Cardiac arrhythmias during intense exercise in Thoroughbred racehorses: frequency and association with subsequent race performance.

Exercise-induced ectopic beats in racehorses are associated with poor race performance.

This risk-based case-control study examined cardiac arrhythmias during high-intensity exercise in 71 Thoroughbred racehorses competing in Hong Kong, utilizing wearable single-lead ECG devices. Researchers recorded 405 ECGs within 21 days before race starts and correlated arrhythmia findings with subsequent race performance (poor = last 3 positions; good = first 3 positions). Arrhythmias were prevalent, detected in 73% of ECGs preceding good performances and 81% preceding poor performances. Ectopic beats during maximal exercise occurred in 57% of good-performance ECGs versus 70% of poor-performance ECGs. Statistical analysis revealed that each additional ectopic beat during exercise increased odds of poor performance (OR 1.15, P=0.01), with horses exhibiting any ectopic activity nearly twice as likely to underperform (OR 1.8, P=0.02). The findings suggest ectopic depolarizations are common occurrences in racing Thoroughbreds and carry adverse prognostic implications for athletic performance. The authors conclude that electrocardiographic monitoring during intense exertion may facilitate detection of clinically significant arrhythmias in equine athletes.

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