Atrial function in horses pertains to the mechanical and electrical activities of the atria, the upper chambers of the heart, which are integral to the overall cardiac cycle. The atria are responsible for receiving blood from the body and lungs and facilitating its movement into the ventricles. Proper atrial function ensures efficient cardiac output and circulation. In equine cardiology, evaluating atrial function involves assessing parameters such as atrial size, contractility, and electrical conduction patterns. Changes or impairments in atrial function can be indicative of underlying cardiac conditions, such as atrial fibrillation or other arrhythmias. This page compiles peer-reviewed research studies and scholarly articles that explore the mechanisms, assessment methods, and clinical implications of atrial function in horses.
Van Loon G, Jordaens L, Muylle E, Nollet H, Sustronck B.A five-year-old warmblood mare with atrial fibrillation was treated with quinidine sulphate. The atrial rhythm changed to atrial flutter and, because there were toxic effects, the treatment was discontinued. Seven months after the occurrence of the atrial flutter, treatment with a rapid atrial pacing technique restored a normal sinus rhythm. One year after the pacing therapy the horse was still in sinus rhythm and had been brought back into training.
Wijnberg ID, van der Kolk JH, van Garderen E, Binkhorst GJ.A 18-year-old Dutch Warmblood mare was referred for colic. Upon arrival, lethargy, blindness, head pressing, ataxia, and circling were the main clinical signs. On rectal examination a hard mass and oedema around the cranial mesenteric artery were palpated. Plasma liver enzyme activities and the ammonia level were elevated. Atrial fibrillation with a pulse frequency of 36-52 beats per minute was noticed. On both sides a holosystolic murmer with the maximum intensity on the right side could be auscultated. Postmortem examination revealed eccentric hypertrophy of the right atrium and a pale spott...
Kuwahara M, Hiraga A, Nishimura T, Tsubone H, Sugano S.This study has demonstrated the power spectral analysis of heart rate variability in a horse with atrial fibrillation. A large peak in the high frequency (HF) area of the power spectrum appeared in the horse. Hourly heart rate, the low frequency (LF) power, the HF power, and LF/HF ratio were almost constant during the recording period. The values of HF and LF power in the horse with atrial fibrillation were much larger than those in normal horses. The normalized unit of HF (HF n.u.) was much larger than that of LF (LF n.u.). Furthermore, the LF/HF ratio was very small in the horse. These resul...
Rivas LJ, Hinchcliff KW.To investigate the effect of i.v. administration of fluids on the furosemide-induced reduction in right atrial pressure (RAP) and relative change in blood volume (BV) of splenectomized mares. Methods: 5 splenectomized mares. Methods: RAP was measured by use of a micromanometer placed in the right atrium. Jugular venous blood was collected for measurement of hematocrit, plasma total protein concentration, and hemoglobin concentration. Right atrial pressure was recorded and blood samples were collected immediately before furosemide (1 mg/kg of body weight, i.v.) administration, then every 15 min...
Mitten LA.Exercise intolerance, due to cardiovascular disease in horses, may be caused by cardiac arrhythmias, valvular regurgitation, congenital abnormalities, myocardial dysfunction, pericardial disease, and vascular thrombosis. The most common cardiovascular cause of exercise intolerance in horses is atrial fibrillation. Cardiovascular abnormalities such as cardiac arrhythmias or murmurs, however, are common in athletic horses and are not always associated with exercise intolerance. Use of an electrocardiography (during rest and exercise) and echocardiography may be necessary to better determine the ...
Mifune H, Richter R, Forssmann WG.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...
Reef VB, Reimer JM, Spencer PA.Forty-one horses were treated for atrial fibrillation (AF) with 22 mg/kg quinidine sulfate via nasogastric tube every 2 hours until conversion to sinus rhythm, a cumulative dose of 88 to 132 mg/kg had been administered in 2-hour increments, or the horse had adverse or toxic effects from the drug. Treatment intervals were prolonged to every 6 hours if conversion had not occurred. Digoxin was administered before treatment if the horse had a fractional shortening < or = 27% (3 horses), was prone to tachycardia (resting heart rate > or = 60 beats/min) (1 horse), or had a previous history of sustai...
Stadler P, Deegen E, Kroker K.Echocardiographic evaluation of 45 horses (43 warm-blooded horses, one Thoroughbred and one Standardbred) with atrial fibrillation was performed, using M-mode, B-mode and pulsed-wave Doppler echocardiography. Seventeen (38%) of these horses had a history of poor performance. An increase of left ventricular shortening fraction was found in 25 horses (56%). Atrial dilatation was seen in 37 horses (82%). Eight horses (18%) had normal atrial dimensions. In nine horses only left atrium and in six horses only right atrium was enlarged. In the other 22 horses both atria were dilated. Correlation was ...
McKeever KH, Hinchcliff KW, Schmall LM, Muir WW.Exercise-induced changes in renal function were examined during steady-state submaximal treadmill exercise in six unfit mares. Horses were randomly assigned to either an exercise or parallel control (no exercise) trial on day 1 and the alternate trial 1 wk later. The mares ran on a treadmill, set at a 6 degrees incline, for 1 h at 55-60% of maximal heart rate. Exercise significantly (P less than 0.05) increased plasma osmolality, plasma [K+], urine flow (+ 45%), Na+ excretion (+ 371%), K+ excretion (+ 57%), osmotic clearance (+ 32%), Na+ clearance (+ 391%), K+ clearance (+ 33%), and fractional...
Mifune H, Suzuki S, Noda Y, Mohri S, Mochizuki K.In the pig, cattle and horse, the right and left atria and ventricles were examined by immunohistochemistry, and the right atrial and auricular cardiocytes were studied by transmission electron microscopy. Moreover, ANP-granules in the cardiocytes were analyzed by ultrastructural morphometry. Immunohistochemically, the most intensely ANP-reacted cardiocytes were localized in the right auricle, particularly more prominent in the pig and cattle than in the horse. Ultrastructurally, ANP-granules were located principally in the perinuclear region associated with the Golgi apparatus and throughout ...
Gelberg HB, Smetzer DL, Foreman JH.Four young horses of various breeds and suffering from atrial fibrillation died of heart failure. All had markedly high pulmonary arterial pressure, right-sided cardiomegaly, and lack of histologic lesions in the right atrium or pulmonary parenchyma. Three horses had hypertrophy and/or necrosis of the tunica media of the pulmonary vasculature. Clinical signs of disease, physiologic data, and pathologic findings indicated that these horses had primary pulmonary hypertension with secondary right-sided cardiac ventricular hypertrophy and dilatation, atrial fibrillation, and heart failure.
Taylor FG, Wotton PR, Hillyer MH, Barr FJ, Lucke VM.Clinical examination of a four-and-a-half-month old foal revealed evidence of progressive heart failure associated with an atrial septal defect and atrial fibrillation. Atrial septal defects are rarely reported in foals and the foal's growth, development and demeanour were normal until a sudden onset of lethargic behaviour. The value of B-mode echocardiography in identifying the congenital lesion is indicated.
Stewart GA, Fulton LJ, McKellar CD.Atrial fibrillation is described in a champion pacer which earlier had been named Australian Harness Horse of the Year as a 3-year-old in 1986-87. Prior to conversion atrial fibrillation had been present for at least 6 weeks, during which the horse had not raced. Successful treatment was achieved with two 10g doses of quinidine sulphate per oesophageal tube, after slow digitalisation with intravenous digoxin over 4d. Four hours after commencement of quinidine therapy the arrhythmia had regressed to atrial flutter and converted to sinus rhythm 10 min later. Considering his age, standard of raci...
Reef VB, Levitan CW, Spencer PA.Sixty-seven horses presented with atrial fibrillation (AF) from January 1, 1980 to August 1, 1986. All horses were evaluated for the type and severity of the underlying cardiac disease and the probable duration of the arrhythmia. Fifty-two (78%) of the horses were treated with quinidine sulfate and/or digoxin. The response to treatment was assessed in each horse. Horses were followed for periods extending from 8 months to 7 years. Standardbreds, young horses, and males predominated in the study group. There were more male horses (stallions and geldings) than mares. Most horses with AF had no e...
Bertone JJ, Traub-Dargatz JL, Wingfield WE.Atrial fibrillation in a pregnant, lactating, 15-year-old mare nursing a 70-day-old foal was converted to normal sinus rhythm, using quinidine sulfate. The maximum concentration of quinidine was 4.3 mg/L in the mare's milk and was 2.6 mg/L in the mare's serum. Treatment with quinidine did not interrupt the pregnancy. Six months after treatment, the mare developed acute volvulus of the large colon and died. At necropsy, the mare did not have macroscopic or microscopic cardiac lesions. The fetus was macroscopically and histologically normal.
Moore EN, Spear JF.We tested the multiple-wavelet hypothesis by studying the initiation and maintenance of atrial fibrillation in normal mules, horses, cows, calves, and goats. Persistence of atrial fibrillation in animals with a large atrial mass was compared with results in adult goats and calves having a smaller atrial mass. Atrial stimulation in clinically normal cows, mules, calves, and goats was accomplished using an intra-atrial stimulating catheter with rapid atrial pacing (30/s). Once initiated, atrial fibrillation persisted for 95,120,125 min, 3 days, and 8 weeks in five adult cows, respectively. In co...
Meijler FL, van der Tweel I.Atrial fibrillation is one of the most common cardiac arrhythmias in humans. It also occurs quite frequently in dogs and horses. Comparative study of this arrhythmia may contribute to better understanding of the pathophysiological mechanisms involved. In this study, we present a quantitative analysis of atrial fibrillation in humans, dogs, horses, and in a kangaroo, making use of histograms and serial autocorrelograms of the ventricular rhythm with and without digitalis medication. Increase in the size of the animal and thus in the size of the heart is accompanied by a decrease in ventricular ...
Holmes JR.This paper discusses certain aspects of circulatory physiology, including foetal circulation and the role of the thorax, and gives parameters for total blood volume, cardiac output, stroke volume and the distribution of blood between the pulmonary and peripheral circulation within the horse. The reader is taken on a journey around the circulatory system, beginning in the left atrium, into which richly oxygenated blood runs from the pulmonary veins. From here the blood is squeezed via the mitral valve into the left ventricular pump, where it is forced under high pressure through the peripheral ...
Button C, Scrutchfield WL, Clark RG, Knauer KW, Schmitz DG.A variety of atrial dysrhythmias including paroxysmal atrial tachycardia, atrial tachycardia with 2nd-grade atrioventricular block, atrial fibrillation, and atrial flutter developed in a 5-year-old Quarter Horse gelding. Quinidine and propranolol were not successful in restoring normal sinus rhythm. Sinus rhythm was re-established during digoxin therapy, but later reverted to atrial dysrhythmia. At necropsy, multiple, discrete pale areas were found on both atria and the interatrial myocardium. Histologic examination of these lesions demonstrated myocytolysis and replacement by fibrous connecti...
Wingfield WE, Miller CW, Voss JL, Bennett DG, Breukels J.Echocardiography is a non-invasive, safe means of assessing intracardiac structures and their motion. In the normal motion of the mitral valve there is anterior motion noted during atrial systole. In 3 horses with atrial fibrillation the mitral valve motion had no anterior motion to correspond with atrial contractions. Quinidine returned the electrocardiogram of one horse to a sinus rhythm after which echocardiography demonstrated the reappearance of the anterior motion of the mitral valve.
Brown CM, Holmes JR.The paper reports observations on the duration of various phases of the cardiac cycle using a bipole ECG record as a time base from which to measure the timing of pressure changes in the chambers of the heart and great vessels. From the findings the likely sequence of mechanical events during the cardiac cycle in the atria and ventricles is described.
Vanselow B, McCarthy M, Gay CC.The occurrence and timing of heart sounds were examined from phonocardiograms taken from the mitral, aortic and tricupsid recording areas in each of 18 horses. 10 sound events could be identified with each cardiac cycle. Atrial contraction produced up to 3 sound events. The first heart sound consisted of 4 components whereas the second sound was single. Two sound events were associated with the 3rd heart sound in early diastole. The occurrence of third and fourth heart sound components varied between horses and between recording areas. The mitral recording area was considered most satisfactory...
Rose RJ, Davis PE.Three young Standardbred pacers with atrial fibrillation were treated with quinidine sulphate (QS) by stomach tube. They were given 10g QS every 2 hours until cardioversion was achieved. Total doses varied between 20 and 30 g. No premedication was given nor any follow up treatment after return to sinus rhythm. All horses were given 3 months rest after the treatment, and when electrocardiographed then, and at 6 months, showed normal sinus rhythm. As all 3 horses won races after cardioversion and showed subsequent normal electrocardiograms it seems likely that atrial fibrillation can occur witho...
Scheck JL.A stallion was presented for surgical treatment of limbal squamous cell carcinoma. Excision with a conjunctival pedicle flap was done to prevent ocular invasion and preserve vision. A complication was the diagnosis of atrial fibrillation, which was not converted to sinus rhythm due to the potential complication of treatment with quinidine sulfate. Traitement d’un carcinome épidermoïde oculaire chez un étalon atteint de fibrillation auriculaire. Un étalon a été présenté pour une chirurgie d’un carcinome épidermoïde limbique. Après l’excision, un lambeau à pédicule conjonctiva...
White R, Nath L, Hebart M, Franklin S.P wave indices are used as non-invasive electrocardiographic markers of atrial remodelling in humans. Few studies have investigated their use in animals. The aim of this study was to measure P wave duration and P wave dispersion (Pd) in healthy standardbred horses and investigate variables that might influence these measurements. A 12-lead electrocardiogram was recorded at rest and P wave indices were calculated in 53 horses. A general linear model was used to investigate the main effects: age, bodyweight, sex, resting heart rate, presence of a murmur, exercise status and the number of years r...
Ter Woort F, Stefanovski D, Reef VB.Hyperthyroidism is a predisposing factor for atrial fibrillation (AF) in humans. The relationship between high thyroid hormone (TH) and AF in horses has not been evaluated. Objective: The aim of this study is to identify whether (1) high TH concentrations were present in horses with AF, (2) other cardiovascular effects were observed in horses with high TH and AF, and (3) TH status affected recurrence rate. Methods: Twenty-three horses presented with naturally occurring AF. Methods: Prospective case-control clinical study. Thyroid hormone concentration was measured in horses presenting with AF....
Button C, Scrutchfield WL, Clark RG, Knauer KW, Schmitz DG.A variety of atrial dysrhythmias including paroxysmal atrial tachycardia, atrial tachycardia with 2nd-grade atrioventricular block, atrial fibrillation, and atrial flutter developed in a 5-year-old Quarter Horse gelding. Quinidine and propranolol were not successful in restoring normal sinus rhythm. Sinus rhythm was re-established during digoxin therapy, but later reverted to atrial dysrhythmia. At necropsy, multiple, discrete pale areas were found on both atria and the interatrial myocardium. Histologic examination of these lesions demonstrated myocytolysis and replacement by fibrous connecti...
Langsetmo I, Weigle GE, Erickson HH, Fedde MR.Exercising horses have extremely high right and left atrial pressures. Limitation in ventricular function (i.e. relaxation) may play a role in these high pressures. We studied relaxation characteristics of the right ventricular myocardium and the impact of frusemide (2.0 mg/kg bwt i.v.) on these characteristics in horses exercising at 8, 10, 12 and 14 m/s. Exercise tests were performed 4 h after administration of frusemide. Right ventricular (RV) pressure was analysed using Fast Fourier Transform techniques to remove non cardiac components of the pressure signal. Mean right atrial (RA) pressur...
Wingfield WE, Miller CW, Voss JL, Bennett DG, Breukels J.Echocardiography is a non-invasive, safe means of assessing intracardiac structures and their motion. In the normal motion of the mitral valve there is anterior motion noted during atrial systole. In 3 horses with atrial fibrillation the mitral valve motion had no anterior motion to correspond with atrial contractions. Quinidine returned the electrocardiogram of one horse to a sinus rhythm after which echocardiography demonstrated the reappearance of the anterior motion of the mitral valve.
Wijnberg ID, van der Kolk JH, van Garderen E, Binkhorst GJ.A 18-year-old Dutch Warmblood mare was referred for colic. Upon arrival, lethargy, blindness, head pressing, ataxia, and circling were the main clinical signs. On rectal examination a hard mass and oedema around the cranial mesenteric artery were palpated. Plasma liver enzyme activities and the ammonia level were elevated. Atrial fibrillation with a pulse frequency of 36-52 beats per minute was noticed. On both sides a holosystolic murmer with the maximum intensity on the right side could be auscultated. Postmortem examination revealed eccentric hypertrophy of the right atrium and a pale spott...
Reef VB, Reimer JM, Spencer PA.Forty-one horses were treated for atrial fibrillation (AF) with 22 mg/kg quinidine sulfate via nasogastric tube every 2 hours until conversion to sinus rhythm, a cumulative dose of 88 to 132 mg/kg had been administered in 2-hour increments, or the horse had adverse or toxic effects from the drug. Treatment intervals were prolonged to every 6 hours if conversion had not occurred. Digoxin was administered before treatment if the horse had a fractional shortening < or = 27% (3 horses), was prone to tachycardia (resting heart rate > or = 60 beats/min) (1 horse), or had a previous history of sustai...
Gehlen H, Bubeck K, Stadler P.In 12 healthy warmblood horses (six trained and six untrained) the pulmonary wedge pressure and heart frequency was measured at rest and during a standardised exercise test on a treadmill. The mean pulmonary wedge pressure at rest was 14.53 +/- 2.36 mmHg. There was no significant difference in pulmonary wedge pressure either at rest or during exercise between trained and untrained horses. During walking (1.8 m/s) the mean pulmonary wedge pressure was 19.62 +/- 4.03 mmHg, during trotting (4 und 5 m/s) it was between 22.38 +/- 3.92 mmHg and 25.28 +/- 3.7 mmHg. During canter (6 m/s) and gallop (8...
Stadler P, Deegen E, Kroker K.Echocardiographic evaluation of 45 horses (43 warm-blooded horses, one Thoroughbred and one Standardbred) with atrial fibrillation was performed, using M-mode, B-mode and pulsed-wave Doppler echocardiography. Seventeen (38%) of these horses had a history of poor performance. An increase of left ventricular shortening fraction was found in 25 horses (56%). Atrial dilatation was seen in 37 horses (82%). Eight horses (18%) had normal atrial dimensions. In nine horses only left atrium and in six horses only right atrium was enlarged. In the other 22 horses both atria were dilated. Correlation was ...
Fenner MF, Gatta G, Sattler S, Kuiper M, Hesselkilde EM, Adler DMT, Smerup M, Schotten U, Sørensen U, Diness JG, Jespersen T, Verheule S....Small-conductance Ca2+-activated K+ (KCa2) channels have been proposed as a possible atrial-selective target to pharmacologically terminate atrial fibrillation (AF) and to maintain sinus rhythm. However, it has been hypothesized that the importance of the KCa2 current-and thereby the efficacy of small-conductance Ca2+-activated K+ current (I K,Ca) inhibition-might be negatively related to AF duration and the extent of AF-induced remodeling. Unassigned: To address the hypothesis of the efficacy of I K,Ca inhibition being dependent on AF duration, the anti-arrhythmic properties of the I K,Ca inh...
Eberhardt C, Schwarzwald CC.In horses, persistent atrial dysfunction is a prognostic indicator of recurrence of atrial fibrillation (AF). The objective of this study was to quantify left atrial (LA) contractile function in Warmblood horses after successful cardioversion of AF to sinus rhythm, using standard two-dimensional echocardiography (2DE) and two-dimensional speckle tracking (2DST) analyses, and to provide proof-of-concept for use of 2DST to detect LA contractile dysfunction in horses. Methods: Nineteen Warmblood horses with AF and successful transvenous electrical cardioversion (TVEC) or medical cardioversion usi...
Asano K, Suzuki K, Chiba M, Sera K, Asano R, Sakai T.To investigate the relationships between trace elements concentrations in hair and atrial fibrillation (AF) in horses, concentrations of nineteen trace elements were detected in hair using the particle induced X-ray emission (PIXE) method. The horses were assigned to either control (n=22, no abnormalities) or AF groups (n=5) based on electrocardiograph findings. The mean concentrations of Ca and Zn in the hair of the AF group were significantly higher than those in the control group. The Zn/Cu ratio of the hair in the AF group (29.8 +/- 5.5) was significantly higher than that in the control gr...
Hinchcliff KW, McKeever KH.The effect of blood volume repletion after frusemide administration on the right atrial and pulmonary artery pressure responses of horses to exercise has not been reported. We examined right atrial and pulmonary artery pressure and plasma atrial natriuretic peptide concentration (ANP) responses to an incremental exercise test in 6 Standardbred mares. Horses were treated, in a 3 way cross over design, with isotonic saline, frusemide (1 mg/kg bwt, i.v.), and frusemide followed 3 h later by lactated Ringer's solution (12 ml/kg bwt, i.v.). Three and a half hours after saline or frusemide administr...
Trachsel DS, Grenacher B, Weishaupt MA, Schwarzwald CC.Atrial natriuretic peptide (ANP) is a cardiovascular biomarker that might be useful in assessing the severity of cardiac disease in horses. Plasma ANP concentrations (Cp(ANP)) were compared between horses with heart disease but normal chamber size and function (Group A; n=6), horses with heart disease associated with left atrial (LA) enlargement, LA dysfunction, and/or left ventricular (LV) enlargement (Group B; n=5), and horses with no clinically apparent cardiovascular disease (Group C; n=13). The median (min-max) for Cp(ANP) was significantly higher in Group B (53.5 (36.0-70.7) pg/mL), comp...
Carstensen H, Hesselkilde EZ, Haugaard MM, Flethøj M, Carlson J, Pehrson S, Jespersen T, Platonov PG, Buhl R.The atrial fibrillatory rate is a potential biomarker in the study of antiarrhythmic drug effects on atrial fibrillation (AF). The purpose of this study was to evaluate whether dose-dependent changes in the atrial fibrillatory rate can be monitored on surface electrocardiography (ECG) following treatment with dofetilide, ranolazine, and a combination of the two in an acute model of AF in horses. Eight horses were subjected to pacing-induced AF on 4 separate days. Saline (control), dofetilide, ranolazine, or a combination of dofetilide and ranolazine was administered in four incremental doses. ...
Buhl R, Hesselkilde EM, Carstensen H, Hopster-Iversen C, van Loon G, Decloedt A, Van Steenkiste G, Marr CM, Reef VB, Schwarzwald CC, Mitchell KJ....The recurrence rate of atrial fibrillation (AF) in horses after cardioversion to sinus rhythm (SR) is relatively high. Atrial fibrillatory rate (AFR) derived from surface ECG is considered a biomarker for electrical remodelling and could potentially be used for the prediction of successful AF cardioversion and AF recurrence. Objective: Evaluate if AFR was associated with successful treatment and could predict AF recurrence in horses. Methods: Retrospective multicentre study. Methods: Electrocardiograms (ECG) from horses with persistent AF admitted for cardioversion with either medical treatmen...
Decloedt A, Verheyen T, Van Der Vekens N, Sys S, De Clercq D, van Loon G.Atrial fibrillation (AF) causes atrial electrical and contractile remodelling in horses. The aim of this study was to quantify left atrial (LA) contractile function and its time course of recovery after cardioversion of naturally-occurring AF in horses. The study population included 42 AF horses which were successfully treated using transvenous electrical cardioversion TVEC (n=39) or quinidine sulfate (n=3), with trivial or mild mitral regurgitation present in 25 horses. Thirty-seven healthy horses were used as controls. AF duration was estimated based on the history and previous examinations....
Hesselkilde EZ, Carstensen H, Haugaard MM, Carlson J, Pehrson S, Jespersen T, Buhl R, Platonov PG.Atrial fibrillatory cycle length has been considered one of the indices of atrial electrical remodelling during atrial fibrillation (AF), which can be assessed from surface ECG by computer-assisted calculation of atrial fibrillatory rate (AFR). Horses have been suggested as a bona fide model for AF studies since horses too, develop lone AF, however data on AF characteristics in horses are extremely sparse and non-invasive characterization of AF complexity using surface ECG processing has not been reported. Objective: The aim was to study characteristics of induced AF and its modification by fl...
Physick-Sheard P, Kraus M, Basrur P, McGurrin K, Kenney D, Schenkel F.To assess evidence for genetic contributions to atrial fibrillation (AF) in the Standardbred horse. Methods: Equine referrals to the Ontario Veterinary College Health Sciences Centre (OVCHSC) for 1985-2009, and age and gait matched breed registry controls. Methods: Breeds presenting ≥ 5 times annually were tabulated (admission year and diagnosis; total 40,039; AF 396; no AF 39,643), and breed and year effects examined. Heritability and inbreeding coefficients were determined for Standardbred AF cases and racing contemporaries, and odds ratios for AF were calculated for frequently occurring s...
Schauvliege S, van Loon G, De Clercq D, Devisscher L, Deprez P, Gasthuys F.To examine the influence of direct current shock application in anaesthetized horses with atrial fibrillation (AF) and to study the effects of cardioversion to sinus rhythm (SR). Methods: Prospective clinical study. Methods: Eight horses successfully treated for AF (transvenous electrical cardioversion after amiodarone pre-treatment). Methods: Cardioversion catheters and a pacing catheter were placed under sedation [detomidine 10 microg kg(-1) intravenously (IV)]. After additional sedation (5-10 microg kg(-1) detomidine, 0.1 mg kg(-1) methadone IV), anaesthesia was induced with ketamine, 2.2 m...
Van Der Vekens N, Hunter I, Timm A, Decloedt A, De Clercq D, Deprez P, Goetze JP, van Loon G.Equine atrial natriuretic peptide (ANP) plasma concentrations are correlated with left atrial size. However, species-specific assays are lacking and the results from human assays are poorly reproducible. A new methodology called processing independent analysis (PIA) that measures the total proANP product in plasma has proven to be successful in human medicine, but has never been used in horses. The aims were to establish an equine proANP reference interval by measurement of the total proANP product using PIA and to examine the proANP concentrations in horses with atrial dilatation. Sample stab...
Holmes JR.This paper discusses certain aspects of circulatory physiology, including foetal circulation and the role of the thorax, and gives parameters for total blood volume, cardiac output, stroke volume and the distribution of blood between the pulmonary and peripheral circulation within the horse. The reader is taken on a journey around the circulatory system, beginning in the left atrium, into which richly oxygenated blood runs from the pulmonary veins. From here the blood is squeezed via the mitral valve into the left ventricular pump, where it is forced under high pressure through the peripheral ...
Burns JJ, MacMillan KM, John EE.Atrial fibrillation (AF) is the most clinically relevant cardiac arrhythmia identified in the Standardbred racehorse. However, there is limited literature regarding athletic ability in Standardbred racehorses following AF conversion. To investigate this issue, the objectives of this review were to: i) determine the success rate in using quinidine sulphate to treat AF in a population of hospitalized equine patients in Atlantic Canada between January 2008 and December 2019; and ii) measure return to athletic ability (using racetrack earnings and top-3 finishes) following cardioversion with quini...
Kraus M, Physick-Sheard PW, Brito LF, Schenkel FS.The number of Standardbred racehorses admitted to the Ontario Veterinary College Teaching Hospital (Guelph, Canada) for treatment of atrial fibrillation (AF) has been on the rise since the early 1990s. A small number of sires have been contributing to a large proportion of cases, indicating there may be a genetic predisposition to the arrhythmia in this breed. Objective: The objectives of this study were to determine the heritability of AF in Standardbred horses and whether heritability of the arrhythmia differs across gaits and/or sexes. Methods: Heritability study based on retrospective revi...
Fenner MF, Carstensen H, Dalgas Nissen S, Melis Hesselkilde E, Scott Lunddahl C, Adler Hess Jensen M, Loft-Andersen AV, Sattler SM, Platonov P....Inhibition of the G-protein gated ACh-activated inward rectifier potassium current, IK,ACh may be an effective atrial selective treatment strategy for atrial fibrillation (AF). Therefore, the anti-arrhythmic and electrophysiological properties of a novel putatively potent and highly specific IK,ACh inhibitor, XAF-1407 (3-methyl-1-[5-phenyl-4-[4-(2-pyrrolidin-1-ylethoxymethyl)-1-piperidyl]thieno[2,3-d]pyrimidin-6-yl]azetidin-3-ol), were characterised for the first time in vitro and investigated in horses with persistent AF. The pharmacological ion channel profile of XAF-1407 was investigated us...
Hesselkilde EZ, Carstensen H, Flethøj M, Fenner M, Kruse DD, Sattler SM, Tfelt-Hansen J, Pehrson S, Braunstein TH, Carlson J, Platonov PG....Large animal models are important in atrial fibrillation (AF) research, as they can be used to study the pathophysiology of AF and new therapeutic approaches. Unlike other animal models, horses spontaneously develop AF and could therefore serve as a bona fide model in AF research. We therefore aimed to study the electrical, functional and structural remodelling caused by chronic AF in a horse model. Nine female horses were included in the study, with six horses tachypaced into self-sustained AF and three that served as a time-matched sham-operated control group. Acceleration in atrial fibrilla...
Pedler C, Nath L, Agne GF, Hebart M, Franklin S.Atrial fibrillation (AF) is the most common performance-limiting arrhythmia of racehorses. A genetic contribution has been suggested in Standardbred racehorses but has not been investigated in Thoroughbreds. The objective of this study was to determine the heritability of AF in Thoroughbred racehorses. Methods: Horses racing between 2007 and 2019 in Hong Kong and Australia that had AF detected postrace via auscultation (n = 463 cases) were compared with five randomly selected racing contemporaries (n = 2,315 controls). The ASReml-R programme was used to fit an animal model to the AF data t...
Van Steenkiste G, Carlson J, Decloedt A, Vera L, Buhl R, Platonov PG, van Loon G.To compare the atrial fibrillatory rate (AFR) derived from a local right atrial intracardiac recording (RA-FR) and from a single-lead surface electrocardiogram (ECG) during atrial fibrillation (AF) and to evaluate the correlation with transvenous electrical cardioversion (TVEC) threshold (in Joules), number of shocks and cardioversion success rate in horses. Methods: ECGs and clinical records of horses with AF treated by TVEC. Horses were included if a simultaneous recording of the right atrial intracardiac electrogram and a modified base-apex ECG were available. Methods: Clinical records of h...
