Performance horses as a model for exercise-associated cardiac arrhythmias and sudden cardiac death.

This paper reviews the myocardial substrate of horses relative to that of humans and discusses the utility of performance horses as a model of exercise-associated cardiac arrhythmias and sudden cardiac death in athletes. The coronary circulation is similar between the species while coronary artery anomalies and myocardial bridging appear to only be associated with athletic mortality in human athletes and not in performance horses. There are subtle differences in the histology of the sinus and atrioventricular nodes, of unknown clinical significance, while the His bundle is more highly innervated in horses. The equine Purkinje network is much more extensive, contributing to a difference in the mean electrical axis between horses and humans. Differences in ion channel expression have been reported, although they are poorly characterized, and are of unknown clinical significance. However, horses may be a particularly good model to investigate the function of Kv1.5 due to its spontaneous ventricular expression, which is lacking in human ventricles. Similarities in cardiac structure, coronary vasculature, and ability to exercise at high levels makes performance horses a good model to investigate exercise-associated cardiac arrhythmias and sudden cardiac death in athletes. However, differences in myocardial substrate should be taken into consideration when designing studies and interpreting results.