Postdoctoral Associate Department of Veterinary Clinical Sciences, University of Minnesota, Minnesota, USA Saint Paul, MN, United States
Abstract: BACKGROUND Complex arrhythmias (CA) are common in racehorses with and without poor performance making interpretation challenging. HYPOTHESIS/OBJECTIVES To determine whether CA in one exercising ECG are associated with lifetime racing performance. ANIMALS ECGs collected over 6 months from 75 Thoroughbreds in race-training. METHODS ECGs during and 2 minutes after breezing were analyzed. When ≥1 ECG was available/horse, the ECG with more premature complexes (PCs) was used. Starts, placing third or better, placing below third, the highest Equibase speed figure and total and average earnings per start over the lifetime of the horse were obtained from Equibase.com (starts were excluded due to multicollinearity). Logistic multivariable regression (covariates: age, sex) was performed using R. Significance was p< 0.05. RESULTS Mean (SD) peak heart rate was 215+7/min. 25/75 horses had CA, and 64/75 horses had ≥1 PC during exercise. Sex, speed, peak heart rate, and age were not significantly different between horses with and without CA (p>0.1). Performance metrics analyzed were not associated with CA in one exercising ECG (p>0.2). CONCLUSIONS AND CLINICAL IMPORTANCE These preliminary results suggest that CA in one exercising ECG are not associated with common lifetime performance metrics. This helps infer potential mechanistic and performance implications. For example, CA may not be associated with performance or intrinsic to the horse (instead, dependent on external factors), CA may be sporadic in an individual, or training cardiac rhythm is not representative of racing rhythm. These potential explanations remain speculative; work is ongoing to evaluate associations between arrhythmias and future/current performance, and safety.
