Evaluation of Cardiac Arrhythmias before, during, and after Treadmill Exercise Testing in Poorly Performing Standardbred Racehorses

SIMPLE SUMMARY: In sport horses, cardiovascular problems, such as arrhythmias, can cause poor performance. However, only the role of atrial fibrillation and severe bradyarrhythmias on athletic performance has been well established. On the other hand, the significance of other arrhythmias, such as supraventricular and ventricular premature complexes, is still not well defined. The present study reports on the prevalence of cardiac arrhythmias during maximal treadmill exercise in poorly performing Standardbreds, and investigates the possible relationship of demographic, cardiac, and performance indices on premature complexes. The results showed weak evidence of the dependence of premature complexes on minimum heart rate, and a tendency for the occurrence of premature complexes to increase with aging and increasing maximum lactate concentration. Our results suggest that premature complexes are frequent in poorly performing Standardbred racehorses, but further studies are necessary to clarify their role and clinical significance. ABSTRACT: The incidence of significant arrhythmias in sport horses and knowledge about their exact influence on athletic performance need to be clarified. The aims of the present study are to report the prevalence of cardiac arrhythmias during maximal treadmill exercise in poorly performing Standardbreds, and to investigate the possible relationship of demographic, cardiac and performance indices on premature complexes (PCs). Electrocardiographic Holter recordings before, during and after treadmill exercise testing of 158 poorly performing Standardbreds were analyzed retrospectively. Fifty horses did not have any type of arrhythmia. One hundred and eight horses had at least one type of arrhythmia, such as sinus arrhythmia (8.2%), sinoatrial block (3.2%), second-degree atrioventricular block (33.5%), supraventricular PCs (7.6%), and ventricular PCs (48.1%). A multiple regression analysis showed weak evidence that the occurrence of premature complexes decreases as the minimum heart rate increases, and a tendency for these arrhythmias to increase with increasing age and maximum lactate concentration. Our results suggest that PCs are frequent in poorly performing Standardbred racehorses, but further studies are necessary to clarify their role and clinical significance.