Atrial fibrillation as a risk factor for exercise-induced pulmonary haemorrhage following a standardised exercise test.
Authors: Hansen Sanni, Otten Nina D, Nissen Sarah D, Carstensen Helena, Hopster-Iversen Charlotte, Fjeldborg Julie, Staun Sophie H, Fenner Merle, Hesselkilde Eva M, Buhl Rikke
Journal: Equine veterinary journal
Summary
# Editorial Summary: Atrial Fibrillation and Exercise-Induced Pulmonary Haemorrhage Left atrial pressure elevation during atrial fibrillation (AF) has been theorised as a potential mechanism predisposing horses to exercise-induced pulmonary haemorrhage (EIPH), yet direct evidence linking the two conditions remains limited. Researchers at Copenhagen University conducted a controlled crossover study using ten untrained Standardbred mares, each performing standardised exercise tests to fatigue both in normal sinus rhythm and again 25–44 days after AF induction via tachypacing, with endoscopic assessment of tracheal blood at 2 hours post-exercise and bronchoalveolar lavage samples collected at 24 hours. During AF exercise, four horses demonstrated markers of pulmonary bleeding—two with visible tracheal blood (grade 1) and free erythrocytes on lavage, and two with erythrophagocytosis alone—compared to none during normal sinus rhythm, alongside significantly reduced maximum velocity (8.9 versus 10.3 m/s), elevated resting heart rates (284 versus 221 bpm) and increased arrhythmias. Whilst this small study provides the first experimental evidence that AF may indeed increase EIPH risk, the mechanism remains incompletely understood, and clinicians should be aware that horses with confirmed AF may face heightened susceptibility to pulmonary bleeding during intense exercise, though further investigation into the haemodynamic relationships involved is needed before drawing firm conclusions about management implications.
Read the full abstract on PubMed
Practical Takeaways
- •Atrial fibrillation may increase risk of exercise-induced pulmonary haemorrhage; affected horses show reduced exercise tolerance and visible tracheal bleeding after exertion
- •AF-positive horses demonstrate impaired aerobic performance with lower maximum velocities and disproportionately elevated heart rates, suggesting compromised cardiac output during exercise
- •Consider cardiac screening before intensive exercise programmes, particularly in untrained or performance horses, as AF may predispose to EIPH
Key Findings
- •Two of ten horses (20%) showed visible blood in the trachea when exercising with atrial fibrillation compared to zero horses in sinus rhythm
- •Maximum velocity during exercise decreased from 10.3 m/s in sinus rhythm to 8.9 m/s with atrial fibrillation (p=0.004)
- •Heart rate was significantly elevated with atrial fibrillation at 284 bpm versus 221 bpm in sinus rhythm during standardised exercise (p=0.003)
- •Four horses showed erythrophagocytosis in bronchoalveolar lavage fluid following atrial fibrillation exercise compared to two horses in sinus rhythm