Evolution of Echocardiographic Dimensions with Age and Training in Young Endurance Horses

Introduction Increasing cardiac dimension with endurance training is well known in adult athletes. However, adaptation of the heart to training in growing Arabian type horses is less well documented. Methods During the national finals for young endurance horses, standardized echocardiographic examinations were performed before the races by two experienced examiners. In 2011 left ventricle (LV) was assessed in 74 horses aged 4-years (18), 5-years (33) and 6-years (23). In 2012 left atrial (LA) dimensions and the great heart vessels were measured in 122 horses aged 4-years (32), 5-years (40) and 6-years (50). Data were normally distributed; age groups and gender were compared by one-way ANOVA (Holm-Sidak test for multiple comparisons, significance P<0.05); relationships between echocardiographic dimensions and body weight (BWT) were assessed by linear regressions. Results BWT was highest in 5-year old horses. LV dimensions increased with age, but for most measurements the difference was significant only for the group of 6-year old horses. The stroke volume (SV) increased (P = 0.0016) and the heart rate decreased (P = 0.06) with increasing age, leading to a constant cardiac output in all age groups. There was a weak relationship between BWT and SV. Two dimensional LA measurements increased between 4 and 5 years but remained constant between 5 and 6 years. LA area measurements and LA functional indices showed no evolution between the groups. Aortic dimension increased with age but pulmonary artery dimension showed no such increase. No influence of gender on echocardiographic dimensions and function could be found. Conclusions Great heart vessels, LA and LV dimensions showed different growth patterns between 4 and 6 years of age. Ethical Animal Research Procedures were approved by the Ethics Committee for the Alfort Veterinary School and the University of Paris-Est under number 12/07/11-1; owner informed consent was obtained. Sources of funding: National Studs (IFCE), The Eperon Funds and the Arabian Horse Association (ACA). Competing interests: none.