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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.
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...
Right ventricular pressure dynamics during exercise: relationship to stress echocardiography. Thorough evaluation of myocardial function remains difficult to evaluate under exercising conditions. This study described right ventricular (RV) pressure dynamics during and immediately following exercise. Nine Thoroughbreds without evidence of cardiac disease completed treadmill exercise at 110% of the speed necessary to elicit VO2max while RV pressures were recorded. RV pressure dynamics were calculated at rest, maximal speed and at 10 s intervals for 2 min after exercise. Stress echocardiography was performed at rest and within 120 s after exercise. Mean dP/dtmax and dP/dtmin values were s...
Heterogeneity of intrapleural pressures during exercise. We determined whether the caudodorsal region of the intrapleural space in exercising horses experiences larger pressure fluctuations than other regions and whether systematic phase-shifting of peak intrapleural pressures along the length of the thorax suggests the existence of locomotor-induced intrapleural pressure waves. We utilised percutaneous introducers and solid-state pressure-tip transducers implanted along the dorsal aspect of the thorax, mid-thorax or oesophagus to measure regional intrapleural pressures while 3 horses galloped on a flat treadmill at 13-14 m/s, then recorded pressure...
Effects of somatotropin and training on indices of exercise capacity in Standardbreds. The recent availability of recombinant equine somatotropin (eST) has led to concern about its use as an ergogenic aid in racehorses. This study was undertaken to investigate the changes in exercise capacity in maturing horses in a training programme, and to assess whether eST is an ergogenic aid to this group. We tested the hypothesis that the combination of training and eST, compared to training alone, would further improve exercise capacity in maturing Standardbreds, by virtue of ST's anabolic effects and potential to enhance cardiac function, circulating fluid volume and red cell mass. Twel...
Physiological responses of young Thoroughbreds during their first year of race training. Yearling horses are typically trained for more than a year before they begin racing; therefore, we questioned how relevant analyses of the initial responses to training are compared to physiological responses that occur over a year of training, and whether young horses with no history of training would respond the same as older horses that had been trained previously. We hypothesised that changes in O2 transport over the last months of a year of training would be different than at the beginning. We trained 5 yearling Thoroughbreds and evaluated metabolism, O2 transport and echocardiograms. Mea...
Effects of ageing and training on maximal heart rate and VO2max. The purpose of this study was to test the hypotheses that ageing would result in a decline in maximal heart rate (HRmax) and maximal aerobic capacity (VO2max) and, secondarily, that those effects would be reversible with training. Eighteen, healthy, unfit Standardbred mares representing 3 age groups: young (Y = mean +/- s.e. 6.8 +/- 0.4 years, n = 6); middle-aged (MA = 15.2 +/- 0.4 years, n = 6); and old (O = 27.0 +/- 0.2 years, n = 6) were used. HRmax, VO2max and oxygen pulse at VO2max (OPmax) and the velocities producing HRmax (VHRmax) and VO2max (VVO2max) were measured during pretraining an...
Potassium and lactate uptake by noncontracting tissue during strenuous exercise. Efflux of potassium (K+) and lactate (lac-) from active skeletal muscle during high intensity exercise leads to increased plasma [K+] and [lac-] in venous and arterial blood. The exercise-induced increases in these ions in human athletes is ameliorated, in part, by uptake by noncontracting tissue, reflected by an increase in the arteriovenous difference across these tissues from rest to exercise. To test the hypothesis that these ions are taken up by noncontracting tissue in strenuously exercising horses, plasma [K+] and [lac-] were measured in blood samples collected simultaneously from the c...
Effect of body incline on cardiac performance. Maximal cardiac performance is improved in man during upright compared to supine exercise. Whether cardiac performance in quadrupeds is dependent upon body position is unknown. Therefore, we undertook the present investigation to determine if peak cardiac output (Qpeak) would be influenced by body inclination in the Thoroughbred horse. To test the hypothesis, four Thoroughbred horses performed an incremental exercise protocol (speed increased by 1 m/s/min to fatigue) on both a level (L) and inclined (I: 6 degrees) treadmill. Specifically, we hypothesised that Qpeak would be increased on the in...
Hyperhydration prior to moderate-intensity exercise causes arterial hypoxaemia. The second day of a 3-day event is the most physically demanding of the 3 days. If this is performed under hot and humid environmental conditions, detrimental effects on cardiovascular and thermoregulatory function and, therefore, on exercise capacity, may occur due to exercise-induced dehydration. We hypothesised that the administration of fluid equivalent to 6% of the horse's bodyweight prior to a simulated second day of a 3-day event would increase plasma volume and limit increases in core temperature. Seven Standardbred geldings underwent a training protocol prior to the study. A standardi...
Thermoregulatory-induced compromise of muscle blood flow in ponies during intense exercise in the heat: a contributor to the onset of fatigue? Cardiac output (Q) and tissue blood flows (BF) were measured in four ponies at rest, after 30 min of moderate exercise (ME) (approximately 30% VO2max) and following moderately intense exercise (M-IE) (approximately 65%) until fatigue, in a mildly hot (MH) environment (dry bulb temperature = 41 degrees C, wet bulb temperature = 27.5 degrees C). Exercise at both intensities resulted in increases in Q (15.6 +/- 1.7 [rest] vs. 35.8 +/- 2.6 [ME] vs. 48.6 +/- 3.9 [M-IE] l/min) and VO2 (4.7 +/- 0.9 vs. 24.5 +/- 1.2 vs. 55.8 +/- 5.8 ml/kg/min). When compared to ME, M-IE resulted in decreases in BF to ...
Heart rate and blood lactate responses during exercise in preparation for eventing competition. The aim of this study was to investigate the heart rate and blood lactate responses to exercise in event horses in normal training, and to compare them to those encountered in eventing competition. It was hypothesised that the responses during exercise in the course of training for CCI*** events would be significantly different from those of the Cross-Country day. Heart rates and blood lactate concentrations were measured in 13 elite event horses after intense exercise sessions conducted during the late stages of preparation for CCI*** or CCI**** 3-day-event competition. Mean +/- s.d. heart ra...
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...
The effect of treadmill incline on maximal oxygen uptake, gas exchange and the metabolic response to exercise in the horse. In healthy man, conditions that change muscle O2 delivery affect the achievable maximum rate of O2 uptake as well as the metabolic (e.g. lactate threshold, LT) and gas exchange (e.g. gas exchange threshold, Tge) responses to incremental exercise. Inclined (I) compared to level (L) running increases locomotory muscle EMG at a given speed in the horse, indicative of elevated metabolic demand. To our knowledge, the effect of treadmill incline on VO2,max, LT and Tge has not been addressed in the exercising quadruped. We used blood sampling and breath-by-breath expired gas analysis to test the hypo...
Infusion of guaifenesin, ketamine, and medetomidine in combination with inhalation of sevoflurane versus inhalation of sevoflurane alone for anesthesia of horses. To evaluate effects of infusion of guaifenesin, ketamine, and medetomidine in combination with inhalation of sevoflurane versus inhalation of sevoflurane alone for anesthesia of horses. Methods: Randomized clinical trial. Methods: 40 horses. Methods: Horses were premedicated with xylazine and anesthetized with diazepam and ketamine. Anesthesia was maintained by infusion of guaifenesin, ketamine, and medetomidine and inhalation of sevoflurane (20 horses) or by inhalation of sevoflurane (20 horses). A surgical plane of anesthesia was maintained by controlling the inhaled concentration of sevoflu...
Clinical comparison of xylazine and medetomidine for premedication of horses. To compare the analgesic and cardiopulmonary effects of medetomidine and xylazine when used for premedication of horses undergoing general anesthesia. Methods: Randomized clinical trial. Methods: 40 horses. Methods: Twenty horses were premedicated with medetomidine (10 microg/kg [4.5 microg/lb], i.m.) and the other 20 were premedicated with xylazine (2 mg/kg [0.9 mg/kg], i.m.). Horses were then anesthetized with a combination of guaifenesin and ketamine; anesthesia was maintained with halothane. Additional doses of medetomidine or xylazine were given if horses were not sufficiently sedated at ...
Effect of administration of a phospholipid emulsion on the initial response of horses administered endotoxin. To evaluate the effect of a phospholipid emulsion (PLE) on the initial response of horses to administration of endotoxin. Methods: 12 healthy adult horses. Methods: Horses were assigned to 2 treatment groups (6 horses/group). The control group was administered 1 L of saline (0.9% NaCl) solution, and the treated group was administered PLE (200 mg/kg, IV); treatments were administered during a period of 120 minutes. An infusion of endotoxin was initiated in both groups starting 1 hour after initiation of the saline or PLE solutions. Physical examination and hemodynamic variables were recorded, a...
Cutaneous analgesia, hemodynamic and respiratory effects, and beta-endorphin concentration in spinal fluid and plasma of horses after acupuncture and electroacupuncture. To determine cutaneous analgesia, hemodynamic and respiratory effects, and beta-endorphin concentration in spinal fluid and plasma of horses after acupuncture and electroacupuncture (EA). Methods: 8 healthy 10- to 20-year-old mares that weighed between 470 and 600 kg. Methods: Each horse received 2 hours of acupuncture and 2 hours of PAES at acupoints Bladder 18, 23, 25, and 28 on both sides of the vertebral column as well as sham needle placement (control treatment). Each treatment was administered in a random order. At least 7 days elapsed between treatments. Nociceptive cutaneous pain thres...
Different contractile effects of alpha1- and alpha2-adrenergic agonists on horse isolated common digital artery smooth muscle ring preparations in vitro. Despite assays on ring preparations in vitro confirmed that the vasoconstrictor sympathetic control in the horse common digital artery mainly depends on alpha(1)-adrenoceptors stimulation, selective alpha(2)-adrenoceptor agonists were investigated under the same experimental conditions. Both detomidine (DET) and UK 14304 differed from noradrenaline (NA) and phenylephrine (PHE) in provoking contractile effects which were slowly onsetting, concentrations-unrelated and unremovable by repeated washings. While prazosin (PRA) clearly antagonized the effects of NA and PHE, neither pre- nor post-treat...
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...
Comparison of lithium dilution and thermodilution cardiac output measurements in anaesthetised neonatal foals. Knowledge of cardiac output is expected to help guide the treatment of hypotension associated with critical illness and/or anaesthesia in neonatal foals. However, a practical and safe method of measuring cardiac output has not been described for the foal. Lithum dilution, a new method of cardiac output determination not requiring cardiac catheterisation, has recently been reported in mature horses. We compared this method to thermodilution in isoflurane-anaesthetised foals age 30-42 h and found good agreement between the 2 methods in a range of cardiac outputs 5.4-20.4 l/min. The lithium dilut...
Equine surgical colic: risk factors for postoperative complications. The reason for undertaking this study was that postoperative complications of colic surgery lead to patient discomfort, prolonged hospitalisation and increased cost. Potential risk factors for the 6 most common postoperative complications (jugular thrombosis, ileus, re-laparotomy, wound suppuration, incisional herniation and colic) were evaluated using multivariable models. Jugular thrombosis was associated significantly with heart rate greater than 60 beats/min and with increased packed cell volume (PCV) at admission. The risk of postoperative ileus also increased with increasing PCV at admis...
Endothelin response during and after exercise in horses. The objective of the present study was to measure plasma endothelin-1 (ET-1) at rest and during exercise in the horse. Six healthy, Standardbred and Thoroughbred mares (5.3+/-0.8 years; 445.2+/-13.1 kg) which were unfit, but otherwise accustomed to running on the treadmill, were used in the study. Plasma ET-1 concentrations were measured using a commercially available radioimmunoassay kit. Horses performed three trials: a standing control (CON) trial where blood was collected from the jugular vein every minute for 5 min; a graded exercise test (GXT) where blood samples were collected at the en...
Ureteral ligation prevents the haemodynamic effect of frusemide in pentobarbitol anaesthetised horses. Frusemide reduces pulmonary vascular pressures in resting horses and attenuates exercise-induced increases in these pressures in exercising horses. The mechanism underlying these effects of frusemide is unclear. We tested the hypothesis that the haemodynamic effects of frusemide are dependent on diuresis by examining the effect of frusemide in anaesthetised horses in which diuresis was prevented by ligation of ureters. Twenty four horses were assigned randomly to one of 4 treatments: 1) frusemide (1 mg/kg bwt i.v.) and intact ureters; 2) frusemide and ligated ureters; 3) saline placebo and lig...
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-...
Cardiopulmonary effects and induction and recovery characteristics of isoflurane and sevoflurane in foals. To compare induction and recovery characteristics and cardiopulmonary effects of isoflurane and sevoflurane in foals. Methods: Prospective crossover study. Methods: 6 healthy foals. Methods: Foals were anesthetized twice (once at 1 month of age and again at 3 months of age). Anesthesia was induced by administration of the agent in oxygen through a nasotracheal tube. During maintenance of anesthesia, foals were positioned in dorsal recumbency; intermittent positive-pressure ventilation was performed. Characteristics of induction and recovery were recorded. Cardiopulmonary variables were recorde...
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.
