Site of conduction delay and electrophysiologic significance of first-degree atrioventricular block in children with heart disease

Abstract

Associated electrophysiologic abnormalities and site of delay were studied in 20 patients, aged 1.5 to 16.5 years, with congenital heart disease and first-degree atrioventricular (AV) block (PR interval above the 98th percentile for age and heart rate). Eight of the 20 patients with first-degree AV block were studied after 1 or more cardiovascular operations. Refractory periods of the atrium, AV node, His-Purkinje system and ventricle were determined. As a further test for AV nodal integrity, rapid atrial pacing was performed and the cycle at which Wenckebach periodicity occurred was noted. Four groups were identified. Group I included 4 patients (20%) with intraatrial conduction delay (long PA interval). Three patients had depressed sinus nodal function and 1 had depressed AV nodal function. Group II included 7 patients (35%) with AV nodal delay (long AH interval). One patient had sinus nodal depression and 2 had AV nodal depression (prolonged AV nodal refractory period or Wenckebach at a long paced cycle length). Group III included 3 patients (15%) with His-Purkinje delay (long HV interval). Measured functions were normal in all patients. Group IV included 6 patients (30%) with normal or high normal intracardiac intervals with long PR. One patient had sinus nodal dysfunction, 2 patients had long atrial refractory periods, 1 had AV nodal depression; 2 had long refractory period of the His-Purkinje system, and 1 had long ventricular refractory period. Atrial flutter was induced in 1 patient. In this heterogenous group of children, the most frequent single site of delay causing first-degree AV block was the AV node, but almost as many had a long PR interval as a result of high normal values at various sites (PA, AH and HV). There was poor correlation with other electrophysiologic abnormalities and the site of conduction delay. Sinus nodal dysfunction was found almost exclusively in patients with intraatrial delay (group I). There was a greater frequency of abnormalities, particularly AV nodal dysfunction, among patients who had undergone operation. Despite first-degree AV block and associated electrophysiologic abnormalities, these patients had no clinical progression of conduction disease during a mean follow-up of 32 months (range 1 month to 5.5 years).