Retrospective review of atrial fibrillation in Standardbred racehorses at a tertiary care facility in Atlantic Canada.

Atrial fibrillation (AF) is the most clinically relevant cardiac arrhythmia identified in the Standardbred racehorse. However, there is limited literature regarding athletic ability in Standardbred racehorses following AF conversion. To investigate this issue, the objectives of this review were to: i) determine the success rate in using quinidine sulphate to treat AF in a population of hospitalized equine patients in Atlantic Canada between January 2008 and December 2019; and ii) measure return to athletic ability (using racetrack earnings and top-3 finishes) following cardioversion with quinidine sulphate in a population of Standardbred racehorses. Overall, 73% (16/22) of AF instances in this study were successfully treated with enteral quinidine sulphate. No significant difference was detected in racetrack earnings or number of top-3 finishes for each horse that raced at least 5 times pre- and post-conversion. Key clinical message: To the authors' knowledge, this is the first published review to assess the athletic ability of Standardbred racehorses following cardioversion with enteral quinidine sulphate. Based on the current information, it does not appear that treatment of AF with quinidine sulphate affects future athletic performance in horses that achieved cardioversion.