Figure 11. Results of the bivariable regression analyses relating SDQT values to the combination of ECG noise with mean NN intervals (A), SDNN (B), RMSSD-NN (C), and mean QT intervals (D). Each panel is composed of a central pie-chart that corresponds to female subjects and of a surrounding donut-chart that corresponds to male subjects. Both the central pie chart and the surrounding donut chart indicate the proportion of subject in whom only the ECG noise was statistically significant in the regression analysis (red sector of the charts), subjects in whom only the other covariate was significant (blue sectors), subjects in whom both the ECG noise and the other covariate were significant (violet sectors), and subjects in whom SDNN was significantly related to neither ECG noise nor the other covariate (light grey sectors).

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  Figure 12. Results of trivariable regression analyses that related SDQT to a combination of mean NN + SDNN + ECG noise (A), mean NN + RMSSD-NN + ECG noise (B), mean NN + mean QT + ECG noise (C) and SDNN + mean QT + ECG noise (D). Each panel is composed of an inner and outer stack of donut-charts that correspond to female and male subjects, respectively. Each stack is composed of three donut-charts that correspond to the individual covariates involved in the regression analysis (see the labels at the left side of the outer stack). Each donut-chart corresponds to the total population of the given sex and indicates subjects for whom the covariate remained significant in the trivariable regression analysis. The light grey sectors of the donut charts correspond to subjects in whom SDQT was significantly related to none of the investigated covariates.