Atresia of the right atrioventricular orifice with complete transposition of the great arteries in a horse.

The abstract discusses a postmortem examination of the heart of a 6-week old Arabian filly with a history of compromised health and exercise intolerance, which revealed several cardiac malformations. These defects included tricuspid atresia, complete transposition of the great arteries, anomalous venae cavae and coronary sinus drainage into the left atrium, narrowing of the aorta, and an open ductus arteriosus.

Explanation of Key Concepts

• Atresia of the right atrioventricular orifice (Tricuspid Atresia): This refers to a condition where the tricuspid valve, which allows the flow of blood from the right atrium to the right ventricle, fails to develop in the foetal stage. This malformation results in a non-existent or an abnormally tiny tricuspid valve, inhibiting proper blood flow.
• Complete transposition of the great arteries: This is a congenital heart defect in which the pulmonary artery and the aorta — the heart’s two main arteries — are switched in position. This leads to a faulty circulation path where oxygenated and non-oxygenated blood are not properly separated, disturbing the overall systemic circulation.
• Anomalous drainage of the venae cavae and coronary sinus: This indicates an abnormal pattern where the venae cavae (large veins returning deoxygenated blood to the right atrium) and the coronary sinus (major vein collecting blood from the heart muscle) are incorrectly connected to the left atrium instead of the right one.
• Coarctation of the aorta: This is a narrowing in the aorta, the main blood vessel carrying oxygen-rich blood from the left ventricle to the rest of the body, causing the heart to work harder to pump blood.
• Ductus Arteriosus: This refers to a blood vessel that allows blood to bypass the fetal lungs, which do not function until after birth, and travel directly to the aorta. Normally this pathway closes soon after birth, but it remained partially open (patent) in this case, leading to an inappropriate mixture of oxygenated and non-oxygenated blood.

Observations from the Postmortem Examination

• The heart of the 6-week old Arabian filly displayed numerous cardiac malformations, which can be attributed to the foal’s poor health and exercise intolerance.
• These cardiac defects disrupted the normal flow of blood through the horse’s heart, further affecting the distribution of oxygenated blood to different body parts of the horse.
• The study briefly hypothesizes the peculiar course of blood flow through this deformed heart, however, it does not provide a detailed discussion or illustrative diagrams in the abstract.

This paper is significant as it contributes to the veterinary literature on congenital heart diseases in young horses, providing insight into possible physical manifestations and the direct effect these defects can have on their general health and physical endurance.