An investigation of the second heart sound in the normal horse.

This study focuses on examining the second heart sound in horses using various sound monitoring and imaging tools. The results showed that in normal horses, this sound is either singular or split into two parts separated by a short interval. Furthermore, the study scrutinized the reasons behind the variation in this sound splitting pattern in a portion of horses.

Study Methodology

• The research was performed on healthy, cognizant horses using a mix of different detection devices that pick up on internal and external sounds.
• Echocardiography, a method that utilizes sound waves to generate live images of the heart, was also used to explore the functionality and structure of the horses’ hearts.

Observations and Findings

• The second heart sound (referred to as S2) was determined to be either unsplit or separated into two parts by a narrow interval, often too slim to be recognized by external phonocardiographic evaluation, an assessment that records the sounds and murmurs of the heart.
• The researchers categorized the splitting of S2 sound into two types: normal (with the aortic component [A2] preceding the pulmonic component [P2]) seen in roughly two-thirds (66.7%) of horses; and reversed (with P2 preceding A2) seen in about a third (33.3%) of horses.

Underlying Causes Of Sound Splitting

• According to the analysis, normal splitting is hypothesized to be a result of the lower impedance or opposition in the pulmonary vasculature which delays the onset of P2, the second component of the second heart sound related to the pulmonary valve’s closure.
• Reversed splitting, alternatively, is assumed to result from a delay in A2, the first component related to the aortic valve closure, due to the protraction of Pre-Ejection Period (PEP) and Left Ventricular Ejection Time (LVET), two important time frames in the cardiac cycle.
• The study found no significant variations in the splitting of S2 based on respiration in the horses where this metric was evaluated.