Precision-controlled echocardiographic left ventricular function parameters by repeated measurement on three consecutive days in trained and untrained warmblood horses

Echocardiographic measurements have to be reliable and reproducible with only a low day to day variability for detecting pathological changes of left ventricular myocardial function in horses. The day dependent fluctuation margin represents an important indicator for the reproducibility of a method. To find out the day to day variability of echocardiographic parameter in healthy warmblood horses, in the present study repeated echocardiographic measurements at three consecutive days were carried out (at the same time and by the same examiner) at 11 untrained and 7 trained warmblood horses. The horses were examined from the right hemithorax, in five different B- and M-Mode views in the long and short heart axis. The echocardiographic measurements in the three-day examination interval showed with coefficient of variation between 3.4 and 25.8% a good reproducibility. In order to calculate the precision of echocardiographic parameters (reproducibility from day to day) statistical analysis was carried out by means of a linear model with random effects. Herefor the variation between repeated measurements over three days and within the horses (day to day intraindividual variation) as well as the variation between the horses (interindividual variation) were taken into account. In dependency of the echocardiographic parameters 46.2-95.7% (median 85.7%) of the variation is caused by the difference between the horses (intraclass correlation) and 4.3-53.8% (median 14.3%) of the variation is caused by the repeated measurements on different days. With a coefficient of variance from 6.6% and an intraclass correlation of 0.957 the left ventricular diastolic diameter at the level of the papillary muscles showed the lowest variation between repeated measurements on different days. The heart rate with a coefficient of variance of 10.3% and an intraclass correlation of 0.462 showed the highest variation with 53.8% between the repeated measurements on different days. The precision of single echocardiographic measurements is confirmed. All parameters were also tested for differences between trained and untrained horses. Significant differences (p<0.05) could be found in the left ventricular diameter at the level of the apex cordis and under the mitral valves as well as in the systolic left ventricular area.     

A comparison of dobutamine infusion to exercise as a cardiac stress test in healthy horses

This study was done to determine whether administration of dobutamine would produce echocardiographic and electrocardiographic alterations comparable to those induced by treadmill exercise in healthy horses. Fourteen horses received maximal treadmill exercise and, separately, intravenous dobutamine infusion up to a maximum rate of 50 microg/kg/min. Ten of the 14 horses were euthanized, and the myocardial tissues were examined grossly and histopathologically. No significant differences were found in the chronotropic effects of dobutamine and exercise (P = .905). Dobutamine induced greater interventricular septal thickening during systole (dobutamine = 4.78 cm, exercise = 4.03 cm; P = .004). and greater left ventricular diameters during diastole (dobutamine = 9.73 cm, exercise = 9.26 cm; P = .037), than did exercise treatment. Horses exhibited transient signs of sweating and restlessness during infusion of moderate to maximum doses of dobutamine. Ventricular ectopy seen in 11 of 14 horses was attributed to the arrhythmogenic properties of dobutamine, as well as to increased vagal tone present at low dobutamine doses. Myocardial lesions characteristic of catecholamine myotoxicity were present in 2 of the 10 horses examined. Although dobutamine induces chronotropic and inotropic changes similar to those induced by exercise, the use of high-dose dobutamine as a cardiac stressor in horses cannot be advocated because of potential development of arrhythmias or myotoxicity.     

M-mode echocardiographic ratio indices in normal dogs, cats, and horses: a novel quantitative method

A novel method for quantitative echocardiographic interpretations is introduced based on the calculation of ratio indices in which each raw M-mode measurement is divided by the aortic root dimension (Ao). "Aorta-based" indices were calculated with the animal's measured aortic root dimension (Ao(m)) as the length standard. Conversely, "weight-based" indices employed an idealized estimate of aortic dimension (Ao(w)) with a weighted least squares linear regression against the cube root of body weight (Ao(w) = kW(1/3)). Use of these indices circumvented undesirable statistical characteristics inherent in linear regression of echocardiographic dimensions against body weight and, to a lesser extent, body surface area. Compared with the regressions, ratio indices resulted in substantial refinement of the predictive range for each M-mode measurement in dogs, particularly with decreasing body size. Weight-based indices outperformed aorta-based indices in this regard. To refine the predictive range, neither type of index was clearly advantageous in cats compared with the simple average method typically employed for that species. Several of the raw M-mode measurements, however, were correlated with body weight in cats and horses, indicating the need for an appropriate correction for body size in these species. The ratio index method was suitable for this purpose. Summary statistics derived from normal dogs (n = 53), cats (n = 32), and horses (n = 17) are presented for each index, including novel clinical indices calculated from area ratios. The latter were designed to represent body size-adjusted lett ventricular stroke area (ie, volume overload) and myocardial wall area (ie, hypertrophy).     

Evaluation of four 2-dimensional echocardiographic methods of assessing left atrial size in dogs

Two-dimensional (2D) echocardiography is the cornerstone of noninvasive evaluation of the cardiac patient, and often involves estimating left atrial (LA) size. However, 2D echocardiographic methods of estimating LA size have been inadequately described, and most reference intervals are based on M-mode echocardiographic measurements. We determined reference intervals for 4 different 2D echocardiographic methods of estimating LA size in adult (> or =9-month-old) dogs without cardiovascular disease. Thirty-six dogs, placed in right lateral recumbency, were examined by 2D echocardiography. The left atrium was measured at specific time points in the cardiac cycle. Measurement methods were LA diameter in short axis, LA diameter in long axis, LA circumference in short axis, and LA cross-sectional area in short axis. Comparisons of these LA dimensions to appropriate aortic dimensions provided body weight-independent estimates of LA size. We found strong associations of LA dimensions with body weight (r2 = .76-.88). Comparable body weight-independent 2D echocardiographic estimates of LA size in short axis exceeded historical M-mode reference intervals. These data provide echocardiographers with reference intervals for 2D echocardiographic estimates of LA size in adult dogs.     

Comparative study of 4 echocardiographic methods of left ventricular measurement in German Shepherd dogs

ObjectivesTo compare dimensions and shortening fraction (SF) of the left ventricle (LV) obtained from two-dimensional (2D) and M-mode imaging of short and long-axis views.Animals40 healthy, adult German Shepherd dogs.MethodsLeft ventricular measurements were obtained using 4 echocardiographic methods: M-mode in short and long-axis and 2D imaging in short and long-axis. The methods were compared by studying the effects of imaging mode and axis on LV parameters, taking into account the influence of weight and gender.ResultsMean LV end-diastolic diameter was greater in short-axis views. However, this difference was not considered clinically relevant. Mean SF was higher when derived from 2D measurements with poor agreement among methods. A combined influence of axis, gender, and weight was observed on interventricular septal thickness in end diastole with poor agreement among methods.ConclusionsSome LV parameters were significantly affected by mode and axis, either in isolation or in combination with weight and gender, although the differences observed were not always clinically relevant. These findings show that using the different echocardiographic methods interchangeably to assess LV dimensions should be done with caution.     

Stress echocardiography in warmblood horses: comparison of dobutamine/atropine with treadmill exercise as cardiac stressors

The purpose of this study was to determine whether the combination of dobutamine and atropine causes cardiac stress equivalent to treadmill exercise. Therefore, electrocardiography and echocardiography were performed on 10 warmblood horses before, during, and after different cardiac stress tests. Stressors consisted of a standardized treadmill exercise and combined administration of dobutamine (7.5 microg/kg/min) and atropine (5 microg/kg). Maxima heart rates were achieved during the treadmill exercise (175 +/- 10 bpm). After exercise, a rapid decrease in heart rate was observed. Subsequently, a stress echocardiography for which a heart rate >100 bpm was required could only be performed within 1 minute after exercise. The mean heart rate during echocardiography was 136 +/- 8 bpm after exercise. The combination of dobutamine and atropine also resulted in a significant increase in heart rate, up to 141 +/- 20 bpm. Maxima heart rate was significantly higher during the treadmill exercise, but the decrease in heart rate was significantly slower after dobutamine and atropine administration. Over a period of 7.9 minutes, the mean heart rate was 123 +/- 8 bpm during dobutamine and atropine administration. Consequently, the combination of both drugs offered sufficient time for detailed examinations. Overall, echocardiographic examination identified a decrease in left ventricular (LV) dimensions, an increase in LV wall thickness, and a decrease in stroke volume after the treadmill exercise and during pharmacologic stress testing compared with baseline. Changes in echocardiographic variables generally were more pronounced during dobutamine and atropine administration. Similar to stress echocardiography in humans, in horses the combination of dobutamine and atropine is useful to produce an increase in heart rate comparable with what is achieved with exercise but without the need of increasing dobutamine dosage.     

Pulmonary artery wedge pressure measurement in healthy warmblood horses and in warmblood horses with mitral valve insufficiencies of various degrees during standardised treadmill exercise

In 12 healthy warmblood horses and 10 horses with mitral valve insufficiencies (MVI) of various degrees heart rate and pulmonary artery wedge pressure (PWP) was measured at rest and during standardised exercise on a high speed treadmill. There was a significant increase in PWP with each change in speed of the treadmill (p < 0.01). The PWP of horses with mild mitral valve regurgitation under working conditions was not significantly different compared to the healthy horses. The horses with moderate mitral valve regurgitation showed a significant higher pulmonary artery wedge pressure at rest and during exercise compared to the healthy horses (p < 0.01) at rest and during treadmill velocity. The tendencies were seen that mild mitral valve regurgitation results only in mild hemodynamic changes during exercise, while moderate MVI have an important influence on haemodynamics.     

Evaluation of the 6-minute walk test in pet dogs

Background: The 6‐minute walk test (6MWT) is widely used in human medicine to objectively assess the degree of impairment, and to provide objective evidence of disease progression or response to therapy. Hypothesis/Objectives: The 6MWT will be easy to perform and well‐tolerated in pet dogs. Dogs with pulmonary disease will walk shorter distances than healthy dogs. Animals: Sixty‐nine healthy dogs were recruited from the hospital community. Six dogs with mild to moderate pulmonary disease were recruited from animals presented for evaluation at the teaching hospital. Methods: Prospective study. Dogs walked for 6 minutes in a hallway and the distance covered was measured. Pulse oximetry and heart rate were recorded before and after walking. Physical characteristics of the dogs, including age, leg length, body condition score, and weight, were recorded. Healthy dogs were compared with affected dogs by a Student's t‐test (P < .05). Correlations were calculated between the age, physical characteristics, and distances walked in the healthy dogs. Results: Healthy dogs walked 522.7 ± 52.4 m, while sick dogs (n = 6) walked 384.8 ± 41.0 m (P < .001). There was low (r= 0.13) to moderate (r= 0.27) correlation in the healthy dogs between physical characteristics and distances walked. Conclusions and Clinical Importance: The 6MWT was easy to perform and discriminated between healthy dogs and dogs with pulmonary disease.     

Influence of valvular insufficiency and recurrent airway obstruction on haemodynamics and therapy in warmblood horses with atrial fibrillation

The aim of this study was to investigate the potential haemodynamic effects of valvular insufficiency and recurrent airway obstruction (RAO) in horses with atrial fibrillation (AF). Therefore in ten healthy horses (group 1) and 40 horses with AF a clinical examination, a lung examination, echocardiography and right heart catheterization for measurement of intracardic and pulmonary pressures were performed. According to the clinical findings the horses with AF were subdivided into 4 groups (group 2: AF; group 3: AF/valvular insufficiency; group 4: AF/RAO; group 5: AF/valvular insufficiency/RAO). Most of the horses of group 3 and 5 suffered from two valvular insufficiencies (mitral and tricuspid valve insufficiency: n=11, mitral and aortic valve insufficiency: n=2). The remaining horses showed a single mitral (n=6), tricuspid (n=2) or aortic valve insufficiency (n=1) or more than two valvular insufficiencies (n=4). In group 2 right ventricular mean pressure (RVPm) was higher than in group 1 and 4 (P<0.025); diastolic right ventricular pressure was higher than in group 1; PWP was higher than in group 1 and group 4; PDP was lower compared to group1. Compared to group1 in group 3 left atrial diameter (LA) was greater; the PAPs was higher and the PDP lower (P<0.05). In group 4 RVPm and PWP was lower compared to group 2. In group 5 LA, fractional shortening and diastolic left ventricular diameter were greater, PWP and PAPs were higher and PDP lower compared to group1. Twenty six of the 40 horses with AF (65%) were treated. Successful cardioversion to sinus rhythm occurred in 15 horses (58%). Therapy was successful in 50% of the treated horses of group 2 and 3, in 67% of the treated horses of group 4 and in 63% of the treated horses in group 5. In conclusion the presence of valvular insufficiency or RAO influences the haemodynamics of horses with AF.     

Interreader agreement of radiographic left atrial enlargement in dogs and comparison to echocardiographic left atrial assessment

Introduction

Assessing left atrial (LA) size is an integral part of the cardiac evaluation in dogs. Left atrial size is routinely evaluated by thoracic radiographs or echocardiography.

Quantification of left ventricular longitudinal strain, strain rate, velocity, and displacement in healthy horses by 2-dimensional speckle tracking

Background: The quantification of equine left ventricular (LV) function is generally limited to short‐axis M‐mode measurements. However, LV deformation is 3‐dimensional (3D) and consists of longitudinal shortening, circumferential shortening, and radial thickening. In human medicine, longitudinal motion is the best marker of subtle myocardial dysfunction. Objectives: To evaluate the feasibility and reliability of 2‐dimensional speckle tracking (2DST) for quantifying equine LV longitudinal function. Animals: Ten healthy untrained trotter horses; 9.6 ± 4.4 years; 509 ± 58 kg. Methods: Prospective study. Repeated echocardiographic examinations were performed by 2 observers from a modified 4‐chamber view. Global, segmental, and averaged peak values and timing of longitudinal strain (SL), strain rate (SrL), velocity (VL), and displacement (DL) were measured in 4 LV wall segments. The inter‐ and intraobserver within‐ and between‐day variability was assessed by calculating the coefficients of variation for repeated measurements. Results: 2DST analysis was feasible in each exam. The variability of peak systolic values and peak timing was low to moderate, whereas peak diastolic values showed a higher variability. Significant segmental differences were demonstrated. DL and VL presented a prominent base‐to‐midwall gradient. SL and SrL values were similar in all segments except the basal septal segment, which showed a significantly lower peak SL occurring about 60 ms later compared with the other segments. Conclusions and Clinical Importance: 2DST is a reliable technique for measuring systolic LV longitudinal motion in healthy horses. This study provides preliminary reference values, which can be used when evaluating the technique in a clinical setting.     

Effects of sedation on echocardiographic variables of left atrial and left ventricular function in healthy cats

Although sedation is frequently used to facilitate patient compliance in feline echocardiography, the effects of sedative drugs on echocardiographic variables have been poorly documented. This study investigated the effects of two sedation protocols on echocardiographic indices in healthy cats, with special emphasis on the assessment of left atrial size and function, as well as left ventricular diastolic performance. Seven cats underwent echocardiography (transthoracic two-dimensional, spectral Doppler, color flow Doppler and tissue Doppler imaging) before and after sedation with both acepromazine (0.1 mg/kg IM) and butorphanol (0.25 mg/kg IM), or acepromazine (0.1 mg/kg IM), butorphanol (0.25 mg/kg IM) and ketamine (1.5 mg/kg IV). Heart rate increased significantly following acepromazine/butorphanol/ketamine (mean ± SD of increase, 40 ± 26 beats/min) and non-invasive systolic blood pressure decreased significantly following acepromazine/butorphanol (mean ± SD of decrease, 12 ± 19 mmHg). The majority of echocardiographic variables were not significantly different after sedation compared with baseline values. Both sedation protocols resulted in mildly decreased left ventricular end-diastolic dimension and mildly increased left ventricular end-diastolic wall thickness. This study therefore failed to demonstrate clinically meaningful effects of these sedation protocols on echocardiographic measurements, suggesting that sedation with acepromazine, butorphanol and/or ketamine can be used to facilitate echocardiography in healthy cats.     

Effect of gender and exercise on haematological and biochemical parameters in Holsteiner horses

The objective of this study was to assess the influence of exercise of average intensity in the haematological and biochemical values, as well as acidic resistance of erythrocytes in mares and stallions of Holsteiner breed. A total of seventeen horses of Holstein breed (seven mares and 10 stallions aged 6 years) were used in this study. The blood samples were assessed for haematocrit (HCT) value, haemoglobin concentration (HGB), the amount of red blood cells (RBC), white blood cells (WBC), platelets (PLT), leucogram, mean corpuscular haemoglobin concentration (MCHC), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), red cell distribution width (RDW) and platelet distribution width (PDW). Serum concentrations of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) as well as oxidative stress biomarkers were analysed. Stallions showed a significant increase in leucocytes and granulocytes amount, as well as erythrocytes, haemoglobin and haematocrit levels after exercise test. Pre‐exercise level of mean corpuscular haemoglobin concentration was higher in stallions. At the same time, mares showed significant decrease in platelet volume after exercise test. Physical effort in stallions leads to significant increase in aspartate aminotransferase activity. Trained mares and stallions showed a decrease in lipid peroxidation after exercise. Exercise also caused increase in oxidative modified protein of erythrocytes in stallions indicating by exercise‐induced oxidative stress. The resistance of erythrocytes in 0.1 m HCl was similar between females and males. No statistically significant differences in the percentage of haemolysed erythrocytes before and after exercise were observed.     

Effect of difference in training skills on stress in horses trained by Kazakh trainers

This study aimed to evaluate the effect of differences in trainer skills on horse training during the early stages of riding habituation by measuring the levels of stress and changes in stress levels. Among nine untrained horses employed, five in Group A were trained by two low-skilled trainers, whereas the remaining four in Group B were trained by two high-skilled trainers using the traditional Kazakh method. Salivary α-amylase concentration was measured as a biomarker of stress immediately before and after each riding session during the training period. In the duration of riding and mooring times to the total riding habituation time for each horse, no significant difference was observed between the two groups. In contrast, the mean total stress and mean final stress were significantly lower in Group B than in Group A, and the mean total change in stress before and after riding habituation was significantly higher in Group B. Differences in trainer skills were evidenced as differences in training methods to suppress the total stress levels through differences in the application of stress burden during the training of individual horses.     

Effect of sulfadiazine and pyrimethamine on selected physiologic and performance parameters in athletically conditioned thoroughbred horses during an incremental exercise stress test

Following the regimen used to treat equine protozoal myeloencephalitis, sulfadiazine (20 mg/kg) and pyrimethamine (1mg/kg) were administered orally once daily to 12 physically conditioned Thoroughbred horses for 4 consecutive days. The horses were randomly assigned to two test groups in a crossover design, with each horse serving as its own control. A stepwise exercise stress test was conducted to exhaustion. No effect on athletic performance was observed, and only marginal effects were noted in some hematologic and serochemical measurements, including decreased total white blood cell counts, red blood cell distribution width, total hemoglobin, serum sodium, and serum chloride. Serum folic acid concentration decreased significantly following sulfadiazine/pyrimethamine treatment.     

Improvement in the national genetic evaluation of warmblood riding horses by including information from related studbooks

Abstract

Young horse performance test data from two warmblood riding horse populations, Norwegian warmblood (NWB) and Swedish warmblood (SWB), were analysed to examine whether including information from a related studbook would increase the accuracy of the genetic evaluations within a population. Ten conformation and performance traits from 31,588 horses, 774 NWB and 30,814 SWB were analysed separately and jointly using single trait animal models. Heritabilities were moderate to high, and varied from 0.15 (conformation, joint data) to 0.74 (jumping technique, NWB data). The genetic similarity (GS) between populations was 31%, with the SWB, as expected given the size of the populations, contributing most to the GS (98%). Genetic correlations between the same traits in the two populations were 0.43–0.90 but with large standard errors (0.2–0.3). Including information from the other population increased the average accuracy of estimated breeding values for common stallions, on average 4% for SWB and 110% for NWB.