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

Mitral valve regurgitation (MR) is frequently detected in horses, but its classification and prognostication remain challenging. This study investigated whether auscultatory findings and left atrial function are associated with MR severity.

Fifty controls (no/trivial MR) and 101 MR horses (58 mild, 36 moderate, seven severe) were retrospectively evaluated. All were in sinus rhythm and underwent auscultation and echocardiography. Mitral regurgitation severity was graded using a scoring system. Systolic murmur characteristics (duration, type and grade) were recorded. Left atrial function was quantified measuring left atrial fractional area change and left atrial and ventricular tissue Doppler indices. Statistics included analysis of variance, Kruskal-Wallis, chi-square, Spearman's rho and Cohen's weighted kappa tests.

A positive association was found between MR severity and left-sided systolic murmur intensity (P < 0.001) and duration (P < 0.001), and between left-sided systolic murmur duration and largest jet duration on ultrasound (P < 0.001). Left atrial fractional area change decreased with increasing MR severity (P < 0.001). Myocardial velocity of the left atrial and ventricular free wall during atrial contraction showed non-significant differences between groups [P = 0.573 and P = 0.039 (within F-test; P ≥ 0.073 after Bonferroni correction for multiple comparisons)].

Study limitations included the absence of a gold standard for equine MR classification and few severe MR horses.

Although auscultation gives an indication about MR severity, echocardiography remains necessary to accurately diagnose MR and determine jet characteristics. Except for left atrial fractional area change, left atrial functional variables did not seem to be associated with MR severity in horses.