SPECTRAL CHARACTERISTICS OF VENTRICULAR RESPONSE TO ATRIAL-FIBRILLATION

To investigate the spectral characteristics of the fluctuation in vent ricular response during atrial fibrillation (AF), R-R interval time se ries obtained from ambulatory electrocardiograms were analyzed in 45 p atients with chronic AF and in 30 age-matched healthy subjects with no rmal sinus rhythm (SR). Although the 24-h R-R interval spectrum during SR showed a 1/f noise-like downsloping linear pattern when plotted as log power against log frequency, the spectrum during AF showed an ang ular shape with a breakpoint at a frequency of 0.005 +/- 0.002 Hz, by which the spectrum was separated into long-term and shortterm componen ts with different spectral characteristics. The short-term component s howed a white noise-like flat spectrum with a spectral exponent (absol ute value of the regression slope) of 0.05 +/- 0.08 and an intercept a t 10(-2) Hz of 4.9 +/- 0.3 log(ms(2)/Hz). The long-term component had a 1/f noise-like spectrum with a spectral exponent of 1.26 +/- 0.40 an d an intercept at 10(-4) Hz of 7.0 +/- 0.3 log(ms(2)/Hz), which did no t differ significantly from those for the spectrum during SR in the sa me frequency range [spectral exponent, 1.36 +/- 0.06; intercept at 10( -4) Hz, 7.1 +/- 0.3 log(ms(2)/Hz)]. The R-R intervals during AF may be a sequence of uncorrelated values over the short term (within several minutes). Over the longer term, however, the R-R interval fluctuation shows the long-range negative correlation suggestive of underlying re gulatory processes, and spectral characteristics indistinguishable fro m those for SR suggest that the long-term fluctuations during AF and S R may originate from similar dynamics of the cardiovascular regulatory systems.