High-resolution digital Holter recording was carried out in 21 patients (15 men, 64 ± 12 yr) with chronic atrial fibrillation. Dominating atrial cycle length (DACL) was derived by frequency domain analysis of QRST-reduced electrocardiograms. Daytime mean DACL was 150 ± 17 ms, and nighttime mean was 157 ± 22 ms ( P = 0.0002). Diurnal fluctuation in DACL differed among patients: it tended to be virtually absent in those with a short mean DACL, but in those with longer DACL the night-day difference was as much as 23 ms ( R = 0.72, P < 0.001, correlation of mean DACL to night-day difference). Mean DACL also correlated with ventricular cycle length ( R = 0.40, P < 0.001), particularly at night ( r = 0.49). The shorter cycle lengths found in this study during the day are consistent with sympathetic and/or other physiological modulation, but since increased vagal tone shortens atrial refractoriness in most models, parasympathetic influences are not likely to play a major role. Alternatively, atrial effective refractory period may not be the sole determinant of atrial cycle length during atrial fibrillation.
Non-invasive assessment of magnitude and dispersion of atrial cycle length during chronic atrial fibrillation in man
