Vectorcardiography at rest and during exercise in horses using the Delta (Δ) 12-lead configuration

BACKGROUND: Twelve-lead electrocardiography (ECG) is essential in human cardiology but remains poorly investigated in equine medicine due to a lack of standardization and inconsistent findings. HYPOTHESIS/OBJECTIVES: Describe the normal vectorcardiogram (VCG) variation in horses at rest and during exercise using Delta 12-lead ECG, including repeatability and intra- and interobserver variations. ANIMALS: One hundred two healthy Warmblood horses, aged 3-20 years, were examined at rest, of which 30 also during exercise. METHODS: Prospective, observational study. Electrocardiograms were recorded using a Δ 12-lead configuration with precordial electrodes positioned at atrial and mid-ventricular levels. Data were processed with custom MATLAB scripts to generate mean ECG and VCG patterns. Repeatability and intra- and interobserver reliability were assessed using cross-correlation and circular statistics in R. RESULTS: Electrocardiographs were obtained during sinus rhythm. The Δ 12-lead configuration and derived VCG showed high repeatability, with significant intra- and interobserver reliability at rest and during exercise. The mean directions of the P wave and the QRS complex were similar during rest and exercise. The P loop and the initial QRS showed leftward and caudoventral orientation on VCG, while the remainder of the QRS loop was oriented in a dorsocranial direction and slightly to the left or right. CONCLUSIONS AND CLINICAL IMPORTANCE: The Δ 12-lead configuration and the derived VCG show consistent patterns during sinus rhythm, both at rest and during exercise. These features hold promise for improving the diagnosis of atrial and ventricular arrhythmias, particularly because the orthogonal XYZ-leads offer a format that is easier for practicing veterinarians to interpret.