ECG Ventricular Repolarization Dynamics during Exercise: Temporal Profile, Relation to Heart Rate Variability and Effects of Age and Physical Health

Figures

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  Figure 1. Computation of dT from an ECG in the Frank lead configuration. (a) T-waves from four consecutive heart beats. (b) Pairs of T-wave vectors from consecutive beats are illustrated in three-dimensional spheres. (c) Angle dT between the consecutive T-wave vectors shown in panel b. (d) Time series of dT for a piece of an ECG recording.

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  Figure 2. Example of the dT angle and RR interval time series for one subject throughout the entire test. Dotted lines separate the different test segments: resting (SREST), cycling (SCY) and recovery (SREC). SCY was divided into three stages corresponding to 60, 70 and 80% of estimated HRmax, denoted as SCY60, SCY70 and SCY80, respectively.

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  Figure 3. Example of the instantaneous power of LF oscillations for: RR variability (PRRV), dT variability (PdTV), dTV unrelated to RRV (PdTVuRRV) and dTV related to RRV (PdTVrRRV) obtained for the same subject as in Figure 2. Dotted lines separate the different test segments: resting (SREST), cycling (SCY) and recovery (SREC). SCY was divided into three stages corresponding to 60, 70 and 80% of estimated HRmax, denoted as SCY60, SCY70 and SCY80, respectively.

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  Figure 4. Example of the time-frequency distribution for RR variability (RRV), dT variability (dTV), dTV unrelated to RRV (PdTVuRRV) and dTV related to RRV (PdTVrRRV) obtained for the same subject as in Figure 2. Dotted lines separate the different test segments: resting (SREST), cycling (SCY) and recovery (SREC). SCY was divided into three stages corresponding to 60, 70 and 80% of estimated HRmax, denoted as SCY60, SCY70 and SCY80, respectively.

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  Figure 5. Box plots representing the distributions of PRRV, PdTV, PdTVuRRV and PdTVuRRVn (N = 66) over the study population (N = 66) for the different test segments: resting (SREST), cycling (SCY) and recovery (SREC). SCY was divided into three stages corresponding to 60, 70 and 80% of estimated HRmax, denoted as SCY60, SCY70 and SCY80. (a) LF oscillations of RR variability (PRRV), with the inset showing the three SCY stages. (b) LF oscillations of dT variability (PdTV). (c) PdTV unrelated to PRRV (PdTVuRRV). (d) Normalized PdTV unrelated to PRRV (PdTVuRRVn). * = Significant differences between test segments (p ≤ 0.05, Friedman’s ANOVA): * 1 = Different to SREST; * 2 = Different to SCY60; * 3 = Different to SCY70; * 4= Different to SCY80; * 5 = Different to SREC; ** = Different to all.

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  Figure 6. Examples of dTV, PdTV and PdTVuRRV at rest obtained for two subjects that are representative of each of the two clusters. A and B, described in the text.