Value of the 12-lead ECG to localize the origin of ventricular tachycardia

The 12-lead electrocardiogram (ECG) recorded during ventricular tachycardia (VT) remains a simple, universally available tool for VT localization. In idiopathic VT, QRS morphology and polarity often reflect the site of earliest activation and can facilitate targeted mapping. In patients with structural heart disease, however, the surface ECG predominantly represents the VT exit region rather than the critical diastolic isthmus; thus, its main clinical value lies in regionalization and in planning ablation strategy and access. A pragmatic stepwise interpretation integrating V1 morphology, precordial transition (V1-V6), and the frontal plane axis can localize VT in most cases, although accuracy is influenced by scar size, conduction abnormalities, antiarrhythmics, and variable exit sites. Emphasis is placed on estimating epicardial or intramural involvement using interval- and morphology-based criteria-especially in nonischemic cardiomyopathy-and on integrating ECG findings with cardiac scar imaging. Key disease-specific ECG patterns are highlighted. Electrocardiographic imaging, automated ECG analysis, and artificial intelligence (AI)-based localization approaches may further improve VT localization.