Correlação clínico-patológica na forma indeterminada da doença de Chagas experimental do cão / Clinico-Pathological Correlation in the Indeterminate Form of Experimental Chagas' Disease in Dogs

PURPOSE: To study the functional cardiac component of the indeterminate form of experimental Chagas' disease in dogs. METHODS: Four dogs chronically infected with Trypanosoma cruzi and eight normal controls were used. They were submitted to several invasive procedures, either in the presence of complete autonomic block or not, to test for disturbances in the origin and conduction of electric stimuli and the function of cardiac muscle. Histological examination of the heart and its conduction systems was performed in all animals. RESULTS: Mild to moderate focal myocarditis was found in infected dogs, often involving the conduction system of the heart. Sections of the heart from control dogs were histologically normal. Functional data on excitability, intra and interatrial conduction time and sinus node recovering time were essentially similar for both infected and control animals. CONCLUSION: Focal myocarditis, the hallmark of the indeterminate form of Chagas' disease, did not alter the normal parameters of cardiac function, as seen after investigation with sensitive invasive techniques. It is probable that subjects considered as belonging to the indeterminate form of Chagas' disease, but presenting mild alterations at sensitive exploratory tests, may have more severe lesions than that usually described or may be already in the early progressive cardiac form of the disease.

Heart rate responses to intravenous serotinin in rats with acute chagasic myocarditis

We administered serotonin to rats with experimentally induced chagasic myocarditis in order to study the Bezold-Jarisch reflex. Sixteen 4-month old Wistar rats were inoculated with 200.000 T. cruzi parasites ("Y"strain). Between days 18 and 21 (acute stage), 8 infected rats and 8 age-matched controls received intravenous serotonin as a bolus injection at the following doses: 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, 12,0, and 14.0 mug/kg. Heart rate was recorded before, during and after each dose of serotonin. The remaining 8 infected animals and 8 controls were subjected to the same experimental procedure during the subacute stage, i.e., days 60 to 70 after inoculation. The baseline heart rate of the infected animals studied during the acute stage (327 + 62 beats/min, mean + SD) was higher than that of the controls (248 + 52, P<0.01). The heart rate changes were expressed as percent changes to correct for the higher baseline heart rate of the infected animals. A dose-response curve was constructed for each group of animals. The slope for the acutely infected animals (r = -0.95, b = -3.98) was not different from that for the control animals (r = -0,92, b = -3.50). The infected animals studied during the subacute stage (r = -0.92, b = -4.33) were not different from the age-matched controls (r = -0.87, b = -4.03). These results suggest that the afferent and efferent pathways which mediate the Bezold-Jarisch reflex are functionally preserved in rats with histologically proved chagasic myocarditis.