Detection of exercising ectopic atrial and ventricular beats using non-linear analysis of clinically normal racehorse electrocardiograms at rest or low-intensity exercise

Cardiac arrhythmias are common in healthy athletic horses and may lead to poor athletic performance or exercise-associated sudden death. Early detection of high-risk horses is an important goal of cardiovascular diagnostics. We hypothesised that non-linear analysis of electrocardiogram disorderliness can be used to identify horses exhibiting intermittent ectopic atrial and ventricular heart rhythm abnormalities at exercise using brief, artifact-free recordings of normal sinus rhythm electrocardiograms collected at submaximal heart rates. In a convenience prospective cross-sectional study, ambulatory electrocardiograms were recorded using the Televet 100 or II devices from 110 Thoroughbred or Standardbred racehorses during routine training. Acceptable quality 60 s electrocardiogram strips with stable heart rate (20-120 beats per minute) were identified automatically. Disorderliness of the electrocardiograms was estimated using Lempel-Ziv'76 and '78, and Titchener complexity, and Shannon, sample, and approximate entropy algorithms. Numerical estimates obtained by these algorithms were corrected to the heart rate. For the optimal performance recordings of 60-100 beats per minute should be used, with Lempel-Ziv '76 complexity, R peak and ends of S and T peaks as fiducial points. The receiver operating curve analysis has demonstrated the area under curve of 0.86 for this combination, indicating acceptable differentiation between cases and controls.