Cardiac responses to training in 2-year-old thoroughbreds: an echocardiographic study.

The research article analyzes the cardiac responses of two-year-old thoroughbred racehorses as they go through flat-race training, using M-mode echocardiography, a type of ultrasound imaging, to measure changes in the horses’ heart structures and functions.

Methodology

In the study, seven 2-year-old Thoroughbreds underwent an M-mode echocardiography exam before starting flat-race training and again 18 weeks later. By this point, all the horses were either racing regularly or had reached full racing fitness.

• The echocardiography used a 2.5 MHz annular phased array ultrasound transducer and a Vingmed 800 Supervision echocardiograph.
• Images were taken of the left ventricle of the heart from the right side of the horse’s chest.
• Specific heart measures – such as the internal diameter of the left ventricle in diastole (when the heart relaxes) and systole (when the heart contracts), left ventricular fractional shortening (%FS), and left ventricular ejection fraction (EF) – were studied.

Findings

• After 18 weeks of training, significant changes were observed in several heart measurements. The left ventricular internal diameter increased significantly with a mean increase of 33% (diameter increased from 11.38 cm to 12.16 cm).
• The calculated muscle mass of the left ventricle also significantly increased.
• Notably, the study found reductions in both the %FS and EF, indicating changes in the heart’s pumping efficiency.
• Despite these changes, the horses’ body weight remained consistent throughout the study.

Interpretations

• The significant increase in relative wall thickness across all horse subjects suggests that a type of heart enlargement, known as eccentric cardiac hypertrophy, occurs in response to flat-race training.
• The post-training relative wall thickness value of 0.45 is comparable to the values found in human athletes who participate in power and endurance disciplines, implying similar heart adaptations across different species and athletic specialties.

The study therefore concludes that flat-race training induces significant alterations in young racehorse cardiac morphology and function, similar to the adaptations seen in human endurance and power athletes.