B-mode and M-mode echocardiography of endurance horses raised in São Paulo State, Brazil

This study aimed to evaluate cardiac dimensions and indexes of cardiac function in endurance horses using bidimensional- (B-) mode and guided unidimensional- (M-) mode echocardiography. Thirty-five Arabian and crossbred Arabian male and female horses, aged 5 to 18 years old, with an average weight of 415.51 ± 36.76 kg and at least 1 year of endurance training and competition experience, were used. The following values were obtained for B-mode echocardiography in the right parasternal window (see “Materials and Methods” for expanded terms): RVIDd 2.54 ± 0.56 cm; RVIDs 2.08 ± 0.68 cm; IVSd 2.60 ± 0.31 cm; IVSs 3.90 ± 0.44 cm; LVIDd 10.07 ± 0.85 cm; LVIDs 6.65 ± 0.92 cm; LVFWd 2.50 ± 0.30 cm; LVFWs 3.74 ± 0.35 cm; Aod 7.86 ± 0.72 cm; LAs 10.84 ± 0.93 cm; Vd 578.40 ± 108 cm³; Vs 232.68 ± 70.61 cm³; FS% 34.99% ± 8.02%; EF% 60.13% ± 8.29%; E-point 2.25 ± 0.49 cm; and LAs:Aod 1.38 ± 0.16 cm. Using guided M-mode, the following values were obtained: RVIDd 2.04 ± 0.55 cm; RVIDs 1.61 ± 0.71 cm; IVSd 2.68 ± 0.29 cm; IVSs 4.17 ± 0.42 cm; LVIDd 9.72 ± 0.72 cm; LVIDs 5.94 ± 0.96 cm; LVFWd 2.69 ± 0.32 cm; LVFWs 4.23 ± 0.69 cm; Aod 7.21 ± 0.75 cm; Vd 534.24 ± 87.53 cm³; Vs 181.75 ± 67.69 cm³; FS% 39.06% ± 7.66%; EF% 66.38% ± 9.41%; and E-point 1.96 ± 0.58 cm.

Introduction

In equine sports medicine, it is important to evaluate the cardiovascular condition of the athlete. More recently, echocardiography has been used for this purpose.Echocardiography is an invaluable diagnostic aid, since it is non-invasive and easy to perform,1, 2 and 3] while offering a dynamic and functional evaluation of the heart. 2, 3, 4 and 5].Initially, studies on the M-mode were made, including measurements of normal cardiac dimensions in horses6 and 7] and foals and for the diagnosis of several cardiac diseases. 1] With the introduction of the B-mode technique in the mid-1980s and its validation, a more detailed anatomic evaluation was possible, 2, 8 and 9] thus allowing the observation of cardiac abnormalities. 10]Though echocardiographic examination could be used to predict the athletic condition of individuals,11] this is possible only if normal echocardiographic reference values are established. As different breeds have different biotypes and develop different aptitudes, it is necessary to provide enough information for each type of work or breed. Research includes data for the Thoroughbred racehorse 3, 12 and 13] and Standardbred trotter, 14 and 15] which perform essentially anaerobic work.The endurance race is a modality that is growing significantly in Brazil, both in number of participants and in quality and training of the animals. The endurance horse demands a physical conditioning that differs from that required for racehorses, especially owing to the development of aerobic work. In addition, the animals are mainly Arabian or Arabian crossbred, which have a particular biotype. Because of these facts, and the lack of data about the echocardiographic behavior of endurance horses, this study aimed to determine the dimensions and indexes of cardiac function for horses with endurance training using B-mode and guided M-mode echocardiography.

Materials and methods

Thirty-five clinically normal endurance Arabian and Arabian crossbred male and female horses between 5 and 18 years old, with an average weight of 415.51 ± 36.76 kg, were included in the study. All animals had at least 1 year of training and experience in competitions and were kept under similar hygienic, sanitary, and nutritional management. Training consisted of trail rides, alternating walking, trotting, and galloping, from 20 to 40 km per day, 3 to 4 times per week.The echocardiographic examination was performed with a Sonosite model 180 Plus v. 1.9 echocardiograph, using a 2-4–MHz electronic microconvex transducer with a maximal depth of 24 cm.The animals were prepared as previously reported,4, 16 and 17] the hair being coated with large amounts of acoustic coupling gel. During the examination, the animals were at rest, calm, and physically restrained only by the halter, in a quiet and dark room.The following echocardiographic measurements, in B-mode as well as guided M-mode, were performed: the left atrium internal diameter in systole (LAs), only in B-mode, in the long axis view, dorsal to the annulus15]; the right ventricle internal diameter, in diastole (RVIDd) and in systole (RVIDs); the interventricular septum thickness, in diastole (IVSd) and in systole (IVSs); the left ventricle internal diameter, in diastole (LVIDd) and in systole (LVIDs); and the left ventricle free wall thickness, in diastole (LVFWd) and in systole (LVFWs), from the left ventricle short axis view at the chordal level; and the aortic root internal diameter (Aod), from the aortic valve short axis view. The B-mode measurements were taken according to Patteson et al, 12] and the M-mode measurements were based on Long et al. 18]Images were obtained from the right hemithorax. The position used for the transducer to obtain the standardized images for B-mode and guided M-mode were determined and used as described in Reef.4 and 17]The echocardiographic examination began using the B-mode echocardiography, with the establishment of the tomographic planes, evaluating morphology of the cardiac structures and their movement in a global manner.The first image obtained was the right parasternal long axis view, with the observation of the ventricle inlets, atrioventricular valves, and both atria. With the transducer positioned to optimize visualization of the left atrium, usually with a minimal dorsal angulation, the LAs measurement was made, immediately before the opening of the mitral valve (Fig 1).