Correlation between norepinephrine plasma levels and Poincaré plot indexes of heart rate variability in heart failure patients

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 nonlinear Poincaré plot indexes (PPI) of HRV reflect similar relationship is not known. The purpose of the study was to assess the association of PPI with plasma norepinephrine (NPE) levels as compared with 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 mL/kg per minute) were studied. Each patient had a 24-hour Holter recording and, beside standard clinical and laboratory examinations, underwent plasma NPE assay within 1 week. The SDNN and the power in the low-frequency band (LFP; 0.04-0.15 Hz) were computed on consecutive 5-minute RR sequences; these linear indexes have been shown to have the highest prognostic value in HF patients. Poincaré plot indexes were obtained by automated quantification of the bidimensional length (L) and tridimensional (peak's number Np, radii of the semi-ellipse of inertia Px, Py, Pz) morphologic characteristics, with a technique whose good reproducibility has been previously shown by the authors. The association between HRV and neurohormonal indexes was assessed by Spearman correlation coefficient. Results: Norepinephrine, LFP, and SDNN were, respectively, (mean ± SD) 363 ± 210 pg/L, 162 ± 171 ms2, and 36 ± 15 milliseconds. Poincaré plot indexes were as follows: L = 576.5 ± 189.9 milliseconds; Np = 28.01 ± 19.38; Px = 56.36 ± 21.31 milliseconds; Py = 113.1 ± 29.44 milliseconds; and Pz =101.6 ± 43.36 milliseconds. Both SDNN and LFP showed a moderate but significant negative correlation with NPE levels (r = ???0.37 and ???0.44, respectively; P b .0001), whereas a weaker association was found for L, Np, and Py ranging from r = ???0.33 to ???0.25 (P although patterns of beat-to-beat variability quantified by PPI provide useful information in the assessment of cardiac autonomic control impairments, the power in the low-frequency band appears to reflect more closely the level of adrenergic activation of HF patients.