[QRS alternans during ventricular tachycardia].

We present electrocardiograms of a 70-year-old man with a history of inferior wall myocardial infarction. Since the infarction he had frequent episodes of ventricular tachycardia that was on many occasions misdiagnosed as either supraventricular tachycardia or atrial flutter. We contribute the mistakes to the presence of relatively narrow QRS complexes and QRS alternans that imitated fusion beats. The QRS morphology similar to that seen in idiopathic ventricular tachycardia suggested participation of the Purkinje fibers of the posterior fascicle in the reentrant circuit. The arrhythmia was ablated with single radiofrequency current application in the mid-paraseptal area of the left ventricle.