Pre-excitation syndrome with a change in terminal QRS vector.

Most accessory pathways in pre-excitation syndrome are capable of antegrade conduction from atrium to ventricle, and identified by characteristic ECG abnormalities such as a delta wave (ventricular pre-excitation) and a shortened PR interval.Therefore, the traditional diagnosis method is to detect the initial changes of the QRS complex. Here we report a patient initially mistaken as having atrioventricular re-entrant tachycardia (AVRT) and concealed pre-excitation syndrome. A diagnosis of incomplete latent pre-excitation syndrome was established on the basis of differences between the ECGs during sinus rhythm and AVRT in terminal QRS vectors, demonstrated by intracardiac electrophysiological radiofrequency catheter ablation.