Premature beats originating from the atrioventricular accessory pathway.

This article reports a case of a 34-year-old male patient with ventricular pre-excitation (WPW). Under sinus rhythm, the patient presented with alternating fully manifest WPW complexes and normal cardiac beats. In addition, premature beats unrelated to P waves were observed, with morphology consistent with the fully manifest WPW complexes. Such premature beats are highly susceptible to misdiagnosis as accelerated idioventricular rhythm or accelerated junctional rhythm with left bundle branch block (LBBB).