title: Power-law behavior of heart rate variability in Chagas' disease.
abstract: Beta slope is a nonlinear index derived from the power-law analysis of 24-hour heart rate variability (HRV); in healthy subjects, the beta index is typically near -1, suggesting a fractal behavior of HRV. There is scarce data on HRV in Chagas' disease. This transversal study intends to describe power-law and linear HRV patterns in different forms of Chagas' disease. Patients and healthy controls (n = 26) without other diseases were submitted to a standardized protocol, including electrocardiography, echocardiography, and 24-hour Holter monitoring. Patients with Chagas' disease were divided into groups according to their left ventricular (LV) systolic function: normal (group 1, n = 85), segmental abnormalities (group 2, n = 49), and reduced ejection fraction (group 3, n = 26). The temporal series were carefully processed to obtain the HRV indexes and beta slope. Despite the differences in the LV systolic function, the 3 groups were comparable in terms of long-term HRV index values. After adjustment for covariates, short-term HRV index values were consistently reduced in the Chagas' disease groups. The beta-index values were also diminished in Chagas' disease groups (group 1: -1.09 +/- 0.03, group 2: -1.11 +/- 0.06; group 3: -1.14 +/- 0.03; and controls: 0.95 +/- 0.03, p <0.001). This breakdown of fractal long-range correlation of RR interval dynamics, a strong predictor of mortality in other cardiomyopathies, may reflect cardiac dysautonomia that may have gone undetected in long-term time-domain analysis. This abnormality may explain the increased risk for arrhythmic sudden death found in Chagas' disease even in the absence of signs of LV dysfunction.
authors.affiliation: Hospital das Clínicas and Post-Graduation in Tropical Medicine, School of Medicine, Belo Horizonte, Brazil. tom@hc.ufmg.br
authors.forename: Antonio Luiz P
authors.initials: AL
authors.lastname: Ribeiro
authors.forename: Federico
authors.initials: F
authors.lastname: Lombardi
authors.forename: Marcos Roberto
authors.initials: MR
authors.lastname: Sousa
authors.forename: Marcio Vinicius
authors.initials: MV
authors.lastname: Lins Barros
authors.forename: Alberto
authors.initials: A
authors.lastname: Porta
authors.forename: Vladimir
authors.initials: V
authors.lastname: Costa Val Barros
authors.forename: Murilo E D
authors.initials: ME
authors.lastname: Gomes
authors.forename: Fernando
authors.initials: F
authors.lastname: Santana Machado
authors.forename: Manoel
authors.initials: M
authors.lastname: Otávio Costa Rocha
mesh_terms: D000328:Adult; D000368:Aged; D014355:Chagas Disease / Q000503:physiopathology*; D005260:Female; D017709:Fractals; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D013318:Stroke Volume; D018487:Ventricular Dysfunction, Left