Evaluation of Systolic Time Intervals in Dogs with Dilated Cardiomyopathy Undergoing Dobutamine Stress Test
Dilated cardiomyopathy is characterized by progressive dilatation of ventricles and impairment of systolic function, leading to signs of congestive heart failure. However, during the development of this disease, the compromise of systolic function can not be remarkable, making difficult to establish the correct diagnosis. Recently, dobutamine stress test had proven to be an interesting tool which can aid diagnosing such cases. Thus, this work was conceived to determine the response of systolic time intervals in dogs with dilated cardiomyopathy undergoing dobutamine stress test.
For such, eight adult dogs were used, which were divided in two groups: (G1) had five healthy dogs with mean weight of 19.5 kg; (G2) had three dogs with mean weight of 31.9 kg, and marked impairment of systolic function, as well as left ventricle dilatation. Such dogs were previously diagnosed with idiopathic dilated cardiomyopathy and were not on therapy yet. 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. It was measured the pre-ejection period (PEP) and left ventricular ejection time (LVET) by Doppler of the aortic flow, as well as the relation between both variables. Mean velocity of fiber shortening (MVFS) was also calculated based on shortening fraction and LVET. Data was submitted to Anova in order to determine differences in relation to the basal value of each parameter.
For G1, it was seen a significant variation of PEP (P=0.0048) from 54.80 ± 3.96 to 33.00 ± 9.13, while for G2 it varied from 70.68 ± 6.02 to 74.00 ± 5.19, which was not considered significant. For LVET, G1 showed a significant variation (P=0.0006) from 238.20 ± 45.90 to 125.00 ± 11.89, while G2 had a non-significant variation from 120.33 ± 10.50 to 133.67 ± 17.78. The relation of PEP and LVET did not vary significantly for both G1 and G2, despite it was observed a marked drop for G1 as long as dobutamine infusion was started. For MVFS, it was observed that G1 showed a significant increase (P<0.0001) from 1.71 ± 0.62 to 5.63 ± 0.65, while G2 remained relatively constant during the infusion of dobutamine, starting at 1.30 ± 0.61 and reaching 2.10 ± 0.25 at the highest dose.
Results allowed concluding that there is a severe compromise of systolic function in dogs with dilated cardiomyopathy. Such compromise is partially unresponsive to the inotropic challenge promoted by dobutamine, which permits supposing that the flow reserve in these patients has been severely affected already.