Cardiac arrhythmias in poorly performing Standardbred and Norwegian-Swedish Coldblooded trotters undergoing high-speed treadmill testing.
Authors: Slack J, Stefanovski D, Madsen T F, Fjordbakk C T, Strand E, Fintl C
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Cardiac arrhythmias are routinely investigated in poorly performing horses, yet their clinical significance and relationship to concurrent upper airway disease remain unclear. Slack and colleagues conducted a retrospective analysis of high-speed treadmill electrocardiograms from 103 Standardbred and Norwegian-Swedish Coldblooded trotters, documenting arrhythmia frequency, morphological characteristics, and any associations with upper airway pathology. The prevalence of arrhythmmic events was remarkably high (77–78%) across all exercise phases when using standard premature beat criteria, though more clinically significant arrhythmias—triplets, salvos, and paroxysmal tachyarrhythmias—were less common (8% during peak exercise), with 15% of horses developing complex ventricular arrhythmias in early recovery. Notably, no significant association emerged between upper airway abnormalities and arrhythmia occurrence, challenging the clinical assumption that airway obstruction drives exercise-induced arrhythmias; however, maximum heart rate during peak effort proved an excellent predictor of post-exercise ventricular complexity. For practitioners managing poorly performing trotters, this work emphasises that high arrhythmia prevalence on treadmill testing does not automatically indicate pathology requiring intervention, and suggests that careful individual assessment of arrhythmia morphology and recovery patterns—rather than airway diagnosis alone—should guide clinical decision-making.
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Practical Takeaways
- •Cardiac arrhythmias are very common in poorly performing trotters (77-78%) but do not appear to be causally related to upper airway obstruction, suggesting other etiologies should be investigated
- •Recovery period arrhythmias (particularly in the first 2 minutes) may be more clinically significant than exercise-induced arrhythmias; monitor peak exercise heart rate as a potential predictor
- •Standard categorization of arrhythmias as supraventricular versus ventricular may be unreliable in horses; descriptive reporting of arrhythmia characteristics is more useful clinically
Key Findings
- •77-78% of poorly performing trotters exhibited at least one arrhythmic event during exercise with 6-10% prematurity criteria
- •8% of horses developed triplets, salvos, or paroxysmal tachyarrhythmias during peak exercise
- •15% of horses exhibited complex ventricular arrhythmias in the first 2 minutes of recovery
- •No association was found between airway diagnosis and arrhythmias during any exercise period; maximum average heart rate during peak exercise was an excellent predictor of complex ventricular arrhythmias during recovery