Background: Atrial fibrillation (AF) is the most common arrhythmia affecting performance in horses. However, no previous studies have quantified the performance reduction in horses suffering from AF.
Objectives: To quantify the effect of AF on maximum velocity (Vmax ), maximum heart rate (HRmax ), heart rate recovery (T100 ), hematologic parameters and development of abnormal QRS complexes.
Animals: Nine Standardbred trotters.
Methods: Two-arm controlled trial. Six horses had AF induced by means of a pacemaker and 3 served as sham-operated controls. All horses were subjected to an exercise test to fatigue before (SET1) and after (SET2) 2 months of AF or sham. The Vmax and HRmax were assessed using a linear mixed normal model. Abnormal QRS complexes were counted manually on surface ECGs.
Results: Atrial fibrillation resulted in a 1.56 m/sec decrease in Vmax (P < .0001). In the AF group, HRmax ± SD increased from 226 ± 11 bpm at SET1 to 311 ± 27 bpm at SET 2. The AF group had higher HRmax at SET2 compared with controls (P < .0001), whereas no difference between the control and AF groups was observed at SET1 (P = .96). Several episodes of wide complex tachycardia were observed during exercise in 3 of the AF horses during SET2.
Conclusions and clinical importance: Atrial fibrillation resulted in a significant reduction in performance, an increase in HR and development of abnormal QRS complexes during exercise, which may be a risk factor for collapse or sudden cardiac death.
Keywords: arrhythmia; atrial fibrillation; cardiology; exercise; heart rate; horse; performance.
Copyright © 2018 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.