[Ventricular tachycardia masquerading as supraventricular tachycardia]

To distinguish supraventricular tachycardia with aberrancy from ventricular tachycardia is sometimes difficult. It seems to be easy to distinguish the two forms in patients with preexisting bundle branch block: if the QRS morphology during tachycardia is identical to those during at rest the tachycardia is supraventricular, if different, ventricular. We present two cases with preexisting bundle branch block and wide complex tachycardia whose QRS morphologies were almost same to those during normal rest rhythm. The atrioventricular dissociation and the response to adenosine and lidocaine strongly suggests ventricular tachycardia. In these cases ventricular tachycardia masqueraded as supraventricular tachycardia and the identical QRS morphology with the preexisting bundle branch block may suggest a misdiagnosis of supraventricular tachycardia.