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Equine veterinary journal2026; doi: 10.1002/evj.70309

Ostium-specific equine pulmonary vein myocardial sleeve gross anatomy and structural evidence of interatrial myocardial continuity with potential implications for ablation strategies.

Abstract: Pulmonary vein (PV) myocardial sleeves (MSs) harbour an arrhythmogenic substrate for atrial fibrillation. However, equine-specific data on MS distribution and wall thickness are limited yet essential for developing ablation strategies. In humans, posterior interatrial connections can compromise right-sided PV isolation. Objective: To study equine PV MS distribution, quantify ostial/branch diameters, antral lengths, characterise MS distal edge morphology, measure wall thickness and explore an interatrial myocardial continuity between the MSs of caudal branches draining through ostium III (PV III) and caudal vena cava (CaVC). Methods: Post-mortem, cross-sectional. Methods: Twenty-three Warmblood hearts underwent left atrial and PV dissection. All four ostia (I-IV) were opened. From calibrated photographs, ostial and branch diameters, antral length, MS length and coverage, distal edge morphology (sharp/blurred), and myocardial thickness were assessed at standardised locations. In 6/23 hearts, a 3 × 1 cm dorsal interatrial septum (IAS) sample including PV III, and CaVC MSs was stained with Masson's trichrome and examined for myocardial continuity. Results: Four principal ostia were present in 20/23 hearts and 5 in 3/23, with variable accessory vein openings. Ostia II and III were largest, I smallest. PV III showed full antral MS coverage with branch extensions, whereas MSs in other PVs were often confined to the antrum. Distal MS edges were often blurred at PV III. The MS thickness was largest at ostia II and III and smallest at ostium I. Histology showed that the dorsal interatrial myocardium was continuous with the PV III and CaVC MSs. Conclusions: Postmortem study, Warmblood cohort, few samples, no electrophysiology. Conclusions: Equine PV MS anatomy is ostium-specific in extent, distal edge, and thickness. These data provide anatomical information relevant to ablation planning and to future catheter design. Morphological evidence suggests a dorsal interatrial myocardial continuity through the IAS that warrants electro-anatomical confirmation.
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Publication Date: 2026-08-20 PubMed ID: 42625338DOI: 10.1002/evj.70309Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigates the anatomical characteristics of myocardial sleeves around the pulmonary veins in horses and explores their connectivity with the interatrial septum, which is important for designing effective cardiac ablation treatments for atrial fibrillation.

Background and Importance

  • Pulmonary vein myocardial sleeves (MSs) are extensions of heart muscle tissue surrounding the pulmonary veins, implicated as sources of arrhythmias like atrial fibrillation.
  • Understanding the detailed anatomy, including thickness and distribution of these myocardial sleeves in horses, helps tailor ablation strategies that target problematic tissues to restore normal heart rhythm.
  • In humans, interatrial myocardial connections can undermine the success of ablation by allowing electrical signals to bypass isolated segments, but equine-specific data on such connections were missing prior to this study.

Objectives

  • To map the distribution of myocardial sleeves around specific pulmonary vein ostia (openings) in horses.
  • To measure diameters of pulmonary vein branches and ostia, length of the antral region (part of the vein close to the atrium), and the extent and morphology of the myocardial sleeves.
  • To quantify myocardial wall thickness at standardized locations around the pulmonary veins.
  • To determine if there is continuity of myocardium between the pulmonary vein sleeves of the caudal branches (PV III) and the caudal vena cava (CaVC) through the dorsal interatrial septum (IAS).

Methods

  • Hearts from 23 Warmblood horses were examined post-mortem.
  • Each heart underwent dissection to expose the left atrium and pulmonary veins; four major ostia (I-IV) were opened for analysis.
  • Measurements taken from calibrated photographs included ostial and branch diameters, antral length, myocardial sleeve length and coverage, distal edge morphology (sharp or blurred), and myocardial thickness at predefined locations.
  • In 6 hearts, tissue samples (3×1 cm) from the dorsal interatrial septum including PV III and CaVC myocardial sleeves were stained using Masson’s trichrome histological method to examine potential myocardial continuity.

Key Findings

  • Most hearts had four principal pulmonary vein ostia; three hearts showed a fifth ostium, along with some variable accessory vein openings.
  • Ostia II and III were the largest in diameter, while ostium I was the smallest.
  • Pulmonary vein III showed comprehensive myocardial sleeve coverage extending onto its branches, unlike other veins where sleeve coverage was often limited to the antral region.
  • The distal edges of the myocardial sleeves were often blurred at PV III, indicating gradual transitions rather than abrupt terminations.
  • Wall thickness of myocardial sleeves was greatest at ostia II and III, thinnest at ostium I, reflecting anatomical specificity relative to location.
  • Histological examination revealed direct myocardial continuity between the myocardial sleeves of PV III and the caudal vena cava through the dorsal interatrial septum, suggesting an anatomical pathway that could be important in conducting electrical signals.

Conclusions and Implications

  • Equine pulmonary vein myocardial sleeve anatomy varies by ostium in terms of extent, distal morphology, and thickness.
  • This detailed anatomical information is critical for planning effective cardiac ablation strategies in horses, providing insights for better catheter design and targeting of arrhythmogenic tissue.
  • The observed interatrial myocardial continuity through the dorsal interatrial septum in horses is a novel finding with potential electrophysiological significance; it could explain conduction pathways that affect ablation outcomes.
  • However, since the study was post-mortem with a limited sample size and lacked electrophysiological data, further studies involving electro-anatomical mapping are required to confirm functional relevance.

Cite This Article

APA
Ibrahim L, Van Hooydonk I, Cornillie P, van Loon G. (2026). Ostium-specific equine pulmonary vein myocardial sleeve gross anatomy and structural evidence of interatrial myocardial continuity with potential implications for ablation strategies. Equine Vet J. https://doi.org/10.1002/evj.70309

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Ibrahim, Lara
  • Department of Morphology, Imaging, Orthopedics, Rehabilitation and Nutrition, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.
Van Hooydonk, Inne
  • Department of Morphology, Imaging, Orthopedics, Rehabilitation and Nutrition, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.
Cornillie, Pieter
  • Department of Morphology, Imaging, Orthopedics, Rehabilitation and Nutrition, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.
van Loon, Gunther
  • Equine Cardioteam Ghent, Department of Internal Medicine, Reproduction and Population Medicine, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.

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