Sudden death in horses, often attributed to lethal arrhythmias, poses significant welfare and economic risks, yet its prediction remains challenging. This study aimed to characterize ventricular micro-potentials using signal-averaged electrocardiography (SAECG) and evaluate their potential for assessing sudden death risk. High-resolution orthogonal X-, Y-, and Z-lead ECGs were recorded in 24 healthy Thoroughbreds (aged 2–31 years), one horse with bupivacaine-induced myocardial injury, and three horses with persistent pathological murmurs. SAECG parameters, including filtered QRS duration (fQRS), LAS40, RMS40, and RMS50, were analyzed from the vector magnitude waveform. In healthy horses, fQRS showed a significant positive correlation with age, with older horses exhibiting a significantly longer fQRS and LAS40 and lower RMS40 and RMS50 compared with younger horses, likely reflecting age-related myocardial fibrosis. The experimental myocardial injury model, characterized by histopathologically confirmed necrosis, resulted in a prolonged fQRS and LAS40 and decreased RMS40 and RMS50, consistent with the development of ventricular late potentials. Conversely, horses with persistent cardiac murmurs showed SAECG parameters within the range of healthy horses, indicating that valvular abnormalities alone do not significantly affect intraventricular conduction. These findings demonstrate that SAECG can effectively detect ventricular micro-potentials and reflect structural myocardial changes such as necrosis and fibrosis in horses. Consequently, SAECG analysis appears to be a promising non-invasive tool for screening the risk of lethal arrhythmias and sudden death in equine clinical practice, especially when combined with other diagnostic modalities.

The aim of this study was to pilot the assessment of sport predispositions in warmblood horse breeds, both domestic and foreign, and to evaluate factors influencing their performance. Data from 293 horses (725 starts) competing in national Grand Prix events with obstacle heights of 140–145 cm were analysed using general mixed models. The origins of Polish Halfbred Horses were examined, and correlations between results in the Young Horse Championships and later Grand Prix performance were assessed. Results showed that performance is significantly influenced by genetic factors, such as breed and sex, and by the random effect of the rider. Stallions, German breeds, and horses aged 15–18 years performed best. Analysis of breed distribution and pedigrees revealed the growing importance of German, Belgian, and Dutch horses in national competitions. Positive correlations between early evaluation and later performance support the use of these data in assessing utility and breeding value. Despite low repeatability, competition results remain a valuable indicator of performance and breeding potential.