# Anatomy of the Right and Left Ventricular Subvalvular Apparatus of the Horse (Equus caballus)

## TL;DR

This study examines the anatomy of the heart's subvalvular structures in horses to improve veterinary cardiology and surgery.

## Contribution

The study provides new comparative anatomical insights into equine ventricular subvalvular apparatuses.

## Key findings

- The study identifies morphological features of papillary muscles and chordae tendineae in equine hearts.
- Comparisons with other species reveal interspecies similarities and differences linked to evolution and adaptation.
- Findings contribute to understanding equine heart pathologies and surgical treatment possibilities.

## Abstract

Understanding the precise anatomy of the left and right subvalvular apparatus in the domestic horse can contribute to the development of normal and comparative animal anatomy, as well as surgery, internal medicine, and biology. This study conducts such an analysis, taking into account the thickness of the left ventricular wall, the right ventricular wall, the interventricular septum, the ventricle’s length, and the entire heart’s width. Additionally, it examines the number of muscle bellies of the papillary muscles, the type of connection between the muscle and the heart wall, the height of muscle origin, and the length of the papillary muscle. This study calculates various proportions and compares them with descriptions of subvalvular apparatuses in other animal species, including humans, available in the literature.

Due to the growing interest among veterinarians and the increasing market demands, the development of equine cardiology is necessary. Currently, veterinary medicine for companion animals needs to catch up to human medicine—equine medicine included. A common condition in older horses is aortic valve regurgitation resulting from fibrosis, while its more severe form occurs in younger horses or develops due to a bacterial infection. Mitral valve regurgitation, especially dangerous due to the possibility of sudden death, has a better prognosis if the horse has valve prolapse. Tricuspid valve regurgitation usually does not pose a clinical problem, although its severe cases may lead to heart failure. Some pathologies can be treated surgically, which requires excellent knowledge of anatomy. The object of this study consisted of twenty domestic horse hearts. The focus was on the normal and comparative anatomy of the left and right subvalvular apparatus. The number of muscular bellies of the papillary muscles and the type of connection of the muscles were analysed. Moreover, the height of muscle originating from the ventricle wall was determined, the morphological regularity of the papillary muscle was assessed, and the chordae tendineae originating from the papillary muscles were examined. The conducted research allowed for comparing domestic horses with different species through other studies, the authors of which described this particular aspect. Interspecies similarities which may be correlated with the evolutionary relatedness, as well as differences that could reflect adaptation to different lifestyles, environmental conditions, or metabolic requirements of the animals, have been found. This study expands the knowledge of animals’ normal and comparative anatomy, and contributes to the development of veterinary surgery, internal medicine, and biology.