Training vs. racing: A comparison of arrhythmias and the repeatability of findings in Thoroughbred Chuckwagon racehorses.
Authors: Massie S L, Bezugley R J, McDonald K J, Léguillette R
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Cardiac arrhythmias during maximal exercise are frequently documented in racehorses, yet regulatory restrictions mean electrocardiograms are only recorded during training rather than competition—a limitation that raises concerns about whether findings are reproducible and clinically meaningful. Researchers acquired 152 ECGs from 52 Thoroughbred chuckwagon racehorses across training and competitive events, examining the frequency and type of arrhythmias (supraventricular and ventricular premature complexes) alongside physiological markers including heart rate, speed, lactate and troponin-T levels. Arrhythmias occurred in similar numbers and patterns during training and competition, with approximately 18% of horses displaying ventricular premature complexes in both contexts, though most were isolated events rather than runs; critically, however, the ability to reliably detect specific arrhythmia types on repeated ECGs was poor to moderate, suggesting considerable variability between recordings. Whilst the overall burden of arrhythmias proved repeatable, practitioners should interpret individual arrhythmia classifications cautiously when making clinical decisions based on single ECG recordings, particularly as the type and frequency of specific complexes may not consistently reappear on subsequent testing. This finding has important implications for risk stratification and veterinary clearance protocols, indicating that repeated recordings rather than single assessments may be necessary to establish genuine arrhythmia patterns in athletic horses.
Read the full abstract on PubMed
Practical Takeaways
- •Training ECGs reliably reflect competition arrhythmia burden in chuckwagon horses, justifying continued regulatory reliance on training-based cardiac screening despite inability to record during racing
- •Single premature complexes are the dominant arrhythmia type in this population and appear benign; focus clinical attention on horses exhibiting arrhythmias during training rather than extrapolating risk from competition-only data
- •When using serial ECG monitoring for individual horses, expect the total arrhythmia count to be repeatable, but do not rely on detecting the same arrhythmia type between recordings
Key Findings
- •No significant difference in arrhythmia type or frequency between training and competition ECGs in 40 horses with clean tracings (VPCs in 7/40 training vs 7/40 competition)
- •Arrhythmias were predominantly single premature complexes with similar lactate and troponin-T levels between training and competition conditions
- •Total arrhythmia count was repeatable across serial ECGs, but reliability to detect specific arrhythmia types (SVPC and VPC) was poor to moderate
- •Training ECGs may be a valid proxy for competition arrhythmias in Thoroughbred chuckwagon horses, supporting continued regulatory use despite lack of on-track monitoring