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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.
Use of biphasic electrical cardioversion for treatment of idiopathic atrial fibrillation in two horses. Rectilinear biphasic cardioversion was used in 2 horses with idiopathic sustained atrial fibrillation; 1 horse converted to sustained sinus rhythm. Variables that potentially affected outcome of the electrical cardioversion procedures in these horses included duration of arrhythmia, placement of cardioverter pads and paddles, serum electrolyte concentrations, and treatment with quinidine. Serum cardiac troponin I concentration, measured to determine whether the myocardium was damaged from the electrical shocks, was within the reference range in both horses after the procedure. Biphasic electri...
Heart size estimated by echocardiography correlates with maximal oxygen uptake. Maximum oxygen uptake also appears to correlate to athletic performance in horses. In the Thoroughbred industry, there has long been an empirical theory that heart size is related to athletic performance, despite a lack of scientific evidence supporting this assertion. To investigate the relationship between peak oxygen consumption (VO2max) and cardiac size measured by echocardiography, guided M-mode and 2-dimensional echocardiography were performed in 17 conditioned Thoroughbreds with a range of VO2max from 126 to 217 ml/min/kg STPD (mean +/- s.d. 158 +/- 28 m/min/kg). Horses were age 2-10 ye...
An equine model of chronic atrial fibrillation: methodology. We describe the development and the different features of an experimental model of chronic atrial fibrillation (AF) in equines. In four healthy ponies a dual-chamber pacemaker, with an adapted pacemaker program, was implanted transvenously in the standing animal. This adapted pacemaker induced episodes of AF by delivering a 2s burst of electrical stimuli (42 Hz) as soon as sinus rhythm was detected. Simultaneous with a surface electrocardiogram, the intra-atrial electrogram could be recorded to determine the atrial electrogram morphology. Programmed electrical stimulation (PES) was used to det...
Two-dimensional and M-mode echocardiographic measurements of cardiac dimensions in healthy standardbred trotters. The aim of the study was to establish normal echocardiographic values of healthy Standardbred trotters not published previously. Twenty-three clinically normal horses weighing between 350 and 490 kg were examined in the same manner: first a thorough physical and then detailed echocardiographic examination were performed. Standardised two-dimensional (2D) and guided M-mode echocardiographic imaging techniques were used to measure interventricular septal thickness (IVS), left ventricular internal diameter (LVID), left ventricular wall thickness (LVW), left atrial internal diameter (LAID) in end-...
Repeatability of standard transthoracic echocardiographic measurements in horses. To assess the repeatability of commonly employed transthoracic echocardiographic measurements in standing horses. Methods: Thirteen healthy 3- to 4-year-old fit Standardbred geldings with a mean weight of 411 (SEM +/- 10) kg were studied. The horses' environment, feeding and management regimens were standardised. All measurements were performed by the same investigator at the same time every day for three consecutive days. Methods: Standard transthoracic measurements were made on all horses. Each measurement was performed over three consecutive cardiac cycles on 1 day and all measurements were...
Giant right atrial diverticulum in a foal. A 5-month-old male Thoroughbred foal with a history of chronic septic arthritis of the tibiotarsal joint and recent respiratory distress was euthanized and a postmortem examination performed. A giant diverticulum communicating with the lateral aspect of the right atrial cavity of the heart was observed. Histologically, the wall was comprised of myocardial tissue containing cavernous vascular spaces. There was gross and histologic evidence of right-sided heart failure. Congenital right atrial diverticula are rare anomalies in humans and have not previously been reported in foals.
Density and binding characteristics of beta-adrenoceptors in the normal and failing equine myocardium. Beta-adrenoceptors are important regulators of cardiac function and their characteristics are known to change in human and canine diseased myocardium. This study aimed to determine the density and subtypes of beta-adrenoceptors in the normal and failing equine ventricular myocardium. Membrane preparations of the left papillary muscles were incubated with increasing concentrations of the nonselective beta-adrenoceptor antagonist [3H]-CGP12177. Saturable and reversible binding of [3H]-CGP12177 to myocardial membranes was demonstrated with Kd values (+/- s.d.) of 0.49 +/- 0.40 and 0.43 +/- 0.22 n...
Expression and coassociation of ERG1, KCNQ1, and KCNE1 potassium channel proteins in horse heart. In dogs and in humans, potassium channels formed by ether-a-go-go-related gene 1 protein ERG1 (KCNH2) and KCNQ1 alpha-subunits, in association with KCNE beta-subunits, play a role in normal repolarization and may contribute to abnormal repolarization associated with long QT syndrome (LQTS). The molecular basis of repolarization in horse heart is unknown, although horses exhibit common cardiac arrhythmias and may receive drugs that induce LQTS. In horse heart, we have used immunoblotting and immunostaining to demonstrate the expression of ERG1, KCNQ1, KCNE1, and KCNE3 proteins and RT-PCR to det...
Congestive heart failure in horses: 14 cases (1984-2001). To identify clinical signs, underlying cardiac conditions, echocardiographic findings, and prognosis for horses with congestive heart failure. Methods: Retrospective study. Methods: 14 horses. Methods: Signalment; history; clinical signs; clinicopathologic, echocardiographic, and radiographic findings; treatment; and outcome were determined by reviewing medical records. Results: All 14 horses were examined because of a heart murmur; tachycardia was identified in all 14. Twelve horses had echocardiographic evidence of enlargement of 1 or more chambers of the heart. Other common clinical finding...
Effects of aqua-treadmill exercise on selected blood parameters and on heart-rate variability of horses. The objectives of the present study were to investigate the effects of Aquatraining of horses (aqua-treadmill exercise; treadmill manufactured by Equitech - L.u.S. Equipment, Warendorf, Germany) on selected blood parameters [lactic acid concentration (mmol/l), haemoglobin content (g/l)] and on heart-rate variability (HRV) [heart rate (beats per min; b.p.m.), standard deviation of all NN-intervals (SDNN; ms), normalized power of the low and high frequency band (LFnorm, Hfnorm; au), % recurrence, % determinism and ratio(corr)]. Seven horses performed six exercise tests with different work loads ...
Effects of body position on intracranial and cerebral perfusion pressures in isoflurane-anesthetized horses. Inhalant anesthetics may interfere with normal cerebrovascular autoregulation. It was, therefore, hypothesized that intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in isoflurane-anesthetized horses would be especially sensitive to body and head position because of the potential for large hydrostatic gradients between the brain and heart in this species. Anesthesia was induced and maintained in six clinically healthy, unmedicated geldings with 1.57% isoflurane in O(2); mechanical ventilation was used to maintain normocapnia. ICP was measured by using a subarachnoid strain-gaug...
Hematuria and a complex congenital heart defect in a newborn foal. A 16-hour-old foal was referred for evaluation of hematuria. A pansystolic heart murmur and left thoracic thrill were detected; laboratory diagnostics and ultrasonography identified a complex congenital heart defect. The diagnosis was confirmed at postmortem.
The new conundrum: do estrogens have any cardiovascular benefits? Clearly, a new era has begun, with increasing numbers of the scientific/medical community asking whether estrogens have any cardiovascular benefits. Doubts have arisen from two randomized prospective trials. The Heart and Estrogen/progestin Replacement Study (women who were generally beyond 65 years of age with preexisting coronary heart disease) found no benefit in reducing coronary events by a combination of estrogens and a progestin. Later, the Estrogen Replacement Atherosclerosis Trial reported that no benefit could be shown for either conjugated equine estrogens only or the combined thera...
Cardiovascular changes associated with intravenous administration of fumonisin B1 in horses. To determine whether cardiovascular dysfunction is evident in horses with leukoencephalomalacia experimentally induced by administration of fumonisin B1. Methods: 11 healthy horses of various breeds (body weight, 252 to 367 kg). Methods: Horses were randomly assigned to 3 groups and administered fumonisin B1 daily. Horses received IV injections of 0 (control horses; n = 4), 0.01 (3), or 0.20 mg (4) of fumonisin B1/kg for 7 to 28 days. Horses were examined daily for evidence of neurologic disease. When neurologic signs consistent with leukoencephalomalacia were evident, horses were anesthetized...
Chronic clenbuterol administration negatively alters cardiac function. Chronic administration of pharmacological levels of beta2-agonists have been shown to have toxic effects on the heart; however, no data exist on cardiac function after chronic clenbuterol administration. The purpose of this study was to examine the effect of therapeutic levels of clenbuterol on cardiac performance. Methods: Twenty unfit Standardbred mares were divided into four experimental groups: clenbuterol (2.4 microg.kg(-1) twice daily 5 d.wk(-1)) plus exercise (20 min at 50% .VO(2max)) (CLENEX; N = 6), clenbuterol (CLEN; N = 6), exercise (EX; N = 4), and control (CON; N = 4). M-mode and ...
Glycogen branching enzyme deficiency in quarter horse foals. Seven related Quarter Horse foals that died by 7 weeks of age were examined for glycogen branching enzyme (GBE) deficiency. Clinical signs varied from stillbirth, transient flexural limb deformities, seizures, and respiratory or cardiac failure to persistent recumbency. Leukopenia (5 of 5 foals) as well as high serum creatine kinase (CK; 5 of 5), aspartate transaminase (AST; 4 of 4), and gamma glutamyl transferase (GGT; 5 of 5) activities were present in most foals, and intermittent hypoglycemia was present in 2 foals. Gross postmortem lesions were minor, except for pulmonary edema in 2 foals....
An assessment of the ability of diplomates, practitioners, and students to describe and interpret recordings of heart murmurs and arrhythmia. The ability of clinicians, ie, 10 veterinary students, 10 general practitioners, and 10 board certified internists, to describe and interpret common normal and abnormal heart sounds was assessed. Recordings of heart sounds from 7 horses with a variety of normal and abnormal rhythms, heart sounds, and murmurs were analyzed by digital sonography. The perception of the presence or absence of the heart sounds S1, S2, and S4 was similar for clinicians irrespective of their level of training and was in agreement with the sonographic interpretation on 89, 82, and 78% of occasions, respectively. Howev...
Accidental monensin toxicosis in horses in Mozambique. Horses on several farms in Mozambique were inadvertently fed with a concentrate containing 69 ppm monensin. The horses developed acute signs of toxicity and several died. The animals were depressed, anorectic and paretic before death. Epistaxis was observed in 1 case. Petechial haemorrhages were present in the muscles, heart, lungs, gastrointestinal tract and spleen in 3 horses necropsied. No significant histopathological cardiac and skeletal muscle lesions were seen, except in 1 case, in which there was focal loss of myofibrils.
Changes in cardiac dimensions and indices of cardiac function during deconditioning in horses. To investigate the effects of deconditioning on cardiac dimensions and indices of cardiac function in horses. Methods: Thirteen 3-to 4-year-old Standardbred geldings. Methods: All horses had echocardiographic measurements performed at the conclusion of 9 months of intense training and at weeks 1.5, 4, 8, and 12 of deconditioning. Direct echocardiographic measurements included interventricular septal thickness, left ventricular internal dimensions, left ventricular freewall thickness, left atrial dimension, aortic diameter, diameter of the pulmonary artery, slopes of the mitral valve, heart rat...
Use of sevoflurane for anesthetic management of horses during thoracotomy. To evaluate sevoflurane as an inhalation anesthetic for thoracotomy in horses. Methods: 18 horses between 2 and 15 years old. Methods: 4 horses were used to develop surgical techniques and were euthanatized at the end of the procedure. The remaining 14 horses were selected, because they had an episode of bleeding from their lungs during strenuous exercise. General anesthesia was induced with xylazine (1.0 mg/kg of body weight, IV) followed by ketamine (2.0 mg/kg, IV). Anesthesia was maintained with sevoflurane in oxygen delivered via a circle anesthetic breathing circuit. Ventilation was contr...
Temporal organization of atrial activity and irregular ventricular rhythm during spontaneous atrial fibrillation: an in vivo study in the horse. Atrial fibrillation (AF) is common in healthy horses. We studied the temporal organization of AF to test the hypothesis that the arrhythmia is governed by a high degree of periodicity and therefore is not random in the horse. Further, we surmised that concealed conduction of AF impulses in the AV node results in an inverse relationship between AF frequency and ventricular frequency. Results: Fast Fourier transform (FFT) analysis of atrial activity was done on signal-averaged ECGs (n = 11) and atrial electrograms (n = 3) of horses with AF at control (C), after quinidine sulfate (22 mg/kg by mou...
Concentration of cardiac troponin I in a horse with a ruptured aortic regurgitation jet lesion and ventricular tachycardia. An 18-year-old Thoroughbred gelding was evaluated because of sudden onset of ventricular tachycardia and signs of colic. Three years earlier, a diastolic decrescendo murmur, consistent with aortic regurgitation, had been detected, but the horse continued to perform well and compete successfully. Cardiac ultrasonographic examination revealed a defect in the interventricular septum below the aortic root, and serum concentrations of cardiac troponin I (cTnI) were higher than those measured in clinically normal horses. Repeated development of tachyarrhythmia during hospitalization prompted a decis...
Beta-adrenoceptors in equine trachea and heart. The density and subtype pattern of beta-adrenoceptors in equine tracheal epithelium, tracheal smooth muscle and heart from 6-9 horses were investigated by radioligand binding studies using the nonselective beta-adrenoceptor antagonist 125I-cyanopindolol (ICYP). The specific binding of ICYP was 341 +/- 162 fmol/mg protein (mean +/- SD) for epithelium, 42 +/- 13 fmol/mg for smooth muscle and 124 +/- 39 and 101+/- 19 fmol/mg for the cardiac atrium and ventricle, respectively. The Kd value of ICYP was 6.7 10.2 pmol/L. In competition studies, different concentrations of either the beta2-selective d...
Analysis of the right ventricular function in the exercising horse: use of the Fourier Transform. The objective of this study was to develop and test a technique to allow dynamic cardiac function to be studied during exercise in the horse. Blood pressure waveforms in the exercising horse are difficult to interpret because of the large influence of stride and respiration. A method has been devised to study dynamic right ventricular variables during high-speed exercise in the horse. A Fast Fourier Transform was performed on the digitised pressure waveforms and the frequency components associated with stride and respiration were removed. An inverse Fourier Transform was then performed to gene...
Cardiac responses to training in 2-year-old thoroughbreds: an echocardiographic study. Guided M-mode echocardiography was performed in seven 2-year-old Thoroughbreds before commencement of commercial flat-race training, and 18 weeks later, when all horses were either racing regularly (5 horses), or at racing fitness (2 horses). M-mode echocardiography was performed using a 2.5 MHz annular phased array ultrasound transducer and a Vingmed 800 Supervision echocardiograph. Images were obtained from the right hemithorax; a short axis view of the left ventricle (LV) at the level of the chordae tendinae was used to position the M-mode cursor. The following variables were measured: left...
