BACKGROUND: Exercise-associated arrhythmias occur commonly and can cause distress, collapse, or rarely, fatalities. On course management of arrhythmias is challenging due to limited access to anti-arrhythmic drugs. Detomidine is a relaxant that has many applications in equine practice. Administration of detomidine to horses with arrhythmias and distress in the post-race period could potentially improve outcomes, but the safety of this practice is unknown.
METHODS: Medical records of horses racing in Victoria, Australia between June 2023 and August 2025 that were identified to have cardiac arrhythmia on post-race examination were enrolled. ECG tracings were collected using the Kardia device, and treatment records were reviewed. Heart rate (HR) and rhythm were determined and classified.
RESULTS: There were 57 horses identified to have an arrhythmia during the study period, of which 13 were distressed and treated with 2mg of detomidine and cold water hosing. The mean ± SD HR initially for treated horses was 152 ± 17 which was not different to untreated horses 148 ± 25, P=0.61. Following treatment, HR was significantly reduced to 121 ± 23, p<0.005. In the untreated group there were 26 horses with uniform atrial fibrillation (UAF), 14 horses with non-uniform AF (NAF), and 4 horses with supraventricular premature complexes. In the treated group, initially there were 7 horses with UAF and 5 horses with NAF. Following treatment, all horses had UAF. A reduction in distress was observed in all treated horses and no adverse effects were appreciated.
CONCLUSIONS: Detomidine and cooling reduced HR and the burden of complexes with abnormal morphology. This study supports the use of this protocol and wider adoption of this practice could improve safety and reduce adverse outcomes for distressed arrhythmic horses.