Heart murmurs and valvular regurgitation in thoroughbred racehorses: epidemiology and associations with athletic performance.
Authors: Young L E, Rogers K, Wood J L N
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Young, Rogers and Wood's 2008 investigation examined 526 race-fit Thoroughbreds across flat and jump racing disciplines using cardiac auscultation and colour flow Doppler echocardiography on 777 occasions, seeking to clarify whether valvular regurgitation and audible cardiac murmurs—both common findings in conditioned racehorses—actually compromise athletic performance. Contrary to expectations, the researchers found no consistent negative association between the presence, grade or severity of cardiac murmurs or regurgitation and objective measures of race performance, including Timeform ratings, regardless of whether analysis focused on all murmurs or only those graded ≥3/6, or regurgitation ≥6/9. Whilst prevalence and severity of both atrioventricular and aortic valve regurgitation varied significantly across disciplines—generally increasing from 2-year-olds to chasers—these differences did not translate into predictable performance deficits. For equine practitioners, this suggests that detection of a cardiac murmur or valvular regurgitation during clinical examination should not automatically disqualify a horse from competition or lead to restrictions on training intensity without additional clinical context or evidence of haemodynamic compromise. However, the findings warrant cautious interpretation: the study captured performance data from horses already deemed fit enough to race, potentially excluding those with more severe lesions precluded from starting, and longitudinal monitoring of individual horses with regurgitation remains prudent given the degenerative nature of valvular disease.
Read the full abstract on PubMed
Practical Takeaways
- •Cardiac murmurs and valvular regurgitation are common findings in race-fit Thoroughbreds but do not reliably predict poor racing performance; presence of a murmur should not automatically disqualify a horse from competition
- •Prevalence patterns differ by racing discipline and age, suggesting discipline-specific cardiac adaptation rather than pathology in many cases
- •Echocardiographic assessment provides more detailed information about regurgitation severity than auscultation alone, but objective performance data should guide clinical decision-making rather than cardiac findings in isolation
Key Findings
- •Prevalence of cardiac murmurs and valvular regurgitation varied significantly between race types (flat vs jump racing) and increased from 2-year-olds to chasers (P<0.02)
- •No consistent associations found between cardiac murmurs or valvular regurgitation severity and published objective measures of race performance
- •Neither regurgitation nor murmurs were negatively associated with Timeform rating (UK racehorse quality index) in any group studied
- •Differences in prevalence and severity of atrioventricular and aortic valve regurgitation murmurs existed between racehorses in different racing disciplines