Prevalence of cardiac arrhythmias and R-R interval variation in healthy Thoroughbred horses during official Chuckwagon races and recovery.

The research article examines the prevalence of heart arrhythmias and their severity in healthy racing Thoroughbred horses. These arrhythmias were tracked during Chuckwagon races and were used to understand the normal heart beat-to-beat variability during extreme exercise conditions.

Objective and Methodology

• The study aimed to better understand heart arrhythmias in healthy Thoroughbred horses during Chuckwagon races. Additionally, it sought to establish the normal beat-to-beat (R-R) variability during supramaximal exercise, which is exercise that is more intense than the body’s capacity to provide oxygen to the muscles.
• The researchers used an Electrocardiograph (ECG) to record the heart activity of 82 Thoroughbred horses during pre-race, race, and active recovery periods.
• These ECG recordings were then analyzed for heart abnormalities and the mean percent R-R deviation. Additionally, blood samples were taken from the horses to measure the plasma lactate and high-sensitivity troponin (hs-cTnT), markers typically used to assess overexertion and heart muscle damage, respectively.

Findings

• Of the 52 ECGs that were included in the analysis, arrhythmias were observed in 48 horses (that’s 92% of the racehorses).
• During the race, 92% of the horses had arrhythmias, with 81% being supraventricular premature complexes (SVPCs – abnormal heartbeats originating from the upper part of the heart) and 33% being ventricular premature complexes (VPCs – abnormal heartbeats originating from the lower part of the heart).
• In the active recovery phase, 58% of the horses still exhibited arrhythmias. SVPCs and VPCs accounted for 56% and 15% of these cases respectively.
• None of the horses showed abnormal levels of hs-cTnT, suggesting that there wasn’t significant heart muscle damage during the race.
• The high lactate measurements indicate that the horses were indeed exercising beyond their maximal aerobic capacity, confirming the supramaximal nature of the exercise.
• The variation in the R-R interval, which represents the time between consecutive heartbeats, was also found to be greater during the race compared to pre-race and recovery periods. This suggests that the horses’ heart rates became more irregular during the race, likely due to the high-intensity exercise.

Conclusions

• The prevalence of SVPCs and VPCs suggests that they are common in healthy Thoroughbred horses during high-intensity activities such as Chuckwagon racing.
• The significant R-R interval variability observed in the study indicates that the horses experienced more heart rate irregularities during the race than previously thought.