His-Purkinje conduction findings after cardiac surgery in children.

Conduction abnormalities of the His-Purkinje (HP) system are common sequelae of surgical repair of heart defects. Standard electrophysiologic recordings may fail to demonstrate abnormalities of the HP system when routine intervals are measured. When the conduction system is stressed, certain HP features that may indicate latent conduction disease within the HP system can be revealed. These features include split His potentials (SH) with spontaneous tachycardia or during rapid atrial pacing (RAP); SH with atrial extrastimuli (AES); and long HV intervals with AES associated with block distal to His during RAP. These findings may represent pathologic or functional properties of the HP system, and were identified in seven of 35 patients after surgical repair of tetralogy of Fallot (29 patients) or ventricular septal defect (six patients) who had electrophysiologic studies 1-8 years after operation. In five of the seven patients, these findings were revealed only when the conduction system was stressed. This incidence does not represent the true frequency of these features in the 35 patients because they were not evaluated under the same electrophysiologic stresses. Clinically, these patients did not differ from those manifesting these HP findings. The electrocardiographic patterns were as follows: normal QRS duration and normal axis (n = 1), right bundle branch block (RBBB) and normal axis (n = 1), RBBB and right-axis deviation (n = 4) (left anterior fascicular block (LAB] with tachycardia developed in one), RBBB and LAB (n = 1). The LAB was diagnosed on the basis of superior axis shift compared with the preoperative tracings. All had normal PR intervals. HP features may be unmasked by stressing the conduction system. The significance of these elicited conduction findings is unclear because data on the normal electrophysiologic properties of the conduction system in children are limited. Therefore, these features may be functional or pathologic.