Usefulness of Dobutamine Stress Test in the Evaluation of Systolic Function of Dogs with Doxorubicin Induced Cardiomyopathy
Dobutamine stress echocardiography has recently shown to be a feasible and more accurate tool in the diagnosis of cardiac dysfunctions in veterinary medicine, especially those related to the systolic capacity. Thus, this work was conceived to evaluate the systolic function of dogs with doxorubicin induced cardiomyopathy submitted to dobutamine stress test.
For such, two groups were set up: G1 with 5 adult mongrel female healthy dogs, with mean weight of 19.5 kg; and G2 with 5 adult mongrel male dogs, with mean weight of 19.4 kg. The dogs of G2 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 undergone echocardiographic evaluation before (1) and during the infusion of incremental doses of dobutamine: (2) 10 ug/kg/min.; (3) 20 ug/kg/min.; (4) 30 ug/kg/min. and (5) 40 ug/kg/min. The following variables were measured: internal diameter of left ventricle in systole (DIVEs); end-systolic left ventricular volume index (IVVEs); ejection fraction (FEJ); shortening fraction (FEC); pre-ejection period (PPE); left ventricular ejection time (TEVE); peak velocity of aortic flow (PVFA); Doppler stroke index (IED) and Doppler cardiac index (ICD).
Results were submitted to a variance analysis, which showed a significant decrease of DIVEs for G1 (P<0.0001) and G2 (P=0.0245); IVVEs for G1 (P<0.0001) and G2 (P=0.0013); PPE for G1 (P=0.0048) and G2 (P=0.0007); and TEVE for G1 (P=0.0006). By the other hand, it was seen a significant increase in FEJ for G1 (P=0.0006) and G2 (P=0.0036); FEC for G1 (P=0.0001) and G2 (P=0.0078); PVFA for G1 (P=0.0168); and ICD for G1 (P=0.0007). It was also observed that the infusion of dobutamine resulted in a better response of G1 parameters, whereas G2 had a mild response during the inotropic challenge.
Such data allowed concluding that dogs treated with doxorubicin in doses up to 240 mg/m2 develop a severe cardiomyopathy, which closely mimics dilated cardiomyopathy in dogs. This cardiomyopathy is characterized by an important systolic dysfunction, which is partially unresponsive to the increasingly inotropic stimuli of dobutamine stress test. Despite dogs with doxorubicin induced cardiomyopathy did change some variables in response to dobutamine infusion, it was observed a marked impairment of myocardium capacity to enhance contraction. This finding is in accordance with the advanced systolic compromise of such dogs.