Electrocardiographic Findings of Fascicular Ventricular Tachycardia Versus Supraventricular Tachycardia With Aberrancy

See Article by Michowitz et al Idiopathic ventricular tachycardia (VT) using the left posterior fascicle can be easily mistaken for supraventricular tachycardia (SVT) with right bundle branch block (RBBB) and left anterior fascicular block (LAFB), and distinguishing these entities via ECG analysis is essential for appropriate management. Discussion of treatment options and risks and procedural planning depend on accurate ECG diagnosis. Preparation for an approach in the event of noninducibility at electrophysiological study must also be considered—empirical slow pathway ablation might be considered in some patients with SVT and dual-atrioventricular nodal physiology,1–4 while a linear ablation strategy can be used for left posterior fascicular VT (LPF-VT).5 Numerous well-known ECG criteria have been developed to distinguish VT from SVT with aberrancy,6–9 though LPF-VT may lack some features typically ascribed to VT, by virtue of involvement of the conduction system. In fact, these criteria were recently shown to have reduced sensitivity for differentiating idiopathic VT in patients without structural heart disease from SVT with aberrancy.10 In 39 patients with idiopathic VT and a RBBB morphology, 79% received a correct diagnosis of VT based on conventional ECG criteria, while 21% were deemed indeterminate, all based on conflicting morphological criteria between leads V1 and V6. On the other hand, 14% of ECGs showing wide-complex SVT were misclassified as VT or felt to be indeterminate.In this issue of Circulation: Arrhythmia and Electrophysiology , Michowitz et al11 analyzed 183 ECG tracings with LPF-VT and 61 ECG tracings with RBBB and LAFB to determine distinguishing characteristics. The authors combined 144 ECG tracings of LPF-VT confirmed via electrophysiological study from the literature with 39 from their own ablation experience, …