Heart Murmurs and Valvular Regurgitation in Thoroughbred Racehorses: Epidemiology and Associations with Athletic Performance

Background: Cardiac murmurs associated with valvular regurgitation occur commonly in conditioned performance horses, but their association with athletic performance is unknown. Hypothesis: Cardiac valvular regurgitation has a negative association with race performance. Animals: Five hundred and twenty‐six “race fit” Thoroughbred racehorses engaged in either flat (race distance 1,000–2,500 m) or jump racing (race distance 3,200–6,400 m). Methods: Cardiac auscultation and color flow Doppler (CFD) echocardiography were performed on 777 occasions. The associations between the presence and severity of either an audible cardiac murmur or valvular regurgitation assessed by CFD, and published, objective measures of race performance were determined using a standard regression approach. Results: The prevalence of murmurs and of regurgitation varied significantly between racetypes ( P <.02), generally increasing from 2‐year olds to chasers. There were no consistent associations between racing performance and either grade of murmur or regurgitation, whether the presence or absence of regurgitation or murmur, or only murmurs ≥3/6 or regurgitation ≥6/9, were considered. Conclusions and Clinical Importance: There were differences in prevalence and severity of murmurs of atrioventricular and aortic valve regurgitation between racehorses in different disciplines. Data also showed that neither regurgitation nor murmurs were negatively associated with Timeform rating, an index of UK racehorse quality, in any of the groups of racehorses studied.