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.
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...
HOLT JP, RHODE EA, PEOPLES SA, KINES H.Studies of left ventricular volume and pressure have been carried out in the control state in four classes of intact anesthetized mammals (horses, cattle, swine, and dogs), body weights of which varied 54-fold. On the basis of these studies of both large and small hearts, extending over a wide range, a pattern of function for the left ventricle of all mammals has been described. Mathematical equations are given describing the interrelationships between left ventricular end-diastolic volume and end-systolic volume, stroke volume, cardiac output, stroke-work, heart rate, and total peripheral res...
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...
Buhl R, Carstensen H, Hesselkilde EZ, Klein BZ, Hougaard KM, Ravn KB, Loft-Andersen AV, Fenner MF, Pipper C, Jespersen T.Atrial fibrillation (AF) is the most common arrhythmia affecting performance in horses. However, no previous studies have quantified the performance reduction in horses suffering from AF. Objective: To quantify the effect of AF on maximum velocity (Vmax ), maximum heart rate (HRmax ), heart rate recovery (T100 ), hematologic parameters and development of abnormal QRS complexes. Methods: Nine Standardbred trotters. Methods: Two-arm controlled trial. Six horses had AF induced by means of a pacemaker and 3 served as sham-operated controls. All horses were subjected to an exercise test to fatigue ...
Decloedt A, Schwarzwald CC, De Clercq D, Van Der Vekens N, Pardon B, Reef VB, van Loon G.Although atrial fibrillation (AF) can be successfully treated in horses, recurrence occurs frequently. In humans, atrial function after cardioversion can predict recurrence. Objective: To examine the prognostic value of atrial mechanical function at 24 hours after cardioversion and other potential predictor variables for AF recurrence in horses. Methods: 117 horses treated for AF at 4 referral centers. Methods: Retrospective study. Inclusion criteria were successful cardioversion, echocardiography at 24 hours after cardioversion and ≥4 months follow-up. To determine factors associated with A...
Buhl R, Nissen SD, Winther MLK, Poulsen SK, Hopster-Iversen C, Jespersen T, Sanders P, Carstensen H, Hesselkilde EM.Limited information is available on paroxysmal atrial fibrillation (PAF) in the horse. Indeed, undiagnosed PAF could result in poor performance. Due to the intermittent occurrence, PAF is difficult to diagnose. However, implanting a small ECG device (implantable loop recorder, ILR) subcutaneously, allows the continuous and automatic detection of PAF. Objective: The aim was to investigate the potential of ILRs as a tool for diagnosing PAF in horses with poor performance. Methods: Prospective field study. Methods: Twelve racing Standardbred trotters with intermittent reduced performance (mean ag...
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 ...
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 ...
Kaese S, Frommeyer G, Verheule S, van Loon G, Gehrmann J, Breithardt G, Eckardt L.The most frequently used animal species in experimental cardiac electrophysiology are mice, rabbits, and dogs. Murine and human electrocardiograms (ECGs) show salient differences, including the occurrence of a pronounced J-wave and a less distinctive T-wave in the murine ECG. Mouse models can resemble human cardiac arrhythmias, although mice differ from human in cardiac electrophysiology. Thus, arrhythmia mechanisms in mice may differ from those in humans and should be transferred to the human situation with caution. Further relevant cardiovascular animal models are rabbits, dogs, and minipigs...
Van Steenkiste G, De Clercq D, Vera L, Decloedt A, van Loon G.Atrial tachycardia including focal atrial tachycardia and macroreentrant atrial tachycardia (atrial flutter), are occasionally found in horses. Diagnosis, treatment and follow-up of these arrhythmias has been inadequately described. Objective: To describe the findings on surface electrocardiography (ECG), intra-atrial electrogram recording and tissue Doppler imaging (TDI), the response to treatment by transvenous electrical cardioversion (TVEC), and TDI follow-up, of sustained atrial tachycardia in horses. Methods: Case series. Methods: Records from horses with sustained atrial tachycardia tre...
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...
Hansen S, Otten ND, Nissen SD, Carstensen H, Hopster-Iversen C, Fjeldborg J, Staun SH, Fenner M, Hesselkilde EM, Buhl R.Atrial fibrillation (AF) has been proposed as a risk factor for exercise-induced pulmonary haemorrhage (EIPH) due to increased pressure in the left atrium. Objective: To evaluate if AF was associated with EIPH following a standardised exercise test (SET) to fatigue. Methods: Two-arm controlled experiment. Methods: Ten untrained Standardbred mares mean (standard deviation [SD]) age 6 (2) years performed a SET on the treadmill in sinus rhythm (SR) (SET1) and 25-44 days after induction of self-sustained AF (SET2). AF was induced by tachypacing using a pacing device. Endoscopy, including trachea...
Wijnberg ID, van der Kolk JH.Atrial fibrillation is a disorder of cardiac rhythmicity, and its importance in the horse depends on the underlying cause and the function of the horse. Before the decision is taken to start treatment, it has first to be ascertained whether treatment is worthwhile and whether the horse is an appropriate candidate for treatment. This article gives a short overview of current opinion on the cause and treatment of atrial fibrillation in the horse. The most used treatment at the moment, oral chinidine sulphate, is discussed. The hemodynamic consequences of atrial fibrillation and the response of a...
Nath LC, Saljic A, Buhl R, Elliott A, La Gerche A, Ye C, Schmidt Royal H, Lundgren Virklund K, Agbaedeng TA, Stent A, Franklin S.Approximately 1-2 per 100,000 young athletes die from sudden cardiac death (SCD) and extreme exercise may be associated with myocardial scar and arrhythmias. Racehorses have a high prevalence of atrial fibrillation (AF) and SCD but the presence of myocardial scar and inflammation has not been evaluated. Cardiac tissues from the left (LAA) and right (RAA) atrial appendages, left ventricular anterior (LVAPM) and posterior (LVPPM) papillary muscles, and right side of the interventricular septum (IVS-R) were harvested from racehorses with sudden cardiac death (SCD, n = 16) or other fatal injur...
Kjeldsen ST, Nissen SD, Christensen NC, Haugaard SL, Schneider MJ, Vinther Z, Sattler SM, Carstensen H, Jøns C, Hopster-Iversen C, Buhl R.Paroxysmal atrial fibrillation (pAF) occurs sporadically and can impair athletic performance. Gold standard for diagnosis is surface electrocardiography (ECG), however, this requires AF to be sustained. Implantable loop recorders (ILRs) are routinely used for AF detection in human medicine. While ILR placement has been studied in horses, its AF detection performance is unknown. Objective: (I) Validation of ILRs for AF detection in horses. (II) Determining pAF incidence using ILRs and estimate the positive predictive value (PPV). Methods: (I) Experimental study; (II) Longitudinal observational ...
Vernemmen I, Buschmann E, Van Steenkiste G, Demeyere M, Verhaeghe LM, De Somer F, Devreese KMJ, Schauvliege S, Decloedt A, van Loon G.Cardiac catheterizations in horses are mainly performed in the right heart, as access to the left heart traditionally requires an arterial approach. Transseptal puncture (TSP) has been adapted for horses but data on follow-up and closure of the iatrogenic atrial septal defect (iASD) are lacking. Objective: To perform TSP and assess postoperative complications and iASD closure over a minimum of 4 weeks. Methods: Eleven healthy adult horses. Methods: Transseptal puncture was performed under general anesthesia. Serum cardiac troponin I concentrations were measured before and after puncture. Wee...
Kuroda T, Minamijima Y, Kinman CK, Takahashi Y, Ebisuda Y, Inoue K, Ishikawa H, Mita H, Tamura N, Nukada T, Toutain PL, Ohta M.Quinidine (QND) sulfate is an effective treatment for atrial fibrillation (AF) in horses, and several dosage regimens have been proposed to address its wide variability in response and potential adverse effects. The purpose of this study was to analyze the variability in plasma quinidine concentrations using population pharmacokinetics to determine an effective and safe dosage regimen for Thoroughbred horses. Unassigned: Six healthy Thoroughbred horses were treated with 20 mg/kg quinidine sulfate dihydrate (16.58 mg/kg QND base) administered PO or 5 mg/kg quinidine hydrochloride monohydr...
Buschmann E, Van Steenkiste G, Vernemmen I, Demeyere M, Schauvliege S, Decloedt A, van Loon G.Myocardial sleeves of the caudal vena cava are the predilection site for atrial tachycardia (AT) in horses. Caudal vena cava isolation guided by the ablation index, a lesion quality marker incorporating power, duration and contact force, might improve outcome. Objective: Describe the feasibility and outcome of caudal vena cava isolation using ablation index-guided radiofrequency catheter ablation (RFCA) to treat AT in horses. Methods: Ten horses with sustained AT. Methods: Records from 10 horses with sustained AT treated by three-dimensional electro-anatomical mapping and ablation index-guided...
Ibrahim L, Vernemmen I, Buschmann E, van Loon G, Cornillie P.The interatrial septum morphology, shaped by the septum primum and secundum fusion, results in the formation of the fossa ovalis (FO) and its limbus. Incomplete fusion can lead to a patent foramen ovale (PFO), while complete fusion may produce septal ridges and pouches (SPs), with SPs in humans linked to ischemic stroke and atrial arrhythmias. In horses, atrial tachycardia and fibrillation often originate near the FO. This study examines adult equine interatrial septum morphology to enhance understanding the region and guide electrophysiological interventions for equine cardiac arrhythmias. Po...
Buschmann E, Easton-Jones C, Van Steenkiste G, De Wilde H, Roberts V, Durando M, Decloedt A, Marr C, van Loon G.Accessory pathways (APs) are muscular bundles directly connecting the atria and ventricles, bypassing the atrioventricular (AV) node-His-Purkinje system. Anterograde conduction along the AP results in ventricular preexcitation. A retrograde conducting AP allows ventriculo-atrial (VA) conduction, creating a reentry circuit that mediates orthodromic atrioventricular reentry tachycardia (OAVRT). This condition is well described in humans and small animals, but has not been reported previously in horses. Objective: Describe clinical and electrocardiographic findings of horses with retrograde AP co...
Libak Haugaard S, Schneider MJ, Nissen SD, Saljic A, Fruergaard Andersen P, Carstensen H, Hopster-Iversen C, Jespersen T, Larsen S, Buhl R.Mitochondrial respiration sustains the high energy demands of endurance exercise, yet the extent to which atrial, ventricular, and skeletal muscle mitochondria adapt remains uncertain. At the same time, endurance athletes face an increased risk of atrial fibrillation (AF), but the role of cardiac metabolism in arrhythmia susceptibility is poorly understood. Here, we compared mitochondrial respiration in skeletal muscle and across all four cardiac chambers between trained and untrained racehorses ( = 34) to investigate adaptations associated with long-term endurance exercise. We further examine...
