Ventricular response during lungeing exercise in horses with lone atrial fibrillation.
Authors: Verheyen T, Decloedt A, van der Vekens N, Sys S, De Clercq D, van Loon G
Journal: Equine veterinary journal
Summary
# Editorial Summary: Ventricular Response During Lungeing Exercise in Horses with Lone Atrial Fibrillation Atrial fibrillation (AF) remains the most clinically significant cardiac dysrhythmia in horses, yet how the ventricles respond to exercise in affected animals has been poorly characterised. Verheyen and colleagues recorded electrocardiograms from 43 horses with lone AF during a standardised lungeing protocol encompassing walk, trot, canter, gallop and recovery phases, capturing beat-to-beat heart rate responses and arrhythmia patterns throughout exercise. The findings were striking: whilst resting heart rates varied considerably (42–175 bpm at walk), peak heart rates during gallop reached 311 bpm in some individuals, with maximum beat-to-beat rates recorded up to 492 bpm, indicating severely disproportionate tachycardia. More concerning still was the extremely high prevalence of ventricular dysrhythmias—ventricular premature depolarisations occurred in 81% of horses (predominantly during exercise rather than at rest), and one-third of the cohort exhibited broad QRS complexes with R-on-T morphology, recognised risk factors for ventricular fibrillation and sudden death. These findings have substantial implications for clinical practice: the presence of QRS broadening and R-on-T patterns emerging at relatively low exercise intensities may explain the weakness, incoordination and collapse episodes reported in AF-affected horses, suggesting that current exercise restrictions for these animals should be reconsidered and that electrocardiographic examination during work—not merely at rest—is essential for comprehensive risk stratification before clearance to athletic activity.
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Practical Takeaways
- •Horses diagnosed with lone atrial fibrillation should be carefully monitored during exercise, as excessive and unpredictable heart rate responses combined with ectopic activity significantly increase collapse and sudden death risk
- •The presence of QRS broadening or R-on-T patterns on resting or baseline ECGs warrants exercise restriction, as these dysrhythmias appear even at walk and trot and are associated with dangerous ventricular arrhythmias
- •Weakness, poor performance, or incoordination in AF-affected horses may reflect underlying dangerous ventricular ectopic activity rather than simple rate control issues, requiring veterinary cardiology evaluation before resuming work
Key Findings
- •Horses with lone AF during exercise showed disproportionate tachycardia with individual average heart rates ranging from 42–311 beats/min depending on gait, with beat-to-beat maximum rates reaching 248–492 beats/min
- •Ventricular premature depolarisations occurred in 81% of horses, present at rest (16%), during exercise (69%), and recovery (2%)
- •QRS broadening and R-on-T morphology were found in 33% of horses, often at low exercise intensities, representing potential risk factors for ventricular tachycardia and fibrillation