Congenital complete atrioventricular block and preexcitation syndrome: a well-matched partner.

A patient who had been previously diagnosed with congenital complete atrioventricular block (CCAVB) twenty years ago developed atrioventricular (AV) conduction through an accessory pathway (AP). With enhanced sympathetic tone (exercise, isoproterenol), 1:1 conduction down the AP occurred. An electrophysiologic study confirmed a suprahissian AV block and the presence of an AP. The AP was located on the left side and posterior. The absence of retrograde conduction through the AP and also a long conduction time were demonstrated.