Pseudo P waves: a cause of diagnostic confusion in wide QRS tachycardia.

A patient with wide QRS tachycardia is described. His initial electrocardiogram revealed P waves in lead V1 that led to a diagnosis of supraventricular tachycardia. Subsequently, during an electrophysiology study, the tachycardia was reproduced and documented to be ventricular in origin. The P waves seen were actually part of the QRS complex and therefore pseudo P waves. The correct diagnosis of the arrhythmia allowed for more appropriate therapy for the patient. This case illustrates that pseudo P waves may be present on the surface electrocardiogram and confuse the diagnosis of wide QRS tachycardia.