Distinctive impaired cardiac autonomic modulation of heart rate variability in chronic Chagas' indeterminate and heart diseases.

INTRODUCTION Cardiac autonomic dysfunction occurs in Chagas' indeterminate and heart disease, but comparison of this disturbance between both forms was not yet performed. METHODS Time- and frequency-domain 5-minute heart rate variability in supine and standing positions were evaluated in 17 subjects with Chagas' disease with the indeterminate form, 13 with heart disease and 15 controls. Trend of variability indices across the groups was also tested. RESULTS In the supine position, reduced time-domain and absolute frequency-domain indices reflecting overall autonomic modulation were observed in both Chagas' disease groups. In the standing position, the coefficient of variation and those frequency-domain indices were also reduced, and the other time-domain indices were reduced only in the cardiac group. Heart rate variability indices hypothesized to reflect relative sympathetic and parasympathetic activity showed no alteration. A significant graded reduction was observed in the altered indices in both postures, from the control to the Chagas' indeterminate and heart disease groups. CONCLUSION Cardiac autonomic dysfunction, with preserved putative measures of sympathetic and parasympathetic modulation in relative terms, was less severe or absent in the indeterminate and pronounced in cardiac form of Chagas' disease.