Effect of induced chronic atrial fibrillation on exercise performance in Standardbred trotters.

Abstract

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 (V), maximum heart rate (HR), heart rate recovery (T), 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 Vand HRwere 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 V(P&#x2009;<&#x2009;.0001). In the AF group, HR&#x2009;&#xb1;&#x2009;SD increased from 226&#x2009;&#xb1;&#x2009;11 bpm at SET1 to 311&#x2009;&#xb1;&#x2009;27 bpm at SET 2. The AF group had higher HRat SET2 compared with controls (P&#x2009;<&#x2009;.0001), whereas no difference between the control and AF groups was observed at SET1 (P&#x2009;=&#x2009;.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.