Impaired autonomic control of heart interval changes to Valsalva manoeuvre in Chagas' disease without overt manifestation.

BACKGROUND: In the apparent indeterminate form of Chagas' disease, which lacks any overt clinical, electrocardiographic, and radiological manifestations of organ damage, lesions of the intrinsic autonomic innervation of heart are not striking features and evidences for cardiac autonomic dysfunction are elusive and conflicting.
OBJECTIVE: To evaluate the cardiac autonomic modulation based on Valsalva manoeuvre-associated heart interval variation in Chagas' disease subjects with apparent indeterminate form. SUBJECTS AND METHODS: We examined 36 outpatient volunteers aged 15-51 years old (median: 36.5), in comparison with 52 healthy control individuals aged 17-49 years old (median: 29) (p<0.001). Each subject sequentially performed in the supine position three to four manoeuvres at an intra-oral pressure of 40 mm Hg during 20 s, under continuous DII lead electrocardiographic registration, and rate- and time-dependent indices of Valsalva manoeuvre-associated R-R interval variation were obtained. The t-test or the Mann-Whitney test was employed to compare the data between the groups.
RESULTS: No correlation was found between every index and age for the control group (p=0.39-0.71). The chagasic group presented similar basal to phase IV median increment (relative bradycardia) (23.7% vs. 22.7%; p = 0.63) and smaller basal to phase III median decrement of R-R interval (relative tachycardia) (-31.7% vs. - 35%; p=0.02) in comparison to the control group, respectively. The median Valsalva ratio showed a tendency for reduction in chagasics (1.78 vs. 1.90; p = 0.08). Prolonged median time (14.2 vs. 10.3 s; p < 0.001) and slowed median velocity (5.1%/s vs. 8.9%/s; p < 0.001) of the phases III-IV bradycardia were also observed in chagasic group. The majority (58.3%) of the chagasics presented exclusively at least one depressed, and 8.3% presented at least one enhanced index of rate- and/or time-dependent heart interval responses beyond the 25th or 75th control percentiles, and 27.8% presented at least one depressed and other enhanced index, while 5.6% showed all indices within the control interquartile range. All the indices outside the 25th or 75th control percentiles were noted in 13.9% of chagasics.
CONCLUSION: Chagas' disease subjects without overt manifestations presented variable and subtle depression and less frequent enhancement or normality of the rate- and time-dependent tachycardia and bradycardia reflex responses related to Valsalva manoeuvre, which demonstrates distinct patterns of finely disturbed cardiac sinus parasympathetic and sympathetic modulation, probably due to inflammatory or autoimmunological damage of intrinsic innervation and/or to autoantibodies-induced derangement in neurotransmitter receptors.