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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.

Purpose: To determine the prevalence of rheumatic fever (RF) among children of a public high school in Belo Horizonte, Brazil., Methods: The study was performed from March to December/92, and involved high school students coming from families of the medium and low-medium social classes. Considering the total of 1,400 students registered in a public school and the estimated RF prevalence in the developing country, 729 students were randomly chosen to be interviewed and examined by a researcher. The children suspected of being affect by RF were submitted to echocardiography in order to find any cardiac lesions., Results: Due to several different factors, only 550 students aging from 10 to 20 years were admitted in this study. Four children, previously under secondary prophylactics, had already had the diagnosis of RF. Among these children, only one had heart disease (combined mitral incompetence and stenosis, and aortic incompetence). From the other three children, only one had the diagnosis of RF confirmed according to the Jones criteria., Conclusion: From the ata obtained, the prevalence of RF was calculated in 3.6/1000.