Any tachycardic rhythm with a left or right bundle branch block that is NOT ventricular tachycardia is considered "supraventricular tachycardia with aberrancy". This would even include sinus ...

If the QRS complex is widened and downwardly deflected in lead V1, a left bundle branch ... tachycardia is helpful to make this distinction. The ECG strip below shows normal sinus rhythm, then ...

One can examine the initiation and termination of tachycardia for clues as to ... ventricular contractions [PVCs], intermittent bundle branch block, or changes in cycle length).