Histological and morphometric study of the components of the sinus and atrioventricular nodes in horses and dogs.

The article provides a microscopic examination of the components of the heart’s electrical impulse generating nodes in horses and dogs. The authors conclude that even in healthy hearts, structural differences in these nodes may affect electrical conduction, and therefore heart function.

Methodology and Objectives

• The researchers analyzed the structure of the sinus and atrioventricular (AV) nodes in ten horse hearts and five dog hearts. These nodes are responsible for generating and transmitting electrical impulses that control heart rhythm.
• Their aim was to understand how the physical characteristics of these nodes could influence the normal/abnormal working of the heart.

Data Collection

• The regions containing these nodes were carefully removed, sectioned, and studied under a microscope.
• Morphometric analysis (measurement of form, in this case the nodes’ components) was carried out using image analysis software (Image-Pro Plus 7.1), which analysed images taken using a Leica DMD108 optic microscope.

Findings

• Notably, the sinus node in horses is oblong in shape, with large P cells (Possibly referring to the primary pacemaker cells). In contrast, dogs have either a rounded or oblong sinus node, and their P cells are large but pale.
• The area of P cells in horses was found to be significantly larger than in dogs (976 vs 106 micrometers).
• The researchers also observed the shape of the atrioventricular node in both animals, noting that horses have an oblong shape, while dogs have a spindle shape.

Conclusions & Implications

• Poor density of cells in these nodes, specifically in the P cells of the sinus node, is associated with decreased electrical signal conduction. This directly impacts how the electrical signals necessary for heart function are processed, potentially resulting in heart arrhythmias (irregular heartbeats) – even in otherwise healthy hearts.
• The information could better inform diagnosis and treatment of heart conditions in these animals and could potentially be useful in understanding similar issues in other species, including humans.