An Unusual Cause of Intermittent Broad QRS Complexes

A 23-year-old asymptomatic male patient was admitted for invasive evaluation of pre-excitation on the surface ECG persisting during exercise testing. The electrophysiological study, performed under sedation with midazolam, revealed a midseptal accessory pathway (AP) with retrograde conduction and a 1:1 conduction during atrial pacing up to a cycle length of 240 ms. No tachycardia could be induced during pacing of the atrium and ventricle. We opted for ablation of the AP due to the malignant anterograde characteristics. Two seconds after the delivery of the first application of radiofrequency energy, the delta wave disappeared and normal atrioventricular conduction was restored. Energy application was continued for an additional 58 seconds. One day after the procedure, a control ECG revealed recurrence of the pre-excitation pattern. A second invasive evaluation was, therefore, scheduled 1 week after the initial electrophysiological study. Surprisingly, the surface ECG was normalized at that time, with AH and HV intervals within normal …