Mechanisms underlying alterations in power spectra of heart rate variability associated with ectopy

The low frequency components in heart rate variability (HRV) spectra are elevated in power spectra of segments with ectopy. The authors considered several hypothetical mechanisms which might give rise to this difference. (1) The phase of oscillations is disturbed by ectopic beats, resulting in lower coherence. (2) Reflex alterations in autonomic activity due to reduced arterial blood pressure may stimulate larger instability oscillations. (3) Underlying changes in autonomic activity give rise to elevated HRV and to increased rate of ectopy. These hypotheses were tested by computing power spectra by the method of average periodograms of segments just before, after, and centered on each ectopic beat. Spectra were not significantly different for segments before and after ectopic beats, or for segments centered on ectopic beats, suggesting that mechanisms 1 and 2 do not contribute significantly to the difference in power