Cardiac arrhythmias in clinically healthy showjumping horses

P>Reasons for performing study: Electrocardiographic reference values of clinically normal horses during exercise are a prerequisite when evaluating horses with poor performance or horses presented with cardiac abnormalities (e.g. valvular regurgitation). No published studies have reported cardiac rhythms of clinically normal showjumping horses. Objectives: To demonstrate the feasibility of obtaining exercise electrocardiogram (ECG) in normal horses during showjumping and also to document the prevalence and frequency of arrhythmias in association with exercise. Methods: Thirty-four healthy showjumping horses aged 4-13 years (mean 7.5 years) underwent clinical examination and resting echocardiography. Modified chest lead ECG examinations were performed during rest, during a standardised showjumping course, as well as for the following 45 min recovery. All ECG recordings were analysed for presence and frequency of arrhythmias. Results: Six horses (17%) were excluded due to ECG recordings of poor diagnostic quality. Echocardiography demonstrated that 11 (39%) horses had one or more mild or moderate valvular regurgitations, but no associations were found between valvular regurgitation and arrhythmias. Supraventricular premature complexes (SVPCs) were found in 9 (32%) horses at rest, 25 (89%) during exercise and 15 (54%) during recovery. Only few arrhythmias occurred in each horse (< 9 SVPCs/horse); however, one horse had 13 single SVPCs during exercise and another developed 41 SVPCs during recovery. SVPCs occurred typically at low HR (40-98 beats/min). Ventricular premature complexes (VPCs) was demonstrated in 5 (18%) horses during exercise and 2 (7%) during recovery, with < 2 VPCs/horse. Conclusions: It is possible to obtain good quality ECG during showjumping. Reference values for normal performing showjumping horses are presented for the first time and showed a high prevalence of SVPCs both during and after exercise, but few VPCs. Potential relevance: Normal reference values enable future studies of cardiac function in showjumping horses presented with poor performance and provide valuable information for veterinary practitioners in the field.