Abstract
REASONS FOR PERFORMING STUDY
There are few data available to determine the effect of training on cardiac valve function.
OBJECTIVES
To investigate the effect of commercial race training on right ventricular (RV) and tricuspid valve function in an untrained group of National Hunt Thoroughbreds (TB).
MATERIAL AND METHODS
Cardiac auscultation, guided M-mode echocardiography of the RV, and colour flow Doppler (CFD) tricuspid valve and right atrium were performed in 90 TB horses (age 2-7 years) 1998-2003. Forty horses were examined at least once and 48 horses were examined on at least 2 occasions. Examinations were then classified as: i) before commencement of race training, ii) after cantering exercise had been sustained for a period of 8-12 weeks and iii) at full race fitness. Tricuspid valve regurgitation (TR) murmurs were graded on a 1-6 scale and CFD echocardiography TR signals were graded on a 1-9 scale. Right ventricular internal diameter (RVID) in diastole and systole (RVIDd and RVIDs) was measured by guided M-mode. Associations between continuous RVID and TR measures and explanatory covariates of weight, age, heart rate, yard and stage of training were examined using general linear mixed models with horse-level random effects.
RESULTS
On average, RVIDd and RVIDs increased by 0.08 and 0.1 cm, respectively, per year increase in age (P = 0.1 and 0.02) and by 0.3 and 0.4 cm, respectively between pretraining and race fitness (P = 0.07 and 0.005). Tricuspid regurgitation score by colour flow Doppler increased by 0.6/year with age (P<0.0001) and by 1.8 between pretraining and race fitness (P<0.0001). No significant associations were found between any outcomes and weight, heart rate and training yard. Due to the high level of colinearity between age and training, multivariable models including both terms were not interpretable.
CONCLUSIONS AND CLINICAL RELEVANCE
Athletic training of horses exerts independent effects on both severity and prevalence of tricuspid valve incompetence. This effect should therefore be taken into account when examinations are performed. Dimensions of RV increase with age and training in TB horses in a manner that appears to be similar to that of the LV.
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