Sustained ventricular tachycardia: Role of the 12-lead electrocardiogram in localizing site of origin

The QRS morphology of the 12-lead ECG of 41 morphologically distinct ventricular tachycardias (VT) was correlated with their site of origin as determined by catheter and intraoperative mapping. Twenty-two VT patterns had a right bundle branch block (VT-RBBB) morphology and 19 a left bundle branch block (VT-LBBB) morphology. All VT-RBBBs arose in the left ventricle. All 16 VT-LBBBs in patients with coronary artery disease (CAD) arose from the LV at sites on or adjacent to the septum. Three VT-LBBBs in patients without CAD arose in the right ventricle. The 12-lead ECG could not precisely identify the site of origin in patients with CAD but could differentiate anterior from posterobasal regions, particularly in VT-LBBB. The ECG was less useful in localizing VT-RBBB because of overlapping patterns. General patterns that were useful in differentiating anterior from posterobasal sites of origin included: The presence of a q wave in leads 1 and V₆ was seen in VT-RBBB or VT-LBBB originating anteriorly but not in VT of posterobasal or posterior septal origin: R waves in leads 1 and V₁ to V₆ in VT-RBBB, and in leads 1, V₂, V₃ and V₆ in VT-LBBB were specific for a posterior origin, and not observed in VT of anterior origin; In VT-LBBB with a superior axis, a q wave in leads 1 and V₆ was specific for origin along the inferior aspect of the anterior septum; All VT-LBBB with an inferior and rightward axis originated from the superior aspect of the anterior septum. We conclude that although selected ECG features are useful in locating the origins of VT, precise localization is not possible by the ECG alone.