Spectral and fractal structures of heart rate variability in coronary artery disease patients without myocardial infarction

Heart rate variability (HRV) allows risk stratification in coronary artery disease (CAD) patients, but only few works evaluated HRV in CAD patients with preserved ejection fraction. Aim of this work is to describe spectral and fractal structures of HRV in CAD patients with normal ejection fraction. We recorded R-R intervals for 15 minutes in 10 CAD patients and in 10 matched controls with the same ejection fraction, estimating broadband power spectra, PSD(f), and the recently proposed temporal spectrum of scale coefficients, α(τ). In CAD patients, PSD(f) was significantly (p<;0.05) lower over a low-frequency band (0.047-0.240 Hz) and over a very-low frequency band (0.007-0.022 Hz); α(τ) was significantly higher between 9 and 25 s (corresponding to low frequencies) but did not difer from controls at scales τ corresponding to very-low frequencies. Therefore, in CAD patients, even when the ejection fraction is preserved, a low frequency spectral component with its own fractal signature is absent. In addition, fluctuations at lower frequencies are reduced but, in this case, the power reduction is not associated with an altered fractal dynamics.