American researchers ran tests on a group of Thoroughbreds before and after racing to get important reference data in a step toward being able to identify horses with heart problems that could cause sudden death.
Thirty Thoroughbreds, aged 3 to 6, were enrolled in the study, all of whom raced at two different weekends at California’s Santa Anita Park after receiving doses of the diuretic furosemide.
Joshua Stern and his colleagues said exercise-induced cardiac fatigue and irregular heartbeats are well described conditions identified in top human athletes. They tend to increase in frequency with intensity and duration of exercise.
However, an understanding of normal pre- and post-race cardiac assessment values are needed to identify them.
Unexplained sudden cardiac death is of great interest in the racing industry, they said.
Sudden deaths amongst thoroughbred racehorses have increased, particularly in California over the past five years.
“Arrhythmic or cardiac causes of these incidences is speculated and warrants further attention.”
Understanding physiological values in this population is important if any meaningful cardiac screening practices are to be proposed, they say.
The University of California, Davis, study team set out to characterize selected measures of cardiac function, electrophysiologic parameters, and biochemical markers of heart dysfunction both before and immediately after high level racing in Thoroughbred horses receiving furosemide.
In doing so, they created pre- and post-race reference values in order to make recommendations on possible screening practices in the future. Each horse served as its own control for the study.
Physical exams, electrocardiograms, and echocardiograms (an ultrasound examination) were performed before racing, which was before they had received their furosemide. They were re-examined with the same protocols 30–60 minutes after the race.
Blood samples were obtained at the pre-race exam, the post-race exam, and at four hours and 24 hours after the race. The samples were assessed for electrolytes, the volume percentage of red blood cells, cardiac troponin I levels (which can be used as a biomarker of cardiac injury), and partial pressure carbon dioxide values.
They traversed their findings, noting that heart rate was significantly increased post-race, with a median difference of 49 beats per minute.
No irregular heartbeats were noted during ECG assessment. Following the race, an increase in the number of horses showing regurgitation through the aorta and atrioventricular valves was noted.
Systolic function increased significantly, with an average difference of 7.9%.
Cardiac troponin I was not different at the pre-race exam and at the first post-race time point, but was significantly increased after four hours. It had returned to baseline value by the 24-hour mark. They believed this was a transient release of troponin and that permanent or more long-lasting damage to the heart muscle had not occurred.
“No horses in our study had detectable evidence of exercise-induced cardiac fatigue (EICF) and no sudden death events were noted,” the study team reported in the journal, BMC Veterinary Research.
“Identification of horses that demonstrated EICF or sudden death would provide highly valuable information in these conditions.
“However, the low incidence of EICF or sudden death suggests that designing a study to identify this condition would require massive sample size which was not feasible within the scope of this work.
“The use of the reference ranges established in this study can however be used to help to early detect horses at high risk of EICF in future races and studies.”
The study comprised Catherine Gunther-Harrington, Rick Arthur, Krista Estell, Beatriz Martinez Lopez, Alexandra Sinnott, Eric Ontiveros, Anita Varga and Stern.
Prospective pre- and post-race evaluation of biochemical, electrophysiologic, and echocardiographic indices in 30 racing thoroughbred horses that received furosemide
Catherine T. Gunther-Harrington, Rick Arthur, Krista Estell, Beatriz Martinez Lopez, Alexandra Sinnott, Eric Ontiveros, Anita Varga and Joshua A. Stern.
BMC Veterinary Research 2018 14:18 https://doi.org/10.1186/s12917-018-1336-0