Key result
In Thoroughbred racehorses, arrhythmia was associated with increased heart rate variability during strenuous exercise (logSDRR B=0.51; 95% CI 0.40-0.62; p<0.001) and recovery.
Why the study?
Heart rate variability indices assess cardiac autonomic modulation and arrhythmias in exercising horses, but their patterns across exercise and recovery and relationships with clinical conditions in Thoroughbred racehorses required investigation.
Cross-Sectional (n=180)
In Thoroughbred racehorses, the presence of arrhythmia increases heart rate variability during exercise and recovery, while lameness decreases it during submaximal exercise.
Answers are grounded in this paper and cite their sources.
HRV changes with arrhythmia in racehorses are hypothesis-generating; leaves open causal links and human applicability pending prospective studies.
BACKGROUND: Heart rate variability (HRV) analysis measures the inter-beat interval variation of successive cardiac cycles. Measurement of these indices has been used to assess cardiac autonomic modulation and for arrhythmia identification in exercising horses. OBJECTIVES: To report HRV indices during submaximal exercise, strenuous exercise and recovery, and explore relationships with clinical conditions (arrhythmias, lameness, equine gastric ulcer syndrome [EGUS], lower airway inflammation and upper respiratory tract obstructions [URTOs]) in Thoroughbred racehorses. STUDY DESIGN: Retrospective, observational cross-sectional study. METHODS: One hundred and eighty Thoroughbred horses underwent a treadmill exercise test with simultaneous electrocardiographic recording. Time-domain HRV indices (standard deviation of the R-R interval [SDRR]; root mean square of successive differences [RMSSD]) were derived for submaximal and strenuous exercise and recovery segments. Clinical conditions (arrhythmia [during each phase of exercise], lameness, EGUS, lower airway inflammation and URTO) were assigned to binary categories for statistical analysis. Relationships between selected HRV indices and the clinical conditions were explored using linear regression models. RESULTS: During submaximal exercise, lameness was associated with decreased logRMSSD (B = -0.19 95% confidence interval [CI] -0.31 to -0.06, p = 0.006) and arrhythmia was associated with increased logRMSSD (B = 0.31 95% CI 0.01-0.608, p = 0.04). During strenuous exercise, arrhythmia was associated with increased HRV indices (logSDRR B = 0.51 95% CI 0.40-0.62, p < 0.001; RMSSD B = 0.60 95% CI 0.49-0.72, p < 0.001). During recovery, arrhythmia was associated with increased HRV indices (logSDRR B = 0.51 95% CI 0.40-0.62, p < 0.001, logRMSSD B = 0.60 95% CI 0.49-0.72, p < 0.001). MAIN LIMITATIONS: The main limitations of this retrospective study were that not every horse had the full range of clinical testing, therefore some horses may have had undetected abnormalities. CONCLUSIONS: The presence of arrhythmia increased HRV in both phases of exercise and recovery. Lameness decreased HRV during submaximal exercise.
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Hammond et al. (2022) conducted a cross-sectional in Poor performance in Thoroughbred racehorses (n=180). Clinical conditions (arrhythmia, lameness) vs. Absence of clinical conditions was evaluated on Heart rate variability indices (SDRR, RMSSD) during exercise and recovery (B 0.51, 95% CI 0.40-0.62, p=<0.001). In Thoroughbred racehorses, arrhythmia was associated with increased heart rate variability during strenuous exercise (logSDRR B=0.51; 95% CI 0.40-0.62; p<0.001) and recovery.
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