Circadian rhythm of atrioventricular conduction predicts long-term survival in patients with chronic atrial fibrillation. 
The R-R interval of the electrocardiogram during atrial fibrillation (AF) appears absolutely irregular.  However, the Poincaré plot of the R-R interval reveals a sector shape of distribution that is unique to AF.  Furthermore, the height of lower envelope (LE1.0) of the distribution and the degree of scatter above the envelope (scattering index) may reflect the refractoriness and concealment of atrioventricular (AV) conduction, respectively.  We previously observed that both the LE1.0 and scattering index show clear circadian rhythms in patients with chronic AF and that the rhythms are blunted in those with congestive heart failure and chronic AF.  In the present study, we examined if the blunted circadian rhythm of the AV conduction has prognostic value in patients with chronic AF.  We studied a retrospective cohort of 120 patients who underwent 24h Holter monitoring at baseline.  During an observation period of 33 +/- 16 mon, there were 25 deaths (21%) including 13 cardiac and 8 stroke deaths.  All patients showed significant circadian rhythms in both LE1.0 and scattering index with acrophases occurring at night; however, patients dying subsequently from cardiac causes, but not those from fatal stroke were blunted in the circadian rhythms (the amplitudes were < 55% of those in surviving patients).  Furthermore, the reduced circadian amplitude of scattering index was an increased risk for cardiac death even after adjustment of coexisting cardiovascular risks [adjusted relative risk (95% confidence interval) per 1-SD decrement, 4.24 (1.54-11.6)].  When patients were divided by the circadian amplitude of the scattering index of 36.5 msec (mean minus 1-SD), the 5yr cardiac mortality below and above the cutoff was 57 and 6%, respectively (log-rank test, p < 0.001).  We conclude that the blunted circadian rhythm of AV conduction is an independent risk for cardiac death in patients with chronic AF.