Echocardiography, a non-invasive method for the investigation of heart morphology and function in laboratory dogs: 1. Method and reference values for M-mode parameters

Echocardiographic evaluation of working dogs of the Military Police of Rio de Janeiro: effects of the breed and body weight

The Military Police of Rio de Janeiro state use dogs as a decisive tool for patrol and detection of drugs, weapons, and explosives. Complementary tests, such as echocardiography, are essential to maintain the integrity of these animals. This study aimed to evaluate the echocardiographic parameters of the working dogs belonging to the Military Police of Rio de Janeiro and compare them with the available data. Echocardiographic evaluation was performed on 48 healthy adult dogs from the Canine Action Battalion of the Military Police of Rio de Janeiro, Brazil. The sample consisted of 13 Labrador Retrievers, 12 Malinois Belgian Shepherds, 10 German Shepherds, 8 Dobermann Pinschers, and 5 Dutch Shepherds. Echocardiographic variables were correlated with body weight (BW). A positive correlation (P=0.0142, r=0.6837) between BW and the diameter of the left atrium was found in Malinois Belgian Shepherds. In German Shepherds, a positive correlation between BW and the internal diameter of the right ventricle during diastole (P=0.0320, r=0.6757) was observed; in addition, a positive correlation between BW and left ventricular internal diameter (P=0.0344, r=0.6689) during diastole was also found. Echocardiographic evaluations of these working dogs differed slightly from those previously established for similar-sized dog breeds.

Left ventricular M-mode prediction intervals in 7651 dogs: Population-wide and selected breed-specific values

BACKGROUND

Echocardiography is a common method to measure heart size in dogs. The heart dimensions are influenced by body weight (BW) and potentially by breed.

OBJECTIVES

To establish BW-dependent prediction intervals (PIs) of the left ventricular (LV) linear dimensions in a population of dogs of many breeds in multicenter environment, and to identify breeds deviating from these intervals. DOGS: Seven thousand six hundred and fifty-one dogs.

METHODS

Retrospectively, data from heart screens conducted between 2009 and 2016 were included. Cardiac dimensional PIs were generated using allometric scaling including all nonsighthound dogs and values were compared to previously published PIs. The values measured in dogs of respective breeds, including sighthounds, were then compared to the overall nonsighthound PIs to identify deviant breeds. The interobserver-variability of the measurements was determined using the explained residual variance.

RESULTS

Prediction intervals for the nonsighthound dogs were in agreement with previously published cardiac PIs, although the upper limits of the generated PIs of our study were slightly below those currently applied (except the interventricular septum in systole and the left ventricular free wall in diastole below 10.0 kg and 15.0 kg, respectively). Values measured in the nonsighthound breed Newfoundland deviated for most dimensions. Most of the sighthound breeds analyzed had greater cardiac dimensions, with the exception of the Irish Wolfhound.

CONCLUSION AND IMPORTANCE

Findings of our study reinforces the value of BW-dependent PIs for cardiac dimensions in dogs and suggest that these PIs are valid for most nonsighthound breeds, but not the sighthound breeds.

Reference Values and Repeatability of B-Mode and M-Mode Echocardiographic Parameters in Healthy Donkey (Equus asinus)-The Guide to Assess Healthy Heart

Donkey (Equus asinus), the cheapest form of agricultural power in Egypt, is used principally as draught or pack animals and may also be ridden, or used for threshing, raising water, milling, and other work. The aim of the present study was to provide B-mode and M-mode echocardiographic reference ranges from a sample of population of donkeys (E. asinus) based on the probability theory and statistics. In the present study, B-mode and 2-dimensional guided M-mode echocardiography were performed on 44 clinically healthy donkeys (E. asinus) (22 males and 22 females), without any neither clinical nor echocardiographic evidence of cardiovascular diseases, aged 2-25 year old, and weighed 150-350 kg. The echocardiographic dimensions, including interventricular septum thickness at end diastole, interventricular septum thickness at end systole, left ventricular internal diameter at end diastole, left ventricular internal diameter at end systole, left ventricular posterior wall thickness at end diastole, and left ventricular posterior wall thickness at end systole were assessed. The cardiac function indices, including end diastolic volume, end systolic volume, stroke volume, ejection fraction, and fractional shortening were also measured. B-mode and guided M-mode echocardiographic examination of healthy donkeys revealed that both the interventricular septum thickness and the left ventricular posterior free wall were greater during systole than diastole. However, the left ventricular dimension during diastole was greater than systole. Furthermore, the recorded data of cardiac function indices, including end diastolic volume, end systolic volume, stroke volume, ejection fraction, and fractional shortening using B-mode echocardiography were closer to those recorded by guided M-mode echocardiography. To our knowledge, this is the first Egyptian study to report the echocardiographic reference ranges of donkeys (E. asinus) based on the probability theory and statistics, the coefficient of variation. The results of the present study can be used as standard and reference values for further echocardiographic studies in donkeys and represent a step in the identification, interpretation, and evaluation of cardiovascular disorders in such animals.

Echocardiographic reference ranges for sedated healthy peccaries ( Tayassu tajacu, Linnaeus , 1758 )

ABSTRACT Peccaries are wild mammals belonging to the Tayassu genus that are found almost everywhere in the Americas and have demonstrated great potential as an experimental model for scientific investigations. Twelve healthy adult animals were sedated to perform echocardiographic examinations in B, M and Doppler mode. The variables that exhibited statistically significant correlation coefficients with weight were LVFWd, LVIDd, LVIDs, E wave, A’RV, MAM, and TAPSE. The HR exhibited a negative relationship with the IVRT. The LA variable showed a positive correlation with the AO. The MAM exhibited correlations with the LVIDd and LVIDs. The TAPSE showed positive correlations with the E’RV and A’RV. The present study provides the first reference values for echocardiographic measurements in B, M and Doppler modes from peccaries anesthetized with ketamine and midazolam. Echocardiography was easy to perform in collared peccaries, and the collected data revealed values that can aid in their clinical management and conservation.

Effect of an extruded pea or rice diet on postprandial insulin and cardiovascular responses in dogs

Peas are increasing in popularity as a source of carbohydrate, protein and fibre in extruded canine diets. The aim of this study was to test the health effects of two canine diets with identical macronutrient profiles, but containing either yellow field peas or white rice as the carbohydrate source on metabolism, cardiovascular outcomes and adiposity. First, the acute glycemic, insulinemic and cardiovascular responses to the pea- or rice-based diets were determined in normal weight beagles (n = 7 dogs). The glycemic index did not differ between the pea diet (56 ± 12) and rice diet (63 ± 9). Next, obese beagles (n = 9) were fed the yellow field pea diet or white rice diet ad libitum for 12 weeks in a crossover study. Adiposity (measured using computed tomography), metabolic (oral glucose tolerance test, plasma leptin, adiponectin, C-reactive protein) and cardiovascular assessments (echocardiography and blood pressure) were performed before and after each crossover study period. After 12 weeks on each diet, peak insulin (p = 0.05) and area under the curve (AUC) for insulin after a 10 g oral glucose tolerance test (p = 0.05) were lower with the pea than the rice diet. Diet did not show a significant effect on body weight, fat distribution, cardiovascular variables, adiponectin or leptin. In conclusion, a diet containing yellow field peas reduced the postprandial insulin response after glucose challenge in dogs despite continued obesity, indicating improved metabolic health.

Short-term obesity results in detrimental metabolic and cardiovascular changes that may not be reversed with weight loss in an obese dog model

The time course of metabolic and cardiovascular changes with weight gain and subsequent weight loss has not been elucidated. The goal of the present study was to determine how weight gain, weight loss and altered body fat distribution affected metabolic and cardiovascular changes in an obese dog model. Testing was performed when the dogs were lean (scores 4-5 on a nine-point scale), after ad libitum feeding for 12 and 32 weeks to promote obesity (>5 score), and after weight loss. Measurements included serum glucose and insulin, plasma leptin, adiponectin and C-reactive protein, echocardiography, flow-mediated dilation and blood pressure. Body fat distribution was assessed by computed tomography. Fasting serum glucose concentrations increased significantly with obesity (P< 0·05). Heart rate increased by 22 (SE 5) bpm after 12 weeks of obesity (P= 0·003). Systolic left ventricular free wall thickness increased after 12 weeks of obesity (P= 0·002), but decreased after weight loss compared with that observed in the lean phase (P= 0·03). Ventricular free wall thickness was more strongly correlated with visceral fat (r 0·6, P= 0·001) than with total body fat (r 0·4, P= 0·03) and was not significantly correlated with subcutaneous body fat (r 0·3, P= 0·1). The present study provides evidence that metabolic and cardiovascular alterations occur within only 12 weeks of obesity in an obese dog model and are strongly predicted by visceral fat. These results emphasise the importance of obesity prevention, as weight loss did not result in the return of all metabolic indicators to their normal levels. Moreover, systolic cardiac muscle thickness was reduced after weight loss compared with the pre-obesity levels, suggesting possible acute adverse cardiovascular effects.

Postprandial impairment of flow-mediated dilation and elevated methylglyoxal after simple but not complex carbohydrate consumption in dogs

Hyperglycemia produces oxidative stress, which may impair endothelial function. Methylglyoxal, a reactive intermediate metabolite of glucose, is known to cause oxidative stress and is produced when excess carbohydrate is consumed in diabetic patients, but postprandial responses in healthy patients are unknown. We hypothesize that methylglyoxal levels will cause impaired endothelial function via increased oxidative stress after consuming a high glycemic index meal in healthy animals. Normal-weight laboratory beagles (n = 6) were used in a crossover study that tested postprandial responses of 4 complex carbohydrate sources (barley, corn, peas, rice) vs a simple carbohydrate (glucose). Blood samples were taken prefeeding and at timed intervals after feeding to measure serum glucose, insulin, nitrotyrosine, and methylglyoxal. Flow-mediated dilation (FMD), cardiac function (echocardiography), and blood pressure measurements were determined before and 60 minutes after feeding. The mean (±SEM) glycemic indices of the complex carbohydrate sources were 29 ± 5 for peas, 47 ± 10 for corn, 51 ± 7 for barley, and 55 ± 6 for rice. Postprandial FMD was lowest in the glucose group and significantly different from both the corn group and the FMD value for all complex carbohydrates combined. Methylglyoxal was significantly elevated at 60 minutes postprandial after glucose compared with the other carbohydrate sources. No significant effects of carbohydrate source were observed for blood pressure, nitrotyrosine, or echocardiographic variables. The novel finding of this study was that methylglyoxal levels increased after a single feeding of simple carbohydrate and may be linked to the observed postprandial decrease in endothelial function. Thus, consuming low-glycemic-index foods may protect the cardiovascular system by reducing oxidative stress.

Preclinical cardiac safety assessment of drugs

The heart is a frequent site of toxicity of pharmaceutical compounds in humans, and when developing a new drug it is critical to conduct a thorough preclinical evaluation of its possible adverse effects on cardiac structure and function. Changes in cardiac morphology such as myocardial necrosis, hypertrophy or valvulopathy are assessed in regulatory toxicity studies in laboratory animals, although specific models may be needed for a more accurate detection of the risk. The potential proarrhythmic risk of new drugs is a major subject of concern and needs to be fully addressed before treatment of volunteers or patients takes place. In vitro assays are conducted to determine the effects on cardiac ion channels, in particular I(Kr) potassium channel antagonism. Prolongation of the QT interval is assessed in vivo, generally in telemetered dogs. Together, these two tests are considered to detect most arrhythmic drugs. The results of this core battery can be refined by additional studies, in particular assays on isolated cardiac tissues determining changes in cardiac action potential duration, shape and variability over time. Triggering of arrhythmia is assessed in hypokalaemic dogs with artificially created bradycardia, or in vitro in isolated whole hearts. The proarrhythmic risk of the new compound is then evaluated by integrating the results of these different tests. Drug adverse effects on cardiac electrophysiological function, in particular impulse formation and conduction, are evaluated through changes in ECG, generally recorded in dogs, pigs or monkeys. Changes in cardiac contractility occurring either as a primary effect of the drug on cardiac function or as a consequence of cardiac lesions should also be carefully assessed. In telemetered or anaesthetised animals, cardiac contractility is evaluated by measurement of left ventricular pressure and its first derivative over time. Echocardiography allows non-invasive measurement of drug-induced changes in ventricular wall movements and cardiac haemodynamics indicative of effects on contractility. In conclusion, a reliable and accurate evaluation of the cardiac safety of a new pharmaceutical agent is based on the results of in vitro tests, with overall moderate to high throughput, and in vivo experiments assessing the effects of the drug on the heart in its physiological environment. The specific sensitivities of the animals used in these assays to cardiac adverse effects should also be considered. The final evaluation of the cardiac risk is therefore based on an integrated analysis of the results from a battery of tests.

Transthoracic echocardiography in Estrela Mountain dogs: reference values for the breed

Of 100 Estrela Mountain dogs, 74 were examined to obtain echocardiographic reference values for the breed. The influence of bodyweight, age and sex on different echocardiographic parameters was studied using either analysis of variance or regression analysis. Statistically significant differences were found between sex and heart rate as well as interventricular septal thickness at end-systole and left ventricular internal dimension at end-diastole. A statistically significant linear correlation was also found between several parameters and (1) age (mean arterial pressure, left ventricular internal dimension at end-systole, fractional shortening, circularity index in systole, aortic valve velocity time integral, pulmonic valve velocity time integral and mitral valve E wave peak velocity), (2) weight (left ventricular posterior wall thickness at end-diastole and end-systole, end-diastolic volume index, left atrium diameter, aortic valve peak velocity and mitral valve E wave deceleration time), (3) sex and age (left ventricle end-diastolic volume), and (4) sex and weight (aortic root diameter and pulmonic valve peak velocity). Reference values for the breed are presented, as well as dispersion graphics for selected parameters, based on a regression equation.

Effect of milrinone on echocardiographic parameters after single dose in Beagle dogs and relationship with drug-induced cardiotoxicity

The aim of this study was to further investigate the mechanism of development of cardiac lesions occurring under treatment with milrinone in dogs, by using echocardiography for assessing the effects of this drug on cardiac function. Milrinone is a cAMP phosphodiesterase 3 inhibitor having positive inotropic and vasodilatory effects. We treated groups of three dogs with milrinone at a single dose of 0.5 or 1 mg/kg and recorded M-mode and Doppler parameters at different time points before and after treatment. The hearts of the high-dose animals were histopathologically examined. The treatment with milrinone at 1 mg/kg produced mild cardiac lesions at two different locations. In the left ventricle, haemorrhages in the subendocardium and myocardium occurred in all three dogs. In the right atrium, subepicardial haemorrhages occurred in one dog and inflammation of the epicardium was observed in two dogs. These lesions were considered to be related to changes in the cardiac function, which were investigated by echocardiography. Milrinone treatment produced a moderate tachycardia and changes in M-mode parameters indicating an increase in contractility, in particular, a decrease in end-systolic volume, an increase in ejection fraction and an increase in the rate of circumferential fiber shortening. In addition, there was an increase in the maximal aortic flow velocity evaluated by Doppler measurements, which is thought to represent a haemodynamic correlate of an increase in left ventricular contractility. This increase in myocardial work is considered to play a key role in the development of the lesions observed in the left ventricle. Doppler measurements also revealed changes in the right atrioventricular flow, probably resulting from cardiac stimulation produced by milrinone. In particular, there was an increase in the Vmax of the A-wave of the tricuspid flow, suggesting an increase in contractility of the right atrium. This change, by increasing blood flow in atrial wall, may be involved in the induction of the lesions observed in the right atrium. In conclusion, Doppler and M-mode echocardiography are useful tools to assess haemodynamic changes occurring upon treatment with vasodilators or cardiac stimulants in order to further understand the mechanism of development of cardiac lesions produced by such compounds.

Comparability of left ventricular M-mode echocardiography in dogs performed in long-axis and short-axis

The purpose of this prospective study was to determine comparability of left ventricular (LV) M-mode echocardiographic indices derived from right parasternal long-axis and short-axis imaging planes. In 104 dogs (37 healthy dogs and 67 dogs with heart disease), LV M-mode echocardiograms were recorded from both long-axis and short-axis views and interventricular septum thickness (IVS), left ventricular internal dimensions (LVD), left ventricular posterior wall thickness (LVPW), and LV shortening fraction (FS) were measured. Statistical analysis included paired t-test and graphical analysis to assess agreement between the two methods of data acquisition. Mean LVD in systole and diastole and mean IVS in systole were significantly (P<0.001) larger when measured from short-axis recordings compared to long-axis measurements. An increased magnitude of measurement resulted in increased differences between the methods for LV dimensions and fractional shortening. Differences between the two methods were small and within clinically acceptable limits in normal dogs. However, in 23 (34%) of the dogs with cardiac abnormality, one or more LV M-mode derived dimension obtained from one imaging plane did not agree sufficiently closely with the same measure from the other plane. Only for measurement of FS was there good agreement between methods in dogs with cardiac disease. Therefore, with the exception of FS, data gained from LV short-axis and long-axis M-mode recordings should not be used interchangeably in dogs with cardiac disease.