# Seasonal Trends in Cardiac Troponin I Concentration and Creatine Kinase and Aspartate Aminotransferase Enzyme Activity in Relation to Myocardial Velocity Rates in Eventing Horses

## TL;DR

This study tracks heart and muscle stress in eventing horses during a competition season, finding that blood tests and heart ultrasounds can detect overexertion.

## Contribution

The study identifies a novel correlation between cardiac troponin I levels and early diastolic myocardial velocity in eventing horses.

## Key findings

- Blood levels of CK, AST, and cTnI showed seasonal variation and partial normalization after exercise.
- Early diastolic myocardial velocity (Em) correlated with cTnI levels, suggesting sensitivity to myocardial injury.
- Biomarkers and echocardiography can detect subclinical fatigue in high-performance horses.

## Abstract

In this study, eventing horses were monitored over the course of a competition season. This study examined the extent to which their skeletal and cardiac muscles were stressed by training and competition. After riding, creatine kinase (CK) and aspartate aminotransferase (AST), as well as cardiac troponin I (cTnI), levels rose briefly but mostly returned to normal. Echocardiographic measurements demonstrated that myocardial velocities remained largely stable but showed slight seasonal fluctuations. A significant correlation was found between cTnI levels and early diastolic myocardial velocity (Em). We conclude that blood tests and cardiac ultrasound can be used to determine whether a horse is overexerting itself. Therefore, regular check-ups help to better protect the health and performance of horses.

This study examines seasonal changes in muscle and heart parameters in eventing horses over the course of a competition season. Blood levels of the enzymes creatine kinase (CK) and aspartate aminotransferase (AST) as well as the heart muscle-specific concentration of cardiac troponin I (cTnI) were measured before (pre), 30 min (p30) and 24 h (p24) after competitions. Creatine kinase (CK: median pre-competition = 175 U/L, 30 min post = 221 U/L, 24 h post = 140 U/L), aspartate aminotransferase (AST: pre = 319 U/L, p30 = 335 U/L, p24 = 333 U/L), and cardiac troponin I concentration (cTnI: pre = 0.006 ng/mL, p30 = 0.011 ng/mL, p24 = 0.007 ng/mL) exhibited partial normalization by 24 h post-exercise but at the same time demonstrated significant seasonal variation (p < 0.001). Echocardiographic assessments revealed sustained high-level myocardial velocities, with occasional modest seasonal declines. A significant correlation was identified between cTnI levels and early diastolic myocardial velocity (Em) (Spearman’s Rho: pre-exercise 0.323, Rho p30: 0.357), whereas a negative correlation was manifest at 24 h (Spearman’s Rho = −0.300). These findings suggest a heightened sensitivity of diastolic myocardial velocity to myocardial injury. Given that diastolic dysfunction frequently constitutes an early manifestation of myocardial compromise, our results underscore the utility of biomarkers alongside myocardial velocity measures as valuable tools for the early detection of subclinical fatigue in high-performance sport horses.