Incidence, recurrence, and outcome of postrace atrial fibrillation in Thoroughbred horses

Abstract

Background: Atrial fibrillation (AF) impacts performance and horse and jockey safety. Understanding the outcomes of AF identified postrace will better inform regulatory policy. Hypothesis/Objectives: To investigate the outcomes after episodes of AF identified postrace and determine whether affected horses are at increased risk of additional episodes compared to the general racing population. Animals: Total of 4684 Thoroughbred racehorses. Methods: Race records for Thoroughbred horses racing in Hong Kong from 2007 to 2017 were reviewed. Horses that performed below expectation were examined by cardiac auscultation and ECG. Incidence and recurrence of AF were compared between horses with and without a history of AF and between horses with paroxysmal and persistent episodes using Fisher's exact test. Results: There were 96 135 race starts during the study. Atrial fibrillation was identified in 4.9% of horses, with an overall incidence of 2.7 episodes per 1000 starts. The incidence of AF in horses after any previous episode (12.8 per 1000 starts) was higher than for horses with no previous episode (2.4 per 1000 starts; odds ratio [OR], 5.3; 95% confidence interval [CI], 3.8-7.6). Recurrence was seen in 64% of horses previously treated for persistent AF, which was higher than recurrence in horses with paroxysmal AF (23%; OR, 5.9; 95% CI, 1.6-21.2). Median duration between episodes was 343 days (range, 34-1065). Conclusions and Clinical Importance: Thoroughbreds are at increased risk of recurrent AF after both paroxysmal and persistent episodes, but the duration of time between episodes varies widely. These findings support a substantial burden of AF among individual Thoroughbred racehorses.

Application of an electrocardiography device (iECG) for heart rhythm analysis after exercise in Thoroughbred horses

“…Both observers were blinded to the results of automated rhythm classification. Previously published criteria 5,13,27 were used determine the rhythm abnormality. Each observer independently classified the heart rhythm as SR, SR with ectopy or AF.…”

“…A trial fibrillation (AF) is the most commonly identified performance limiting arrhythmia in racehorses. [1][2][3][4][5] The estimated frequency of AF occurring after racing varies amongst jurisdictions from 0.2 to 2.7 per 1000 starts. 1,[3][4][5] AF identified after exercise is typically paroxysmal (PAF), converting to sinus rhythm (SR) within 72 h. [1][2][3][4][5][6] In addition to AF, other arrhythmias occurring immediately post exercise can be very short lived and challenging to capture in the absence of wearable technology.…”

“…[1][2][3][4][5] The estimated frequency of AF occurring after racing varies amongst jurisdictions from 0.2 to 2.7 per 1000 starts. 1,[3][4][5] AF identified after exercise is typically paroxysmal (PAF), converting to sinus rhythm (SR) within 72 h. [1][2][3][4][5][6] In addition to AF, other arrhythmias occurring immediately post exercise can be very short lived and challenging to capture in the absence of wearable technology. 7 Cardiac arrhythmias are reliably identified by trained practitioners through auscultation; however, ECG is needed to document and definitively classify the heart rhythm.…”

“…8 Recently, changes in QRS conformation have been identified concurrently in horses with AF and elevated heart rates (HRs). 5,[9][10][11] Such complexes with abnormal conformation could reflect more widespread cardiac pathology and increased concern for safety. 12,13 The AliveCor Kardia iECG device is a single lead bipolar ECG, which is recorded through a smartphone app.…”

Highlights of recent clinically relevant papers

“…In this study Laura Nath and co‐workers in Australia and Hong Kong investigated the outcomes after episodes of atrial fibrillation (AF) identified post‐race and determined whether affected horses are at increased risk of further episodes .…”