Incidence, recurrence, and outcome of postrace atrial fibrillation in Thoroughbred horses.
Authors: Nath Laura C, Elliott Adrian D, Weir Joe, Curl Peter, Rosanowski Sarah M, Franklin Samantha
Journal: Journal of veterinary internal medicine
Summary
# Postrace Atrial Fibrillation in Thoroughbreds: Recurrence Risk and Regulatory Implications Over a decade of racing records from Hong Kong (96,135 race starts across 4,684 Thoroughbreds) revealed that atrial fibrillation affects nearly 5% of the racing population, occurring at 2.7 episodes per 1000 starts. Horses with a prior AF episode faced substantially elevated recurrence risk—5.3 times higher than the general racing population—with particularly poor prognosis for persistent AF cases, where 64% experienced recurrence compared to 23% of those with paroxysmal episodes. Whilst median time between episodes was 343 days, the wide variation (34–1065 days) underscores the unpredictability of recurrence in individual horses, complicating return-to-racing decisions. These findings have direct implications for racing regulations, veterinary clearance protocols, and informed consent discussions with owners and trainers, as the substantial AF burden suggests current detection and management strategies may warrant reassessment. Given that horses with persistent AF show markedly worse outcomes, distinguishing between paroxysmal and persistent presentations should inform both clinical management and policy decisions regarding eligibility to compete.
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Practical Takeaways
- •Horses diagnosed with AF postrace, particularly persistent AF, carry substantial risk of recurrence and should receive appropriate monitoring and management protocols before return to racing
- •The wide variation in time between episodes (34-1065 days) means clinical decision-making about return-to-racing timelines must be individualized and evidence-based rather than following fixed protocols
- •Racing regulatory bodies should consider AF recurrence risk data when establishing rules around horse eligibility for return to competition following cardiac events
Key Findings
- •Atrial fibrillation was identified in 4.9% of Thoroughbred racehorses with an overall incidence of 2.7 episodes per 1000 starts
- •Horses with previous AF episodes had 5.3 times higher risk of recurrence (12.8 per 1000 starts) compared to those with no prior history (2.4 per 1000 starts)
- •Persistent AF showed higher recurrence rate (64%) compared to paroxysmal AF (23%; OR 5.9)
- •Median duration between AF episodes was 343 days with wide variation (34-1065 days)