Study of autonomic modulation by non-linear analysis of heart rate variability in different age groups and analysis of health status, disease and risk of death in dogs

The symbolic analysis of heart rate variability (biomarker of cardiac autonomic homeostasis) is a nonlinear and effective tool for pattern extraction and classification in a series analysis, which implies the transformation of an original time series into symbols, represented by numbers. Autonomic heart rate control is influenced by different factors, and better indicators of heart rate variability are found in healthy young individuals than in older and sicker individuals. The aim of this study was to compare the indicators of heart rate variability among healthy dogs in different age groups and in health status using the nonlinear method of symbolic analysis to evaluate the diagnostic accuracy of this method for the risk of death in dogs. An increase in cardiac sympathetic modulation was observed in puppies and dogs at risk of death, which was evidenced by a marked increase of 0 V% (without variation - associated with sympathetic modulation) and a decrease in patterns of 2 V% (two variations - associated with parasympathetic modulation), while the opposite was observed in young adult dogs with increased parasympathetic modulation. Elderly dogs showed a gradual decrease in parasympathetic activity, which tended to worsen with loss of health. It is concluded that the variables of symbolic analysis may be useful to evaluate autonomic modulation in dogs and assist in the differentiation between health states, advanced disease and death throughout the life cycle and have been shown to be indices with high specificity, sensitivity and diagnostic accuracy to help identify dogs at risk of death.

Normal echocardiographic and radiographic reference values for crab-eating fox (Cerdocyon thous) anesthetized with ketamine and midazolam

The cardiac evaluation of wild animals is still a wide and largely unknown field for several species. Therefore, through complimentary examinations such as radiography, echocardiography and serum troponin levels, this study aimed at describing the values observed in 12 crab-eating foxes (Cerdocyon thous) anesthetized with a combination of intramuscular ketamine and midazolam. Thus, through complementary exams such as radiography, echocardiography and serum troponin levels, the aim of this study was to describe the cardiac values in 12 wild foxes (C. thous) anesthetized with an intramuscular injection of ketamine and midazolam. After anaesthetization, the radiographic, echocardiographic and immunoenzymatic reference values for the 12 males in the sample group were determined. Compared with those in domestic canids, there was a decrease in the sizes of the septum, wall and left ventricular cavity as well as decreases in the transmitral blood flow velocity indices, correlated with preserved serum cardiac troponin (cTnI) levels. Thus, M-mode echocardiography proved to be safer, with results that were comparative to those for other species of wild canids with indexed values. In addition, when evaluating the systolic function and segmentary contractions, the anesthetic combination did not have any effects on the results of complementary examinations performed in crab-eating foxes (C. thous) included in this study.

Use of aortic flow indexes derived from transthoracic echocardiography to evaluate response to a fluid challenge in anesthetized dogs

OBJECTIVE

To evaluate the ability of transthoracic echocardiographic aortic flow measurements to discriminate response to a fluid challenge (FC) in healthy anesthetized dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 48 isoflurane-anesthetized dogs (14.2-35.0 kg) undergoing elective surgery.

METHODS

Fluid responsiveness was evaluated before surgery by FC (lactated Ringer's 10 mL kg^-1 intravenously over 5 minutes). Percentage increases in transpulmonary thermodilution stroke volume (ΔSV_TPTD) >15% from values recorded before FC defined responders to volume expansion. A group of 24 animals were assigned as nonresponders (ΔSV_TPTD ≤15%). When ΔSV_TPTD was >15% after the first FC, additional FC were administered until ΔSV_TPTD was ≤15%. Final fluid responsiveness status was based on the response to the last FC. Percentage increases after FC in aortic flow indexes [velocity time integral (ΔVTI_FC) and maximum acceleration (ΔVmax_FC)] and in mean arterial pressure (ΔMAP_FC) were compared with ΔSV_TPTD.

RESULTS

After one FC, 24 animals were responders. For nonresponders, ΔSV_TPTD was ≤15% after one, two and three FCs in eight/24, 15/24 and one/24 animals, respectively. The FC that defined responsiveness increased ΔSV_TPTD by 29 (18-53)% in responders and by 8 (-3 to 15)% in nonresponders [mean (range)]. The area under the receiver operating characteristics curve (AUROC) of ΔVTI_FC (0.901) was larger than the AUROCs of ΔVmax_FC (0.774, p = 0.041) and ΔMAP_FC (0.519, p < 0.0001). ΔMAP_FC did not predict responsiveness (p = 0.826). Best cut-off thresholds for discriminating responders, with respective zones of diagnostic uncertainty (gray zones) were >14.7 (10.8-17.6)% for ΔVTI_FC and >8.6 (-0.3 to 14.7)% for ΔVmax_FC. Animals within the gray zone were 17% (ΔVTI_FC) and 50% (ΔVmax_FC).

CONCLUSIONS AND CLINICAL RELEVANCE

Changes in VTI induced by FC can determine responsiveness with reasonable accuracy in dogs and could play an important role in goal-directed fluid therapy.