Bundle of His recordings in congenital complete heart block.

Six children, aged between 3 and 19 years, with congenital complete heart block without associated cardiac disease were studied by His bundle electrography. All were symptomatic with resting ventricular rates over 40 beats/min, and electrocardiograms that showed a normal axis and QRS complex. His bundle to ventricular activation was within the normal range in all and the block was proximal to the bundle of His. Ventricular and atrial pacing did not result in retrograde or antegrade conduction. All the patients were thought to have a lesion proximal to the site where the bundle of His potential was recorded and, therefore, were unlikely to develop symptoms or require treatment.