Heart rate variability during high-speed treadmill exercise and recovery in Thoroughbred racehorses presented for poor performance.
Authors: Hammond Anna, Sage William, Hezzell Melanie, Smith Sarah, Franklin Samantha, Allen Kate
Journal: Equine veterinary journal
Summary
# Editorial Summary Heart rate variability (HRV)—the variation in time intervals between successive heartbeats—offers a non-invasive window into cardiac autonomic function during exercise, yet its clinical utility in underperforming racehorses remains underexplored. Hammond and colleagues analysed HRV indices across submaximal exercise, strenuous exertion, and recovery phases in 180 Thoroughbreds presenting for poor performance, using time-domain measures (standard deviation of R-R intervals and root mean square of successive differences) derived from simultaneous treadmill testing and electrocardiography. The most striking finding was a robust association between cardiac arrhythmias and elevated HRV indices during both strenuous exercise (logSDRR increase of 0.51, p<0.001) and recovery (logRMSSD increase of 0.60, p<0.001), whilst lameness during submaximal work showed the opposite pattern—a significant decrease in logRMSSD (−0.19, p=0.006). For equine practitioners, these results suggest HRV could serve as a practical marker to distinguish between different pathophysiological states in poor performers: heightened variability may signal arrhythmic conditions requiring further investigation, whilst dampened variability during low-intensity exercise warrants evaluation for musculoskeletal compromise. The retrospective design and incomplete clinical screening across all subjects temper interpretation, but the specificity of phase-dependent associations points to a clinically relevant diagnostic tool worthy of prospective validation in field conditions.
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Practical Takeaways
- •Heart rate variability analysis during treadmill exercise testing can help identify cardiac arrhythmias and lameness in Thoroughbreds presenting with poor performance
- •Lower HRV during submaximal exercise may indicate lameness, while higher HRV across all phases may signal underlying arrhythmias requiring further investigation
- •Treadmill exercise testing with HRV analysis provides objective data to differentiate between cardiac and musculoskeletal causes of poor performance in racehorses
Key Findings
- •During submaximal exercise, lameness was associated with decreased logRMSSD (B = -0.19, p = 0.006)
- •During submaximal exercise, arrhythmia was associated with increased logRMSSD (B = 0.31, p = 0.04)
- •During strenuous exercise and recovery, arrhythmia was associated with significantly increased HRV indices (logSDRR B = 0.51, p < 0.001; RMSSD B = 0.60, p < 0.001)
- •Presence of arrhythmia increased HRV in both exercise phases and recovery, while lameness decreased HRV during submaximal exercise