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Topic:Heart
The equine cardiovascular system, particularly the heart, is fundamental to maintaining the health and performance of horses. The heart is responsible for pumping oxygenated blood throughout the body, supporting vital functions and physical activity. In horses, the heart's structure and function are adapted to meet the demands of both rest and exertion, with notable features such as a large cardiac output and efficient blood circulation. Conditions affecting the equine heart, such as arrhythmias, valvular diseases, and myocardial disorders, can significantly impact a horse's well-being and athletic capability. This page aggregates peer-reviewed research studies and scholarly articles that explore the anatomy, physiology, and pathophysiology of the equine heart, as well as diagnostic and therapeutic approaches to managing cardiac health in horses.
Echocardiographic measurements of cardiac dimensions in normal ponies and horses. Echocardiographic examinations were performed on 41 clinically normal small ponies, large ponies and horses. Using standardised two-dimensional (2-D) echocardiographic images to guide M-mode studies, the interventricular septal thickness, left ventricular internal dimension and left ventricular wall in systole and diastole, and aortic diameter in diastole were measured. Normal values for these echocardiographic dimensions were obtained across a wide range of bodyweights. Although there was a trend for echocardiographic dimensions to increase with bodyweight across the whole range of animals ex...
An echocardiographic study of atrial fibrillation in horses: before and after conversion to sinus rhythm. Two-dimensional and M-mode echocardiograms were recorded from 41 horses before they were successfully treated for atrial fibrillation. In addition, these examinations were performed in a subgroup of 20 horses after treatment, and the results were compared with pretreatment values. Atrial fibrillation in this group of horses was associated with a reduction of mean left ventricular fractional shortening (mean 31% +/- 5.24%), and 22 of the 41 horses were below the reference range. The remaining mean M-mode variables were within the normal reference range, although 12 horses had increased left ven...
The haemodynamic effects of milrinone HCl in halothane anaesthetised horses. The haemodynamic effects of milrinone hydrochloride were determined in halothane-anaesthetised horses. Six healthy adult horses were anaesthetised with guaifenesin and thiamylal and maintained with halothane in oxygen (end-tidal halothane concentration of 1.15%). Baseline haemodynamic data were recorded after a 45 min stabilisation period. All 6 horses received a single loading dose of milrinone HCl, 0.2 microgram/kg i.v., followed by progressively increasing infusions of 2.5, 5, 10 and 20 micrograms/kg bwt/min. Each infusion lasted for 15 min and produced dose related increases in heart rate,...
Colour flow Doppler echocardiography in normal horses. Colour flow Doppler echocardiography is a technique that is used with two-dimensional (2-D) echocardiography to study blood flow patterns in the heart and blood vessels. This method was used to define normal flow patterns and to evaluate valvular function in 40 clinically normal Thoroughbred and Thoroughbred cross horses. Flow patterns from 10 standardised echocardiographic images were described in relation to anatomic landmarks and timing during the cardiac cycle. Consistent intracardiac flow patterns were identified in the normal horses. High velocity flow signals or regurgitant jets were re...
Colour flow Doppler echocardiography in horses with cardiac murmurs. Thirty-two horses with cardiac murmurs typical of tricuspid, mitral and aortic regurgitation were studied using colour flow Doppler echocardiography. The dimensions and duration of any regurgitant signals, recorded at the cardiac valve suspected as being the site of origin of the murmur, were measured. Results were compared with flow signals described at the valves of normal horses (Blissitt and Bonagura 1995). Horses with murmurs suggestive of tricuspid (n = 8) and aortic (n = 8) regurgitation showed larger regurgitant signals at the tricuspid and aortic valves respectively, than has been rep...
Echocardiography. Echocardiography encompasses a number of specific imaging techniques. The two-dimensional (2-D) echocardiogram is used to identify lesions of the heart and great vessels, assess myocardial function and provide a template for guiding contrast echocardiography, colour-coded Doppler echocardiography and spectral Doppler studies. M-mode echocardiography is used to measure cardiac size and ventricular function and can be combined with contrast or colour-coded Doppler studies for accurate timing of flow events. Pulsed wave and continuous wave Doppler echocardiography display the direction and veloci...
Effects of sedation with detomidine hydrochloride on echocardiographic measurements of cardiac dimensions and indices of cardiac function in horses. Twenty-six horses were sedated with detomidine hydrochloride (Domosedan, SmithKline Beecham Animal Health, Tadworth, Surrey, UK) at a dose of 10 micrograms/kg bwt, administered i.v. Echocardiograms were recorded before and after sedation, measurements of cardiac dimensions were made and functional indices were calculated. The pre- and post sedation values were compared. No significant change was detected following sedation in the ejection time (ET), left ventricular dimension, left atrial diameter at the sinotubular junction at end-systole or end-diastole or at the sinus of Valsalva at end-dia...
Echocardiographic measurements of cardiac dimensions and indices of cardiac function in normal adult thoroughbred horses. Cardiac dimensions and indices of cardiac function were measured in 29 clinically normal adult Thoroughbreds (TB) which performed minimal exercise using guided M-mode and two-dimensional (2-D) echocardiography, from a variety of image planes and measurement methods, and standardised imaging planes based on intracardiac anatomical landmarks. The different methods of measuring these variables were compared. The variables which were considered to be most valuable for quantitative echocardiography were measured in a further 9 horses. Comparable measurements of cardiac dimensions can be obtained fr...
Physiological valvular regurgitation in clinically normal young racehorses: prevalence and two-dimensional colour flow Doppler echocardiographic characteristics. Colour flow Doppler echocardiographic examinations were performed on 15 horses; 10 Thoroughbreds and 5 Standardbreds; 9 mares, 5 geldings and 1 stallion; mean +/- s.d. 3.4 +/- 1.1 years. Cardiac murmurs were audible in 12 horses (80%), but these had characteristics consistent with functional murmurs in all horses. A standardised two-dimensional (2-D) and M-mode echocardiographic examination was unremarkable in all horses except that aortic valve prolapse was identified in 3 horses, tricuspid valve prolapse in 2 horses and mitral valve prolapse was present in one horse. Colour flow Doppler echo...
Pseudomonas spp. associated vegetative endocarditis in two horses. This paper describes the case histories of two Thoroughbred horses, a 2-year-old colt in training and a 7-year-old broodmare, that were presented with histories of weight loss, exercise intolerance, intermittent fever, limb oedema and anaemia. Vegetative endocarditis of the mitral and tricuspid valves was diagnosed in the colt by means of echocardiography. Pseudomonas sp. endocarditis of the mitral valve was diagnosed in the mare using echocardiography and bacterial culture. The colt had secondary congestive heart failure and was euthanased on humane grounds. Pseudomonas cepacia was isolated f...
Feasibility of transoesophageal echocardiography for evaluation of left ventricular performance in anaesthetised horses. Transoesophageal Doppler echocardiography was performed in 7 Thoroughbred horses anaesthetised with halothane. The procedure was performed on 4 occasions under standard conditions. On one occasion dobutamine hydrochloride was infused at 4 micrograms/kg/min for 20 min. Recordings of aortic blood velocity, obtained using high pulsed repetition frequency Doppler echocardiography (HPRF), were used to derive maximum acceleration (dv/dtmax), maximum velocity (Vmax), left ventricular ejection time (ET), pre-ejection period (PEP), velocity time integral (VTI) and cardiac output (CO). The coefficient o...
Evaluation of ventricular septal defects in horses using two-dimensional and Doppler echocardiography. Ventricular septal defects (VSDs) were diagnosed in 27 horses; in 26 affected horses systolic murmurs were detected over both sides of the chest. Holodiastolic decrescendo murmurs were also detected in 5 horses. Standardbreds and Arabian horses were over-represented, while Thoroughbred horses were under-represented, when compared to the hospital population (P < 0.0001). Five horses had previously raced successfully, one 2-year-old was training successfully and close to racing, and 4 horses had competed successfully in other types of competition. Eleven horses had a history of exercise intolera...
Pulsed wave Doppler echocardiography in normal horses. Reference values were established for selected Doppler derived variables from a group of 40 normal Thoroughbred and Thoroughbred cross horses. Standard two-dimensional (2-D) images used for guiding the Doppler sampling site allowed accurate alignment with flow. Tricuspid inflow velocities during rapid filling (E) and atrial contraction (A) were significantly higher when recorded from a right parasternal angled view than from a right parasternal long-axis view. In 8 horses the tricuspid inflow peak A velocity was higher than the peak E velocity. The peak acceleration of blood flow was higher (P...
Comparison of the workload of Dutch warmblood horses ridden normally and on a treadmill. Six Dutch warmblood horses, ridden by an experienced rider, cantered 3320 m at a speed adapted to the individual horse's anaerobic threshold, under four different conditions: 1, on a firm shell track with the speed varying from 6.5 to 9.4 m/s; 2, on a horizontal treadmill at the same speeds and for the same duration as in test 1; 3, on a horizontal treadmill for the same duration as in tests 1 and 2, but at a 10 per cent higher speed; and 4, on a treadmill at the same speed and for the same duration as in test 1, but at an inclination of 1 to 2 per cent adjusted individually to obtain heart ra...
Detection of immunoreactive atrial and brain natriuretic peptides in the equine atrium. The distribution of immunoreactivity (IR) for cardiodilatin/atrial natriuretic peptide (CDD/ANP) and brain natriuretic peptide (BNP) was examined immunohistochemically and immuno-electron-microscopically in the equine atrium, using specific antibodies. In the immunohistochemical studies, IR-CDD/ANP and IR-pBNP-26 (porcine BNP-26 immunoreactivity) was detected in the cytoplasm of the auricular cardiocytes, but IR-hBNP-32 (human BNP-32 immunoreactivity) was not. The double immunogold labelling method for IR-hBNP-28 and IR-pBNP-26 revealed that gold particles of different sizes were located in th...
[Heart rate fluctuations in the horse at rest: (1) Investigation of heart rate changes by spectrum analysis]. The heart rate fluctuations at rest were studied in order to explore the emotionality of the horses by isolating the influence of the autonomic control. This paper presents a method of spectral analysis which was used to analyse the heart rate variability in the frequency domain. The heartbeat intervals were recorded during 1 h and a series of 1,024 heartbeats was extracted to compute a power spectrum of density. This was obtained by calculating the Fourier transform of the autocorrelation function of the series. This spectral analysis was applied to heart rate recordings in order to illustrat...
Effects of glyceryl trinitrate (nitroglycerin) on pulmonary vascular pressures in standing thoroughbred horses. Strenuously exercising Thoroughbreds exhibit a dramatic increase in pulmonary capillary blood pressure, which contributes to stress failure of pulmonary capillaries resulting in exercise induced pulmonary haemorrhage (EIPH). One strategy to prevent EIPH is, therefore, to lower the pulmonary capillary blood pressure of exercising horses. Recent work in several species suggests that nitric oxide plays a significant role in maintaining low vascular resistance in the pulmonary circulation; however, the effects of nitrovasodilators (which work via the same mechanism as nitric oxide) on equine pulmo...
Blood parameter and heart rate response to training in Andalusian horses. A study was performed on Andalusian horses in order to assess the response of heart rate and various blood parameters to training. Two tests were performed, at two and four months of training respectively. Exercise schedules were of increasing intensity, over a distance of 1000 meters. Speed was progressively increased, from 4 m/s to 8.5 m/s, over four exercise stages. In both tests, a recovery period of 5 min followed each stage. Sample collection (by puncture of the external jugular vein) was performed with the animals at rest, within the first minute after each exercise stage, and at 10, 15...
The accuracy of predicting Thoroughbred heart scores. Veterinarians commonly predict mature heart scores for yearling and 2-year-old horses to aid clients in assessing a horse's racing potential. Sixty-six thoroughbreds were assessed as a yearlings or 2-year-olds, then re-assessed as a mature horse (over the age of 3). Of these horses, 82% of the yearlings and 87% of the 2-year-olds had a correctly predicted mature heart score within one heart score range (i.e. three points).
Validation of the shrinkage temperature of animal tissue for bioprosthetic heart valve application by differential scanning calorimetry. Shrinkage temperature is most often used to report the degree of cross-linking in glutaraldehyde-fixed animal tissue for use in bioprosthetic heart valve fabrication. Present practice utilizes the measurement of hydrothermal shrinkage observed when a sample is subjected to a temperature programme. This measurement at best gives a general indication of the efficiency of the treatment, i.e. the extent of cross-linking in the tissue. When differential scanning calorimetry has been used, the ambiguity arising from the scant reporting of the protocols used does not permit easy comparison of experim...
Haemodynamic effects of hyoscine-N-butylbromide in ponies. The haemodynamic effects of hyoscine-N-butylbromide (0.30 mg/kg, intravenously) were studied in eight adult ponies in a blinded two-period crossover experiment with repeated measures. Values for heart rate were 63%, 48% and 13% greater than control values at 1, 16 and 46 min, respectively, after administration of hyoscine-N-butylbromide. Cardiac output increased by 16% at 16 min after drug injection. Mean right atrial pressure was decreased by 79%, 63%, 45% and 52% at 1, 16, 46 and 61 min, respectively, after drug administration. Stroke volume was decreased by 32% at 1 min and pulmonary arteri...
[Preliminary results using a combined xylose absorption/hydrogen exhalation test in horses]. In the present study the breath hydrogen (H2) excretion test was combined with the xylose absorption test in 4 normal horses and 9 clinical patients with chronic diarrhea (n = 3) or chronic weight loss without diarrhea (n = 6). All horses underwent a thorough clinical examination. Laboratory evaluations consisted of haematology and serum biochemistry as well as bacteriological and parasitological examination of feces. In addition, serum electrophoresis and abdominocentesis was performed in all the clinical patients. Gastroscopy was carried out in 6 patients and rectal biopsies were obtained fr...
Ventricular tachycardia and myocardial dysfunction in a horse. Ventricular tachycardia develops less frequently than supraventricular dysrhythmias and generally is more indicative of cardiac disease. The horse in this report had clinical signs of lethargy and hypophagia and was determined to have sustained ventricular tachycardia. Echocardiography was a valuable diagnostic tool and revealed an echodense area in the left ventricle that had subnormal ventricular performance. A primary heart problem of an inflammatory nature was suspected. The horse responded favorably to treatment with lidocaine, antimicrobials, and aspirin, as well as stall rest. The horse...
Relationships between electrocardiographic findings, racing performance and training in standardbred horses. The presence of abnormal T waves in three or more electrocardiographic leads has been used to diagnose the cause of poor race performance in horses. This study investigated the relationship between previous racing performance in Standardbred horses and T waves, and the effect of training on the T wave. Thirty-two horses were electrocardiographed in two Sydney racing stables. Sixteen horses (50%) had ECGs with three or more leads with abnormal T waves, and these horses had won more races, had a greater ratio of wins per start and a greater number of dollars earned per start than horses with les...
Equine echocardiography–sound advice at the heart of the matter. Echocardiography is an extremely versatile tool for both the equine clinician and physiologist. There are three useful forms of echocardiography, B mode, M mode and Doppler. Together they provide complementary information on cardiac disease and haemodynamic status. B mode is used to image the cardiac chambers, valves, myocardium and pericardium. M mode allows determination of motion of cardiac structures; it is superior to B mode for timing of events and it is used to make precise measurements of the heart. Doppler echocardiography can assess intracardiac blood flow and its velocity. Echocardi...
Pulmonary vascular pressures of thoroughbreds increase rapidly and to a higher level with rapid onset of high-intensity exercise than slow onset. Previous studies of pulmonary vascular pressures have utilised gradual incremental step exercise protocols, but in competitive racing at the track, horses perform rapid acceleration high-intensity exercise. The rate of rise in pulmonary vascular pressures under conditions of quick onset high-intensity exercise is unknown. Catheter mounted manometers, whose in vivo signals were matched with pressure signals obtained via transducers connected to fluid-filled lumens from same cardiovascular sites, were used to compare right heart and pulmonary vascular pressures in 8 healthy Thoroughbreds perform...
Presence of African horse sickness virus in equine tissues, as determined by in situ hybridization. In a retrospective study, a negative-sense digoxigenin-labeled RNA probe, corresponding to the gene encoding nonstructural protein-1 of African horse sickness virus (AHSV) serotype 4, was applied to formalin-fixed, paraffin-embedded tissue taken from horses in the terminal stages of infection with AHSV. Fifteen infected ponies and one noninfected control were studied. Ponies exhibited a range of clinical signs and lesions. Thirteen ponies were infected with serotype 4, one with serotype 1, and one with serotype 2. Ponies were monitored clinically and euthanatized when severely clinically ill. ...
Atrial and ventricular myocardial blood flows in horses at rest and during exercise. Right atrial, pulmonary artery, pulmonary capillary, pulmonary artery wedge, and systemic blood pressures of strenuously exercising horses increase markedly. As a consequence, myocardial metabolic O2 demand in exercising horses must be high. Experiments were, therefore, carried out on 9 healthy, exercise-conditioned horses (2.5 to 8 years old; 481 +/- 16 kg) to ascertain the regional distribution of myocardial blood supply in the atria and ventricles at rest and during exercise. Blood flow was measured, using 15-micron-diameter radionuclide-labeled microspheres that were injected into the left...
Endocarditis and pulmonary aspergillosis in a horse. No abstract available
