Auscultatory findings and left atrial function as indicators of mitral valve regurgitation severity in horses.

Overview

• This research explored how heart sound characteristics (auscultation) and left atrial function relate to the severity of mitral valve regurgitation (MR) in horses.
• The study found that while certain heart sound features correlate with MR severity, echocardiography remains essential for accurate diagnosis, and only one measure of left atrial function showed a clear association with MR severity.

Background and Purpose

• Mitral valve regurgitation (MR) is a common heart valve disorder in horses where the mitral valve does not close properly, causing blood to leak backward in the heart.
• Determining how severe MR is in horses—and predicting outcomes—is challenging due to the lack of standardized classification methods.
• This study aimed to assess whether traditional auscultatory findings (listening to heart murmurs) and measurements of left atrial function could serve as indicators of MR severity.

Study Design and Methods

• The study was retrospective and involved 151 horses divided into groups: 50 controls with no or trivial MR, and 101 horses with MR of varying severity (58 mild, 36 moderate, 7 severe).
• All horses had a normal heart rhythm (sinus rhythm) and underwent both heart auscultation and echocardiography.
• MR severity was graded using a scoring system based on echocardiographic findings.
• Auscultatory examination focused on characteristics of left-sided systolic murmurs including:
• Duration (how long the murmur lasts during systole)
• Type (quality or nature of the murmur)
• Grade (intensity or loudness)
• Left atrial function was evaluated using several echocardiographic parameters:
• Left atrial fractional area change (how much the left atrium changes size between heartbeats)
• Myocardial tissue Doppler imaging indices for the left atrial and left ventricular walls during atrial contraction (to assess atrial muscle function)
• Statistical analyses included tests to compare groups and evaluate associations, such as analysis of variance, Kruskal-Wallis, chi-square, Spearman’s rho correlation, and Cohen’s weighted kappa.

Key Findings

• There was a clear positive association between MR severity and both the intensity and duration of left-sided systolic heart murmurs (P < 0.001 for both).
• The duration of the murmur correlated with the duration of the largest mitral regurgitation jet seen during ultrasound imaging (P < 0.001), linking auscultation findings with echocardiographic measurements.
• Left atrial fractional area change decreased progressively as MR severity increased, indicating impaired left atrial function in more severe MR cases (P < 0.001).
• Measures of myocardial velocity during atrial contraction in the left atrial and ventricular free walls did not differ significantly between groups after correcting for multiple comparisons, suggesting limited utility of these measurements in assessing MR severity.

Conclusions and Clinical Implications

• Auscultation (listening to the heart) can provide helpful clues regarding the severity of MR but is not sufficient on its own for precise classification.
• Echocardiography remains necessary to accurately diagnose MR severity and to evaluate detailed jet characteristics.
• Among left atrial functional parameters, only left atrial fractional area change reliably correlates with MR severity in horses.
• Other measures of atrial function, such as myocardial velocities assessed by tissue Doppler imaging, do not appear to be useful indicators of MR severity.
• Study limitations included the lack of an established gold standard for grading MR severity in horses and a small number of horses with severe MR, which may affect the generalizability of the findings.

Summary

• The research highlights the value and limitations of traditional heart sound examination and advanced echocardiographic techniques in evaluating mitral valve disease in equine patients.
• While heart murmurs offer a noninvasive screening index, comprehensive echocardiography remains essential for full assessment.
• The left atrium’s size change during heartbeats (fractional area change) is a promising functional parameter related to MR severity, warranting further research and clinical consideration.