title: Abnormalities in fractal heart rate dynamics in Chagas disease.
abstract: METHODS
  In order to study fractal HR dynamics in Chagas disease, we performed detrended fluctuation analysis (DFA)-along with analysis of power-law beta slope (beta index) and standard deviation of N-N intervals (SDNN)-in edited and unedited (with ventricular premature beats - VPBs, only in DFA analysis) series of R-R intervals from Holter monitoring of healthy controls (Group 0, n = 27) and Chagas disease patients with left ventricular (LV) ejection fraction >50% (Group 1, n = 137) and with LV ejection fraction <50% (Group 2, n = 23).
  
  
  RESULTS
  When analyzed from the edited R-R interval data, the long-term scaling exponent alpha(2) is altered both among the Chagas patients with and without LV dysfunction. The short-term scaling exponent alpha(1) was higher in Group 1 Chagas patients as compared to controls (P < 0.01) and did not differ between Group 2 and controls. In unedited R-R interval series, alpha(1) was significantly reduced in Group 2 Chagas patients (0.55 +/- 0.002) as compared to controls (0.90 +/- 0.002) and Group 1 (0.91 +/- 0.003) (P < 0.001), but did not differ between Group 1 and controls. Similarly alpha(2) was lower in Group 2 compared to other groups (P < 0.001). SDNN did not differ between the groups, but the beta index derived from 1/f model was reduced both in Group 1 and 2 Chagas patients as compared to controls (P < 0.01). There was strong correlation (rs = 0.82; P < 0.001) between the beta and alpha(2) index from edited series. There was an inverse correlation (rs =-0.63, P < 0.01) between the number of VPBs and alpha(1) index of unedited series.
  
  
  CONCLUSIONS
  The long-term fractal HR dynamics altered in chagasic patients with and without LV dysfunction could be an early sign of autonomic dysfunction. Patients with impaired LV function show marked alterations in short-term fractal HR dynamics toward more random behavior, mainly due to frequent ectopy. Prospective studies are necessary to define the value of these indices as predictors of death in Chagas disease.
authors.affiliation: Hospital das Clínicas and Internal Medicine Department, School of Medicine, Federal University of Minas Gerais, Minas Gerais, Brazil. mrsousa@ufmg.br
authors.forename: Marcos Roberto
authors.initials: MR
authors.lastname: de Sousa
authors.forename: Heikki V
authors.initials: HV
authors.lastname: Huikuri
authors.forename: Federico
authors.initials: F
authors.lastname: Lombardi
authors.forename: Amanda A
authors.initials: AA
authors.lastname: Perez
authors.forename: Murilo E D
authors.initials: ME
authors.lastname: Gomes
authors.forename: Marcio Vinícius Lins
authors.initials: MV
authors.lastname: Barros
authors.forename: Vladimir Costa Val
authors.initials: VC
authors.lastname: Barros
authors.forename: Manoel Otávio Costa
authors.initials: MO
authors.lastname: Rocha
authors.forename: Antonio Luiz Pinho
authors.initials: AL
authors.lastname: Ribeiro
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D014355:Chagas Disease / Q000503:physiopathology*; D016009:Chi-Square Distribution; D015716:Electrocardiography, Ambulatory; D017709:Fractals; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D017711:Nonlinear Dynamics; D018709:Statistics, Nonparametric; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology; D018879:Ventricular Premature Complexes / Q000503:physiopathology