Dobutamine stress test (DST) has recently shown to be a feasible tool for diagnosing cardiomyopathies not well established yet. However, data still lacks about the effects of DST on systolic time intervals (STI) in experimental models of dilated cardiomyopathy. Therefore, this study aimed at determining the response of STI in dogs with both chagasic and doxorubicin-induced cardiomyopathies undergoing DST.

Fifteen adult dogs were used, which were assigned to one of three groups: (G1) had five healthy dogs (mean weight 19.5kg); (G2) had five dogs with chagasic cardiomyopathy (mean weight 9.5kg) and abnormal ventricular relaxation; (G3) had five dogs with doxorubicin-induced cardiomyopathy (mean weight 19.4kg), exhibiting severe left ventricular dilatation, compromise of systolic function, and a mild restriction to late ventricular filling. The dogs of G3 were given intravenously doxorubicin at 30 mg/m² each 21 days, until a total dose of 240 mg/m² was reached. The experiment was carried out in accordance with the university's Committee for ethical experimentation, which follows the Brazilian rules for animal experimentation. All dogs underwent echocardiographic evaluation before (1) and during the infusion of dobutamine in increasingly doses: (2) 10 ug/kg/min.; (3) 20 ug/kg/min.; (4) 30 ug/kg/min.; and (5) 40 ug/kg/min. Pre-ejection period (PEP) and left ventricular ejection time (LVET) were measured and it was established the relation between them. Mean velocity of fiber shortening (MVFS) was also calculated based on shortening fraction and LVET. Data was submitted to ANOVA to determine differences in relation to the basal value of each parameter.

For PEP, G1 decreased significantly (P=0.0048) from 54.80±3.96 to 33.00±9.13; for G2 it decreased significantly (P=0.0004) from 56.80±8.64 to 38.40±7.50; for G3, a significant variation (P=0.0007) from 69.00±5.65 to 47.60±11.19 was observed. For LVET, G1 showed a significant variation (P=0.0006) from 238.20±45.90 to 125.00±11.89; G2 had a significant variation (P=0.0123) from 146.20±22.91 to 107.40±21.09; and G3 had a non-significant variation from 174.20±53.45 to 146.00±17.21. The relation between PEP and LVET did not change significantly in any group. For MVFS, G1 increased significantly (P<0.0001) from 1.71±0.62 to 5.63±0.65; G2 varied significantly (P<0.0001) from 2.35±0.89 to 5.20±0.66; G3 varied significantly (P=0.0179) from 1.26±0.54 to 2.72±0.51.

Results allowed concluding that Chagas disease does not affect systolic function severely, as much as it impairs diastolic function. On the other hand, in spite of the important decrease in systolic capacity, dogs with doxorubicin-induced cardiomyopathy seem to respond to inotropic challenge of dobutamine. It is likely that the flow reserve of these animals is not deeply compromised by the toxic cardiomyopathy.