(E04) Exercising Electrocardiograms in Eventing Horses in the Field

Abstract: Background- Exercising arrhythmias can cause poor performance or sudden death.
Hypothesis/Objectives- To describe the association of exercising arrhythmias in field recordings with type, intensity and duration of exercise and presence of previous cardiac signs.
Animals- Cohort study of 36 Eventing horses in active competition
Methods- 571 recordings [median(IQR), 7(4-12)ECGs/horse] were evaluated and 167 were < 95% readable and discarded. Mixed-effects logistic regression tested the association of the dichotomous outcomes presence of arrhythmia (arrhythmia) and presence of complex arrhythmia (arrhyhmiacomplex). Duration of recording(mins) (duration), average heart rate(beats/min) (HRaverage) and peak heart rate(beats/min) (HRpeak) were set as the fixed effects. Analysis was confounded by exercise type and prior cardiac signs (horses enrolled after referral for cardiac evaluation) with horse id as the random effect. Mixed-effects Poisson regression analyzed number of premature complexes (n°PC) analogously.
Results- There was arrhythmia in 33.2% of the recordings, arrhyhmiacomplex in 5.7% and the n°PC was 0(0-1) [range 0-99PC/ECG]. 32.7% of the recordings were gallops, 23.8% flat sessions, 16.3% hacks, 15.1% jump-ing sessions, 5.2% cross-county schooling sessions, 4.7% trotting sessions and 2.2% cross-country compe-tition. HRpeak was (mean±SD) 169±35 and HRaverage 94±19. Increased likelihood of arrhythmia was associat-ed with duration (OR=1.022,CI[1.004,1.041],p=0.017) and HRpeak (OR=1.037,CI[1.019,1.055],p < 0.001. Risk of arrhyhmiacomplex was increased with HRpeak (OR=1.040,CI[1.017, 1.064],p=0.001) and cardiac signs (OR=6.157,CI[1.390,27.270],p=0.017). Increased n°PC was associated with duration (IRR=1.013,CI[1.009,1.017],p= < 0.001), HRaverage (IRR=1.033,CI[1.027,1.041],p < 0.001) and hacks (IRR=2.44,CI[1.079,5.539],p=0.0320). None of the horses developed cardiac signs during the study.
Conclusions and clinical importance- Intensity, duration, type of exercise and previous cardiac signs are relevant when evaluating exercising ECGs in Eventers.