Prevalence of exercise-associated arrhythmias in normal performing dressage horses.

Abstract: Exercise-associated arrhythmias are important differentials when evaluating poor performance sport horses. However, most studies of arrhythmias have been conducted in racehorses and therefore there is a paucity of knowledge concerning the prevalence and significance of exercise-associated arrhythmias in riding horses. Objective: The objective of this study was to examine the prevalence of arrhythmias, particularly supraventricular premature complex (SVPCs) and ventricular premature complex (VPCs), associated with exercise in normal performing dressage horses. Methods: In total, 21 normal performing dressage horses, aged 5-16 years (mean 9 years), were examined clinically and echocardiographically to detect the prevalence of valvular regurgitation. Electrocardiographic (ECG) examinations were performed during rest and during a standardised dressage exercise programme, as well as during recovery period 1 h after exercise. All ECG recordings were analysed for presence and frequency of arrhythmias and arrhythmias were correlated with HR. Mean HR for walk, trot, canter and for specific dressage movements, as well as maximum HR was calculated. Fisher's exact test was used to test for associations between arrhythmias, valvular regurgitation, age and gender. Results: SVPCs occurred rarely during rest, but occurred during exercise in 6 (28.6%), and in 13 (61.9%) horses during recovery period. Most horses had ≤ 3 SVPCs. Ventricular premature complex were seen in one horse, which developed twice during exercise. Mild valvular regurgitation was seen in 11 (52%) of the horses. No significant associations between arrhythmia and age, gender or valvular regurgitation were observed. Conclusions: Reference values for normal performing dressage horses are presented for the first time, demonstrating that arrhythmias occur infrequently during exercise and recovery. Maximum HR in dressage horses is low compared to both showjumping and racehorses. Studies of dressage horses with moderate to severe valvular regurgitation at rest or poor performance are needed to further elucidate the significance of cardiac arrhythmias.