Electrocardiographic evaluation of baby opossum ( Didelphis albiventris )

2018). In our experiment, the value found was 0.05 ms (±0.02), which is a slight variation from most reference values for numerous species (Tilley and Burtnik, 2004). Such discrepancy can be explained because the electrocardiographic wave of the studied species has a lower amplitude than those of the species available in the literature. Myocardial cells and transverse tubules (t-tubules) are known to complete their development after birth during the first days of life (Hirakow and Krause, 1980). The t-tubules propagate action potential into myocardial cells (Orchad et al ., 2009). Most cardiac cells are differentiated from the 105 th postnatal day in D. virginiana (Hirakow and Krause, 1980). At this age, animals body mass between 180 and 200g, which is higher than the animals studied in this study. Thus, some changes could be justified, especially when compared to another adult Didelphis. This is the first electrocardiographic description for Didelphis albiventris and the first study with pups without anesthetic effect. Our results can help in the care of these animals in clinical routine, in addition to serving as basic information about the species. Therefore, it was observed that it was possible to perform the ECG in baby opossum, and there was no influence of sex or body mass on the measurements performed. The morphology and the mean values found for the measured parameters differed from those described for small animals and other animal species.


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The white-eared opossum (Didelphis albiventris) is a marsupial widely distributed in South America (Tyndale-Biscoe, 2006;Gardner, 2008).It is not an endangered species but has been often referred to the Wild Animal Screening Centers (CETAS) for complementary diagnostic tests for various conditions, especially imaging tests (Massari et al., 2019;Cavalcanti et al., 2021).Little is known about the cardiovascular system of this species, but it has been studied in some didelphic species, such as Didelphis virginiana, in which heart disease has been reported as an important condition in these animals over 2 years of age (Nascimento and Horta, 2020).

Szabuniewicz
and Szabuniewicz (1978) established some electrocardiographic parameters for adults of the D. virginiana species, such as P, QRS, and T wave values; however, there are no studies with Brazilian species or with baby opossums.
Thus, this study aimed to establish electrocardiogram reference values for whiteeared opossum pups (D. albiventris).Pups of the species D. albiventris (n=41), 20 males and 21 females, body mass between 100 and 180g, were treated at the Wildlife Rehabilitation Centre (NURFS).The animals were clinically examined and considered healthy by general and specific clinical examinations.Therefore, they were subjected to electrocardiographic evaluation.Some tracings had to be excluded from the present study due to motion artefact, increasing the reliability of parameters obtained here.Thus, 32 exams were used, 16 for males and 16 for females.
The digital electrocardiograph used was InCardio Duo® (InPulse Animal Health, Brazil) along with its software interface (InCardio Duo® -Inpulse Animal Health, Brazil).The animals were manually restrained and positioned in the right lateral decubitus, with limbs parallel and perpendicular to the long axis of the body, on a rubber mat.Electrocardiograph cables were attached as follows: red to the right thoracic limb, yellow to the left thoracic limb, black to the right pelvic limb, and green to the left pelvic limb.Before placing the electrodes, the skin was moistened with alcohol.The electrodes were positioned above the humerus-radio-ulnar and femoral-tibial-patellar joints through metallic "alligator" connectors.From the electrocardiographic tracing, the P wave represents atrial depolarization, its duration indicates the time in which electrical impulse travels from the sinus node to the atrioventricular node.For instance, the P wave in dogs, cats, and lions, in Lead II, is positive (Muzzi and Nogueira, 2007;Larsson et al., 2008;Santilli et al., 2018).Szabuniewicz and Szabuniewicz (1978) found a negative deflection in D. virginiana.In our study, most of the deflections were positive and some negative (18.7%; 6/32).
A negative P wave can occur as a function of cardiac depolarization orientation.Depolarization usually occurs from right to left and from superior to inferior.In opossums, Szabuniewicz and Szabuniewicz (1978) described the direction from left to ventralcaudal (anterior-inferior).
The QRS complex represents ventricular depolarization and is composed of Q waves (first negative deflection), followed by R (positive) and S (negative) waves, with different morphological presentations.For the opossums studied here, the QRS complex showed an RS morphology in about 31% (10/32) of the evaluated tracings, that is, a variation that can also occur in other species (Tilley and Burtnik, 2004;Larsson et al., 2008).Szabuniewicz and Szabuniewicz (1978) described a morphology with the presence of Q wave in some cases and absence of S wave, which was not noticed in this study.Moreover, the QRS complex lasted longer than that of felines (Tilley and Burtnik, 2004).
The T wave represents ventricular repolarization, and, for D. virginiana, it is negative (Szabuniewicz and Szabuniewicz, 1978).In small animals (Tilley and Burtnik, 2004) and the present study, this electrocardiographic wave had varied morphology and may be positive, negative, or biphasic.According to Larsson ( 2004), the T wave should not exceed 25% of the R wave in dogs or 0.03mV in cats.In the current study, a T wave was observed in some cases greater than the R wave, but with a mean T amplitude of 0.04mV, while for R it was 0.22mV.Therefore, for the most part, the amplitude of the T wave in D. albiventris pups was 20% less than that of the R wave.
PR interval is the time required for an electrical impulse to travel from the sinus node to ventricular activation.In healthy dogs and cats, it is not less than 0.06s (Larsson, 2004), while the opossums studied here had an average of 0.05s (±0.08s).Such a difference can be explained by anatomical differences and potential smaller myocardial mass of opossums.
For Fillipi (2011), QT interval represents ventricular depolarization and repolarization and varies as a function of heart rate.In cats, this interval lasts from 0.12 to 0.18s (Tilley and Burtnik, 2004).For opossums, we observed a range from 0.08 to 0.21s, whose minimum is below the reference for dogs and cats and the maximum is near the maximum for dogs (from 0.15 to 0, 25s).Probably such a difference is due to the high heart rate in baby opossums.S-T segment represents the interval from the end of the QRS complex to the beginning of the T wave.In other words, the initial phase of ventricular repolarization may vary from the baseline of the electrocardiographic tracing (Santilli et al., 2018).In our experiment, the value found was 0.05 ms (±0.02), which is a slight variation from most reference values for numerous species (Tilley and Burtnik, 2004).Such discrepancy can be explained because the electrocardiographic wave of the studied species has a lower amplitude than those of the species available in the literature.

Arq. Bras. Med. Vet. Zootec., v.74, n.4, p.745-748, 2022
Means and standard deviations were calculated using the BioEstat® software.Normality was tested by the Shapiro-Wilk test.Data were subjected to analysis of variance (ANOVA) by the F-test (p≤0.05), with means compared by the Tukey's test (p<0,05), using the BioEstat® software as well.The experiment was approved by the Instituto Chico Mendes (ICMBio) under nº 76962-, and by the Ethics Committee for Animal Use of the Federal University of Pelotas (CEEA/UFPel) under nº 012630/2021-18.The Table1show the results of this study.