12-lead electrocardiogram (ECG) showing idiopathic left ventricular tachycardia

The typical ECG features of an idiopathic left ventricular tachycardia are QRS complexes that are relatively narrow (0.12 sec) and have a right bundle branch morphology (tall R waves in V1 and V2 and a terminal S wave in V5 and V6); the frontal plane axis is extremely leftward (negative QRS complexes in leads II, III, and aVF), suggesting a left anterior fascicular block. The tachycardia was localized to the inferior apical left ventricular septum, accounting for the extreme leftward axis.