Right atrial-related structures in horses of interest during electrophysiological studies.

Background: Arrhythmias are common in horses, but catheter-based minimally invasive electrophysiological studies and therapeutic interventions have been poorly explored in equine medicine, partly due to the lack of detailed anatomical knowledge of the equine heart.

Objectives: To describe the dimensions and anatomical features of some electrophysiologically important landmarks of the right atrium in detail and assess their correlation with bodyweight and aortic diameter.

Study Design: Ex vivo cadaveric study.

Methods: Twenty-one hearts of Warmblood horses, subjected to euthanasia for noncardiovascular reasons, were examined post-mortem. The dimensions and anatomical features of the coronary sinus, the great cardiac vein and the oval fossa were recorded. Spearman's Rho correlation coefficients were calculated for correlations between the quantitative parameters and bodyweight and aortic diameter.

Results: Median dimensions for coronary sinus, great cardiac vein and oval fossa were obtained. A Thebesian valve, partially covering the ostium of the coronary sinus, was present in 9 of the 21 hearts. A median of 6.5 (range 4-9) valves were present in the great cardiac vein. Several parameters, among which the dimensions of the oval fossa and the length of the great cardiac vein, were significantly positively correlated with bodyweight and aortic diameter.

Main Limitations: Measurements do not consider the dynamic changes during the cardiac cycle as measurements were performed ex vivo. All specimens were retrieved from Warmblood horses, therefore measurements might not apply to other breeds.

Conclusions: This study delivers a detailed description of important right atrial-related structures, necessary for the development of minimally invasive intracardiac procedures in horses. Adequate imaging techniques will have to be explored in order to guide these procedures.