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

Overview

• This study investigates the occurrence and characteristics of cardiac arrhythmias during intense exercise in Thoroughbred racehorses and examines how these arrhythmias relate to their subsequent race performance.
• The research aimed to determine if the presence of arrhythmias detected by exercise ECG monitoring correlates with poorer race results.

Background and Objective

• Cardiac arrhythmias, or irregular heartbeats, can occur in horses during intense physical activity.
• The frequency and types of these arrhythmias, as well as their impact on athletic performance in Thoroughbred racehorses, are not well understood.
• The objective was to describe how often arrhythmias happen during high-intensity exercise and whether they are linked to race outcomes.

Methods

• Study Population:
  • 71 Thoroughbred racehorses competing in races sanctioned by the Hong Kong Jockey Club were studied.
• Study Design:
  • Risk-based case-control approach comparing horses that performed well versus poorly in races.
• Data Collection:
  • Single-lead electrocardiograms (ECGs) were recorded during high-intensity exercise trials using wearable devices.
  • Recordings captured electrical heart activity during several phases: warm-up, maximal exercise, fast recovery, and slow recovery.
• Arrhythmia Identification and Characterization:
  • Ectopic depolarizations (extra heartbeats) were identified and analyzed for frequency (how many beats) and morphology (appearance).
• Performance Measurement:
  • Race results were categorized as ‘good performance’ (finishing in the first 3 positions) or ‘poor performance’ (finishing in the last 3 positions).
  • Only horses with ECG recordings within 21 days before a race start were included for analysis.
• Statistical Analysis:
  • Associations between ECG features and race performance were assessed using odds ratios (OR) to quantify the likelihood of poor performance linked to arrhythmias.

Results

• ECG Data:
  • 405 ECG recordings from 224 race starts were analyzed (82 poor performance starts, 142 good performance starts).
• Arrhythmia Frequency:
  • Arrhythmias were common, found in 73% of ECGs before good performances and 81% before poor performances.
  • During maximal exercise, ectopic beats were detected in 57% of ECGs prior to good performances and 70% prior to poor performances.
• Association with Performance:
  • Each additional ectopic beat increased the odds of finishing poorly by 15% (OR = 1.15 per beat).
  • Horses exhibiting any ectopic beat during maximal exercise were nearly twice as likely to have a poor race outcome (OR = 1.8).
  • These findings were statistically significant, indicating a real association rather than chance.

Conclusions and Implications

• Ectopic heartbeats are a common phenomenon in Thoroughbred racehorses during intense exercise.
• The presence and frequency of these arrhythmias are negatively associated with race performance, suggesting they impair athletic ability.
• Monitoring racehorses’ cardiac rhythms during maximal exertion using wearable ECG devices may help detect clinically important arrhythmias.
• This detection could allow trainers and veterinarians to manage or investigate horses at risk, potentially improving safety and performance outcomes.