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The site of congenital and surgical heart block in children

Catheter recordings of His bundle (BH) electrograms were obtained in five children with asymptomatic congenital heart block (CHB) and two children with symptomatic surgical heart block (SHB). In the SHB patients, block followed repair of tetralogy of Fallot in one of A-V canal in the other. One patient with CHB had an associated secundum atrial septal defect. A-V dissociation was present in all patients with atrial rates of 80–100 and ventricular rates of 36–52 per minute. In the patients with CHB, BH spikes were unrelated to P waves and preceded every QRS. Intraventricular conduction was normal in four patients with CHB, who had H-Q intervals of 35–40 msec. (normal 35–55) and QRS duration of less than 0.10 seconds. One patients with CHB had a wide QRS (0.12 seconds) with initial delay suggesting type B pre-excitation. In the latter patient, H-Q was only 25–30 msec and the right ventricular (RV) electrogram preceded that of the left, suggesting either anomalous insertion of BH into the RV or an accessory infranodal communication to the RV. In the patients with SHB, H spikes followed P waves with P-H of 125 and 115 msec respectively. In the later two patients, there was complete block distal to BH.In conclusion, CHB was characterized by block proximal to the BH recording site (RS), consistent with block in either the A-V node or proximal His bundle. This was in contrast to SHB, where block was distal to the BH RS consistent with a lesion in the distal His bundle.