Atrial fibrillation in horses Part 2: Diagnosis, treatment and prognosis.
Authors: Decloedt Annelies, Van Steenkiste Glenn, Vera Lisse, Buhl Rikke, van Loon Gunther
Journal: Veterinary journal (London, England : 1997)
Summary
# Atrial Fibrillation in Horses Part 2: Diagnosis, Treatment and Prognosis Atrial fibrillation remains a significant concern in equine practice, particularly in performance horses, yet diagnosis and management decisions require careful clinical reasoning beyond the characteristic irregularly irregular rhythm detected on auscultation. Decloedt and colleagues comprehensively reviewed diagnostic modalities and therapeutic options, confirming that whilst electrocardiography remains the gold standard for confirmation, heart rate monitoring during exercise and at rest offers practical value for early detection by owners, with disproportionately elevated exercise heart rates or abnormal variability warranting further investigation. Pharmacological cardioversion using quinidine sulphate achieves approximately 80% success rates via oral administration, whilst transvenous electrical cardioversion (TVEC) substantially outperforms this at over 95% success, though the recurrence rate of up to 39% following either approach represents a critical clinical consideration—with risk factors including previous failed treatment attempts, valvular regurgitation, atrial premature depolarisations, enlarged atria, and prolonged AF duration. The decision to attempt cardioversion should be individualised based on performance demands, with horses exhibiting maximal exercise heart rates exceeding 220 bpm or abnormal ventricular complexes under stress being stronger candidates, whilst those with severe underlying cardiac disease warrant conservative management due to poor recurrence outcomes. Practitioners should counsel clients that whilst most horses return to previous performance levels post-treatment, preventing recurrence remains challenging, and emerging pharmacological options such as sotalol require further clinical validation to establish their role in long-term management protocols.
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Practical Takeaways
- •Detect AF early by noting irregularly irregular rhythms at rest and disproportionate heart rate responses during exercise; confirm with ECG before treatment planning
- •Severe underlying cardiac disease is a contraindication for cardioversion due to high recurrence risk; reserve cardioversion for performance horses or those with abnormal exercise responses (>220 bpm maximal heart rate)
- •Understand that TVEC offers superior success (>95%) compared to pharmacological options (~80%), but expect up to 39% recurrence regardless of method; plan long-term monitoring and consider preventive sotalol therapy post-conversion
Key Findings
- •Pharmacological cardioversion with quinidine sulphate achieves approximately 80% success rate in treating equine atrial fibrillation
- •Transvenous electrical cardioversion (TVEC) has a success rate exceeding 95% for AF conversion
- •Recurrence rate after cardioversion is up to 39%, associated with previous failed treatments, valvular regurgitation, and low atrial contractile function
- •Most horses return to previous performance levels after successful cardioversion, though large atrial size and long AF duration increase recurrence risk