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Figure 5 Spectral changes in the total (TFP) (a), low frequency (LFP) (b) and high frequency (HFP) (c) power and low/high frequency ratio (d) preceding the arrhythmia with respect to ectopic beat frequency. Power spectral analysis was repeated after removal of data segments not meeting the frequency threshold criteria: >50%, >75% and >85% normal beats. *p < 0.05 compared to the 24-h average. **p < 0.01 compared to the 24-h average.