Signal-averaged electrocardiography in horses: characteristics of ventricular late potentials in healthy Thoroughbreds and horses with cardiac abnormalities

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.