Cardiac electrophysiological adaptations in the equine athlete-Restitution analysis of electrocardiographic features.
Authors: Li Mengye, Chadda Karan R, Matthews Gareth D K, Marr Celia M, Huang Christopher L-H, Jeevaratnam Kamalan
Journal: PloS one
Summary
# Editorial Summary Thoroughbred horses demonstrate remarkable cardiac adaptations when accelerating from walk to canter, increasing their heart rate sevenfold whilst maintaining electrical stability—a capacity rarely seen in other species. Li and colleagues analysed electrocardiographic data collected via telemetry during exercise, calculating action potential restitution properties (the heart's ability to recover electrical excitability between beats) by measuring QT intervals, QRS durations and diastolic intervals. During exercise, critical QT and TQ intervals shortened by approximately 39% and 86% respectively compared to resting values, with these changes driven primarily by shortening of the QT interval rather than alterations in QRS duration, allowing the heart to maintain normal electrical conduction across a heart rate range of 33 to 129 bpm without triggering arrhythmias or heart block. These findings reveal coordinated electrophysiological restitution mechanisms that enable the equine heart's extraordinary functional flexibility—a feature with direct relevance for understanding exercise-induced cardiac stress and sudden cardiac events in athletic horses, and suggesting horses merit consideration as a translational model for human sports cardiology. For practitioners, this underscores why horses tolerate intense training without the arrhythmic complications that would incapacitate other mammals, though individual variation in these restitution properties may help identify animals at risk during peak performance.
Read the full abstract on PubMed
Practical Takeaways
- •Horses have remarkable cardiac electrophysiological adaptations that permit extreme heart rate increases during exercise without inducing dangerous arrhythmias—understanding these mechanisms may inform recognition of abnormal cardiac responses in individual horses
- •The equine heart's natural tolerance for 7-8 fold heart rate increases provides a unique model for studying sudden cardiac death in athletic populations; practitioners should be aware that horses exhibiting arrhythmias or conduction blocks during exercise may have pathological deviations from these normal adaptive responses
Key Findings
- •Thoroughbred horses demonstrate a 7-8 fold increase in heart rate during acceleration from walk to canter without arrhythmias or heart block
- •QT intervals were reduced by 38.9% and resting TQ intervals by 86.2% relative to resting values during exercise
- •Action potential wavelength indices (λ and λ0) decreased by 34.1% and 85.9% respectively, with changes attributable to QT interval reduction rather than QRS duration changes
- •Critical heart rates (117-129 bpm) at which electrophysiological restitution occurs differ substantially from baseline resting heart rates (32.9 bpm)