Long-Term Training Increases Atrial Fibrillation Sustainability in Standardbred Racehorses

Carstensen, Helena; Nissen, Sarah Dalgas; Saljic, Arnela; Hesselkilde, Eva Melis; Hunnik, Arne van; Hohl, Mathias; Sattler, Stefan; Fløgstad, Cecilie; Hopster‐Iversen, Charlotte; Verheule, Sander; Böhm, Michael; Schotten, Ulrich; Jespersen, Thomas; Buhl, Rikke

doi:10.1007/s12265-023-10378-6

Cited by 5 publications

(1 citation statement)

References 76 publications

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“…Wenckebach cycle length was assessed in 22 of the 35 horses during general anesthesia, who had been included in a former study exploring training-induced atrial remodeling ( 24 ). During open-chest surgery a high-density epicardial multi-electrode device was placed on the right atrium (RA) and used to generate extra stimulus protocols to obtain functional data as previously described ( 25 ).…”

Section: Methodsmentioning

confidence: 99%

Muscarinic acetylcholine receptors M2 are upregulated in the atrioventricular nodal tract in horses with a high burden of second-degree atrioventricular block

Nissen,

Saljic,

Carstensen

et al. 2023

Front. Cardiovasc. Med.

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BackgroundSecond-degree atrioventricular (AV) block at rest is very common in horses. The underlying molecular mechanisms are unexplored, but commonly attributed to high vagal tone.AimTo assess whether AV block in horses is due to altered expression of the effectors of vagal signalling in the AV node, with specific emphasis on the muscarinic acetylcholine receptor (M2) and the G protein-gated inwardly rectifying K+ (GIRK4) channel that mediates the cardiac IK,ACh current.MethodEighteen horses with a low burden of second-degree AV block (median 8 block per 20 h, IQR: 32 per 20 h) were assigned to the control group, while 17 horses with a high burden of second-degree AV block (median: 408 block per 20 h, IQR: 1,436 per 20 h) were assigned to the AV block group. Radiotelemetry ECG recordings were performed to assess PR interval and incidence of second-degree AV block episodes at baseline and on pharmacological blockade of the autonomic nervous system (ANS). Wenckebach cycle length was measured by intracardiac pacing (n = 16). Furthermore, the expression levels of the M2 receptor and the GIRK4 subunit of the IKACh channel were quantified in biopsies from the right atrium, the AV node and right ventricle using immunohistochemistry and machine learning-based automated segmentation analysis (n = 9 + 9).ResultsThe AV block group had a significantly longer PR interval (mean ± SD, 0.40 ± 0.05 s; p < 0.001) and a longer Wenckebach cycle length (mean ± SD, 995 ± 86 ms; p = 0.007) at baseline. After blocking the ANS, all second-degree AV block episodes were abolished, and the difference in PR interval disappered (p = 0.80). The AV block group had significantly higher expression of the M2 receptor (p = 0.02), but not the GIRK4 (p = 0.25) in the AV node compared to the control group. Both M2 and GIRK4 were highly expressed in the AV node and less expressed in the atria and the ventricles.ConclusionHere, we demonstrate the involvement of the m2R-IK,ACh pathway in underlying second-degree AV block in horses. The high expression level of the M2 receptor may be responsible for the high burden of second-degree AV blocks seen in some horses.

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Section: Methodsmentioning

confidence: 99%

Muscarinic acetylcholine receptors M2 are upregulated in the atrioventricular nodal tract in horses with a high burden of second-degree atrioventricular block

Nissen,

Saljic,

Carstensen

et al. 2023

Front. Cardiovasc. Med.

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Histological evaluation of cardiac remodelling in equine athletes

Nath,

Saljic,

Buhl

et al. 2024

Sci Rep

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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 injuries (OFI, n = 17), constituting the athletic group (ATH, n = 33), and compared to sedentary horses (SED, n = 10). Horses in the ATH group had myocyte hypertrophy at all sites; increased fibrosis at all sites other than the LAA; increased fibroblast infiltration but a reduction in the overall extracellular matrix (ECM) volume in the RAA, LVAPM, and IVS-R compared to SED horses. In this horse model, athletic conditioning was associated with myocyte hypertrophy and a reduction in ECM. There was an excess of fibrocyte infiltration and focal fibrosis that was not present in non-athletic horses, raising the possibility of an exercise-induced pro-fibrotic substrate.

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Development of an atrial transseptal puncture procedure in horses to access the left heart: An ultrasound‐guided jugular vein and transhepatic approach

Vernemmen,

Van Steenkiste,

Buschmann

et al. 2024

Equine Veterinary Journal

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BackgroundRadiofrequency ablation has been successfully applied to treat right atrial arrhythmias in horses. Ablation of left‐sided arrhythmias requires a retrograde transarterial approach which is complicated. In human medicine, the left atrium is accessed through transseptal puncture (TSP) of the fossa ovalis (FO) using a caudal approach via the femoral vein.ObjectivesTo develop a zero fluoroscopy TSP technique for horses using a jugular vein (cranial) and transhepatic (caudal) approach.Study designIn vivo experimental study.MethodsTransseptal puncture was performed in 18 horses admitted for euthanasia and donated for scientific research under general anaesthesia: using a jugular vein approach (10 horses), a transhepatic approach (2 horses) or both (6 horses). Radiofrequency energy was applied on a guidewire to perforate the FO and allow sheath advancement under intracardiac and transthoracic echocardiographic guidance. Puncture lesions were inspected post‐mortem.ResultsTransseptal puncture was successful in 17/18 horses, of which 15/16 jugular vein approaches and 5/8 transhepatic approaches. Failure was due to technical malfunction, inability to advance the guidewire toward the heart and inability to advance the sheath through the FO. Intracardiac echocardiography was essential to safely guide the puncture process. Atrial arrhythmias caused by the TSP occurred in 13/18 horses. Puncture lesions were found in the right atrium in the FO region, and left atrium ventral to pulmonary vein ostium III.Main limitationsBecause in several horses two approaches were tested consecutively, it cannot be excluded that the second TSP was performed at the previous puncture site. Due to the developmental nature of the study the approaches were not randomised and did not allow comparison.ConclusionTransseptal puncture is feasible in horses using ultrasound guidance and allows for electrophysiological exploration of the left heart. Further studies are needed to evaluate post‐operative follow‐up.

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Long-Term Training Increases Atrial Fibrillation Sustainability in Standardbred Racehorses

Cited by 5 publications

References 76 publications

Muscarinic acetylcholine receptors M2 are upregulated in the atrioventricular nodal tract in horses with a high burden of second-degree atrioventricular block

Muscarinic acetylcholine receptors M2 are upregulated in the atrioventricular nodal tract in horses with a high burden of second-degree atrioventricular block

Histological evaluation of cardiac remodelling in equine athletes

Development of an atrial transseptal puncture procedure in horses to access the left heart: An ultrasound‐guided jugular vein and transhepatic approach

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