A case of septal Wolff-Parkinson-White syndrome associated with newly developed delta waves due to disappearance of impedance mismatch.

A 65-year-old woman who had shown no delta waves or atrioventricular block when seen in February 1989, suddenly developed advanced atrioventricular block in April 1990. The first electrophysiologic study revealed that atrioventricular block was caused by His ventricular block, and only weak retrograde conduction was documented. A DDD-type permanent pacemaker was implanted. One month after implantation, delta waves developed. The second electrophysiologic study, performed in February 1993, disclosed that a Kent bundle with bidirectional conduction capacity was located at the posterior septum and that the normal conduction system remained blocked at the His ventricular site. The etiology of the newly developed delta waves seems to be the disappearance of impedance mismatch at the ventricular insertion site of the Kent bundle.