Diurnal variations of the dominant cycle length of chronic atrial fibrillation

1 Department of Cardiology, Lund University Hospital, Lund, Sweden; 2 Department of Cardiological Sciences, St. George's Hospital Medical School, London, United Kingdom; and 3 Department of Medicine, Kuopio University Hospital, Kuopio, Finland 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