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Equine veterinary journal2023; 56(5); 1059-1067; doi: 10.1111/evj.13996

Morphological and histological investigation of the conduction system in the equine atrial muscle sleeve of pulmonary veins.

Abstract: Atrial fibrillation is the most common arrhythmia in horses causing poor performance. The role of pulmonary vein triggers in the pathogenesis has been identified in horses. Ablation methods have been investigated, but the available information on anatomical, histological and immunohistochemical assessment of the pulmonary vein ostia and the conduction system of the myocardial sleeve is still limited. Objective: The aim of the study was to describe the morphological properties of the myocardial sleeve in healthy horses. Methods: Cross-sectional. Methods: Eighty-three equine hearts were dissected. The number and diameters of pulmonary vein ostia were determined, and anatomical localisation was described. Fifty-eight tissue samples were collected for routine histology and 12 of these were used for immunohistochemistry (connexin 43, 45, S100, and tyrosine hydroxylase antibodies). Results: The mean number of pulmonary vein ostia was 4.5 (4 veins: 46 horse, 5 veins: 31 horses, 6 veins: 6 horses). Diameters (mean ± SD) of the main ostia were as follows: vein I: 20.2 ± 7.0 mm, vein II: 32.7 ± 7.1 mm, vein III: 33.4 ± 5.9 mm, vein IV: 18.1 ± 4.5 mm. Diameters of supernumerary vein ostia varied between 3.0 and 28.0 mm (11.5 ± 5.5 mm). Early branching was found in 26 horses (31.3%) and 30 veins (vein I: 14, vein II: 9, vein III: 5, vein IV: 2). Histology confirmed the presence of a muscle sleeve composed of myocardial tissue in each pulmonary vein. S100 and TH positivity was detected in each vein, and it confirmed the presence of adrenergic and non-adrenergic nerve fibres within the myocardial sleeve. Cx43 and 45 positivity were also found in each vein indicating the presence of gap junctions. Conclusions: The effect of bodyweight on pulmonary vein dimensions is unknown. Conclusions: Future ablation techniques should consider that conductive tissue is present in the entire myocardial sleeve in all pulmonary vein ostia.
© 2023 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2023-09-02 PubMed ID: 37658818DOI: 10.1111/evj.13996Google Scholar: Lookup
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Summary

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The research investigated the characteristics and structure of the conduction system in the equine atrial muscle sleeve of pulmonary veins, crucial in understanding atrial fibrillation, a common condition in horses that negatively impacts performance.

Methodology

  • 83 horse hearts were dissected as part of this study, with focus on their pulmonary veins – particularly, the number and diameters of the vein ostia, or openings. The researchers described the ostia’s anatomical location.
  • From these hearts, 58 tissue samples were collected and subjected to routine histology, a microscope-based study of the minute structures of biological tissues.
  • Additionally, 12 samples were used for immunohistochemistry, a technique that identifies specific components (proteins, carbohydrates etc.) within tissues. The researchers used antibodies for connexin 43, 45, S100, and tyrosine hydroxylase (proteins involved in cell communications, neural activities, and enzyme activity, respectively).

Findings

  • The research found that, on average, there were 4.5 pulmonary vein ostia in the horses’ hearts with various diameters for each vein.
  • Remarkably, early branching was observed in 31.3% of the horses’ veins.
  • Importantly, histology identified the presence of a muscle sleeve made of myocardial tissue in every pulmonary vein.
  • The immunohistochemical technique revealed that each vein contained adrenergic and non-adrenergic nerve fibers, evidenced by S100 and Tyrosine Hydroxylase positivity. These fibers are linked with the regulation of heart rate and force of contraction.
  • Moreover, connexin 43 and 45 were present in each vein, which indicate the presence of gap junctions, essential for signal transmission in the heart.

Conclusions

  • The research possibility of bodyweight influencing pulmonary vein dimensions remains unknown and suggests that additional work is necessary in that realm.
  • Significantly, reflexive upon the findings, the authors proposed that future techniques for ablation (a procedure used to cure arrhythmia) should acknowledge that the conductive tissue pervades throughout the myocardial sleeve in all pulmonary vein ostia. This discovery could impact the choice and effectiveness of treatment interventions for equine atrial fibrillation.

Cite This Article

APA
Kovacs S, Racz B, Sotonyi P, Bakos Z. (2023). Morphological and histological investigation of the conduction system in the equine atrial muscle sleeve of pulmonary veins. Equine Vet J, 56(5), 1059-1067. https://doi.org/10.1111/evj.13996

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 56
Issue: 5
Pages: 1059-1067

Researcher Affiliations

Kovacs, Szilvia
  • Department and Clinic of Equine Medicine, University of Veterinary Medicine, Budapest, Hungary.
Racz, Bence
  • Department of Anatomy and Histology, University of Veterinary Medicine, Budapest, Hungary.
Sotonyi, Peter
  • Department of Anatomy and Histology, University of Veterinary Medicine, Budapest, Hungary.
Bakos, Zoltan
  • Department and Clinic of Equine Medicine, University of Veterinary Medicine, Budapest, Hungary.

MeSH Terms

  • Animals
  • Horses
  • Pulmonary Veins / anatomy & histology
  • Heart Atria
  • Heart Conduction System
  • Female
  • Male
  • Cross-Sectional Studies
  • Atrial Fibrillation / veterinary
  • Atrial Fibrillation / pathology

Grant Funding

  • University of Veterinary Medicine Budapest

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