Characterization of cardiac veins morphometry in horses compared with other animal species

Background: Coronary sinus (CS) and great cardiac vein (GCV) are important in catheter-based electrophysiological studies in horses. Aim: This study aimed to describe the cardiac venous system of horses, detailing its morphology, morphometric characteristics, and the distribution of vascular patterns. Methods: A 2.0 silk suture was placed around the CS, and a 14-G catheter was inserted to infuse unsaturated polyester resin Palatal® GP40L (BASF Química Colombiana S.A., ID: 30284751, Lot: 30648215), consisting of an orthophthalic polyester dissolved in styrene monomer (~35% w/w). The viscosity of the resin was reduced by diluting the base resin with additional styrene in an-85:15 w/w ratio to facilitate vascular injection. Visual vessel contrast was achieved by adding a blue organic pigment (copper phthalocyanine, 1.0% w/w). Results: GCV origin was observed at the apex in 90% of cases. The diameter of this vessel at the drainage point at the CS was 8.72 ± 1.41 mm. In all specimens, the arteriovenous trigone (AVT) was observed with an open configuration in the lower segment and a closed configuration in the upper segment. A very short left marginal vein originating in the upper third of the left ventricle was observed. The distal diameter of the middle cardiac vein was 7.33 ± 1.13 mm. Drainage of this vessel into the right atrium was observed in 12 hearts (60%). The CS length was 41.74 ± 4.27 mm. The CS was cylindrical in 55% and funnel-shaped in 45% of the specimens. The CS internal valve was observed in 80% of cases at the point where the GCV drains into the CS. Conclusion: The anatomical variations of the CS and its tributaries in horses should be considered when performing ablation catheterization procedures to treat complex arrhythmia in this species or when using horses as an animal model.