Delta (Δ) 12-lead electrocardiography and vectorcardiography to identify the origin of focally induced atrial and ventricular premature depolarizations in horses

BACKGROUND: Cardiac arrhythmias are common in horses, but their clinical and prognostic relevance remains poorly defined. Despite the importance of localization for diagnosis and treatment, noninvasive methods to identify arrhythmogenic foci are limited. HYPOTHESIS/OBJECTIVES: Evaluate the ability of delta (Δ) 3- and 12-lead ECGs and 2-dimensional (2D) and 3-dimensional (3D) vectorcardiography (VCG) to identify the site of origin of focally induced atrial and ventricular premature depolarizations in horses. ANIMALS: Eight healthy horses underwent 2 electrophysiological studies, 1 standing, and 1 under general anesthesia. METHODS: Premature atrial and ventricular complexes were induced by intracardiac pacing at 29 anatomical sites. Simultaneous Δ 12-lead ECG and VCG recordings were obtained. Mean vector directions were analyzed, and classification accuracy was assessed at the chamber, regional, and site-specific levels. RESULTS: Distinct pacing sites produced reproducible and location-specific activation patterns. For differentiating left- from right-sided origins, 3D-VCG had 99% and 82% accuracies for ventricular and atrial origins, respectively. The simplified Δ-based 2D-VCG also showed strong performance on the chamber level, with accuracies of 94% and 78%, respectively. Accuracy was lower for fine-grained intra-chamber localization, especially in the atria. CONCLUSIONS AND CLINICAL IMPORTANCE: Although 3D-VCG offers superior spatial resolution, 2D-VCG provides a good balance between diagnostic accuracy and practical applicability, especially for left- vs right-sided localization. Combined Δ 12-lead ECG and VCG enables accurate, noninvasive chamber-level localization of arrhythmia origins in horses. Standardized application in larger cohorts with naturally occurring arrhythmias may support targeted ablation strategies and improve arrhythmia management and sudden cardiac death risk stratification.