Pre-excited tachycardia: Atrial tachycardia with a bystander left lateral accessory pathway

Introduction Wide complex tachycardias have a broad differential diagnosis including ventricular tachycardia (VT), antidromic reciprocating tachycardia (ART), supraventricular tachycardia (SVT) with aberrancy, atrial tachycardia (AT) or atrioventricular nodal reentry tachycardia (AVNRT) with a bystander accessory pathway, or unusual tachycardias involving nodoventricular or atriofascicular pathways. Diagnostic criteria for differentiating VT from SVT with aberrancy have been developed, all having similar diagnostic accuracy, but are limited in the ability to distinguish VT from pre-excited tachycardias because morphology on surface electrocardiogram (ECG) is identical to VT originating from the basilar segment of the ventricle. In this case of wide complex tachycardia, we use observations of intracardiac electrograms during tachycardia as well as a single atrial extrastimulus to make a diagnosis in our patient.