Hypercapnia and hyperlactatemia were positively associated with higher-grade arrhythmias during peak exercise in horses during poor performance evaluation on a high-speed treadmill.
Authors: Reef V B, Davidson E J, Slack J, Stefanovski D
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Cardiac arrhythmias during high-speed treadmill exercise testing are common in performance horses, yet their relationship to metabolic stress during peak exertion remains poorly characterised. A large prospective study of 368 horses undergoing incremental exercise testing with concurrent electrocardiography and arterial blood gas sampling revealed that elevated carbon dioxide (PaCO2) and lactate concentrations at peak exercise were independently associated with more severe arrhythmias, with complex arrhythmias (couplets, triplets, multiform complexes or tachycardias) detected in 4.4% of the population. Notably, both hypercapnia and hyperlactatemia correlated with arrhythmia progression—as these values increased, so too did arrhythmia grade—whereas blood pH changes only became significant in the immediate post-exercise period. Upper respiratory tract obstruction, inflammatory airway disease and exercise-induced pulmonary haemorrhage were not significantly associated with higher-grade arrhythmias, suggesting metabolic factors rather than airway compromise drive exercise-associated cardiac dysrhythmias during poor performance evaluations. For practitioners, these findings indicate that severe metabolic acidosis and carbon dioxide retention during maximal effort warrant careful cardiac monitoring and may reflect systemic exercise intolerance requiring further investigation beyond routine airway assessment.
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Practical Takeaways
- •Monitor blood gas values during exercise testing as elevated CO2 and lactate are objective markers predicting higher-risk arrhythmias in poor-performing horses
- •Upper airway obstruction status alone does not predict exercise arrhythmias; metabolic changes (hypercapnia/hyperlactatemia) are the key risk factors to assess
- •Consider exercise intolerance and poor performance in conjunction with arterial blood gas analysis rather than relying solely on respiratory disease diagnosis
Key Findings
- •Grade 1 arrhythmias occurred in 6.9% of horses at peak exercise and 16% at 0-2 min post-exercise
- •Elevated PaCO2 (P=0.008) and lactate (P=0.031) were significantly associated with higher-grade arrhythmias at peak exercise but not immediately post-exercise
- •As PaCO2 and lactate increased, arrhythmia severity increased in a dose-dependent manner
- •Higher PaCO2 concentrations were associated with increased likelihood of grades 2-3 arrhythmias in horses with and without upper respiratory tract obstruction (P<0.01)