Norepinephrine and heart rate variability: a marker of dysautonomia in chronic Chagas cardiopathy.

The involvement of the autonomic nervous system (ANS) in Chagas' disease has been the subject of many studies, which have become more numerous since Köberle's pioneering work in the 1950s, showing the partial or total destruction of cardiac neurons. In order to investigate ANS involvement in the pathogenesis of chronic Chagas cardiopathy, seventy-five patients with the condition were examined and divided into four groups, according to the Los Andes classification: I-A, I-B, II and III. Groups I-A and I-B included patients at an early stage of cardiac involvement; group II, patients at an advanced stage without heart failure (HF); and group III, patients at an advanced stage with HF. Norepinephrine (NE) levels were measured in 24 h urine collected from fifty-two chronic Chagas patients (69%); twelve cardiopathic patients of other etiologies, in functional class IV of the New York Heart Association (NYHA), selected as the control group; and ten normal individuals. 24-hour Holter monitoring was performed in fifty-six patients (74.6%) to assess heart rate variability (HRV). HRV parameters were analyzed and distributed according to the Los Andes classification. Norepinephrine levels were significantly higher (p = 0.0001) in the controls (non-Chagas cardiopathic patients, NYHA IV) than in group III (chronic Chagas cardiopathic patients) according to the Los Andes classification. Reduction of HRV was observed in Chagas patients, but unrelated to functional class, and the indices reflecting parasympathetic activity (pNN50 and rMSSD) were increased in our Chagas patients. Our study concluded that the NE levels in Chagas patients in an advanced stage of cardiac involvement (group III) did not rise as in cardiopathic patients of other etiologies with a similar degree of cardiac involvement, which might be interpreted as an impairment of the sympathetic nervous system in the cases studied, but the increased levels of NE in groups I-A and I-B of the Chagas patients can be interpreted as an early impairment of the autonomic nervous system (sympathetic). HRV was reduced in our patients, but the indices reflecting parasympathetic activity (pNN50 and rMSSD) were preserved in almost all Chagas patients. However, the pNN50 index was reduced in group I-A, suggesting that parasympathetic dysautonomia may be an early phenomenon and may precede left ventricular systolic dysfunction.