Late onset of accessory pathway conduction in a patient with complete AV block.

This case report discusses a patient with complete AV block in early childhood. The patient required a permanent pacemaker. At 6 years of age, intermittent preexcited beats were noted on telephonic transmissions. At 7 years of age, 1:1 preexcitation was noted in sinus rhythm. Therefore, late onset of antegrade accessory pathway function is demonstrated. This case provides evidence of developmental changes in accessory pathways. This may explain age related differences in the onset of narrow complex tachycardia in the school age years.