Effect of age and training on murmurs of atrioventricular valvular regurgitation in young thoroughbreds.
Authors: Young L E, Wood J L
Journal: Equine veterinary journal
Summary
# Editorial Summary: Age, Training and Cardiac Valve Murmurs in Young Thoroughbreds Young and Wood's longitudinal study tracked 55 Thoroughbreds before and after race training commenced, supplemented by cross-sectional data from 56 horses aged 2–5 years already in full training, using cardiac auscultation validated against colour-flow Doppler echocardiography. Over nine months of athletic conditioning, the prevalence of mitral regurgitation murmurs nearly tripled from 7.3% to 21.8%, whilst tricuspid regurgitation prevalence doubled from 12.7% to 25.5%, with both increases statistically significant and accompanied by increases in murmur grading. Importantly, auscultation proved highly specific (100%) and reasonably sensitive for detecting these murmurs (negative predictive values of 84% for mitral and 65% for tricuspid regurgitation), though no age-related effect on valve pathology was observed in the cross-sectional group. For practitioners managing young racehorses, these findings suggest that cardiac auscultation should be incorporated into pre-training baseline assessments and repeated post-conditioning, as the physiological demands of racing can precipitate or exacerbate atrioventricular valve regurgitation; however, the clinical significance of these mostly low-grade murmurs remains to be established through prospective follow-up of athletic performance and long-term outcomes.
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Practical Takeaways
- •Young racehorses in training develop cardiac valve murmurs at significantly higher rates than untrained horses, suggesting athletic training itself may contribute to valvular regurgitation development
- •Auscultation is a reliable screening tool for detecting atrioventricular valve murmurs in young horses; negative auscultation findings carry reasonable confidence for ruling out clinically significant regurgitation
- •Trainers and veterinarians should monitor 2-year-old Thoroughbreds for development of new cardiac murmurs during the first year of racing, as emergence or progression may indicate training-related cardiac stress
Key Findings
- •Mitral regurgitation murmur prevalence increased from 7.3% to 21.8% (p=0.019) after 9 months of training in 2-year-old Thoroughbreds
- •Tricuspid regurgitation murmur prevalence increased from 12.7% to 25.5% (p=0.007) after 9 months of training
- •Mean murmur grades increased significantly for both mitral (p=0.018) and tricuspid regurgitation (p=0.0006) after training
- •Cardiac auscultation showed 100% specificity and high sensitivity (84% negative predictive value for mitral, 65% for tricuspid regurgitation) when validated against echocardiography