Background: Higher neurohormonal activation levels are known markers of severity and adverse prognosis in heart failure (HF) patients. Classical linear indexes of heart rate variability (HRV) have been shown to be associated with neurohormonal activation. Whether and to what extent non linear Poincaré plot indexes (PPI) of HRV reflect similar relationship is not known. Purpose of the study was to assess the association of PPI with plasma norepinephrine (NPE) levels and functional parameters as compared to classical linear indexes of HRV. Methods: Ninety-nine stable mild-to-moderate HF patients in sinus rhythm (age: 51±8 years, NYHA class II-III 88%, LVEF 24±6 %, VO2max during exercise tests 14±4 mlxKg-1xmin-1) were studied. Each patient had a 24-hour Holter recording and, besides standard clinical and laboratory examinations, underwent within one week plasma NPE assay. The SDNN and the power in the low frequency band (LFP, 0.04-0.15 Hz) were computed on consecutive 5-min RR sequences, these have been shown to have the highest prognostic value in HF patients. PPI were obtained by automated quantification of the bi-dimensional length, L and tri-dimensional (peak's number Np, radii of the semi-ellipse of inertia Px, Py, Pz) morphological characteristics, with a technique whose good reproducibility has been previously shown by the authors. The association between HRV and neurohormonal and functional indexes was assessed by Spearman correlation coefficient. Results: NPE, LFP and SDNN were respectively (mean ± SD): 363±210 pg/l, 162±171 ms2, 36±15 ms. PPI were L=576.5±189.9 ms; Np=28.01±19.38; Px=56.36±21.31 ms; Py=113.1±29.44 ms; Pz=101.6 ±43.36 ms. Both SDNN and LFP showed a moderate but significant negative correlation with NPE levels (r=-0.37 and-0.44 respectively, p<0.0001); while a weaker association was found for L, Np and Py ranging from r=-0.33 to-0.25, p<0.0001). Linear indexes were significantly associated with VO2max (r=0.31 and 0.36 respectively, p<0.001), and between PPI similar correlation were found for L, Py and Pz (r= 0.33, 0.37 and 0.32 respectively, p<0.001). Similar relationships were found with EF (r=0.35, 0.34, 0.36, 0.33, 0.34) for SDNN, LFP, L, Np, Pz, respectively, p<0.001) with a negative correlation of r=-0.38 p<0.0001 for Px. Conclusions: These findings suggest that although the association of linear and PPI of HRV with functional parameters is similar, the former, particularly the power in the low frequency band, appear to reflect more closely the level of adrenergic activation of HF patients.
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