Equine coronary sinus and great cardiac vein anatomy relevant to cardiac electrophysiology.

Objective Overview

The study investigates the detailed anatomy of the coronary sinus (CS) and great cardiac vein (GCV) in horses to improve understanding of their relationships with surrounding heart structures, which is important for cardiac electrophysiology, especially in diagnosing and treating arrhythmias using catheterization.

Introduction and Background

• The coronary sinus (CS) and great cardiac vein (GCV) play a key role in cardiac electrophysiology in humans, sometimes contributing to arrhythmias.
• In equine medicine, catheterization of these veins is increasingly used for diagnosing and treating cardiac arrhythmias.
• Detailed anatomical knowledge of these structures in horses is limited but important to optimize procedures and understand potential arrhythmogenic mechanisms.

Methods

• Postmortem examination was performed on 64 adult warmblood horse hearts.
• Researchers described the anatomical locations of the middle cardiac vein and vein of Marshall ostia (openings).
• Length of the right atrial myocardial sleeve (MS), which is an extension of heart muscle into the CS, was measured starting from the CS ostium (opening).
• In a subset of 23 horses, the team measured:
• Length of the CS and GCV within the coronary groove.
• Distances from the GCV to surrounding heart muscle structures including left atrial myocardium (LAm), left ventricular myocardium (LVm), and the mitral annulus measured at eight defined levels.
• Histological analysis was performed to examine the relationship and connections between myocardial sleeve and left atrial myocardium.

Results

• The middle cardiac vein more frequently opened into the right atrium rather than the CS, which differs from typical human anatomy.
• The vein of Marshall was consistently present near the Vieussens valve, an anatomical landmark within the right atrium.
• The average (mean ± SD) length of the coronary sinus was 28 ± 13 mm.
• The right atrial myocardial sleeve extended approximately 52 ± 18 mm into the great cardiac vein in 63 of the 64 examined horses, indicating a substantial sleeve of muscle extending into the venous system.
• The combined CS/GCV length within the coronary groove averaged 240 ± 36 mm.
• Distance between the GCV and the left atrial myocardium varied along the vein:
• Near the CS end: median 10 mm (interquartile range 6 mm) – relatively close to the atrial myocardium.
• At the mid-left free wall: median 2 mm (IQR 2 mm) – very close proximity.
• Near the paraconal interventricular sulcus: median 32 mm (IQR 13 mm) – farther away from the atrial myocardium.
• An opposite (inverse) relationship was seen with the left ventricular myocardium around these points.
• Histological studies showed myocardial connections between the myocardial sleeve and left atrial myocardium, suggesting electrical continuity.

Conclusions

• The anatomy and trajectory of the coronary sinus and great cardiac vein are crucial for effective catheter placement during electrophysiological procedures in horses.
• The presence and length of the right atrial myocardial sleeve suggest that this muscle extension could be involved in arrhythmia formation in horses, similar to humans.
• Variations in tributary vein anatomy may affect the success and approach of CS/GCV catheterization in equine cardiology.

Limitations

• Study used postmortem hearts from warmblood horses, which may not fully represent the in vivo (living) conditions or other horse breeds.
• Measurements were performed by a single observer, which could introduce bias or measurement variability.
• The absence of live imaging data limits understanding of the dynamic physiological state during catheterization.

Implications

• This study provides veterinary cardiologists with enhanced anatomical knowledge crucial for performing electrophysiological interventions in horses.
• Understanding the myocardial sleeve’s extent highlights potential sites of arrhythmogenicity and might influence strategies to map or ablate arrhythmias.
• Anatomical variations in vein openings and their relations to atrial or ventricular muscle must be considered to reduce procedural complications.