Rapid screening for cardiac arrhythmias in competition draft horses

Cardiac arrhythmias may cause decreased performance and sudden death during exercise. Our objectives were: (1) to determine prevalence of unrecognised arrhythmias in a population of competition draft horses by performing short duration screening electrocardiograms (ECGs) at rest; and (2) to assess utility of a commercial handheld device for recording equine ECGs. Owners or trainers of 244 draft horses (age 0.5-16 years), including 82 Percherons, 69 Belgians, 69 Clydesdales, 11 Belgian mules, 8 Shires, and 5 Percheron mules, were queried to determine signalment, performance history, and known arrhythmias. All horses were auscultated for 30 s and ECGs were obtained in 204 horses using a handheld recording device (AliveCor®). ECGs were reviewed for quality and used to determine heart rate (HR) and rhythm. When ECG tracing quality permitted, PQ and QT intervals were also measured. ECGs displaying RR intervals adequate for HR determination and rhythm assessment were recorded from 161 horses (79%) while tracings with consistent P waves, QRS complexes, and T waves were recorded from only 47 horses (23%). Four arrhythmias were detected by both auscultation and ECG: atrial fibrillation (1), premature complexes (1), and second-degree atrioventricular block (2). None of these horses had a history of poor performance or previous recognition of an arrhythmia. The prevalence of unrecognised, and potentially clinically significant, arrhythmias in draft horses at rest appears to be low (2/244; 0.8%, 95% confidence interval 0.1-2.9%). Longer recordings at rest, as well as recordings during and immediately after exercise, would likely have revealed a higher prevalence of arrhythmias.