The fourth heart sound in the equine.

This research paper explores the two components of a horse’s fourth heart sound and presents evidence suggesting that the late component of this sound is caused by the presystolic closure and tensing of the atrioventricular (A-V) valves.

Components of the Fourth Heart Sound

• The authors discuss the presence of two components in the fourth heart sound in horses, in line with previous observations in humans and dogs.
• The early, typically inaudible, component is believed to be a result of the contraction of the atria, a part of the heart.
• The late, audible, component is the focus of several attributions regarding its cause, and its origin is identified as the subject of this study.

Attributions for the Late Component

• Three major theories stand in place to explain the genesis of the late component. It could be due to the impact of blood ejected by the atria onto the standing blood column in the ventricles.
• Alternatively, it could be vibrations produced in the ventricle walls by the rush of blood from the contracting atria.
• Finally, it could be caused by the presystolic closure of the A-V valves.

Significance of the Fourth Sound

• In humans, the presence of an exaggerated fourth heart sound can serve as an indicator of certain heart conditions like ventricular hypertrophy (enlarged ventricles), ventricular ischemia (reduced blood flow to the heart), or A-V conduction disturbances (disruption of electrical signals within the heart).
• In horses, however, the presence of the fourth heart sound is considered normal.

Objective of the Study

• The study aims to detail the two distinct components of a horse’s fourth heart sound.
• It presents evidence indirectly supporting the concept that the late component of this sound is generated due to the presystolic closure and tensing of the A-V valves.