Topic:Cardiovascular Health
Cardiovascular health in horses encompasses the study of the heart and blood vessels, focusing on their structure, function, and associated disorders. The equine cardiovascular system is responsible for the circulation of blood, delivering oxygen and nutrients to tissues, and removing waste products. Research in this area includes the examination of cardiac anatomy, the electrophysiology of the heart, and common cardiovascular conditions such as arrhythmias, valvular diseases, and heart murmurs. Diagnostic tools such as echocardiography, electrocardiography, and cardiac biomarkers are utilized to assess cardiovascular function and detect abnormalities. This page compiles peer-reviewed research studies and scholarly articles that explore the physiological mechanisms, diagnostic approaches, and therapeutic strategies related to cardiovascular health in horses.
Effects of additional premedication on romifidine and ketamine anaesthesia in horses. The clinical and cardiorespiratory effects of premedication with acepromazine, butorphanol or diazepam in addition to romifidine before induction of anaesthesia with ketamine were studied in 6 horses on 4 random occasions. Administration of romifidine alone or in combination with butorphanol resulted in an increase in arterial blood pressure, accompanied by a significant decrease in heart rate with second-degree atrio-ventricular heart block. Induction of anaesthesia with ketamine returned the heart rate to baseline value, but the arterial blood pressure was significantly increased compared to...
Cardiac rod body: hypertrophic Z-line in an aged pony. Numerous rod bodies were found in a heart sample from a 33-year-old pony by a conventional electron-microscopic technique. The rod bodies were concentrated in localized areas of both atria and ventricles, without a specific pattern of distribution. The rods appear to have a typical crystalline-like structure which presumably contains actin backbone filaments and alpha-actinin as major protein constituents. Diminution, fragmentation, and disorganization of the myofibrils, random expansion of electron-dense materials, especially at the fasciae adherens of the intercalated disc, an increase of in...
The vasomotor effects of 5-hydroxytryptamine on equine basilar arteries in vitro. The vasomotor effects of 5-hydroxytryptamine (5-HT) on isolated equine basilar arteries were studied. 5-HT induced contractions of equine basilar arteries in a concentration-dependent manner, with a pEC50 value (with 95% confidence limits) of 7.35 (7.08-7.62). Similar results were obtained with endothelium-denuded basilar arteries. Contractions were not competitively inhibited by the 5-HT2 receptor antagonist ketanserin at low concentrations of 5-HT. Conversely, at high concentrations of 5-HT, contractions were inhibited by ketanserin in a concentration-dependent manner, with a pA2 value of 8....
Metabolic, hormonal, and hemodynamic changes during dopamine infusions in halothane anesthetized horses. Selected metabolites, hormones and cardiovascular variables were measured in halothane anesthetized horses during 1 hour of dopamine infusion at a rate of 5 micrograms/kg/min (low) and 10 micrograms/kg/min (high), and for 1 hour after infusion. Plasma cortisol increased twofold in the low-infusion group but did not change significantly in the high-infusion group. Plasma nonesterified fatty acids, blood glucose, blood lactate, and plasma insulin increased in the high-infusion group. There was little difference in heart rate, systolic, diastolic, and mean arterial blood pressure between the two ...
Evidence for endothelium-derived relaxing factor/nitric oxide in equine digital arteries. To test the hypothesis that endothelium-derived nitric oxide modulates vasomotor reactivity in equine digital arteries. Methods: Digital arteries were isolated from adult horses, and their vasodilator properties were examined in an in vitro controlled environment. Methods: Five adult horses (1 gelding, 4 mares) without evidence of hoof or vascular disease were studied. Methods: Arterial rings with or without endothelium were exposed to endothelium-dependent vasodilator drugs in the presence or absence of a pharmacologic inhibitor of the enzyme nitric oxide synthase. Results: Vasodilator effect...
Heart rate response and plasma lactate concentrations of horses competing in the cross-country phase of combined training events. The exercise intensity of horses (n = 175) competing in the cross-country phase of 4 combined training events at 5 levels of competition [novice (N), training (T), preliminary (P), intermediate (I) and advanced (A)] was investigated. Environmental conditions varied from cool and humid (mean +/- s.d. temperature and humidity = 12.1 degrees C +/- 0.6 and 88.4% +/- 8.9 RH) to moderately hot and humid (27.8 degrees C +/- 2.1 and 62.5% +/- 7.8 RH). Heart rates (beats/min) were recorded continuously at 5 s intervals with a heart monitor. Mean +/- s.d. heart rates (beats/min) for each level of compet...
Thermal and cardiorespiratory responses of horses to submaximal exercise under hot and humid conditions. The objective of this study is to determine the effects of heat, and heat and high relative humidity (RH) on the thermal and cardiorespiratory responses to exercise and recovery. Five Thoroughbred horses (age 3 to 6) completed exercise tests under each of 3 environmental conditions: cool, dry (CD, room temperature (T) = 20 degrees C, RH = 45-55%), hot, dry (HD, T = 32-34 degrees C, RH = 45-55%) and hot, humid (HH, T = 32-34 degrees C, RH = 80-85%). Horses were exercised at a workload equal to 50% of VO2max on a treadmill set at a 10% slope until attainment of a pulmonary artery blood (PA) temp...
[Intravenous anesthesia in the horse: comparison of xylazine-ketamine and xylazine-tiletamine-zolazepam combinations]. Intravenous anesthesia in the horse: Comparison of xylazine-ketamine and xylaxine-tiletamine-zolazepam combinations. Six healthy adult horses were anesthetized twice at random with following intravenous combinations: 1.1 mg/kg of body weight (BW) of xylazine followed by 2.2 mg/kg BW of ketamine (X-K) and 1.1 mg/kg BW of xylazine followed by 1.65 mg/kg BW of tiletamine-zolazepam (X-TZ). The modifications of some cardiorespiratory parameters and the duration of anesthesia were evaluated and compared for the 2 protocols used. Few significant differences were observed between the 2 protocols in re...
Thyroid, renal, and splanchnic circulation in horses at rest and during short-term exercise. Using radionuclide-labeled 15-microm-diameter microspheres injected into the left ventricle, we examined blood flow to the thyroid gland, adrenal glands, kidneys, and various gastrointestinal tract tissues in 9 healthy horses while they were standing quietly (rest) and during exercise at 2 work intensities (8 and 1 m/s). Hemodynamic measurements were made during steady-state conditions, as judged by the stability of heart rate as well as aortic, pulmonary, and right atrial pressures. The similarity of blood flow values for the left and the right kidneys during each of the 3 conditions indicate...
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...
Effect of treadmill incline and speed on metabolic rate during exercise in thoroughbred horses. We examined the effect of treadmill speed and incline on O2 uptake (VO2), CO2 production, heart rate (HR), plasma lactate concentration, economy of locomotion, stride frequency, and stride length. A further aim was to examine the relationships between HR and VO2 and lactate and VO2 and whether these relationships vary with alterations in treadmill incline. The experiment was a latin square design, using five horses and five treadmill inclines (0, 2.5, 5.0, 7.5, and 10.0%). Fit Thoroughbred horses exercised for 4 min at 3 m/s at 0% slope, after which the treadmill was set to the allocated incli...
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...
Quinidine administration increases steady state serum digoxin concentration in horses. The aim of this study was to determine if quinidine administration increases steady state serum digoxin concentration in horses. Digoxin (0.01 mg/kg q. 12 h per os) was administered to 6 horses for 7 days. Steady state was confirmed by identifying statistically indistinguishable peak and trough serum digoxin concentrations on Days 4, 5, and 6. On Day 6, serum digoxin concentration was measured at baseline and 0.25, 0.5, 1, 2, 4, 6, 8 and 12 h after digoxin administration. On Day 7, quinidine (20 g at baseline and 10 g at 2, 4 and 6 h) was administered per os and serum digoxin concentration was...
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...
Heart murmurs in horses: determining their significance with echocardiography. Physiological flow murmurs occur frequently in horses and may be difficult to distinguish from murmurs associated with underlying cardiac disease. The significance of heart murmurs auscultated in horses is often difficult to determine if the horse is not exhibiting any clinical signs or if the signs, such as poor performance, are nonspecific. A complete echocardiographic examination (M-mode, 2-dimensional (2-D) and Doppler) provides an objective assessment of the severity of the horse's underlying cardiac disease. Valvular regurgitation and ventricular septal defects (VSDs) occur frequently an...
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...
Characterisation of beta-adrenoceptors in equine digital veins: implications of the modes of vasodilatory action of isoxsuprine. Isolated equine digital veins (EDVs) were used to study beta-adrenoceptor mediated vasodilation and to examine isoxsuprine's vasodilatory mechanism of action. When the blood vessel wall tension was raised with potassium chloride solution (KCl; 59 mmol/l), the order of vasodilator potency of beta-agonists was: isoprenaline > fenoterol > noradrenaline > dobutamine > isoxsuprine. The beta 2-selective adrenoceptor antagonist, ICI 118551 (1 nmol/l) caused a 6.74 and 6.65-fold parallel shift to the right in the dose response curves to fenoterol and noradrenaline respectively. Propranolol...
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...
Ventricular tachycardia associated with exhaustive exercise in a horse. Ventricular tachycardia was diagnosed in a 12-year-old unconditioned Appaloosa gelding after a 3-day trail ride. Initial signs were those of abdominal discomfort, ileus, and dehydration. Medical treatment included IV administration of lactated Ringer's solution. During hospitalization, the horse developed ventricular tachycardia. Serum potassium concentrations were within reference limits; however, assessment of total body potassium stores was not performed. Resolution of the arrhythmia occurred with further fluid treatment and potassium supplementation. Cardiac arrhythmias should be considere...