Standard Strain and Strain Rate by Two-Dimensional Speckle Tracking in Agoutis (Dasyprocta prymnolopha) Anesthetized with Ketamine and Xylazine

Abstract

Background: The agouti (Dasyprocta prymnolopha, Wagler, 1831) is a wild rodent widely found throughout America which has stood out as a good animal model for scientific investigations. The aim of this study was to study the cardiovascular function of chemically contained agoutis, by performing echocardiographic examinations and measuring Strain and Strain Rate by Speckle Tracking to obtain reference values for the species and verify the applicability of these animals as models for the study of cardiovascular changes in humans.Materials, Methods & Results: It was selected 16 animals, sedated by the combination of ketamine hydrochloride and xylazine and submitted to transthoracic echocardiography. To obtain the standard measurements, B, M and Doppler mode images were taken. The analysis of the radial and longitudinal myocardial deformation of the left ventricle was carried out. The right parasternal window was used for access to the short cardiac axis and the left for access to the long axis. Six radial profiles of strain (ST) and Strain rate (SR) values were obtained, corresponding to the mean of the values for each segment. A total of 18 myocardial segments were analyzed for each specimen and the mean values were used to compose the statistical analysis. The comparison of the means between the genders did not show statistical difference, being the other statistical treatments based on the total sample of 16 animals. The variables that showed statistically significant correlation coefficients in relation to weight were: LA, LA/AO, HR, AVmax, E’ wave, E/IVRT (P > 0.05). HR showed a positive correlation with IVSd (r = 0.51), EPSS (r = 0.55) and E’ wave (r = 0.68); negative with IVRT (r = - 0.41), A wave (r = - 0.54), AVmax (r = - 0.53) and Pmax (r = - 0.65).Discussion: Although presumptively normal echocardiographic values were reported for not anesthetized agoutis, this was the first study to show the measurement of these variables for chemically contained agoutis, in addition to the use of Strain and strain rate by speckle tracking in the assessment of cardiac function. The sudden exposure of an external stimulus (environmental or physical) to which the body is not adapted can trigger an acute stress, and its effects may interfere significantly in the measurement of hemodynamic variables, justifying the need for chemical containment. The values found for the thickness of agoutis cardiac walls and chambers obtained in M mode, both in systole and in diastole, when compared with mammals of different size, confirm the positive linear correlation between body weight and cardiac dimensions for the various evaluated parameters. The velocity obtained by the Strain radial for the apical systolic peak was slightly lower than that obtained for the basal systolic peak, while the opposite was observed for the circumferential Strain, which showed apical peak greater than the basal peak, also to the found for human beings. The values obtained for circumferential, radial and longitudinal strain for agoutis were within the ranges of normality observed in healthy domestic animals and humans.