AFibDI – Atrial Fibrillation Diurnal Index. The index for risk assessment derived from twenty-four hours Holter monitoring

The autonomic nervous system (ANS) adapts heart rate (HR) to current person’s needs increasing HR during a daytime for physical and mental activities and decreasing HR during rest conditions and a nighttime. The prognostic significance of heart rate (HR) diurnal pattern had not been widely studied in permanent atrial fibrillation (PAF) patients. In total of 463 PAF patients exposed to Holter monitoring in 2007 – 2012 four simple indexes characterizing twenty-four hours HR behavior (average day and night HR ratio and difference, maximum and minimum HR ratio and difference) were calculated, checked for diagnostic and predictive accuracy, and dichotomized by using ROC curves, and then included in Kaplan-Meijer survival analysis. The indexes were grouped into newly created Atrial Fibrillation Diurnal Index (AFibDI, range 0-4). For 5 years follow-up 180 deaths were documented in study patients’ group. AFibDI showed fair accuracy for death prediction (AUC-.745 (.698;.972) p-.000) and statistically significant survival prediction value (p<.000). Decrease of diurnal heart rate variability (higher AFDI) conferred higher death risk after adjustment for CHA2DS2-VASc score and age (hazard ratio 1.39 (95% CI: 1.25; 1.54) for each AFibDI point increment. The AFibDI was included in survival analysis together with left ventricle ejection fraction (LV EF). Combination of AFDI together with LV EF distinguished patients at higher death risk among ones with the same range of LV EF. AFibDI improves risk assessment in PAF patients and adds predictive accuracy for death risk prediction in patients with similar other risk predictors.  The index can be applied for every technic, which registers continuous twenty-four hours ECG.