Assessment of P Wave Indices in Healthy Standardbred Horses

SIMPLE SUMMARY: Electrical activity of the heart is recorded using an electrocardiogram and represented as a series of waveforms. Measurements of the P wave component are used as non-invasive markers of remodelling and susceptibility to heart disease in humans. However, their usefulness has not been fully investigated in animals. The aim of this study was to measure P wave indices in healthy standardbred horses and investigate variables that might influence them. We found significant associations with exercise status as well as a positive correlation with exercise duration (number of years raced). These findings are similar to those reported in human athletes versus sedentary individuals. These changes are likely to be associated with the remodelling of the heart chambers that occurs with exercise training and may explain why these athletes are at increased risk of heart rhythm disturbances. ABSTRACT: P wave indices are used as non-invasive electrocardiographic markers of atrial remodelling in humans. Few studies have investigated their use in animals. The aim of this study was to measure P wave duration and P wave dispersion (Pd) in healthy standardbred horses and investigate variables that might influence these measurements. A 12-lead electrocardiogram was recorded at rest and P wave indices were calculated in 53 horses. A general linear model was used to investigate the main effects: age, bodyweight, sex, resting heart rate, presence of a murmur, exercise status and the number of years raced. There were significant associations with exercise status for both the maximum P wave duration and Pd, with both values being increased in strenuously exercising versus non-active horses. Furthermore, a significant moderate positive correlation was identified between the duration of exercise (number of years raced) and both Pmax and Pd. No other significant associations were identified. These findings are similar to those reported in elite human athletes versus sedentary individuals. The increases in these P wave indices most likely occur due to prolongation and heterogeneity in atrial conduction time, which are associated with structural and electrical remodelling, and may explain the increased risk of atrial fibrillation in athletic horses.