CIRCADIAN-RHYTHMS OF ATRIOVENTRICULAR-CONDUCTION PROPERTIES IN CHRONIC ATRIAL-FIBRILLATION WITH AND WITHOUT HEART-FAILURE

Objectives. We examined the circadian variations in atrioventricular ( AV) conduction properties during atrial fibrillation (AF) by a techniq ue based on the Lorenz plot of successive ventricular response (VR) in tervals and analyzed their relations with clinical features. Backgroun d. The VR interval in chronic AF shows circadian variation, which is a ttenuated in patients,vith an increased risk of death, Although the VR interval is determined by the dynamic processes in the AV node random ly stimulated by rapid atrial activity, the circadian variations of th e AV conduction properties related to this mechanism are unknown. Meth ods. In 48 patients with chronic AF, Lorenz plots were generated on ov erlapping sequential segments of 512 VR intervals in 24-h ambulatory e lectrocardiograms, For each scatter plot, the 1.0-s intercept of the l ower envelope (LE1.0) of the plot and the degree of scatter above the envelope (root mean square difference from the envelope [scattering in dex]) were measured for estimating AV node refractoriness and conceale d AV conduction, respectively. Results. In all patients, a significant circadian rhythm was observed for the average VR interval, LE1.0 and scattering index, with an acrophase occurring at night, The mesor, amp litude and acrophase of LE1.0 and the scattering index closely and ind ependently correlated with the corresponding rhythm variables of the a verage VR interval (partial r(2) 0.98, 0.86 and 0.68 for LE1.0 and 0.9 8, 0.92 and 0.92 for scattering index), The amplitudes of these measur es were lower in patients with congestive heart failure (CHF) even aft er adjustment for the effects of age, duration of AF, medications, lef t atrial diameter and blood pressure (p < 0.01 for all). Conclusions. These results suggest that 1) both AV node refractoriness and the degr ee of concealed AV conduction during AF may show a circadian rhythm; 2 ) the circadian rhythms of these properties may independently contribu te to the circadian variation of the VR interval; and 3) these circadi an rhythms may be attenuated in patients with CHF. (C) 1998 by the Ame rican College of Cardiology.